Demonstration of 3-D Security Imaging at 24 GHz With a 1-D Sparse MIMO Array

A 3-D security imaging experiment at 24 GHz is demonstrated with a 1-D sparse multi-input multi-output (MIMO) array. The MIMO array is an 8 transmission/16 reception arc array to achieve real-aperture imaging along the vertical dimension. It is time-switching multiplexed with a low-cost frequency modulated continuous wave transceiver working at 22-26 GHz. A calibration procedure is proposed to calibrate the channel imbalance across the MIMO array. The experiment is conducted on humans moving on a cart, where we take advantage of the linear motion of humans to form inverse synthetic aperture along the horizontal dimension. To track the motion of humans, a 3-D depth camera is used as an auxiliary sensor to capture the rough position of the target to aid synthetic aperture radar imaging. The back-projection imaging algorithm is implemented on a graphics processing unit for quasi-real-time operations. Finally, experiments are conducted with a real human with concealed objects and a preliminary automatic object detection algorithm based on convolutional neural networks is developed and evaluated on real data.