f/nf harmonic radar system with optimal detection of vital signs

In this work, a continuous-wave radar system for vital signs detection is proposed and demonstrated. The radar operates at both 12 GHz and 24 GHz (first harmonic) within the same transceiver, in order to improve the system accuracy. This harmonics-diversity system is designed with multi-band (dual-band in this case) or wideband components (mixer, coupler, etc.), then providing a very compact and efficient radar architecture. It is shown that the use of an adequate phase shift between both signals (12 and 24 GHz) in this case suppresses all the null points, a well-known problem in bio-medical Doppler radar. These null points appear at specific distances where the power output of the mixer in the receiver is almost zero. The phase shift enhances the sensitivity of the system without increasing significantly its complexity. Theoretical and experimental results are presented to validate the analysis and the proposed concept.