Asynchronous Space-Time-Coding Direct Antenna Modulation-Enabled Automated Beam-Scanning Multi-Target Vital Sign Radar Sensing

This work introduces a new kind of asynchronous space-time-coding (ASTC) direct antenna modulation (DAM)-enabled radar sensor designed for automatic beam-scanning in multi-target vital sign monitoring. Each element of the ASTC array receives a fixed modulation sequence with 2-bit phase ramps and a frequency offset of 8 kHz between adjacent elements, centered at a carrier frequency of 2 GHz. This configuration maintains only the +1st-order harmonic at 2.000008 GHz in the radiation of the ASTC array, facilitating the automatic counterclockwise 1-D half-space beam scanning with a scanning period of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$125~\mu $</tex-math> </inline-formula>s. By isolating data points corresponding to each target within each scanning period and applying Fourier analysis, the vital signs of multiple targets can be precisely differentiated and extracted. The proposed radar system combines automatic scanning with fixed settings and a straightforward structure, making it especially suitable for smart home/healthcare applications.