The Design Of High Frequency Bandpass Filter Based On Surface Acoustic Wave Resonator In The Communication System

The SAW filter (Surface Acoustics Wave Filter, SAWF) is widely used in the navigation,television intermediate frequency range and communication system for its repeatability, massproducibility and high performance. With the development of mobile communication system,the SAW filter is required to have better performance, such as miniaturization, lower insertionloss and better square ratio.In this paper, we designed a band-pass filter with1.95GHz based on Ladder-Type filter.Firstly, the thesis introduced the basic characteristics of Surface Acoustics Wave and theprinciple of IDT (Inter-digital Transducer). Then we investigated the three kinds of IDT moduleand analysis the second order effect. The widely used transverse SAWF is discussed andanalysis the frequency response theoretically, theory and the simulation result are in agreement.The one port resonator and two port resonator is introduced. The paper analysis their workprinciple and equivalent circuit, and deduced the ladder-type filter frequency response.According to the design target, we study the influence of the resonator’s capacitance ratio, thecascade number N, adding shunt capacitance to the input and adding series capacitance to theparallel branch. We add designated capacitance and inductance based on five order ladder-typefilter structure. The result showed that the pass-band is more stable and the transition band issteeper and the final frequency response meets the design requirements.