The geometric optics condition for zero crosspolarization in offset Cassegrain antennas is discussed. It is shown that with a feed having perfect pattern symmetry the crosspolar performance of the offset Cassegrain is limited by diffraction. As a result, minimum crosspolarization is only achieved at the geometric optics condition when the subreflector diameter is at least 40 wavelengths. 9 refs.
|Number of pages
|Published - 1 Jan 1981