Synthetic Aperture Radar Interferometry Based on Vortex Electromagnetic Waves

The vortex electromagnetic (EM) wave carrying orbital angular momentum (OAM) offers a new degree of freedom for synthetic aperture radar (SAR) imaging. Because vortex EM waves have helical wavefronts, the vortex EM wave-based SAR echo contains the three-dimensional (3D) information of the target. In this paper, an OAM-based synthetic aperture radar interferometry (InSAR) technique is proposed to obtain 3D target information accurately without the existence of baseline. First, a vortex EM waves' SAR imaging model is established, and an improved range-Doppler algorithm is proposed correspondingly. Subsequently, the scheme of the OAM-based InSAR without the physical baseline is proposed. Compared with the conventional InSAR, the OAM-based InSAR can avoid the baseline decorrelation and reduce the requirement of the platform. Besides, the processing procedure of the OAM-based InSAR is simplified, which avoids the image registration and the interferogram flattening. The simulation results demonstrate the effectiveness of the proposed technique. Besides, the height estimation accuracy of the OAM-based InSAR was analyzed, in terms of interferometric phase error and OAM mode error. The height estimation accuracy can be improved by increasing the OAM mode difference appropriately. The OAM, which is completely independent of time, frequency, and polarization, offers a new scheme for the InSAR.