Geometrical optics shaping of large dual offset reflectors for contoured beam radiation

It is shown that simple ray tracing techniques can be used to shape either the subreflector or the main reflector of a dual offset reflector system to realize prescribed phase distribution at the aperture. Main reflector shaping introduces negligible amplitude distortion when the reflector diameter, in terms of wavelengths, is large. Subreflector shaping, on the other hand, produces noticeable amplitude distortions, along with degradations in the far-field cross-polar performance. However, for the geometry considered here, the amplitude distortions are not sufficient to cause significant variations in the copolar gain contours. The overall aim of this study was to establish the feasibility of using shaped reflector antennas for high-definition TV broadcast from a satellite. For the purpose of this exercise the target coverage was that of Italy as viewed from 19 degrees west satellite orbital position.<
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