Small-scale displacement measurement with passive harmonic RF tag using Doppler radar

Measurement accuracy of the displacement from human cardiopulmonary activities has potential in predicting physiological information for the purpose of biomedical remote sensing and non-contact monitoring. In this paper, an RF frequency doubling tag was used for detecting small displacement with high accuracy. A heterodyne and a homodyne quadrature radar receiving systems were used to detect small scale tag motion and non-tagged motion from a distance, respectively. Arctangent demodulation algorithm and imbalance compensation technique were applied to the raw radar data for displacement estimation. Simulation and experimental results were compared, indicating that by using the frequency doubling tag, a better accuracy can be achieved for small displacement estimation with Doppler radar.