Hybrid MoM/SBR and FEM/SBR methods for scattering by large bodies with inhomogeneous protrusions

A hybrid technique was developed for computing scattering by large bodies with cracks and cavities (Jin et al. 1995). This technique employs the shooting and bouncing ray (SBR) method to compute the scattering by large bodies and uses the finite-element method (FEM) to characterize the cracks and cavities. The two methods are combined through a coupling scheme based on the EM equivalence principle and the reciprocity theorem. The coupling scheme is designed in such a manner that it includes all significant interactions between the FEM and the SBR methods and it permits the SBR and FEM computations to be done separately. The resulting technique is efficient and accurate and, because of this, is extended to the calculation of the radiation patterns of conformal antennas in a complex environment (Greenwood et al. 1996). We further extend the hybrid FEM/SBR method and also develop a new hybrid method-of-moments (MoM)/SBR method to compute scattering by large bodies with small protruding scatterers. To be more specific, we first employ the field equivalence principle to replace the protruding scatterers by a set of equivalent electric and magnetic currents. The total scattered field then becomes the superposition of the field scattered by the large body without protrusions, which is calculated using the SBR method, and the field radiated by the equivalent currents in the presence of the large body, which is also calculated using the SBR method with the aid of the reciprocity theorem. The required equivalent currents are computed using the FEM of MoM, which permits the handling of complex material composition of the protrusions.