Millimeter-Wave 3-D Imaging Testbed With MIMO Array

Millimeter wave is widely used in concealed weapon detection for its capability of penetrating clothing, especially in the low-frequency region. Compared with the monostatic modality, multi-input multi-output (MIMO, also termed multi-static) array imaging is characterized by real-time sampling and diversity. In this article, a millimeter-wave imaging testbed in the Ka-band with MIMO array is developed to reconstruct 3-D images. The magnetoelectric (ME) dipole with the dielectric substrate integrated waveguide (SIW) structure is used in antenna design, which is characterized by low transmission loss, convenience for integration, and broad beam radiation in a wide frequency band. A modified MIMO back projection algorithm (BPA) is exploited to achieve high-precision imaging. To accommodate the system, a two-step calibrating approach is proposed using a simple attenuator. As demonstrated with the simulation and experimental results, the proposed calibration method outperforms a state-of-the-art convex-optimization-based one in terms of computational efficiency and image quality, which is assessed with a structural similarity (SSIM) index quantitatively.