Frequency-Offset Self-Injection-Locked (FOSIL) Radar for Noncontact Vital Sign Monitoring

This paper presents a novel frequency-offset self-injection-locked (FOSIL) radar that uses up/down-mixers to combine two self-injection-locked (SIL) radars. By properly adjusting the injection phases and amplitudes, the transmit frequency of the proposed architecture is held constant, and the electromagnetic interference (EMI) issue associated with a conventional SIL radar is thus resolved, allowing multiple wireless devices to coexist within a limited bandwidth. Also, the Doppler sensitivity is improved by the up-converted transmit frequency of the radar. In the experiments, a 5.8 GHz ISM-band FOSIL prototype that was composed of 2.8 and 3.0 GHz SIL radars was used to detect a moving metal plate and a seated subject. The theoretical predictions and measurements were in good agreement.