Resonance Behavior of Radar Targets With Aperture: Example of an Open Rectangular Cavity

In the resonance region, the radar scattering response of any object can be modelled by natural poles with the formalism of the singularity expansion method. These natural poles are resonance parameters which provide useful information for the discrimination of radar targets as their general shape, characteristic dimensions and constitution. In the case of an open radar target, high-Q internal resonances and low-Q external resonances occur respectively inside the target and on its surface. Because internal resonances have a higher Q, they may have a higher total energy and can thus be used for target identification. In this paper, we choose to study the resonance behavior of a perfectly conducting rectangular cavity with a rectangular aperture. With this simple example, we intend to show how to distinguish between the two origins of these resonances: external resonances corresponding to traveling waves on the surface of the target and internal resonances corresponding to cavity waves. Indeed, this can be applied to characterize aircrafts, whose apertures (such as inlets, open ducts, air-intakes, cavities etc.) contribute significantly to the overall radar cross section.