TLM analysis of microwave and millimeter wave structures with embedded nonlinear devices.

Abstract

A methodology has been developed such that electromagnetic structures with embedded non-linear devices can be accurately analyzed by the three-dimensional (3D) condensed node TLM algorithm. The method is based on incorporating a variable time step differential equation integration scheme, simulating the electrical behaviour of the devices, into the 3D TLM electromagnetic field simulation algorithm. The scheme can accommodate existing piece-wise linear SPICE device models of arbitrary complexity without non-physical instabilities or other spurious behaviour. A set of new 3D TLM node structures have been developed to complement the condensed node to better model the field at sharp conductor strip edges. These node structures provide substantial improvement in the accuracy of modelling strip-like transmission-line structures with a coarse mesh. They also provide a direct interface to the device model resulting in a more accurate simulation of the driving point impedance as seen by the device. A propagation analysis of the TLM condensed node was performed resulting in a derivation of the general dispersion relation. The superior dispersion characteristics of the condensed node relative to other TLM and FD-TD formulations was demonstrated based on the dispersion equation. Further exploration of the dispersion equation led to the discovery and characterization of spurious modes supported by the condensed node mesh. A derivation of the recursion equations of the equivalent FD-TD scheme representing the condensed node was then performed to establish the origin of the spurious modes and methods of suppressing them.