Generalized Cut Poles Extracted Chebyshev Filter Synthesis And Design

With the rapid development of modern microwave communication techniques, the spectrum is becoming more and more precious and crowded. The requirements for microwave filters with high selectivity, low loss, small size and low cost are increasing, which promotes the deeper research for the microwave filters.The generalised Chebyshev approximation provides a filter with equiripple passband amplitude characteristics but with arbitrarily placed attenuation poles(APs) in the stopband. Extraction technique of APs based on generalised Chebyshev function was studied by many researchers in the eighties of last century. But it is not widely used because of the weak precision, hard tuning and long design period of traditional equivalent circuit method.Nowadays, with the improvement of computer technique of microwave CAD, the precision and efficiency of the high frequency simulation soft is raising highly. We can associate the equivalent circuit method with the soft of high frequency simulation to improve the characteristics and shorten the design period.The purpose of this paper is to present extracted pole techniques based on generalised Chebyshev function, providing the fast and precise design methods for microwave bandpass filters. The main works are described as follows:1. Transfer function polynomial and reflection function polynomial of generalised Chebyshev are generated by attenuation poles, and then the synthesis of coupling matrix based on the theory of passive networks.2. A general and direct synthesis technique of inline filters with arbitrarily placed attenuation poles at real frequencies is presented, the nonresonating nodes(NRNs) are introduced in models to eliminate some of their inherent limitations.3. Some examples of bandpass filters are given using the synthesized coupling matrix and HFSS, including cross coupled and direct coupled. Theoretical results are compared with measurement to demonstrate the validity of the presented theory.