Monolithic integrated ceramic waveguide filters

Design techniques for a new class of monolithic integrated high permittivity ceramic rectangular waveguide microwave filters are presented in this thesis. These filters enable a size reduction of 50 % as compared to air filled coaxial resonator filters with the same unloaded Q-factor. Initially, an integrated ceramic rectangular waveguide resonator structure is investigated. It consists of a metal plated high permittivity ceramic rectangular block with Q-factor comparable to transverse electromagnetic (TEM) coaxial resonator but in a much miniaturised volume with good out of band spurious performance. The three dimensional finite element method (FEM) electromagnetic solver HFSSTM is used to analyse the resonant modes, Q-factor and field patterns of the ceramic waveguide resonator.
High performance Chebyshev and generalised Chebyshev monolithic integrated ceramic rectangular waveguide filters are designed to meet the stringent electrical requirement for cellular radio base station. Inter-resonator couplings are achieved by placing various through and blind holes in the broad dimension of the waveguide. In the generalised chebyshev filter, both negative and positive cross couplings are introduced to achieve transmission zeros on both sides of the passband. Metal tuning screws are added to the generalised chebyshev design to correct any practical imperfections. The ceramic waveguide filters are excited through coaxial probes placed at the centre of the broad wall of the external resonators.
An integrated ceramic rectangular waveguide diplexer design is also presented to be used at mobile base station front end to replace an existing TEM diplexer without degrading electrical performance in a much miniaturised volume. The both filters and the common junction of the diplexer consist of single metal coated ceramic block with various blind and through holes to realize a complex coupling scheme.
Finally a low pass ceramic corrugated waveguide filter design is presented to be used along with diplexer at cellular base station to achieve very wide spurious free out of band bandwidth. The miniaturisation techniques discussed in this thesis will provide overall cost reduction for cellular communication systems requiring low loss narrowband bandpass filters.