Satellite Phased Arrays: Use of Imaging Reflectors with Spatial Filtering in the Focal Plane to Reduce Grating Lobes

Phased arrays will be needed1 in satellites that form rapidly movable beams to communicate efficiently with ground stations in the U.S.A. Large antenna apertures will be needed to produce narrow beams. Thus, in a previous article" a large image of a small array was obtained, using an arrangement of confocal reflectors. The large image was formed at the aperture of the main reflector, and the magnification was chosen so that the image had the same dimensions as the main reflector, thus illuminating efficiently its aperture and essentially eliminating spillover. However, since the aperture distribution in that arrangement was the image of the array distribution, the antenna far field was a replica of the array far field and, therefore, it contained the array grating lobes. To reduce them, we propose here use of a filter placed in the focal plane of the main reflector, as shown in Fig. 1. The filter is designed to eliminate the field components caused in the focal plane 449 focal plane, grating lobes can be suppressed.