The Research And Design Of Interdigital Filters And Duplexers With Cross-Coupled

Generalized Chebyshev filter and duplexer are kinds of microwave passivecomponents which have been widely used in communication systems, especially thecross-coupled filter which can generate transmission zeroes.At the very beginning, this paper introduces readers the basic theory of generalizedChebyshev filter, through which I synthesize the initial coupling matrix，then eliminatethe unwanted coupling elements by using matrix similarity transformation theory. Afterthat this paper would do the analysis of how to transform basic wheel topology into CT,CQ structure along with specific examples and the reduction steps.Next, I write a program about the basic theory of generalized Chebyshev filter byusing MATLAB. The program can calculate the coupling coefficient and the groupdelay, which will simplify and accelerate the design of the filters.Then, I improve the form of physical implementation by doing some research onthe CT topology，after that a new topology structure—inline CT structure—is obtained.The filters using the inline CT structure have the same size as the common Chebyshevfilters, while they have the high out-of-side rejection as the generalized Chebyshevfilters. The design in this paper uses not only inline CT structures, but also strongcoupling structures. After solving the ‘fixed’ problem of the coupling structure, thefilters get a high rectangular coefficient. At last, a duplexer in which two pass bands areclose is designed by matching the two filters with a common interface.To verify whether the technical indicators and parameters would be met, I willmake a comparison between simulation results and the actual results by testing after theprocessing, testing and debugging to the duplexer. The debugging to the MATLABprogram proves that the data of the coupling coefficient and group delay is important tothe design of the General Chebyshev filter.