Patent ID: 6150991
Filing Date: 2000-11-21
Classification: H01Q

Abstract:
An electronically scanned Cassegrain antenna system, comprising:a dielectric radome, said radome having a first electrically conductive grid to permit incident perpendicularly polarized energy rays to pass therethrough;a twist reflector spaced from the radome, said reflector comprising a dielectric substrate having a thickness equivalent to one-quarter wavelength at said frequency of operation and having formed on an interior surface thereof a second electrically conductive grid oriented by 45 degrees relative to an incident polarization of said incident energy rays, and a conductive ground layer formed on an exterior surface of the substrate;wherein said radome and said twist reflector are adapted such that radiation reflected by the ground layer and passing through the dielectric substrate is shifted by 180 degrees in phase and is rotated in polarization when combined with energy reflected from the second conductive grid by 90 degrees relative to radiation incident on said twist reflector, and wherein said reflected energy from the polarization twist reflector is reflected by said first grid formed on said radome surface to a focal region;an electromagnetic feed structure located at said focal region, said feed structure including a plurality of spaced feed elements, each feed element for providing a corresponding discrete antenna beam such that the plurality of feed elements produce a corresponding plurality of angularly offset antenna beams at corresponding scan angles;switching apparatus coupled to the plurality of feed elements; anda beam controller coupled to the switching apparatus for selecting one of said feed elements to electronically select a desired antenna beam at a selected scan angle.