Research Of Filtering Network Based On Surface Acoustic Wave Resonator

In the face of the trend of miniaturization and integration of mobile communication systems,Surface Acoustic Wave(SAW)filters have become the mainstream solution for RF filters due to their advantages such as small size,low loss,and high frequency selectivity.In the design process of SAW filters,the design of the resonator topology network is critical to achieving the filtering response.Therefore,based on the resonator unit of SAW,this thesis conducted research on the design of filtering topology network,with three main research contents and contributions as follows:1.According to the traditional filter synthesis theory,a comprehensive method for designing a surface acoustic wave ladder topology network has been developed.Firstly,based on the equivalent deformation structure of the SAW resonator’s electrical model,a serial coupling topology network is proposed,and the generalized Chebyshev filter function is used to extract the parameters of the proposed structure.Finally,the resonator parameters of the bandpass filter response are obtained through frequency substitution.Subsequently,a lumped element extension method is proposed to optimize the inconsistent problem of the electromechanical coupling coefficient in the comprehensive extraction of the resonator,and to optimize the electromechanical coupling coefficient within the achievable range of the preparation process without changing the network filtering response.The proposed ladder topology comprehensive method and electromechanical coupling coefficient optimization technology can quickly solve the BVD model parameters required for the target response,and have good practical engineering value.2.A multi-transmission zero notch filter structure based on SAW resonators is designed.On the basis of the series-coupled stopband network,the parallel resonant unit and the impedance transformer are equivalently transformed into the electrical model of the SAW resonator through the component merger method.This stopband structure can fully utilize the resonant characteristics of the resonator to provide transmission zeros for the stopband.A six-order dual-zero stopband filter and a four-order quadruple-zero stopband filter are designed in this thesis to demonstrate the good scalability and stopband synthesis characteristics of the proposed stopband structure.3.The design method of SAW absorptive filters is studied.First,based on the design idea of complementary dual-port structure,a single-port absorptive filter is designed by coupling the bandpass path and the bandstop path.Then,based on the odd-even mode theory of symmetric networks,a dual-port absorptive filter is designed by replacing the resonant unit with a SAW resonator on the basis of the lumped structure with no reflection characteristics,and optimizing its resonant characteristics by loading lumped elements.The simulation and measurement results of the above two absorptive filters are consistent,which proves that the proposed circuit structures have good absorption characteristics in the stopband.Through the above research,this thesis provides new design methods and research ideas for the design of filtering topology networks based on SAW resonators.