Research And Design Of Negative Group Delay Controllable Filter

With the rapid development of radio frequency microwave communication technology,the problem of signal distortion caused by group delay in communication systems needs to be effectively solved.The negative group delay filter has attracted more and more attention because of its special group delay characteristics.However,most of the current research on negative group delay filters is limited to the circuit structure level,and there is a lack of more complete design theory.The research on the controllability of negative group delay is more scarce,which greatly limits the further development of negative group delay filters.Based on the synthesis method of ideal lossless filters,this dissertation analyzes the synthesis of ideal filter characteristic polynomials and its group delay characteristics,and obtains the important conclusion that loss is a necessary condition to achieve negative group delay,which lays a foundation for studying the design theory of negative group delay filter.At the same time,the coupling matrix theory is researched and organized to establish the conditions for the physical realization of the filter.Based on the above theoretical research,this dissertation proposes a new design method for negative group delay filters.First of all,according to the necessary conditions to realize negative group delay,the realization conditions of negative group delay with characteristic polynomials are proposed.Then,through recursive algorithm and minimum order condition,the synthesis of negative group delay characteristic polynomial and the synthesis of coupling matrix are realized.At the same time,the relationship between the negative group delay and the amplitude is analyzed,and the conversion relationship between the negative group delay in the low-pass domain and the band-pass domain is studied.This design method realizes the controllability of negative group delay in design theory,and can design various filters that meet the requirements of different negative group delays.Based on the new design method of negative group delay filter proposed in this dissertation,a third-order negative group delay filter with a specified negative group delay response is designed.The designed filter uses a half-wavelength open-circuit microstrip resonator,lossy cross-coupling uses a quarter-wavelength microstrip line loaded resistor structure,and improves the loss characteristics by adding input / output matching circuits.After physical production and testing,the simulation and test results are in good agreement.Compared with similar research results,this filter has a larger negative group delay and better return loss.In order to study the controllability of each performance index of the negative group delay filter on the circuit structure,this dissertation proposes a transmission-type reconfigurable negative group delay filter.The designed reconfigurable filter consists of two cascaded resonant units in reverse cascade.The center frequency and negative group delay of the filter are controlled by loading varactor diodes and PIN diodes,and the return loss is improved by matching circuits,simulation and theoretical analysis results are in good agreement.