Monopulse Electromagnetic Vortex Imaging Method by Multiplexing OAM Modes Based on Frequency Diversity

In recent years, electromagnetic (EM) vortex imaging has emerged as a novel technique in the field of radar super-resolution imaging. This approach fundamentally differs from conventional methods by the relative lateral motion between the target and the platform. Although super-resolution azimuthal imaging can be achieved, different orbital angular momentum (OAM) modes should be modulated in different signal pulses. In contrast, a new OAM modulation and monopulse imaging method is proposed in this article, which involves multiplexing OAM modes based on frequency diversity in one pulse and can considerably improve imaging efficiency. By introducing tiny frequency offsets among the elements of a uniform circular frequency diverse array (UC-FDA), the OAM multiplexing beams are generated. Subsequently, the EM vortex imaging model for the coherent UC-FDA is established, and the imaging method is proposed. The theoretical performance analyses of spatial azimuthal resolution and efficiency are derived. Finally, the results demonstrate that the proposed method exhibits comparable imaging performance to the conventional EM vortex imaging method, even when only a single pulse is transmitted.