Abstract
Orbital angular momentum (OAM) beams have attracted great attention owing to their excellent performances in imaging and communication. In this paper, a dual-arm Archimedean spiral antenna (DASA) is proposed to generate multiple OAM states with positive and negative values by feeding at the inner and outer ends, respectively. The topological charge of radiated vortex waves is reconfigurable by tuning the operating frequency. Dual-mode OAM states are generated at different working frequencies (l = ±1 at 3 GHz, l = ±2 at 4 GHz, and l = ±3 at 4.8 GHz). Both the simulation and measurement results demonstrate that OAM beams can be generated effectively by the DASA. In addition, a conical cavity is used to increase the gain of the proposed DASA for more than 5 dBi in comparison to the traditional cylindrical cavity. Furthermore, the qualities of the generated OAM modes by the proposed DASA have been evaluated at different operating frequencies of 3 GHz, 4 GHz, and 4.8 GHz, respectively. The OAM modes purities of l = −1, −2, −3, 1, 2, and 3 are predominate with the proportion of about 81%, 70%, 74%, 78%, 77%, and 75%, respectively. Our results demonstrate that the proposed DASA has great potentials in OAM multiplexing communication systems.
Highlights
Since orbital angular momentum (OAM)characteristics of the optical vortex beam was proposed by Allen et al in 1992, OAM has been substantially studied [1,2,3,4], which has been expanded from optical regions to low-frequency radio domain [5,6]
Modes has been proposed in the radio frequency region based on the Archimedean spiral antenna [26], but it only radiates positive OAM modes that are determined by the direction of spiral winding
The Archimedean spiral and other structures have attracted a great deal of attention due to their broad bandwidth [21,22,23,24,25]. Another broadband method for generating multiple OAM modes has been proposed in the radio frequency region based on the Archimedean spiral antenna [26], but it only radiates positive OAM modes that are determined by the direction of spiral winding
Summary
Since orbital angular momentum (OAM)characteristics of the optical vortex beam was proposed by Allen et al in 1992, OAM has been substantially studied [1,2,3,4], which has been expanded from optical regions to low-frequency radio domain [5,6]. Helical antennas have been designed to radiate vortex radio waves with multiple OAM states owing to their travelling wave current characteristics [20]. The Archimedean spiral and other structures have attracted a great deal of attention due to their broad bandwidth [21,22,23,24,25] Another broadband method for generating multiple OAM modes has been proposed in the radio frequency region based on the Archimedean spiral antenna [26], but it only radiates positive OAM modes that are determined by the direction of spiral winding. A single antenna structure for generating multiple OAM modes is highly desirable for improving information capacity in communication technology. The spectrum of OAM is performed, and the purity of each OAM mode is investigated
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