Multi-passband filters and tunable filters design based on coupled resonator circuits

This thesis investigates multi-passband and tunable microwave filters, it includes a new generalised design technique for multi-passband filters and a new coupling tuning structure for tunable waveguide filters. \nThe synthesis technique is an analytical approach and offers very fast solutions to the design once the desired filter specifications are given. The technique calculates the coupling matrix and external Q-factors for a wide range of filter specifications. The centre frequency and bandwidth of each passband, and the number of passbands can all be arbitrarily chosen. To verity the calculations, multi-passband filters are realised by using inverter coupled resonator sections. Two X-band waveguide multi-passband filter examples are given to validate the theory. Besides the innovation in synthesis technique, new designs of fully tunable waveguide filters are also presented. These filters are based on the new coupling tuning structure and a separate frequency tuning structure offering tuning in both centre frequency and bandwidth of the filter. One tunable bandpass filter and one tunable notch filter is implemented in X-band waveguide circuit.