A comparison of temperature performance of SAW filters made on ST and LST-cut quartz

The authors built several narrowband SAW (surface acoustic wave) bandpass filters centered at 200, 250, and 740 MHz on several orientations of LST-cut quartz. Devices were also made on ST-cut quartz for direct comparison. The authors report the performance of these devices with emphasis on temperature stability of frequency, transmission phase, and insertion loss. The LST-cut of quartz demonstrates superior frequency and phase stability over a wide temperature range when compared with the ST-cut devices. It is also demonstrated that the quasilongitudinal plate modes of LST-cut SAW filters are more attenuated than those of the ST-cut devices. The LST-cut is also a singly-rotated T-cut with X-propagation; hence the energy power flow angle on the XZ plane remains zero for all temperatures. LST-cut devices exhibit a greater increase in insertion loss as temperature rises as comprised to the ST-cut devices