Development of analysis techniques for SAW transverse-coupled waveguide resonator filters

This paper describes an effective analysis method for the transverse-coupled SAW filter (TCF), which comprises two adjacent one-port resonators close enough to have useful acoustic coupling. Waveguiding is an essential feature of this device, and here waveguiding is analysed by a novel technique which has the versatility of the well-known stack matrix method but is simpler to apply. To obtain good agreement with experiment, it is found that it is essential to include anisotropy in the waveguide analysis. For each of the two waveguide modes (symmetric, antisymmetric), the device is analysed as if it were a conventional one-port, one-track resonator, using coupled mode (COM) analysis. The resulting admittances are combined to give the device Y-matrix, from which the scattering matrix S is easily found. The parameters required for the COM analysis (velocities etc.) are deduced from plane-wave data given in the literature. Theoretical results agree well with experiment, for 190 MHz devices using ST-cut quartz.