Abstract

Electromagnetic scattering is investigated for assemblages of parallel open cavities recessed in a perfectly conducting ground plane. Cavities of a variety of shapes are treated, with cross-sectional dimensions of the order of one or two electromagnetic wavelengths. Under the assumption that the cavities form grooves of effectively infinite length, a two-dimensional analysis treats transverse incidence under both $E$- and $H$-polarized illumination ($E$ and $H$ fields parallel to groove axis, respectively). For the most part, any coupling between cavity responses on the surface produces negligible effects on far-field diffraction patterns, even when cavities are extremely close together and when induced currents flow between adjacent cavities. Thus one may usually construct diffraction patterns for assemblages of grooves by simply superposing responses calculated for each cavity in isolation. Despite possibly substantial differences among the individual scattering patterns from contributing cavities, regularly spaced arrangements of two or more cavities produced grating-type diffraction patterns. This allows inference of the distance between grooves, based on separation between the pattern’s peaks and troughs. Combinations of dissimilar cavities may produce diffraction patterns with peaks that are shifted away from locations expected on the basis of the grating equation, but with a characteristic spacing between the peaks approximately preserved. Random perturbation of groove locations relative to uniform spacing produces a decay in ensemble-average diffraction pattern as scattering angles diverge from the specular direction. A simple theory quantifies the exponential dependency of this grating pattern suppression and shows its effect on the angular range available for identification of scattering characteristics. Monte Carlo–type backscatter simulations including all intercavity coupling demonstrate the success of the theory and thereby explain the type of pattern suppression seen in measurements.

© 1997 Optical Society of America

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