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

With the development of wireless communication technology in recent years,the application of various communication standards has made the research of multi-frequency filters a hot topic in the field of microwave circuits.However,the application of a variety of communication standards and the addition of various types of stations have also caused the increasingly complex electromagnetic environment derivative problems,so the balanced microwave filter with good anti-interference characteristics has become a hot spot.Based on the above background,the design of multi-frequency bandpass filter and balanced filter is studied and explored by using multi-mode resonator technology.Aiming at the application of various communication standards,a three-frequency wideband bandpass filter based on coupled microstrip line loaded T-shaped multimode resonator is designed.The center frequency of the three passbands are1.8GHz/3.5GHz/5.2GHz,respectively corresponding to GSM?Wi Max and WLAN.The three passbands have good passband selectivity and isolation degree,and compared with many current multi-frequency filters,the three-frequency bandpass filter has the advantage of three passband relative bandwidth of more than 10%.The ultra-wideband filter is constructed by using the microstrip coupling line and the half-wavelength transmission line,and then the ultra-wideband is divided into three passbands by using the transmission zero generated by the T-shaped resonator loaded at the end of the coupling line.The performance adjustment of the filter is studied by means of parameter analysis,and the design method is further summarized.In addition,based on SLSIR,a dual-band bandpass filter with wide stopband suppression is designed,whose operating frequencies are located in 2.4GHz(WLAN)and3.5GHz(Wi Max).The resonant frequency of the filter can be adjusted flexibly by changing the impedance ratio and length ratio of SLSIR.The introduction of Zero-degree feed enhances the passband selectivity of the filter.The 20d B suppression effect of the upper stopband is up to 9GHz(3f₀).Therefore,the filter has the advantages of independent control of central frequency,high passband isolation and compact circuit structure.In view of the increasingly complex electromagnetic environment,two balanced single-frequency and a dual-frequency bandpass filters is designed.Firstly,a wideband balanced bandpass filter based on ring coupled-line resonator loaded coupled-line stubs is designed.Secondly,a balanced bandpass filter with wide bandwidth,wide common-mode(CM)suppression range and high CM suppression effect is successfully designed by using coupling feed line and stub loading technology.The structure characteristic of these filters are analyzed by means of network analysis method,the mechanism of transmission zero is illustrated by means of the analysis of stub loading,and the influence of each circuit parameter on the electrical performance is analyzed by means of simulation experiment,then the design steps of the balanced filters are summarized.Finally,the zero-degree microstrip-slot line feed structure(ZDFS)is proposed,and a balanced dual-frequency bandpass filter with independent control of central frequency is designed based on SLR.The operating frequencies are 3.5GHz(Wi Max)and 5.2GHz(WLAN)respectively.The resonance characteristics of SLR are analyzed,and the influence of each parameter on the electrical performance is explained from the angle of parameter analysis,and the design steps of balanced dual-frequency bandpass filter based on ZDFS are given.The structure of the proposed ZDFS can realize high CM suppression in the full frequency range,so the design of the balanced filter can only consider the design of the differential mode passband response,which is of great help to simplify the whole design process.Various filters designed in this paper have good electrical performance and meet the relevant design criteria,which can be well applied to modern wireless communication systems.