A Novel Compact Ultra Wide Band Planar Antenna Based on the Composite Right/Left-Handed Transmission Line Accompanying Improvement Gain

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HCTL Open Int. J. of Technology Innovations and ResearchHCTL Open IJTIR, Volume 2, March 2013e-ISSN: 2321-1814ISBN (Print): 978-1-62776-111-6

A Novel Compact UltraWide Band PlanarAntenna Based on theComposite Right / Left -

Handed TransmissionLine AccompanyingImprovement Gain

Mohammad Alibakhshi-Kenar i ∗

[email protected]

Abstract

In this paper, a novel compact and ultra wide band (UWB) planarantenna based on the composite right-left handed transmissionline (CRLH-TL) structure with enhancement gain is proposed

and investigated. With CRLH metamaterial technology embedded,

the proposed compact and broadband antenna is presented with best

∗Department of Electrical Engineering at Shahid Bahonar University of Kerman, Kerman,

Iran

Mohammad Alibakhshi-KenariA Novel Compact Ultra Wide Band Planar Antenna Based on the CompositeRight/Left-Handed Transmission Line Accompanying Improvement Gain.

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in size, bandwidth, efficiency and radiation pattern. To realize char-acteristics of the antenna, the printed I-shaped gaps into the rect-angular patches of the radiation patches are used. The physical sizeand the operational frequency of the antenna depend on the unit cellsize and the equivalent transmission line (TL) model parameters of the CRLH-TL, including series inductance, series capacitance, shuntinductance and shunt capacitance. The compact and UWB antennaaccompanying high gain with two unit cell is designed from 0.5 GHzto 3.25 GHz which corresponding to 146% bandwidth, each of whichoccupies only 7.5 mm x 10.5 mm or 0.025λ0 x 0.03λ0 at the operat-ing frequency f = 1 GHz ( where λ0 is free space wavelength). The

physical length, width and height of the presented antenna are 15mm, 10.5 mm and 1.6 mm or 0.05λ0, 0.03λ0 and 0.005λ0, respec-tively, in terms of free space wavelength. The radiation peak gainand maximum efficiency are 7 dBi and 99%, respectively.

Keywords

Compact Antenna, Ultra Wide Band (UWB) Antenna, Composite Right/Left-Handed Transmission Line (CRLH-TL), Metamaterial (MTM).

Introduction

In Recent years, with development of minimizing and broadband technology forfoot print area reduction and high resolution and high data transmission ratesin modern communication systems, there is increasing demand for small low-cost antenna with unidirectional radiation patterns, dispersive and broad bandcharacteristics. The printed antennas have received great attention in broad-band applications due to their advantages of compact, planar, low cost, lightweight, broadband, compatibility and easy integration with other microstripcircuits. Applications in present-day mobile communication systems usuallyrequire smaller antenna size in order to meet the miniaturization requirementsof mobile units. Thus, size reduction and bandwidth enhancement are becoming

major design considerations for practical applications of microstrip antennas [1].

Metamaterial (MTM) [2], have recently been extensively discussed and studiedfor special properties. Metamaterials (MTMs) are man-made composite materi-als, engineered to produce desired electromagnetic propagation behaviour notfound in natural media [2, 3]. Those unusual properties were used to improvedperformances of antennas and circuits. Microstrip antennas had been developed

Mohammad Alibakhshi-Kenari

A Novel Compact Ultra Wide Band Planar Antenna Based on the CompositeRight/Left-Handed Transmission Line Accompanying Improvement Gain.

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for applications in present communication systems [4, 5], but there is a fact thatthe size reduction levels remain unsatisfactory to the electromagnetic community.Several techniques were suggested to reduce antenna size [6], however, suchtechniques usually suffer from increasing the design complexity. The occurrenceof metamaterial may be a solution for this challenge [7, 8]. In this work, weusing of the metamterial technology and the simple techniques for foot printarea reduction, enhancement bandwidth and improvement gain of the antenna,which consist of employing of the printed planar mushroom structure basedon CRLH-TL and suitable structural parameters. Various implementations of

metamaterial structures have been reported and demonstrated [2]. In this papera metamaterial CRLH antenna with two unit cells which each unit cell embrace

of two printed I-shaped gaps capacitors and the spiral inductor accompanyingmetallic via connected to ground plane is presented. The printed I-shapedstructure exhibit compact, broadband and improvement gain property whichuseful for compact and wideband antennas.

This paper is organized in the following way: a small and UWB antennaprototype with high gain and efficiency employing the proposed concept will bedepicted in section 2. Followed by section 3 where various performance includingdimension, impedance bandwidth and radiation patterns characteristics of therecommended antenna are demonstrated. Further discussion and conclusionare raised at last.

Theory of the Proposed Antenna

As discussed in [2, 9], several implementations can be used to realize the CRLH-TL unit cell including surface mount technology (SMT) chip components anddistributed lines. However, lumped elements are not appropriate in antennadesign because of their lossy characteristics and discrete values. We usingprinted planar technique for our antenna design, since printed planar structuresare good candidate for antenna design because of their advantages which includefoot print area reduction, loss less and non-discrete values. A novel compactand UWB antenna with improvement gain based on CRLH-TL presented inhere, which consists of two unit cells while each unit cell built by two rectan-gular patches with printed I-shaped gaps into patches, and the spiral inductoraccompanying metallic via connected to the ground plane. Figure 1 showsgeometry of the proposed antenna and figure 2 displays an equivalent circuitmodel of each cell as CRLH unit cell.



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In this structure, port 1 is excited with input signal and port 2 is matched with50Ω load impedance. The antenna structure is based on a composite right-lefthanded (CRLH) transmission line (TL) model used as a periodic structure.Because the lowest mode of operation is a LH mode, the propagation constantapproaches negative infinity at the cut-off frequency, and reduce its magnitudeas frequency is increased. Making use of this phenomenon, an electrically largebut physically small antenna can be developed.

Figure 1: Configuration of the presented small and ultra wide band (UWB) antenna composed of the two unit cells based on CRLH-TL.

By means of the I-shaped gaps and spiral inductors with shorting via-holeconnecting to ground plane, the series capacitance (C L) and shunt inductance



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Figure 2: Proposed Antenna: Equivalent circuit model of the CRLH MTM antenna for one unit cell

(LL) can be easily implemented in a compact fashion. The host TL possess theright-handed parasitic effect that can be seen as shunt capacitance (C R) andseries inductance (LR).

In this paper, we employing of metamaterial (MTM) technology and the printedplanar approach that results to foot print area reduction of the proposed an-tenna. Overall size of this antenna is 0.05λ0 x 0.03λ0 x 0.005λ0 at the operating

frequency f = 1 GHz where λ0 is the free space wavelength and also withchoosing smaller distance between printed I-shaped gaps edges, we will beobtained wide bandwidth from 0.5 to 3.25 GHz which corresponding to 2.75GHz bandwidth. Furthermore, with acceptable selecting of the number unitcells (N) constructing antenna structure and structural parameters of the spiralinductors such as number of turns (N), inner radius measured to the center of the conductor (Ri), conductor width (W) and conductor spacing (S) we will beachieved excellent radiate performances. The gain and efficiency of the proposedantenna are changed from 0.2 dBi to 7 dBi and 25% to 99% into frequencyband 0.5 - 3.25 GHz, respectively, that shown very good radiation characteristics.

Therefore, the MTM antenna designed is compact and ultra wide band (UWB)with high gain. The proposed antenna based on CRLH-TL made very smallsize and broadband to support today’s multi-band modern wireless applicationsand mobile handsets.

Figure 1, shows configuration of the recommended antenna constructed of thetwo unit cells based on CRLH-TL structure that was built on a Rogers RT Duroid5880



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substrate, with a dielectric constant of 2.2 and a thickness of 1.6 mm. Thismushroom type unit cell consisted of 10 mm x 10.5 mm or 0.03λ0 x 0.03λ0 toppatch, printed on top of the Substrate which in each unit cell, the series capaci-tance (C L) is developed by two the printed I-shaped gaps into patches, and theshunt inductance (LL) is resulted from the spiral inductor shorted to the groundthrough the metallic via. The structure possess the right-handed parasitic effectthat can be seen as shunt capacitance (C R) and series inductance (LR). Theshunt capacitance C R is mostly come from the gap capacitance between thepatch and the ground plane, and the unavoidable current that flow on the patchestablish series inductance LR , which indicates that these capacitance andinductance cannot be ignored. In this structure, port 1 is excited with input

signal and port 2 is matched to 50Ω load impedance, as illustrated in Figure 1.The proposed design keeps the overall size of the unit cell compact while aimsat reducing the ohmic loss to improve radiation efficiency. This antenna cansupport all cellular frequency bands from 0.5 GHz to 3.25 GHz, using singleor multiple feed designs, which eliminates the need for antenna switches. Allof these attributes make the proposed antenna well suitable for the emergingwireless applications [10, 11] and mobile handsets.

Figure 3: Simulated return loss ( S 11) parameter



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Simulation Results and DiscussionThe proposed metamaterial antenna is designed as a CRLH antenna where thesubstrate has dielectric constant r = 2.2 and thickness h = 1.6 mm. Compactand broad band recommended antenna is simulated by using the full-wave

simulator (ADS). The simulated reflection coefficient (S 11 parameter) displayedin Figure 3 and simulated radiation gain patterns in 1.4, 2.4 and 3.2 GHzare plotted in figures 4, 5 and 6. The radiation patterns are unidirectionalcharacteristics. The simulated gains at 1.4, 2.4, 3.2 GHz are 2.6, 6.9, and 7 dBi,respectively. The simulated radiation efficiency is 37.7% at 1.4 GHz, 95% at2.4 GHz, and 99% at 3.2 GHz. To validate the design procedure the proposed

antenna was compared with some of the antennas and their dimension andradiation characteristics were summarized in Table 1.

Figure 4: Radiation pattern (gain) in elevation ( φ = 0 degree) at f = 1.4 GHz.

The two unit cell compact and broadband antenna is designed from 0.5 GHzto 3.25 GHz and this antenna exhibit good matching between this frequency

band for 50Ω impedance port. The physical length, width and height of thesuggested antenna are 15 mm, 10.5 mm and 1.6 mm (0.05λ0 x 0.03λ0 x 0.005λ0),respectively. In the center frequency 1.87 GHz, the gain and efficiency are 6.8dBi and 90%, respectively.



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Conclusion

In this paper, we introduced a new concept of antenna size reduction withbroad bandwidth accompanying enhancement gain based on a metamaterialdesign methodology. A practical compact, broad band and high gain antennawith a simple feed structure and planar circuit integration possibilities has



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HCTL Open Int. J. of Technology Innovations and ResearchHCTL Open IJTIR, Volume 2, March 2013e-ISSN: 2321-1814ISBN (Print): 978-1-62776-111-6 References

Table 1: Dimension and radiation characteristics of the antennas

Parameters Proposed An-tenna

Antenna Designedin [12]

Antenna Designedin [11]

Dimension 0.05λ0 x 0.03λ0 x0.005λ0

0.07λ0 x 0.07λ0 x0.03λ0

0.4λ0 x 0.03λ0 x0.03λ0

Gain 7 dBi 0.6 dBi 0.45 dBi

Bandwidth 0.5 - 3.25 GHz 1 - 2 GHz 0.8 - 2.5 GHz

Effiiciency 99% 26% 53.6%

been demonstrated. Overall size of the recommended antenna is 15 mm x 10.5mm x 1.6 mm or 0.05λ0 x 0.03λ0 x 0.005λ0 at the operating frequency f = 1GHz where λ0 is free space wavelength. A return loss below -10 dB from 0.5- 3.25 GHz was obtained which corresponding to 146% bandwidth. The peakgain and the maximum efficiency of the proposed antenna are 7 dBi and 99%,

respectively. This antenna has the advantages of compact size, broadband, highgain, unidirectional radiation pattern and simple implementation. The recom-

mended antenna can be used for mobile handset and wireless communicationapplications.

Acknowledgement

The author would like to express his sincere thanks to Research Institute forICT of Iran (Contract number 6987/500/T).

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A Novel Compact Ultra Wide Band Planar Antenna Based on the Composite Right/Left-Handed Transmission Line Accompanying Improvement Gain