Detection of vital signs for multiple subjects by using self-injection-locked radar and mutually injection-locked beam scanning array

This study combines self-injection-locked (SIL) radar and ILO-based phased array to conduct non-contact vital sign detection on multiple users. For this purpose, multiple injection-locked oscillators (ILOs) are mutual injection locked to each other at a common frequency. By adjusting the tuning voltages of ILOs, the phase shift among ILOs can be controlled, and therefore the beam scanning of the array can be achieved. Moreover, the signals reflected from the chest of the subjects are injected into the ILOs to enter an SIL state for radar operation. In the experiment, the prototype operating in the 2.4-GHz ISM band is utilized to detect the vital signs of three subjects within two meters at different azimuth angles relative to the array.