Orbital angular momentum (OAM), providing an additional degree of freedom, has attracted much attention for spectral efficiency and its potential in communications. The need for more compact OAM-based communication systems has inspired research into quasi-circular arrays (QCAs) producing quasi-OAM beams. In this letter, a QCA-based communication system prototype is designed to transmit and receive quasi-OAM beams of dominant mode order $l=-1$, over a free-space link at 8.5 GHz. The performance of quasi-OAM beams generated by QCAs is analyzed through bit-error-rate (BER) measurements in a lab setting. The BER results are then analyzed against BER of a conventional OAM circular array and augmented quasi-OAM by a QCA to investigate their performance. Furthermore, the intermode interference is analyzed by adding mode $l=0$. The results indicate the feasibility of a quasi-OAM communication system, and proved to be similar, or better than conventional OAM-based systems, where there is no mode cross-talk. Augmenting OAM modes is also proven to make a quasi-OAM communication link similar to conventional OAM, in the presence of cross-talk.

中文翻译：

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用于 OAM 通信的准圆形阵列天线的实验 BER 性能

轨道角动量 (OAM) 提供了额外的自由度，因其频谱效率及其在通信中的潜力而备受关注。对更紧凑的基于 OAM 的通信系统的需求激发了对产生准 OAM 波束的准圆形阵列 (QCA) 的研究。在这封信中，设计了一个基于 QCA 的通信系统原型来发送和接收主模阶的准 OAM 波束$l=-1$，通过 8.5 GHz 的自由空间链路。在实验室环境中通过误码率 (BER) 测量来分析 QCA 生成的准 OAM 波束的性能。然后通过 QCA 将 BER 结果与传统 OAM 圆形阵列的 BER 和增强的准 OAM 进行比较，以研究它们的性能。此外，通过添加模式来分析模式间干扰$l=0$. 结果表明准 OAM 通信系统的可行性，并证明与传统的基于 OAM 的系统相似或更好，后者没有模式串扰。在存在串扰的情况下，增强 OAM 模式也被证明可以建立类似于传统 OAM 的准 OAM 通信链路。