Reduction of Cross Polarization in Circularly Polarized Broadband Waveguide Antenna Using an L-shaped Probe

This paper presents a circularly polarized broadband waveguide antenna with low cross polarization. The center frequency is chosen to be close to the middle value of the cutoff frequency between that of the dominant mode (TE10/TE01) and the second higher-order mode (TE20/TE02). The cross polarization gets worse at a higher frequency which is close to the cutoff frequency of the TE20/TE02. For avoiding this effect, four thin metal poles (2 mm x 2 mm x 52 mm) are installed at the inside corners of the waveguide. The cross polarization becomes lower in the wide azimuth rang. As a result, circular polarization with low cross polarization over a wide azimuth range is also achieved even in the higher frequency.