VARIATIONAL ESTIMATION OF RADAR CROSS-SECTIONS

To date, deterministic calculations of radar cross-section (RCS) have dealt with structures composed of idealised geometric shapes such as flat plates. In contrast, real objects are composed of distorted shapes, such as buckled or dented plates. This is particularly evident in the case of surface ships. A major RCS control technique for ships is shaping, e.g., canting plates and making corner reflectors nonorthogonal. The effectiveness of various shaping rules has, in the past, been evaluated assuming flat plates using geometric optics; this approach is difficult to extend to distorted structures. The effect of distortion on the RCS return of dihedrals and other bodies may be accounted for if the integral equations for the scattering of electromagnetic radiation are reformulated in terms of a variational principle. The general application of such techniques to the calculation of radar cross-sections is reviewed. Several variational estimators for the radar cross-sections may be constructed. These take the form of nonlinear functionals of trial surface currents. The nonlinearities of one estimator in particular account in part for the interactions taking place in multiple scattering geometries, without the introduction of ray-tracing techniques. An application of the method to dihedral corner reflectors is presented.