Performance of offset paraboloid reflectors with offset matched feeds

The performance of offset reflector antennas with offset matched feeds is investigated. Mathematical expressions for the reflector pattern calculations are presented, and both scalar aperture and vector current methods are used to compute the patterns. It is found that the scalar aperture method can predict the co-polar patterns accurately, but always yields lower cross-polarization levels than the vector current method. The cross-polarization of the reflector for various feed displacements and polarizations is also investigated. The results indicate that displacing the feed along the reflector axis of symmetry yields lower cross-polarizations and, in particular, when the feed displacement is towards the reflector side, the level of the cross-polarization decreases initially with the feed displacement.