Adjustable Saw Filter Simulation And Simulation

Based on the application value of frequency Tunable Surface-Acoustic-Wave Filter (TSF), the configuration of electrical TSF, surperconduct film control TSF and filter banks TSF were analyzed. Comparing with multi-IDT input TSF, which is simple in structure, practical in daily application and little size in volumn, electrical TSF is difficult in technics and complex in structure, superconduct film control TSF is not practical in daily application, and filter bank TSF is large in volumn. It is obvious that multi-IDT input TSF had great potencial in pratical using.Multi-IDT input TSF is placed on a plane in parallel plumb to the propagation direction of SAW. In this confuguration, IDTs are used efficientlly through selecting different IDT as input or output port. The volumn is reduced greatly than traditional filter bank TSF and the frequency adjustment is flexible.In order to model and simulate multi-IDT input TSF, this dissertation began with the caculation of acoustic wave's velocity in piezoelectrical materials. After analyzing the transmission matrics of material parameters, coding relevant coodinates transform routine, material constants of 128°Y rotated X propagating LiNbO3 were caculated, and the velocity of bulk sheer wave in the same direction of 128°Y rotated X propagating surface acoustic wave was achieved, which would provide great convenience to the simulation of multi-IDT input TSF in later charpter. Method of solving effective permittivity was also discussed, approximation equation solution cited from some literature was adopted to caculate the approximation of the simulating parameter ? ? ? ?. Considered that there were IDTs hadn't been used between the input and output port, frequency dispersion characteristics in periodic metal grating was analyzed and thus, the influence of unused IDTs had been caculated approximately. In the process of simulating multi-IDT input TSF, by comparing with different factors influencing the insertion loss(IL), interdigital electral pairs were found playing a key role. Simulation results showed that, frequency of multi-IDT input TSF was sensitive to the change of electrical pair numbers. For instance, electrical pairs, whose width were 5um and 6um respectively, could have their frequency tunabled from 163MHz to 203MHz million hertz by million hertz, while their electrical pairs number avriable from 1 to 20 respectively. Thinking of the properties mentioned above, this dissertation provide an idea that central frequency might be changed by using multi-electric-pairs configuration, and also sum up a few basic design rules. Multi-electric-pairs input/output structure could avoid the shortages of unused IDTs as it was in multi-IDT input configuration, hence, it could be caculated accurately by using models at hand, such as delta function model, which would greatly reduce the difficulties in designing.