Transverse beam scanning for an offset dual-reflector system with symmetric main reflector

A new type of unblocked, offset-fed dual-reflector antenna system is described. Any surface of revolution is the large main reflector for this system. It is noted that typical systems have been designed with equivalent aperture efficiencies of 65%, copolar sidelobes below -24 dB, and cross-polar levels below -38 dB. The transverse-scan characteristics depend to a marked extent on geometry and appear to require axial components of defocusing and feed-tilt for optimum scan. The scan loss in the symmetry plane is less than is the case transverse to it. The system geometry derives from the requirement of a cophasal aperture field. The aperture-field intensity distribution that results is necessarily somewhat nonuniform. Any attempt to attain a constant intensity distribution will require the introduction of an additional degree of freedom into the design, that is a second subreflector.