Full W-Band Circularly Polarized Antenna With Waveguide Polarizer Based on Evanescent and Propagation Modes

A novel full W-band circularly polarized (CP) horn antenna is proposed. It contains a rectangular waveguide (RWG) for feeding, a waveguide polarizer based on evanescent and propagation modes and a large pyramidal horn. The proposed polarizer is a ridge waveguide-to-RWG structure, where the ridge waveguide (RW) is the primary polarizer based on evanescent and propagation modes, and the RWG is the secondary one based on propagation modes. The polarizer overcomes the inherent limits of traditional ones that solely employ propagation modes and achieves both broadband and miniaturization. With the proposed polarizer, a CP horn antenna is fabricated and measured. The entire antenna is a low-cost unibody construction, which avoids redundant splitting and assembly. Experimental results indicate that the proposed CP horn antenna performs well, with $\vert {S}_{11}\vert $ less than −14.2 dB, axial ratio (AR) lower than 2.7 dB, and realized gain (RG) better than 18.1 dBi in the full W-band (75–110 GHz).