Bandwidth Enhancement and Mutual Coupling Reduction Using ...downloads.hindawi.com/journals/ijap/2019/8945386.pdf · Bandwidth Enhancement and Mutual Coupling Reduction Using a Notch

Research ArticleBandwidth Enhancement and Mutual Coupling Reduction Usinga Notch and a Parasitic Structure in a UWB-MIMO Antenna

Jiwan Ghimire 1 Kwang-Wook Choi2 and Dong-You Choi 1

1Department of Information and Communication Engineering Chosun University 375 Susuk-dong Dong-guGwangju 501-759 Republic of Korea2Department of Electronic and Computer Engineering Chonnam National University 77 Yongbong-roYongbong-dong Buk-gu Kwangju Republic of Korea

Correspondence should be addressed to Dong-You Choi dychoichosunackr

Received 24 February 2019 Revised 29 April 2019 Accepted 6 May 2019 Published 2 June 2019

Academic Editor Shiwen Yang

Copyright copy 2019 Jiwan Ghimire et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

The correlation between the antennas of multiple-input multiple-output (MIMO) systems in limited spaces and size degradesthe performance and capacity by either using complex coupling or decoupling structures For isolation improvement this paperpresents the simple design of a compact high-isolation ultra-wideband (UWB) MIMO antenna with a circular parasitic element atthe back side of the radiating patch thereby creating the reverse coupling and helping reduce the mutual coupling at the upper partof the frequency bands and a small rectangular notch at the ground plane to extend the impedance bandwidth of the monopoleantenna This approach eliminates the use of complex coupling or decoupling structures and complex feeding networks A novelfeature of our design is that theMIMOantenna exhibits a very low envelope correlation coefficient (ECClt 0007)with high diversitygain (DG gt 999) and wide impedance bandwidth of 139 from 31 to 175 GHz applicable for not only UWB application but alsonext generation wireless communication 5GThe high peak gain over the entire UWB and the upper part of the overall frequencyband ensure that the antenna can be used inMIMO applications owing to the close agreement between the simulated andmeasuredresults

1 Introduction

The need for high data rates with efficient spectrummanage-ment utilizingmultiple antennas in a single physical substrateis a recent requirement in modern wireless communicationand UWB systems To that end multiple-input multiple-output (MIMO) technology takes advantage ofmultipath fad-ing problems through diversity gain to improve link reliabil-ity increase data throughput and improve wireless capacityand range which is not possible in a single-antenna system[1] Even though MIMO technology is better than single-input multiple-output (SIMO) or multiple-input single-output (MISO) in terms of channel capacity it has somelimitations regarding the correlation between the antennasand realizing space efficiency [2] Improving the isolationfactor or correlation in a MIMO antenna using various typesof coupling and decoupling structures is achieved at theexpense of size and space [3]

Using decoupling structures such as active devices andpassive resonators implementing defective ground structures(DGSs) electromagnetic bandgap parasitic elements addingneutralization lines shortening pins and loading slots on theantenna geometry for to avoid mutual coupling and improvethe antenna bandwidth are proposed in various studies In[4] a UWB amplifier was inserted to achieve widebandantenna matching and radiation efficiency Similarly a pas-sivemicrostrip-based feed networkwas introduced in [5] anda cylindrical dielectric resonator antenna (CDRA) in [6] forgood MIMO operations at higher frequencies A number ofradiating elements in MIMO antenna systems were designedto improve isolation with DGS using different shapes (TF 4 arch) and slot lines rectangular rings and groundslits were also employed [7ndash14] In [15] the electromagneticbandgap structure was applied to closely placed arrays in theground plane resulting in a significant reduction of mutualcoupling across a wide operating band The use of parasitic

HindawiInternational Journal of Antennas and PropagationVolume 2019 Article ID 8945386 9 pageshttpsdoiorg10115520198945386

2 International Journal of Antennas and Propagation

Ws Ws

Ls Ls

Lf

R1

R2 R3

Lg

Wg

WnLn

R4

Wf

X

YZ

(a) (b)

Figure 1 Geometry of the proposed UWB antenna (a) Top view (b) bottom view of the antenna

monopoles or resonators helped induce reverse coupling andhence reduced mutual coupling in [16 17] In [18] adding aneutralization line increased the effectiveness of the antennasystem in terms of isolation and bandwidth within a smallspace without modifying the ground plane

Similarly E C and H-shaped patch antennas were loadedby U and V slots to achieve desired bandwidth characteristics[24] In addition developing efficient bandwidth enhance-ment with existing different technique in an area of limitedsize within a MIMO system is still a difficult task

In this paper the UWB MIMO antenna with enhancedisolation is proposed The proposed MIMO antenna hasa very low mutual coupling (|S

21S12| lt minus21 dB) and

is composed of two monopole antennas with a commonradiating surface The two radiating patches are connectedby two quad-circular structures The ground plane is on theopposite side of the radiating patch etched to increase theimpedance bandwidth characteristics A circular parasiticelement introduced at the centre of the substrate acts asan isolator and exhibits low mutual coupling for the upperfrequency bands of the antenna In the absence of couplingor decoupling structures a good isolation is achieved withoutthe expense of increase in size The results obtained fromthe proposed MIMO antenna without the use of complexstructures reveal that it has good performance in terms ofhigh impedance bandwidth and antenna gain high radiationefficiency high diversity gain and low envelope correlationcoefficient (ECC) The omnidirectional radiation patternof the purposed MIMO antenna element proves that theantenna possesses good pattern diversity for aMIMO system

2 Antenna Characteristics

The proposed geometry of the UWB-MIMO antenna isshown in Figure 1 where Figures 1(a) and 1(b) representthe top and bottom geometrical view of the substrate with

Table 1 Dimensions of the Antenna Parameters

Parameter Dimension (mm)Ls 65Ws 65Lf 163R1 178R2 89R3 8R4 4Lg 16Wg 327Ln 4Wn 5Wf 18

the optimal dimension listed in Table 1 The antenna wasdesigned on a Taconic substrate (120576

119903= 45 tan 120575 = 00035)

The size of the antenna is 65 mm times 65 mm times 162 mm Theantenna is composed of a microstrip patch with a commonradiating patch and a ground plane designed on the topand bottom side of the substrate respectively Here to meetthe operating frequency requirement the return loss at the10 dB lower frequency bandwidth is adjusted to 31 GHzapproximated using the following frequency calculation [25]

119891119899= 1198882119897119905radic1 + 120576

1199032 (1)

where119891119899is the first operating frequency c is the speed of light

in the vacuum and 119897119905is the combine total effective lengths

of the circular patch radii R1 and R2 The feed line and asmall notch in the ground plane employed to obtain the linecharacteristic impedance of 50 Ω are set to 18 mm and 4mm times 5 mm respectively The radiating patch is structurally

International Journal of Antennas and Propagation 3

(a) (b)

(c) (d)

Figure 2 Geometry of the proposed UWB antenna with different evolution steps (a) Without the connecting radiation patch (b) with theconnecting radiation patch (c) with the ground plane etched and (d) with the parasitic resonator

a combination of a quad circular structure with a semi-circleof half the radius of the quad circle placed on its topThe tworadiating patches are commonly connected by two small quadcircular structures positioned opposite to each other wherethe circular parasitic strip is located below it along the centreof the substrate to improve isolation between the monopoleantennas The need of connecting two radiating patches bytwo small quad circles is to not only improve the isolation butalso have a common signal reference weather it is a groundplane or the radiating patch A split in both ground plane andradiating patch is not practical since in the real system thesignal should have the common reference plane so that allsignal levels within the systems can be interpreted properlybased on that reference level [17] However the proposeddesign is similar to a microstrip patch antenna with feedingpoints placed opposite to each other the optimized antennastructure isolation enhancement without the use of couplingand decoupling structure makes it preferable in terms ofbandwidth diversity gain and multiplexing efficiency whichare the significant parameters for any diversity antennas

3 Design Strategy

Figure 2 illustrates the antenna designing steps and the effectof each step on the antenna bandwidth and mutual couplingare shown in Figure 3 Figure 2(a) shows that the antennadesign with radiating patches facing indirectly opposite to

each other allows space utilization within a limited spaceof the antenna Similarly the geometrical structure of theradiating patch enables the MIMO antenna to be directionalwhich could supply good pattern diversity for the MIMOsystem The simulated parameters of the antenna reflectioncoefficient (S

11) and coupling coefficient (S

21) in Figures

3(a) and 3(b) reveal that the antenna has poor isolationin the higher frequency range and a high impedance mis-match in the entire UWB range for the antenna shownin Figure 2(a) With the placement of two quad circularstructures connecting two radiating patches (Figure 2(b))mutual coupling between the proposed antennas is reducedbut the characteristic line impedance of the antenna remainsthe same as that of the antenna design taken at the firststage Further to improve the impedance bandwidth of theantenna in the entire UWB range a small rectangular etchingis carved at the ground plane (Figure 2(c)) The etchingnot only improves the characteristic line impedance butalso decreases the isolation factors in the lower frequencyspectrum of the proposed UWBMIMO antenna with a slightincrease in isolation factor at the upper-frequency range Acircular parasitic microstrip patch resonator is introducedat the backside of the substrate plane (Figure 2(d)) Thecurrent flowing in the radiating patch excites the resonatorThe excited reverse current on the resonator prevents theflow of current in the other radiating patch preventing itfrom further coupling on properly designing the antenna


Without connecting radiating patchWith connecting radiating patchWith etched ground edgeWith parasitic resonators

Frequency (GHz)

S 11(d

B)0

minus10

minus20

minus30

minus40

3 6 9 12 15

(a)

Frequency (GHz)

S 21(d

B)

With connecting radiation patchWithout connecting radiating patchWith etched ground edgeWith parasitic resonators

3 6 9 12 15

minus10

minus20

minus30

minus40

minus50

minus60

minus70

(b)

Figure 3 Simulated S-parameters to illustrate different stages of antenna variation in design for improving the antenna bandwidth andreducing the mutual coupling (a) Simulated reflection coefficient S

11(dB) (b) simulated coupling coefficient S

21(dB)

Jsurf (Am)700441279

111070044028018011007004

176

003002001001

(a)

Jsurf (Am)700441279

111070044028018011007004

176

003002001001

(b)

Figure 4 Simulated surface current distribution at 165 GHz (a) Without circular parasitic resonator (b) with the resonator

configuration the mutual coupling between the radiatingpatch gets reduced considerably

The surface current distribution along the radiating andground patch validates the antenna performance of reducingthe mutual coupling As a comparison the current distribu-tions with and without the circular parasitic monopoles areplotted in Figure 4 when one of the ports is excited As shownin Figure 4(a) high coupling is achieved at the other radiatingpatch and the ground plane because the current concentra-tion is equally spread all around the patch and the groundplane significantly By the insertion of the circular resonatingstructure depicted in Figure 4(b) it can be observed that thecurrent is concentrated at the radiating patch of the excited

port and gets trapped all around the periphery of the circularresonating structure Because of this effect the ground planeof the other radiator and the patch has coupled much lesscurrent concentration and hence less isolation is achieved inbetween the two radiating patches In addition the simula-tion result shows that most of the current above 147 GHz isconcentrated around the resonating patch which explains thereduced mutual coupling (S

21) observed in Figure 3(b)

4 Result and Discussion

For the optimization and simulation of the proposed antennathe commercially available High-Frequency Structure


Frequency (GHz)

S-pa

ram

eter

s (dB

)0

minus10

minus20

minus30

minus40

3 6 9 12 15

３11 | ３22 (Measured)

３11 | ３22 (Simulated)

(a)

Frequency (GHz)

S-pa

ram

eter

s (dB

)

minus10

minus20

minus30

minus40

minus50

minus60



3 6 9 12 15

(b)

Figure 5 Simulated and measured S-parameters of the proposed UWB-MIMO antenna (a) S11(dB) (b) S

21(dB)

Simulator (HFSS) software is used The simulation andmeasurement results are shown in Figure 5 Figure 5(a)shows impedance bandwidth with S

11lt minus10 dB from 31

to 175 GHz The mutual coupling between the antennas(S21) shown in Figure 5(b) is below minus15 dB for 31ndash35 GHz

and below minus21 dB over 35ndash175 GHz with close agreementbetween the measured and simulated results The simulatedandmeasured reflection coefficients differ slightly and can beindorsed by the losses taking place in connector imperfectsoldering and fabrication errors

Themeasured and simulated 2D radiation patterns at 4565 115 and 165 GHz frequency are shown in Figures 6(a)6(b) 6(c) and 6(d) respectively The measurements weretaken with one of the ports terminated by a 50-Ω load andvice versa The radiation patterns are almost omnidirectionalin both the E-plane (xndashz plane) and H-plane (yndashz plane)which is one of the required characteristics for a MIMOantenna

In order to verify the capability of the proposed MIMOantenna ECC between the antennas must be as low aspossible a lower ECC signifies higher pattern diversity TheECC between the two antenna elements can be calculated by[26]

119864119862119862 = 1003816100381610038161003816119878lowast1111987812 + 119878lowast211198782210038161003816100381610038162(1 minus 10038161003816100381610038161198781110038161003816100381610038162 minus 10038161003816100381610038161198782110038161003816100381610038162) (1 minus 10038161003816100381610038161198782210038161003816100381610038162 minus 10038161003816100381610038161198781210038161003816100381610038162) (2)

From the measurement results of return loss and isolationfactor the ECC was analysed as shown in Figure 8 The ECCideally should be zero practically lt 05 is an acceptable limit

Conventionally the overall effect of a MIMO antenna ischaracterized by diversity gain (DG) and MIMO capacityHowever MIMO capacity is the complicated function of theantenna parameters To simplify the antenna design a simpleand intuitive metric like multiplexing efficiency and TARC

are proposed The multiplexing efficiency defines the lossesor degradation of power efficiency required when using aMIMO antenna under test to achieve the same performanceor capacity as that of a reference antenna system in thesame propagation channel within uniform 3D angular powerspectrumThe signal-to-noise ratio (SNR) degradation due toMIMO antenna ndashchannel losses for a given MIMO capacity120578119898119906119909

is given by [27]

120578119898119906119909= radic(1 minus 100381610038161003816100381612058811988821003816100381610038161003816) 12057811205782 (3)

where 12057811205782are the total efficiency of two radiating antenna

elements and 120588119888represents the complex correlation coeffi-

cient between them Since the total efficiency of the antennais very high for this ECC is nearly equal to |120588

119888

2|The DG ofthe proposed UWB MIMO antenna can be calculated usingrelation

119863119866 = 10radic1 minus 1198641198621198622 (4)

All the ECC values are less than 0007 and the DG ishigh greater than 999 for the entire frequency band Therealized gain and the multiplexing efficiency are shown inFigure 9 where its high measurement values on the entirefrequency range make the antenna applicable for UWB5G communication devices and sensor applications Thefabricated prototype of UWB MIMO antenna with top andbottom view is shown in Figures 7(a) and 7(b)

Figure 10 shows the plot of the total active reflectioncoefficient (TARC) where the value of TARC of the proposedantenna is less than -13 dB for the entire frequency bandTARC calculates the actual antenna behaviour in terms ofratio of square root of the sum of powers of reflected wave tothe incident wave By predicting the return loss of the overall


E- plane (Measured) H - plane (Measured)E- plane (Simulated) H- plane (Simulated)

0

30

60

90

120

150

180

210

240

270

300

330

0

-10

-20

-30

-40

-50

(a)


0

30

60

90

120

150

180

210

240

270

300

330

0

-10

-20

-30

-40

-50

(b)


0

30

60

90

120

150

180

210

240

270

300

330

0

-10

-20

-30

-40

-50

(c)


0

30

60

90

120

150

180

210

240

270

300

330

0

-10

-20

-30

-40

-50

(d)

Figure 6 Measured and simulation radiation pattern at (a) 45 (b) 65 (c) 115 and (d) 165 GHz

2X2 MIMO antenna system TARC can be calculated by thefollowing relations [28]

TARC = radic (S11 + S12)2 + (S21 + S22)22 (5)

The comparison of the proposed MIMO Antenna betweenother existing antennas in the literature is listed in Table 2The designed antenna has a wide impedance bandwidth

overall with good isolation factor and diversity gain provingthat the antenna is a good candidate for MIMO application

5 Conclusion

The design of a compact high-isolation ultra-wideband(UWB) MIMO antenna with a circular parasitic element atthe backside of the radiating patch is proposed Withoutthe presence of coupling or decoupling element and by


(a) (b)

Figure 7 Fabricated UWBMIMO Antenna (a) Top view (b) bottom view

Frequency (GHz)

ECC

Div

ersit

y G

ain

(dB)

Diversity GainECC

0010

0008

0006

0004

0002

00003 6 9 12 15

1000

999

998

997

996

995

Figure 8 Measured ECC and DG of the proposed antenna

Frequency (GHz)

Mul

tiple

xing

Effi

cien

cy (d

B)

Gai

n (d

B)

Multiplexing EfficiencyRealized Gain

00

minus02

minus04

minus06

minus08

minus10

3 6 9 12 15

15

13

11

9

7

5

3

1

Figure 9 Realized gain and multiplexing efficiency of the proposed antenna


Table 2 Performance Comparison of Existing Antennas

Ref Size (mm) Bandwidth (GHz) Isolation (dB) ECC Diversity Gain[12] 30 times 50 25ndash145 lt minus20 lt 004 gt 74[19] 60 times 40 31ndash106 lt minus20 lt 006 gt 989[20] 50 times 80 31ndash106 lt minus17 lt0056 NA[21] 32 times 32 31ndash106 lt minus15 lt 004 NA[22] 26 times 40 21ndash106 lt minus15 NA NA[23] 45 times 25 3 ndash12 lt minus15 lt02 gt 979Proposed Work 65 times 65 31ndash175 lt minus20 lt 0007 gt 999

Frequency (GHz)

TARC

(dB)

TARC (measured)

0

minus1

minus2

minus3

minus4

3 6 9 12 15

Figure 10 TARC for the proposed MIMO antenna

introducing a parasitic circular structure high isolation isachieved at the upper part of the frequency band whereas asmall rectangular notch at the ground plane helps widen theantenna operating bandwidth and improve the impedancematching of the two connecting radiating elements Tovalidate the design strategy for reducingmutual coupling andincrease the operating bandwidth essential features such asECC (lt 0007) DG (gt 999) isolation less than -21dB almostomnidirectional radiation pattern andhigh gain performanceand multiplexing efficiency were shown and verified withsimulation and measurement results to describe the MIMOperformance of the UWB antenna

Data Availability

The data used to support the findings of this study areincluded within the article

Conflicts of Interest

The authors declare that they have no competing interests

Acknowledgments

This research was supported by the Basic Science ResearchProgram through the National Research Foundation

of Korea (NRF) funded by the Ministry of Education(2016R1D1A1B03931806) Also the research was partiallyfunded by the MIST (Ministry of Science amp ICT) Koreaunder the National Program for Excellence in SW supervisedby the IITP (Institute for Information amp communicationsTechnology Promotion) (2017-0-00137)

References

[1] M A Jensen and J W Wallace ldquoA review of antennas andpropagation for MIMOwireless communicationsrdquo IEEE Trans-actions on Antennas and Propagation vol 52 no 11 pp 2810ndash2824 2004

[2] J Park and B Clerckx ldquoMulti-User linear precoding for multi-polarized massive MIMO system under imperfect CSITrdquo IEEETransactions on Wireless Communications vol 14 no 5 pp2532ndash2547 2015

[3] I Nadeem andD-Y Choi ldquoStudy onmutual coupling reductiontechnique for mimo antennasrdquo IEEE Access vol 7 pp 563ndash5862019

[4] S K Dhar M S Sharawi O Hammi and F M GhannouchildquoAn active integrated ultra-widebandMIMO antennardquo Instituteof Electrical and Electronics Engineers Transactions on Antennasand Propagation vol 64 no 4 pp 1573ndash1578 2016

[5] M T Hussain M S Sharawi S Podilchack and Y M MAntar ldquoClosely packed millimeter-wave MIMO antenna arrayswith dielectric resonator elementsrdquo in Proceedings of the 10th


European Conference on Antennas and Propagation EuCAP2016 pp 1ndash4 Switzerland April 2016

[6] A Sharma G Das and R K Gangwar ldquoDesign and analysisof tri-band dual-port dielectric resonator based hybrid antennaforWLANWiMAX applicationsrdquo IETMicrowaves AntennasampPropagation vol 12 no 6 pp 986ndash992 2018

[7] M S Sharawi A B Numan M U Khan and D N Aloi ldquoAdual-element dual-bandMIMO antenna systemwith enhancedisolation for mobile terminalsrdquo IEEE Antennas and WirelessPropagation Letters vol 11 pp 1006ndash1009 2012

[8] M A Abdalla and A A Ibrahim ldquoCompact and closely spacedmetamaterial MIMO antenna with high isolation for wirelessapplicationsrdquo IEEE Antennas and Wireless Propagation Lettersvol 12 pp 1452ndash1455 2013

[9] Y Wu and Q Chu ldquoDual-band multiple input multiple outputantenna with slitted groundrdquo IET Microwaves Antennas ampPropagation vol 8 no 13 pp 1007ndash1013 2014

[10] C-M Luo J-S Hong and L-L Zhong ldquoIsolation Enhance-ment of a Very Compact UWB-MIMO Slot Antenna withTwo Defected Ground Structuresrdquo IEEE Antennas and WirelessPropagation Letters vol 14 pp 1766ndash1769 2015

[11] S F Jilani and A Alomainy ldquoMillimetre-wave T-shapedMIMOantenna with defected ground structures for 5G cellular net-worksrdquo IET Microwaves Antennas amp Propagation vol 12 no5 pp 672ndash677 2018

[12] A Iqbal O A Saraereh A W Ahmad and S Bashir ldquoMutualCoupling Reduction Using F-Shaped Stubs in UWB-MIMOAntennardquo IEEE Access 2017

[13] R Karimian H Oraizi S Fakhte and M Farahani ldquoNovelF-shaped quad-band printed slot antenna for WLAN andWiMAX MIMO systemsrdquo IEEE Antennas and Wireless Propa-gation Letters vol 12 pp 405ndash408 2013

[14] B Yang M Chen and L Li ldquoDesign of a four-elementWLANLTEUWB MIMO antenna using half-slot structurerdquoAEU - International Journal of Electronics and Communicationsvol 93 pp 354ndash359 2018

[15] Q Li A P Feresidis MMavridou and P S Hall ldquoMiniaturizeddouble-layer EBG structures for broadband mutual couplingreduction between UWB monopolesrdquo IEEE Transactions onAntennas and Propagation vol 63 no 3 pp 1168ndash1171 2015

[16] Z Li Z Du M Takahashi K Saito and K Ito ldquoReducingmutual coupling of MIMO antennas with parasitic elementsfor mobile terminalsrdquo IEEE Transactions on Antennas andPropagation vol 60 no 2 pp 473ndash481 2012

[17] S Zhang and G F Pedersen ldquoMutual Coupling Reduction forUWBMIMO Antennas with a Wideband Neutralization LinerdquoIEEEAntennas andWireless Propagation Letters vol 15 pp 166ndash169 2016

[18] M S Sharawi ldquoCurrent misuses and future prospects forprintedmultiple-input multiple-output antenna systems [wire-less corner]rdquo IEEE Antennas and PropagationMagazine vol 59no 2 pp 162ndash170 2017

[19] C-X Mao Q-X Chu Y-T Wu and Y-H Qian ldquoDesignand investigation of closely-packed diversityUWB slot-antennawith high isolationrdquo Progress in Electromagnetics Research Cvol 41 pp 13ndash25 2013

[20] S S Jehangir and M S Sharawi ldquoA miniaturized uwb biplanaryagi-like mimo antenna systemrdquo IEEE Antennas and WirelessPropagation Letters vol 16 pp 2320ndash2323 2017

[21] J Ren W Hu Y Yin and R Fan ldquoCompact printed MIMOantenna for UWB applicationsrdquo IEEE Antennas and WirelessPropagation Letters vol 13 pp 1517ndash1520 2014

[22] L Liu S W Cheung and T I Yuk ldquoCompact MIMO antennafor portable devices in UWB applicationsrdquo IEEE TransactionsonAntennas and Propagation vol 61 no 8 pp 4257ndash4264 2013

[23] R Mathur and S Dwari ldquoCompact CPW-Fed ultrawidebandMIMO antenna using hexagonal ring monopole antenna ele-mentsrdquo AEU - International Journal of Electronics and Commu-nications vol 93 pp 1ndash6 2018

[24] Y Chen S Yang and Z Nie ldquoBandwidth enhancementmethodfor low profile E-shaped microstrip patch antennasrdquo IEEETransactions on Antennas and Propagation vol 58 no 7 pp2442ndash2447 2010

[25] A B Constantine ldquoAntenna theory analysis and designrdquo inMicrostrip Antennas pp 64-65 JohnWiley amp Sons 3rd edition2005

[26] S Blanch J Romeu and I Corbella ldquoExact representation ofantenna system diversity performance from input parameterdescriptionrdquo IEEE Electronics Letters vol 39 no 9 pp 705ndash7072003

[27] R Tian B K Lau and Z Ying ldquoMultiplexing efficiencyof MIMO antennas in arbitrary propagation scenariosrdquo inProceedings of the 6th European Conference on Antennas andPropagation (EuCAP rsquo12) pp 373ndash377 IEEE Prague CzechRepublic March 2012

[28] M Manteghi and Y Rahmat-Samii ldquoMultiport characteristicsof a wide-band cavity backed annular patch antenna for mul-tipolarization operationsrdquo IEEE Transactions on Antennas andPropagation vol 53 no 1 pp 466ndash474 2005

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Ws Ws

Ls Ls

Lf

R1

R2 R3

Lg

Wg

WnLn

R4

Wf

X

YZ

(a) (b)

Figure 1 Geometry of the proposed UWB antenna (a) Top view (b) bottom view of the antenna

monopoles or resonators helped induce reverse coupling andhence reduced mutual coupling in [16 17] In [18] adding aneutralization line increased the effectiveness of the antennasystem in terms of isolation and bandwidth within a smallspace without modifying the ground plane

Similarly E C and H-shaped patch antennas were loadedby U and V slots to achieve desired bandwidth characteristics[24] In addition developing efficient bandwidth enhance-ment with existing different technique in an area of limitedsize within a MIMO system is still a difficult task

In this paper the UWB MIMO antenna with enhancedisolation is proposed The proposed MIMO antenna hasa very low mutual coupling (|S

21S12| lt minus21 dB) and

is composed of two monopole antennas with a commonradiating surface The two radiating patches are connectedby two quad-circular structures The ground plane is on theopposite side of the radiating patch etched to increase theimpedance bandwidth characteristics A circular parasiticelement introduced at the centre of the substrate acts asan isolator and exhibits low mutual coupling for the upperfrequency bands of the antenna In the absence of couplingor decoupling structures a good isolation is achieved withoutthe expense of increase in size The results obtained fromthe proposed MIMO antenna without the use of complexstructures reveal that it has good performance in terms ofhigh impedance bandwidth and antenna gain high radiationefficiency high diversity gain and low envelope correlationcoefficient (ECC) The omnidirectional radiation patternof the purposed MIMO antenna element proves that theantenna possesses good pattern diversity for aMIMO system

2 Antenna Characteristics

The proposed geometry of the UWB-MIMO antenna isshown in Figure 1 where Figures 1(a) and 1(b) representthe top and bottom geometrical view of the substrate with

Table 1 Dimensions of the Antenna Parameters

Parameter Dimension (mm)Ls 65Ws 65Lf 163R1 178R2 89R3 8R4 4Lg 16Wg 327Ln 4Wn 5Wf 18

the optimal dimension listed in Table 1 The antenna wasdesigned on a Taconic substrate (120576

119903= 45 tan 120575 = 00035)

The size of the antenna is 65 mm times 65 mm times 162 mm Theantenna is composed of a microstrip patch with a commonradiating patch and a ground plane designed on the topand bottom side of the substrate respectively Here to meetthe operating frequency requirement the return loss at the10 dB lower frequency bandwidth is adjusted to 31 GHzapproximated using the following frequency calculation [25]

119891119899= 1198882119897119905radic1 + 120576

1199032 (1)

where119891119899is the first operating frequency c is the speed of light

in the vacuum and 119897119905is the combine total effective lengths

of the circular patch radii R1 and R2 The feed line and asmall notch in the ground plane employed to obtain the linecharacteristic impedance of 50 Ω are set to 18 mm and 4mm times 5 mm respectively The radiating patch is structurally


(a) (b)

(c) (d)



3 Design Strategy




21) in Figures




Frequency (GHz)

S 11(d

B)0

minus10

minus20

minus30

minus40

3 6 9 12 15

(a)

Frequency (GHz)

S 21(d

B)


3 6 9 12 15

minus10

minus20

minus30

minus40

minus50

minus60

minus70

(b)



21(dB)

Jsurf (Am)700441279

111070044028018011007004

176

003002001001

(a)

Jsurf (Am)700441279

111070044028018011007004

176

003002001001

(b)









Frequency (GHz)

S-pa

ram

eter

s (dB

)0

minus10

minus20

minus30

minus40

3 6 9 12 15



(a)

Frequency (GHz)

S-pa

ram

eter

s (dB

)

minus10

minus20

minus30

minus40

minus50

minus60



3 6 9 12 15

(b)


21(dB)











is given by [27]

120578119898119906119909= radic(1 minus 100381610038161003816100381612058811988821003816100381610038161003816) 12057811205782 (3)




119888


119863119866 = 10radic1 minus 1198641198621198622 (4)





0

30

60

90

120

150

180

210

240

270

300

330

0

-10

-20

-30

-40

-50

(a)


0

30

60

90

120

150

180

210

240

270

300

330

0

-10

-20

-30

-40

-50

(b)


0

30

60

90

120

150

180

210

240

270

300

330

0

-10

-20

-30

-40

-50

(c)


0

30

60

90

120

150

180

210

240

270

300

330

0

-10

-20

-30

-40

-50

(d)



TARC = radic (S11 + S12)2 + (S21 + S22)22 (5)



5 Conclusion



(a) (b)


Frequency (GHz)

ECC

Div

ersit

y G

ain

(dB)

Diversity GainECC

0010

0008

0006

0004

0002

00003 6 9 12 15

1000

999

998

997

996

995


Frequency (GHz)

Mul

tiple

xing

Effi

cien

cy (d

B)

Gai

n (d

B)


00

minus02

minus04

minus06

minus08

minus10

3 6 9 12 15

15

13

11

9

7

5

3

1





Frequency (GHz)

TARC

(dB)

TARC (measured)

0

minus1

minus2

minus3

minus4

3 6 9 12 15



Data Availability




Acknowledgments



References

































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia



(a) (b)

(c) (d)



3 Design Strategy




21) in Figures




Frequency (GHz)

S 11(d

B)0

minus10

minus20

minus30

minus40

3 6 9 12 15

(a)

Frequency (GHz)

S 21(d

B)


3 6 9 12 15

minus10

minus20

minus30

minus40

minus50

minus60

minus70

(b)



21(dB)

Jsurf (Am)700441279

111070044028018011007004

176

003002001001

(a)

Jsurf (Am)700441279

111070044028018011007004

176

003002001001

(b)









Frequency (GHz)

S-pa

ram

eter

s (dB

)0

minus10

minus20

minus30

minus40

3 6 9 12 15



(a)

Frequency (GHz)

S-pa

ram

eter

s (dB

)

minus10

minus20

minus30

minus40

minus50

minus60



3 6 9 12 15

(b)


21(dB)











is given by [27]

120578119898119906119909= radic(1 minus 100381610038161003816100381612058811988821003816100381610038161003816) 12057811205782 (3)




119888


119863119866 = 10radic1 minus 1198641198621198622 (4)





0

30

60

90

120

150

180

210

240

270

300

330

0

-10

-20

-30

-40

-50

(a)


0

30

60

90

120

150

180

210

240

270

300

330

0

-10

-20

-30

-40

-50

(b)


0

30

60

90

120

150

180

210

240

270

300

330

0

-10

-20

-30

-40

-50

(c)


0

30

60

90

120

150

180

210

240

270

300

330

0

-10

-20

-30

-40

-50

(d)



TARC = radic (S11 + S12)2 + (S21 + S22)22 (5)



5 Conclusion



(a) (b)


Frequency (GHz)

ECC

Div

ersit

y G

ain

(dB)

Diversity GainECC

0010

0008

0006

0004

0002

00003 6 9 12 15

1000

999

998

997

996

995


Frequency (GHz)

Mul

tiple

xing

Effi

cien

cy (d

B)

Gai

n (d

B)


00

minus02

minus04

minus06

minus08

minus10

3 6 9 12 15

15

13

11

9

7

5

3

1





Frequency (GHz)

TARC

(dB)

TARC (measured)

0

minus1

minus2

minus3

minus4

3 6 9 12 15



Data Availability




Acknowledgments



References

































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia




Frequency (GHz)

S 11(d

B)0

minus10

minus20

minus30

minus40

3 6 9 12 15

(a)

Frequency (GHz)

S 21(d

B)


3 6 9 12 15

minus10

minus20

minus30

minus40

minus50

minus60

minus70

(b)



21(dB)

Jsurf (Am)700441279

111070044028018011007004

176

003002001001

(a)

Jsurf (Am)700441279

111070044028018011007004

176

003002001001

(b)









Frequency (GHz)

S-pa

ram

eter

s (dB

)0

minus10

minus20

minus30

minus40

3 6 9 12 15



(a)

Frequency (GHz)

S-pa

ram

eter

s (dB

)

minus10

minus20

minus30

minus40

minus50

minus60



3 6 9 12 15

(b)


21(dB)











is given by [27]

120578119898119906119909= radic(1 minus 100381610038161003816100381612058811988821003816100381610038161003816) 12057811205782 (3)




119888


119863119866 = 10radic1 minus 1198641198621198622 (4)





0

30

60

90

120

150

180

210

240

270

300

330

0

-10

-20

-30

-40

-50

(a)


0

30

60

90

120

150

180

210

240

270

300

330

0

-10

-20

-30

-40

-50

(b)


0

30

60

90

120

150

180

210

240

270

300

330

0

-10

-20

-30

-40

-50

(c)


0

30

60

90

120

150

180

210

240

270

300

330

0

-10

-20

-30

-40

-50

(d)



TARC = radic (S11 + S12)2 + (S21 + S22)22 (5)



5 Conclusion



(a) (b)


Frequency (GHz)

ECC

Div

ersit

y G

ain

(dB)

Diversity GainECC

0010

0008

0006

0004

0002

00003 6 9 12 15

1000

999

998

997

996

995


Frequency (GHz)

Mul

tiple

xing

Effi

cien

cy (d

B)

Gai

n (d

B)


00

minus02

minus04

minus06

minus08

minus10

3 6 9 12 15

15

13

11

9

7

5

3

1





Frequency (GHz)

TARC

(dB)

TARC (measured)

0

minus1

minus2

minus3

minus4

3 6 9 12 15



Data Availability




Acknowledgments



References

































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia



Frequency (GHz)

S-pa

ram

eter

s (dB

)0

minus10

minus20

minus30

minus40

3 6 9 12 15



(a)

Frequency (GHz)

S-pa

ram

eter

s (dB

)

minus10

minus20

minus30

minus40

minus50

minus60



3 6 9 12 15

(b)


21(dB)











is given by [27]

120578119898119906119909= radic(1 minus 100381610038161003816100381612058811988821003816100381610038161003816) 12057811205782 (3)




119888


119863119866 = 10radic1 minus 1198641198621198622 (4)





0

30

60

90

120

150

180

210

240

270

300

330

0

-10

-20

-30

-40

-50

(a)


0

30

60

90

120

150

180

210

240

270

300

330

0

-10

-20

-30

-40

-50

(b)


0

30

60

90

120

150

180

210

240

270

300

330

0

-10

-20

-30

-40

-50

(c)


0

30

60

90

120

150

180

210

240

270

300

330

0

-10

-20

-30

-40

-50

(d)



TARC = radic (S11 + S12)2 + (S21 + S22)22 (5)



5 Conclusion



(a) (b)


Frequency (GHz)

ECC

Div

ersit

y G

ain

(dB)

Diversity GainECC

0010

0008

0006

0004

0002

00003 6 9 12 15

1000

999

998

997

996

995


Frequency (GHz)

Mul

tiple

xing

Effi

cien

cy (d

B)

Gai

n (d

B)


00

minus02

minus04

minus06

minus08

minus10

3 6 9 12 15

15

13

11

9

7

5

3

1





Frequency (GHz)

TARC

(dB)

TARC (measured)

0

minus1

minus2

minus3

minus4

3 6 9 12 15



Data Availability




Acknowledgments



References

































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia




0

30

60

90

120

150

180

210

240

270

300

330

0

-10

-20

-30

-40

-50

(a)


0

30

60

90

120

150

180

210

240

270

300

330

0

-10

-20

-30

-40

-50

(b)


0

30

60

90

120

150

180

210

240

270

300

330

0

-10

-20

-30

-40

-50

(c)


0

30

60

90

120

150

180

210

240

270

300

330

0

-10

-20

-30

-40

-50

(d)



TARC = radic (S11 + S12)2 + (S21 + S22)22 (5)



5 Conclusion



(a) (b)


Frequency (GHz)

ECC

Div

ersit

y G

ain

(dB)

Diversity GainECC

0010

0008

0006

0004

0002

00003 6 9 12 15

1000

999

998

997

996

995


Frequency (GHz)

Mul

tiple

xing

Effi

cien

cy (d

B)

Gai

n (d

B)


00

minus02

minus04

minus06

minus08

minus10

3 6 9 12 15

15

13

11

9

7

5

3

1





Frequency (GHz)

TARC

(dB)

TARC (measured)

0

minus1

minus2

minus3

minus4

3 6 9 12 15



Data Availability




Acknowledgments



References

































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia



(a) (b)


Frequency (GHz)

ECC

Div

ersit

y G

ain

(dB)

Diversity GainECC

0010

0008

0006

0004

0002

00003 6 9 12 15

1000

999

998

997

996

995


Frequency (GHz)

Mul

tiple

xing

Effi

cien

cy (d

B)

Gai

n (d

B)


00

minus02

minus04

minus06

minus08

minus10

3 6 9 12 15

15

13

11

9

7

5

3

1





Frequency (GHz)

TARC

(dB)

TARC (measured)

0

minus1

minus2

minus3

minus4

3 6 9 12 15



Data Availability




Acknowledgments



References

































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia





Frequency (GHz)

TARC

(dB)

TARC (measured)

0

minus1

minus2

minus3

minus4

3 6 9 12 15



Data Availability




Acknowledgments



References

































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia





























RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia




RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia


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