Analysis of slotted cylindrical ring resonator

Abstract

The design of microwave filters for mobile communication base station filters is of critical importance, thereby requiring thorough knowledge of many aspects of a filter. Of these many aspects, coupling is essential as it determines the characteristic of the filter, or the shape of the passband. Realisation of filter characteristics can be achieved using various resonators, but the slotted cylindrical ring (SCR) resonator has been recognized very promising in the development of compact microwave filters for use in mobile communication bands. The resonator has a compact structure that is capable of providing medium to high Q factors and large frequency separation between the resonant frequencies of the fundamental and higher order modes. The aim of the research project is to assess the coupling coefficient of a 2GHz filter so as to provide a comprehensive data for filter design purposes. The optimum dimensions of the resonator were first determined. The effects of the magnetic and electric walls on the even and odd resonant frequencies that are necessary for determining the coupling coefficients between two coupled SCR resonators oriented with their gaps facing in opposite directions, are investigated and discussed. The magnetic and electric couplings between the coupled resonators are also investigated. A thorough analysis on the coupling coefficients of the aperture opening is carried-out between the coupled resonators. The investigation is performed by use of computer simulation software (CST Microwave Studio). The Eigenmode Solver method incorporated in this simulation package is used to simulate the resonant frequencies, coupling coefficients, and the field distributions of the resonators. The results confirm that for the magnetic coupling, the value of the eigen-frequency when the boundary wall is replaced by the magnetic wall, is greater than the one where the boundary wall is electric between two coupled SCR resonators. The effects of the aperture parameters on the eigenvalues necessary for the determination of the coupling coefficient have been noted. Simulated results are compared with other similar theoretical results. This project concludes by outlining the main achievements and some future work of this project.