A Compact Diplexer for Circularly Polarized 20/30 GHz SIW-Antennas

This contribution deals with a 20/30 GHz diplexer intended to feed substrate integrated waveguide (SIW) antennas. As these feature circular polarization, they have a square cross section which is implemented in a thick multilayer. The transition between the thick antenna and the thin front end is part of the proposed diplexer. Realizing it as a step yields a low-loss and very compact component occupying approximately 5 x 8 mm². The paper describes the structure and reports its design and realization. The functionality is demonstrated in simulation and verified experimentally. The measured insertion loss is 1 dB in the 20 GHz receive (Rx) path and 1.6 dB in the 30 GHz transmit (Tx) one. The port isolation exceeds 30 dB at 30 GHz.