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 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, a phase-locked loop 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 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. The experimental results show that all the measured results with different displacements have a root-mean-square error smaller than 1%. In addition, the PQSIL radar can detect the frequency and displacement of the cardiopulmonary activities of the subject.