Multiple reflections and improvement of edge scattering in GRECO RCS prediction code

Abstract

GRECO code for monostatic RCS prediction in real time has been extended by considering multiple reflections between surfaces and improving the edge diffraction coefficients. Multiple reflections are analysed through a very efficient ray-tracing algorithm based on the graphical processing technique. Method of equivalent currents for edge scattering has been improved by Mitzner's and Michaeli's incremental length diffraction coefficients (ILDC).This communication presents the general features of GRECO code, in particular the advantages of the new graphical processing technique. Emphasis will be placed in the new features of GRECO still unpublished: the ray-tracing algorithm and the implementation of incremental length diffraction coefficients. Graphical Electromagnetic Computing (GRECO)During the last four years, the development of graphical processing techniques for high-frequency monostatic RCS prediction has given rise to GRECO code (1), (2), (3). Real-time computation is achieved through graphical processing of an image of the target present at the screen of a workstation, using the hardware capabilities of a 3-D graphics accelerator. The two main advantages of the graphical processing approach over classical techniques are: a) Hardware graphics accelerator removes hidden surfaces and edges: they do not contribute to the surface or line integrals when they are performed by the graphical processing technique. b) Reduced CPU time and RAM requirements. They are independent of target electrical size and complexity. The main features of GRECO code are the following:a) The I-DEAS computer aided design package for geometric modelling of solids has been used for modelling target geometry. The target is described as a collection of parametric surfaces, defined with two-dimensional NURBS (non-uniform rational Bsplines). Parametric surfaces require less mass storage memory that the faceting approach, and adjust more accurately to the real target surface. b) Physical Optics (PO) approach for perfectly conducting surfaces and Impedance Boundary Condition (IBC) + Physical Optics for radar absorbent coatings. c) Method of Equivalent Currents (MEC) with either Physical Theory of Diffraction (PTD), Mitzner's or Michaeli's Incremental Length Diffraction Coefficients (ILDC) for perfectly conducting edges. A comparative study of the results for the three kinds of ILDC's will be presented in this communication.d) Double reflection analysis by geometric optics (GO) raytracing for the first reflection and bistatic physical optics for the second. A new and very efficient ray-tracing algorithm has been developed and will be also presented in this communication. Ray-TracingDouble reflections between surfaces are analysed by a hybrid GO-PO scheme. The GO reflection at the first surface assumes that specular reflection occurs, according to stationary phase principle. The PO reflection at the second surface ensures that the correct scattered field is obtained when there is no specular reflection to the observer.For each pixel on...