Alternative current expressions for overcoming shadowing treatment arising in the Physical Optics approach

Abstract

The Physical Optics (PO) method has been widely used when analysing electrically large EM problems. It considers only the illuminated parts of the geometry for computing the scattered fields, assuming null currents in the shadowed parts of the bodies under analysis. However, the shadowing problem can be even more problematic than the field calculation itself, particularly when dealing with curved surfaces in complex geometries and multiple interactions, where many eclipse effects may appear. In these cases, illuminated regions must be obtained by using expensive minimization algorithms. The set of illuminated regions must be accurately determined, which implies many ray-tracing intersection tests. In this communication, an alternative treatment of the PO currents is considered. New electric and magnetic current expressions are proposed from the Equivalence Principle in order to bypass the shadowing problem. The currents calculated this way can be expressed in terms of current modes, providing an efficient storage and field calculation. A combination of these currents with some acceleration techniques, such as the angular Z-Buffer or quasi-analytical integration procedures, makes possible to maintain the PO efficiency when analysing simple cases, greatly improving it in more complex environments.