An analytical review of cross polarization reduction in offset reflector antennas

In this paper, the cross polarization reduction is reviewed in offset reflector antennas by expressing the primary feed radiation patterns in terms of analytic functions. The feed under study is a dual-mode circular waveguide antenna, operating at the fundamental mode, TE₁₁, and the higher order TE₂₁ mode. Closed-form analytical functions are selected to approximate each mode which allows selection of symmetric and asymmetrical patterns with different field tapers in the principal planes and arbitrary excitation coefficients. It will be shown that, the asymmetrical aperture distribution of the dominant TE₁₁ mode in the presence of the higher TE₂₁ mode is sufficient to reduce the cross polarization of offset reflector antenna in both asymmetric and inter-cardinal planes, i.e. φ=90° and 45°.