A comparative study of an ABC and an artificial absorber for truncating 3-D finite element meshes

The type of mesh termination used in the context of finite element formulations plays a major role on the efficiency and accuracy of the field solution. In this work, we evaluate the performance of an absorbing boundary condition (ABC) and an artificial absorber (a new concept) for terminating the finite element mesh. The artificial absorber consists of a metal-backed lossy dielectric layer which was designed to minimize the TE and TM reflection coefficients at all (real) incidence angles. Based on this design, the thickness of the metal-backed artificial absorber was selected to be 0.15/spl lambda/ and its relative permittivity and permeability were selected to be /spl epsiv//sub r/=/spl mu//sub r/=1.-j2.7. In this paper, the two approximate mesh truncation schemes (one using ABCs and the other artificial absorber) are compared with the exact finite element-boundary integral (FEM-BI) method in terms of accuracy and efficiency. This analysis is done in connection with the problem of scattering by a three dimensional finite slot array in a thick ground plane. The array slots are of thickness d and, for this study, they are assumed to have a square aperture of width W. In all cases, it is assumed that the excitation is a plane impinging from above at some angle with respect to the array normal.<>