Ray-mode analysis of complex resonances of an open cavity [radar targets]

Complex resonances furnish valuable inputs for classification of radar signatures from irregularly shaped objects. An important class of targets involves open-ended enclosures with exterior-interior coupling. If the interior has waveguide-like properties, modal expansions can model the wave phenomena there, while ray methods can be employed to account for multiple diffraction at the aperture edges, and for wave interactions around the exterior boundary. By self-consistent ray-mode coupling in a hybrid format, one can construct a global resonance equation whose solutions yield the complex resonant frequencies for the composite object. The importance of evanescent modes and of coupling to nearest neighbor modes is investigated, as is the contribution from low-Q interactions around the external circumference