Displacement monitoring system based on a quadrature self-injection-locked radar technology

This paper presents a quadrature self-injection-locked (SIL) radar to detect the displacement of a moving target. Owing to the quadrature phase-switching architecture and corresponding digital signal processing techniques, this proposed system is capable of achieving excellent detection sensitivity and determining the target's Doppler phase shift without being affected by nonlinear distortion caused by the SIL phenomenon. In the experiment, a metal plate is driven by a laptop-controlled linear stage, and a 2.4-GHz ISM-band prototype is placed 1.25 m away from the target to detect its motion. As a result, the measured error is less than 3 mm for the moving plate with a peak-to-peak displacement up to 5 cm.