In recent years, the hybrid branch-line coupler has attracted much attention due to its appealing features such as of low cost and ease in fabrication for wireless communications. The fifth-generation cellular networks promise to support several wireless technologies by capitalizing a multitude of frequencies and increase data rates. To achieve that, the butler matrix technique can be used to enhance both bandwidth and data rate with the implementation of beamforming. Conventional hybrid couplers are the main component to build a butler matrix, but they are generally bulky in size and narrow in bandwidth. Moreover, requirements imposed by newer wireless technologies makes the efforts in improving size compactness and bandwidth even more challenging. On the other hand, several techniques have been proposed in literature to solve both issues. This study focuses on the design challenges and issues of hybrid coupler designs and technologies, besides underlining their promising potential. In this context, several techniques for hybrid coupler to achieve the required bandwidth and size reduction are highlighted, such as the T-shape, meander line, two sections, three-section, and parallel couple lines.

中文翻译：

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混合耦合器综述：最新技术、应用、设计问题和挑战

近年来，混合支线耦合器因其低成本和易于无线通信制造等吸引人的特点而备受关注。第五代蜂窝网络有望通过利用多种频率和提高数据速率来支持多种无线技术。为了实现这一点，巴特勒矩阵技术可用于通过实施波束成形来提高带宽和数据速率。传统的混合耦合器是构建管家矩阵的主要组件，但它们通常体积庞大且带宽窄。此外，较新的无线技术强加的要求使得提高尺寸紧凑性和带宽的努力更具挑战性。另一方面，文献中已经提出了几种技术来解决这两个问题。本研究重点关注混合耦合器设计和技术的设计挑战和问题，此外还强调了它们的潜力。在此背景下，重点介绍了混合耦合器实现所需带宽和尺寸减小的几种技术，例如 T 形、曲折线、两段、三段和平行耦合线。