# Adaptive 3D Imaging for Moving Targets Based on a SIMO InISAR Imaging System in 0.2 THz Band
A representative of this scheme is the Terascreen program launched by the Europe Union (EU) in 2013 [10]. This scheme combines the MIMO array with quasi-optical scanning, aiming to get the three-dimensional (3D) image of working passengers in a certain range. Besides, the R&S Corporation developed the Quick Personnel Security Scanner (QPS) system by designing a planner multi-static sparse array [11; 12]. The scanner can achieve the high-quality images of humans with concealed objects in real-time, and has got commercial applications. Although the system can image the moving targets near real-time, the targets are only allowed to move in a pre-defined area. In the second scheme, the inverse synthetic-aperture radar (ISAR) technique is universally adopted [22; 23; 24; 25]. In the reported research so far, high-resolution ISAR images of the moving targets on a turntable are obtained with THz radar systems, where the targets are resolved in the cross-range direction by exploiting the Doppler frequency induced by angular rotation of the targets. The 0.3 THz radar system Miranda300 developed by Fraunhofer Institute for High Frequency Physics and Radar Techniques (FHR) is a representative system of this scheme [23]. The system is able to get millimeter-scale ISAR images of the targets under turntable motion. However, ISAR imaging of targets with translational movement have not been reported by the current systems. Recently, the interferometric technique is applied to the THz ISAR imaging system, for the purpose of acquiring the 3D images of moving targets. Researchers from the National University of Defense Technology (NUDT) developed an interferometric inverse synthetic aperture radar (InISAR) imaging system in the 0.22 THz band [26; 27], and achieved 3D images of targets undergoing turntable rotation or equivalent translational movement. However, the effective FOV is still restricted by the antenna aperture, once the targets move out the FOV, they cannot be imaged continuously. In this paper, a 3D adaptive imaging scheme for non-cooperative moving targets is proposed based on an InISAR system in the 0.2 THz band. With a specially designed single input and multi-output (SIMO) antenna array, the moving targets can be accurately located and tracked using the angle measuring technique based on phase-comparisonmonopulse technique, thus the imaging FOV can be adaptively adjusted as the targets move. With a combined motion compensation method proposed in this paper, focused and coherent ISAR images of the moving targets can be achieved by each receiving channel. Furthermore, since interferometric baselines are formed by different receiving channels, the target size information in the vertical and horizontal directions can be acquired by means of interferometry, which enables 3D imaging of the moving targets. Benefiting from the continuous observation, the system can get the 3D images of the targets in different windows, which provides more information about the dynamic target status. In order to verify the proposed scheme, proof-of-principle experiments were conducted with a SIMO InISAR imaging system in 0.2 THz band. In the experiments, the targets undergo noncooperative motion at a range of 4.5 m from the imaging system. The targets were stably tracked and well-focused images were obtained. The excellent experimental results verified the effectiveness of the proposed imaging scheme and methods, which shows superior performance over the existing THz imaging system. The remainder of the paper is organized as follows. The architecture of the SIMO InISAR imaging system is demonstrated in Section 2. Section 3 introduces the signal model and the target tracking method based on phase-comparison monopulse technique. Section 4 presents the proposed combined motion compensation method and the detailed InISAR imaging procedure. The experimental results are presented in Section 5. Finally, a conclusion is drawn in Section 6.