Research on an offset double-grid reflector for multibeam antennas in communications satellites

For communications satellites using multiple beam antennas, it is preferable to use a potential polarization sensitivity of the reflector instead of the feed system if cross-polarization isolation is required. A dual gridded reflector is introduced for such frequency reuse which consists of two reflecting shells axially displaced and located one behind the other. The shells consist of a three-layered sandwich structure of low reflectivity, each shell covered by an orthogonally oriented strip grid. Waveguide simulation measurements and free space measurements within the 8.5-12.4 GHz frequency range were performed. The problem area of tolerances is outlined and the copolar and cross-polar radiation patterns are discussed as calculated for the composite antenna system with a feed cluster of 23 elements. The corresponding coverage contours are compared with those valid for the cross-polar radiation, if the gridded reflector is replaced by a solid and metallic reflector.