Spherical reflecting antennas with corrected line sources

A portion of a spherical reflecting surface possesses inherent scanning advantages over a paraboloidal reflector. These advantages can only be realized, however, if spherical aberration is eliminated. A composite illuminator is described which does eliminate this form of aberration, enabling beam scanning through as much as 110 degrees to be obtained without beam degradation. Efficiency for the illuminated portion of the aperture is about 55 per cent and sidelobe levels from 18 to 20 db below the main beam are obtained. A set of high gain polyrods provides paraxial zone illumination while the wide-angle primary illumination is derived from a line source consisting of back-to-back channel guides. The phase velocity in the channels varies in such fashion as just to compensate for the path length deviations experienced by nonaxial rays, thereby eliminating spherical aberration. Experimental results for spherical reflecting antennas at
X, K_{u}
and
K_{a}
band are given. Use of ad hoc primary illumination functions has allowed theoretical calculations of secondary patterns. These are in qualitative agreement with observed results.