A Low-Power Low-Latency 84.5-GHz GaAs pHEMT Self-Injection-Locked Radar with Integrated Frequency Differentiator for Vital Sign Detection

A low-power high-sensitivity W-band vital sign radar sensor implemented in a 160/240-GHz fT /fmax 0.1-μm GaAs pHEMT technology is presented. Based on the self-injection-locked (SIL) architecture, the radar sensor consists of an 84.5-GHz single-transistor oscillator, a directional coupler, an integrated frequency differentiator, and a substrate-integrated waveguide (SIW) monopole antenna. With the proposed integrated first-order mm-wave differentiator, the data post-processing time is significantly accelerated, allowing a ten-fold decrease in latency while preserving the sensitivity of the radar sensor. The experimental results validate its effectiveness in accurately detecting vital sign information (RR and HR) from the human target at a distance of 0.9 m while achieving excellent agreement with the ground truth. Finally, the radar consumes only 46 mW from a 2-V supply.