A Wideband Circularly Polarized Filtering Antenna Based on Slot-Patch Structure

This letter presents a wideband circularly polarized (CP) antenna with filtering radiation response based on a slot-patch structure. The proposed CP filtering antenna is composed of a top patch, a middle microstrip-to- (“+”-shape) slot structure, and a bottom metallic reflector. The middle layer not only functions as a slot-coupled feeding structure but also operates as a driven slot CP antenna. The top and bottom layers are used to reduce the slot antenna backside radiation and enhance the antenna axial ratio (AR) bandwidth. In addition, a diagonal slot etched on the patch and an additional E-shaped slot on the middle layer can generate the lower- and upper-band radiation zeros, respectively. For verification, the antenna is implemented. The measured results show that the overlapping bandwidth of the impedance and AR bandwidth is 46.9% (3.35–5.40 GHz). The measured average CP gain is about 7.6 dBic. High frequency selectivity and better than 10 dB out-of-band radiation rejection level is obtained. Compared to the conventional filtering CP design method, which employs the filter or resonator feeding circuit, the proposed design features a simple structure, higher realized gain and wider AR/impedance overlapping bandwidth.