Pulse-Doppler Self-Injection-Locked (PDSIL) Radar for Noncontact Vital Sign Monitoring

This paper, for the first time, integrates self-injection-locked technology into a pulse-Doppler radar to simultaneously detect target range and Doppler information under extremely low equivalent isotropic radiated power. The radar adopts a single-step frequency architecture, where up/down mixers and pulse-modulated signals transmit RF pulses. Thereafter, the received echoes are fed back into the oscillator to form a self-injection-locked loop. This configuration enhances Doppler sensitivity and reduces the required output power. The output of a noncoherent pulse frequency discriminator was processed using the proposed signal-processing flow, allowing the frequency shifts from different targets to be distinctly identified. Consequently, the range-resolution limitation of pulse radars was overcome, achieving a 64% improvement. The experiments across multiple subjects demonstrated average cardiopulmonary measurement errors of approximately 1.7% and average range errors below 3 cm.