Automatic delay and phase mismatch calibration in FMCW MIMO radar

This paper presents a technique for automatically calibrating the delay or phase mismatch between independent virtual antenna elements in frequency modulated continuous wave (FMCW) multiple-input multiple-output (MIMO) radar systems. Calibration takes place exclusively in the digital domain during data processing. The automatic estimation of phase or time offsets is performed with an optimizer that iterates towards the highest possible image contrast. Different metrics for image contrast are investigated, e.g. entropy and variance. No calibration target at a known position is required, the calibration algorithm works as long as there is backscattered signal energy. Also, calibration can be done in real-time, so that changes in phase mismatch can be tracked during operation. The algorithm was tested in simulation and in a practical environment and improves image clarity visibly.