a new phase-locked and self-injection-locked radar sensor with a self-oscillating active-integrated-antenna and a phase-locked-loop demodulator is presented for noncontact vital sign detection. The AIA is developed to simultaneously radiate the radio-frequency signal and receive the scattered-back injection signal, which is phase-modulated by the chest movement of the human subject. According to the injection-locking theory, the oscillation frequency of the AIA will be shifted by injecting a signal with a phase variation, which amounts to the frequency modulation. Hence, the vital sign can be demodulated by a PLL demodulator. The developed radar sensor has been experimentally verified as the human subject is located at the distances of 1.5 m away from the radar sensor.