A Near-Field Motion Detection Technique Based on a Resonant Magnetic Probe

This letter proposes a near-field motion detection technique based on a resonant magnetic-field probe. The resonant magnetic-field probe consists of a parallel metal plate and a quarter-wave impedance transformer to make the input impedance 50 Ω. The 5.8-GHz radio frequency (RF) front-end is designed, which consists of a hybrid coupler and the proposed resonant magnetic-field probe that can be regarded as a full duplex antenna. Then, a 5.8-GHz continuous-wave Doppler radar transceiver is designed and integrated with the RF front-end to build the near-field radar system. The equivalent circuit of the RF front-end while detecting the targets in near-field is analyzed, in which the probe loop and the matching circuitry are modeled as a parallel RLC circuit and the coupler and transmission lines are equivalent to a lossy transmission line and an attenuator. The experimental results demonstrate that the proposed system can detect submillimeter displacement motions in the near-field.