Polarization-controllable TE21 mode converter

We report the concept and development of a Ka-band 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 composed of a power-dividing section, a mode-converting section, and a polarization-transitioning section. The converting process in each section is displayed and the working principles are discussed. A prototype has been built and tested. The measured results agree well with the numerical calculations for both linear and circular polarizations. The measured optimum back-to-back transmission is 94% with a 1-dB bandwidth of 4.1 GHz for the linear polarization. As for the circular polarization, the measured optimum transmission is 97%, but the corresponding bandwidth is indistinct due to some resonant dips. The reasons and impact for the dips are discussed. A bandwidth of 3.9 GHz is obtained for a single circular converter; meanwhile, an approach to eliminating these un...

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