A new minimum blocking condition including subreflector and quadrupod shadow for the design of dual reflector systems

Earlier minimum blocking conditions (MBC's) for paraboloidal reflector antennas formulated by Hannan and Gillitzer did not take into acount the significant blocking contribution of the shadow of the legs supporting the feed or subreflector. A numerical-integration study to determine conditions under which the combined blocking shadow of the subreflector and its supports are minimized is described. Two types of MBC's are found: one which is based on the sidelobe level-more important in radioastronomy (polarization measurements)-and a second type which is related to the aperture efficiency (directivity)-more important for spectroscopy and telecommunications. Both MBC's are compared and it is shown that they are only slightly different from each other.