Circularly Polarized Filtering Antenna Based on Integrated Substrate Gap Waveguide

This paper presents a novel circularly polarized (CP) filtering antenna based on integrated substrate gap waveguide (ISGW). Circularly polarized wave radiation is obtained by etching irregular slots on the ISGW transmission waveguide to form perturbation, and filtering is introduced by interdigital coupling line feed on the ISGW transmission line. The simulation results show that the CP filtering antenna has a center frequency of 31 GHz, and $\vert \mathrm{S}_{11}\vert dB from 25.5 to 36.4 GHz, i.e., a relative bandwidth of 35.06%. The 3-dB axial ratio (AR) bandwidth is 27.7-30.8 GHz, i.e., a relative axial ratio bandwidth of 10%. The antenna gain in the 3-dB AR bandwidth range is greater than 6.2 dBi, and the out-of-band suppression is above 14.4 dB.