Coaxial Cavity Asymmetric Generalized Cut Chebyshev Filter Analysis And Design

With the rapid development of microwave technology, the demands for filters used in microwave communications, microwave navigation, remote control, satellite communications and military electric countermeasures are increasing. In order to cope with the increasing demand for capacity in restricted spectral bandwidths, specifications for filter rejections have tended to become asymmetric. This is especially true for the front-end transmit/receive diplexers in the base stations of mobile communications systems, the rejection of whose outer sides of the Tx and Rx channels tend to be less severe. Asymmetric rejection specifications are best met with asymmetric filtering characteristic, reducing filter degree to a minimum and, therefore, minimizing insertion loss, inband distortions, and mass as compared with the symmetric equivalent achieving the same critical rejection levels.Since the transmission zeros of generalized Chebyshev filters can be placed arbitrarily in the stopband then the selectivity is greatly improved. The TZs can be realized in the complex frequency region rather than real region, hence the calculation, analysis and design are flexible to realize symmetrical and asymmetrical stopband rejection,narrow bandwidth and high rectangular coefficient, it has become widely studied home and overseas。The main purpose of this paper is to research the synthesis and design of generalized Chebyshev filters with asymmetrically located TZs, and gives the design method and process with a coaxial resonant cavity filter form. The main tasks are given as follows:1. Systematically introduce the generalized Chebyshev filtering function with symmetrically and asymmetrically located TZs, including the calculation of TZs, the synthesis of transmission and reflection polynomials, prototype networks and coupling matrices and its reduction.2. Using 3D EM simulation software HFSS, detailedly analyze the effects of the post length, the position and size of coupling slot in a coaxial resonant cavity filter on its resonant frequency and magnetic/electrical couplings.3. According to given specifications, provide some symmetrical and asymmetric coaxial cavity generalized Chebyshev filters, and present the corresponding simulation and testing results.This dissertation present the study of generalized Chebyshev filter with asymmetrically located TZs, and realize it in the synthesis and design of coaxial resonant filters. The test of the product designed according to the theoretical method is consistent with the simulation result and satisfies the specification requirement, which approves the program design and simulation.