A W-Band Self-Injection-Locked Vital Sign Radar Sensor with On-Chip SIW Monopole Antenna in 0.1-µm GaAs pHEMT

This paper presents a highly sensitive and low-power W-band (75–110 GHz) vital sign radar sensor with an integrated monopole antenna using a 0.1-µm GaAs pHEMT technology. The proposed self-injection-locked (SIL) radar sensor consists of an 85.09-GHz single-transistor oscillator, a 4-dB directional coupler, and a -6.7-dBi substrate-integrated-waveguide (SIW) monopole antenna while consuming only 56 mW from a 2-V supply. The frequency-modulated signal at millimeter-wave (mm-wave) frequency is extracted using the directional coupler and downconverted via an external harmonic mixer to the baseband (1 MHz) for subsequent signal processing and data acquisition. To estimate the detected vital sign signal, a two-step Fourier analysis technique based on non-overlapped Short-Time Fourier Transform (STFT) and Fast Fourier Transform (FFT) is adopted. The experimental results show that the proposed SIL radar sensor can accurately detect vital signs at a distance up to 0.9 m while achieving an excellent agreement with the ground truth.