Research On Compact Multi-band And Balanced Microwave Filters Based On Multiple Mode Resonator

With the ever-increasing rapid development of wireless communication technique,the multi-band bandpass filter(BPF)which is compatible with various communication standards becomes a hot topic in the field of microwave circuits in recent years.At the same time,facing the challenges of electromagnetic compatibility problem of wireless communication equipment under the severe electromagnetic environment,the multi-band bandstop filter(BSF)which could suppress the interference electromagnetic signals,and the balanced microwave filter which has strong anti-interference characteristics have garnered an increasing number of research interests by numerous microwave researchers and engineers.In this dissertation,on the basis of multiple mode technique,the research and design method of multi-band BPFs,multi-band BSFs and wideband balanced BPFs are discussed under the background of modern wireless communication.The main work can be summarized as follows:1.To solve the problems of large circuit size and the complexity in layout topology of quad-band and quint-band BPFs by combining several different resonators,a synthesis design method is proposed to realize quad-band BPF based on ?/4 resonators and alternative J/K inverters.On this basis,a quint-band BPF which combines multiple mode resonator and mixed electric and magnetic coupling(MEMC)?/4 resonators is further proposed.Because of the parallel transmission path in the proposed quad-band BPF,the dual-band filtering responses of the upper and lower path cells can be designed individually.Besides,the proposed quad-band BPF realizes compact size while the central frequencies and bandwidths of each passband can be controlled independently.For the proposed quint-band BPF,both the central frequencies and in band return losses of each passband can be adjusted independently.Also,the proposed quint-band BPF has the merits of small size,low insertion losses and high band-to-band isolations while handling the ability of flexible circuit design.Due to MEMC cancelling effect,virtual grounds in feeding lines,and source-load cross coupling,multiple transmission zeros can be yielded to obtain sharp passband roll-off skirts.2.A sext-band BPF based on a single multiple mode resonator is proposed for the first time.Based on the resonance characteristic of the proposed symmetrical open stubs loaded stepped impedance resonator,a plurality of resonant modes can be separated into several groups in order to obtain multi-band response.In addition,several perturbation methods and coupling feeding structures,i.e.high impedance short-circuited loaded stub,narrow side coupling,radical stub-loaded short-circuited lines and two I/O tapped branches are introduced in order to increase design freedoms for improving filter performance.The proposed sext-band BPF has the merits of excellent electrical characteristic and compact physical dimension.It could overcome the drawbacks such as large insertion losses,narrow bandwidths,low band-to-band isolations and large circuit sizes by using several resonators to construct multi-band BPFs.3.Design of miniaturized frequency controllable multi-band BSFs by using multiple mode resonator technology is investigated,which enrichs the design ideas and architectures on the multi-band BSFs.A design method of realizing multi-band BSFs and lowpass filter(LPF)with multiple notch bands by using coupled-line stub-loaded shorted stepped-impedance resonator(CLSLSSIR)is proposed,especially a quint-band BSF with adjustable frequencies by using multiple mode resonator is proposed for the first time.Based on the resonance characteristic of the proposed CLSLSSIR,a series of tri-band,quad-band and quint-band BSFs and a LPF with triple notch bands have been proposed.Furthermore,the tuning methods of the stopband frequencies or notch band frequency locations of these above filters are studied,then the circuit design procedures are demonstrated from the point of parameter analysis view.Besides,the controllability of stopband attenuations and the generation mechanism of transmission poles in the multiband BSFs are also investigated.Owing to their compact sizes,enhanced stopband attenuations and sharp transition band roll-off skirts,the proposed multi-band BSFs and LPF with triple notch bands represent good candidates to suppress the interference electromagnetic signals for the wireless communication equipment under the complex electromagnetic environment.4.A compact wideband balanced BPF using T resonator with parallel path transmission structure is proposed,and the parameter analysis on its electrical performance is studied.Besides,based on the ring resonator with new type of feeding lines,a high selectivity balanced BPF is proposed,also its design procedure is given through the circuit parameter analysis method.The generation mechanism of the transmission zeros is further investigated.It is shown that the proposed balanced BPF can realize sharp transition band roll-off skirts by utilizing loaded transmission lines and the shorted-circuited coupled line stubs.The proposed wideband balanced BPFs,which have the merits of low insertion losses,compact sizes and good common mode suppressions,become promising candidates for the modern wireless communication system which imperatively needs the high immunity to the electromagnetic interference signals.