Study On Design Method And Reliability Of Compact Multi-Frequency Microstrip Filters

As the rapid development of wireless communication technologies in recent years,higher requirements for microwave devices used in wireless communication systems have been raised.In order to satisfy the communication system which may involve multiple communication standards.The multi-band bandpass filter,as a necessary device in wireless communication system,has attracted an increasing research attention.Besides,more and more attention has been also paid to the multi-band bandstop filter,because it can restrain the interference of spectrum signals and therefore improve the anti-interference ability of communication systems.Taking into consideration the application requirements of modern wireless communication systems,this dissertation proposes novel structures of multi-mode resonators through studying their characteristics,so as to achieve the design and development of compact high-performance multi-band bandpass as well as bandstop filters.Moreover,reliability analysis of the multi-band filters operating under complex electromagnetic environment has been conducted through the time domain hybrid method.The main research work of this dissertation is as follows:1.The characteristics of multimode resonators are studied while the design and implementation of compact high-performance multi-band band pass filters are presented.During the design process of multi-band bandpass filters,the topological structures of the filter circuits gradually become complex with the increase of passband numbers.For the sake of good electrical performance of each passband,the number of circuit parameters that need to be adjusted and controlled greatly increases,which leads to the significantly increased design difficulty.Firstly,based on the split-structure multi-mode resonator,a design method of a frequency controllable multi-band bandpass filter is proposed.The multi-frequency design can be implemented separately or in combination by adding symmetric open branches on the single split structure or by coupling the split structure units through the parallel coupled transmission line.While implementing the multiple bands and miniaturization of the filter circuit,the center frequency of each passband is controllable.Then,in order to achieve higher isolation between the passbands,a multi-band bandpass filter design method with high isolation is proposed based on the ?/4 impedance resonator loaded with open-circuit multi-mode resonator.The multi-frequency design of filter circuit is realized by controlling the number of symmetrical branches.Finally,based on the resonator loaded with symmetrical branches,a miniaturized multi-band bandpass filter design is proposed.The multi-frequency design of the filter circuit is realized by the superposition of fundamental resonance and high-order harmonics wave,which helps the reduction of circuit topology complexity.The miniaturization of the circuit is realized with good in-band and out-of-band electrical performances.2.Based on the multi-mode resonator technology,the design of miniaturized multi-band bandstop filter is accomplished.Relatively few controllable modes feature the traditional design ideas and methods of multi-band bandstop filter,which restricts the realization of multi-band bandstop filter circuits.Firstly,based on the symmetric short-circuit branch multi-mode resonator,a design method of a multi-band stopband filter with controllable stopband center frequency is proposed.By increasing the number of stop bands by adding symmetric open branches on the split structure,the multi-frequency design of the bandstop filter circuit is realized,and the center frequency of each stop band is controllable and easy to adjust.Then,in order to achieve higher stopband attenuation,a design method of multi-band stopband filter with high stopband attenuation is proposed based on symmetrical open-branch multi-mode resonator.The multi-frequency design of the filter circuit is realized by controlling the number of stopbands by controlling the number of symmetrical branches.Finally,based on the asymmetric tree-shaped branch multi-mode resonator,a miniaturized multi-band bandstop filter design method is proposed.The multi-band bandstop filters are compact and have good stop-band reflection characteristics.3.An efficient time-domain hybrid method is presented to evaluate the reliability of multi-band filters in complex electromagnetic environment.Multi-band filters are mostly microstrip line structures,which lead to a fact that the tolerant power of these filters is small.The interference signals are inevitably coupled on the transmission lines in communication systems under the excitation of strong electromagnetic interference sources,which should act on the filters to affect their reliability.Therefore,it is necessary to obtain the voltage responses on the input and output ports of the filters to evaluate their reliability.Due to the tiny microstrip structures of multi-band filters,it is difficult to directly model the filters.In this dissertation,an efficient time domain hybrid method is presented to rapidly calculate the responses at the ports of the filters,which can avoid modeling the filter structures directly.Firstly,the parallel FDTD-TL method consisting of the hybrid FDTD and transmission line equations method(called as FDTD-TL method),MPI-based parallel technique and auto mesh generator technique are studied,which can rapidly realize the coupling simulation of transmission lines in the shielding cavity of communication system excited by space electromagnetic fields.Then,the functions of the filters are equivalent by its S parameters to avoid modeling the actual structures of the filters directly.The signal flow graph models of interference signals acting on the filters are established.Based on this,combining with the parallel FDTD-TL method,the efficient time domain hybrid method is studied to fast calculate the voltage responses at the input and output ports of the filters after the interference signals acting on the filters.Then the voltage responses on the input and output ports of the multi-band filters excited by strong electromagnetic pulse sources and broadband electromagnetic signals are simulated and analyzed to evaluate the reliability of the filters in complex electromagnetic environment.To ensure the filters can suppress noise signals and simultaneously improve its reliability in complex electromagnetic environment,it is necessary to apply appropriate limiting devices before the signals are fed into the filters,according to the features of interference signals.