High-frequency wideband cellular communications over mmWave and sub-THz offer the opportunity for high data rates. However, it also presents high path loss, resulting in limited coverage. High-gain beamforming brought by the antenna array is essential to mitigate the coverage limitations. The conventional phased antenna arrays (PAA) cause high scheduling latency owing to analog beam constraints, i.e., only one frequency-flat beam is generated. Recently introduced joint phase-time array (JPTA) architecture, which utilizes both true-time-delay (TTD) units and phase shifters (PSs), alleviates analog beam constraints by creating multiple frequency-dependent beams for scheduling multiple users at different directions in a frequency-division manner. One class of previous studies offered solutions with "rainbow" beams, which tend to allocate a small bandwidth per beam direction. Another class focused on uniform linear array (ULA) antenna architecture, whose frequency-dependent beams were designed along a single axis of either azimuth or elevation direction. This paper presents a novel 3D beamforming design that maximizes beamforming gain toward desired azimuth and elevation directions and across sub-bands partitioned according to scheduled users' bandwidth requirements. We provide analytical solutions and iterative algorithms to design the PSs and TTD units for a desired subband beam pattern. Through simulations of the beamforming gain, we observe that our proposed solutions outperform the state-of-the-art solutions reported elsewhere.

翻译：高频毫米波与亚太赫兹频段的宽带蜂窝通信提供了高数据速率的潜力，但同时也面临高路径损耗导致的覆盖范围受限问题。天线阵列带来的高增益波束赋形技术是缓解覆盖限制的关键。传统相控阵天线（PAA）由于只能生成单一频率平坦波束，受限于模拟波束约束，导致较高的调度延迟。最新提出的联合相时阵列（JPTA）架构通过同时使用真时延（TTD）单元与移相器（PS），可生成多个频率依赖波束，以频分方式在不同方向调度多个用户，从而缓解模拟波束约束。以往研究一类提出采用"彩虹"波束的方案，倾向于为每个波束方向分配较小带宽；另一类聚焦于均匀线性阵列（ULA）架构，其频率依赖波束仅沿方位角或俯仰角单个轴设计。本文提出一种新型三维波束赋形设计方案，能够针对期望的方位角和俯仰角方向，以及根据调度用户带宽需求划分的子带，最大化波束赋形增益。通过解析求解与迭代算法，本文设计了移相器和真时延单元的参数以实现期望的子带波束方向图。基于波束赋形增益的仿真结果表明，本文提出的方案优于现有文献报道的先进方法。