Abstract:
In this thesis several configurations of variable-length cylindrical conducting posts in rectangular waveguide are examined. The posts axes are orientated parallel to the narrow dimension of the waveguide and their effect on the propagating TE10 mode fields is modelled by a T-equivalent circuit. In each of the studies the emphasis is on the development of accurate and efficient analytical models for the equivalent circuit reactance. Firstly, an accurate experimental technique is used to obtain a data set for the reactance of solid, hollow and hemispherical-cap posts. From this data set length adjustment factors are determined, relating the shunt reactance of each post form. The data set is shown to be in excellent agreement with results obtained from a numerical procedure based on the finite-difference time-domain technique. Next, four configurations of variable-length cylindrical posts in rectangular waveguide are _analysed by an approach in which the electric field off the variable-length post is represented as a Gegenbauer polynomial series whose coefficients are determined from the solution of an integral equation. The first is a solid variable-length post. The second is a modified variablelength post, incorporating a coaxial choke, which is more suitable for use in high power applications. The third and fourth are configurations where there is a solid variable-length post and either one or two full waveguide height posts at one waveguide plane, which are shown to be capable of producing a relatively large range _of shunt reactances. In each of these studies the incident electric field is assumed to be axially symmetric about the post surface, resulting in an equivalent circuit that contains only a shunt reactance. Theoretical results for the shunt reactance are shown to be in excellent agreement with experimental and numerical results when the posts are electrically thin in diameter, and when the posts are excited symmetrically from both waveguide ports. In the later part of this thesis an extension is made to deduce approximate, yet accurate, expressions for the equivalent series reactance term, thus allowing results to be calculated for the full T-equivalent circuit of each post configuration. In the final part of this thesis, waveguide impedance matching networks, formed from variablelength cylindrical posts, are investigated. Two impedance matching networks are designed and one is built and tested in an industrial application.