| With the rapid development of communication technology and the increasing number of communication frequency bands in today’s society,the available spectrum resources are becoming increasingly scarce,which leads to more stringent requirements for the performance of microwave filters in communication systems.As one of the most commonly used microwave filters,cavity filters have many advantages such as low insertion loss,high Q value,high power capacity,and flexible topology.They are widely used in radar monitoring,communication base stations,broadcasting and television and other fields,but their size is larger than other types of filters.How to develop a small volume and low cost microwave cavity filter has also become a research hotspot for scholars and researchers at home and abroad.With the improvement of computer performance and the simulation accuracy and efficiency of various simulation software(such as HFSS,ADS),the design cycle of cavity filter has been greatly shortened.The main purpose of this paper is to study the miniaturization scheme of the cavity filter and use the simulation software to design and optimize the cavity filter.The main content of this paper can be summarized as follows:1.A brief analysis of several common transmission matrices of microwave filter two-port network is made,including impedance matrix [Z],admittance matrix [Y],[ABCD] matrix and scattering matrix [S].The synthesis and simplification of the N+2 coupling matrix of the filter are derived in detail and verified by examples.Finally,several commonly used coupling structures between the resonators of the microwave cavity filter are briefly simulated.2.Two commonly used cross-coupling topologies of CT and CQ are analyzed and simulated in detail,and the influence of electrical coupling and magnetic coupling on the position of transmission zero outside the passband is expounds.Then a miniaturized cross-coupled cavity filter is designed to solve the problem of weak anti-jamming ability of traditional L-band middle and low altitude warning radar receiver.HFSS and ADS simulation software are used to simulate and optimize it,and the final processing test is carried out.The insertion loss in the passband(1371MHz-1413MHz)of the cavity filter is less than 0.1d B,and the return loss is below-20 d B.At the same time,due to the introduction of CQ cross-coupling structure,a transmission zero is generated at the low frequency and high frequency outside the passband,which enhances the out-of-band suppression and can meet the requirements of the technical specifications.Compared with the traditional cavity filter,the number of resonators and the volume of the filter are reduced under the same performance.3.Aiming at the problems of large volume and high order of traditional dual-mode dual-passband cavity filter,the odd-mode and even-mode separation in the resonator is realized by increasing the number of metal inner conductors by analogy with the parity mode analysis method of microstrip parallel coupled lines,and on this basis,a miniaturized dual-mode dual-passband cavity filter is designed in HFSS simulation software.From the final simulation results,the center frequencies of the two passbands of the filter are 1.6GHz and 5.6GHz,respectively,the return loss in the passband is less than-20 d B,and the out-of-band suppression is good.Compared with the traditional dual-mode dual-passband cavity filter,the number of resonators is reduced from two to one,which effectively reduces the volume of the filter. |
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