Experimental Study of Subreflector Support Structures in a Cassegrainian Antenna

摘要

The effects of various support structures on the radiation patterns of a Cassegrainian antenna have been investigated experimentally. Detailed two-dimensional contour plots of the wide-angle radiation are presented primarily for support member dimensions up to about one wavelength. We show that the disturbing effects decrease rapidly for perpendicular polarization when the dimensions are decreased below wavelength/ 2 Furthermore, the on-axis geometrical shadowing due to the support members does not give the correct level and shape of the wide-angle radiation. Account must be taken of the polarization and orientation of the members relative to the antenna axis. The performance of dielectric members is shown to be generally poorer than that of metallic members. The alternative of supporting the subreflector with a thin-wall axial dielectric cylinder is shown to be electrically acceptable for thicknesses of the order of 0.01 wavelength. The data presented should be useful in designing and evaluating various types of support structures for Cassegrainian and front-fed reflectors. (Author)