A novel Doppler-based phase unwrapping algorithm for mmWave MIMO radars and its application to displacement estimation in structural health monitoring

In this manuscript, the problem of estimating dynamic structural displacements through mmWave multiple-input multiple-output frequency modulated continuous wave radars is investigated. These devices allow to potentially achieve high accuracy in the measurement of radial displacements. However, in the presence of moving targets, their resolution is affected by the phase wrapping phenomenon; this occurs when, in the time interval separating consecutive measurements, the target to be tracked moves by more than a quarter of the radar wavelength. To mitigate this problem, a novel iterative method for performing phase unwrapping on the basis of estimated Doppler information is developed. Our experimental results evidence that the proposed method can be exploited to faithfully reconstruct the phase trajectory associated with specific points of quickly moving objects and, consequently, to carefully estimate their radial displacement also in those scenarios where traditional techniques are bound to fail, at the price of a small computational complexity.