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.

In the study, a coupled line trans‐directional (CL‐TRD) coupler that allows for equal complex termination impedances with arbitrary power divisions is presented. It is composed of two pairs of coupled lines with an overall electrical length of 90°, two types of shunt capacitors and three pairs of short‐circuited stubs. By adjusting the electrical length of each short‐circuited stub, as well as the values of the shunt capacitors, arbitrary equal complex termination impedances and power divisions are achieved. Moreover, since capacitors are shunted between the coupled lines, the proposed CL‐TRD coupler has an inherent feature of dc blocking. Design equations for the CL‐TRD were derived using even–odd mode decomposition analysis. To validate the theory, several numerical examples extracted from the design procedure were listed. Eventually, two prototypes of the proposed CL‐TRD coupler are fabricated, and experiments are carried out. The measured results indicate that the coupler is able to realise arbitrary power divisions for equal complex termination impedance with good matching and isolation.

A low-profile dual-band circular polarized (CP) patch antenna with wide half-power beamwidths (HPBWs) is presented for CNSS applications. Simple stacked circular patches are used to achieve dual-band radiation. To enhance the HPBW for the two operation bands, a dual annular parasitic metal strip (D-APMS) combined with reduced ground plane (R-GP) is presented. A single-input feed network based on the coupled line transdirectional (CL-TRD) coupler is also proposed to provide two orthogonal modes at the two frequency bands simultaneously. Experimental results show that the 10 dB impedance bandwidth is 32.7%. The 3 dB axial ratio (AR) bandwidths for the lower and upper bands are 4.1% and 6.5%, respectively. At 1.207 GHz, the antenna has the HPBW of 123° and 103° in the xoz and yoz planes, separately. And the values are 127° and 113° at 1.561 GHz.

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