A discrete one component wave model and its application to SAW resonator filters

A one component acoustic bulk wave model is presented for the description of SAW devices using plane waves or waveguide modes. No equivalent circuit components are used, and the calculations always remain on the level of acoustic waves. As fundamental elements the transfer matrix and the source vector of one electrode region are derived. Using these elements, the particle displacements in an array consisting of striplike electrodes can be calculated as a function of all single capacitor voltages taking into account the boundary conditions including the amplitudes of foreign waves meeting the array. After determining the waveguide mode velocities and profiles the model is applied to transversely coupled waveguide resonator filters resulting in the admittance matrix which is needed to calculate the filter insertion loss. Two filter examples are investigated, and a sufficiently good agreement of the theoretical and experimental results is found. The resonance splitting due to cascading of two (or more) single resonator filters can be increased by a coupling inductor yielding a smaller insertion loss under matched conditions at a given bandwidth.<
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