Research On Microstrip Microwave Filters Based On Multi-Mode Resonators

This paper presents the research on the microstrip microwave filters based on multi-mode resonators. Based on the design of multi-mode resonator structures, a number of microwave bandpass filters with different filtering characteristics have been introduced, including wideband bandpass filters with high selectivity and deep stopband rejection level, dual-band bandpass filters with separately controllable bandwidths and electrically reconfigurable bandpass filters.In the first chapter, a detailed explanation of the trends of modern wireless communication system and the development of the microwave filters structure and design theory. Then, the requirements and developments of filtering parameters in the design of practical microwave bandpass filters are fully described and analyzed. By comparing the practical needs and the current research situations, we draw the conclusion that to obtain high selectivity and good out-of-band rejection performance at the same time is the most demanding characteristics of the novel filter structures.In the second chapter, three different wideband bandpass filter structures are proposed which are all using the improved stub-loaded resonators. The second section introduces a novel of modified quad-mode stub-loaded resonator which is used to build a bandpass filter with high selectivity. In the third section, a type of stepped-impedance stub-loaded resonator is presented to design a banpass filter with high selectivity and good stopband rejection simultaneously. Novel stepped-impedance stub-loaded resonator is proposed in the fourth section.Then a bandpass filter with ultra-wide stopband is constructed by using it.In the third chapter, a compact wideband bandpass filter with excellent selectivity and good out-of-band rejection is proposed. The filter structure is constructed by cascading two symmetrical parallel-coupled line structures with a novel multiple-mode resonator.Three transmission zeros are obtained by the parallel-coupled line structure which can guarantee the high out-of-band rejection performance. Two transmission zeros beside the passband respectively are created by the multi-mode resonatorwhich can improve the passband selectivity significantly.In the fourth chapter, two different dual-band bandpass filters are designed based on multi-mode resonators. In the second section, a compact dual-band bandpass filteris presented using a single quadruple-mode resonator associated with a source-load coupling structure. And in the third section, a novel dual-mode stub-loaded resonator is proposed with independently controllable coupling coefficients under different resonant modes.a dual-band bandpass filter (BPF) with independently controllable bandwidths as well as a single-band BPF are designed and fabricated to provide an experimental validation on the predicted performances of the proposed filters.In the fifth chapter,a high performance tunable bandpass filter with separately reconfigurable passband edges is presented based on a novel varactor-tuned stepped-impendence stub-loaded resonator. It can be summarized that this proposed work has the widest passband edges and3-dB FBW tuning ranges, best in-band return loss performance as well as good out-of-band rejection performance among the filters using only tunable multi-mode resonators technology.