IMPROVEMENT OF ITERATIVE PHYSICAL OPTICS USING THE PHYSICAL OPTICS SHADOW RADIATION

Abstract

The prediction of Radar Cross Section (RCS) of complex targets which present shadowing efiects is an interesting challenge. This paper deals with the problem of shadowing efiects in the computation of electromagnetic scattering by a complex target using Iterative Physical Optics (IPO). The original IPO is limited to cavities applications, but a generalized IPO can be applied to arbitrary geometries. This paper proposes a comparison between the classical PO approach and a physical approach based on shadow radiation (around forward direction) with PO approximation for the consideration of shadowing efiects in generalized IPO. Based on the integral equations, a rigorous demonstration of this physical shadowing is provided. Then simulation results illustrate the interest of using physical shadowing both from the transmitter and towards the receiver, compared to the classical approach. Computing electromagnetic signature of complex targets presenting shadowing efiects is a complex problem for which many solutions have been proposed. Each of these solutions presents beneflts and drawbacks, and two difierent kinds of methods can be used for arbitrary shaped cavities: rigorous numerical methods and asymptotic methods. Numerical methods, like Method of Moments (MoM), can be used to calculate RCS (Radar Cross Section) of targets with a good precision. These methods, which do not apply any approximation (but approximation linked to meshing), are known to provide excellent results, but their complexity is high. MoM has a complexity of O(N 3 ), N being the number of unknowns (which is equal to the number of non boundary edges of a meshed target). Thus, in case of great target's dimensions (compared to wavelength), these methods are generally not used, due to their computing time and memory requirement. Nevertheless, MoM will be used in this paper as a reference method. To overcome this issue, asymptotic methods have been developed and can be used in high- frequency domain for arbitrarily shaped targets with a reduced complexity. These methods are based on Geometrical Optics (GO), based on ray trajectories, and/or Physical Optics (PO), using surface currents to calculate scattered flelds. When multiple re∞ections occur, PO is generally preferred to GO, as GO is less precise, particularly in case of highly curved geometries. Iterative Physical Optics (IPO) (1{3) is an asymptotic method based on PO. The method has been originally developed to calculate RCS of cavities (1) and has been generalized to arbitrary geometries (4). This method can be described by an algorithm in 4 steps: