Delay Dependence of Phase Noise in SAW Filters

Measurements of phase noise in a number of lithium niobate and ST-quartz delay lines have been performed. Our observations indicate that noise in these devices is produced in the transducer region as well as in the delay path. Linear and quadratic models for the delay dependence are proposed and compared to the experimental data. With the present data we are unable to differentiate between these models. The use of an acoustic absorber on the ends of the device is shown to reduce phase noise between -5 dBc/Hz and -10 dBc/Hz. We suggest that any acoustic scattering process, from the saw cut at the end of the device or from crystal imperfections in the delay path, may contribute to the total device noise.