Scattering characteristics of finite arrays of cylindrical cavities in an infinite ground plane

In this paper, we investigate the scattering characteristics of finite one-dimensional (1D) and two-dimensional arrays of cylindrical cavities embedded within an infinite perfect electric conducting ground plane. Fundamental radar cross-section (RCS) features of said arrays are illustrated, with the RCS computed with respect to the scattered (diffracted) field component, obtained directly from the aperture currents. The aperture currents on the finite structure are computed using a hybrid space/spectral-domain MoM formulation. The complete set of (TE,TM) cylindrical eigenmodes are used to represent the unknowns. The dependence of the current distribution on the source polarization is shown for the canonical cavity. Three-dimensional plots of the RCS signature of a 1D finite array illustrate the unique radiation characteristics of such structures, e.g., the constant-directivity surfaces form cones about the array axis in 3D space. The effects of a superstrate layer on the radiation behavior of a 2D finite array are also shown. We find that the layer can in fact either enhance or diminish the radiation, depending on the source polarization. It also tends to reduce endfire radiation in all cases. The scattering signature of large finite arrays is computed approximately by the introduction of an active element factor defined specifically for scattering problems. Using the MoM solution of a reduced window array, we obtain the far-field patterns of larger structures by a simple computation of the array factor. An improvement to this approximation makes use of an exterior equivalent source, which models the localized edge effects. Finally, the use of nonuniform arrays for sidelobe suppression and 2D "masked" structures is illustrated.