Accurate Microwave Near-Field Imaging of Deep Concave Objects Using a Sequential High-Order Scattering Reconstruction Algorithm

In microwave and millimeter-wave imaging, artifacts caused by high-order scattering from concave structures can significantly affect the reconstruction accuracy, target detection, and recognition. Previous studies have demonstrated the effectiveness of the accurate near-field reconstruction by considering multiple reflections in typical concave targets. However, these studies primarily focus on shallow concave structures and lack effective approaches for deep structures. Compared with shallow concave structures, backscattering from deep concave structures is primarily caused by multiple reflections and involves a more intricate propagation process, posing significant challenges for imaging such structures. To address these problems, this article starts with the analysis of rectangular deep concave structures. Based on the principle of geometrical and physical optics, the propagation characteristics of multiple reflections in rectangular deep concave structures are formulated, and the forward propagation and backward imaging models are established. In this article, a sequential high-order scattering reconstruction algorithm is proposed. The algorithm makes specific phase compensation for wave components undergoing different reflection times to gradually recover into the deeper parts of the concave structure. And the targets with varied scattering strengths can be accurately reconstructed through successive iterations of reflection times. Extensive simulation and experimental results are performed to verify the effectiveness and practicability of the proposed algorithm.