Novel Polarization-Controllable TE21 Mode Converter

Summary form only given. We report the concept and development of a Ka-band two-port mode and polarization converter that efficiently converts a TE₁₀ rectangular waveguide mode into either a linearly or a circularly polarized TE₂₁ cylindrical waveguide mode. The converter is formed of a power-dividing section, a mode-converting section, and a polarization-transitioning section. The conversion process in each section is analyzed and the design considerations are discussed. A proto-type has been designed, constructed, and tested. The measurement results agree well with the numerical calculations for both linear and circular polarizations. The measured optimum back-to-back transmissions are 94% with a 3-dB bandwidth of 5.7 GHz for linear polarization and 97% with a 3-dB bandwidth of 4.5 GHz for circular polarization. For further diagnostics, the field pattern of either polarization is directly displayed on a temperature sensitive liquid crystal display sheet, where the electric field strength can be discerned from the color spectrum. In addition to high conversion efficiency and broad bandwidth, this converter features easy construction, high mode purity, and polarization controllability