Terahertz (THz) communication is widely deemed the next frontier of wireless networks owing to the abundant spectrum resources in the THz band. Whilst THz signals suffer from severe propagation losses, a massive antenna array can be deployed at the base station (BS) to mitigate those losses through beamforming. Nevertheless, a very large number of antennas increases the BS's hardware complexity and power consumption, and hence it can lead to poor energy efficiency (EE). To surmount this fundamental problem, we propose a novel array design based on superdirectivity and nonuniform inter-element spacing. Specifically, we exploit the mutual coupling between closely spaced elements to form superdirective pairs. A unique property of them is that all require the same excitation amplitude, and thus can be driven by a single radio frequency chain akin to conventional phased arrays. Moreover, they facilitate multi-port impedance matching, which ensures maximum power transfer for any beamforming angle. After addressing the implementation issues of superdirectivity, we show that the number of BS antennas can be effectively reduced without sacrificing the achievable rate. Simulation results demonstrate that our design offers huge EE gains compared to uncoupled arrays with uniform spacing, and hence could be a radical solution for future THz systems.

翻译：太赫兹（THz）通信因其在太赫兹频段丰富的频谱资源被广泛视为无线网络的下一前沿。尽管THz信号遭受严重的传播损耗，但可在基站（BS）部署大规模天线阵列通过波束赋形来缓解这些损耗。然而，极大规模天线会增加基站硬件复杂度与功耗，进而导致能效（EE）低下。为克服这一根本性问题，我们提出一种基于超方向性与非均匀阵元间距的新型阵列设计。具体而言，我们利用紧密排列阵元间的互耦效应构建超方向天线对。这些天线对具有独特性质：所有天线对均需相同激励幅度，因此可像传统相控阵一样由单条射频链驱动。此外，它们支持多端口阻抗匹配，确保任意波束赋形角度下实现最大功率传输。在解决超方向性的实现问题后，我们证明在不牺牲可达速率的前提下可有效减少基站天线数量。仿真结果表明，与均匀间距非耦合阵列相比，我们的设计可带来巨大的能效增益，因此有望成为未来太赫兹系统的革命性解决方案。