Frequency-Dependent Vortex Electromagnetic Wave Imaging

Vortex electromagnetic (EM) wave radars provide a promising solution to forward-looking imaging with high azimuth resolution, while the previous systems require multiple radar pulses or complex hardware to transmit vortex EM waves carrying different orbital angular momentum (OAM) modes. To address this problem, a frequency-dependent vortex EM wave imaging method is proposed in this paper, in which frequency-dependent OAM modes carried by a single radar pulse are generated by a simple structure consisting of time delay units and a uniform circular array (UCA). In the receiver, an image construction method is proposed to address the frequency and OAM mode coupling, enabling fast imaging from a single radar pulse echo. A theoretical model is established, and numerical simulation is conducted to investigate the properties of frequency-dependent vortex EM waves and verify their feasibility for 2-D forward-looking imaging. The proposed method provides important technical support for efficient vortex EM wave imaging radars.