Design Of Bandstop Filter Based On Multi-Section Complementary Split-Ring Resonators

With the in-depth development of modern communication technology,the demand for novel filters with miniaturization and integration characteristics is growing rapidly in wireless communication systems.Especially with the popularization of fifthgeneration communication systems,traditional filters have been unable to meet the development requirements of new-generation communication systems due to their complex structure,large size,difficulty in integration and other disadvantages.Therefore,the design of novel filters that can meet the complex requirements of communication standards has become one of the hot research topics in this field.As an important member of microwave filters,bandstop filters play an indispensable role in suppressing harmonics and noise.Complementary split-ring resonator(CSRR)is one of the metamaterials with many special properties that can be used in the miniaturized design of filters.In this paper,a design method of bandstop filter based on multi-section CSRR is proposed to satisfy the applications of communication system.Three bandstop filters with compact structure,easy fabrication,controllable transmission zero frequency and stopband bandwidth are designed and fabricated.The specific work contents are as follows:Firstly,the research background and status of bandstop filter and CSRR are summarized in this paper.The basic theory of transmission line,bandstop filter and CSRR is introduced.The equivalent circuit model and electromagnetic properties of CSRR are analyzed in detail.Then the principle basis and performance advantages of CSRR-based bandstop filter are expounded.Secondly,the structure of splitter/combiner microstrip section loaded with CSRR units is investigated.Transmission line theory and circuit principles are used to analyze its equivalent circuit model,and then the calculation formula of the transmission zero frequency is deduced.Simulation software was used to construct circuit models,and the performance advantages of this structure were identified.The influence of the geometric dimensions of the structure on the transmission zero frequency is discussed Scattering parameters are utilized to extract the lumped circuit parameters of the circuit example.Therefore,the correctness of the equivalent circuit model and the calculation formula of the transmission zero frequency is verified.Finally,a multi-section CSRR based bandstop filter design method is proposed in this paper,and the splitter/combiner microstrip section loaded with CSRR unit is the basic structure of the method.According to this method,three bandstop filters based on2-section,3-section and 4-section CSRRs are designed.Their circuit simulation,EM simulation and lumped circuit parameters are given.Three bandstop filter circuit are fabricated and measured.The measured results show that the three designed bandstop filters have achieved good performance index.As the number of CSRR sections increases,the number of transmission zeros increases,and the fractional bandwidth of the stopband also increases significantly.Four transmission zeros can be found in the stopband of the bandstop filter based on 4-section CSRR,and its fractional bandwidth of 17.7 d B can reach 37.2%.The measured results show favorable agreement with the simulation results,which verifies the correctness and feasibility of the design method.In this paper,three bandstop filters based on multi-section CSRR structure are designed.Therefore,a bandstop filter design scheme that simultaneously meets the requirements of compact structure,easy fabrication,controllable transmission zero frequency and stopband bandwidth is provided,and it is obviously feasible.