![]() The reflector surface can either be solid for circularly polarized waves or gridded for linearly polarized waves. A design somewhere in between is probably most desirable. A spherical reflector, however, is free of coma and astigmatism. The most popular type of reflector is the single offset parabolic reflector as shown in Figure 7.11a. The size of a reflector depends on the gain and beamwidth requirement and whether we have a single-beam or multibeam system (larger reflector required). Degradations include beam-shape distortion, gain, loss, beamwidth, and higher side lobes. Reflector antennas are not good for continuous beam scanning, as beam degradation does occur. When such is the case, no cross-polarization will appear in the radiated electric field from the reflector. The basic polarization generated by the feed point is that of a circularly polarized beam. The focal surface is the plane which is perpendicular to the offset axis.
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