Antenna geometries for shaped dual reflector antennas

The geometry of a shaped dual reflector antenna customarily evolves from the classical Gregorian ( or Cassegranian) which satisfies the Mizugutch condition. The reasons for choosing this initial antenna geometry are, partially, due to lack of knowledge, and partially, due to convenience. Indeed most of shaped dual reflector antennas were designed with such a process. The principal polarization contours are, in general, satisfactory. The cross-polarization level, nevertheless, becomes too high when the angular coverage area is large. Because of such results, the application of shaped dual reflector antennas has been questioned. Occasionally, this approach is abandoned in favor of an expensive dual grided shaped reflector design in order to achieve high polarization purity. This investigation discovers that the major cause of this high cross polarization behavior is not due to the reflector being shaped. It is due to the antenna geometry. Thus, with an "improved" antenna geometry, the cross polarization level can be significantly reduced.