Compact microwave filter designs based on cavity resonators
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Cavity resonators are widely used in microwave filters and multiplexers due to their high quality factor and high power handling capability. Compact designs of these filters are important for practical applications, as they are generally bulky. In this thesis, two types of compact microwave filter designs based on cavity resonators are developed. Firstly, through the use of additional posts in irises of a dielectric resonator filter (DRF), a dual-band filter can be achieved. Metal posts, which can be realized using screws, are applied in the irises of dielectric resonator filters working as capacitive obstacles. These posts along with the irises and dielectric resonator enclosure, which work below cut-off, can form the resonators to function as an evanescent mode filter. With the existing dielectric resonator filter, a dual-band filter design can be achieved. Using a properly designed coaxial input/output structure, the two passbands can be tuned individually and then combined together. An example of the dual-band filter is designed and simulated to verify the design concept. A new compact design of a hybrid-coupled filter module (HCFM) is also introduced in this thesis, for applications in communication satellites as a combiner. A conventional HCFM consists of two complete 3dB hybrid couplers and two identical passband filters in the middle. In this work, we use the inter-resonator couplings between two filters to replace one of the branches in a 3dB hybrid coupler used in HCFM to make the design more compact. Implementation of the new design is realized using waveguide filters, dielectric resonator filters and coaxial cavity filters. In all cases, the new structure preserves the responses of a conventional design. The circuit model in ADS and the 3D structure in electromagnetic (EM) simulator HFSS are built to verify the concept. Moreover, by using tuning screws in both cavity resonators and waveguide T-junctions, we achieve the tunability of the HCFM.