This paper proposes a novel flexible coupler antenna (FCA) that translates passive coupling elements around a fixed-position active antenna to reshape the induced currents on the passive elements for radiation. A new form of mechanical beamforming is achieved by moving only the passive coupling elements while keeping the active antenna stationary. The proposed design significantly reduces the antenna and radio-frequency (RF) chain costs of conventional active array beamforming with low mechanical control complexity and energy consumption. For the purpose of exposition, we consider a point-to-point communication system with one FCA at the transmitter and one fixed antenna at the receiver. Specifically, based on multi-port circuit theory, we establish both the line-of-sight (LoS) and multipath channel models and derive the mechanical beamforming weights of the passive couplers as functions of their positions. Then, we formulate a new problem to maximize the received signal-to-noise ratio (SNR) by optimizing the positions of passive couplers at the transmitter, subject to coupler movement and transmit power constraints. Solving the resulting problem is inherently difficult because coupled channel and mechanical beamforming create non-linearity in the objective function.To tackle this problem, we propose an efficient block-coordinate conditional gradient method to search for the best positions of all passive couplers by sequentially optimizing the position of each coupler with those of the other couplers fixed in an iterative manner.Simulation results demonstrate that the proposed system significantly outperforms benchmark schemes in terms of achievable rate, but with significantly reduced active antennas and RF chains.

翻译：本文提出了一种新型柔性耦合天线（FCA），通过将无源耦合元件在固定位置的有源天线周围移动，重塑无源元件上的感应电流以实现辐射。在保持有源天线固定的情况下，仅移动无源耦合元件即可实现一种新型的机械波束赋形。所提出的设计显著降低了传统有源阵列波束赋形的天线和射频（RF）链路成本，并具有较低的机械控制复杂性和能耗。为便于阐述，我们考虑一个点对点通信系统，其中发射端配备一个FCA，接收端配备一个固定天线。具体而言，基于多端口电路理论，我们建立了视距（LoS）和多径信道模型，并推导了无源耦合器的机械波束赋形权重作为其位置的函数。随后，我们构建了一个新问题，通过优化发射端无源耦合器的位置，在耦合器移动和发射功率约束下最大化接收信噪比（SNR）。由于耦合信道与机械波束赋形在目标函数中产生非线性，求解该问题本质上具有难度。为解决这一问题，我们提出了一种高效的块坐标条件梯度方法，通过迭代方式依次优化每个耦合器的位置（同时固定其他耦合器的位置），以搜索所有无源耦合器的最佳位置。仿真结果表明，所提出的系统在可达速率上显著优于基准方案，同时大幅减少了有源天线和射频链路数量。