The orbital angular momentum (OAM) in radio frequency is expected to provide a new dimension to the OAM mode and benefit the degree of freedom of the electromagnetic wave. However, a central energy hollow exists in the OAM-carrying beam, and its radius varies with the OAM mode values, which is the main bottleneck in the radio frequency OAM applications. This article proposes a solution to eliminate the central hollow, by fundamentally changing the transmitted signal of the uniform circular array (UCA). To generate the unidirectional beam pattern, defined as the beaming OAM (BOAM), the orthogonal waveforms are radiated by UCA with an equidifferent initial phase. The BOAM wave can be received by one single antenna, and the separate OAM mode demodulation is then achieved based on the waveform diversity. This article studies the theoretical model of the BOAM field distribution and shows that the waveform diversity among distributed units can not only alter the doughnut-like shape into the closed beam, but also maintain the intact vortex characteristic. On this basis, the extended OAM mode multiplexing system is designed with one single UCA. A 16-element UCA is shown to be capable of generating 15 OAM modes simultaneously, with all modes superposing on the same direction. Furthermore, it is verified by the simulation that the vortex phase of each single mode can be precisely extracted from the OAM-mode-multiplexing signal.

中文翻译：

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基于波形分集的承载轨道角动量的会聚光束的生成

射频中的轨道角动量（OAM）有望为 OAM 模式提供新的维度，并有利于电磁波的自由度。然而，OAM承载波束中存在中心能量空洞，其半径随OAM模式值的变化而变化，这是射频OAM应用的主要瓶颈。本文提出了一种消除中心空洞的解决方案，从根本上改变了均匀圆阵列（UCA）的发射信号。为了生成单向波束模式，定义为波束 OAM (BOAM)，正交波形由 UCA 辐射，具有等不同的初始相位。BOAM波可以由一根天线接收，然后基于波形分集实现单独的OAM模式解调。本文研究了 BOAM 场分布的理论模型，表明分布单元之间的波形多样性不仅可以将甜甜圈形状变成闭合光束，而且可以保持完整的涡流特性。在此基础上，设计了一个单UCA的扩展OAM模式复用系统。一个 16 单元的 UCA 被证明能够同时产生 15 个 OAM 模式，所有模式都在同一方向上叠加。此外，仿真验证了可以从OAM模式复用信号中精确提取每个单模式的涡旋相位。扩展的 OAM 模式复用系统设计为一个单一的 UCA。一个 16 单元的 UCA 被证明能够同时产生 15 个 OAM 模式，所有模式都在同一方向上叠加。此外，仿真验证了可以从OAM模式复用信号中精确提取每个单模式的涡旋相位。扩展的 OAM 模式复用系统设计为一个单一的 UCA。一个 16 单元的 UCA 被证明能够同时产生 15 个 OAM 模式，所有模式都在同一方向上叠加。此外，仿真验证了可以从OAM模式复用信号中精确提取每个单模式的涡旋相位。