Quasi-optical diplexer and filter based on a polarization ring interferometer

The operation of a quasi-optical polarization ring interferometer (PRI) performing the function of a diplexer, bandpass filter, and band-stop filter is demonstrated for the first time. It is shown that the beam focusing losses in this interferometer can be reduced using spherical low-permittivity lenses. The results of measurements of the transmission characteristics of a PRI prototype in a 3-mm wavelength range are presented.