Design And Research On High-performance Band-pass Filter Based On Square Ring Loaded Resonators

The21stcentury, information technology has been rapid development, especially in thescope of wireless communications. Also, in order to satisfy the development demand of shortdistance of mobile communication, weather radar, radio astronomy and space technology, thesystem for wireless communication is developing to the direction of miniaturization, highperformance and multi-function. Therefore, filter, as the key components of the wireless RFfront end, is tendency to the research hotspot of miniaturization, high performance,multi-mode and multi-band. This dissertation is concentrate on the research of design methodfor planar multi-band microstrip bandpass filter (BPF), and analysis and research the excellentcharacteristics of multi-mode resonator based on the square ring loaded resonant methoddeeply. Furthermore, multiple high performance multi-band filters are designed by adoptingthe square ring loaded resonator (SRLR). The mainly innovations of this thesis are as follows:Firstly, a dual-band microstrip BPF appliedd in WLAN and WIMAX is designed byadopting a square ring loaded stepped impedance resonator (SIR) and a half-wavelengthresonator. Three controllable resonant modes will be excited by loading a square ring stub onthe SIR that with dual-band characteristic, also the theory of even and odd-mode is used toexplain the resonant mechanism of three modes. In addition, not only the half-wavelengthresonator produces the fourth controllable resonant mode, but also introduces a couplingbetween the source and load, thus multiple transmission zeros will be created, which improvethe rectangular coefficient of filter greatly.Secondly, a quad-mode SRLR is proposed based on the research basis of square ringloaded SIR firstly. The equivalent menthod of even and odd-mode is firstly applied to analysisthe four resonant modes deeply and two resonant formulas are given. Then, two design graphsthat respect to the relationship between the key physical parameters of SRLR and resonancefrequencies are drawn by using MATLAB software, which used to guide the filter design. Andlastly, according to the design specifications, a miniaturized dual-band BPF for WLANapplication is designed.Finally, a quad-band high-temperature superconducting (HTS) BPF is designed byadopting the metarial of superconductor, which enhance the transmission performance of filtergreatly. The first step is choosing the appropriate electrical parameters of SRLR based on thetarget specifications and two grid graphs, and then to calibrate the deviation frequencies ofsome resonant modes by meader coupl-line technique. At last, two meandering SRLRscoupled with pseudo-interdigital structure are used to design a miniaturization and high performance quad-band HTS BPF. In addition, further analysis about the characteristics ofresonance and zeros of SRLR have been made in the dissertation.All of designed BPFs discussed above are fabricated and measured, and themeasurements match well with EM simulations, which validate the design schemes proposedin this dissertation. Meanwhile, a good foundation of theory and practice will be establishedfor the research and its application of multi-band filter.