See-Through-Wall (STW) Life Detector Using Self-Injection-Locked (SIL) Technology

This study presents a see-through-wall (STW) life detector using self-injection-locked (SIL) technology. The SIL radar is operated at 433 MHz ISM band to achieve excellent penetration capability and coverage. Moreover, an additional phase shifter is utilized to eliminate the large frequency shift, which is caused by strong clutter signals and often causes the SIL mechanism to fail. The output signal of the SIL oscillator (SILO) passes sequentially through a quintupler, an amplifier, and a 2165 MHz injection-locked oscillator (ILO) to increase the frequency modulation bandwidth and output power. The Doppler information is then extracted using an IQ delay discriminator. Experimental results indicate that the prototype provides an accurate respiration signal of the subject behind a 35-cm-thick concrete wall in 108 cases, comprising 9 positions × 4 facing directions × 3 postures.