Synthesis Design Of Novel Microwave Commensurate-line Filter

Recently,with the rapid development of satellite communication and radar technology,the traditional filters cannot meet the corresponding needs.They have put forward higher requirements for the filter performance,such as reducing the filter volume,boosting the frequency selectivity,alleviating the linear distortion when the signal passes through the filter,and improving the group delay.The commensurate-line filter has the characteristics of small size,easy integration and so on,and its components have the same electrical length.When designing,it can fully refer to the existing lumped prototype filter results.When producing,it has low cost,short cycle,high reliability.Because of these advantages,the commensurate-line filter has been widely concerned by researchers at home and abroad.This paper is mainly aimed at improving the in-band performance of the commensurate-line filter,and the main contributions are summarized as follows:1.Introducing a synthesis design method which the filter can achieve the flattest group delay when ensuring the equal-ripple response in magnitude.The method is applied to three bandpass filters based on Schiffman structure successfully,making them have the equal-ripple response in magnitude and the flattest group delay response at the same time.The results show that it can improve performance of filters effectively and verify the validity of this method;2.Three bandpass filters based on series open stub are studied.By introducing series open stub,the sideband frequency selectivity of the filter is improved when the equal-ripple response in magnitude is satisfied.And by combining the series open stub with the Schiffman structure,the sideband frequency selectivity of the filter is also improved when the equal-ripple response in magnitude and the flattest group delay response are satisfied;3.A dual-band bandpass filter based on open and short stub is studied.The stopband bandwidth between two passband can be changed by moving the center frequency of the first passband.By analysis and derivation,some equivalent structure transformations and corresponding equivalent formula transformations are given.