Higher harmonic surface transverse wave filters

The operation of SAW (surface acoustic waves) filters at high spatial harmonics was investigated theoretically and experimentally. Transducers with constant geometric period were chosen for reasons of manufacturability and predictability of electrical characteristics. An analytical method was used to calculate the transducers' relative coupling coefficient. Bulk-wave conversion losses, which are very important for higher-harmonic and STW (surface transverse wave) resonator design considerations, were calculated with two different techniques, a perturbation model and an antenna model. The results show very good agreement with measurements. Various transducer types were realized using the STW on AT-cut quartz, which has higher propagation velocity and lower bulk-wave conversion loss than the Rayleigh wave. A highly developed standard photolithographic process was used for the reproducible fabrication of delay lines with center frequencies up to 2.78 GHz, Q values of 3400 at 2.65 GHz, and an unmatched insertion loss of 15 dB at 2.49 GHz.<
>