The concept of radar imaging based on orbital angular momentum (OAM) modulation, which has the ability of azimuthal resolution without relative motion, has recently been proposed. We investigate this imaging technique further in greater detail. We first analyze the principle of the technique, accounting for its resolving ability physically. The phase and intensity distributions of the OAM-carrying fields produced by phased uniform circular array antenna, which have significant effects on the imaging results, are investigated. The imaging model shows that the received signal has the form of inverse discrete Fourier transform with the use of OAM and frequency diversities. The two-dimensional Fourier transform is employed to reconstruct the target images in the case of large and small elevation angles. Due to the peculiar phase and intensity characteristics, the small elevation is more suitable for practical application than the large one. The minimum elevation angle is then obtained given the array parameters. The imaging capability is analyzed by means of the point spread function. All results are verified through numerical simulations. The proposed staring imaging technique can achieve extremely high azimuthal resolution with the use of plentiful OAM modes.
Electromagnetic (EM) vortex carrying Orbital Angular Momentum (OAM) has received more attention recently due to infinite degree of information modulation and unique methods of information acquisition. This paper clarified multi- OAM generation method and introduced a novel radar imaging theory to improve azimuthal resolution by utilizing abundant OAM modes. Subsequently radiated characteristics were analyzed with EM software simulation and numerical simulation to evaluate the potential of EM vortex imaging. The results show that phase distribution and OAM purity in main lobe can satisfy imaging performance. Incoherent pattern direction problem and side lobe energy depressing can be solved by adjusting the radius of concentric uniform circular array.
This paper reports the experimental results of radar imaging using radio waves carrying orbital angular momentum (OAM) for the first time. The phased uniform circular array is employed to generate radio waves carrying various OAM modes. The echoes of all modes are measured sequentially in time by a single antenna. The phase distributions of several modes are measured through near-field measurement system. The azimuthal profiles of single and double corner reflectors are reconstructed by Fourier technique and the azimuth resolution is analyzed. Imaging results verify the ability of azimuth resolution without relative motion using OAM modulation.
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