Analysis of obliquely propagating SAWs in periodic arrays of metal strips

In many surface acoustic wave (SAW) filters, the diffraction of the surface wave occurring in the interdigital transducers (IDTs) is as important as the diffraction on the free surface. The accurate simulation of diffraction effects requires knowledge of the slowness curves for waves propagating in the IDTs. The transducer is modeled as a periodic array of massless, infinitely long metal strips. The task is the determination of the phase velocity of the straight crested wave, which propagates with an arbitrary propagation angle in this array. The method of solution employed is valid for all frequencies, including the stopbands, and allows the determination of stopband frequencies for obliquely propagating waves. The substrate material is characterized by the numerically computed effective permittivity. Examples of slowness diagrams as well as dispersion diagrams are presented. The results of SAW device simulations using models for the SAW slowness curves are compared with each other and with measurements