2-D Self-Injection-Locked Doppler Radar for Locating Multiple People and Monitoring Their Vital Signs

This article presents the combination of a self-injection-locked (SIL) radar with frequency-modulated continuous-wave (FMCW) and switched phased-array (SPA) techniques to locate multiple people and detect their vital signs with high resolution and high sensitivity. The proposed system utilizes a subharmonic upconverter/downconverter with a 1.675-2.175-GHz chirp local oscillator (LO) signal to convert between a 2.45-GHz SIL IF signal and a 5.8-6.8-GHz FMCW RF signal. It transmits the FMCW RF signal and receives the echo signal using a transmit (Tx) antenna and a switched receive (Rx) antenna array, respectively, and processes the SIL IF signal to produce a range-azimuth map (RAM) that displays the positions of all people, their respiration rates (RRs), and their heart rates (HRs) in the monitoring region. The key advantage of combining the FMCW and SPA techniques is the provision of higher spatial resolution than obtained using each technique alone. This article also proposes a Doppler-weighted RAM to improve the identifiability of the images that are generated by two persons close to each other. Finally, the presented system was experimentally validated by measuring the locations and vital signs of up to five seated persons at a range of more than 1.5 m, of which two persons were seated almost shoulder by shoulder.