A Novel Calibration-Free Motion Sensing TechniqueWith Single-Channel Interferometric Radars

Radar interferometry is widely used for detecting versatile displacement motions. The conventional techniques for motion extraction depend on the quadrature
$I/ Q$
signals, and the proper calibration of the
$I/ Q$
signals is a necessary step to ensure accurate motion detection. However, the calibration process and the
$I/ Q$
architecture inevitably add up to the system complexity. In this article, a novel single-channel-based phase demodulation (ScPD) technique is proposed to reconstruct the precise phase information of the displacement motions, which not only employs only one single receiver channel but also eliminates the
$I/ Q$
signals calibration. In addition, the proposed technique is immune to the phase ambiguity issue. To detect versatile motions with both regular and irregular patterns, approaches including envelope unwrapping, null point rejection, and outlier elimination are proposed and integrated to increase the robustness of the proposed technique. Both simulation and experiments were carried out to validate the proposed technique. The experimental results show that the proposed ScPD technique can obtain both periodic and irregular motions with high accuracy of a root mean square error (RMSE) of 0.011 mm and strong robustness to low signal-to-noise ratio (SNR) and
$I/ Q$
mismatch with an RMSE of 0.015 mm. Moreover, the proposed technique is superior in detecting subtle motions, e.g., 3-
$\mu \text{m}$
displacement motion with an RMSE of 0.43
$\mu \text{m}$
.