Journal Paper

Bio-Radar (BR) systems measure physiological activity by using the micro-Doppler effect to detect signal reflections from the human body. The quality of the received signal is influenced by several factors, most notably the Radar Cross Section (RCS) of the subject, which becomes especially complex in close-proximity conditions. To optimize BR system performance, this paper investigates the radio channel propagation in short-range conditions, focusing on RCS variations at close distances. The study was conducted using a Continuous-Wave (CW) radar system operating at 5.8 GHz, with measurements taken in an anechoic chamber. Ten human subjects with varying characteristics were analyzed. The findings demonstrate that RCS fluctuates with distance, exhibiting oscillatory behavior at short-range distances, with values ranging between −45 dBsm and −20 dBsm. They also reveal a correlation between RCS measurements and the extraction of vital signs, identifying specific conditions under which vital sign detection is significantly compromised. Additionally, the data indicate that male subjects tend to have higher RCS values than female subjects.