Research On Cubic Cavity Filter Based On TM₀₁₀ Mode Dielectric Resonator

With the rapid development of mobile communication technology,higher requirements have been put forward for cavity filters as frequency selective devices,which are developing in the direction of miniaturization,high selectivity,low loss,easy tuning and assembly,low cost and so on.Cavity filter plays an important role in many microwave systems,such as communication base station,microwave relay,digital microwave circuit and so on.Studies have shown that the TE_01?mode dielectric resonator has the advantages of low insertion loss and high temperature stability,but the filter volume is still relatively large.In fact,the intrinsic Q of the TM₀₁₀ mode dielectric resonator is not as high as that of the TE_01?mode dielectric resonator,but it also has a high intrinsic Q,which can achieve good insertion loss and very high out-of-band rejection.The TM₀₁₀ mode dielectric resonator has a smaller Dimensions,which can greatly reduce the volume of the TM₀₁₀mode dielectric cavity filter.There is little research on the design of high-performance dielectric cavity filters using TM₀₁₀ mode dielectric resonators.Therefore,in order to miniaturize the dielectric cavity filter,TM₀₁₀ mode dielectric resonators are used and a three-dimensional configuration is adopted.At present,the cavity filters used in civil mobile communication base stations are single-layer structures,and most of the TE_01?mode dielectric filters are used.There are many research papers on multi-cavity filter and the main research context includes those:?1?How to achieve the magnetic coupling or electric coupling through the air openings or probes between side-by-side resonators.?2?How to control the strength of the magnetic coupling or electric coupling by changing the position and size of the openings or the thickness and length of the probes.?3?How to make transmission zeros by setting cross couplings between resonators so as to achieve the high close-to-band rejections.However,so far there is no cavity filter with cube-shaped structure,and the research papers on the cavity filter of mobile communication base stations do not involve the coupling between the upper and lower resonators.We emphasize that,to the best of authors'knowledge,this is the first work that the three-dimensional layout dielectric cavity filter is proposed,studied and designed for practical products.Firstly,the research background and significance of dielectric filters and other microwave filter devices are briefly described,and the current status and development prospects of dielectric filters are analyzed and summarized.Then,the comprehensive theory and topology of the filter are briefly analyzed,and the transmission zeros are introduced through cross-couplings to improve the out-of-band rejections.The field component and resonant frequency of the TM₀₁₀ mode are solved in the form of an analytical solution.At the size of a particular cylindrical cavity,?17²×20 mm³,the loaded Q of pure TM₀₁₀ mode is more than 5000 and that of quasi-TM₀₁₀ mode is more than 8000.Besides,in order to realize the dielectric cavity filter of the three-dimensional layout,we deeply analyze the coupling structure of the adjacent dielectric resonator,and find that it is difficult to achieve electric coupling by air window,so we have proposed a new electric coupling structure,the dielectric window coupling structure,which fills the dielectric in the air window.Finally,the design and fabrication process of TM₀₁₀ mode dielectric cavity filter which can be used for the three-dimensional layout of mobile communication base station is summarized,and the structure of inductive coupling and capacitive coupling between upper and lower resonators is studied,analyzed and designed.The 8-cavity dielectric cavity filter is used as a design example.The simulation and test results verify that the TM₀₁₀ mode dielectric filter can achieve high-band rejection,low insertion loss and small volume.These research conclusions and development experience will provide some reference for related research projects.