A Compact Digital Low-IF Dual-PLL Doppler Radar for Remote Vital Sign Detection

In this paper, a compact digital 1ow-IF Doppler radar using two phase-locked loops (PLLs) is proposed to remotely detect vital sign signal of the human subject. The system operates at 2. 41GHz with -6.5dBm transmitting power. By feeding the two PLLs with the same reference signal and configuring them to operate at different frequencies, a l-kHz low- IF signal can be achieved without quadrature mixer involved in the system and the intermediate frequency (IF) signal is directly sampled and processed in the digital domain. Phase coherence of the two PLL output signals has been testified and after that, the vital sign movement of the subject is measured and compared with a pulse oximeter reference. The measured result well agrees with the reference signal at a detection distance of 1.8 m.