Research And Design Of A Tuned Filter At X-band

The method of the equivalent circuit being analysed first,as a conventional method of designing the filter, makes use of a low-pass prototype filter as a basis. A filter using only inductances or only capacitances is realized by "K"(impedance) or "J"(admittance) inverters.Then through the frequency transformer,the objective character is realized.The structure values of the discontinuities are obtained mostly from tabulations,graphs or program calculations. Using this method,the engineer can resolve complicated electromagnetic issues only by simple calculations to get a satisfactory filter.But it also has the disadvantage of low accuracy and is difficult to keep the consistency.As to the X-band tunable filter in this paper, we must analyse the E_Plane capacitor and the H_plane inductance discontinuities.We do many works as follows:Spatial complex variables and conformal mapping function were presented to analyze in detail the capacitive post in rectangular waveguide. The reflection coefficient and transmission coefficient, from which the parameters of T shape equivalent circuit of full-height capacitive post in rectangular waveguide can be received, are calculated. The partial height capacitive post is also analyzed mainly by microwave software and some valuable data gained. All these directly guides the design of the X-band tunable rectangular waveguide filter in the range of7800—8500MHz.The basic principle of mode-matching method is discussed.The field and the modes in equal column waveguide system are analysed.The modes of the dual-port network discontinuity are analysed by introducing the conception of nomoralized power,then the common expression of the general scattering matrix is deduced.A special coefficient structure is raised based on the academic value of S21.Thus the practical structure of the X-band tunable filter is gained, keeping the absolute bandpass and the filter character invariable in the tunable range, low insert loss and high rejectiong realized.According to the applications,the X-band tunable filter is designed and realized, applying the3D simulation software,for example HFSS,CST etc, for the simulation and the latter optimization.The X-band filter has been applied in the practical project.The results of simulation and measurement are given out.