Low-IF Doppler Radar Using Delay- and Self-Injection-Locking Technology with Clutter Cancellation for Biomedical Monitoring

This paper presents a low-IF Doppler radar that can measure the displacement of a moving target with high sensitivity and high linearity. The radar consists of an RF front-end, an IF transceiver, and a digital delay- and self-injection-locking (DSIL) block, operating at a fixed RF and IF frequency of 5.8 GHz and 40 kHz, respectively, and can function well in a highly cluttered environment with the help of an IF clutter canceller. In the performance test experiments, the radar can identify the vibration frequency of a stationary and constant-velocity object with a minimum peak-to-peak displacement of 40 and 100 μm, respectively. Moreover, it can successfully detect the vital signs of a human subject moving at a roughly constant velocity toward its antennas.