Enhanced Resolution Method for Electromagnetic Vortex Imaging Based on Electromagnetic Information Theory

The electromagnetic vortex imaging possesses independent orbital angular momentum (OAM) with orthogonal degrees of freedom (DoFs), which implies the existence of enhanced information capacity. However, high-mode OAM beams have stringent generation conditions and inefficient information carrying capacity, which results in limited resolution. This article proposes a method to combine the electromagnetic information theory (EIT) with the traditional electromagnetic vortex imaging technique, which allows that one may obtain more target azimuth information. The DoF, as the main component of information, has been increased to achieve higher azimuth resolution. First, the propagation and imaging model for the electromagnetic vortex with statistical characteristics is constructed. Second, an initial phase modulation method is provided to improve the azimuth resolution by designing the emission of OAM beams. Then, considering that the electromagnetic vortex radar echo is a complex number, a mutual information maximization algorithm suitable for the electromagnetic signals with gradient enhancement is proposed to increase the imaging DoF and obtain super-resolution azimuth reconstruction of the target. Simulation results show that in comparison with the traditional electromagnetic vortex imaging, the proposed OAM imaging method with enhanced DoF is able to achieve superior azimuth resolution performance within the same mode range. Furthermore, this work will be used to the EIT application in OAM-carrying radar imaging and the development of high-resolution imaging technology.