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 f(T)/f(max) 0.1-mu m 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 tenfold decrease in latency while preserving the sensitivity of the radar sensor. The experimental results validate its effectiveness in accurately detecting the vital sign information (RR and HR) from a human target at a distance of 0.9 m while achieving excellent agreement with the ground truth. Finally, the radar sensor consumes only 46 mW from a 2-V supply.