Analysis of secondary scattering for strut lobes in reflector antenna

The feed support struts used in reflector antennas often cause significant effects on their sidelobe patterns. The plane wave illumination of each strut by the reflector results in the strut scattering cone. The purpose of the paper is to present some results on the secondary scattering of the strut lobes. The two mechanisms addressed are: 1. Secondary scattering by another strut which is designated as the reflector-strut-strut (RSS) scattering, 2. Secondary scattering by the reflector surface which is designated as the reflector-strut-reflector (RSR) scattering. The primary strut scattering is designated as RS scattering. The main effect of RSS scattering is to cause the peaks of the RS lobes to decrease by as much as 3 dB, for typical center-fed reflector geometries. Consequently, measured strut lobe peaks are typically 1-3 dB lower than strut lobes calculated using RS analysis, i.e., no RSS. The RSR scattering effect is most significant for reflectors with very low sidelobes. For verification purposes, the authors measured a reflector with a thick cylinder oriented at an angle to emphasise the RSR effect. Comparison of measured and calculated results are given.<>