Analysis of SAW grating waveguides using 2-D coupling-of-modes equations

In surface acoustic wave (SAW) periodic structures, the phase velocity in the grating region has a velocity dispersion caused by the periodic perturbation. Therefore, a grating waveguide with a finite width needs to be analyzed considering the frequency dependence. In this paper, the paraxial two-dimensional coupling-of-modes equations (2-D COM equations) presented by Haus and Wang (1978) are extended to take into account substrate anisotropy, propagation loss, and electrical terminals. A distributed-parameter equivalent circuit for each guided mode is derived from the solution of the 2-D COM equations and some electrical transmission responses calculated using this circuit are compared with measured results.