In this paper, the absorbing property of the discrete Green's function ABC, which was based on a powerful concept of the TLM method, has been improved by relocating loss process from the time domain to the space domain. The proposed scheme simply adds a loss matrix to the connection matrix in the basic TLM algorithm to make the formulation of the ABC more efficient. Various lengths of absorbing layers discretized for a WR-90 empty waveguide have been tested in terms of reflection property. An expression for an optimum absorbing property has been also derived with respect to the length of the layer. Comparison of the layer with the discrete Green's function ABC shows that the layer in this study has improved reflection property better than approximately 3 and 6 dB, respectively, when 50Δ and 60Δ absorbing layers have been adopted for the WR-90 waveguide. Finally, the layer has been applied to a WR-75 metal insert filter as an example.

This paper describes a diakoptics approach to the field simulation of shielded structures. If the structure can be divided so that the sliced cross section is homogeneously filled with a medium in the metal-surrounded region, the frequency domain diakoptics can be effectively formulated. In the method, the partial eigenfunction expansion (or modal expansion) is utilized at the interface between the divided structures, and the finite difference time domain calculation is used to characterize some of the divided parts. The synthesis of total characteristics is demonstrated using a simple example. The issue of term truncation in the eigenfunction expansion is also addressed and an effective algorithm for the term selection (mode selection) is proposed. The techniques described here are applicable to metal package designs for efficient structure optimization.