The Study Of Hinght Performance And Compact Microstrip Multiband Bandpass Filter

In order to improve the communication system capacity and speed, now many communication system work in multiple frequency bands.The usage of multiband bandpass filter in the design of multimode terminal can greatly reduce the volume of the system, which aroused people’s wide attention.This article will study the design of multiband bandpass filter.In this thesis, the research content mainly includes the following aspects:In this thesis, a second order dual-band bandpass filter and a fourth order dual-band bandpass filter is designed using uniform impedance resonator(UIR) and the step impedance resonator(SIR). Firstly, the influence for the existence of transmision zero in the transmission response of the filter by the different feeding ways and the different coupling structure is studied. On the basis of previous study, a two-order dual-band bandpass filter is designed and this filter has a very compact size. There is a transmission zero on both ends of the two passband, greatly improved the suppression outside the passband and the selectivity of frequency response of filter. Then a four order dual-band bandpass filter with very good performance is designed using the CQ type coupling structure.In this thesis, the resonant characteristics of the short-end stub-loaded resonator is discussed in detail, and using the short-end stub load on a uniform impedance resonator central and uncentral in both cases design two dual-band bandpass filter.Based on the studied of the field distribution of two different resonators,we design two dual-band bandpass filter using the well-designed coupling structure. This two filter both have dual passband with controllable bandwidth.Finally, in the thesis, the analyses in detail of the balanced filter design theory and method is presented. Then, a balanced dual-band bandpass filter is designed using the stub-loaded resonator. By using the well-designed feed line, a transmission zero is made both in differential mode response and common mode response of the balanced filter.The existence of the transmission zero optimize the response of both differential mode and common mode response of the balanced filter.