A SCANNING SPHERICAL TRI-REFLECTOR ANTENNA WITH A MOVING FLAT MIRROR

Spherical reflector systems can achieve pattern scanning without rotat ion of the main reflector through the use of multiple subreflectors th at can move. Also, two subreflectors can be shaped to correct for sphe rical aberration and to control the aperture distribution on the spher ical main reflector. In a previous paper [1] we introduced a method th at offers both aperture phase and intensity control and scans the main beam without an accompanying movement of the illuminated area over ma in reflector. The method can overcome the poor aperture utilization pr oblem common in spherical reflector antenna systems; however, it requi res motion of the entire subreflector system, including the feed, duri ng scan, In this paper we discuss a method that does not require motio n of the subreflector system during scan, This method employs a flat m irror that creates a virtual image of the subreflector system, The mot ion of the subreflector system in the previous design is replaced by t he motion of the virtual image that is controlled by the motion of the flat mirror, The new design offers simplified mechanical motion, whil e maintaining beam efficiency performance comparable to that of tradit ional spherical tri-reflector scanning antennas, but with some sacrifi ce in aperture efficiency and cross-polarization performance.