Differential delay line on X-cut LiTaO3

The authors describe the design of a differential delay line on the X-cut of LiTaO₃, which gives a better temperature stability than other substrates commonly used for broadband SAW (surface acoustic wave) filters. The analysis of the device transfer function is described, taking into account the asymmetric slowness curve used in the compensation of second-order effects. The agreement of design and measurement is better than ±0.1 dB in magnitude and ±1° in the phase within the filter passband. Stop-band suppression was better than -55 dB with an inline configuration and was not degraded by bulk modes. The surface velocity on the free surface was determined using group delay measurements of the differential delay, allowing a better estimate of the group delay for future designs