On the practical use of layered absorbers for the simulation of planar microwave circuits using the SCN-TLM method

In this paper we report on the practical use of matched layer (ML) and perfectly matched layer (PML) absorbers for simulating plan microwave circuits using the SCN-TLM method. It emerges, that a recently proposed PML-SCN node suffers from serious stability problems when applied to layered three-dimensional problems and its practical use is hence very limited. However, revisiting the well-known matched layer technique, it emerges that a parabolic conductivity profile is not the best choice to achieve optimum absorption in contrast to common belief. Rather, the optimum conductivity profile depends on the number of matched layers. In the cases of 5 and 10 matched layer, a linear conductivity profile gave the best results in terms of minimum return loss, whereas for 15 matched layer, a steep profile witch p = 2.4 gave the best results. Furthermore, we show that the main source of reflection in the matched layer does not come from parasitic numerical reflections due to the abrupt change in conductivity, but from the differing dispersion in neighbouring media with different media parameters.