In this paper, high-order orbital angular momentum (OAM) vortex beams (OAMVBs) are generated using reflective metasurface. Generating high-order OAMVBs using traditional reflective metasurface methods deteriorates the radiation performance that affects the mode purity of OAMVBs. A reflective metasurface is proposed to generate the OAMVBs with l = 4 mode at the designed frequency of 6 GHz. It is revealed that the radiation performance has been improved and mode purity for l = 4 is increased 12.6% by using quarter wavelength unit cell and circular aperture metasurface as compared to the conventional metasurface at the designed frequency. Moreover, the reflective metasurface can generate the OAMVBs with l = 4 mode from 5 GHz to 7.5 GHz. The measured gain is 17.93 dBi which agrees well with the simulated gain. INDEX TERMS Orbital angular momentum (OAM), reflective metasurface, radiation performance, vortex beam.
A broadband four-feed circular patch antenna is demonstrated to generate high-purity dual-mode vortex beams carrying orbital angular momentum (OAM) for the first time. The electric field formula of the circularly polarized (CP) component is derived for analyzing radiation characteristics of different OAM modes, such as the CP property, phase and amplitude distributions. Theoretical calculation and numerical simulation results show that the four-feed patch antenna operating in the TMn1 mode can generate ±n OAM waves. A prototype of a four-feed circular TM21-mode patch antenna is fabricated and measured to verify the effectiveness of the theoretical analysis. The proposed antenna consists of a four-feed patch with an air-coupled parasitic patch and a four-way phase-shifting feeding network. Experimental results show that the proposed antenna can generate a left-hand CP OAM with mode l = +2 and a right-hand CP OAM with mode l = −2. The OAM beams are generated in a wide band from 5.50 to 6.50 GHz with a mode purity over 90%. The proposed method is very suitable for the generation of wideband, dual-mode and high-purity OAM beams in the microwave and millimeter wave bands.
The multimode orbital angular momentum (OAM) radio waves can be used to multiplex multiple transmission channels to increase the capacity of communication system without adding additional bandwidth. However, the divergence of the OAM beams and beam inconsistency escalate by increasing OAM mode number. Moreover, the worse sidelobe level (SLL) always appears along with a better convergent beam. In this article, the fruit fly optimization algorithm (FOA) is proposed to suppress the SLL in multimode OAM scenario. Based on the concentric circular array antenna (CCAA), the feeding amplitudes and the radii of the array are synthesized simultaneously to realize less than −30 dB SLL of the multimode OAM patterns. When the main lobes with different OAM modes steered to a uniform azimuth of
θ = 0°, the SLLs of these OAM modes are also suppressed to less than −21 dB. The advantages of FOA used in the OAM pattern synthesis are verified by comparing it with the genetic algorithm (GA). The FOA‐based synthesis has a simpler implementation flow diagram which reduces the time of synthesis to 39.5% of GA.
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