Displacement Monitoring Using a Four-Channel Phase- and Quadrature Self-Injection-Locked (PQSIL) Radar with Channel Compression Demodulation (CCD) for Sensitivity Improvement

This study proposed a channel compression demodulation (CCD) for a 2.4-GHz four-channel phase- and quadrature self-injection-locked radar system for improving its detection sensitivity. The CCD can demodulate and recover the Doppler phase for tiny displacement without requiring a trajectory fitting method for the accurate DC offset calibration, thus improving the sensitivity of the radar. Moreover, it is not susceptible to clutter owing to the channel compression technique. Simulations were conducted for displacements from λ/128 to λ/32 under different signal-to-noise ratios to evaluate the phase recovery performance of the CCD. Furthermore, the results were verified by performing experiments on an actuator or a subject with static metal plates around the target. The demodulated results for the actuator, placed 1 m away from the radar, has a root-mean-square error of 3.2%, and the proposed CCD successfully detected the chest motion and vital sign of a subject seated at a distance of 3 m.