A quasi-optical polarization-independent diplexer for use in the beam feed system of millimeter-wave antennas

The theory and performance of a quasi-optical Fabry-Perot diplexer employing two rectangular meshes and capable of polarization-independent operation at large angles of incidence are presented. The diplexer is suitable for use in a dual-polarization dual-frequency beam feed system for millimeter-wave antennas. An experimental diplexer operating at an angle of incidence of
56.5\deg \pm 1\deg
was found to separate two 1.1-GHz bands centered at 21 and 31.5 GHz with a loss of less than 0.3 dB in either band and a cross-polarization discrimination of more than 40 dB in the higher band and 30 dB in the lower band.