Design Of High-performance Microstrip Filters Based On Multi-mode Resonators

Due to the rapid development of the modern wireless communication systems,the performance requirements of the circuit network components become increasingly high.Filters are one of the key components at the front end of communication systems,one class of them are microstrip filters which have the merit of easily integrated with other microwave components.Therefore,the study on high performance microstrip filters becomes a hotspot in microwave component designing fields.Meanwhile,filter designs using multi-mode resonators have the merits of compact size and low insertion losses,so the study of multi-mode resonators with different shapes and stubs becomes the emphasis of high performance filter designs.The analysis method and synthesis method are two different ways with each other advantages in filter designs.The even-odd mode analysis method which is one of the analysis methods is used in this dissertation to analyze the resonant modes of the multi-mode resonators.And some novel synthesis models are presented to design wideband and multi-band bandpass filters(BPFs)with high performances as well.The major works and contributions of this dissertation are outlined as follows.1.The presented multi-mode resonators are analyzed by the even-odd mode analysis method and used to design BPFs.The even-odd mode analysis method is studied in detail to show its application condition and core idea.The even-odd mode analysis method is used to analyze the half guided wavelength and a quarter guided wavelength stepped-impedance resonators(SIRs).The relationship of the resonant modes of SIRs with the parameters of impedance and electrical length ratios is shown.And the relationship between different resonant modes is also analyzed by the even-odd mode analysis method.Two resonators that can excite dual and triple modes are presented and used to design two BPFs,respectively.The parameters analyzing related to the resonant modes of the resonators are used to show the effectiveness of the even-odd mode analysis method.2.The stepped-impedance and stubs-loaded ring resonators are presented to design wideband and dual-band BPFs.The even-odd mode analysis method is used to analyze the resonant modes of the resonators.Due to the two-path effect of the ring resonator,the transversal signal interference theory is used to analyze the relationship of transmission zeros(TZs)with parameters of the resonators.A shorted stub loaded stepped-impedance ring resonator is presented to design wideband BPF with wide upper stopband.Three resonant modes are excited in the passband and five TZs are produced in the upper stopband to restrain the higher resonant modes by tuning the distributions of the resonant modes and TZs.An open and shorted stubs loaded ring resonator is presented to design dual wideband BPF by tuning the distributions of the resonant modes and TZs.The two passbands each have three resonant modes.The stopband between the passbands and the upper stopband each have three TZs to realize wide stopband and sharp roll-off performances.A shorted multi-stepped impedance ring resonator is presented to design dual wideband BPF with quint-mode excited in the two passbands.The ring resonators loaded with differents stubs and with multi-stepped impedance have the characteristics of exciting multiple modes and producing multiple transmission zeros,which are illustrated by the presented three design examples.3.A novel synthesis method with its circuit model is presented to design multi-band BPFs.By controlling the number of the open stubs loaded on the shorted stub,the number of the TZs is exactly determined.And the TZ frequencies can be calculated by parameters of the open stubs loaded-shorted stub.After analyzing the relationship of transfer and reflection functions with the equivalent lumped elements of the filter model,the synthesis method has the characteristics of controllable center frequencies and last passband bandwidth(BW),and the synthesis method is practicable from theoretical analysis.Since the TZs and reflection zeros can not be expressed linearly by the lumped element values,the optimization algorithm is used to obtain the required lumped element values.The lumped elements are realized by the microstrip distributed elements.Due to the discontinuities of the microstrip lines,the final mcrostrip configuration dimensions satisfying the design requirements are optimized by the full-wave electromagnetic simulation software.The single-band to tri-band BPFs are designed to demonstrate the reliability of the synthesis method and summarize the design procedure of multi-band BPFs.Quad-band to oct-band BPFs are designed to illustrate the effectiveness of the synthesis method and to show the merit of widely tunable ability of the last passband BW.4.Three novel different synthesis circuit models loaded with unsymmetrical subs and parallel dual stubs are presented to design multi-band BPFs.The transfer and reflection functions of each model are theoretically analyzed in detail to show the merits of each model.The optimization algorithm is used to obtain the required lumped element values of each model.And the related physical dimensions of the microstrip filters to the lumped element values are optimized by the full-wave electromagnetic simulation software to satisfy the design specifications.A dual-band and a tri-band BPFs loaded with unsymmetrical stubs are designed with two tunable TZs in the stopband between passbands to show the merit of tunable stopband BWs.BPFs loaded with parallel open and shorted stubs are designed with widely tunable passband BWs.A dual-band BPF with narrow passband BWs and a dual-band BPF with wide passband BWs are designed to illustrate the synthesis model merit.Two BPFs loaded with parallel dual shorted stubs are designed with multiple narrow passband BWs to illustrate the merit of the proposed synthesis model,which is the feasibility of multiple narrow passband BWs.