Study Of Microwave Band-pass Filter

With the development of modern communication technologies, the Electromagnetic spectrum is limited and has to be shared; filters are used to select or confine the RF/microwave signals within assigned spectral limits. Filters play important roles in many RF/microwave applications. They are used to separate or combine different frequencies. Emerging applications such as wireless communications continue to challenge RF/microwave filters with ever more stringent requirements—higher performance, smaller size, lighter weight, and lower cost.In this paper, based on the method of generalized Chebyshev synthesis, a cavity band-pass filter is studied and designed in order to satisfy the WCDMA mobile system demands. Generalized Chebyshev filter realize the finite-frequency transmission zeros, by adding transmission zero point in stop-band arbitrarily, the characteristic of out-of band is improved and the filter have the similar function with the elliptic functions filters. The main works of this paper is following:Band-pass filter is studies based upon the generalized Chebyshev filter synthesis principle: Through recursions technique, the transfer and reflection function polynomials and coupling matrix is constructed with a return-loss level and prescribed zeros, and detailed deducing of formulations is given in this paper.Several common forms of cavity filter are introduced, and the coaxial rectangle cavity structure is chosen to meet the design requirements of the filter. With given prescribed zeros and return-loss level, an example is presented in which the calculated results agree well with the available results and the synthesized process is validated.Based on the generalized Chebyshev theory, a sixth-degree coaxial rectangle band-pass filter applied in WCDMA communication is designed and simulated by commercial software - HFSS. The experiment results show that the characteristics given by network analysis satisfy the designed requirement. The feasibility of formulation deducing and programming are further verified.Lots of tuning works must be done in filter design and the procedure is also described in the papers.