Novel trigonal dual-mode filter with controllable transmission zeros

A novel design method for trigonal dual-mode filters with controllable transmission zeros is presented. The filters consist of a trigonal open stub dual-mode resonator with cross-coupling between source and load. The field patterns of this type of resonator are investigated using full-wave electromagnetic simulations. The technique of utilising capacitive and inductive source-load coupling to improve the performance of this type of filter is explored intensively. Advantages of this type of filter include not only its dual-mode response, but also its controllable transmission zeros. Two bandpass filters are designed, fabricated and tested to validate the design concept. The simulated and measured results are in agreement generally.