  A 3D ISAR security imaging experiment at 24GHz is demonstrated with a sparse
MIMO array. The MIMO array is an 8Tx/16Rx linear array to achieve real-aperture
imaging along the vertical dimension. It is time-switching multiplexed with a
low-cost FMCW transceiver working at 22GHz-26GHz. A calibration procedure is
proposed to calibrate the channel imbalance across the MIMO array. The
experiment is conducted on human moving on a cart, where we take advantage of
the linear motion of human to form inverse synthetic aperture along the
horizontal dimension. To track the motion of human, a 3D depth camera is used
as an auxiliary sensor to capture the rough position of target to aid ISAR
imaging. The back projection imaging algorithm is implemented on GPU for
quasi-real-time operation. Finally, experiments are conducted with real human
with concealed objects and a preliminary automatic object recognition algorithm
based on convolutional neural networks are developed and evaluated on real
data.
