  Millimeter-wave radars are being increasingly integrated into commercial
vehicles to support advanced driver-assistance system features. A key
shortcoming for present-day vehicular radar imaging is poor azimuth resolution
(for side-looking operation) due to the form factor limits on antenna size and
placement. In this paper, we propose a solution via a new multiple-input and
multiple-output synthetic aperture radar (MIMO-SAR) imaging technique, that
applies coherent SAR principles to vehicular MIMO radar to improve the
side-view (angular) resolution. The proposed 2-stage hierarchical MIMO-SAR
processing workflow drastically reduces the computation load while preserving
image resolution. To enable coherent processing over the synthetic aperture, we
integrate a radar odometry algorithm that estimates the trajectory of
ego-radar. The MIMO-SAR algorithm is validated by both simulations and real
experiment data collected by a vehicle-mounted radar platform.
