Antoine Thomet

Improvement of Iterative Physical Optics Using the Physical Optics Shadow Radiation

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 targets 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:

Optimizing iterative physical optics by using an ACA compression on interaction matrices

This paper presents a numerical compression of Iterative Physical Optics (IPO), known as an efficient asymptotic method for computation of Radar Cross Section (RCS) of complex targets including cavities. The compression is applied to interaction matrices of IPO between coupled surfaces. It is made by using the algebraic Adaptive Cross Approximation (ACA), which is known to provide a good compression and acceleration when used with dense matrices involved in rigorous numerical methods. Results show that this method highly compresses the IPO matrices, without damaging the RCS prediction by IPO.

Optimized segmented iterative physical optics for RCS computation of large cavities

This paper presents a numerical compression of the Segmented Iterative Physical Optics (S-IPO), known as an efficient asymptotic method for computation of Radar Cross Section (RCS) of large complex cavities. The compression is applied to interaction matrices of IPO between coupled surfaces. It is made by using the algebraic Adaptive Cross Approximation (ACA), which is known to provide a good compression and acceleration when used with dense matrices involved in rigorous numerical methods. Results show that this method highly compresses the S-IPO matrices, without damaging the RCS prediction.

Optimized iterative physical optics for EM scattering from large structures

The modelization of electromagnetic interactions between antennas and structures is an important challenge for systems carrying antennas such as aircrafts, satellites, frigates. This problem deals with electromagnetic scattering from large structures with shadowing effect and multiple scattering. A similar problem is the Radar Cross Section computation of large cavities. For both cases, several methods can be used, and Iterative Physical Optics (IPO) is an asymptotic method based on Physical Optics (PO), which has shown good results for such kind of problems. In IPO, several techniques can be used to take into account shadowing effects. The geometrical shadowing, based on ray tracing, is classically used. But a recent method has been proposed and is based on a physical approach: the shadow radiation (around forward direction) with PO approximation. Moreover, the IPO method can be optimized by applying an algebraic compression, the Adaptive Cross Approximation, of the interaction matrices of IPO between coupled surfaces. Results show that IPO matrices can be highly compressed, without degrading the accuracy.

Low computational cost method for scattering of large cavities based on ACA compression of Iterative Physical Optics

This paper is about Radar Cross Section (RCS) calculation of large cavities. For such targets, Iterative Physical Optics (IPO) is a method known to provide a good trade-off between complexity and accuracy. In this article, a numerical compression is applied to interaction matrices of IPO between coupled surfaces. The compression is made by using the algebraic Adaptive Cross Approximation (ACA) technique, which is known to provide a good compression and acceleration when used with dense matrices involved in rigorous numerical methods. It is also improved by a recompression (RACA). Results show that this technique highly compresses the IPO matrices, without damaging the RCS prediction by IPO.

Using Physical Optics shadow radiation to improve shadowing in Iterative Physical Optics

Predicting aircraft ducts Radar Cross Section (RCS) is an interesting challenge. In order to calculate electromagnetic scattering in such open-ended cavities, several methods have been developed: some rigorous methods, and some asymptotic ones. Iterative Physical Optics (IPO) is an asymptotic method based on Physical Optics (PO), which has shown good results. This paper shows an improvement of IPO method for calculation of electromagnetic scattering by cavities, by using a physical approach (and not a geometrical technique as in classical PO method) to take into account shadowing effects. The method, called physical shadowing, is based on using shadow radiation (around forward direction) with PO approximation in the magnetic field integral equation applied to two coupled objects.