A hybrid moment method/finite-difference time-domain approach to electromagnetic coupling and aperture penetration into complex geometries

An approach is presented for the direct modeling of electromagnetic penetration problems which involves a hybrid technique combining the frequency-domain method of moments (MM) and the finite-difference time-domain (FD-TD) method. The hybriding is based upon a novel use of a field equivalence theorem due to Schelkunoff, which permits a field penetration problem to be analyzed in steps by treating the relatively simple external region and the relatively complex internal region separately. The method involves first, determination of an equivalent short-circuit current excitation in the aperture regions of the structure using MM for a given external illumination. This equivalent current excitation over the aperture is next used to excite the complex loaded interior region, and the penetrating fields and induced currents are computed by the FD-TD method. A significant advantage of this frequency domain/time domain hybriding is that no Green´s function need be calculated for the interior region. This hybrid approach takes advantage of the ability of MM to solve exterior problems using patch models and also takes advantage of the ability of FD-TD to model in great detail localized space regions containing metal structures, dielectrics, permeable media, anisotropic or nonlinear media, as well as wires.