COMPACT DUAL-BAND CIRCULARLY POLARIZED PATCH ANTENNA WITH WIDE 3-DB AXIAL RATIO BEAMWIDTH FOR BEIDOU APPLICATIONS

A dual-band circularly polarized (CP) patch antenna with wide 3-dB axial ratio beamwidth (ARBW) is presented for BeiDou Navigation System (BDS). Simple stacked circular patches are used as the main radiations for achieving dual-band operation. To enhance the ARBW for the two operation bands, an annular metal strip loaded ground plane (AMSL-GP) is presented. Besides, edge resistors are inserted to the GP for further ARBW enhancement at the lower band. In realization, a compact singleinput feed network based on a coupled-line trans-directional (CL-TRD) coupler is designed to provide two orthogonal modes at the two frequency bands simultaneously. Experimental results show that the bandwidth for 10-dB return loss is from 1.15 GHz to 1.65 GHz, which covers BDS B1 (1.561 GHz) and B2 (1.207 GHz). The 3-dB axial ratio (AR) bandwidths for the lower and upper bands are 9.6% and 7.1%, respectively. At 1.207 GHz, the antenna has 3-dB ARBWs of 185◦ and 187◦ in the xoz and yoz planes, respectively. And the values are 192◦ and 194◦ at 1.561 GHz.