Modal and TLM-based analyses of discontinuities in the non-radiating dielectric waveguide and components

This thesis discusses the development of a full-wave modal analysis method based on the Transmission Line Matrix (TLM) method which can be used to characterize discontinuities in guided wave structures in general and also serve as a powerful tool for the analysis and design of circuit components. The motivation for this work arose from the need to ascertain the reactance and conductance of an isolated slot in the ground plane of a Non-Radiating Dielectric Waveguide (NRD) without relying on experimental data.; The NRD has been recognized as an ideal candidate for millimeter-wave applications largely because of its unique characteristics of suppressing radiation from bends and discontinuities and its inherent low loss. A review of NRD guide technology has been included in this document.; Problems involving the slot and typically other discontinuities and components based on the NRD are particularly amenable to solution using a time-domain technique like the TLM algorithm because of the inhomogeneous and complex nature of the NRD. Moreover, the availability of a TLM Simulation Engine at that time provided further impetus to develop a methodology to solve problems involving discontinuities in the NRD in general and the NRD slot in particular, and if possible, to extend it to treat any given discontinuity in a general guided wave structure.; The existing absorbing boundary condition incorporated in the TLM code, viz. the Matched Condition for Normal Incidence, though suitable for terminating TEM structures like the microstrip was found to give insufficient absorption for a non-TEM hybrid structure like the NRD which was under investigation. Hence the Perfectly Matched Layer absorbing boundary condition (PML) was implemented and incorporated in the TLM code for use as matched terminations in the NRD. A rigorous Modal Extraction Approach was developed by which the incident and scattered powers in all modes were individually extracted and verified using the Power Conservation and Poynting's Theorems. Moreover, it was possible to estimate the modal power distribution in the scattered modes in the presence of evanescent modes near a discontinuity. Thus, observation surfaces used for modal extraction could be located close to the discontinuity resulting in a considerable reduction in computational domain and simulation times. A full-wave modal analysis of several discontinuities in the NRD and the rectangular waveguide was achieved using this new approach. Thereafter, the method was applied to rigorously analyze different circuit components used in the NRD guide technology, taking into account all scattered propagating modes.