Analysis of surface acoustic wave grating waveguides considering velocity dispersion caused by reflectivity

Conventional surface acoustic wave (SAW) grating waveguide analyses ignore the changes in phase velocity in the grating region. In reality, velocity dispersion is caused by the reflectivity of finger electrodes, and phase velocity changes near the stop band. In this paper, a new approximate analytical model of a SAW grating waveguide is proposed. This model considers the dispersion of phase velocity, by placing a wave number along waveguide of a transverse mode in such a way that it becomes a solution of the coupling-of-modes (COM) theory. The results of the new model differ from those of conventional analyses. The frequency characteristics of 2-port resonators on 36.5°Y-X quartz and 45°X-Z Li2B4O7 are measured. Calculations using this new model show good agreement with measurements in terms of resonance frequencies and response levels, while those using conventional analyses vary largely. The adequacy of this model is confirmed by the experimental results.