Analytical Models of Dual-Polarized Primary Matched Feeds for Offset Reflector Antennas With Low Cross-Polarization Properties at Both Asymmetry and Diagonal Planes

Conjugate-matched primary feeds for offset reflector antennas are reviewed and investigated for both xand y-polarized cases. Tapered dual-mode circular waveguide feeds are analytically modeled to support a TE11-type mode with unequal beamwidths and the TE21-type mode for the two orthogonal polarizations. First, required mode content factors and tapering numbers of the TE11 mode are addressed for the y-polarized case in offset reflectors with different focal length-to-diameter ratios. Then, the model is appropriately tailored for the x-polarized primary feeds. It is shown that when the polarization orientation changes, the corresponding beamwidths of the TE11 mode should be swapped in the principal Eand H-planes. This is particularly important to simultaneously realize low cross-polarization levels at both asymmetry and diagonal planes, when a dual-polarized matched feed is utilized in offset reflector antennas.