Electromagnetic scattering from metallic cylinders with longitudinal corrugations

Anisotropic surfaces, obtained by corrugating conducting smooth surfaces, have been widely used in realizing high-frequency antennas. For instance, special efforts have been made in designing and analyzing artificially hard and soft surfaces [Kildal 1990], often realized by periodically corrugating metallic surfaces and then filling the corrugations with a dielectric material. In this context, a problem of remarkable importance is the scattering from corrugated cylinders of different cross-sections, which can be used for realizing low-blockage feed-support struts in the design of high performance reflector antennas. From a practical point of view, in order to avoid calculating the field inside corrugations, equivalent surface impedances are defined at the outer surface of the cylinder. The range of validity of this kind of approximation cannot be easily determined, and the availability of rigorous reference solutions is of great importance for validating approximate procedures. The main purpose of this paper is to derive a rigorous modal solution for the case of circular cross-section cylinders with longitudinal corrugations.