Design of a Circularly-polarized Microstrip Antenna with BroadBand and Wide Beamwidth

keywords:broad band  wide beamwidth  circular polarization  sequential-rotation feed

Abstract:In this paper, a broadband circularly-polarized microstrip antenna is designed. The antenna adopts a stacked double-lay-er circular patch structure, combined with a four-point sequential-rotation feed, to achieve broadband circularly polarized radiation per-formance. A ring array of vertically grounded metal columns is loaded around the laminated circular patch, which introduces the beam steering effect and equivalent zero mode resonance characteristics to effectively broaden the half-power beam width (HPBW) over a broadband and ensure the circular polarization radiation performance within the broadband and broad beam volume. A prototype antenna is fabricated and measured. Measured results show that the impedance bandwidth (4. 54 GHz~11. 50 GHz) of S11 less than -10 dB is 87%, covering the expected application working frequency band of 6 GHz~10 GHz. The bandwidth with axial ratio less than 3 dB rea-ches 33. 1% (6. 71 GHz~ 9. 36 GHz). HPBW approaches 100° in the range of 6 GHz ~ 8 GHz, and more than 75° in the whole bandwidth. Except for the frequency band above 9. 5 GHz, the 6 dB axial ratio beamwidth coverage in the working frequency band is close to 200°, indicating that the antenna has good circular polarization performance during a broad band and wide beamwidth.