Aperture transformation sidelobe canceller

Abstract

An aperture transformation sidelobe canceller includes a plurality of auxiliary feed elements disposed in the vicinity of, but critically offset from, a main feed horn. The signal paths for the auxiliary feed horns are coupled through a low loss cascade RF variable direction coupler network to be combined with the RF signal path for the main antenna feed. The combined signal path is coupled to a performance monitoring processor which, in turn, adjusts the coupling action of each variable directional coupler to achieve the necessary weighting and combining of the auxiliary feed signal paths. The critically offset auxiliary feed elements provide the capability of achieving very broadband and deep nulls from the simple variable directional coupler network. The null availability makes it possible to null the entirety of the main elements sidelobe region, including backlobe and even the first sidelobe region of the antenna pattern, as the offset auxiliary feed horns provide substantial coverage in this region. These offset auxiliary feed elements provide low differential dispersion, require reduced waveguide runs, enjoy polarization diversity by slightly depolarizing and rotating each feed and suffer essentially no grating problems.