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Dual-Band Circularly Polarized Antenna With CPWFeeding Structure

O. H. Hassan(1), Shoukry I. Shams(2), A. M. M. A. Allam(3).(1) Student, IET, German University in Cairo (GUC), Egypt.

osama.hassan@student.guc.edu.eg(2) T.A., M.sc., IET, German University in Cairo (GUC), Egypt.

(3) Professor, Ph.D, IET German University in Cairo (GUC) Cairo, Egypt.shoukry.ibrahim@student.guc.edu.eg

Abstract—A new design of a dual-band circularly polarizedantenna is introduced. The introduced antenna consists of arectangular patch surrounded by a circular ground with ad-ditional two circles, one located above the radiating patch andthe other on lower right side, result in both right hand andleft hand circular polarized radiation. The antenna operates intwo bands 3.3 GHz and 4.8 GHz. The first band is used inWiMax applications. The second band is used in some WLANapplications, it also works in WiMax applications. The antennais compact in size with overall dimensions 40mm× 40mm . Theantenna has a low profile and printed on a single side of thesubstrate. The feeding structure is a 50Ω CPW. The antenna isRHCP and LHCP at 3.3 GHz and 4.8 GHz, respectively. Theantenna is fabricated on FR4 substrate and the results of thereturn loss are measured and are in a good agreement with thesimulated results.

Index Terms—Circular polarized Antennas, dual band, CPW-Feed Antenna

I. INTRODUCTION

Recently, circularly polarized antennas has received a con-siderable attention due to the fact that it transmits in all planesthus providing any communication link with better receivingfactor[1]. CP also proved that it is much susceptible to multi-path and absorption as compared with linear polarization. Theproposed design is circularly polarized coplanar waveguidefed structure, thus it is printed on a single side making it easyin fabrication. The antenna operates in two bands at 3.3 GHzand 4.8 GHz, therefore it can be used for various applications.WiMedia OFDM uses a band from 3.3 GHz to 4.8 GHz,such an application could be applied in both bands. WiMaxfrequency ranges covered today: 1.765 to 1.815 GHz, 2.15 to2.7 GHz, 3.3 to 3.8 GHz and 4.8 to 6.0 GHz thus the proposedantenna design works on the middle and last band of WiMax.The Federal 4 GHz spectrum spans from 4.4 GHz to 4.99 GHz.This spectrum is designated in the U.S. and NATO countriesfor military fixed and mobile communications. Typical usesinclude point-to-point microwave, drone vehicle control andtelemetry. Some WLAN applications work on the 4.8 GHzband as set by IEEE.

The proposed antenna is compact with overall size of40mm× 40mm printed on FR4 substrate. The feeding line isa 50Ω CPW and it produces right hand and left hand circularpolarized radiation due to the circles located between apartfrom each other almost diagonally.

Figure 1. Geometry and configuration of the proposed antenna design

The antenna is fabricated and measured. The measuredresults were satisfactory compared to the simulated results.

II. ANTENNA DESIGN

The geometry of the proposed antenna is shown in Figure1 . The antenna consists of a circular substrate of thickness xmm and diameter G mm. The feeding line of widthWf mmand length of Lf mm. The main radiation comes from thecenter patch following the feeder, it has width of Wcmm andlength of Lcmm . The antenna was made first without the twocircles as shown in Figure 2 , it results in a wide bandwidth.Figure 3 shows the return loss of this antenna. Upon presentingthe two circles, a dualband appeared instead of a widebanddesign. These circles are equal in size with diameter of Dtmm.Different values for the variables in the design were varied andthe outcome is studied to get the satisfactory results. Figure4 shows the return loss curve on changing the location of thecircles. Several variations for the variables Lf and Wf weremade and the results of the return loss curves were shown inFigure 5 and Figure 6 .

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Figure 2. Wideband design

Figure 3. Return loss curve of the wideband design

Figure 4. Return loss curve with different variations for the circles centrelocation

Figure 5. Return loss curve with different variations for the patch length

Figure 6. Return loss curve with different variations for the patch width

On varying the width and length of the radiation patch,the axial ratio changes but in random variation. The finaldimensions were retrieved based on having a suitable axialratio in the bands of radiation. The variation of the locationof the circles, caused great change in both return loss andaxial ratio. The best results were also in the given dimensionand this is due to having a suitable axial ratio in the band ofradiation.

The substrate of the antenna is FR4 material with εr =4.4mm, loss tangent tanδ = 0.019 and thickness of h mm.The antenna designed in this paper is right-hand CP for thelower band and left-hand CP for the upper band.

III. EXPERIMENTAL RESULTS AND DISCUSSION

The design is made to be simple, small in size and the finaldimensions after the trials discussed in the previous section islisted in Table I.

Table IVALUES OF THE USED VARIABLES

Variable Value (mm)G 44

Wc 8Lc 22Wf 4.4Lf 9.0X 3.0h 1.5

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Figure 7. Return loss curve for the proposed design

Figure 8. Axial ratio curve of the proposed design

The return loss curve in Figure 7 shows that the antennaradiates in two bands which are the 3.3 GHz and 4.8 GHz.The first band radiates from 3.05 GHz to 3.45 GHz, with apercentage bandwidth of 12.1 %. The second band radiatesfrom 4.7 GHz to 5.7 GHz, with a percentage bandwidth of20.83 %.

Figure 8 shows that the axial ratio curve of the proposeddesign reaches 1 dB and it reaches 2 dB at the second band.Figure 9 shows the radiation pattern at 3.3 GHz, it is clearlyshown that it RHCP in the +ve z-direction and LHCP in the -ve z-direction. The radiation pattern in Figure 10 shows that isLHCP +ve z-direction and RHCP in the -ve z-direction whichis opposite to the case of the 3.3 GHz. This shows that theantenna is not only dual-band, but also a dual sense circularlypolarized antenna.

On approaching the desired results from the simulation, theproposed antenna is fabricated. The fabricated antenna shownin Figure 11 is measured on the vector network analyzer andthe results are compared to simulated one . The results werein a good agreement and this is clearly identified in the returnloss curve of the measured and simulated antenna design inFigure 13

Figure 9. Radiation pattern at 3.3 GHz

Figure 10. Radiation pattern at 4.8 GHz

Figure 11. Fabricated antenna

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Figure 12. Fabricated antenna with the network analyzer

Figure 13. Return loss curve of the simulated antenna in comparison to thefabricated antenna

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IV. CONCLUSION

A novel compact dual-band circularly polarized CPW an-tenna introduced. The antenna is fabricated on FR4 substrate.The design is compact in size which makes it easy to beimplemented in applications requiring small sized antennas.The fabricated antenna results are similar and quite satisfac-tory to the simulated results. Circular polarized radiation isachieved by introducing two circles in an almost diagonaldistribution. The antenna could be used in WiMax applicationand broadband multiplexers for point to point or multi pointto point communication systems.

REFERENCES

[1] C. A. Balanis, Antenna Theory: Analysis and Design, 3rd Edition, JoneWiley & sons, 1997.

[2] J. D. Kraus, Antennas: for all applications, 3rd Edition, McGraw-Hill,1997.

[3] W. L. Stutzman & G. A. Thiele, Antenna Theory and Design, 2nd Edition,Jone Wiley & sons, 1981.

[4] Canhui Chen and E. K. N. Yung, “Dual-Band Dual-Sense Circularly-Polarized CPW-Fed Slot Antenna With Two Spiral Slots Loaded”, IEEETRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 57,NO. 6, JUNE 2009.

[5] Jia-Yi Sze, Member, IEEE, and Chi-Chaan Chang, “Circularly PolarizedSquare Slot Antenna With a Pair of Inverted-L Grounded Strips” , IEEEANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 7,2008.