Synthesis And Design Of Extracted Pole Filters

With the rapid development of modern wireless communication techniques in recent years, the spectrum resource is becoming more and more precious and crowded. Available frequency intervals assigned to various types of communication systems become narrow, which result in a high requirement of filter performance. It means that the filters, especially for those used in communication base station duplexers and multiplexers, must have high attenuation out of band, besides the common requirement of small size, high selectivity and low insertion loss.To have a high attenuation out of band, the common method is to increase the number of transmission zeros at finite position. We usually generate a transmission zero by introducing a cross-coupling between two nonadjacent resonators for a General Chebyshev filter. However, on some high power conditions or at high frequency, capacitive cross-coupling is difficult to realize, the coupling coefficient is negative, such as the cross-coupling in the highpass filter of duplexer. To avoid this disadvantage of cross-coupling, we may use a rejection resonator to realize a transmission zero. The rejection resonator is also called pole cavity as its resonate frequency is just at the position of the transmission zero. The resonators of rejection-resonator filter is inline combined, and its transmission zero is only controlled by rejection resonator and coupling structure, so the design is very flexible.The purpose of this paper is to present extracted pole techniques of General Chebyshev filters, providing the fast and efficient design methods for this kind of dielectric waveguide filters and duplexers. The main works are described as follows:1. The synthesis of the cross-coupling General Chebyshev filters. This process is started from the synthesis of characteristic polynomials of the filters, and then ended with the transformations of coupling matrix.2. The research of extracted pole techniques of rejection-resonator filters. Two methods are used to extract the equivalent circuit parameters, the first is by means of transmission matrix, and another use the method of input and output admittance.3. A dielectric waveguide duplexer using rejection resonator is designed based on extracted pole techniques, and two kinds of waveguide-coaxial connectors are proposed. Then the method to design filters using Y matrix and group delay is also presented.4. Two software based on MATLAB are wrote to synthesize rejection-resonator filters, one of them uses the synthesis theory and another is based on optimization theory. They are proved to be helpful in engineering applications.