Scattering by screw heads in reflecting surfaces and their effect on the sidelobes of reflector antennas

摘要

Screws are often used to fasten the main reflector of a reflector antenna to its support structure. The screw heads may then cause bumps in an otherwise smooth reflector surface. Thereby, they disturb the reflected fields and cause increased sidelobes. In this paper; a perturbation theory is introduced in order to calculate efficiently the increased sidelobes due to scattering from the screw heads. Screw heads are approximated as half spheres, whereby it becomes very efficient to calculate the scattering from them by using a spherical wove expansion algorithm, GIDMULT. This method has been verified by measurements in a low sidelobe antenna. We also describe some ways to reduce the scattering, such as dielectric coating of the screw heads and optimization of their locations.