Noise and Sensitivity of Harmonic Radar Architecture for Remote Sensing and Detection of Vital Signs

This paper addresses noise and sensitivity issues in remote sensing and detection of vital signs based on a continuous wave biomedical radar operating at multiple harmonic carrier frequencies or channels. This Doppler radar makes use of a single mixer, taking advantage of the inherent nonlinearity and harmonic characteristics of the mixer. Other system building elements such as antennas, amplifiers, and circulators can also operate at and comply with multiple harmonic frequencies or channels requirements, which makes the system compact. Noise is one of the most important factors that affect the sensitivity of this type of system. The total noise is the combined contribution of thermal noise, residual phase noise, and flicker noise. Flicker noise is found to be the critical parameter for the baseband detection. Experimental results show that with the use of the harmonic radar technique, the flicker noise can be reduced by 20 dB around 1-Hz baseband frequency compared with the counterpart in a conventional radar operating at single frequency. The noise and sensitivity of a harmonic radar system operating at 12 and 24 GHz for vital signs detection are studied theoretically and experimentally. It is proven that the harmonic radar solution is able to increase detection sensitivity by increasing the signal-to-noise ratio. The performance of the harmonic radar is tested experimentally with a moving plate and also a real patient. For the heartbeat detection, an oximeter giving the oxygen saturation of blood and heart rate is used as the reference.