Improved Microwave Resonator Measurements using Pound-Drever-Hall Sensing

We use the Pound-Drever-Hall (PDH) method to measure the center frequency of a microwave Surface Acoustic Wave (SAW) resonator. We show the advantages of the PDH approach relative to a standard Phase-Locked Loop (PLL) technique. We find that PDH is insensitive to phase error and exhibits a reduced Allan deviation of the center frequency measurement, in each case by up to an order of magnitude.  The method rejects frequency noise and drift from spurious sources. For more on the SAW device, see Ref. [1].  Easy PDH implementation is enabled by a modern digital lock-in amplifier.  Our study demonstrates the enhancements possible with PDH-based measurements. These enhancements can be realized in a wide range of resonator-based devices, not only at microwave frequencies but at lower frequencies as well. 

[1] Pranaya Rath et al., Pound–Drever–Hall-Based Spectroscopy of Multi-Mode Surface Acoustic Wave Resonators, APS Global Physics Summit 2026.