A Grating-Based Circular Polarization Duplexer for Submillimeter-Wave Transceivers

A quasioptical duplexer based on a metallic grating polarizer has been designed and demonstrated in a submillimeter-wave imaging radar system. The grating converts between linear and circular polarization with low loss and high isolation, and it is simple to manufacture by cutting grooves into a scanning sub-reflector. The grating profile and period were optimized to provide good polarizing efficiency over the radar's 4.5% bandwidth of 660-690 GHz, with two-way mismatch loss simulated to be better than 0.1 dB over an 8% bandwidth. Similarly negligible loss is also predicted for grating rotations of +/-3 degrees, which span the radar's field of view. The circular polarization grating duplexer is shown to improve the signal-to-noise ratio by 4.5 dB compared to a beam splitter.