Displacement Evaluation by mmWave FMCW Radars: Method and Performance Metrics

The radar interferometry is a technique able to measure the displacement of a target through an electromagnetic signal. Such a possibility can be of interest in different application fields from civil infrastructure monitoring to human vital signals extraction. In recent years, frequency-modulated continuous wave (FMCW) radars have raised huge interest and become popular in the automotive industry, as key sensing elements for detection and tracking in advanced driver assistance systems (ADASs). As they get more widespread and less expensive, it is interesting to study the performance attainable by FMCW automotive radars in measuring the vibration displacement of a target through interferometry. A powerful feature to exploit in these sensors is the multiple-input multiple-output (MIMO), which gives the opportunity to reveal not only the distance or the velocity of a target but also its angle of arrival (AoA). This can be also exploited to measure the displacement of many targets at different angles. In this work, the performance of a mmWave automotive MIMO FMCW radar in estimating the displacement of a vibrating target is experimentally evaluated by comparing the results provided by the radar with a laser Doppler vibrometer. Experiments are performed at different frequency and amplitude values of the target vibration and with different radar configurations. The angle and the distance of the target are changed to obtain a deeper understanding of how these parameters influence the results. The proposed performance evaluation procedure is inspired by ISO 16063–11 used as a reference standard, and the results obtained show that the radar bandwidth does not affect the displacement estimation results, unlike the target range distance and AoA.