Accurate 3-D Microwave Near-Field Imaging of Typical Concave Objects

High-resolution microwave and millimeter-wave (MMW) detection and recognition are often plagued with artifacts when facing complex objects with concave structures due to the ignorance of high-order scattering propagation. Previous works have demonstrated the effectiveness of accurate near-field reconstruction by considering multiple reflections reconstruction in planar dihedral structures. In this letter, we extend the proposed imaging model to three-dimensional (3-D) imaging scenario. Based on the shooting and bouncing ray (SBR) concept, we first analyze the mechanism of multiple scattering and establish a 3-D forward model. Utilizing circularly polarized measurements, each number of reflection times (RTs) echo can be separated. Also, by calculating and compensating for the multiple reflection propagation paths, the accurate 3-D reconstruction of dihedrals is realized. Numerical simulations and experiments show that the proposed method can obtain the high resolution in the z-axis and effectively restore the pattern of reflectivity distribution on the target surface.