Displacement Monitoring Using Phase- and Quadrature Self-Injection-Locked (PQSIL) Radar

This study proposes a system that deploys a phase-and quadrature self-injection-locked (PQSIL) radar to recover the Doppler phase shifts caused by the relative motion between a subject and the radar. Specifically, this architecture contains an SIL oscillator (SILO), a phase-locked loop (PLL) circuit to cancel the frequency shift caused by the SIL mechanism, and a phase shifter that repeatedly provides a 0- and 90-degree phase delay for the injection signal. As a consequence, the electromagnetic interference (EMI) and nonlinear distortion effects can be resolved to recover the Doppler phase. Particularly, for a 2.4 GHz PQSIL radar system, displacement monitoring experiments for a moving metal plate are conducted from a maximum displacement of 10 to 125 mm, which is equivalent to 0.08 λ to 1 λ, respectively. The experimental results show that all the measured results with different displacements have a root-mean-square error (RMSE) smaller than 1%. In addition, the PQSIL radar can also successfully detect the frequency and displacement of the chest movement caused by the cardiopulmonary activities of the subject.