Abstract
In this paper, a nested dual-arm spiral antenna (NDASA) is proposed to generate multiple orbital angular momentum (OAM) modes at the same operating frequency. The NDASA consists of the feeding network and three nested dual-arm spiral structures with different sizes. Meanwhile, a metal reflector is located between the spiral structures and the feeding network to enhance the radiation directivity, which can also reduce the impact of the radio frequency (RF) coaxial cables. Both the experimental and simulated results show OAM waves with topological charges of $l = 1$ , $l = 3$ and $l = 5$ can be independently generated at $f = 3$ GHz, and their maximum gains are 6.94dBi, 6.76dBi and 5.49dBi, respectively. In addition, the OAM modes multiplexing and demultiplexing technology are investigated in simulations and experiments. The isolations between the OAM modes of $l = 1$ , $l = 3$ and $l = 5$ and the other different OAM modes are greater than 13.8dB, 13.2dB and 25.1dB, respectively, which proves the potential ability of the proposed NDASA for multiplexing and demultiplexing multiple OAM modes.
Highlights
In 1992, Allen et al [1] discovered that orbital angular momentum (OAM) is a basic property of vortex waves, possessing a helical phase wavefront of e−jlφ, where φ represents the azimuthal angle, and l is the OAM mode number called as the topological charge [2]
The results show that the isolations among the different OAM modes are all greater than 13.2dB
Modes of l = 1, l = 3 and l = 5 and the other different OAM modes are greater than 13.8dB, 13.2dB and 25.1dB, respectively, which demonstrates the ability of the proposed method to demultiplex and detect multiple OAM modes
Summary
In 1992, Allen et al [1] discovered that orbital angular momentum (OAM) is a basic property of vortex waves, possessing a helical phase wavefront of e−jlφ, where φ represents the azimuthal angle, and l is the OAM mode number called as the topological charge [2]. Different OAM states can be generated efficiently through the phased antenna array, but the complex feeding networks are necessary [8]–[13]. The spiral phase plate (SPP) structures do not require feeding network and can generate OAM beams in optical and terahertz bands through electromagnetic field diffraction [22], [23]. This method is restricted in the RF domain due to the intrinsic loss and reflection of SPP structures. It’s demonstrated that the designed NDASA has the potential ability for multiplexing and demultiplexing multiple OAM modes in efficiency
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