A prospective theoretical study of double offset with spherical main reflector application to Ku band ground stations

Double reflector offset antennas with spherical main reflector have recently been considered as an interesting alternative for fixed satellite services applications subjected to the newest CCIR radiation pattern recommendation. The great appeal of this configuration is the possibility of reducing main reflector manufacturing cost, which contrary to shaped and classical double reflector offset antennas can be achieved by manufacturing spinning machines or by fitting panels of the same radius of curvature. However this configuration has a serious competitor widely employed in the range of aperture diameters above 150/spl lambda/, these are the symmetrical double reflector antennas. This configuration also has as its main advantage the facility of manufacture, since both main and subreflector are axially symmetric, and the control over antenna aperture power distribution, which can he accomplished through reflectors shaping. On the other hand this same configuration presents some significant drawbacks; these are subreflector aperture blockage and strut scattering which degrade antenna gain and result in sidelobe radiation pattern levels increasing. Regarding the double offset reflector configuration with spherical main reflector, although it is not impaired by blockage, it presents limited aperture illumination control, since the subreflector is basically designed as a phase corrector intended to yield an aperture constant phase wavefront. Recently some papers describing synthesis methods for double offset with spherical main reflector configuration, as well as parametric studies and comparisons between this and other double offset configurations have been published. In this paper the intention is to investigate the viability of employing this configuration by comparing its electrical performance with the one presented by a symmetrical double reflector antenna of similar gain. The study was carried out in a diameter range immediately superior to 150/spl lambda/ in the Ku band allocated for fixed satellite service (10.7-12.75GHz and 13.8-14.8GHz).