Some Application Examples of a Frequency Domain Hybrid Technique for Scattering Problems on Disjunct Geometries

We have investigated and applied a hybrid method for the electromagnetic scattering and radiation problem in the mid to high frequency range. The method is based on Geometrical Theory of Diffraction (GTD) and standard Galerkin Boundary Element Method (BEM, also called MM) such that BEM is used on details that are small compared to the wavelength, and the GTD-approximation is used on details which are large in the same sense. The method have been tested on geometries that reveal both the benefits and drawbacks of the approximations used. The hybrid is validated on a RCS test case and compared with a numerically exact solution. To illustrate the capabilities and drawbacks of the hybrid it is also illustrated how the hybrid may be applied to a radiation case. The hybrid modifies the incoming field on the BEM-geometry by using GTD [3]. Also the scattered field is modified with GTD-terms. The test cases show that the hybrid is an efficient and accurate method if the two geometries, represented by two methods, are separated by more than a few wavelengths. A short outline will also be given about how the method will be refined to take into account the GTD shadowing in a more accurate way and how the coupling between the GTDand BEM-scatterers may be included in the method. The major part of the material in this paper is based on the two papers [1] and [2]. This work was supported by the GEMS-project where ESB, SES, FOA, KTH, Uppsala University and EMW are partners. The author especially want to acknowledge Jonas Gustafsson at ESB and colleagues at KTH and Uppsala University for helping out with some of the results in the paper