SAW propagation and reflections in transducers behaving as waveguides in the sense of supporting bound and leaky modes

The design of narrowband SAW filters involves the calculation of SAW propagation in transducers which are long compared to the square of their apertures, all in wavelengths. Due to different short-circuit conditions and mechanical loading in the transducer finger region and the busbars, a transducer behaves as a waveguide in the sense of supporting possible bound modes and leaky modes. We present a method for calculating diffraction with waveguidance (including both possible bound modes and leaky modes) of both forward and backward propagating SAWs which are coupled by reflections inside the transducers. Diffraction with waveguidance is simulated by dividing the transducers into tracks (across the transducers' apertures). By allowing for a direct acoustic coupling between these tracks, we simulate diffraction with waveguidance by a coupling theory.