Abstract
This paper gives a feasible and simple solution of generating OAM-carrying radio beams. Eight Vivaldi antenna elements connect sequentially and fold into a hollow cylinder. The circular Vivaldi antenna array is fed with unit amplitude but with a successive phase difference from element to element. By changing the phase difference at the steps of 0, ±45°, ±90°, ±135°, and 180°, the OAM radio beam can be generated with mode numbers 0, ±1, ±2, ±3, and 4. Simulations show that the OAM states of ±2 and ±3 are the same as the traditional states, while the OAM states of 0, ±1, and 4 differ at the boresight. This phenomenon can be explained by the radiation pattern difference between Vivaldi antenna and tripole antenna. A solution of distinguishing OAM states is also proposed. The mode number of OAM can be distinguished with only 2 receivers.
Highlights
Electromagnetic (EM) fields can carry energy and angular momentum [1]
In 2012, they experimentally demonstrated that two radio waves encoded in different orbital angular momentum (OAM) states on the same frequency band can be decoded in the far field for the first time [12]
They concluded that communicating over the subchannels given by OAM states is a subset of the solutions offered by multiple-in multiple-out (MIMO)
Summary
Electromagnetic (EM) fields can carry energy and angular momentum [1]. The angular momentum is composed of spin angular momentum (SAM) and orbital angular momentum (OAM) describing its polarization state and the phase structure distribution, respectively [2]. In 2007, Thide et al numerically simulated that OAM beams can be generated in radio frequency with the help of vector antenna arrays [11]. In 2012, they experimentally demonstrated that two radio waves encoded in different OAM states on the same frequency band can be decoded in the far field for the first time [12]. Simulations showed that, for certain array configurations in free space, traditional MIMO theory leads to eigenmodes identical to the OAM states. Based on this result, they concluded that communicating over the subchannels given by OAM states is a subset of the solutions offered by MIMO. Simulations show that the proposed antenna array is a simple and promising candidate to generate OAM
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