Synthesis And Design Of Microwave Filters

The development of modern communication's technology requires microwave filters have better frequency selectivity, such as in-band insertion as low as possible, band rejection as steep as possible,pass-band phase characteristic more nearly in the linear and so on. Filters with the transfer function of generalized Chebyshev function have the advantages of elliptic function filters and Chebyshev function filters which can satisfy the requirement. In order to improve the performances of the filter while not increasing the size of the filter, the cross-coupled filter introduces finite transmission zeros. Thus filters with transfer function of General Chebyshev function are widely used in communication networks.In this thesis, a comprehensive study on the generalized Chebyshev filter's theory and design is made. Firstly, based on the corresponding equivalent circuit model, the characteristic function of the network can be gotten, and the corresponding admittance function can be calculated. And then, according to the admittance function and the generalized Chebyshev function, the normalized coupling matrix can be achieved. Secondly, the location of the generalized Chebyshev function filter's transmission zeros can be determined based on the relationship of the filter's transmission zeros and poles. At the same time, in this thesis synthesis on the cross-coupling matrix is extracted, and then coupling-matrix reduction is practical in the line with similarity transformation to make sure that the topologies can be realized. After that, method, which can be verified by specific design examples,is given to extracted coupling coefficient from the actual microwave circuit. Finally, the process of the cross-coupled filter is given and in order to verify the feasibility of the theory, a 4-pole cavity filter and a SIW filter are simulated and invested by EM software.