Using the phase change of a reflected microwave to detect a human subject behind a barrier

In a pulsed radar system, the amplitude and sign of the echo from a particular target will depend on the phase of the echo signal relative to that of the local oscillator signal. If the wavelength of the radar signal is very short, the phase of the echo can change greatly if the target moves even slightly. Based on this physical behavior, the pulsed radar system can serve as a life-detection system to detect a human subject's movements, which include breathing and heartbeat. In this paper, a pulsed microwave life-detection system was developed from a pulsed training radar system to successfully detect the presence of human subjects behind a simulated earthquake rubble wall. The sampled echo signals from the background noise, a dummy, and a female human subject are presented directly in the time domain without being transferred into the frequency domain, differentiating this work from recent works by other authors. Furthermore, we also demonstrate several superiorities of a pulsed system over and above the original continuous-wave approach with the experimental results.