Coupling between coaxially fed monopoles in waveguides

Abstract

Coaxially fed monopoles in waveguides are important feeding structures in microwave and millimeter wave frequencies. Therefore, it would be of practical interest to obtain analytic solutions for a variety of coaxial-waveguide junction structures. They are not only mathematically tractable but also give a physical insight into the scattering mechanism. This thesis presents such analytic solutions for various coaxial-waveguide junction structures. The analysis method is based on the Fourier transform, mode matching, superposition principle, and image method. Residue calculus and Poisson``s summation formula are used to represent the solution in a fast convergent series, which is amenable to computations. In chapter 1, we briefly review the study of coaxially fed monopoles hitherto researched and introduce the need of our research. A theory for coupling between coaxially fed monopoles in a parallel-plate waveguide is presented in chapter 2. The method introduced in chapter 2 is useful to solve the problem of a variety of coaxial-waveguide junction structures. Chapter 3, 4, 5, and 6 show how to apply the solution presented in chapter 2 to the problem of coaxially fed monopoles in a shorted parallel-plate waveguide, rectangular waveguide, shorted waveguides, and rectangular cavity, respectively. In order to apply the solution presented in chapter 2 to a problem of various coaxial-waveguide junction structures, the image method must be invoked beforehand. The image method allows us to transform the problem of various coaxial-waveguide junction structures into the equivalent problem of coaxially fed monopoles in a parallel-plate waveguide. In chapter 7, the problem of two coaxially fed monopoles arranged on the opposite side of a parallel-plate waveguide is solved. Chapter 8 presents the solution for the problem of two coaxial lines cross-coupled to a rectangular waveguide. Throughout this thesis an $e^{-iwt}$ time convention is assumed.