Scattering from elongated open cavities in a perfectly conducting surface

Electromagnetic scattering was investigated for assemblages of parallel elongated cavities in a perfectly conducting surface. For cavity cross sections as large as two or three incident wavelengths, the two-dimensional analysis treats transverse incidence under both E and H polarization (E and H fields parallel to longitudinal cavity axes). On the whole, coupling between responses of neighboring cavities was minor, when viewed from the far field, even with very small separations. Independent scattering from nearby cavities allowed superposition of responses. When individual cavity scattering patterns were identical, this is tantamount to pattern multiplication of the single cavity pattern by a grating pattern. While the former distorts the appearance of the latter, it was still possible to infer cavity spacing from backscatter patterns in all cases with regular spacing between two or more cavities. When cavities were not identical it was still generally possible to infer separation between cavities through spectral analysis. A simple theory was developed for predicting average backscatter from arrays of cavities subject to random displacements from a perfectly periodic arrangement. Monte Carlo type simulations verified the predicted decay of backscatter grating pattern with incidence angle. Similar decay he dependency was also seen in lab measurements using randomized surfaces. Analytical expressions identified the angular range over which average cavity spacing can still be determined from an underlying grating pattern, as a function of variance of cavity location