An accurate design and modeling tool for the design of RF SAW filters

The main work for the SAW RF designer is to improve the filter performances and especially the insertion loss which has to be very low in the entire bandwidth, meaning that the control of the passband shape has to be very precise, Due to the proximity of SSBW when using LSAW, it is well known that standard P-matrix or COM models do not accurately predict the performance. The other difficulty is the 3D effects that could have a major impact on performances, especially when using ladder type filters. The third effect is the impact of electrical stray elements which can no longer be neglected. Our model can be separated in different parts. The acoustical model is used to analyze resonators or transducers. For this purpose, one possibility is to characterize test devices. We prefer to base our design directly on theoretical results. One way is to use the periodic FEM/BEM model to extract physical parameters describing the propagation of the wave and to use these parameters in a phenomenological model similar to COM or P matrix. This approach is well suited to periodic or almost periodic structures, as for example the resonators inside a ladder filter