Millimetre-Wave FMCW Radar Thickness Measurement Under Environmental Vibration Using Hardware Synchronization and Reference Reflector Compensations

Millimetre-wave FMCW radar enables non-contact, high-precision thickness measurement; however, practical micrometre-level precision is limited by mechanical vibration, local-oscillator (LO) phase noise, and frequency drift. This study quantitatively evaluates these error sources and implements two countermeasures: hardware synchronization using a common LO, clock, and trigger, and differential correction using a reference reflector. Under vertical vibration of 0.1 G at 20 Hz, the synchronized configuration suppressed periodic errors and reduced the standard deviation to 4.2 µm. A three-hour evaluation further showed that an XO configuration with reference-reflector subtraction provided higher long-term stability than a standalone OCXO. These results demonstrate the effectiveness of synchronised architectures with reference compensation in practical vibrational environments.