Highly Selective Quasi-elliptic Function Filters

Microwave filter is applied in Radar, Navigation, Electronic-war, Satellite communication and Mobile communication. The resource of frequency becomes more and more crowded. All of this demands filter with critical electrical performance such as low insertion loss, greater skirt selectivity, minimization of cubage and high power-capacity. Quasi-elliptic function filter has the character that the transmission zero (TZ) can be placed in anywhere in imaginary axis, thus it can gain excellent performance. This filter is focused on by scholars in inland and abroad. The design method can be also applied in all kinds of transmission-line filter and in all kinds of filter made by different material such as LTCC. It can be used the frequency range from RF to millimeter-wave.The aim of this paper is to study the generalized chebychev transfer function and the synthesis of coupling matrix and is to give the design method .The main works are as follows:1. Introduces the basic theory on quasi-elliptic function filter including general theory on microwave filter,some topology, the relation between phase and TZ, coupling.2. Describes the procedure of the synthesis of the passive network.3. Describes the design of the quasi-elliptic function filter. First locates the TZ according the design goal by optimization. Then configures the transfer and reflection function polynomials. Three methods are used: One is to use the method of Darlinton, the second is to use the method of partial fraction expansion, the third is to use optimization.Gets the physical size between resonator by HFSS softerware.Locating the I/O coupling by Qe.Gives some design examples including Ku Band 6 poles coaxial chebychev filter, S Band 4 poles Quadruplet coaxia filters S Band 3 poles Ttriplets coaxial filter, and S Band 10 poles one zero coaxial filter.