Analysis of dispersion relations and coupling characteristics of shielded waveguide using image method

Abstract

The electromagnetic wave propagations and coupling charactristics of a shielded waveguide are rigorously studied in the literature. Combining the Fourier-transform with the image theorem offers a new technique by converting a shielded transmission-line into an equivalent periodic transmission-line structure such as the infinite number of a multiple waveguide. Our approach is different from other existing approaches based on the Floquet`s theorem or a Fourier-series expansion. Our approach based on the Fourier-transform and image theorem is a new concept dealing with a periodic function without recourse to the Floquet`s theorem. Chapter 1 shows how to combine the Fourier-transform with the image theorem to obtain the dispersion relation. We divide the periodic transmission-line structures into open and closed regions. We then use the Fourier-transform to represent the scattered field in the open region. The residue calculus is performed to evaluate the integral representation for the scattered field in the open region. The image method is equivalent to the simple method related to the Green`s function approach shown in Sect. 1.4. The Green`s function approach allows us to reduce the amount of computational effort such as the residue calculus in Sect. 1.2. In chapter 2, we present the analysis of the image method and the overlapping T-block approach to obtain the dispersion relation and coupling characteristics of a double-ridge waveguide. In order to apply the Fourier-transform to a ridge waveguide, the image theorem must be invoked beforehand. A use of the image theorem allows us to transform the ridge waveguide into an equivalent infinite number of multiple groove guide. It is also possible to apply the T-block (TB) approach in Sect. 1.4 to the dispersion analysis for a double-ridge waveguide. The purpose of chapter 3 is to derive a rigorous and analytic dispersion equation for a groove nonradiative dielectric waveguide, based on the techn...