Research On Modeling Of SAW Device And Design Of A Measurement And Impedance Matching System

Surface acoustic wave technology is an emerging technology that involved in the fields of the electronics,the acoustics,the information science and other disciplines.With a series of advantages including the small size,the good frequency selectivity,and the reliable performance,the surface acoustic wave device has been widely used in the military radar,the radio and the television and the communications electronics fields.As the main parts of the surface acoustic wave device,it is beneficial for the design and the analysis of the whole device to research on the IDT.However,for the apodized weighting IDT,there is a lack of comprehensive analysis of the interdigital electrodes in the current modeling,which can not accurately characterize the transmission characteristics of the device.In addition,it will have a big return loss that is caused by the mismatch during the device measurement process.In order to solve these problems,a new delta function modeling scheme for the device with the apodized weighting IDT structure is proposed,and a measurement and matching system with the input and output passive load impedance matching networks is designed for the surface acoustic wave device.In the function modeling scheme,the functional relation between the IDT structure determined by the apodized weighting function and the aperture of the transducer is deduced.The actual impulse response is obtained by using the ? sound sources intensity generated by the different lengths of the interdigital electrodes.The modeling simulation experiments is done by using a surface acoustic wave device with the 128° YX-LiNbO3 as the piezoelectric substrate,the Al material as the electrode,and the apodized weighting structure as the input IDT,the uniform structure output as the output IDT.The experimental results show that the IDT aperture length w,which is determined by a certain apodized weighting function,varies with the coordinate xi of the interdigital electrode.It reaches the longest at the center position of the 49 th interdigital electrode with a value of 2?m.Compared with the actual measurement and the simulation of the surface acoustic wave device frequency response curve,the simulation result is-13.78 dB,and the insertion loss of the original device is-11.89 dB.The measurement and impedance matching system is designed of two modules.One is the measurement module and the other is the impedance matching module.The measurement module can remotely perform the amplitude,phase frequency and Smith characteristic measurements for various types of surface acoustic wave devices.In addition,it can save the images and data results.The impedance matching module can accomplish all the following tasks,extracting the Smith impedance measurement results,completing the normalization calculation,selecting the algorithm path and giving the input and output matching networks and the corresponding circuit device values.Some experiments were carried out on the surface acoustic wave device with a center frequency of 101.764 MHz.Compared with the situation of the input and output ports before suing the passive impedance matching network and after.The experimental results show that the reflection loss values of input and output is-49.36 dB and-34.96 d B under matching state,which are 44.99 dB and 26.27 dB less than that of the mismatching state.