The Study Of Multi-Band Tunable Cavity Filter And Diplexer

With the development of wireless communication,spectrum resources are becoming scarce.From the first generation communication system to the latest fourth generation communication system and even the fifth generation communication system in the near future,the competition for spectrum resources will be more intense and the spectrum utilization will also extend from centimeter to millimeter wave.Nowadays,2G,3G and 4G are deployed on the base stations of each communication operator simultaneously,and 5G will be deployed in the future,a higher requirement for RF front-end devices.This requires antennas,filters,or duplexers to serve multiple communication systems at the same time,which can greatly reduce the volume of RF devices,improve the utilization ratio of RF devices,and reduce costs.In this paper,a single-cavity multi-band tunable filters and duplexer are proposed,which are well adapted to the above needs of development.This paper mainly consists of the following three parts.I.A single-cavity dual-band and tri-band tunable filters are proposed.Cavity resonators use the classic coaxial cavity resonator.Due to the loading-capacity effect exist between the open end of metallic post and the bottom of the cavity,changing the coaxial metallic post can change the value of the loading capacitance,so as to control the resonant frequency of the cavity resonator.In the design of second order cavity filter,in order to control the coupling coefficient between the two modes,a movable coaxial metallic post is adopted.And the electromagnetic coupling transmission zeros are created by discarding the intermediate coupling wall and improves the performance of filters.The L-typed magnetic coupling feed structure is used as input/output ports to achieve adjustable frequency and multi-band performance.II.A third order single/dual-band cavity filters are proposed.In order to achieve better filtering performance,a third order tunable filters are designed.Each passband consists of three coaxial metallic posts,which can control the resonant frequency and coupling coefficient of each passband.Finally,the third order single/dual-band tunable filters are designed which have shaper passbands than second order filters.III.A quadruple-band tunable cavity duplexer is proposed.The duplexer consists of two second order dual-band filter with four passbands,each passband consists of two coaxial metallic posts to control the resonant frequency and coupling coefficient of the passband.Input port use a one-four branch short circuit structure,to match the adjustable quad-band passband.For the passbands can work better independently,add a wall in the middle of the two cavities to increase the isolation of the duplexer.