Band-stop Filter Design Method

As the Microwave band-stop filters have been extensively used in telecommunication and broadcast systems, to suppress the spurious outputs from a high power transmitter and harmonic pass-bands from a nonlinear power amplifier or a band-pass filter. Using exactly the same coupling topologies that have been used in band-pass filters to design band-stop filters are possible, and extracting equivalent circuit parameters for filters in a wide variety of coupling topologies becomes the key of designing filters.In this thesis, the main research contents are the principle of band-stop filters, the synthesis of the rational polynomials for scattering parameters, combining Genetic Algorithm with Downhill simplex Algorithm to extract equivalent circuit parameters for filters. Selectivity duplexer is designed with band-stop filters with coaxial cavity structures. The main tasks are listed as follows:1. The synthesis of the rational polynomials for scattering parameters. With the given requirement to realize, the numbers and positions of the transmission/reflection zeros are presented. The synthesis of the rational polynomials for scattering parameters is described for the recursive technique and power conservation law. Combining equivalent circuit of narrow-band coupled-resonator filter and the define of scattering parameters of a two-port network, scattering parameters are presented in terms of coupling coefficients.2. The optimization algorithm to extract equivalent circuit parameters. Based on the given topology of the circuit and the numbers and positions of the transmission/reflection zeros, in this paper we combine Genetic Algorithm with Downhill simplex Algorithm to provide a novel flexible and effective method to extract equivalent circuit parameters for General Chebyshev filter, which MATLAB is utilized to implement. What is more, we show the physical meaning of each normalized coupling coefficient and its engineering coefficient transformation formula.3. The change in the band-pass and band-stop filters. Comparing the band-pass and band-stop responses, the method of transformation is presented. The synthesis of cross-coupled band reject filters with non-resonating nodes and their characters are described.4. The Sensitivity Analysis and compare in a wide variety of topologies. Based on the expressions for the sensitivity of coupled resonator filters with respect to the entries of the coupling matrix and the MATLAB, we compare the sensitivity in a wide variety of topologies, so that the proper topology can be cheese and manufacturing tolerance can be reduced.5. A process design of a selectivity duplexer. The duplexer is implemented with coaxial cavity band-stop filters, the practicality of the duplexer is verified by analysis the measured results, the technique for the improvement with non-resonating nodes filters is proposed.