Anomalous Behavior of Thin-Wire Gratings

Abstract

A known, rigorous electromagnetic solution for the scattering of plane waves by a circular cylinder is applied to the problem of thin-wire gratings, of few wires, to obtain an accurate theory that includes both multiple scattering and end effects. We have obtained computer solutions for both S and P polarizations and for both conducting- and nonconducting-wire gratings. Experimental results confirm the theory, insofar as measurements are practical. The results for dielectric gratings in S polarization are only qualitative because of the excessively weak scattering by the grating. The theory predicts anomalous behavior as the result of multiple scattering, in agreement with Twersky’s theory. It is shown that metallic gratings give dark anomalies, stronger for P polarization than for S, and that dielectric gratings have bright anomalies that may be displaced from the Rayleigh angles, as suggested by Twersky. Thick-wire gratings also exhibit anomalous behavior, different from that of thin wires, and not described directly by our theory.