Research ArticlePlanar Dual-Band Monopole Antenna with an ExtendedGround Plane for WLAN Applications

Ayman S Al-Zayed and V A Shameena

Department of Electrical Engineering Kuwait University PO Box 5969 Al-Safat 13060 Kuwait City Kuwait

Correspondence should be addressed to Ayman S Al-Zayed aymanalzayedkuedukw

Received 10 May 2016 Revised 6 July 2016 Accepted 26 July 2016

Academic Editor Claudio Gennarelli

Copyright copy 2016 A S Al-Zayed and V A Shameena This is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

A compact planar microstrip-fed monopole antenna designed for dual-band operation is proposed for WLAN applications Theantenna is composed of a rectangular strip monopole in addition to an inverted-L parasitic element that is connected to thetruncated ground plane of themicrostrip feed Besides exciting an additional band of operation the parasitic element also improvesthe bandwidth of the band excited by the strip monopole Several simulated parametric studies are conducted to investigate theeffects of each geometrical parameter on the behavior of the antenna Experimental and simulation results demonstrate thatthe proposed antenna covers the 24 and 58GHz bands utilized in WLAN In both bands the proposed antenna exhibits goodimpedance match moderate gain (approximately 2 dBi) and sustainable omnidirectional-like radiation patterns in both principalplanes An equivalent circuit model of the antenna is also developed

1 Introduction

The drastic growth in the demand for wireless communica-tions necessitates an accelerated development of wireless sys-tems and their components in terms of size cost bandwidthfunctionality and so forth In that regard antennas whichare an integral part of wireless systems are required to be ofcompact size multiband operation andmultiple polarizationstates among other requirements Printed monopoles areconsidered to be suitable candidates for modern wirelesssystems because of their ease of fabrication size and cost Forexample it has been demonstrated that printed monopolescan be used in WLAN (Wireless Local Area Network)applications [1 2] and WiMAX (Worldwide Interoperabilityfor Microwave Access) applications [3 4]

In printed monopoles implementing multiband opera-tion such as that required in WLAN and WiMAX applica-tions can be achieved by incorporating parasitic resonators tothe antenna These resonators can be attached to the radiatoritself [5 6] andplaced on the sameplane as the radiator (top of

the substrate) [7 8] on the plane opposite to it (bottom of thesubstrate) [9 10] or on a combination of both [11 12] Firstattaching resonators to the radiating monopole creates addi-tional current paths that result in multiband operation Anexample of this can be found in [5] where two resonators havebeen attached to a conventional monopole creating a fork-shaped antenna resulting in a triple-band operation coveringthe WLAN and WiMAX bands Multiband operation canalso be achieved by loading the monopole with metamaterialresonators This has been implemented in [6] where a stripmonopole has been loaded with a CRLH (Composite Right-Left-Handed) unit cell resulting in triple-band operationInstead of directly connecting the resonators to themonopoleradiator parasitic resonators can be placed on the same planeas the radiator or opposite to it [7ndash12] One of the well-knownantennas that utilize this technique is the sleeve monopoleantenna [7 8] It consists of the monopole along with twocoplanar shorted resonators The configuration results in adual-band operation that can produce a wideband perfor-mance by carefully selecting the lengths of the resonators

Hindawi Publishing CorporationInternational Journal of Antennas and PropagationVolume 2016 Article ID 6798960 10 pageshttpdxdoiorg10115520166798960

2 International Journal of Antennas and Propagation

[7] Another way to utilize parasitic resonators is to placethem on the bottom side of the substrate For example anopen-ended inverted-L parasitic resonator is placed on thebottom plane of the monopole antenna presented in [9]Thisresonator contributed to one of the three bands of operationof this antenna In [10] placing a shorted parasitic resonatorin the ground plane of a microstrip-fed monopole resultedin a dual-band operation where the parasitic resonatorcontributed to an additional band besides that excited by themain monopole A combination of the preceding techniquescan be used to increase the number of bands operable by amonopole For example a modified fork-shaped monopolewith two identical open-ended resonators on the bottom sidehas been proposed in [11] to cover threeWLANbands and theWiMAX band of operation In [12] three parasitic resonatorsof different types have been incorporated in the design of amonopole antenna to achieve triple-band operation Two ofthese resonators were on the top side with one being shortedand the other being open-ended The third resonator wasopen-ended and placed on the bottom side of the substrate

In this paper a simple planar dual-band microstrip-fed printed monopole antenna is proposed The antennais basically a conventional strip monopole with a shortedinverted-L parasitic resonator connected to the truncatedground plane on the bottom side of the substrate Theantenna supports two frequency bands of 24 and 58GHzwhich are those of the WLAN The first band (24GHz)and the second band (58GHz) are excited by the resonanceof the parasitic resonator and the resonance of the stripmonopole respectively Several simulated parametric studiesare conducted to investigate the effects of the truncatedgrounds dimensions along with the impact of the othergeometrical parameters of the antenna The antenna designalong with measured and simulated results is presented anddiscussed in detail in the upcoming sections

2 Antenna Design

The geometry of the proposed planar dual-band monopoleantenna is shown in Figure 1 The radiator of the antenna is aconventional rectangular strip monopole printed on the topside of a substrate and it is fed by a 50Ωmicrostrip line Thewidth of the radiator (119882) is the same as that of the feeder andthe total length of the radiator along with the feeder is givenby (119871) On the bottom side of the substrate the truncatedground plane of the feeder is present with a size of 119871g times 119882gThe shorted inverted-L parasitic element consists of a verticalstrip of size 119871p1 times119882p1 loaded from the top with a horizontalstrip of size (119871p2 + 119882p1) times 119882p2 The dual-band operation ofthe proposed antenna can be understood by considering thecontribution of each of its parts as shown in Figure 2 Themain part of the antenna shown in Figure 2(a) (AntennaA) is a conventional microstrip-fed quarter-wave monopolewhich contributes to the higher band of operation

To realize the lower band a strip is attached to theground plane of the monopole antenna as shown in Fig-ure 2(b) (Antenna B) This strip is considered to be a shortedparasitic resonator which is excited by the reverse current

Lp2

Lp1

Wp1

Wg

Lg

Wp2

W

L

Vertical strip

Horizontal strip

Average current path

Parasitic resonator

Top conductorBottom conductor

Figure 1 Geometry of the proposed dual-band monopole antenna

Table 1 Dimensions of the proposed antenna

Symbol Value (mm)119871 15119871g 6119871p1 12119871p2 842119882 3119882g 10119882p1 05119882p2 7

of the microstrip feeder The parasitic strip is then loadedwith an additional horizontal strip with a different width asshown in Figure 2(c) (Antenna C) to improve the impedancematching and to further lower the resonant frequency ofthe operational band The three antennas shown in Figure 2are simulated and their reflection coefficients are displayedin Figure 3 for comparison The simulated antennas areimplemented on FR-4 substrate with a dielectric constant of120598119903= 44 and height ℎ = 16mmThe dimensions of the three

antennas are identical and are given in Table 1For the monopole shown in Figure 2(a) a single reso-

nance is observed at 62 GHz As for Antenna B two reso-nances are observed the lower resonance is attributed to theshorted parasitic resonator whereas the higher is attributedto the monopole It can be noticed that the loading effects ofthe parasitic resonator resulted in a lower resonant frequencyof the monopole in Antenna B It can also be seen that thelower band is poorly matched As for the proposed antenna(Antenna C) the two resonances are observed at 24GHzand 56GHz The top loading introduced to the ground

International Journal of Antennas and Propagation 3

X

YZ

(a)

X

YZ

(b)

X

YZ

X

YZ

(c)

Figure 2 Evolution of the proposed antennas design (a) Conventional stripmonopole (AntennaA) (b)Themonopole with a shorted groundplane parasitic resonator (Antenna B) (c) The proposed antenna (Antenna C)

Antenna AAntenna B

Antenna C

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

3 4 5 6 72

Frequency (GHz)

Figure 3 Reflection coefficients of antennas shown in Figure 2

plane parasitic resonator led to a good matching at the lowerband and lowered its resonant frequency The higher bandis further lowered due to the increased loading effects of theground plane parasitic resonator

The two resonant frequencies of the proposed antennacan be theoretically estimated The frequency of the higherband (the resonance of themonopole) can be calculated usingthe following expression (all lengths in cm) [13]

119891high =72

(119871m +1198822120587) times 119896GHz (1)

where 119871m is the length of the monopole which in our case is119871 minus 119871g Factor 119896 is intuitively equal to radic(120598119903 + 1)2 Howeverempirical values of 119896 have been found for different substrates

so that the estimates are within 10 from the measuredresultsThe value of 119896 for the used substrate is 115 [13] Evalu-ation of (1) results in 119891high = 66GHz which is close to that ofAntennaA (within 10)The lower resonant frequency is thatof a quarter-wave shorted parasitic resonator and thereforeits average current path length shown in Figure 1 is equal toa quarter of the guided wavelength This resonant frequencycan be theoretically estimated by modifying (1) as follows (alllengths in cm)

119891low =72

(119871p1 + 119871p2 + 05 times119882p1 + 05 times119882p2) times 119896GHz (2)

The lengths in the denominator of (1) are replaced withthe average current path length For the proposed antennaevaluating (2) results in 119891low = 248GHz which is close tothe simulated results In the same context given the designfrequencies (1) and (2) will provide an initial estimate of thedimensions of themonopole as well as the parasitic resonatorA full-wave EM simulator can then be used to optimize thesedimensions The parametric studies conducted in the nextsection can aid in designing the antenna as they providean insight into the effect of varying each parameter on thefrequency response

3 Design and Analysis

In this section a number of parametric studies are conductedusing a full-wave electromagnetic simulation software toinvestigate the effects of several geometrical design param-eters on the performance of the proposed antenna In eachstudy only one parameter is varied while the rest are keptunchanged as shown in Table 1 Also the surface currentdistribution and the radiation patterns at each resonance aresimulated

4 International Journal of Antennas and Propagation

3 4 5 6 72

Frequency (GHz)

minus30

minus25

minus20

minus15

minus10

minus5

01003816 1003816 1003816 1003816S

111003816 1003816 1003816 1003816

(dB)

Lg = 2mm

Lg = 4mm

Lg = 6mm

Lg = 8mm

Lg = 10mm

(a)

3 4 5 6 72

Frequency (GHz)

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

L = 11mm

L = 13mm

L = 15mm

L = 17mm

L = 19mm

(b)Figure 4 (a) The effects of varying length 119871g on the reflection coefficient of the proposed antenna Other parameters are the same as thoselisted in Table 1 (b) The effects of varying length 119871 on the reflection coefficient of the proposed antenna Other parameters are the same asthose listed in Table 1

3 4 5 6 72

Frequency (GHz)

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

Lp1 = 8mm

Lp1 = 10mm

Lp1 = 12mm

Lp1 = 14mm

Lp1 = 16mm

(a)

3 4 5 6 72

Frequency (GHz)

minus35

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

Wp1 = 03 mm

Wp1 = 05 mm

Wp1 = 07 mm

Wp1 = 09 mm

Wp1 = 11 mm

(b)

minus35

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

3 4 5 6 72

Frequency (GHz)

Lp2 = 55mm

Lp2 = 75mm

Lp2 = 95mm

Lp2 = 115 mm

Lp2 = 135mm

(c)

minus40

minus30

minus20

minus10

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

3 4 5 6 72

Frequency (GHz)

Wp2 = 3mm

Wp2 = 5mm

Wp2 = 7mm

Wp2 = 9mm

Wp2 = 11mm

(d)Figure 5 The effects of varying the four parameters of the parasitic resonator on the reflection coefficient of the proposed antenna (a) 119871p1(b)119882p1 (c) 119871p2 (d)119882p2 (In each study the other parameters are the same as those listed in Table 1)

International Journal of Antennas and Propagation 5

0852

2893

3245

3595

395

4298

500

J surf

(Am

m)

(a)

0852

2893

3245

3595

395

4298

500

J surf

(Am

m)

(b)

Figure 6 Surface current distribution of the proposed antenna at (a) the first band at 24GHz and (b) the second band at 56GHzG

ain

(dBi

)

2100

1978

1855

1732

1609

1486

1363

(a)

Gai

n (d

Bi)

2100

1978

1855

1732

1609

1486

1363

(b)

Figure 7 Three-dimensional radiation patterns of the proposed antenna at (a) the first band at 24GHz and (b) the second band at 56GHz

31 Parametric Studies The geometrical parameters to bestudied in this section are the length of the ground plane(119871g) the total length of the strip monopole (119871) and the fourparameters of the parasitic resonator which are 119871p1119882p1 119871p2and 119882p2 These studies are conducted with a fixed groundplane width of 119882g = 10mm and a monopole (and feeder)width of 119882 = 3mm so that the line impedance of themicrostrip feeder remains 50Ω It should be mentioned thatin the studies the results corresponding to the parameterslisted in Table 1 (and those of the final design) are plottedusing solid lines First the effect of the truncated groundplane length 119871g is investigated as shown in Figure 4(a)

It can be seen that this parameter is of great impacton both resonances in terms of resonance frequency andimpedance matching which is mainly because of the groundbeing truncated This can be beneficial to the antenna designas a good performance can be achieved with a small valueof 119871g leading to a compact design Afterwards the effectof length 119871 is analyzed and the results are depicted inFigure 4(b) As expected the second resonance is strongly

affected with the variation in 119871 since it represents theresonant length of the monopole A small shift in the lowerresonant frequency along with impedance matching effects isobserved and these are attributed to the coupling betweenthe parasitic resonator and the monopole

The impact of the four parameters related to the para-sitic resonator (119871p1 119882p1 119871p2 and 119882p2) is investigated asshown in Figures 5(a)ndash5(d) It can be observed that the fourparameters have similar effects on both bands of the proposedantenna When each parameter is varied the first band istuned whereas a variation in the second bands impedancebandwidth is observed The shift in the first band can beexplained by considering the average current path in theparasitic resonator shown in Figure 1 Varying any of thefour parameters results in a change in the resonators averagecurrent path length and accordingly its resonant frequencyOn the other hand the impedance bandwidth variationof the second band can be explained by investigating therelationship between the monopole radiator and the parasiticresonator The horizontal strip of the parasitic resonator acts

6 International Journal of Antennas and Propagation

(a) (b)

Figure 8 A photograph of the proposed dual-band monopole antenna (a) Front view (b) Back view

as a parasitic plane for the monopole which is known toaffect the impedance matching bandwidth at the monopolesoperating band as in [14] This applies to the proposedantenna as the size of the horizontal strip (determined by119882p1 119871p2 and 119882p2) and its position from the monopole(determined by 119871p1) affect the impedance bandwidth at thesecond band It is worthmentioning that when the horizontalstrip gets closer to the monopole a shift in the second band isobserved (see Figure 5(a)) To bemore specific the horizontalstrip starts to be directly beneath the monopole (for 119871p2 lessthan 12mm) which affects its resonance frequency

32 Current Distribution and Radiation Patterns The surfacecurrent distribution of the proposed dual-band antenna atboth of its resonant frequencies is shown in Figure 6 At thelower resonant frequency the current distribution shown inFigure 6(a) is mainly excited on the ground plane parasiticresonator with a quarter- wave variation On the other handthe current distribution at the higher resonant frequencywhich is shown in Figure 6(b) is prominent on themonopolewhich is observed to be of a quarter-wave variationThe sim-ulated three-dimensional radiation patterns of the antenna atboth resonant frequencies are shown in Figure 7 It is obviousthat the patterns are omnidirectional in both frequencies Itshould be mentioned that similar to conventional printedmonopoles the radiation at both bands is linearly polarized

4 Experimental Results

The proposed antenna shown in Figure 1 is fabricated on theFR-4 substrate with the dimensions stated in Section 2 Aphotograph of the fabricated antenna is shown in Figure 8

The measured reflection coefficient is plotted in Figure 9where it is found to be in good agreement with its simulatedcounterparts From the measured plots the first band is

MeasuredSimulated

3 4 5 6 72

Frequency (GHz)

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

Figure 9 Measured and simulated reflection coefficient of theproposed dual-band monopole

centered at 237GHz with a minus10 dB bandwidth of 03 GHzwhereas the second band is centered at 564GHz with aminus10 dB bandwidth of 16 GHz From applications standpointthe first band covers the 24GHz WLAN band whereasthe second band can cover both 52 and 58GHz WLANbands Also the first band is wide enough to cover the IEEEspecified PCS (Personal Communications Service) 24GHzcommunication band

The measured and simulated radiation patterns of thelinearly polarized antenna at the first and second bands areshown in Figures 10 and 11 respectively It can be clearly seenfrom both figures that the radiation patterns of the antennaat both bands exhibit omnidirectional-like behavior (witha maximum variation of 5 dB) Also low cross-polarization

International Journal of Antennas and Propagation 7

0

30

60

90

120

150

180

210

240

270

300

330

minus50 minus40 minus30 minus20 minus10 0

Hco simulatedHcx simulated

Hco measuredHcx measured

X

Y

Z

(a)

0

30

60

90

120

150

180

210

240

270

300

330

minus50 minus40 minus30 minus20 minus10 0

Eco simulatedEcx simulated

Eco measuredEcx measured

X

Y

Z

(b)

Figure 10 Measured and simulated radiation patterns of the antenna at the first band (24GHz) (a) H-plane (b) E-plane

0

30

60

90

120

150

180

210

240

270

300

330

minus50 minus40 minus30 minus20 minus10 0

Hco simulatedHcx simulated

Hco measuredHcx measured

X

Y

Z

(a)

0

30

60

90

120

150

180

210

240

270

300

330

minus50 minus40 minus30 minus20 minus10 0

Eco simulatedEcx simulated

Eco measuredEcx measured

X

Y

Z

(b)

Figure 11 Measured and simulated radiation patterns of the antenna at the second band (58GHz) (a) H-plane (b) E-plane

levels can be observed from the measured patterns The gainof the proposed antenna has been measured at both bands ofoperation and the results are shown in Figure 12(a) At thefirst band (around 24GHz) the antenna has an average gainof 18 dBi whereas it is 21 dBi at the second band (around56GHz) The measured efficiency of the proposed antenna

at both bands is shown in Figure 12(b) Peak efficiency of83 and 96 is obtained in the 24GHz and 58GHz bandsrespectively

A comparison between monopole antennas loaded withparasitic resonators and the proposed antenna in terms ofsize operating bands the bandwidth and the average peak

8 International Journal of Antennas and Propagation

220 225 230 235 240 245 250 255

Frequency (GHz)

Frequency (GHz)

24 GHz band58 GHz band

50 52 54 56 58 60 62

00

05

10

15

20

25

Gai

n (d

Bi)

(a)

220 225 230 235 240 245 250 255

Frequency (GHz)

Frequency (GHz)

24 GHz band58 GHz band

50 52 54 56 58 60 62

0

20

40

60

80

100

Effici

ency

()

(b)

Figure 12 Measured radiation performance of the proposed antenna (a) Gain (b) Efficiency

Table 2 Performance comparison of the proposed antenna with other antennas in the literature

Reference Size (mm)3 Operating bands (GHz) Bandwidth (GHz) andfractional bandwidth () Average peak gain (dBi)

[1] 30 times 30 times 08 34ndash762 422 (76) 4[2] 36 times 26 times 16 24ndash248 and 515ndash535 008 (33) and 02 (38) 36

[3] 30 times 20 times 16 214ndash252 282ndash374 and 515ndash602 038 (163) 092 (28) and087 (156) 246 245 and 3

[4] 30 times 18 times 16 239ndash269 338ndash373 and 50ndash599 03 (118) 035 (98) and099 (18) 252 237 and 415

[5] 37 times 20 times 0508 24ndash265 33ndash405 and 5ndash598 025 (99) 075 (204) and098 (178) Not mentioned

[6] 95 times 56 times 157 088ndash096 122ndash126 and 156ndash27 008 (87) 004 (322) and114 (535) 28 31 and 32

[9] 30 times 25 times 16 247ndash273 3-4 and 488ndash612 026 (10) 1 (286) and 124(225) 37 31 and 48

[10] 50 times 35 times 16 205ndash286 and 555ndash614 081 (33) and 124 (225) 373 and 359

[11] 345 times 18 times 16 235ndash249 327ndash38 and 465ndash589 014 (58) 053 (15) and124 (235)

284 228 and 429 (peakgains at center frequency)

[12] 22 times 28 times 08 249ndash266 341ndash373 and 473ndash593 017 (66) 032 (9) and 12(225)

3 42 and 45 (peak gains atcenter frequency)

[14] 50 times 35 times 16 086ndash098 17ndash25 and 472ndash661 012 (13) 08 (38) and 19(334) 113 201 and 374

Proposed antenna 25 times 10 times 16 222ndash255 and 48ndash65 033 (138) and 17 (3) 22

gain is given in Table 2 It is evident from Table 2 that theproposed antenna has a very compact size compared with theother antennas

5 Equivalent Circuit Modelling

In this section an R-L-C equivalent circuit model of theantenna is developed and verified with the aid of techniques

presented in [15] The equivalent circuit model of the pro-posed antenna is given in Figure 13The circuit consists of twoparallel R-L-C tanks along with a shunt branch The first twotank circuits correspond to the first and second resonancewhereas the shunt branch with R3 and L3 contributes to theinput impedance of the antenna

The parameters of the tank circuit can be computedby solving a set of equations formed as follows First

International Journal of Antennas and Propagation 9

C1

L1

R1

L2

C2

R2

L3

R3

Figure 13 The equivalent circuit model of the dual-band antenna

the series impedance of the circuit at any frequency (119891) willbe

119885Series at 119891 =1

radic(1198621120596 minus 1119871

1120596)2

+ 11198772

1

+1

radic(1198622120596 minus 1119871

2120596)2

+ 11198772

2

(3)

where 120596 = 2120587119891 At the first resonance the expression for theseries impedance is reduced to

119885Series at 1198651 = 1198771 +1

radic(11986221205961minus 1119871

21205961)2

+ 11198772

2

(4)

Similarly the expression for the series impedance at thesecond resonance is reduced to

119885Series at 1198652 = 1198772 +1

radic(11986211205962minus 1119871

11205962)2

+ 11198772

1

(5)

The shunt impedance of the circuit at a frequency 119891 will be

119885Shunt at 119891 = radic(1198713120596)2

+ 1198772

3 (6)

According to voltage dividing principle the ratio of outputvoltage to input voltage which is a measure of transmissioncoefficient can be obtained as

119881119900

119881119894

= 10(1minus11987811)20=119885Shunt

119885Shunt + 119885Series (7)

There are eight parameters in the model and to find themwe need eight equations These equations can be formulatedby choosing eight frequencies then substituting (3) and (6)into (7) By solving the formulated equations all the circuitparameters can be computed For the proposed antenna thevalues of the circuit elements in the model are 119871

1= 032 nH

1198712= 569 nH 119871

3= 0696 nH 119862

1= 14298 pF 119862

2= 1412 pF

1198771= 484Ω 119877

2= 5463Ω and 119877

3= 3623Ω The resonant

frequencies obtained from the equivalent circuit are 235GHzand 56GHz with a bandwidth of 024GHz in the first bandand 153GHz in the second band These results are in a verygood agreement with the experimental result as shown inFigure 14

3 4 5 6 72

Frequency (GHz)

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

MeasuredEquivalent circuit

Figure 14 Comparison between the measured reflection coefficientand that produced by the equivalent circuit model of the proposedantenna

6 Conclusion

A planar dual-band microstrip-fed monopole antenna of asimple and compact structure is presented Besides the bandexcited by the monopole radiator an additional band ofoperation is excited by placing a shorted inverted-L parasiticresonator on the bottom of the substrate The parasitic res-onator also improves the impedance bandwidth of the orig-inal band The microstrip feed is a truncated ground whosedimensions can be optimized to achieve a good performancewith compact sizeThe proposed antenna is designed to coverthe 2452ndash58GHz bands utilized in WLAN applicationsThe impact of the geometrical parameters on the perfor-mance of the dual-band monopole antenna is investigatedthrough a series of simulated parametric studies Measuredand simulated results show that the antenna operates at bothbandswith good impedancematching typicalmonopole-likeradiation patterns and flat gain An equivalent circuit modelof the proposed antenna which gives accurate results whencompared to measurements is presenteda

Competing Interests

The authors declare that there are no competing interestsregarding the publication of this paper

References

[1] W-C Liu C-M Wu and Y-J Tseng ldquoParasitically loadedCPW-fed monopole antenna for broadband operationrdquo IEEETransactions on Antennas and Propagation vol 59 no 6 pp2415ndash2419 2011

[2] K H Sayidmarie and T A Nagem ldquoCompact dual-band dual-ring printed mono-pole antennas for WLAN applicationsrdquoProgress in Electromagnetics ResearchB no 43 pp 313ndash331 2012

10 International Journal of Antennas and Propagation

[3] W-C Liu C-M Wu and Y Dai ldquoDesign of triple-frequencymicrostrip-fedmonopole antenna using defected ground struc-turerdquo IEEE Transactions on Antennas and Propagation vol 59no 7 pp 2457ndash2463 2011

[4] S S Huang J Li and J Z Zhao ldquoCompact CPW-fed tri-band antenna for WLANWIMAX applicationsrdquo Progress inElectromagnetics Research C vol 49 pp 39ndash45 2014

[5] L Xu Z Y Xin and J He ldquoA compact triple-band fork-shaped antenna for WLANWiMAX applicationsrdquo Progress inElectromagnetics Research Letters vol 40 pp 61ndash69 2013

[6] A A Ibrahim and A M E Safwat ldquoMicrostrip-fed monopoleantennas loaded with CRLH unit cellsrdquo IEEE Transactions onAntennas and Propagation vol 60 no 9 pp 4027ndash4036 2012

[7] H-D Chen ldquoGround plane effects on the microstrip-line-fed broadband sleeve monopole antennasrdquo IET MicrowavesAntennas and Propagation vol 2 no 6 pp 601ndash605 2008

[8] H-D Chen ldquoCompact broadband microstrip-line-fed sleevemonopole antenna for DTV application and ground planeeffectrdquo IEEE Antennas and Wireless Propagation Letters vol 7pp 497ndash500 2008

[9] J H Lu and B J Huang ldquoPlanar multi-bandmonopole antennawith L-shaped parasitic strip for WiMAX applicationrdquo IETElectronics Letters vol 46 no 10 pp 671ndash672 2010

[10] J R Panda and R S Kshetrimayum ldquoA printed 24 ghz58ghzdual-band monopole antenna with a protruding stub in theground plane for WLAN and RFID applicationsrdquo Progress inElectromagnetics Research vol 117 pp 425ndash434 2011

[11] P Xu Z-H Yan and C Wang ldquoMulti-band modified fork-shaped monopole antenna with dual L-shaped parasitic planerdquoElectronics Letters vol 47 no 6 pp 364ndash365 2011

[12] J-H Lu and Y-Y Lee ldquoPlanar compact triple-band monopoleantenna for IEEE 80216m worldwide interoperability formicrowave access systemrdquo IET Microwaves Antennas andPropagation vol 7 no 13 pp 1045ndash1054 2013

[13] K P Ray ldquoDesign aspects of printed monopole antennas forultra-wide band applicationsrdquo International Journal of Antennasand Propagation vol 2008 Article ID 713858 8 pages 2008

[14] K Seol J Jung and J Choi ldquoMulti-band monopole antennawith inverted U-shaped parasitic planerdquo IET Electronics lettersvol 42 no 15 pp 844ndash845 2006

[15] Q-X Chu and Y-Y Yang ldquoA compact ultrawideband antennawith 3455 GHz dual band-notched characteristicsrdquo IEEETransactions on Antennas and Propagation vol 56 no 12 pp3637ndash3644 2008

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

2 International Journal of Antennas and Propagation

[7] Another way to utilize parasitic resonators is to placethem on the bottom side of the substrate For example anopen-ended inverted-L parasitic resonator is placed on thebottom plane of the monopole antenna presented in [9]Thisresonator contributed to one of the three bands of operationof this antenna In [10] placing a shorted parasitic resonatorin the ground plane of a microstrip-fed monopole resultedin a dual-band operation where the parasitic resonatorcontributed to an additional band besides that excited by themain monopole A combination of the preceding techniquescan be used to increase the number of bands operable by amonopole For example a modified fork-shaped monopolewith two identical open-ended resonators on the bottom sidehas been proposed in [11] to cover threeWLANbands and theWiMAX band of operation In [12] three parasitic resonatorsof different types have been incorporated in the design of amonopole antenna to achieve triple-band operation Two ofthese resonators were on the top side with one being shortedand the other being open-ended The third resonator wasopen-ended and placed on the bottom side of the substrate

In this paper a simple planar dual-band microstrip-fed printed monopole antenna is proposed The antennais basically a conventional strip monopole with a shortedinverted-L parasitic resonator connected to the truncatedground plane on the bottom side of the substrate Theantenna supports two frequency bands of 24 and 58GHzwhich are those of the WLAN The first band (24GHz)and the second band (58GHz) are excited by the resonanceof the parasitic resonator and the resonance of the stripmonopole respectively Several simulated parametric studiesare conducted to investigate the effects of the truncatedgrounds dimensions along with the impact of the othergeometrical parameters of the antenna The antenna designalong with measured and simulated results is presented anddiscussed in detail in the upcoming sections

2 Antenna Design

The geometry of the proposed planar dual-band monopoleantenna is shown in Figure 1 The radiator of the antenna is aconventional rectangular strip monopole printed on the topside of a substrate and it is fed by a 50Ωmicrostrip line Thewidth of the radiator (119882) is the same as that of the feeder andthe total length of the radiator along with the feeder is givenby (119871) On the bottom side of the substrate the truncatedground plane of the feeder is present with a size of 119871g times 119882gThe shorted inverted-L parasitic element consists of a verticalstrip of size 119871p1 times119882p1 loaded from the top with a horizontalstrip of size (119871p2 + 119882p1) times 119882p2 The dual-band operation ofthe proposed antenna can be understood by considering thecontribution of each of its parts as shown in Figure 2 Themain part of the antenna shown in Figure 2(a) (AntennaA) is a conventional microstrip-fed quarter-wave monopolewhich contributes to the higher band of operation

To realize the lower band a strip is attached to theground plane of the monopole antenna as shown in Fig-ure 2(b) (Antenna B) This strip is considered to be a shortedparasitic resonator which is excited by the reverse current

Lp2

Lp1

Wp1

Wg

Lg

Wp2

W

L

Vertical strip

Horizontal strip

Average current path

Parasitic resonator

Top conductorBottom conductor

Figure 1 Geometry of the proposed dual-band monopole antenna

Table 1 Dimensions of the proposed antenna

Symbol Value (mm)119871 15119871g 6119871p1 12119871p2 842119882 3119882g 10119882p1 05119882p2 7

of the microstrip feeder The parasitic strip is then loadedwith an additional horizontal strip with a different width asshown in Figure 2(c) (Antenna C) to improve the impedancematching and to further lower the resonant frequency ofthe operational band The three antennas shown in Figure 2are simulated and their reflection coefficients are displayedin Figure 3 for comparison The simulated antennas areimplemented on FR-4 substrate with a dielectric constant of120598119903= 44 and height ℎ = 16mmThe dimensions of the three

antennas are identical and are given in Table 1For the monopole shown in Figure 2(a) a single reso-

nance is observed at 62 GHz As for Antenna B two reso-nances are observed the lower resonance is attributed to theshorted parasitic resonator whereas the higher is attributedto the monopole It can be noticed that the loading effects ofthe parasitic resonator resulted in a lower resonant frequencyof the monopole in Antenna B It can also be seen that thelower band is poorly matched As for the proposed antenna(Antenna C) the two resonances are observed at 24GHzand 56GHz The top loading introduced to the ground

International Journal of Antennas and Propagation 3

X

YZ

(a)

X

YZ

(b)

X

YZ

X

YZ

(c)

Figure 2 Evolution of the proposed antennas design (a) Conventional stripmonopole (AntennaA) (b)Themonopole with a shorted groundplane parasitic resonator (Antenna B) (c) The proposed antenna (Antenna C)

Antenna AAntenna B

Antenna C

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

3 4 5 6 72

Frequency (GHz)

Figure 3 Reflection coefficients of antennas shown in Figure 2

plane parasitic resonator led to a good matching at the lowerband and lowered its resonant frequency The higher bandis further lowered due to the increased loading effects of theground plane parasitic resonator

The two resonant frequencies of the proposed antennacan be theoretically estimated The frequency of the higherband (the resonance of themonopole) can be calculated usingthe following expression (all lengths in cm) [13]

119891high =72

(119871m +1198822120587) times 119896GHz (1)

where 119871m is the length of the monopole which in our case is119871 minus 119871g Factor 119896 is intuitively equal to radic(120598119903 + 1)2 Howeverempirical values of 119896 have been found for different substrates

so that the estimates are within 10 from the measuredresultsThe value of 119896 for the used substrate is 115 [13] Evalu-ation of (1) results in 119891high = 66GHz which is close to that ofAntennaA (within 10)The lower resonant frequency is thatof a quarter-wave shorted parasitic resonator and thereforeits average current path length shown in Figure 1 is equal toa quarter of the guided wavelength This resonant frequencycan be theoretically estimated by modifying (1) as follows (alllengths in cm)

119891low =72

(119871p1 + 119871p2 + 05 times119882p1 + 05 times119882p2) times 119896GHz (2)

The lengths in the denominator of (1) are replaced withthe average current path length For the proposed antennaevaluating (2) results in 119891low = 248GHz which is close tothe simulated results In the same context given the designfrequencies (1) and (2) will provide an initial estimate of thedimensions of themonopole as well as the parasitic resonatorA full-wave EM simulator can then be used to optimize thesedimensions The parametric studies conducted in the nextsection can aid in designing the antenna as they providean insight into the effect of varying each parameter on thefrequency response

3 Design and Analysis

In this section a number of parametric studies are conductedusing a full-wave electromagnetic simulation software toinvestigate the effects of several geometrical design param-eters on the performance of the proposed antenna In eachstudy only one parameter is varied while the rest are keptunchanged as shown in Table 1 Also the surface currentdistribution and the radiation patterns at each resonance aresimulated

4 International Journal of Antennas and Propagation

3 4 5 6 72

Frequency (GHz)

minus30

minus25

minus20

minus15

minus10

minus5

01003816 1003816 1003816 1003816S

111003816 1003816 1003816 1003816

(dB)

Lg = 2mm

Lg = 4mm

Lg = 6mm

Lg = 8mm

Lg = 10mm

(a)

3 4 5 6 72

Frequency (GHz)

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

L = 11mm

L = 13mm

L = 15mm

L = 17mm

L = 19mm

(b)Figure 4 (a) The effects of varying length 119871g on the reflection coefficient of the proposed antenna Other parameters are the same as thoselisted in Table 1 (b) The effects of varying length 119871 on the reflection coefficient of the proposed antenna Other parameters are the same asthose listed in Table 1

3 4 5 6 72

Frequency (GHz)

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

Lp1 = 8mm

Lp1 = 10mm

Lp1 = 12mm

Lp1 = 14mm

Lp1 = 16mm

(a)

3 4 5 6 72

Frequency (GHz)

minus35

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

Wp1 = 03 mm

Wp1 = 05 mm

Wp1 = 07 mm

Wp1 = 09 mm

Wp1 = 11 mm

(b)

minus35

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

3 4 5 6 72

Frequency (GHz)

Lp2 = 55mm

Lp2 = 75mm

Lp2 = 95mm

Lp2 = 115 mm

Lp2 = 135mm

(c)

minus40

minus30

minus20

minus10

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

3 4 5 6 72

Frequency (GHz)

Wp2 = 3mm

Wp2 = 5mm

Wp2 = 7mm

Wp2 = 9mm

Wp2 = 11mm

(d)Figure 5 The effects of varying the four parameters of the parasitic resonator on the reflection coefficient of the proposed antenna (a) 119871p1(b)119882p1 (c) 119871p2 (d)119882p2 (In each study the other parameters are the same as those listed in Table 1)

International Journal of Antennas and Propagation 5

0852

2893

3245

3595

395

4298

500

J surf

(Am

m)

(a)

0852

2893

3245

3595

395

4298

500

J surf

(Am

m)

(b)

Figure 6 Surface current distribution of the proposed antenna at (a) the first band at 24GHz and (b) the second band at 56GHzG

ain

(dBi

)

2100

1978

1855

1732

1609

1486

1363

(a)

Gai

n (d

Bi)

2100

1978

1855

1732

1609

1486

1363

(b)

Figure 7 Three-dimensional radiation patterns of the proposed antenna at (a) the first band at 24GHz and (b) the second band at 56GHz

31 Parametric Studies The geometrical parameters to bestudied in this section are the length of the ground plane(119871g) the total length of the strip monopole (119871) and the fourparameters of the parasitic resonator which are 119871p1119882p1 119871p2and 119882p2 These studies are conducted with a fixed groundplane width of 119882g = 10mm and a monopole (and feeder)width of 119882 = 3mm so that the line impedance of themicrostrip feeder remains 50Ω It should be mentioned thatin the studies the results corresponding to the parameterslisted in Table 1 (and those of the final design) are plottedusing solid lines First the effect of the truncated groundplane length 119871g is investigated as shown in Figure 4(a)

It can be seen that this parameter is of great impacton both resonances in terms of resonance frequency andimpedance matching which is mainly because of the groundbeing truncated This can be beneficial to the antenna designas a good performance can be achieved with a small valueof 119871g leading to a compact design Afterwards the effectof length 119871 is analyzed and the results are depicted inFigure 4(b) As expected the second resonance is strongly

affected with the variation in 119871 since it represents theresonant length of the monopole A small shift in the lowerresonant frequency along with impedance matching effects isobserved and these are attributed to the coupling betweenthe parasitic resonator and the monopole

The impact of the four parameters related to the para-sitic resonator (119871p1 119882p1 119871p2 and 119882p2) is investigated asshown in Figures 5(a)ndash5(d) It can be observed that the fourparameters have similar effects on both bands of the proposedantenna When each parameter is varied the first band istuned whereas a variation in the second bands impedancebandwidth is observed The shift in the first band can beexplained by considering the average current path in theparasitic resonator shown in Figure 1 Varying any of thefour parameters results in a change in the resonators averagecurrent path length and accordingly its resonant frequencyOn the other hand the impedance bandwidth variationof the second band can be explained by investigating therelationship between the monopole radiator and the parasiticresonator The horizontal strip of the parasitic resonator acts

6 International Journal of Antennas and Propagation

(a) (b)

Figure 8 A photograph of the proposed dual-band monopole antenna (a) Front view (b) Back view

as a parasitic plane for the monopole which is known toaffect the impedance matching bandwidth at the monopolesoperating band as in [14] This applies to the proposedantenna as the size of the horizontal strip (determined by119882p1 119871p2 and 119882p2) and its position from the monopole(determined by 119871p1) affect the impedance bandwidth at thesecond band It is worthmentioning that when the horizontalstrip gets closer to the monopole a shift in the second band isobserved (see Figure 5(a)) To bemore specific the horizontalstrip starts to be directly beneath the monopole (for 119871p2 lessthan 12mm) which affects its resonance frequency

32 Current Distribution and Radiation Patterns The surfacecurrent distribution of the proposed dual-band antenna atboth of its resonant frequencies is shown in Figure 6 At thelower resonant frequency the current distribution shown inFigure 6(a) is mainly excited on the ground plane parasiticresonator with a quarter- wave variation On the other handthe current distribution at the higher resonant frequencywhich is shown in Figure 6(b) is prominent on themonopolewhich is observed to be of a quarter-wave variationThe sim-ulated three-dimensional radiation patterns of the antenna atboth resonant frequencies are shown in Figure 7 It is obviousthat the patterns are omnidirectional in both frequencies Itshould be mentioned that similar to conventional printedmonopoles the radiation at both bands is linearly polarized

4 Experimental Results

The proposed antenna shown in Figure 1 is fabricated on theFR-4 substrate with the dimensions stated in Section 2 Aphotograph of the fabricated antenna is shown in Figure 8

The measured reflection coefficient is plotted in Figure 9where it is found to be in good agreement with its simulatedcounterparts From the measured plots the first band is

MeasuredSimulated

3 4 5 6 72

Frequency (GHz)

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

Figure 9 Measured and simulated reflection coefficient of theproposed dual-band monopole

centered at 237GHz with a minus10 dB bandwidth of 03 GHzwhereas the second band is centered at 564GHz with aminus10 dB bandwidth of 16 GHz From applications standpointthe first band covers the 24GHz WLAN band whereasthe second band can cover both 52 and 58GHz WLANbands Also the first band is wide enough to cover the IEEEspecified PCS (Personal Communications Service) 24GHzcommunication band

The measured and simulated radiation patterns of thelinearly polarized antenna at the first and second bands areshown in Figures 10 and 11 respectively It can be clearly seenfrom both figures that the radiation patterns of the antennaat both bands exhibit omnidirectional-like behavior (witha maximum variation of 5 dB) Also low cross-polarization

International Journal of Antennas and Propagation 7

0

30

60

90

120

150

180

210

240

270

300

330

minus50 minus40 minus30 minus20 minus10 0

Hco simulatedHcx simulated

Hco measuredHcx measured

X

Y

Z

(a)

0

30

60

90

120

150

180

210

240

270

300

330

minus50 minus40 minus30 minus20 minus10 0

Eco simulatedEcx simulated

Eco measuredEcx measured

X

Y

Z

(b)

Figure 10 Measured and simulated radiation patterns of the antenna at the first band (24GHz) (a) H-plane (b) E-plane

0

30

60

90

120

150

180

210

240

270

300

330

minus50 minus40 minus30 minus20 minus10 0

Hco simulatedHcx simulated

Hco measuredHcx measured

X

Y

Z

(a)

0

30

60

90

120

150

180

210

240

270

300

330

minus50 minus40 minus30 minus20 minus10 0

Eco simulatedEcx simulated

Eco measuredEcx measured

X

Y

Z

(b)

Figure 11 Measured and simulated radiation patterns of the antenna at the second band (58GHz) (a) H-plane (b) E-plane

levels can be observed from the measured patterns The gainof the proposed antenna has been measured at both bands ofoperation and the results are shown in Figure 12(a) At thefirst band (around 24GHz) the antenna has an average gainof 18 dBi whereas it is 21 dBi at the second band (around56GHz) The measured efficiency of the proposed antenna

at both bands is shown in Figure 12(b) Peak efficiency of83 and 96 is obtained in the 24GHz and 58GHz bandsrespectively

A comparison between monopole antennas loaded withparasitic resonators and the proposed antenna in terms ofsize operating bands the bandwidth and the average peak

8 International Journal of Antennas and Propagation

220 225 230 235 240 245 250 255

Frequency (GHz)

Frequency (GHz)

24 GHz band58 GHz band

50 52 54 56 58 60 62

00

05

10

15

20

25

Gai

n (d

Bi)

(a)

220 225 230 235 240 245 250 255

Frequency (GHz)

Frequency (GHz)

24 GHz band58 GHz band

50 52 54 56 58 60 62

0

20

40

60

80

100

Effici

ency

()

(b)

Figure 12 Measured radiation performance of the proposed antenna (a) Gain (b) Efficiency

Table 2 Performance comparison of the proposed antenna with other antennas in the literature

Reference Size (mm)3 Operating bands (GHz) Bandwidth (GHz) andfractional bandwidth () Average peak gain (dBi)

[1] 30 times 30 times 08 34ndash762 422 (76) 4[2] 36 times 26 times 16 24ndash248 and 515ndash535 008 (33) and 02 (38) 36

[3] 30 times 20 times 16 214ndash252 282ndash374 and 515ndash602 038 (163) 092 (28) and087 (156) 246 245 and 3

[4] 30 times 18 times 16 239ndash269 338ndash373 and 50ndash599 03 (118) 035 (98) and099 (18) 252 237 and 415

[5] 37 times 20 times 0508 24ndash265 33ndash405 and 5ndash598 025 (99) 075 (204) and098 (178) Not mentioned

[6] 95 times 56 times 157 088ndash096 122ndash126 and 156ndash27 008 (87) 004 (322) and114 (535) 28 31 and 32

[9] 30 times 25 times 16 247ndash273 3-4 and 488ndash612 026 (10) 1 (286) and 124(225) 37 31 and 48

[10] 50 times 35 times 16 205ndash286 and 555ndash614 081 (33) and 124 (225) 373 and 359

[11] 345 times 18 times 16 235ndash249 327ndash38 and 465ndash589 014 (58) 053 (15) and124 (235)

284 228 and 429 (peakgains at center frequency)

[12] 22 times 28 times 08 249ndash266 341ndash373 and 473ndash593 017 (66) 032 (9) and 12(225)

3 42 and 45 (peak gains atcenter frequency)

[14] 50 times 35 times 16 086ndash098 17ndash25 and 472ndash661 012 (13) 08 (38) and 19(334) 113 201 and 374

Proposed antenna 25 times 10 times 16 222ndash255 and 48ndash65 033 (138) and 17 (3) 22

gain is given in Table 2 It is evident from Table 2 that theproposed antenna has a very compact size compared with theother antennas

5 Equivalent Circuit Modelling

In this section an R-L-C equivalent circuit model of theantenna is developed and verified with the aid of techniques

presented in [15] The equivalent circuit model of the pro-posed antenna is given in Figure 13The circuit consists of twoparallel R-L-C tanks along with a shunt branch The first twotank circuits correspond to the first and second resonancewhereas the shunt branch with R3 and L3 contributes to theinput impedance of the antenna

The parameters of the tank circuit can be computedby solving a set of equations formed as follows First

International Journal of Antennas and Propagation 9

C1

L1

R1

L2

C2

R2

L3

R3

Figure 13 The equivalent circuit model of the dual-band antenna

the series impedance of the circuit at any frequency (119891) willbe

119885Series at 119891 =1

radic(1198621120596 minus 1119871

1120596)2

+ 11198772

1

+1

radic(1198622120596 minus 1119871

2120596)2

+ 11198772

2

(3)

where 120596 = 2120587119891 At the first resonance the expression for theseries impedance is reduced to

119885Series at 1198651 = 1198771 +1

radic(11986221205961minus 1119871

21205961)2

+ 11198772

2

(4)

Similarly the expression for the series impedance at thesecond resonance is reduced to

119885Series at 1198652 = 1198772 +1

radic(11986211205962minus 1119871

11205962)2

+ 11198772

1

(5)

The shunt impedance of the circuit at a frequency 119891 will be

119885Shunt at 119891 = radic(1198713120596)2

+ 1198772

3 (6)

According to voltage dividing principle the ratio of outputvoltage to input voltage which is a measure of transmissioncoefficient can be obtained as

119881119900

119881119894

= 10(1minus11987811)20=119885Shunt

119885Shunt + 119885Series (7)

There are eight parameters in the model and to find themwe need eight equations These equations can be formulatedby choosing eight frequencies then substituting (3) and (6)into (7) By solving the formulated equations all the circuitparameters can be computed For the proposed antenna thevalues of the circuit elements in the model are 119871

1= 032 nH

1198712= 569 nH 119871

3= 0696 nH 119862

1= 14298 pF 119862

2= 1412 pF

1198771= 484Ω 119877

2= 5463Ω and 119877

3= 3623Ω The resonant

frequencies obtained from the equivalent circuit are 235GHzand 56GHz with a bandwidth of 024GHz in the first bandand 153GHz in the second band These results are in a verygood agreement with the experimental result as shown inFigure 14

3 4 5 6 72

Frequency (GHz)

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

MeasuredEquivalent circuit

Figure 14 Comparison between the measured reflection coefficientand that produced by the equivalent circuit model of the proposedantenna

6 Conclusion

A planar dual-band microstrip-fed monopole antenna of asimple and compact structure is presented Besides the bandexcited by the monopole radiator an additional band ofoperation is excited by placing a shorted inverted-L parasiticresonator on the bottom of the substrate The parasitic res-onator also improves the impedance bandwidth of the orig-inal band The microstrip feed is a truncated ground whosedimensions can be optimized to achieve a good performancewith compact sizeThe proposed antenna is designed to coverthe 2452ndash58GHz bands utilized in WLAN applicationsThe impact of the geometrical parameters on the perfor-mance of the dual-band monopole antenna is investigatedthrough a series of simulated parametric studies Measuredand simulated results show that the antenna operates at bothbandswith good impedancematching typicalmonopole-likeradiation patterns and flat gain An equivalent circuit modelof the proposed antenna which gives accurate results whencompared to measurements is presenteda

Competing Interests

The authors declare that there are no competing interestsregarding the publication of this paper

References

[1] W-C Liu C-M Wu and Y-J Tseng ldquoParasitically loadedCPW-fed monopole antenna for broadband operationrdquo IEEETransactions on Antennas and Propagation vol 59 no 6 pp2415ndash2419 2011

[2] K H Sayidmarie and T A Nagem ldquoCompact dual-band dual-ring printed mono-pole antennas for WLAN applicationsrdquoProgress in Electromagnetics ResearchB no 43 pp 313ndash331 2012

10 International Journal of Antennas and Propagation

[3] W-C Liu C-M Wu and Y Dai ldquoDesign of triple-frequencymicrostrip-fedmonopole antenna using defected ground struc-turerdquo IEEE Transactions on Antennas and Propagation vol 59no 7 pp 2457ndash2463 2011

[4] S S Huang J Li and J Z Zhao ldquoCompact CPW-fed tri-band antenna for WLANWIMAX applicationsrdquo Progress inElectromagnetics Research C vol 49 pp 39ndash45 2014

[5] L Xu Z Y Xin and J He ldquoA compact triple-band fork-shaped antenna for WLANWiMAX applicationsrdquo Progress inElectromagnetics Research Letters vol 40 pp 61ndash69 2013

[6] A A Ibrahim and A M E Safwat ldquoMicrostrip-fed monopoleantennas loaded with CRLH unit cellsrdquo IEEE Transactions onAntennas and Propagation vol 60 no 9 pp 4027ndash4036 2012

[7] H-D Chen ldquoGround plane effects on the microstrip-line-fed broadband sleeve monopole antennasrdquo IET MicrowavesAntennas and Propagation vol 2 no 6 pp 601ndash605 2008

[8] H-D Chen ldquoCompact broadband microstrip-line-fed sleevemonopole antenna for DTV application and ground planeeffectrdquo IEEE Antennas and Wireless Propagation Letters vol 7pp 497ndash500 2008

[9] J H Lu and B J Huang ldquoPlanar multi-bandmonopole antennawith L-shaped parasitic strip for WiMAX applicationrdquo IETElectronics Letters vol 46 no 10 pp 671ndash672 2010

[10] J R Panda and R S Kshetrimayum ldquoA printed 24 ghz58ghzdual-band monopole antenna with a protruding stub in theground plane for WLAN and RFID applicationsrdquo Progress inElectromagnetics Research vol 117 pp 425ndash434 2011

[11] P Xu Z-H Yan and C Wang ldquoMulti-band modified fork-shaped monopole antenna with dual L-shaped parasitic planerdquoElectronics Letters vol 47 no 6 pp 364ndash365 2011

[12] J-H Lu and Y-Y Lee ldquoPlanar compact triple-band monopoleantenna for IEEE 80216m worldwide interoperability formicrowave access systemrdquo IET Microwaves Antennas andPropagation vol 7 no 13 pp 1045ndash1054 2013

[13] K P Ray ldquoDesign aspects of printed monopole antennas forultra-wide band applicationsrdquo International Journal of Antennasand Propagation vol 2008 Article ID 713858 8 pages 2008

[14] K Seol J Jung and J Choi ldquoMulti-band monopole antennawith inverted U-shaped parasitic planerdquo IET Electronics lettersvol 42 no 15 pp 844ndash845 2006

[15] Q-X Chu and Y-Y Yang ldquoA compact ultrawideband antennawith 3455 GHz dual band-notched characteristicsrdquo IEEETransactions on Antennas and Propagation vol 56 no 12 pp3637ndash3644 2008

International Journal of

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RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

International Journal of Antennas and Propagation 3

X

YZ

(a)

X

YZ

(b)

X

YZ

X

YZ

(c)

Figure 2 Evolution of the proposed antennas design (a) Conventional stripmonopole (AntennaA) (b)Themonopole with a shorted groundplane parasitic resonator (Antenna B) (c) The proposed antenna (Antenna C)

Antenna AAntenna B

Antenna C

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

3 4 5 6 72

Frequency (GHz)

Figure 3 Reflection coefficients of antennas shown in Figure 2

plane parasitic resonator led to a good matching at the lowerband and lowered its resonant frequency The higher bandis further lowered due to the increased loading effects of theground plane parasitic resonator

The two resonant frequencies of the proposed antennacan be theoretically estimated The frequency of the higherband (the resonance of themonopole) can be calculated usingthe following expression (all lengths in cm) [13]

119891high =72

(119871m +1198822120587) times 119896GHz (1)

where 119871m is the length of the monopole which in our case is119871 minus 119871g Factor 119896 is intuitively equal to radic(120598119903 + 1)2 Howeverempirical values of 119896 have been found for different substrates

so that the estimates are within 10 from the measuredresultsThe value of 119896 for the used substrate is 115 [13] Evalu-ation of (1) results in 119891high = 66GHz which is close to that ofAntennaA (within 10)The lower resonant frequency is thatof a quarter-wave shorted parasitic resonator and thereforeits average current path length shown in Figure 1 is equal toa quarter of the guided wavelength This resonant frequencycan be theoretically estimated by modifying (1) as follows (alllengths in cm)

119891low =72

(119871p1 + 119871p2 + 05 times119882p1 + 05 times119882p2) times 119896GHz (2)

The lengths in the denominator of (1) are replaced withthe average current path length For the proposed antennaevaluating (2) results in 119891low = 248GHz which is close tothe simulated results In the same context given the designfrequencies (1) and (2) will provide an initial estimate of thedimensions of themonopole as well as the parasitic resonatorA full-wave EM simulator can then be used to optimize thesedimensions The parametric studies conducted in the nextsection can aid in designing the antenna as they providean insight into the effect of varying each parameter on thefrequency response

3 Design and Analysis

In this section a number of parametric studies are conductedusing a full-wave electromagnetic simulation software toinvestigate the effects of several geometrical design param-eters on the performance of the proposed antenna In eachstudy only one parameter is varied while the rest are keptunchanged as shown in Table 1 Also the surface currentdistribution and the radiation patterns at each resonance aresimulated

4 International Journal of Antennas and Propagation

3 4 5 6 72

Frequency (GHz)

minus30

minus25

minus20

minus15

minus10

minus5

01003816 1003816 1003816 1003816S

111003816 1003816 1003816 1003816

(dB)

Lg = 2mm

Lg = 4mm

Lg = 6mm

Lg = 8mm

Lg = 10mm

(a)

3 4 5 6 72

Frequency (GHz)

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

L = 11mm

L = 13mm

L = 15mm

L = 17mm

L = 19mm

(b)Figure 4 (a) The effects of varying length 119871g on the reflection coefficient of the proposed antenna Other parameters are the same as thoselisted in Table 1 (b) The effects of varying length 119871 on the reflection coefficient of the proposed antenna Other parameters are the same asthose listed in Table 1

3 4 5 6 72

Frequency (GHz)

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

Lp1 = 8mm

Lp1 = 10mm

Lp1 = 12mm

Lp1 = 14mm

Lp1 = 16mm

(a)

3 4 5 6 72

Frequency (GHz)

minus35

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

Wp1 = 03 mm

Wp1 = 05 mm

Wp1 = 07 mm

Wp1 = 09 mm

Wp1 = 11 mm

(b)

minus35

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

3 4 5 6 72

Frequency (GHz)

Lp2 = 55mm

Lp2 = 75mm

Lp2 = 95mm

Lp2 = 115 mm

Lp2 = 135mm

(c)

minus40

minus30

minus20

minus10

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

3 4 5 6 72

Frequency (GHz)

Wp2 = 3mm

Wp2 = 5mm

Wp2 = 7mm

Wp2 = 9mm

Wp2 = 11mm

(d)Figure 5 The effects of varying the four parameters of the parasitic resonator on the reflection coefficient of the proposed antenna (a) 119871p1(b)119882p1 (c) 119871p2 (d)119882p2 (In each study the other parameters are the same as those listed in Table 1)

International Journal of Antennas and Propagation 5

0852

2893

3245

3595

395

4298

500

J surf

(Am

m)

(a)

0852

2893

3245

3595

395

4298

500

J surf

(Am

m)

(b)

Figure 6 Surface current distribution of the proposed antenna at (a) the first band at 24GHz and (b) the second band at 56GHzG

ain

(dBi

)

2100

1978

1855

1732

1609

1486

1363

(a)

Gai

n (d

Bi)

2100

1978

1855

1732

1609

1486

1363

(b)

Figure 7 Three-dimensional radiation patterns of the proposed antenna at (a) the first band at 24GHz and (b) the second band at 56GHz

31 Parametric Studies The geometrical parameters to bestudied in this section are the length of the ground plane(119871g) the total length of the strip monopole (119871) and the fourparameters of the parasitic resonator which are 119871p1119882p1 119871p2and 119882p2 These studies are conducted with a fixed groundplane width of 119882g = 10mm and a monopole (and feeder)width of 119882 = 3mm so that the line impedance of themicrostrip feeder remains 50Ω It should be mentioned thatin the studies the results corresponding to the parameterslisted in Table 1 (and those of the final design) are plottedusing solid lines First the effect of the truncated groundplane length 119871g is investigated as shown in Figure 4(a)

It can be seen that this parameter is of great impacton both resonances in terms of resonance frequency andimpedance matching which is mainly because of the groundbeing truncated This can be beneficial to the antenna designas a good performance can be achieved with a small valueof 119871g leading to a compact design Afterwards the effectof length 119871 is analyzed and the results are depicted inFigure 4(b) As expected the second resonance is strongly

affected with the variation in 119871 since it represents theresonant length of the monopole A small shift in the lowerresonant frequency along with impedance matching effects isobserved and these are attributed to the coupling betweenthe parasitic resonator and the monopole

The impact of the four parameters related to the para-sitic resonator (119871p1 119882p1 119871p2 and 119882p2) is investigated asshown in Figures 5(a)ndash5(d) It can be observed that the fourparameters have similar effects on both bands of the proposedantenna When each parameter is varied the first band istuned whereas a variation in the second bands impedancebandwidth is observed The shift in the first band can beexplained by considering the average current path in theparasitic resonator shown in Figure 1 Varying any of thefour parameters results in a change in the resonators averagecurrent path length and accordingly its resonant frequencyOn the other hand the impedance bandwidth variationof the second band can be explained by investigating therelationship between the monopole radiator and the parasiticresonator The horizontal strip of the parasitic resonator acts

6 International Journal of Antennas and Propagation

(a) (b)

Figure 8 A photograph of the proposed dual-band monopole antenna (a) Front view (b) Back view

as a parasitic plane for the monopole which is known toaffect the impedance matching bandwidth at the monopolesoperating band as in [14] This applies to the proposedantenna as the size of the horizontal strip (determined by119882p1 119871p2 and 119882p2) and its position from the monopole(determined by 119871p1) affect the impedance bandwidth at thesecond band It is worthmentioning that when the horizontalstrip gets closer to the monopole a shift in the second band isobserved (see Figure 5(a)) To bemore specific the horizontalstrip starts to be directly beneath the monopole (for 119871p2 lessthan 12mm) which affects its resonance frequency

32 Current Distribution and Radiation Patterns The surfacecurrent distribution of the proposed dual-band antenna atboth of its resonant frequencies is shown in Figure 6 At thelower resonant frequency the current distribution shown inFigure 6(a) is mainly excited on the ground plane parasiticresonator with a quarter- wave variation On the other handthe current distribution at the higher resonant frequencywhich is shown in Figure 6(b) is prominent on themonopolewhich is observed to be of a quarter-wave variationThe sim-ulated three-dimensional radiation patterns of the antenna atboth resonant frequencies are shown in Figure 7 It is obviousthat the patterns are omnidirectional in both frequencies Itshould be mentioned that similar to conventional printedmonopoles the radiation at both bands is linearly polarized

4 Experimental Results

The proposed antenna shown in Figure 1 is fabricated on theFR-4 substrate with the dimensions stated in Section 2 Aphotograph of the fabricated antenna is shown in Figure 8

The measured reflection coefficient is plotted in Figure 9where it is found to be in good agreement with its simulatedcounterparts From the measured plots the first band is

MeasuredSimulated

3 4 5 6 72

Frequency (GHz)

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

Figure 9 Measured and simulated reflection coefficient of theproposed dual-band monopole

centered at 237GHz with a minus10 dB bandwidth of 03 GHzwhereas the second band is centered at 564GHz with aminus10 dB bandwidth of 16 GHz From applications standpointthe first band covers the 24GHz WLAN band whereasthe second band can cover both 52 and 58GHz WLANbands Also the first band is wide enough to cover the IEEEspecified PCS (Personal Communications Service) 24GHzcommunication band

The measured and simulated radiation patterns of thelinearly polarized antenna at the first and second bands areshown in Figures 10 and 11 respectively It can be clearly seenfrom both figures that the radiation patterns of the antennaat both bands exhibit omnidirectional-like behavior (witha maximum variation of 5 dB) Also low cross-polarization

International Journal of Antennas and Propagation 7

0

30

60

90

120

150

180

210

240

270

300

330

minus50 minus40 minus30 minus20 minus10 0

Hco simulatedHcx simulated

Hco measuredHcx measured

X

Y

Z

(a)

0

30

60

90

120

150

180

210

240

270

300

330

minus50 minus40 minus30 minus20 minus10 0

Eco simulatedEcx simulated

Eco measuredEcx measured

X

Y

Z

(b)

Figure 10 Measured and simulated radiation patterns of the antenna at the first band (24GHz) (a) H-plane (b) E-plane

0

30

60

90

120

150

180

210

240

270

300

330

minus50 minus40 minus30 minus20 minus10 0

Hco simulatedHcx simulated

Hco measuredHcx measured

X

Y

Z

(a)

0

30

60

90

120

150

180

210

240

270

300

330

minus50 minus40 minus30 minus20 minus10 0

Eco simulatedEcx simulated

Eco measuredEcx measured

X

Y

Z

(b)

Figure 11 Measured and simulated radiation patterns of the antenna at the second band (58GHz) (a) H-plane (b) E-plane

levels can be observed from the measured patterns The gainof the proposed antenna has been measured at both bands ofoperation and the results are shown in Figure 12(a) At thefirst band (around 24GHz) the antenna has an average gainof 18 dBi whereas it is 21 dBi at the second band (around56GHz) The measured efficiency of the proposed antenna

at both bands is shown in Figure 12(b) Peak efficiency of83 and 96 is obtained in the 24GHz and 58GHz bandsrespectively

A comparison between monopole antennas loaded withparasitic resonators and the proposed antenna in terms ofsize operating bands the bandwidth and the average peak

8 International Journal of Antennas and Propagation

220 225 230 235 240 245 250 255

Frequency (GHz)

Frequency (GHz)

24 GHz band58 GHz band

50 52 54 56 58 60 62

00

05

10

15

20

25

Gai

n (d

Bi)

(a)

220 225 230 235 240 245 250 255

Frequency (GHz)

Frequency (GHz)

24 GHz band58 GHz band

50 52 54 56 58 60 62

0

20

40

60

80

100

Effici

ency

()

(b)

Figure 12 Measured radiation performance of the proposed antenna (a) Gain (b) Efficiency

Table 2 Performance comparison of the proposed antenna with other antennas in the literature

Reference Size (mm)3 Operating bands (GHz) Bandwidth (GHz) andfractional bandwidth () Average peak gain (dBi)

[1] 30 times 30 times 08 34ndash762 422 (76) 4[2] 36 times 26 times 16 24ndash248 and 515ndash535 008 (33) and 02 (38) 36

[3] 30 times 20 times 16 214ndash252 282ndash374 and 515ndash602 038 (163) 092 (28) and087 (156) 246 245 and 3

[4] 30 times 18 times 16 239ndash269 338ndash373 and 50ndash599 03 (118) 035 (98) and099 (18) 252 237 and 415

[5] 37 times 20 times 0508 24ndash265 33ndash405 and 5ndash598 025 (99) 075 (204) and098 (178) Not mentioned

[6] 95 times 56 times 157 088ndash096 122ndash126 and 156ndash27 008 (87) 004 (322) and114 (535) 28 31 and 32

[9] 30 times 25 times 16 247ndash273 3-4 and 488ndash612 026 (10) 1 (286) and 124(225) 37 31 and 48

[10] 50 times 35 times 16 205ndash286 and 555ndash614 081 (33) and 124 (225) 373 and 359

[11] 345 times 18 times 16 235ndash249 327ndash38 and 465ndash589 014 (58) 053 (15) and124 (235)

284 228 and 429 (peakgains at center frequency)

[12] 22 times 28 times 08 249ndash266 341ndash373 and 473ndash593 017 (66) 032 (9) and 12(225)

3 42 and 45 (peak gains atcenter frequency)

[14] 50 times 35 times 16 086ndash098 17ndash25 and 472ndash661 012 (13) 08 (38) and 19(334) 113 201 and 374

Proposed antenna 25 times 10 times 16 222ndash255 and 48ndash65 033 (138) and 17 (3) 22

gain is given in Table 2 It is evident from Table 2 that theproposed antenna has a very compact size compared with theother antennas

5 Equivalent Circuit Modelling

In this section an R-L-C equivalent circuit model of theantenna is developed and verified with the aid of techniques

presented in [15] The equivalent circuit model of the pro-posed antenna is given in Figure 13The circuit consists of twoparallel R-L-C tanks along with a shunt branch The first twotank circuits correspond to the first and second resonancewhereas the shunt branch with R3 and L3 contributes to theinput impedance of the antenna

The parameters of the tank circuit can be computedby solving a set of equations formed as follows First

International Journal of Antennas and Propagation 9

C1

L1

R1

L2

C2

R2

L3

R3

Figure 13 The equivalent circuit model of the dual-band antenna

the series impedance of the circuit at any frequency (119891) willbe

119885Series at 119891 =1

radic(1198621120596 minus 1119871

1120596)2

+ 11198772

1

+1

radic(1198622120596 minus 1119871

2120596)2

+ 11198772

2

(3)

where 120596 = 2120587119891 At the first resonance the expression for theseries impedance is reduced to

119885Series at 1198651 = 1198771 +1

radic(11986221205961minus 1119871

21205961)2

+ 11198772

2

(4)

Similarly the expression for the series impedance at thesecond resonance is reduced to

119885Series at 1198652 = 1198772 +1

radic(11986211205962minus 1119871

11205962)2

+ 11198772

1

(5)

The shunt impedance of the circuit at a frequency 119891 will be

119885Shunt at 119891 = radic(1198713120596)2

+ 1198772

3 (6)

According to voltage dividing principle the ratio of outputvoltage to input voltage which is a measure of transmissioncoefficient can be obtained as

119881119900

119881119894

= 10(1minus11987811)20=119885Shunt

119885Shunt + 119885Series (7)

There are eight parameters in the model and to find themwe need eight equations These equations can be formulatedby choosing eight frequencies then substituting (3) and (6)into (7) By solving the formulated equations all the circuitparameters can be computed For the proposed antenna thevalues of the circuit elements in the model are 119871

1= 032 nH

1198712= 569 nH 119871

3= 0696 nH 119862

1= 14298 pF 119862

2= 1412 pF

1198771= 484Ω 119877

2= 5463Ω and 119877

3= 3623Ω The resonant

frequencies obtained from the equivalent circuit are 235GHzand 56GHz with a bandwidth of 024GHz in the first bandand 153GHz in the second band These results are in a verygood agreement with the experimental result as shown inFigure 14

3 4 5 6 72

Frequency (GHz)

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

MeasuredEquivalent circuit

Figure 14 Comparison between the measured reflection coefficientand that produced by the equivalent circuit model of the proposedantenna

6 Conclusion

A planar dual-band microstrip-fed monopole antenna of asimple and compact structure is presented Besides the bandexcited by the monopole radiator an additional band ofoperation is excited by placing a shorted inverted-L parasiticresonator on the bottom of the substrate The parasitic res-onator also improves the impedance bandwidth of the orig-inal band The microstrip feed is a truncated ground whosedimensions can be optimized to achieve a good performancewith compact sizeThe proposed antenna is designed to coverthe 2452ndash58GHz bands utilized in WLAN applicationsThe impact of the geometrical parameters on the perfor-mance of the dual-band monopole antenna is investigatedthrough a series of simulated parametric studies Measuredand simulated results show that the antenna operates at bothbandswith good impedancematching typicalmonopole-likeradiation patterns and flat gain An equivalent circuit modelof the proposed antenna which gives accurate results whencompared to measurements is presenteda

Competing Interests

The authors declare that there are no competing interestsregarding the publication of this paper

References

[1] W-C Liu C-M Wu and Y-J Tseng ldquoParasitically loadedCPW-fed monopole antenna for broadband operationrdquo IEEETransactions on Antennas and Propagation vol 59 no 6 pp2415ndash2419 2011

[2] K H Sayidmarie and T A Nagem ldquoCompact dual-band dual-ring printed mono-pole antennas for WLAN applicationsrdquoProgress in Electromagnetics ResearchB no 43 pp 313ndash331 2012

10 International Journal of Antennas and Propagation

[3] W-C Liu C-M Wu and Y Dai ldquoDesign of triple-frequencymicrostrip-fedmonopole antenna using defected ground struc-turerdquo IEEE Transactions on Antennas and Propagation vol 59no 7 pp 2457ndash2463 2011

[4] S S Huang J Li and J Z Zhao ldquoCompact CPW-fed tri-band antenna for WLANWIMAX applicationsrdquo Progress inElectromagnetics Research C vol 49 pp 39ndash45 2014

[5] L Xu Z Y Xin and J He ldquoA compact triple-band fork-shaped antenna for WLANWiMAX applicationsrdquo Progress inElectromagnetics Research Letters vol 40 pp 61ndash69 2013

[6] A A Ibrahim and A M E Safwat ldquoMicrostrip-fed monopoleantennas loaded with CRLH unit cellsrdquo IEEE Transactions onAntennas and Propagation vol 60 no 9 pp 4027ndash4036 2012

[7] H-D Chen ldquoGround plane effects on the microstrip-line-fed broadband sleeve monopole antennasrdquo IET MicrowavesAntennas and Propagation vol 2 no 6 pp 601ndash605 2008

[8] H-D Chen ldquoCompact broadband microstrip-line-fed sleevemonopole antenna for DTV application and ground planeeffectrdquo IEEE Antennas and Wireless Propagation Letters vol 7pp 497ndash500 2008

[9] J H Lu and B J Huang ldquoPlanar multi-bandmonopole antennawith L-shaped parasitic strip for WiMAX applicationrdquo IETElectronics Letters vol 46 no 10 pp 671ndash672 2010

[10] J R Panda and R S Kshetrimayum ldquoA printed 24 ghz58ghzdual-band monopole antenna with a protruding stub in theground plane for WLAN and RFID applicationsrdquo Progress inElectromagnetics Research vol 117 pp 425ndash434 2011

[11] P Xu Z-H Yan and C Wang ldquoMulti-band modified fork-shaped monopole antenna with dual L-shaped parasitic planerdquoElectronics Letters vol 47 no 6 pp 364ndash365 2011

[12] J-H Lu and Y-Y Lee ldquoPlanar compact triple-band monopoleantenna for IEEE 80216m worldwide interoperability formicrowave access systemrdquo IET Microwaves Antennas andPropagation vol 7 no 13 pp 1045ndash1054 2013

[13] K P Ray ldquoDesign aspects of printed monopole antennas forultra-wide band applicationsrdquo International Journal of Antennasand Propagation vol 2008 Article ID 713858 8 pages 2008

[14] K Seol J Jung and J Choi ldquoMulti-band monopole antennawith inverted U-shaped parasitic planerdquo IET Electronics lettersvol 42 no 15 pp 844ndash845 2006

[15] Q-X Chu and Y-Y Yang ldquoA compact ultrawideband antennawith 3455 GHz dual band-notched characteristicsrdquo IEEETransactions on Antennas and Propagation vol 56 no 12 pp3637ndash3644 2008

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DistributedSensor Networks

International Journal of

4 International Journal of Antennas and Propagation

3 4 5 6 72

Frequency (GHz)

minus30

minus25

minus20

minus15

minus10

minus5

01003816 1003816 1003816 1003816S

111003816 1003816 1003816 1003816

(dB)

Lg = 2mm

Lg = 4mm

Lg = 6mm

Lg = 8mm

Lg = 10mm

(a)

3 4 5 6 72

Frequency (GHz)

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

L = 11mm

L = 13mm

L = 15mm

L = 17mm

L = 19mm

(b)Figure 4 (a) The effects of varying length 119871g on the reflection coefficient of the proposed antenna Other parameters are the same as thoselisted in Table 1 (b) The effects of varying length 119871 on the reflection coefficient of the proposed antenna Other parameters are the same asthose listed in Table 1

3 4 5 6 72

Frequency (GHz)

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

Lp1 = 8mm

Lp1 = 10mm

Lp1 = 12mm

Lp1 = 14mm

Lp1 = 16mm

(a)

3 4 5 6 72

Frequency (GHz)

minus35

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

Wp1 = 03 mm

Wp1 = 05 mm

Wp1 = 07 mm

Wp1 = 09 mm

Wp1 = 11 mm

(b)

minus35

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

3 4 5 6 72

Frequency (GHz)

Lp2 = 55mm

Lp2 = 75mm

Lp2 = 95mm

Lp2 = 115 mm

Lp2 = 135mm

(c)

minus40

minus30

minus20

minus10

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

3 4 5 6 72

Frequency (GHz)

Wp2 = 3mm

Wp2 = 5mm

Wp2 = 7mm

Wp2 = 9mm

Wp2 = 11mm

(d)Figure 5 The effects of varying the four parameters of the parasitic resonator on the reflection coefficient of the proposed antenna (a) 119871p1(b)119882p1 (c) 119871p2 (d)119882p2 (In each study the other parameters are the same as those listed in Table 1)

International Journal of Antennas and Propagation 5

0852

2893

3245

3595

395

4298

500

J surf

(Am

m)

(a)

0852

2893

3245

3595

395

4298

500

J surf

(Am

m)

(b)

Figure 6 Surface current distribution of the proposed antenna at (a) the first band at 24GHz and (b) the second band at 56GHzG

ain

(dBi

)

2100

1978

1855

1732

1609

1486

1363

(a)

Gai

n (d

Bi)

2100

1978

1855

1732

1609

1486

1363

(b)

Figure 7 Three-dimensional radiation patterns of the proposed antenna at (a) the first band at 24GHz and (b) the second band at 56GHz

31 Parametric Studies The geometrical parameters to bestudied in this section are the length of the ground plane(119871g) the total length of the strip monopole (119871) and the fourparameters of the parasitic resonator which are 119871p1119882p1 119871p2and 119882p2 These studies are conducted with a fixed groundplane width of 119882g = 10mm and a monopole (and feeder)width of 119882 = 3mm so that the line impedance of themicrostrip feeder remains 50Ω It should be mentioned thatin the studies the results corresponding to the parameterslisted in Table 1 (and those of the final design) are plottedusing solid lines First the effect of the truncated groundplane length 119871g is investigated as shown in Figure 4(a)

It can be seen that this parameter is of great impacton both resonances in terms of resonance frequency andimpedance matching which is mainly because of the groundbeing truncated This can be beneficial to the antenna designas a good performance can be achieved with a small valueof 119871g leading to a compact design Afterwards the effectof length 119871 is analyzed and the results are depicted inFigure 4(b) As expected the second resonance is strongly

affected with the variation in 119871 since it represents theresonant length of the monopole A small shift in the lowerresonant frequency along with impedance matching effects isobserved and these are attributed to the coupling betweenthe parasitic resonator and the monopole

The impact of the four parameters related to the para-sitic resonator (119871p1 119882p1 119871p2 and 119882p2) is investigated asshown in Figures 5(a)ndash5(d) It can be observed that the fourparameters have similar effects on both bands of the proposedantenna When each parameter is varied the first band istuned whereas a variation in the second bands impedancebandwidth is observed The shift in the first band can beexplained by considering the average current path in theparasitic resonator shown in Figure 1 Varying any of thefour parameters results in a change in the resonators averagecurrent path length and accordingly its resonant frequencyOn the other hand the impedance bandwidth variationof the second band can be explained by investigating therelationship between the monopole radiator and the parasiticresonator The horizontal strip of the parasitic resonator acts

6 International Journal of Antennas and Propagation

(a) (b)

Figure 8 A photograph of the proposed dual-band monopole antenna (a) Front view (b) Back view

as a parasitic plane for the monopole which is known toaffect the impedance matching bandwidth at the monopolesoperating band as in [14] This applies to the proposedantenna as the size of the horizontal strip (determined by119882p1 119871p2 and 119882p2) and its position from the monopole(determined by 119871p1) affect the impedance bandwidth at thesecond band It is worthmentioning that when the horizontalstrip gets closer to the monopole a shift in the second band isobserved (see Figure 5(a)) To bemore specific the horizontalstrip starts to be directly beneath the monopole (for 119871p2 lessthan 12mm) which affects its resonance frequency

32 Current Distribution and Radiation Patterns The surfacecurrent distribution of the proposed dual-band antenna atboth of its resonant frequencies is shown in Figure 6 At thelower resonant frequency the current distribution shown inFigure 6(a) is mainly excited on the ground plane parasiticresonator with a quarter- wave variation On the other handthe current distribution at the higher resonant frequencywhich is shown in Figure 6(b) is prominent on themonopolewhich is observed to be of a quarter-wave variationThe sim-ulated three-dimensional radiation patterns of the antenna atboth resonant frequencies are shown in Figure 7 It is obviousthat the patterns are omnidirectional in both frequencies Itshould be mentioned that similar to conventional printedmonopoles the radiation at both bands is linearly polarized

4 Experimental Results

The proposed antenna shown in Figure 1 is fabricated on theFR-4 substrate with the dimensions stated in Section 2 Aphotograph of the fabricated antenna is shown in Figure 8

The measured reflection coefficient is plotted in Figure 9where it is found to be in good agreement with its simulatedcounterparts From the measured plots the first band is

MeasuredSimulated

3 4 5 6 72

Frequency (GHz)

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

Figure 9 Measured and simulated reflection coefficient of theproposed dual-band monopole

centered at 237GHz with a minus10 dB bandwidth of 03 GHzwhereas the second band is centered at 564GHz with aminus10 dB bandwidth of 16 GHz From applications standpointthe first band covers the 24GHz WLAN band whereasthe second band can cover both 52 and 58GHz WLANbands Also the first band is wide enough to cover the IEEEspecified PCS (Personal Communications Service) 24GHzcommunication band

The measured and simulated radiation patterns of thelinearly polarized antenna at the first and second bands areshown in Figures 10 and 11 respectively It can be clearly seenfrom both figures that the radiation patterns of the antennaat both bands exhibit omnidirectional-like behavior (witha maximum variation of 5 dB) Also low cross-polarization

International Journal of Antennas and Propagation 7

0

30

60

90

120

150

180

210

240

270

300

330

minus50 minus40 minus30 minus20 minus10 0

Hco simulatedHcx simulated

Hco measuredHcx measured

X

Y

Z

(a)

0

30

60

90

120

150

180

210

240

270

300

330

minus50 minus40 minus30 minus20 minus10 0

Eco simulatedEcx simulated

Eco measuredEcx measured

X

Y

Z

(b)

Figure 10 Measured and simulated radiation patterns of the antenna at the first band (24GHz) (a) H-plane (b) E-plane

0

30

60

90

120

150

180

210

240

270

300

330

minus50 minus40 minus30 minus20 minus10 0

Hco simulatedHcx simulated

Hco measuredHcx measured

X

Y

Z

(a)

0

30

60

90

120

150

180

210

240

270

300

330

minus50 minus40 minus30 minus20 minus10 0

Eco simulatedEcx simulated

Eco measuredEcx measured

X

Y

Z

(b)

Figure 11 Measured and simulated radiation patterns of the antenna at the second band (58GHz) (a) H-plane (b) E-plane

levels can be observed from the measured patterns The gainof the proposed antenna has been measured at both bands ofoperation and the results are shown in Figure 12(a) At thefirst band (around 24GHz) the antenna has an average gainof 18 dBi whereas it is 21 dBi at the second band (around56GHz) The measured efficiency of the proposed antenna

at both bands is shown in Figure 12(b) Peak efficiency of83 and 96 is obtained in the 24GHz and 58GHz bandsrespectively

A comparison between monopole antennas loaded withparasitic resonators and the proposed antenna in terms ofsize operating bands the bandwidth and the average peak

8 International Journal of Antennas and Propagation

220 225 230 235 240 245 250 255

Frequency (GHz)

Frequency (GHz)

24 GHz band58 GHz band

50 52 54 56 58 60 62

00

05

10

15

20

25

Gai

n (d

Bi)

(a)

220 225 230 235 240 245 250 255

Frequency (GHz)

Frequency (GHz)

24 GHz band58 GHz band

50 52 54 56 58 60 62

0

20

40

60

80

100

Effici

ency

()

(b)

Figure 12 Measured radiation performance of the proposed antenna (a) Gain (b) Efficiency

Table 2 Performance comparison of the proposed antenna with other antennas in the literature

Reference Size (mm)3 Operating bands (GHz) Bandwidth (GHz) andfractional bandwidth () Average peak gain (dBi)

[1] 30 times 30 times 08 34ndash762 422 (76) 4[2] 36 times 26 times 16 24ndash248 and 515ndash535 008 (33) and 02 (38) 36

[3] 30 times 20 times 16 214ndash252 282ndash374 and 515ndash602 038 (163) 092 (28) and087 (156) 246 245 and 3

[4] 30 times 18 times 16 239ndash269 338ndash373 and 50ndash599 03 (118) 035 (98) and099 (18) 252 237 and 415

[5] 37 times 20 times 0508 24ndash265 33ndash405 and 5ndash598 025 (99) 075 (204) and098 (178) Not mentioned

[6] 95 times 56 times 157 088ndash096 122ndash126 and 156ndash27 008 (87) 004 (322) and114 (535) 28 31 and 32

[9] 30 times 25 times 16 247ndash273 3-4 and 488ndash612 026 (10) 1 (286) and 124(225) 37 31 and 48

[10] 50 times 35 times 16 205ndash286 and 555ndash614 081 (33) and 124 (225) 373 and 359

[11] 345 times 18 times 16 235ndash249 327ndash38 and 465ndash589 014 (58) 053 (15) and124 (235)

284 228 and 429 (peakgains at center frequency)

[12] 22 times 28 times 08 249ndash266 341ndash373 and 473ndash593 017 (66) 032 (9) and 12(225)

3 42 and 45 (peak gains atcenter frequency)

[14] 50 times 35 times 16 086ndash098 17ndash25 and 472ndash661 012 (13) 08 (38) and 19(334) 113 201 and 374

Proposed antenna 25 times 10 times 16 222ndash255 and 48ndash65 033 (138) and 17 (3) 22

gain is given in Table 2 It is evident from Table 2 that theproposed antenna has a very compact size compared with theother antennas

5 Equivalent Circuit Modelling

In this section an R-L-C equivalent circuit model of theantenna is developed and verified with the aid of techniques

presented in [15] The equivalent circuit model of the pro-posed antenna is given in Figure 13The circuit consists of twoparallel R-L-C tanks along with a shunt branch The first twotank circuits correspond to the first and second resonancewhereas the shunt branch with R3 and L3 contributes to theinput impedance of the antenna

The parameters of the tank circuit can be computedby solving a set of equations formed as follows First

International Journal of Antennas and Propagation 9

C1

L1

R1

L2

C2

R2

L3

R3

Figure 13 The equivalent circuit model of the dual-band antenna

the series impedance of the circuit at any frequency (119891) willbe

119885Series at 119891 =1

radic(1198621120596 minus 1119871

1120596)2

+ 11198772

1

+1

radic(1198622120596 minus 1119871

2120596)2

+ 11198772

2

(3)

where 120596 = 2120587119891 At the first resonance the expression for theseries impedance is reduced to

119885Series at 1198651 = 1198771 +1

radic(11986221205961minus 1119871

21205961)2

+ 11198772

2

(4)

Similarly the expression for the series impedance at thesecond resonance is reduced to

119885Series at 1198652 = 1198772 +1

radic(11986211205962minus 1119871

11205962)2

+ 11198772

1

(5)

The shunt impedance of the circuit at a frequency 119891 will be

119885Shunt at 119891 = radic(1198713120596)2

+ 1198772

3 (6)

According to voltage dividing principle the ratio of outputvoltage to input voltage which is a measure of transmissioncoefficient can be obtained as

119881119900

119881119894

= 10(1minus11987811)20=119885Shunt

119885Shunt + 119885Series (7)

There are eight parameters in the model and to find themwe need eight equations These equations can be formulatedby choosing eight frequencies then substituting (3) and (6)into (7) By solving the formulated equations all the circuitparameters can be computed For the proposed antenna thevalues of the circuit elements in the model are 119871

1= 032 nH

1198712= 569 nH 119871

3= 0696 nH 119862

1= 14298 pF 119862

2= 1412 pF

1198771= 484Ω 119877

2= 5463Ω and 119877

3= 3623Ω The resonant

frequencies obtained from the equivalent circuit are 235GHzand 56GHz with a bandwidth of 024GHz in the first bandand 153GHz in the second band These results are in a verygood agreement with the experimental result as shown inFigure 14

3 4 5 6 72

Frequency (GHz)

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

MeasuredEquivalent circuit

Figure 14 Comparison between the measured reflection coefficientand that produced by the equivalent circuit model of the proposedantenna

6 Conclusion

A planar dual-band microstrip-fed monopole antenna of asimple and compact structure is presented Besides the bandexcited by the monopole radiator an additional band ofoperation is excited by placing a shorted inverted-L parasiticresonator on the bottom of the substrate The parasitic res-onator also improves the impedance bandwidth of the orig-inal band The microstrip feed is a truncated ground whosedimensions can be optimized to achieve a good performancewith compact sizeThe proposed antenna is designed to coverthe 2452ndash58GHz bands utilized in WLAN applicationsThe impact of the geometrical parameters on the perfor-mance of the dual-band monopole antenna is investigatedthrough a series of simulated parametric studies Measuredand simulated results show that the antenna operates at bothbandswith good impedancematching typicalmonopole-likeradiation patterns and flat gain An equivalent circuit modelof the proposed antenna which gives accurate results whencompared to measurements is presenteda

Competing Interests

The authors declare that there are no competing interestsregarding the publication of this paper

References

[1] W-C Liu C-M Wu and Y-J Tseng ldquoParasitically loadedCPW-fed monopole antenna for broadband operationrdquo IEEETransactions on Antennas and Propagation vol 59 no 6 pp2415ndash2419 2011

[2] K H Sayidmarie and T A Nagem ldquoCompact dual-band dual-ring printed mono-pole antennas for WLAN applicationsrdquoProgress in Electromagnetics ResearchB no 43 pp 313ndash331 2012

10 International Journal of Antennas and Propagation

[3] W-C Liu C-M Wu and Y Dai ldquoDesign of triple-frequencymicrostrip-fedmonopole antenna using defected ground struc-turerdquo IEEE Transactions on Antennas and Propagation vol 59no 7 pp 2457ndash2463 2011

[4] S S Huang J Li and J Z Zhao ldquoCompact CPW-fed tri-band antenna for WLANWIMAX applicationsrdquo Progress inElectromagnetics Research C vol 49 pp 39ndash45 2014

[5] L Xu Z Y Xin and J He ldquoA compact triple-band fork-shaped antenna for WLANWiMAX applicationsrdquo Progress inElectromagnetics Research Letters vol 40 pp 61ndash69 2013

[6] A A Ibrahim and A M E Safwat ldquoMicrostrip-fed monopoleantennas loaded with CRLH unit cellsrdquo IEEE Transactions onAntennas and Propagation vol 60 no 9 pp 4027ndash4036 2012

[7] H-D Chen ldquoGround plane effects on the microstrip-line-fed broadband sleeve monopole antennasrdquo IET MicrowavesAntennas and Propagation vol 2 no 6 pp 601ndash605 2008

[8] H-D Chen ldquoCompact broadband microstrip-line-fed sleevemonopole antenna for DTV application and ground planeeffectrdquo IEEE Antennas and Wireless Propagation Letters vol 7pp 497ndash500 2008

[9] J H Lu and B J Huang ldquoPlanar multi-bandmonopole antennawith L-shaped parasitic strip for WiMAX applicationrdquo IETElectronics Letters vol 46 no 10 pp 671ndash672 2010

[10] J R Panda and R S Kshetrimayum ldquoA printed 24 ghz58ghzdual-band monopole antenna with a protruding stub in theground plane for WLAN and RFID applicationsrdquo Progress inElectromagnetics Research vol 117 pp 425ndash434 2011

[11] P Xu Z-H Yan and C Wang ldquoMulti-band modified fork-shaped monopole antenna with dual L-shaped parasitic planerdquoElectronics Letters vol 47 no 6 pp 364ndash365 2011

[12] J-H Lu and Y-Y Lee ldquoPlanar compact triple-band monopoleantenna for IEEE 80216m worldwide interoperability formicrowave access systemrdquo IET Microwaves Antennas andPropagation vol 7 no 13 pp 1045ndash1054 2013

[13] K P Ray ldquoDesign aspects of printed monopole antennas forultra-wide band applicationsrdquo International Journal of Antennasand Propagation vol 2008 Article ID 713858 8 pages 2008

[14] K Seol J Jung and J Choi ldquoMulti-band monopole antennawith inverted U-shaped parasitic planerdquo IET Electronics lettersvol 42 no 15 pp 844ndash845 2006

[15] Q-X Chu and Y-Y Yang ldquoA compact ultrawideband antennawith 3455 GHz dual band-notched characteristicsrdquo IEEETransactions on Antennas and Propagation vol 56 no 12 pp3637ndash3644 2008

International Journal of

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VLSI Design

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Electrical and Computer Engineering

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Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

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Chemical EngineeringInternational Journal of Antennas and

Propagation

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Navigation and Observation

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DistributedSensor Networks

International Journal of

International Journal of Antennas and Propagation 5

0852

2893

3245

3595

395

4298

500

J surf

(Am

m)

(a)

0852

2893

3245

3595

395

4298

500

J surf

(Am

m)

(b)

Figure 6 Surface current distribution of the proposed antenna at (a) the first band at 24GHz and (b) the second band at 56GHzG

ain

(dBi

)

2100

1978

1855

1732

1609

1486

1363

(a)

Gai

n (d

Bi)

2100

1978

1855

1732

1609

1486

1363

(b)

Figure 7 Three-dimensional radiation patterns of the proposed antenna at (a) the first band at 24GHz and (b) the second band at 56GHz

31 Parametric Studies The geometrical parameters to bestudied in this section are the length of the ground plane(119871g) the total length of the strip monopole (119871) and the fourparameters of the parasitic resonator which are 119871p1119882p1 119871p2and 119882p2 These studies are conducted with a fixed groundplane width of 119882g = 10mm and a monopole (and feeder)width of 119882 = 3mm so that the line impedance of themicrostrip feeder remains 50Ω It should be mentioned thatin the studies the results corresponding to the parameterslisted in Table 1 (and those of the final design) are plottedusing solid lines First the effect of the truncated groundplane length 119871g is investigated as shown in Figure 4(a)

It can be seen that this parameter is of great impacton both resonances in terms of resonance frequency andimpedance matching which is mainly because of the groundbeing truncated This can be beneficial to the antenna designas a good performance can be achieved with a small valueof 119871g leading to a compact design Afterwards the effectof length 119871 is analyzed and the results are depicted inFigure 4(b) As expected the second resonance is strongly

affected with the variation in 119871 since it represents theresonant length of the monopole A small shift in the lowerresonant frequency along with impedance matching effects isobserved and these are attributed to the coupling betweenthe parasitic resonator and the monopole

The impact of the four parameters related to the para-sitic resonator (119871p1 119882p1 119871p2 and 119882p2) is investigated asshown in Figures 5(a)ndash5(d) It can be observed that the fourparameters have similar effects on both bands of the proposedantenna When each parameter is varied the first band istuned whereas a variation in the second bands impedancebandwidth is observed The shift in the first band can beexplained by considering the average current path in theparasitic resonator shown in Figure 1 Varying any of thefour parameters results in a change in the resonators averagecurrent path length and accordingly its resonant frequencyOn the other hand the impedance bandwidth variationof the second band can be explained by investigating therelationship between the monopole radiator and the parasiticresonator The horizontal strip of the parasitic resonator acts

6 International Journal of Antennas and Propagation

(a) (b)

Figure 8 A photograph of the proposed dual-band monopole antenna (a) Front view (b) Back view

as a parasitic plane for the monopole which is known toaffect the impedance matching bandwidth at the monopolesoperating band as in [14] This applies to the proposedantenna as the size of the horizontal strip (determined by119882p1 119871p2 and 119882p2) and its position from the monopole(determined by 119871p1) affect the impedance bandwidth at thesecond band It is worthmentioning that when the horizontalstrip gets closer to the monopole a shift in the second band isobserved (see Figure 5(a)) To bemore specific the horizontalstrip starts to be directly beneath the monopole (for 119871p2 lessthan 12mm) which affects its resonance frequency

32 Current Distribution and Radiation Patterns The surfacecurrent distribution of the proposed dual-band antenna atboth of its resonant frequencies is shown in Figure 6 At thelower resonant frequency the current distribution shown inFigure 6(a) is mainly excited on the ground plane parasiticresonator with a quarter- wave variation On the other handthe current distribution at the higher resonant frequencywhich is shown in Figure 6(b) is prominent on themonopolewhich is observed to be of a quarter-wave variationThe sim-ulated three-dimensional radiation patterns of the antenna atboth resonant frequencies are shown in Figure 7 It is obviousthat the patterns are omnidirectional in both frequencies Itshould be mentioned that similar to conventional printedmonopoles the radiation at both bands is linearly polarized

4 Experimental Results

The proposed antenna shown in Figure 1 is fabricated on theFR-4 substrate with the dimensions stated in Section 2 Aphotograph of the fabricated antenna is shown in Figure 8

The measured reflection coefficient is plotted in Figure 9where it is found to be in good agreement with its simulatedcounterparts From the measured plots the first band is

MeasuredSimulated

3 4 5 6 72

Frequency (GHz)

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

Figure 9 Measured and simulated reflection coefficient of theproposed dual-band monopole

centered at 237GHz with a minus10 dB bandwidth of 03 GHzwhereas the second band is centered at 564GHz with aminus10 dB bandwidth of 16 GHz From applications standpointthe first band covers the 24GHz WLAN band whereasthe second band can cover both 52 and 58GHz WLANbands Also the first band is wide enough to cover the IEEEspecified PCS (Personal Communications Service) 24GHzcommunication band

The measured and simulated radiation patterns of thelinearly polarized antenna at the first and second bands areshown in Figures 10 and 11 respectively It can be clearly seenfrom both figures that the radiation patterns of the antennaat both bands exhibit omnidirectional-like behavior (witha maximum variation of 5 dB) Also low cross-polarization

International Journal of Antennas and Propagation 7

0

30

60

90

120

150

180

210

240

270

300

330

minus50 minus40 minus30 minus20 minus10 0

Hco simulatedHcx simulated

Hco measuredHcx measured

X

Y

Z

(a)

0

30

60

90

120

150

180

210

240

270

300

330

minus50 minus40 minus30 minus20 minus10 0

Eco simulatedEcx simulated

Eco measuredEcx measured

X

Y

Z

(b)

Figure 10 Measured and simulated radiation patterns of the antenna at the first band (24GHz) (a) H-plane (b) E-plane

0

30

60

90

120

150

180

210

240

270

300

330

minus50 minus40 minus30 minus20 minus10 0

Hco simulatedHcx simulated

Hco measuredHcx measured

X

Y

Z

(a)

0

30

60

90

120

150

180

210

240

270

300

330

minus50 minus40 minus30 minus20 minus10 0

Eco simulatedEcx simulated

Eco measuredEcx measured

X

Y

Z

(b)

Figure 11 Measured and simulated radiation patterns of the antenna at the second band (58GHz) (a) H-plane (b) E-plane

levels can be observed from the measured patterns The gainof the proposed antenna has been measured at both bands ofoperation and the results are shown in Figure 12(a) At thefirst band (around 24GHz) the antenna has an average gainof 18 dBi whereas it is 21 dBi at the second band (around56GHz) The measured efficiency of the proposed antenna

at both bands is shown in Figure 12(b) Peak efficiency of83 and 96 is obtained in the 24GHz and 58GHz bandsrespectively

A comparison between monopole antennas loaded withparasitic resonators and the proposed antenna in terms ofsize operating bands the bandwidth and the average peak

8 International Journal of Antennas and Propagation

220 225 230 235 240 245 250 255

Frequency (GHz)

Frequency (GHz)

24 GHz band58 GHz band

50 52 54 56 58 60 62

00

05

10

15

20

25

Gai

n (d

Bi)

(a)

220 225 230 235 240 245 250 255

Frequency (GHz)

Frequency (GHz)

24 GHz band58 GHz band

50 52 54 56 58 60 62

0

20

40

60

80

100

Effici

ency

()

(b)

Figure 12 Measured radiation performance of the proposed antenna (a) Gain (b) Efficiency

Table 2 Performance comparison of the proposed antenna with other antennas in the literature

Reference Size (mm)3 Operating bands (GHz) Bandwidth (GHz) andfractional bandwidth () Average peak gain (dBi)

[1] 30 times 30 times 08 34ndash762 422 (76) 4[2] 36 times 26 times 16 24ndash248 and 515ndash535 008 (33) and 02 (38) 36

[3] 30 times 20 times 16 214ndash252 282ndash374 and 515ndash602 038 (163) 092 (28) and087 (156) 246 245 and 3

[4] 30 times 18 times 16 239ndash269 338ndash373 and 50ndash599 03 (118) 035 (98) and099 (18) 252 237 and 415

[5] 37 times 20 times 0508 24ndash265 33ndash405 and 5ndash598 025 (99) 075 (204) and098 (178) Not mentioned

[6] 95 times 56 times 157 088ndash096 122ndash126 and 156ndash27 008 (87) 004 (322) and114 (535) 28 31 and 32

[9] 30 times 25 times 16 247ndash273 3-4 and 488ndash612 026 (10) 1 (286) and 124(225) 37 31 and 48

[10] 50 times 35 times 16 205ndash286 and 555ndash614 081 (33) and 124 (225) 373 and 359

[11] 345 times 18 times 16 235ndash249 327ndash38 and 465ndash589 014 (58) 053 (15) and124 (235)

284 228 and 429 (peakgains at center frequency)

[12] 22 times 28 times 08 249ndash266 341ndash373 and 473ndash593 017 (66) 032 (9) and 12(225)

3 42 and 45 (peak gains atcenter frequency)

[14] 50 times 35 times 16 086ndash098 17ndash25 and 472ndash661 012 (13) 08 (38) and 19(334) 113 201 and 374

Proposed antenna 25 times 10 times 16 222ndash255 and 48ndash65 033 (138) and 17 (3) 22

gain is given in Table 2 It is evident from Table 2 that theproposed antenna has a very compact size compared with theother antennas

5 Equivalent Circuit Modelling

In this section an R-L-C equivalent circuit model of theantenna is developed and verified with the aid of techniques

presented in [15] The equivalent circuit model of the pro-posed antenna is given in Figure 13The circuit consists of twoparallel R-L-C tanks along with a shunt branch The first twotank circuits correspond to the first and second resonancewhereas the shunt branch with R3 and L3 contributes to theinput impedance of the antenna

The parameters of the tank circuit can be computedby solving a set of equations formed as follows First

International Journal of Antennas and Propagation 9

C1

L1

R1

L2

C2

R2

L3

R3

Figure 13 The equivalent circuit model of the dual-band antenna

the series impedance of the circuit at any frequency (119891) willbe

119885Series at 119891 =1

radic(1198621120596 minus 1119871

1120596)2

+ 11198772

1

+1

radic(1198622120596 minus 1119871

2120596)2

+ 11198772

2

(3)

where 120596 = 2120587119891 At the first resonance the expression for theseries impedance is reduced to

119885Series at 1198651 = 1198771 +1

radic(11986221205961minus 1119871

21205961)2

+ 11198772

2

(4)

Similarly the expression for the series impedance at thesecond resonance is reduced to

119885Series at 1198652 = 1198772 +1

radic(11986211205962minus 1119871

11205962)2

+ 11198772

1

(5)

The shunt impedance of the circuit at a frequency 119891 will be

119885Shunt at 119891 = radic(1198713120596)2

+ 1198772

3 (6)

According to voltage dividing principle the ratio of outputvoltage to input voltage which is a measure of transmissioncoefficient can be obtained as

119881119900

119881119894

= 10(1minus11987811)20=119885Shunt

119885Shunt + 119885Series (7)

There are eight parameters in the model and to find themwe need eight equations These equations can be formulatedby choosing eight frequencies then substituting (3) and (6)into (7) By solving the formulated equations all the circuitparameters can be computed For the proposed antenna thevalues of the circuit elements in the model are 119871

1= 032 nH

1198712= 569 nH 119871

3= 0696 nH 119862

1= 14298 pF 119862

2= 1412 pF

1198771= 484Ω 119877

2= 5463Ω and 119877

3= 3623Ω The resonant

frequencies obtained from the equivalent circuit are 235GHzand 56GHz with a bandwidth of 024GHz in the first bandand 153GHz in the second band These results are in a verygood agreement with the experimental result as shown inFigure 14

3 4 5 6 72

Frequency (GHz)

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

MeasuredEquivalent circuit

Figure 14 Comparison between the measured reflection coefficientand that produced by the equivalent circuit model of the proposedantenna

6 Conclusion

A planar dual-band microstrip-fed monopole antenna of asimple and compact structure is presented Besides the bandexcited by the monopole radiator an additional band ofoperation is excited by placing a shorted inverted-L parasiticresonator on the bottom of the substrate The parasitic res-onator also improves the impedance bandwidth of the orig-inal band The microstrip feed is a truncated ground whosedimensions can be optimized to achieve a good performancewith compact sizeThe proposed antenna is designed to coverthe 2452ndash58GHz bands utilized in WLAN applicationsThe impact of the geometrical parameters on the perfor-mance of the dual-band monopole antenna is investigatedthrough a series of simulated parametric studies Measuredand simulated results show that the antenna operates at bothbandswith good impedancematching typicalmonopole-likeradiation patterns and flat gain An equivalent circuit modelof the proposed antenna which gives accurate results whencompared to measurements is presenteda

Competing Interests

The authors declare that there are no competing interestsregarding the publication of this paper

References

[1] W-C Liu C-M Wu and Y-J Tseng ldquoParasitically loadedCPW-fed monopole antenna for broadband operationrdquo IEEETransactions on Antennas and Propagation vol 59 no 6 pp2415ndash2419 2011

[2] K H Sayidmarie and T A Nagem ldquoCompact dual-band dual-ring printed mono-pole antennas for WLAN applicationsrdquoProgress in Electromagnetics ResearchB no 43 pp 313ndash331 2012

10 International Journal of Antennas and Propagation

[3] W-C Liu C-M Wu and Y Dai ldquoDesign of triple-frequencymicrostrip-fedmonopole antenna using defected ground struc-turerdquo IEEE Transactions on Antennas and Propagation vol 59no 7 pp 2457ndash2463 2011

[4] S S Huang J Li and J Z Zhao ldquoCompact CPW-fed tri-band antenna for WLANWIMAX applicationsrdquo Progress inElectromagnetics Research C vol 49 pp 39ndash45 2014

[5] L Xu Z Y Xin and J He ldquoA compact triple-band fork-shaped antenna for WLANWiMAX applicationsrdquo Progress inElectromagnetics Research Letters vol 40 pp 61ndash69 2013

[6] A A Ibrahim and A M E Safwat ldquoMicrostrip-fed monopoleantennas loaded with CRLH unit cellsrdquo IEEE Transactions onAntennas and Propagation vol 60 no 9 pp 4027ndash4036 2012

[7] H-D Chen ldquoGround plane effects on the microstrip-line-fed broadband sleeve monopole antennasrdquo IET MicrowavesAntennas and Propagation vol 2 no 6 pp 601ndash605 2008

[8] H-D Chen ldquoCompact broadband microstrip-line-fed sleevemonopole antenna for DTV application and ground planeeffectrdquo IEEE Antennas and Wireless Propagation Letters vol 7pp 497ndash500 2008

[9] J H Lu and B J Huang ldquoPlanar multi-bandmonopole antennawith L-shaped parasitic strip for WiMAX applicationrdquo IETElectronics Letters vol 46 no 10 pp 671ndash672 2010

[10] J R Panda and R S Kshetrimayum ldquoA printed 24 ghz58ghzdual-band monopole antenna with a protruding stub in theground plane for WLAN and RFID applicationsrdquo Progress inElectromagnetics Research vol 117 pp 425ndash434 2011

[11] P Xu Z-H Yan and C Wang ldquoMulti-band modified fork-shaped monopole antenna with dual L-shaped parasitic planerdquoElectronics Letters vol 47 no 6 pp 364ndash365 2011

[12] J-H Lu and Y-Y Lee ldquoPlanar compact triple-band monopoleantenna for IEEE 80216m worldwide interoperability formicrowave access systemrdquo IET Microwaves Antennas andPropagation vol 7 no 13 pp 1045ndash1054 2013

[13] K P Ray ldquoDesign aspects of printed monopole antennas forultra-wide band applicationsrdquo International Journal of Antennasand Propagation vol 2008 Article ID 713858 8 pages 2008

[14] K Seol J Jung and J Choi ldquoMulti-band monopole antennawith inverted U-shaped parasitic planerdquo IET Electronics lettersvol 42 no 15 pp 844ndash845 2006

[15] Q-X Chu and Y-Y Yang ldquoA compact ultrawideband antennawith 3455 GHz dual band-notched characteristicsrdquo IEEETransactions on Antennas and Propagation vol 56 no 12 pp3637ndash3644 2008

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

6 International Journal of Antennas and Propagation

(a) (b)

Figure 8 A photograph of the proposed dual-band monopole antenna (a) Front view (b) Back view

as a parasitic plane for the monopole which is known toaffect the impedance matching bandwidth at the monopolesoperating band as in [14] This applies to the proposedantenna as the size of the horizontal strip (determined by119882p1 119871p2 and 119882p2) and its position from the monopole(determined by 119871p1) affect the impedance bandwidth at thesecond band It is worthmentioning that when the horizontalstrip gets closer to the monopole a shift in the second band isobserved (see Figure 5(a)) To bemore specific the horizontalstrip starts to be directly beneath the monopole (for 119871p2 lessthan 12mm) which affects its resonance frequency

32 Current Distribution and Radiation Patterns The surfacecurrent distribution of the proposed dual-band antenna atboth of its resonant frequencies is shown in Figure 6 At thelower resonant frequency the current distribution shown inFigure 6(a) is mainly excited on the ground plane parasiticresonator with a quarter- wave variation On the other handthe current distribution at the higher resonant frequencywhich is shown in Figure 6(b) is prominent on themonopolewhich is observed to be of a quarter-wave variationThe sim-ulated three-dimensional radiation patterns of the antenna atboth resonant frequencies are shown in Figure 7 It is obviousthat the patterns are omnidirectional in both frequencies Itshould be mentioned that similar to conventional printedmonopoles the radiation at both bands is linearly polarized

4 Experimental Results

The proposed antenna shown in Figure 1 is fabricated on theFR-4 substrate with the dimensions stated in Section 2 Aphotograph of the fabricated antenna is shown in Figure 8

The measured reflection coefficient is plotted in Figure 9where it is found to be in good agreement with its simulatedcounterparts From the measured plots the first band is

MeasuredSimulated

3 4 5 6 72

Frequency (GHz)

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

Figure 9 Measured and simulated reflection coefficient of theproposed dual-band monopole

centered at 237GHz with a minus10 dB bandwidth of 03 GHzwhereas the second band is centered at 564GHz with aminus10 dB bandwidth of 16 GHz From applications standpointthe first band covers the 24GHz WLAN band whereasthe second band can cover both 52 and 58GHz WLANbands Also the first band is wide enough to cover the IEEEspecified PCS (Personal Communications Service) 24GHzcommunication band

The measured and simulated radiation patterns of thelinearly polarized antenna at the first and second bands areshown in Figures 10 and 11 respectively It can be clearly seenfrom both figures that the radiation patterns of the antennaat both bands exhibit omnidirectional-like behavior (witha maximum variation of 5 dB) Also low cross-polarization

International Journal of Antennas and Propagation 7

0

30

60

90

120

150

180

210

240

270

300

330

minus50 minus40 minus30 minus20 minus10 0

Hco simulatedHcx simulated

Hco measuredHcx measured

X

Y

Z

(a)

0

30

60

90

120

150

180

210

240

270

300

330

minus50 minus40 minus30 minus20 minus10 0

Eco simulatedEcx simulated

Eco measuredEcx measured

X

Y

Z

(b)

Figure 10 Measured and simulated radiation patterns of the antenna at the first band (24GHz) (a) H-plane (b) E-plane

0

30

60

90

120

150

180

210

240

270

300

330

minus50 minus40 minus30 minus20 minus10 0

Hco simulatedHcx simulated

Hco measuredHcx measured

X

Y

Z

(a)

0

30

60

90

120

150

180

210

240

270

300

330

minus50 minus40 minus30 minus20 minus10 0

Eco simulatedEcx simulated

Eco measuredEcx measured

X

Y

Z

(b)

Figure 11 Measured and simulated radiation patterns of the antenna at the second band (58GHz) (a) H-plane (b) E-plane

levels can be observed from the measured patterns The gainof the proposed antenna has been measured at both bands ofoperation and the results are shown in Figure 12(a) At thefirst band (around 24GHz) the antenna has an average gainof 18 dBi whereas it is 21 dBi at the second band (around56GHz) The measured efficiency of the proposed antenna

at both bands is shown in Figure 12(b) Peak efficiency of83 and 96 is obtained in the 24GHz and 58GHz bandsrespectively

A comparison between monopole antennas loaded withparasitic resonators and the proposed antenna in terms ofsize operating bands the bandwidth and the average peak

8 International Journal of Antennas and Propagation

220 225 230 235 240 245 250 255

Frequency (GHz)

Frequency (GHz)

24 GHz band58 GHz band

50 52 54 56 58 60 62

00

05

10

15

20

25

Gai

n (d

Bi)

(a)

220 225 230 235 240 245 250 255

Frequency (GHz)

Frequency (GHz)

24 GHz band58 GHz band

50 52 54 56 58 60 62

0

20

40

60

80

100

Effici

ency

()

(b)

Figure 12 Measured radiation performance of the proposed antenna (a) Gain (b) Efficiency

Table 2 Performance comparison of the proposed antenna with other antennas in the literature

Reference Size (mm)3 Operating bands (GHz) Bandwidth (GHz) andfractional bandwidth () Average peak gain (dBi)

[1] 30 times 30 times 08 34ndash762 422 (76) 4[2] 36 times 26 times 16 24ndash248 and 515ndash535 008 (33) and 02 (38) 36

[3] 30 times 20 times 16 214ndash252 282ndash374 and 515ndash602 038 (163) 092 (28) and087 (156) 246 245 and 3

[4] 30 times 18 times 16 239ndash269 338ndash373 and 50ndash599 03 (118) 035 (98) and099 (18) 252 237 and 415

[5] 37 times 20 times 0508 24ndash265 33ndash405 and 5ndash598 025 (99) 075 (204) and098 (178) Not mentioned

[6] 95 times 56 times 157 088ndash096 122ndash126 and 156ndash27 008 (87) 004 (322) and114 (535) 28 31 and 32

[9] 30 times 25 times 16 247ndash273 3-4 and 488ndash612 026 (10) 1 (286) and 124(225) 37 31 and 48

[10] 50 times 35 times 16 205ndash286 and 555ndash614 081 (33) and 124 (225) 373 and 359

[11] 345 times 18 times 16 235ndash249 327ndash38 and 465ndash589 014 (58) 053 (15) and124 (235)

284 228 and 429 (peakgains at center frequency)

[12] 22 times 28 times 08 249ndash266 341ndash373 and 473ndash593 017 (66) 032 (9) and 12(225)

3 42 and 45 (peak gains atcenter frequency)

[14] 50 times 35 times 16 086ndash098 17ndash25 and 472ndash661 012 (13) 08 (38) and 19(334) 113 201 and 374

Proposed antenna 25 times 10 times 16 222ndash255 and 48ndash65 033 (138) and 17 (3) 22

gain is given in Table 2 It is evident from Table 2 that theproposed antenna has a very compact size compared with theother antennas

5 Equivalent Circuit Modelling

In this section an R-L-C equivalent circuit model of theantenna is developed and verified with the aid of techniques

presented in [15] The equivalent circuit model of the pro-posed antenna is given in Figure 13The circuit consists of twoparallel R-L-C tanks along with a shunt branch The first twotank circuits correspond to the first and second resonancewhereas the shunt branch with R3 and L3 contributes to theinput impedance of the antenna

The parameters of the tank circuit can be computedby solving a set of equations formed as follows First

International Journal of Antennas and Propagation 9

C1

L1

R1

L2

C2

R2

L3

R3

Figure 13 The equivalent circuit model of the dual-band antenna

the series impedance of the circuit at any frequency (119891) willbe

119885Series at 119891 =1

radic(1198621120596 minus 1119871

1120596)2

+ 11198772

1

+1

radic(1198622120596 minus 1119871

2120596)2

+ 11198772

2

(3)

where 120596 = 2120587119891 At the first resonance the expression for theseries impedance is reduced to

119885Series at 1198651 = 1198771 +1

radic(11986221205961minus 1119871

21205961)2

+ 11198772

2

(4)

Similarly the expression for the series impedance at thesecond resonance is reduced to

119885Series at 1198652 = 1198772 +1

radic(11986211205962minus 1119871

11205962)2

+ 11198772

1

(5)

The shunt impedance of the circuit at a frequency 119891 will be

119885Shunt at 119891 = radic(1198713120596)2

+ 1198772

3 (6)

According to voltage dividing principle the ratio of outputvoltage to input voltage which is a measure of transmissioncoefficient can be obtained as

119881119900

119881119894

= 10(1minus11987811)20=119885Shunt

119885Shunt + 119885Series (7)

There are eight parameters in the model and to find themwe need eight equations These equations can be formulatedby choosing eight frequencies then substituting (3) and (6)into (7) By solving the formulated equations all the circuitparameters can be computed For the proposed antenna thevalues of the circuit elements in the model are 119871

1= 032 nH

1198712= 569 nH 119871

3= 0696 nH 119862

1= 14298 pF 119862

2= 1412 pF

1198771= 484Ω 119877

2= 5463Ω and 119877

3= 3623Ω The resonant

frequencies obtained from the equivalent circuit are 235GHzand 56GHz with a bandwidth of 024GHz in the first bandand 153GHz in the second band These results are in a verygood agreement with the experimental result as shown inFigure 14

3 4 5 6 72

Frequency (GHz)

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

MeasuredEquivalent circuit

Figure 14 Comparison between the measured reflection coefficientand that produced by the equivalent circuit model of the proposedantenna

6 Conclusion

A planar dual-band microstrip-fed monopole antenna of asimple and compact structure is presented Besides the bandexcited by the monopole radiator an additional band ofoperation is excited by placing a shorted inverted-L parasiticresonator on the bottom of the substrate The parasitic res-onator also improves the impedance bandwidth of the orig-inal band The microstrip feed is a truncated ground whosedimensions can be optimized to achieve a good performancewith compact sizeThe proposed antenna is designed to coverthe 2452ndash58GHz bands utilized in WLAN applicationsThe impact of the geometrical parameters on the perfor-mance of the dual-band monopole antenna is investigatedthrough a series of simulated parametric studies Measuredand simulated results show that the antenna operates at bothbandswith good impedancematching typicalmonopole-likeradiation patterns and flat gain An equivalent circuit modelof the proposed antenna which gives accurate results whencompared to measurements is presenteda

Competing Interests

The authors declare that there are no competing interestsregarding the publication of this paper

References

[1] W-C Liu C-M Wu and Y-J Tseng ldquoParasitically loadedCPW-fed monopole antenna for broadband operationrdquo IEEETransactions on Antennas and Propagation vol 59 no 6 pp2415ndash2419 2011

[2] K H Sayidmarie and T A Nagem ldquoCompact dual-band dual-ring printed mono-pole antennas for WLAN applicationsrdquoProgress in Electromagnetics ResearchB no 43 pp 313ndash331 2012

10 International Journal of Antennas and Propagation

[3] W-C Liu C-M Wu and Y Dai ldquoDesign of triple-frequencymicrostrip-fedmonopole antenna using defected ground struc-turerdquo IEEE Transactions on Antennas and Propagation vol 59no 7 pp 2457ndash2463 2011

[4] S S Huang J Li and J Z Zhao ldquoCompact CPW-fed tri-band antenna for WLANWIMAX applicationsrdquo Progress inElectromagnetics Research C vol 49 pp 39ndash45 2014

[5] L Xu Z Y Xin and J He ldquoA compact triple-band fork-shaped antenna for WLANWiMAX applicationsrdquo Progress inElectromagnetics Research Letters vol 40 pp 61ndash69 2013

[6] A A Ibrahim and A M E Safwat ldquoMicrostrip-fed monopoleantennas loaded with CRLH unit cellsrdquo IEEE Transactions onAntennas and Propagation vol 60 no 9 pp 4027ndash4036 2012

[7] H-D Chen ldquoGround plane effects on the microstrip-line-fed broadband sleeve monopole antennasrdquo IET MicrowavesAntennas and Propagation vol 2 no 6 pp 601ndash605 2008

[8] H-D Chen ldquoCompact broadband microstrip-line-fed sleevemonopole antenna for DTV application and ground planeeffectrdquo IEEE Antennas and Wireless Propagation Letters vol 7pp 497ndash500 2008

[9] J H Lu and B J Huang ldquoPlanar multi-bandmonopole antennawith L-shaped parasitic strip for WiMAX applicationrdquo IETElectronics Letters vol 46 no 10 pp 671ndash672 2010

[10] J R Panda and R S Kshetrimayum ldquoA printed 24 ghz58ghzdual-band monopole antenna with a protruding stub in theground plane for WLAN and RFID applicationsrdquo Progress inElectromagnetics Research vol 117 pp 425ndash434 2011

[11] P Xu Z-H Yan and C Wang ldquoMulti-band modified fork-shaped monopole antenna with dual L-shaped parasitic planerdquoElectronics Letters vol 47 no 6 pp 364ndash365 2011

[12] J-H Lu and Y-Y Lee ldquoPlanar compact triple-band monopoleantenna for IEEE 80216m worldwide interoperability formicrowave access systemrdquo IET Microwaves Antennas andPropagation vol 7 no 13 pp 1045ndash1054 2013

[13] K P Ray ldquoDesign aspects of printed monopole antennas forultra-wide band applicationsrdquo International Journal of Antennasand Propagation vol 2008 Article ID 713858 8 pages 2008

[14] K Seol J Jung and J Choi ldquoMulti-band monopole antennawith inverted U-shaped parasitic planerdquo IET Electronics lettersvol 42 no 15 pp 844ndash845 2006

[15] Q-X Chu and Y-Y Yang ldquoA compact ultrawideband antennawith 3455 GHz dual band-notched characteristicsrdquo IEEETransactions on Antennas and Propagation vol 56 no 12 pp3637ndash3644 2008

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

International Journal of Antennas and Propagation 7

0

30

60

90

120

150

180

210

240

270

300

330

minus50 minus40 minus30 minus20 minus10 0

Hco simulatedHcx simulated

Hco measuredHcx measured

X

Y

Z

(a)

0

30

60

90

120

150

180

210

240

270

300

330

minus50 minus40 minus30 minus20 minus10 0

Eco simulatedEcx simulated

Eco measuredEcx measured

X

Y

Z

(b)

Figure 10 Measured and simulated radiation patterns of the antenna at the first band (24GHz) (a) H-plane (b) E-plane

0

30

60

90

120

150

180

210

240

270

300

330

minus50 minus40 minus30 minus20 minus10 0

Hco simulatedHcx simulated

Hco measuredHcx measured

X

Y

Z

(a)

0

30

60

90

120

150

180

210

240

270

300

330

minus50 minus40 minus30 minus20 minus10 0

Eco simulatedEcx simulated

Eco measuredEcx measured

X

Y

Z

(b)

Figure 11 Measured and simulated radiation patterns of the antenna at the second band (58GHz) (a) H-plane (b) E-plane

levels can be observed from the measured patterns The gainof the proposed antenna has been measured at both bands ofoperation and the results are shown in Figure 12(a) At thefirst band (around 24GHz) the antenna has an average gainof 18 dBi whereas it is 21 dBi at the second band (around56GHz) The measured efficiency of the proposed antenna

at both bands is shown in Figure 12(b) Peak efficiency of83 and 96 is obtained in the 24GHz and 58GHz bandsrespectively

A comparison between monopole antennas loaded withparasitic resonators and the proposed antenna in terms ofsize operating bands the bandwidth and the average peak

8 International Journal of Antennas and Propagation

220 225 230 235 240 245 250 255

Frequency (GHz)

Frequency (GHz)

24 GHz band58 GHz band

50 52 54 56 58 60 62

00

05

10

15

20

25

Gai

n (d

Bi)

(a)

220 225 230 235 240 245 250 255

Frequency (GHz)

Frequency (GHz)

24 GHz band58 GHz band

50 52 54 56 58 60 62

0

20

40

60

80

100

Effici

ency

()

(b)

Figure 12 Measured radiation performance of the proposed antenna (a) Gain (b) Efficiency

Table 2 Performance comparison of the proposed antenna with other antennas in the literature

Reference Size (mm)3 Operating bands (GHz) Bandwidth (GHz) andfractional bandwidth () Average peak gain (dBi)

[1] 30 times 30 times 08 34ndash762 422 (76) 4[2] 36 times 26 times 16 24ndash248 and 515ndash535 008 (33) and 02 (38) 36

[3] 30 times 20 times 16 214ndash252 282ndash374 and 515ndash602 038 (163) 092 (28) and087 (156) 246 245 and 3

[4] 30 times 18 times 16 239ndash269 338ndash373 and 50ndash599 03 (118) 035 (98) and099 (18) 252 237 and 415

[5] 37 times 20 times 0508 24ndash265 33ndash405 and 5ndash598 025 (99) 075 (204) and098 (178) Not mentioned

[6] 95 times 56 times 157 088ndash096 122ndash126 and 156ndash27 008 (87) 004 (322) and114 (535) 28 31 and 32

[9] 30 times 25 times 16 247ndash273 3-4 and 488ndash612 026 (10) 1 (286) and 124(225) 37 31 and 48

[10] 50 times 35 times 16 205ndash286 and 555ndash614 081 (33) and 124 (225) 373 and 359

[11] 345 times 18 times 16 235ndash249 327ndash38 and 465ndash589 014 (58) 053 (15) and124 (235)

284 228 and 429 (peakgains at center frequency)

[12] 22 times 28 times 08 249ndash266 341ndash373 and 473ndash593 017 (66) 032 (9) and 12(225)

3 42 and 45 (peak gains atcenter frequency)

[14] 50 times 35 times 16 086ndash098 17ndash25 and 472ndash661 012 (13) 08 (38) and 19(334) 113 201 and 374

Proposed antenna 25 times 10 times 16 222ndash255 and 48ndash65 033 (138) and 17 (3) 22

gain is given in Table 2 It is evident from Table 2 that theproposed antenna has a very compact size compared with theother antennas

5 Equivalent Circuit Modelling

In this section an R-L-C equivalent circuit model of theantenna is developed and verified with the aid of techniques

presented in [15] The equivalent circuit model of the pro-posed antenna is given in Figure 13The circuit consists of twoparallel R-L-C tanks along with a shunt branch The first twotank circuits correspond to the first and second resonancewhereas the shunt branch with R3 and L3 contributes to theinput impedance of the antenna

The parameters of the tank circuit can be computedby solving a set of equations formed as follows First

International Journal of Antennas and Propagation 9

C1

L1

R1

L2

C2

R2

L3

R3

Figure 13 The equivalent circuit model of the dual-band antenna

the series impedance of the circuit at any frequency (119891) willbe

119885Series at 119891 =1

radic(1198621120596 minus 1119871

1120596)2

+ 11198772

1

+1

radic(1198622120596 minus 1119871

2120596)2

+ 11198772

2

(3)

where 120596 = 2120587119891 At the first resonance the expression for theseries impedance is reduced to

119885Series at 1198651 = 1198771 +1

radic(11986221205961minus 1119871

21205961)2

+ 11198772

2

(4)

Similarly the expression for the series impedance at thesecond resonance is reduced to

119885Series at 1198652 = 1198772 +1

radic(11986211205962minus 1119871

11205962)2

+ 11198772

1

(5)

The shunt impedance of the circuit at a frequency 119891 will be

119885Shunt at 119891 = radic(1198713120596)2

+ 1198772

3 (6)

According to voltage dividing principle the ratio of outputvoltage to input voltage which is a measure of transmissioncoefficient can be obtained as

119881119900

119881119894

= 10(1minus11987811)20=119885Shunt

119885Shunt + 119885Series (7)

There are eight parameters in the model and to find themwe need eight equations These equations can be formulatedby choosing eight frequencies then substituting (3) and (6)into (7) By solving the formulated equations all the circuitparameters can be computed For the proposed antenna thevalues of the circuit elements in the model are 119871

1= 032 nH

1198712= 569 nH 119871

3= 0696 nH 119862

1= 14298 pF 119862

2= 1412 pF

1198771= 484Ω 119877

2= 5463Ω and 119877

3= 3623Ω The resonant

frequencies obtained from the equivalent circuit are 235GHzand 56GHz with a bandwidth of 024GHz in the first bandand 153GHz in the second band These results are in a verygood agreement with the experimental result as shown inFigure 14

3 4 5 6 72

Frequency (GHz)

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

MeasuredEquivalent circuit

Figure 14 Comparison between the measured reflection coefficientand that produced by the equivalent circuit model of the proposedantenna

6 Conclusion

A planar dual-band microstrip-fed monopole antenna of asimple and compact structure is presented Besides the bandexcited by the monopole radiator an additional band ofoperation is excited by placing a shorted inverted-L parasiticresonator on the bottom of the substrate The parasitic res-onator also improves the impedance bandwidth of the orig-inal band The microstrip feed is a truncated ground whosedimensions can be optimized to achieve a good performancewith compact sizeThe proposed antenna is designed to coverthe 2452ndash58GHz bands utilized in WLAN applicationsThe impact of the geometrical parameters on the perfor-mance of the dual-band monopole antenna is investigatedthrough a series of simulated parametric studies Measuredand simulated results show that the antenna operates at bothbandswith good impedancematching typicalmonopole-likeradiation patterns and flat gain An equivalent circuit modelof the proposed antenna which gives accurate results whencompared to measurements is presenteda

Competing Interests

The authors declare that there are no competing interestsregarding the publication of this paper

References

[1] W-C Liu C-M Wu and Y-J Tseng ldquoParasitically loadedCPW-fed monopole antenna for broadband operationrdquo IEEETransactions on Antennas and Propagation vol 59 no 6 pp2415ndash2419 2011

[2] K H Sayidmarie and T A Nagem ldquoCompact dual-band dual-ring printed mono-pole antennas for WLAN applicationsrdquoProgress in Electromagnetics ResearchB no 43 pp 313ndash331 2012

10 International Journal of Antennas and Propagation

[3] W-C Liu C-M Wu and Y Dai ldquoDesign of triple-frequencymicrostrip-fedmonopole antenna using defected ground struc-turerdquo IEEE Transactions on Antennas and Propagation vol 59no 7 pp 2457ndash2463 2011

[4] S S Huang J Li and J Z Zhao ldquoCompact CPW-fed tri-band antenna for WLANWIMAX applicationsrdquo Progress inElectromagnetics Research C vol 49 pp 39ndash45 2014

[5] L Xu Z Y Xin and J He ldquoA compact triple-band fork-shaped antenna for WLANWiMAX applicationsrdquo Progress inElectromagnetics Research Letters vol 40 pp 61ndash69 2013

[6] A A Ibrahim and A M E Safwat ldquoMicrostrip-fed monopoleantennas loaded with CRLH unit cellsrdquo IEEE Transactions onAntennas and Propagation vol 60 no 9 pp 4027ndash4036 2012

[7] H-D Chen ldquoGround plane effects on the microstrip-line-fed broadband sleeve monopole antennasrdquo IET MicrowavesAntennas and Propagation vol 2 no 6 pp 601ndash605 2008

[8] H-D Chen ldquoCompact broadband microstrip-line-fed sleevemonopole antenna for DTV application and ground planeeffectrdquo IEEE Antennas and Wireless Propagation Letters vol 7pp 497ndash500 2008

[9] J H Lu and B J Huang ldquoPlanar multi-bandmonopole antennawith L-shaped parasitic strip for WiMAX applicationrdquo IETElectronics Letters vol 46 no 10 pp 671ndash672 2010

[10] J R Panda and R S Kshetrimayum ldquoA printed 24 ghz58ghzdual-band monopole antenna with a protruding stub in theground plane for WLAN and RFID applicationsrdquo Progress inElectromagnetics Research vol 117 pp 425ndash434 2011

[11] P Xu Z-H Yan and C Wang ldquoMulti-band modified fork-shaped monopole antenna with dual L-shaped parasitic planerdquoElectronics Letters vol 47 no 6 pp 364ndash365 2011

[12] J-H Lu and Y-Y Lee ldquoPlanar compact triple-band monopoleantenna for IEEE 80216m worldwide interoperability formicrowave access systemrdquo IET Microwaves Antennas andPropagation vol 7 no 13 pp 1045ndash1054 2013

[13] K P Ray ldquoDesign aspects of printed monopole antennas forultra-wide band applicationsrdquo International Journal of Antennasand Propagation vol 2008 Article ID 713858 8 pages 2008

[14] K Seol J Jung and J Choi ldquoMulti-band monopole antennawith inverted U-shaped parasitic planerdquo IET Electronics lettersvol 42 no 15 pp 844ndash845 2006

[15] Q-X Chu and Y-Y Yang ldquoA compact ultrawideband antennawith 3455 GHz dual band-notched characteristicsrdquo IEEETransactions on Antennas and Propagation vol 56 no 12 pp3637ndash3644 2008

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

8 International Journal of Antennas and Propagation

220 225 230 235 240 245 250 255

Frequency (GHz)

Frequency (GHz)

24 GHz band58 GHz band

50 52 54 56 58 60 62

00

05

10

15

20

25

Gai

n (d

Bi)

(a)

220 225 230 235 240 245 250 255

Frequency (GHz)

Frequency (GHz)

24 GHz band58 GHz band

50 52 54 56 58 60 62

0

20

40

60

80

100

Effici

ency

()

(b)

Figure 12 Measured radiation performance of the proposed antenna (a) Gain (b) Efficiency

Table 2 Performance comparison of the proposed antenna with other antennas in the literature

Reference Size (mm)3 Operating bands (GHz) Bandwidth (GHz) andfractional bandwidth () Average peak gain (dBi)

[1] 30 times 30 times 08 34ndash762 422 (76) 4[2] 36 times 26 times 16 24ndash248 and 515ndash535 008 (33) and 02 (38) 36

[3] 30 times 20 times 16 214ndash252 282ndash374 and 515ndash602 038 (163) 092 (28) and087 (156) 246 245 and 3

[4] 30 times 18 times 16 239ndash269 338ndash373 and 50ndash599 03 (118) 035 (98) and099 (18) 252 237 and 415

[5] 37 times 20 times 0508 24ndash265 33ndash405 and 5ndash598 025 (99) 075 (204) and098 (178) Not mentioned

[6] 95 times 56 times 157 088ndash096 122ndash126 and 156ndash27 008 (87) 004 (322) and114 (535) 28 31 and 32

[9] 30 times 25 times 16 247ndash273 3-4 and 488ndash612 026 (10) 1 (286) and 124(225) 37 31 and 48

[10] 50 times 35 times 16 205ndash286 and 555ndash614 081 (33) and 124 (225) 373 and 359

[11] 345 times 18 times 16 235ndash249 327ndash38 and 465ndash589 014 (58) 053 (15) and124 (235)

284 228 and 429 (peakgains at center frequency)

[12] 22 times 28 times 08 249ndash266 341ndash373 and 473ndash593 017 (66) 032 (9) and 12(225)

3 42 and 45 (peak gains atcenter frequency)

[14] 50 times 35 times 16 086ndash098 17ndash25 and 472ndash661 012 (13) 08 (38) and 19(334) 113 201 and 374

Proposed antenna 25 times 10 times 16 222ndash255 and 48ndash65 033 (138) and 17 (3) 22

gain is given in Table 2 It is evident from Table 2 that theproposed antenna has a very compact size compared with theother antennas

5 Equivalent Circuit Modelling

In this section an R-L-C equivalent circuit model of theantenna is developed and verified with the aid of techniques

presented in [15] The equivalent circuit model of the pro-posed antenna is given in Figure 13The circuit consists of twoparallel R-L-C tanks along with a shunt branch The first twotank circuits correspond to the first and second resonancewhereas the shunt branch with R3 and L3 contributes to theinput impedance of the antenna

The parameters of the tank circuit can be computedby solving a set of equations formed as follows First

International Journal of Antennas and Propagation 9

C1

L1

R1

L2

C2

R2

L3

R3

Figure 13 The equivalent circuit model of the dual-band antenna

the series impedance of the circuit at any frequency (119891) willbe

119885Series at 119891 =1

radic(1198621120596 minus 1119871

1120596)2

+ 11198772

1

+1

radic(1198622120596 minus 1119871

2120596)2

+ 11198772

2

(3)

where 120596 = 2120587119891 At the first resonance the expression for theseries impedance is reduced to

119885Series at 1198651 = 1198771 +1

radic(11986221205961minus 1119871

21205961)2

+ 11198772

2

(4)

Similarly the expression for the series impedance at thesecond resonance is reduced to

119885Series at 1198652 = 1198772 +1

radic(11986211205962minus 1119871

11205962)2

+ 11198772

1

(5)

The shunt impedance of the circuit at a frequency 119891 will be

119885Shunt at 119891 = radic(1198713120596)2

+ 1198772

3 (6)

According to voltage dividing principle the ratio of outputvoltage to input voltage which is a measure of transmissioncoefficient can be obtained as

119881119900

119881119894

= 10(1minus11987811)20=119885Shunt

119885Shunt + 119885Series (7)

There are eight parameters in the model and to find themwe need eight equations These equations can be formulatedby choosing eight frequencies then substituting (3) and (6)into (7) By solving the formulated equations all the circuitparameters can be computed For the proposed antenna thevalues of the circuit elements in the model are 119871

1= 032 nH

1198712= 569 nH 119871

3= 0696 nH 119862

1= 14298 pF 119862

2= 1412 pF

1198771= 484Ω 119877

2= 5463Ω and 119877

3= 3623Ω The resonant

frequencies obtained from the equivalent circuit are 235GHzand 56GHz with a bandwidth of 024GHz in the first bandand 153GHz in the second band These results are in a verygood agreement with the experimental result as shown inFigure 14

3 4 5 6 72

Frequency (GHz)

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

MeasuredEquivalent circuit

Figure 14 Comparison between the measured reflection coefficientand that produced by the equivalent circuit model of the proposedantenna

6 Conclusion

A planar dual-band microstrip-fed monopole antenna of asimple and compact structure is presented Besides the bandexcited by the monopole radiator an additional band ofoperation is excited by placing a shorted inverted-L parasiticresonator on the bottom of the substrate The parasitic res-onator also improves the impedance bandwidth of the orig-inal band The microstrip feed is a truncated ground whosedimensions can be optimized to achieve a good performancewith compact sizeThe proposed antenna is designed to coverthe 2452ndash58GHz bands utilized in WLAN applicationsThe impact of the geometrical parameters on the perfor-mance of the dual-band monopole antenna is investigatedthrough a series of simulated parametric studies Measuredand simulated results show that the antenna operates at bothbandswith good impedancematching typicalmonopole-likeradiation patterns and flat gain An equivalent circuit modelof the proposed antenna which gives accurate results whencompared to measurements is presenteda

Competing Interests

The authors declare that there are no competing interestsregarding the publication of this paper

References

[1] W-C Liu C-M Wu and Y-J Tseng ldquoParasitically loadedCPW-fed monopole antenna for broadband operationrdquo IEEETransactions on Antennas and Propagation vol 59 no 6 pp2415ndash2419 2011

[2] K H Sayidmarie and T A Nagem ldquoCompact dual-band dual-ring printed mono-pole antennas for WLAN applicationsrdquoProgress in Electromagnetics ResearchB no 43 pp 313ndash331 2012

10 International Journal of Antennas and Propagation

[3] W-C Liu C-M Wu and Y Dai ldquoDesign of triple-frequencymicrostrip-fedmonopole antenna using defected ground struc-turerdquo IEEE Transactions on Antennas and Propagation vol 59no 7 pp 2457ndash2463 2011

[4] S S Huang J Li and J Z Zhao ldquoCompact CPW-fed tri-band antenna for WLANWIMAX applicationsrdquo Progress inElectromagnetics Research C vol 49 pp 39ndash45 2014

[5] L Xu Z Y Xin and J He ldquoA compact triple-band fork-shaped antenna for WLANWiMAX applicationsrdquo Progress inElectromagnetics Research Letters vol 40 pp 61ndash69 2013

[6] A A Ibrahim and A M E Safwat ldquoMicrostrip-fed monopoleantennas loaded with CRLH unit cellsrdquo IEEE Transactions onAntennas and Propagation vol 60 no 9 pp 4027ndash4036 2012

[7] H-D Chen ldquoGround plane effects on the microstrip-line-fed broadband sleeve monopole antennasrdquo IET MicrowavesAntennas and Propagation vol 2 no 6 pp 601ndash605 2008

[8] H-D Chen ldquoCompact broadband microstrip-line-fed sleevemonopole antenna for DTV application and ground planeeffectrdquo IEEE Antennas and Wireless Propagation Letters vol 7pp 497ndash500 2008

[9] J H Lu and B J Huang ldquoPlanar multi-bandmonopole antennawith L-shaped parasitic strip for WiMAX applicationrdquo IETElectronics Letters vol 46 no 10 pp 671ndash672 2010

[10] J R Panda and R S Kshetrimayum ldquoA printed 24 ghz58ghzdual-band monopole antenna with a protruding stub in theground plane for WLAN and RFID applicationsrdquo Progress inElectromagnetics Research vol 117 pp 425ndash434 2011

[11] P Xu Z-H Yan and C Wang ldquoMulti-band modified fork-shaped monopole antenna with dual L-shaped parasitic planerdquoElectronics Letters vol 47 no 6 pp 364ndash365 2011

[12] J-H Lu and Y-Y Lee ldquoPlanar compact triple-band monopoleantenna for IEEE 80216m worldwide interoperability formicrowave access systemrdquo IET Microwaves Antennas andPropagation vol 7 no 13 pp 1045ndash1054 2013

[13] K P Ray ldquoDesign aspects of printed monopole antennas forultra-wide band applicationsrdquo International Journal of Antennasand Propagation vol 2008 Article ID 713858 8 pages 2008

[14] K Seol J Jung and J Choi ldquoMulti-band monopole antennawith inverted U-shaped parasitic planerdquo IET Electronics lettersvol 42 no 15 pp 844ndash845 2006

[15] Q-X Chu and Y-Y Yang ldquoA compact ultrawideband antennawith 3455 GHz dual band-notched characteristicsrdquo IEEETransactions on Antennas and Propagation vol 56 no 12 pp3637ndash3644 2008

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

International Journal of Antennas and Propagation 9

C1

L1

R1

L2

C2

R2

L3

R3

Figure 13 The equivalent circuit model of the dual-band antenna

the series impedance of the circuit at any frequency (119891) willbe

119885Series at 119891 =1

radic(1198621120596 minus 1119871

1120596)2

+ 11198772

1

+1

radic(1198622120596 minus 1119871

2120596)2

+ 11198772

2

(3)

where 120596 = 2120587119891 At the first resonance the expression for theseries impedance is reduced to

119885Series at 1198651 = 1198771 +1

radic(11986221205961minus 1119871

21205961)2

+ 11198772

2

(4)

Similarly the expression for the series impedance at thesecond resonance is reduced to

119885Series at 1198652 = 1198772 +1

radic(11986211205962minus 1119871

11205962)2

+ 11198772

1

(5)

The shunt impedance of the circuit at a frequency 119891 will be

119885Shunt at 119891 = radic(1198713120596)2

+ 1198772

3 (6)

According to voltage dividing principle the ratio of outputvoltage to input voltage which is a measure of transmissioncoefficient can be obtained as

119881119900

119881119894

= 10(1minus11987811)20=119885Shunt

119885Shunt + 119885Series (7)

There are eight parameters in the model and to find themwe need eight equations These equations can be formulatedby choosing eight frequencies then substituting (3) and (6)into (7) By solving the formulated equations all the circuitparameters can be computed For the proposed antenna thevalues of the circuit elements in the model are 119871

1= 032 nH

1198712= 569 nH 119871

3= 0696 nH 119862

1= 14298 pF 119862

2= 1412 pF

1198771= 484Ω 119877

2= 5463Ω and 119877

3= 3623Ω The resonant

frequencies obtained from the equivalent circuit are 235GHzand 56GHz with a bandwidth of 024GHz in the first bandand 153GHz in the second band These results are in a verygood agreement with the experimental result as shown inFigure 14

3 4 5 6 72

Frequency (GHz)

minus30

minus25

minus20

minus15

minus10

minus5

0

1003816 1003816 1003816 1003816S111003816 1003816 1003816 1003816

(dB)

MeasuredEquivalent circuit

Figure 14 Comparison between the measured reflection coefficientand that produced by the equivalent circuit model of the proposedantenna

6 Conclusion

A planar dual-band microstrip-fed monopole antenna of asimple and compact structure is presented Besides the bandexcited by the monopole radiator an additional band ofoperation is excited by placing a shorted inverted-L parasiticresonator on the bottom of the substrate The parasitic res-onator also improves the impedance bandwidth of the orig-inal band The microstrip feed is a truncated ground whosedimensions can be optimized to achieve a good performancewith compact sizeThe proposed antenna is designed to coverthe 2452ndash58GHz bands utilized in WLAN applicationsThe impact of the geometrical parameters on the perfor-mance of the dual-band monopole antenna is investigatedthrough a series of simulated parametric studies Measuredand simulated results show that the antenna operates at bothbandswith good impedancematching typicalmonopole-likeradiation patterns and flat gain An equivalent circuit modelof the proposed antenna which gives accurate results whencompared to measurements is presenteda

Competing Interests

The authors declare that there are no competing interestsregarding the publication of this paper

References

[1] W-C Liu C-M Wu and Y-J Tseng ldquoParasitically loadedCPW-fed monopole antenna for broadband operationrdquo IEEETransactions on Antennas and Propagation vol 59 no 6 pp2415ndash2419 2011

[2] K H Sayidmarie and T A Nagem ldquoCompact dual-band dual-ring printed mono-pole antennas for WLAN applicationsrdquoProgress in Electromagnetics ResearchB no 43 pp 313ndash331 2012

10 International Journal of Antennas and Propagation

[3] W-C Liu C-M Wu and Y Dai ldquoDesign of triple-frequencymicrostrip-fedmonopole antenna using defected ground struc-turerdquo IEEE Transactions on Antennas and Propagation vol 59no 7 pp 2457ndash2463 2011

[4] S S Huang J Li and J Z Zhao ldquoCompact CPW-fed tri-band antenna for WLANWIMAX applicationsrdquo Progress inElectromagnetics Research C vol 49 pp 39ndash45 2014

[5] L Xu Z Y Xin and J He ldquoA compact triple-band fork-shaped antenna for WLANWiMAX applicationsrdquo Progress inElectromagnetics Research Letters vol 40 pp 61ndash69 2013

[6] A A Ibrahim and A M E Safwat ldquoMicrostrip-fed monopoleantennas loaded with CRLH unit cellsrdquo IEEE Transactions onAntennas and Propagation vol 60 no 9 pp 4027ndash4036 2012

[7] H-D Chen ldquoGround plane effects on the microstrip-line-fed broadband sleeve monopole antennasrdquo IET MicrowavesAntennas and Propagation vol 2 no 6 pp 601ndash605 2008

[8] H-D Chen ldquoCompact broadband microstrip-line-fed sleevemonopole antenna for DTV application and ground planeeffectrdquo IEEE Antennas and Wireless Propagation Letters vol 7pp 497ndash500 2008

[9] J H Lu and B J Huang ldquoPlanar multi-bandmonopole antennawith L-shaped parasitic strip for WiMAX applicationrdquo IETElectronics Letters vol 46 no 10 pp 671ndash672 2010

[10] J R Panda and R S Kshetrimayum ldquoA printed 24 ghz58ghzdual-band monopole antenna with a protruding stub in theground plane for WLAN and RFID applicationsrdquo Progress inElectromagnetics Research vol 117 pp 425ndash434 2011

[11] P Xu Z-H Yan and C Wang ldquoMulti-band modified fork-shaped monopole antenna with dual L-shaped parasitic planerdquoElectronics Letters vol 47 no 6 pp 364ndash365 2011

[12] J-H Lu and Y-Y Lee ldquoPlanar compact triple-band monopoleantenna for IEEE 80216m worldwide interoperability formicrowave access systemrdquo IET Microwaves Antennas andPropagation vol 7 no 13 pp 1045ndash1054 2013

[13] K P Ray ldquoDesign aspects of printed monopole antennas forultra-wide band applicationsrdquo International Journal of Antennasand Propagation vol 2008 Article ID 713858 8 pages 2008

[14] K Seol J Jung and J Choi ldquoMulti-band monopole antennawith inverted U-shaped parasitic planerdquo IET Electronics lettersvol 42 no 15 pp 844ndash845 2006

[15] Q-X Chu and Y-Y Yang ldquoA compact ultrawideband antennawith 3455 GHz dual band-notched characteristicsrdquo IEEETransactions on Antennas and Propagation vol 56 no 12 pp3637ndash3644 2008

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

10 International Journal of Antennas and Propagation

[3] W-C Liu C-M Wu and Y Dai ldquoDesign of triple-frequencymicrostrip-fedmonopole antenna using defected ground struc-turerdquo IEEE Transactions on Antennas and Propagation vol 59no 7 pp 2457ndash2463 2011

[4] S S Huang J Li and J Z Zhao ldquoCompact CPW-fed tri-band antenna for WLANWIMAX applicationsrdquo Progress inElectromagnetics Research C vol 49 pp 39ndash45 2014

[5] L Xu Z Y Xin and J He ldquoA compact triple-band fork-shaped antenna for WLANWiMAX applicationsrdquo Progress inElectromagnetics Research Letters vol 40 pp 61ndash69 2013

[6] A A Ibrahim and A M E Safwat ldquoMicrostrip-fed monopoleantennas loaded with CRLH unit cellsrdquo IEEE Transactions onAntennas and Propagation vol 60 no 9 pp 4027ndash4036 2012

[7] H-D Chen ldquoGround plane effects on the microstrip-line-fed broadband sleeve monopole antennasrdquo IET MicrowavesAntennas and Propagation vol 2 no 6 pp 601ndash605 2008

[8] H-D Chen ldquoCompact broadband microstrip-line-fed sleevemonopole antenna for DTV application and ground planeeffectrdquo IEEE Antennas and Wireless Propagation Letters vol 7pp 497ndash500 2008

[9] J H Lu and B J Huang ldquoPlanar multi-bandmonopole antennawith L-shaped parasitic strip for WiMAX applicationrdquo IETElectronics Letters vol 46 no 10 pp 671ndash672 2010

[10] J R Panda and R S Kshetrimayum ldquoA printed 24 ghz58ghzdual-band monopole antenna with a protruding stub in theground plane for WLAN and RFID applicationsrdquo Progress inElectromagnetics Research vol 117 pp 425ndash434 2011

[11] P Xu Z-H Yan and C Wang ldquoMulti-band modified fork-shaped monopole antenna with dual L-shaped parasitic planerdquoElectronics Letters vol 47 no 6 pp 364ndash365 2011

[12] J-H Lu and Y-Y Lee ldquoPlanar compact triple-band monopoleantenna for IEEE 80216m worldwide interoperability formicrowave access systemrdquo IET Microwaves Antennas andPropagation vol 7 no 13 pp 1045ndash1054 2013

[13] K P Ray ldquoDesign aspects of printed monopole antennas forultra-wide band applicationsrdquo International Journal of Antennasand Propagation vol 2008 Article ID 713858 8 pages 2008

[14] K Seol J Jung and J Choi ldquoMulti-band monopole antennawith inverted U-shaped parasitic planerdquo IET Electronics lettersvol 42 no 15 pp 844ndash845 2006

[15] Q-X Chu and Y-Y Yang ldquoA compact ultrawideband antennawith 3455 GHz dual band-notched characteristicsrdquo IEEETransactions on Antennas and Propagation vol 56 no 12 pp3637ndash3644 2008

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

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Chemical EngineeringInternational Journal of Antennas and

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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