A Novel Circularly Polarized Filtering Antenna with Wide Axial-ratio Beamwidth and High Selectivity

This paper introduces a compact, circularly polarized (CP) integrated antenna that offers both wide axial ratio and highly selective filtering performance. Designed with dimensions of 0.44λ0×0.44λ0×0.04λ0, the filtering antenna comprises a microwave bandpass filter (BPF) circuit and a patch antenna. The BPF circuit is constructed using coupled stripline open-loop resonators (SOLRs), while the patch antenna features diagonal slots and truncated corners to achieve low CP axial ratio (AR). The proposed antenna delivers a wide 3dB AR beamwidth of 175° and a 3.3% impedance bandwidth spanning from 2.4 GHz to 2.48 GHz. It also delivers a flat gain of approximately 6.2dBi within the operating band. Furthermore, simulations reveal over 45 dB out-of-band suppression levels, indicating highly effective performance.