New developments in the transmission line matrix and the finite element methods for numerical modeling of microwave and millimeter wave structures.

Abstract

New and efficient numerical modeling concepts and procedures based on Transmission Line Matrix and Finite Element methods have been developed for the analysis of generalized microwave and millimeter-wave structures. An algorithm, based on a vectorial Finite Element approach, has been developed to determine the dispersion characteristics, field distributions, pseudo-impedances and, losses of shielded transmission media of arbitrary cross-section. The structures analysed with this algorithm include dielectrically loaded ridged waveguides, bilateral finlines in rectangular and circular waveguide enclosures and ridged finlines. The major contributions to the literature are the estimation of losses of bilateral finlines in rectangular waveguide enclosures, the effect of substrate bending and mounting grooves on the dispersion characteristics, the study of finlines in circular waveguide enclosures, and, the analysis of a new modified finline structure called "Ridged Finline". New algorithms to apply the principles of Diakoptics to the TLM method for field partitioning in large structures have been developed. Diakoptics leads to considerable reduction in memory and CPU requirements for large structures since it allows numerical preprocessing of parts of a large electromagnetic structure which remain unchanged during an analysis and optimization procedure. A space interpolation technique based on the transverse field distribution of the propagation mode has been proposed for efficient field partitioning in single-mode structures. Frequency dispersive boundaries are represented in the time domain by their characteristic impulse response or numerical/discrete Green's function. This discrete Green's function has been named the "Johns matrix" in honour of the late P. B. Johns, pioneer of TLM and time domain Diakoptics. The parasitic reflections from the absorbing boundaries in 3-D structures, due to the finite space and time discretization have been reduced to less than one percent by exponentially tapering the impulse response, or Johns Matrix, of frequency dispersive boundaries. This allows wideband S--parameter extraction of waveguide discontinuities and components from a single impulsive TLM simulation. This tapered impulse response has been named the "Tapered Johns Matrix".