Synthesis Technology Of Microwave Filter

Microwave filter is the absolutely necessarily components of modern microwave relay communication system, microwave satellite communications system, information countermeasure system, etc. It is also the most important and most techno-content microwave passive components, its performance always directly affect the quality of system.In this paper, synthsis theory and realization method of microwave filter are comprehensive studied. Generalized Chebyshev and generalized Butterworth function that introduce finite position transmission zeros are investigated. In addition, quasi-elliptic function with enhanced stop-band rejection performance is obtained. The rational polynomial expressions of these filtering functions are derived. The fully canonical"N +2"coupling matrix of filter is synthesized by using the rational polynomial expressions of filtering function and microwave network parameters. Three coupling matrixes configurations (folded configuration, parallel-connected tow-port network configuration and"cul-de-sac"configuration) are gotten that can be realized by different similarity transform methods. Predistortion technology is utilized for improvement of filters performance. The loss of practical structure of filters is compensated by moving the positions of transmission poles. The aim of reducing filter size by using low quality factor cavities to realize equivalent response of filter that composed with high quality factor cavities is achieved.Finally, several microwave filters that respectively adopt different filtering functions and coupling configurations are designed. Predistortion technology applied to one of them and the performance improvement is observed. The correctness and feasibility of the theory are validated by the simulated results.