Research On The Characteristics Of Miniaturization And Multi-Passband For Microwave Bandpass Filters

With the rapid development of modern wireless communication technologies,people's demand for communication devices is gradually developing towards miniaturization and multi-function.In the face of endless wearable devices and multi-purpose portable mobile terminals,the increasingly strained spectrum resources have reached a point of unprecedented crowded.In order to ensure high-quality communications,the system's anti-jamming capability faces enormous challenges.Band-pass filter(BPF)is an indispensable part in the RF front-ends of communication systems.It plays an important role in separating spectrum,improving communication quality and preventing channel crosstalk.The miniaturized and multi-passband BPFs not only can effectively reduce the size and weight of the communication devices,but also can reduce the complexity of the systems to some extent.Therefore,the research on the characteristics of miniaturization and multi-passband for the filter not only has important academic value,but also has a strong practical significance.This dissertation focuses on the study and design of the miniaturization and multipassband characteristics of microwave BPFs.With respect to the miniaturization design of the filter,this dissertation focuses on the application of fractal structures and fractal resonators in this field.By adoptting stepped impedance resonators(SIRs)and stub-loaded resonators(SLRs),various types of filters such as single-passband,dual-passband,and tri-passband are designed.The main work of this dissertation is summarized as follows:1.Briefly described the research background and significance of the miniaturization and multi-passband design for microwave BPFs,and reviewed the current developments in the field and the latest research results for the two characteristics of miniaturization and multi-passband of microwave BPFs.2.The basic parameters of the filter design are summarized.The transmission line impedance equation is given,and the input impedance of several cases is analyzed.The odd-even mode analytical method for studying symmetric networks is dissected in depth,which provides theoretical guidance for the analysis of resonators with symmetrical structures.3.The development of fractal theory and the application of fractal structure in microwave BPFs design are briefly reviewed.The characteristics and mechanism of some common fractal curves and fractal structures are studied.By introducing a scaling factor in the structure of a typical Sierpi?nski carpet fractal resonator,the control of resonator's resonance characteristics is realized.Based on this modified Sierpi?nski carpet fractal resonator,a dual-mode dual-passband bandpass filter is designed,fabricated and measured.The measurement results show that the dual-mode dual-passband bandpass filter has good frequency characteristics.4.The process of producing the Greek-cross fractal structure by using the method based on generator-iteration is presented in detail.Based on this,the Greek cross fractal structure is applied to the design of microstrip resonators,which forms a new type of fractal resonator – Greek-cross fractal resonator(GCFR).By comparing the resonance characteristics of the fractal resonators with different iterations,it is proved that the proposed GCFR has outstanding miniaturization characteristics.A miniaturized BPF based on the 3rd iteration GCFR is designed,fabricated and measured.Good agreement between the measurement results and the simulation ones is achieved.5.Systematically study on the resonance characteristics of SIRs and SLRs,respectively.The factors influencing the resonance characteristics of the resonators are analyzed and discussed.In order to improve the flexibility and freedom of the filter design,the structure of the resonator used is a transition from a single SIR to a stub-loaded SIR(SL-SIR),and finally to a stepped-impedance stub-loaded SIR(SI-SL-SIR).The structural parameters taken into consideration gradually increase,and the design complexity also gradually increases.Dual-passband and tir-passband filters are designed based on the above three types of resonators.Since the loaded stubs are located inside the resonator,there is no additional increase in the size of the resonators.Therefore,these filters have the advantage of miniaturization while achieving multi-passband frequency responses.