A Stable-Gain Millimeter-Wave Fabry-Perot Antenna Based on Circular Polarizer-Integrated PRS with Positive Reflective Phase Gradient

In this paper, we present a millimeter-wave Fabry-Perot antenna with dual resonances, circular polarization, and stable gain. To achieve circularly polarized radiation, we integrate a receiver-transmitter circular polarizer into the partially reflective surface (PRS) of the antenna. The PRS is specifically designed with a positive reflective phase gradient, which contributes to a stable gain in the dual-resonance frequency band. For the radiation source, we adopt a linearly-polarized substrate-integrated waveguide cavity-backed slot fed by a printed ridge gap waveguide. Experimental measurements conducted on a fabricated prototype of the proposed antenna demonstrate its impedance and axial ratio bandwidths of 28.6-30.0 GHz and 28.6-29.6 GHz, respectively. Furthermore, the antenna exhibits a peak gain of 12.1 dBi and a gain fluctuation lower than 0.6 dB within the operational frequency band.