Research And Design Of Bandpass Filter Based On Elliptical Multimode Resonator

With the rapid development of wireless communication technology,the functional requirements for filters have become increasingly complex.Filters are trending towards miniaturization,interference resistance,ultra-wideband（UWB）and multi-band.As a result,balanced filters that can resist noise interference,UWB filters suitable for UWB systems,and multi-band filters have become research hotspots in the field of microwave circuits.In this thesis,through the combination of multimode and multilayer,folding,and 1/4 mode technologies,the miniaturization of various types of filters was studied.Based on substrate integrated waveguide（SIW）multimode resonators and microstrip multimode resonators,multilayer balanced filters,folded UWB filters with high shape factor and wide stopband,and dual-band filters with wide stopbands between bands based on 1/4 mode SIW were designed.The specific research work is as follows:1.Balanced Filter Research:Firstly,the theoretical basis of using elliptical substrate integrated waveguide（ESIW）as a balanced resonator is analyzed,and a single ESIW balanced filter is designed by etching an E-shaped slot line structure to reduce the central frequency of the differential mode passband,making the filter more compact.Two transmission zeros are generated on the left side of the differential mode passband through source-load coupling and metal pillar perturbation.To adjust the bandwidth of the differential mode passband and reduce the size of the filter,a balanced filter based on a double-layer dielectric substrate is also designed.Both balanced filters have central frequencies in the K-band,with common mode suppression better than 30 d B in the multi-layer filter differential mode passband,and have the advantage of miniaturization.2.UWB Filter Research:By replacing part of the rectangular microstrip line with an elliptical microstrip line,the impedance mismatch at the junction of different impedance microstrip lines in the resonator is reduced.A novel elliptical open stub-loaded resonator（EOSLR）is proposed,and the even and odd mode resonance frequencies of the Multimode Resonator（MMR）are theoretically analyzed.EOSLR has five resonant modes within the frequency range of 3 GHz to 14 GHz,and has transmission zeros on the left side of the passband.Defected Ground Structures（DGSs）is added to the bottom of the filter to generate transmission zeros on the right side of the passband and suppress higher harmonics,greatly extending the upper stopband width.Both measured and simulated results show that the designed UWB filter has a high shape factor and an extremely wide upper stopband.Finally,by folding EOSLR,the vertical size of the UWB filter is reduced.3.Dual-Band Filter Research:A Quarter-Mode Elliptical SIW（QMESIW）with 75%size reduction is proposed by cutting the Elliptical SIW（ESIW）.QMESIW retains the first,fourth,and sixth resonant modes(TM_C010,TM_C210,and TM_S210modes)of the first six resonant modes of ESIW.By etching rectangular and snake DGS at the bottom of the filter to further suppress the middle TM_C210mode,two passbands are excited,with TM_C010and TM_S210modes constituting the two passbands respectively,located in the X-band and Ka-band.By cutting the resonator and adding DGS,the designed dual-band filter suppresses four resonant modes between the passbands,resulting in five transmission zeros outside the passbands,with the characteristics of miniaturization,high selectivity,and wide stopband between the passbands.