CUCA Based Equivalent Fractional Order OAM Mode for Electromagnetic Vortex Imaging

Abstract

An equivalent fractional order orbital angular momentum (OAM) mode based on concentric uniform circular array (CUCA) is proposed in this paper. It is known that the azimuthal resolution of electromagnetic vortex imaging is closely related to the number of OAM modes. Although the multiplein-multiple-out (MIMO) scheme gives better azimuthal resolution than the multiple-in-single-out (MISO) scheme, it suffers aliasing problem, which means the scattering points with their azimuthal difference larger than 180 degree can not be separated correctly. One possible way to solve this is adding fractional modes in MIMO scheme, but unfortunately, fractional modes are unstable and can not transmit to far field. In this paper, an equivalent fractional order OAM mode is introduced to deal with the problem to achieve higher azimuthal resolution by MIMO scheme. The transmitted and received modes are set to be two adjacent integer modes to realize an equivalent fractional mode. Since the radiation patterns generated by uniform circular array (UCA) for different modes are not aligned, concentric uniform circular array (CUCA) is applied and optimized to overcome this shortage. Simulation results demonstrate the validity of the proposed method. INDEX TERMS Orbital angular momentum, radar imaging, fractional mode, concentric uniform circular antenna.

Three-Dimensional Imaging with Bistatic Vortex Electromagnetic Wave Radar

“…In the last ten years, a large number of research results have appeared regarding vortex EM wave imaging technology [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. Ref.…”

“…[10,11] realized that radar coincidence imaging (RCI) depends on spatial phase distribution characteristics of the vortex EM wave in the different modes. The vortex EM wave radar with fractional modes has good anti-noise performance [12,13]. Ref.…”

“…However, it has no ability to achieve three-dimensional imaging of radar target because of the correlation problem of scattering points. In summary, the above research [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] reconstructs the imaging of radar targets with the monostatic geometry by using UCA. The transmitter is usually set at the center of the UCA, and the receiver uses the UCA in this observation geometry, thus only two-dimensional imaging can be obtained with this monostatic configuration.…”

Twisted Beams With Variable OAM Order and Consistent Beam Angle via Single Uniform Circular Arrays

“…CAs have found recent applications in vortex imaging systems [11], [12], [37], [41]- [44], where the simultaneous use of multiple OAM orders allows for increasing the az-imuthal resolution. In this frame, it is important to ensure that the elevation pattern be consistent among all the excited OAM orders.…”

“…However, CAs operating in free space produce twisted conical patterns whose beam angle is strongly dependent both on the array radius and on the OAM order. Hence, the use of multiple, concentric CAs (Concentric Uniform CAs, CUCAs) has been proposed [41], [42], [44], where each CA radiates a different OAM order with the same beam angle.…”