Generation of Orbital Angular Momentum Beams for Electromagnetic Vortex Imaging

The vortex electromagnetic (EM) wave, which carries orbital angular momentum (OAM), may provide extra rotational degree of freedom and can potentially be exploited in microwave staring imaging. Based on the concentric uniform circular array, the generation method of OAM beams for the EM vortex imaging is studied. The array radius and excitation signal for each ring are carefully designed to ensure that the main lobes of beams with different topological charges can simultaneously illuminate the area where the target may exist. Subsequently, the imaging model based on the linear frequency modulation signal is established. The fast Fourier transform (FFT) and other spectrum estimation methods are applied to obtain the cross-range profile of the target. Results demonstrate that the algorithms of power spectrum density estimation based on autoregressive model can achieve much higher resolution than the FFT method. Moreover, the imaging performance of the proposed method is robust against the noise influence. The work and results can benefit the development of remote sensing as well as the research on microwave staring imaging.