Orbital-Angular-Momentum-Based ISAR Imaging at Terahertz Frequencies

The electromagnetic (EM) wave carrying orbital angular momentum (OAM) is usually named vortex EM wave, which has been found great potential to improve the target imaging performance. For conventional ISAR imaging, only 2-D target image can be obtained. In this paper, the OAM-based ISAR technique is developed to achieve 3-D target image with high resolution at terahertz frequencies. First, the imaging model is derived, and the point spread function is analyzed. Subsequently, two imaging algorithms, namely the FFT-based imaging method and the imaging method based on convolution backprojection and power spectrum density estimation, are proposed. Simulation results validate the effectiveness of the proposed methods and indicate that the high-resolution cross-range profile can still be obtained at terahertz frequencies with small rotational angle. This paper can provide a novel manner to realize 3-D imaging of universal targets with high resolution.