Design And Research Of Microstrip Filter With High Selectivity

Nowadays,with the increase of the capacity of wireless communication systems,the interference between adjacent channels is becoming more and more serious.Microwave filters are important components of modern communication system,study on technology of multi-band and high selectivity filter can effectively solve the problem of spectrum utilization.Therefore,in the premise of keeping the signal quality of the communication system,to achieve high selectivity and multi-band filter with compact size has attracted more and more attention.In this paper,the current research status of wide-stopband filter,double band and multi-band passband filter are firstly investigated,and focus on the research of the key technologies to achieve wide stopband,high selectivity and multi-band.Based on the above research work,the following kinds of filters are designed and analyzed.1.The resonant characteristics of step impedance resonators with two different transmission lines?SIRs?are studied.Based on the split-end half wavelength?1/2??SIRs and coupled resonator filter design theory,a bandpass filter with high selectivity,low insertion loss and a wide stopband up to 20 f₀ was designed,and was verified by the practical model.2.The even-odd theory was used to analyze the resonant characteristics of a novel dual-mode resonator?rectangular ring with step impedance stubs loaded?.A dual-band passband filter with high selectivity and wide upper stopband was designed with the proposed dual mode resonator.This paper presents the design process of multimode dual-band bandpass filter,the consistency of the measured results and simulation results verifys the correctness of the analysis.3.Although the two center frequencies of the proposed dual-mode dual-band filter can be adjusted independently.However,there are some disadvantages that the bandwidths of the two passbands cannot be adjusted independently.Based on stub-loaded dual-mode resonators,two passbands can be designed separately,thus both the center frequencies and bandwidths can be adjusted independently.What's more,the source-load coupling was applied to improve the selectivity.4.The resonant characteristics of step impedance resonators with three sections transmission lines?tri-sections SIRs?and modified tri-section SIR are researched.Make further research on the structure parameters and field distribution of the tri-section SIR.Based on the above two multi-mode resonators,a compact tri-band bandpass filter with flexible center frequencies was designed in this paper.Considering that the bandwidths of the tri-band filter cannot be adjusted independently,Resonators based on short stub were used to improve this shortcoming.Finally these two filters were fabricated and the comparison and analysis were given.