bandwidthenhancementof narrowband rectangularmicrostrip antenna...

2006 INTERNATIONAL RF AND MICROWAVE CONFERENCE PROCEEDINGS, SEPTEMBER 12 - 14, 2006, PUTRAJAYA, MALAYSIA

Bandwidth Enhancement of a Narrowband Rectangular Microstrip Antennaon a Spiral Fan-Shape Electromagnetic Band-Gap (EBG) Patch Structure

T. Masri, M. K. A. Rahim, M. H. Jamaluddin and A. Asrokin

Wireless Communication Centre, Faculty of Electrical Engineering,Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia

ithelaha@yahoo.com.my, mkamal@fke.utm.my, haizal@fke.utm.my, awil982@yahoo.com

Abstract - An innovative and novel technique has beenexplored in enhancing the bandwidth of a rectangularpatch antenna by introducing a spiral fan-shapeElectromagnetic Band Gap (EBG) structure between anarrowband patch antenna and its ground plane.Measured result shows an excellent return loss andgood impedance matching which resulted in anincrement of the bandwidth from about 4 % for asingle layered narrow band rectangular microstrippatch, to more than 17 % after the EBG structure wasintroduced. This paper present the methodology,simulations and experimental works carried out inaccomplishing the objective above. Microwave Office2006 software has been used to initially simulate andfind the optimum design and results.

Keywords: Microstrip, Antenna, electromagnetic Band-Gap,Narrow Ban & Broad bandAntenna

1. Introduction

Electromagnetic band-gap (EBG) structureshave two commonly employed configurations, namelythe perforated dielectric and the metallodielectricstructures. The perforated EBG structures consists of aperiodically arranged air-columns, which effectivelysuppress unwanted substrate modes commonly exist inmicrostrip antennas, but it also createsdisadvantageous in terms of fabrication. On theother hand, the metallodielectric EBG structuresconsists of printed array of metallized elements, usedto suppressed substrate modes [1]. The later was morepractical and proofed to exhibits an attractivereflection phase future where the reflected fieldchanges continuously from 180° to -180° versusfrequency. It allows a low profile wire antenna toradiate efficiently with enhance bore sight gain,reduced back radiation and side lobes levels [2].

EBG substrates have found possibleapplications in the antenna technology to improveperformance like reducing mutual coupling between

antennas on the same substrate or reduce side lobeeffects due to truncated surface waves that would beexcited in a standard antenna substrate [3]. EBGsubstrates can also be used to eliminate scan blindnessphenomena presented in array antennas. EBG layershave also been used as a top cover of a Fabry-PerotCavities to produce highly-directive radiators [4].Recently, EBG structures have been used to mimicperfect magnetic conductors (PMC) over a narrowfrequency range, for use as a ground plane in a low-profile antenna configuration [5].

In this research, we focus our study on theeffect of introducing an EBG structures in the form ofperiodic spiral fan-shape patches between a narrowband resonator, a rectangular patch for this case, andthe ground plane. A parametric study on theperformance of the antenna, especially on enhancingthe bandwidth was done using AWR simulationsoftware and the optimum results was confirmedthrough fabrication of a model of the antenna. It wasfound that the results were excellent.

2. Parametric Study

A spiral fan-shape EBG patch structure wasintroduced between a narrowband; coaxial feedrectangular patch and its ground plane. This structurewas chosen due to its simplicity of design and lesstime consuming when simulated using the AWRsoftware. Figure 1 show the geometry of the antennainvolves, which consist of two 1.6 mm thick FR4substrate with an gr of 4.6, one with a rectangularresonator patch on the top plane and the other, with thespiral fan-shape EBG patch structure, on top of aground plane. The width and length of the rectangularpatch was calculated to resonate at 2.4 GHz while thewidth and radius of the spiral fan-shape EBG patchstructure was varied proportionally (Figure l.b) toobtain the optimum results, as mentioned above.

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Figure 2: Simulated results of the (9 and 13 units) spiral fan-shaped EBG Structure.

4. EBG Patch Size

(a)

IDTL4W- 4m

(b)

(C) (jJ)Figure 1: (a) Perspective view (b) the circuit schematics ofthe radial fan (c) The spiral fan-shaped EBG patch structure

(d) Rectangular patch Microstrip Antenna.

3. The Effect of Introducing the EBGStructure

Figure 2 shows the simulated return loss forthe narrowband antenna with a spiral fan-shaped EBGstructure. By increasing the number of spiral fan-shaped EBG patch structure, some good matchingcharacteristics were observed. The best results wereobserved when the number reached 13 units andabove. From the simulation results, the bandwidth wasenhanced up to 7.5%. But this also means that thestructure or the size of the overall patch increases too.

The ultimate goal in most AMC surfaces is toincorporate an antenna into the system to achieve asmaller, thinner and potentially lighter weight designcompared to what would be possible using aconventional metallic (PEC) ground plane. So, in ourstudy, the effect of the number of spiral fan-shape andthe overall EBG structures' size on the antennaperformance was also investigated. Two different sizeof the EBG structure were designed, simulated,fabricated and measured. Both of the spiral fan-shapedstructure was fabricated on a 100mm x 100mm x1.6mm and a 80mm x 80 mm x 1.6mm FR4 substratewith dielectric constant of 4.6.

The number of spiral fan-shaped was varieduntil an optimum result obtained. From the measuredresults, it was observed that the bandwidth increaseswhen the number of spiral fan-shaped increases andthe rectangular patch positioned at a particular positionas shown in the diagram in Figure 3.

As predicted, it can be seen (figure 4) that asignificant improvement of bandwidth up to more than17% was observed with the lower frequency at 2.38GHz and the higher frequency at 2.82 GHz at -lOdBreference level. The overall thickness of the antenna is3.2mm.

Figure3: The fabricated spiral fan-shape EBG patchStructure.

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References

Figure 4: Measured results of the spiral fan-shape EBGstructure shows bandwidth enhancements up to more than17% with the lower frequency at 2.38 GHz and the

higher frequency at 2.82 GHz at -1OdB reference level.

5. Summary

An initial parametric study was done on thespiral fan-shape EBG structure positioned between anarrowband rectangular microstrip antenna and itsground plane. Measured result shows an excellentreturn loss and good impedance matching whichresulted in an increment of the bandwidth from about 4% for a single layered narrow band rectangularmicrostrip patch, to more than 17 % after the EBGstructure was introduced. Further investigation on theradiation characteristic will be carried out in the futureand different EBG structure's shapes and sizes willalso be look upon to.

[1] Simon Tse, Paul Young, John Batchelor, " EBGGround Plane Combines the Periodic MetalizedElements and the Perforated Dielectric Effectsfor Enhance Performance," Proceedings of the2006 Antennas & Propagation Conference,Burleigh Court Conference Centre,Loubhborough University, UK, April 2006, pp.353-356.

[2] M. Hosseini, A. Pirhadi, M. Hakkak, "Design ofan AMC with Little Sensitivity to the Angle ofIncident and with Compact Size" Proceedings ofthe 2006 Antennas & Propagation Conference,Burleigh Court Conference Centre,Loubhborough University, UK, April 2006, pp.301-304.

[3] F. Yang and Y. Rahmat-Samii,"Mutual couplingreduction of microstrip antennas usingelectromagnetic band-gap structure," in IEEEAP-SIURSI symp. Dig., vol 2, Jul 2001,pp 478-481.

[4] R. Gonzalo Garcia and P. de Maagt and M.Sorolla,"Enhanced patch-antenna performance bysuppressing surface waves using photonic-band-gap substrate," IEEE Transaction on MicrowaveTheory and Techniques, Vol. 47 N. 11, pp. 213 1-2138, November 1999.

[5] Y. Zhang, J. Von Hagen, M. Younis, C. Fischer,W. Wiesbeck,"Planar artificial magneticconductors and patch antennas," IEEE Trans.Antennas Propagat., Vol.51, No. 10, pp. 2704-2712, 2003.

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