Design Of High Frequency Ladder Type Surface Acoustic Wave Bandpass Filter

The study of surface acoustic wave theory first began in 1885,when British physicist John Reilly wrote an academic paper entitled "Waves propagating along the smooth surface of an elastic body".With the development of fundamental research on surface acoustic wave,various powerful surface acoustic wave devices have been designed,developed and manufactured.Among them,the most fully researched and widely applied technology belongs to the surface acoustic wave filters.Compared with other filtering technologies,the surface acoustic wave filter has low loss,small size,light weight,high power resistance,good temperature stability,and is suitable for mass production.Therefore,it has gradually become an important research and development hotspot in the field of global electronic communication technology.Globally,annual surface acoustic wave filters production is several billion pieces,and this market demand may continue in the future.So it is of great significance to the research and application of the surface acoustic wave filter.This paper introduces the research background,research history and development trend of surface acoustic wave filter at home and abroad,and expounds the basic principle of surface acoustic wave bandpass filter,as well as its advantages compared with the traditional filters.Based on the RLC equivalent circuit model of one port surface acoustic wave resonator,a ladder type surface acoustic wave bandpass filter with a center frequency of 2GHz is designed and applied to the receiving end of communication equipment.Firstly,the structural parameters of the one port surface acoustic wave resonator were determined by means of the electromagnetic simulation software ADS and the finite element analysis software COMSOL.Then type out the one-port resonator with the electrode width of 450 nm,and S parameter of the resonator type out successfully was measured on the built test platform.After that the RLC equivalent circuit parameters of the resonator were extracted based on the measured S parameters through a series of data processing,and the extracted equivalent circuit parameters were verified.The results show that the RLC equivalent circuit model can approximately represent the electrical characteristics of the resonator near the resonant frequency,which further verifies the applicability of the RLC equivalent circuit model.Finally,with the extracted resonator parameters,the simulation analysis of the ladder type surface acousticwave bandpass filter is carried out again.The results show that the extracted equivalent circuit parameters of the resonator can be used to simulate the desired bandpass filter.The center frequency of the filter is 2GHz,the minimum insertion loss is 2d B within the range of 50 MHz bandwidth,and the out-of-band suppression is more than 25 d B.