Stability of phase shift on quartz SAW devices

New results involving two types of phase variation on surface acoustic wave (SAW) are discussed. It has been observed that short period fluctuations occur in SAW delay lines fabricated on ST-cut quartz; these fluctuations are the dominant source of close-to-carrier FM noise in SAW controlled oscillators. Since the SAW device itself is the source of the noise, a modified expression for calculating the FM noise power spectrum is presented. On a longer time scale, the temperature dependence of the SAW velocity is the dominant source of variations in the phase shift. A theoretical capability for calculating the first-order and second-order temperature coefficients has been developed, and these calculations support the experimental results on the doubly rotated cut of Hauden et al. (1978). A comparison between theory and experiment is presented for 14 different cuts and/or propagation directions.