Large reflector antenna scan by feed beam waveguide motion

The authors study a Cassegrain configuration fed by beam waveguides. The E-plane scan is accomplished by translating one of the reflectors along its axis. The H-plane scan is done by rotating the same reflector with respect to its axis. As a consequence of these motions, the virtual feed position moves on specified paths. The subreflector is extended 20% beyond its geometrical boundary to reduce the spillover loss. With F/D=0.4 and 1-dB scan loss, this antenna scans 30 and 22 beamwidths in the E- and H-planes, respectively. The method of analysis is shooting and bouncing ray (SBR), based on geometrical optics and aperture integration. The diffraction loss between reflectors is calculated separately by conventional optics integration.<>