Offset multireflector antennas with perfect pattern symmetry and polarization discrimination

The design of reflector antennas with excellent cross-polarization discrimination and circular pattern symmetry is numerically examined. In particular, the transformation of a symmetrical beam by an arbitrary arrangement of N confocal reflectors is examined. It is found that in order to preserve symmetry the principal ray must coincide with the equivalent axis. The equivalent axis may be found by a geometrical procedure if the last reflector is a paraboloid. An expression is presented for finding the angle of incidence and the magnification of the first or last reflector in order to ensure symmetry.