PO-based analysis of double-bounce scattering

Kurzfassung

Multiple reflections between different parts of a non-convex scattering surface or between a scatterer and its environment may significantly contribute to the radar cross section (RCS) of the scattering configuration. The incident wave gets reflected at different parts of the scattering surface and, when some of these parts are flat and oriented as in a corner reflector such that the conditions for a chain of specular reflections are satisfied, the scattering diagram shows a pronounced peak at the corresponding scattering direction. The effect is particularly strong at high frequencies when the wavelength is shorter than the typical size of the reflecting sub-areas. Shooting and bouncing of rays (SBR) is an established method to simulate the multiple reflections between interacting parts of a scatterer. The approach is based on the laws of geometrical optics (GO) which, as is known, assumes sharp shadow boundaries and fails to describe the transformation of the plane wave reflected at a flat scattering surface into a spherical wave as the distance from the scattering surface increases. Thus, the use of SBR may lead to significant errors in the RCS values if the scattering geometry includes distant features (i.e. lying in the far zone of each other) that interact via the multiple-bounce mechanism. To model correctly the far-zone interactions, physical optics (PO) solutions are necessary, and in the paper a PO-based solution is used for modeling the double-bounce reflection. Furthermore, a simple test geometry consisting of two rectangular metallic plates, each several wavelengths in size, is proposed which can serve as a canonical geometry for modeling the double-bounce mechanism. This geometry is employed to compare accuracy of GO and PO solutions. The parameters of the scattering configuration are the distance between the plates, their mutual location (lit or not lit by the GO reflection), the frequency, and the incident and scattering directions. These parameters are varied and the GO solution is shown to become inadequate when the plates are in the far field of each other.