A Ray-Tracing-Based Synthetic Imaging Technique for Nonfocal Region of Real-Aperture Imaging Systems

This article proposes a novel synthetic imaging technique for the nonfocal region of millimeter-wave real-aperture imaging systems. It is based on ray tracing and uses the backprojection algorithm (BPA) for imaging. First, an equivalent model of the echo signal is established, where the target rotates around the rotation center. Second, ray-tracing records the trajectories of the electromagnetic (EM) waves through a single-side hyperbolic cylindrical lens and the interpolation is utilized to obtain the round-trip history of uniform grids in the nonfocal region. Finally, BPA is performed for the target reconstruction. The detailed steps for calculating the round-trip history are given for both 2-D and 3-D cases. In the 3-D case, this technique uses multiple 2-D interpolations instead of direct 3-D interpolations to speed up the computation. The experimental results of the acquired data showed that the proposed method extended the imaging depth of the real-aperture system.