Off-axis polarization characteristics of Cassegrainian and front-fed paraboloidal antennas

Cross polarized field intensities and values of cross polar isolation at off-axis incidence are evaluated for Cassegrainianfed and front-fed paraboloidal antennas. It is shown that the cross polar isolation of symmetrical Cassegrainian antennas at off-axis incidence is much superior to equivalent front-fed antennas, due to the fact that the convex subreflector compensates to a high degree for cross polarization caused by the concave main reflector. The conclusion is drawn that for dual polarized use of parabolic antennas in radio systems the Cassegrainian structure will give much improved suppression of cross polarization for clear weather (multipath) reflection effects, and much less critical alignment requirements.