A shadow-radiation-based fast iterative physical optics (IPO) scheme, for the analysis of the scattering from large complex geometries involving multiple reflection and occlusion effects, is proposed. By employing a “shadow-radiation” mechanism, the scheme alleviates the need for expensive computation and storage of a geometric visibility function. In a nested fashion, shadow radiation iterations are performed for each “bounce” in the conventional multiple reflection IPO scheme. The resulting method makes use of simple field integrals which are all accelerable using a multilevel nonuniform grid-based field evaluation algorithm, with a modification tailored to the scheme’s integral kernels. The proposed scheme is also shown analytically to be a more stable (faster converging) equivalent of existing IPO schemes. The method is studied in terms of accuracy and performance for representative examples and compared with alternative physical optics and numerically exact solution techniques.

Shadow Radiation Iterative Physical Optics Method for High-Frequency Scattering

A fast iterative physical optics (IPO) algorithm for the analysis of scattering from large complex geometries involving multiple scattering and self-shadowing effects is presented. The algorithm comprises two types of nested iterations: reflection ("bounce") iterations and self-shadowing iterations. Both types of iterations involve time consuming surface integrations carrying an O (N2) computational cost (N being the number of quadrature points). The nested iterative formulation is accelerated by using the multilevel non-uniform grid algorithm reducing the computational complexity to O(NlogN). The procedure's applicability to complex geometries and numerical efficiency are demonstrated by comparison to a numerically exact method and to the conventional physical optics.

Fast iterative physical optics with shadowing

This article deals with the acceleration of the physical optics (PO) approximation for the backscattering computation in the near and far fields, for both single-bounce (SB) and double-bounce (DB) PO contributions. It is based on physical arguments, which allow us to apply either a closed-form expression (rapid calculation) or a numerical double integration to evaluate the scattered field from subsurfaces of a given mesh. The use of the closed-form expression is governed by two criteria, which must be extended to the bistatic case and also to the DB: the conventional Fraunhofer (related to the far-field zone) criterion and the chord error (related to the surface curvature) criterion. The proposed method is tested on a dihedral geometry.

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Accelerated Computation of the Physical Optics Approximation for Near-Field Single- and Double-Bounces Backscattering

The improved Iterative Physical Optics (IPO) approximation recently developed by the authors have been used to simulate the Perfect Electric Conductor (PEC) reflector antennas in this paper The IPO surface current is iteratively updated to correct the PEC electric field boundary condition until it converges Numerical simulation of a parabolic dish antenna of different focus lengths shows that the IPO approximation improves the accuracy of the surface current by more than two orders of magnitude, compared to the conventional PO image approximation method Finally, the IPO algorithm usually converges within 10 iterations

Iterative Physical Optics (IPO) for Fast and Accurate Simulation of Reflector Antennas

The Iterative Physical Optics (IPO) method, which was originally developed for computing electromagnetic scattering from cavities and later extended to more general geometries, has been shown to be accurate for many types of targets. In this paper, we examine the IPO method from the standpoint of its potential use for engineering electromagnetic scattering predictions. Using an IPO engineering computer code that we developed recently as a basis for discussion, we describe the problems encountered, the techniques we used for overcoming those problems, and the effectiveness of those techniques. We also show comparisons of our IPO results with method of moments and ray-based methods.

Electromagnetic scattering calculations by Iterative Physical Optics for engineering applications

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:

and Philippe Pouliguen

Papers

Improvement of Iterative Physical Optics Using the Physical Optics Shadow Radiation