Design Of Multi-band Filter And Balanced Filter Based On Multi-mode Resonators

At present,the coexistence of multi-communication standards and the popularity of multi-service intelligent terminals have brought forward multi-service communication requirements for RF front-end circuits of receivers,and thus have placed major demands on multi-band filters that satisfy multi-service communication.At the same time,integrated circuits have achieved rapid development,high degree of circuit integration will increase circuit noise,which will reduce the signal-to-noise ratio and sensitivity of receiver,balanced multi-band filters have multi-band differential-mode(DM)response,a high-performance balanced filter can also suppress common-mode(CM)noise,which will increase the sensitivity of receiver.Multi-mode resonators are the basis of multi-band filters and balanced filters;Realizing miniaturization of circuits and excellent CM suppression over a wide frequency band are two major challenges in design of balanced multi-band filters.This paper systematically studied compact multi-mode resonators,multi-band filters,multi-band balanced filters,and high CM suppression under the guidance of my supervisor.The main research contents are as follow:(1)A doubly short-ended ?-type multi-section stepped-impedance resonator(SIR)is proposed.Based on the resonator,a tri-band bandpass filter(BPF)with wide stop-band performance is designed.Firstly,the resonant characteristics of the multi-section SIR are analyzed,the numerical relationship between the resonant frequency and the impedance ratio and the electrical length ratio is established.Then,a suitable combination of impedance ratio and electrical length ratio was selected to obtain the desired frequencies for GPS,Wi-Fi and WiMax,and the fourth harmonic' frequency of the resonator is also extended to achieve wide stop-band performance.Finally,zero-degree feed-lines are used to design tri-band BPF to introduce transmission zeros(TZs),which can improve the selectivity of pass-bands.(2)A compact octo-section stepped-impedance ring resonator(SIRR)is proposed.Firstly,the DMs and CMs resonant characteristics of the resonator are analyzed,and relationships between DMs,CMs and impedance ratio and the electrical length ratio are established;Then,based on the SIRR,a balanced tri-band filter was proposed,which has good in-band CM suppression.Finally,in order to improve the out-of-band CM suppression of the DM response,a balanced tri-band BPF with high CM suppression in a wide frequency band isrealized by sepataring away CMs by loading stubs with different lengths in the symmetrical plane of the SIRR.(3)In order to reduce the size of balanced BPF and achieve high CM suppression over a wide frequency band.Firstly,theory of the composite right and left hand transmission line(CRLH-TL)are introduced.Based on the ?-type CRLH-TL,a dual-mode resonator with metamaterial properties under DM excitation is proposed.Then,a balanced dual-band filter with ultra-compact size and perfect CM suppression was designed and the dispersion characteristics of the balanced filter were analyzed.The balanced BPF has ultra-compact size,and high CM suppression over wide frequency band without additional CM suppression circuits.