Research On Microwave Mutil-mode And Transverse Combination Bandpass Filter

With the development of communications technology, the research and application ofcircuit in microwave and RF field have become more and more importance. Because of it willdirectly affect the size and performance of the whole communication system， the filterminiaturization and high performance are worth researching. Among many techniques of highperformance filter, an effective method is to adopt the multimode resonators and filters. In thispaper, the transverse combination filter theory and implementation method is studied based onthe planar single resonator multimode filter research. The main contents are as follows.Firstly, a ring loaded multimode filter is proposed. By loading a square ring and twoT-shaped stubs in a square ring resonator，four resonant modes are excited. Then, circuit issimplified to get the relationship between the model and the resonator parameters by using theeven-odd mode theory. The four resonant modes are kept in one band by controlling theparameters of the resonator. A quad-mode bandpass filter will be implemented withappropriate external coupling. A good agreement between simulation and measurementverifies the validity of proposed design methodology.Secondly, the theory of transverse combination filter design and implementationtechnology is studied. Use a DGS dual-mode resonator and a microstrip triple-mode resonatorto achieve a transverse combination filter. Coupling matrix is obtained by building couplingtopologies of circuit models. The size of the coupling coefficient respectively decided bylocation of mode frequency and the distance between the resonators of the DGS andmicrostrip multi-mode resonator. Microstrip resonator and DGS resonator respectively indifferent layers, reduced the size of the circuit and achieve the goal of the circuitminiaturization.Thirdly, a three order filter mixed two microstrip resonators and a SIW resonator isproposed. The three order bandpass filter is realized by connecting two stepped impedancemicrostrip resonator and a SIW resonator through microstrip invertors. Different resonator, aslong as the resonance frequency is equal, and susceptance slope parameters meet therequirements, can achieve the given performance of the filter. The parasitic passband is inhibitand the stopband is expand effectively because of the harmonic is different of differentresonator.Finally, the multi-pole filter design theory is studied based on different SIW resonator.The SIW filter is realized by using two degenerate modes (TE102mode and TE201mode) of asquare cavity and a main mode (TE101mode) of a rectangular cavity. The separation ofdegenerate modes can be controlled by the offset of feed line from the center and the length of microstrip feed line. The coupling of the rectangular cavity and the square cavity can be tunedby the width of iris. Three transmission zeros are produced in stopband by this novel structure,which improve the stopband characteristics of the filter. A good agreement betweensimulation and measurement verifies the validity of proposed design methodology.