Wide-angle Beamscanning Gradient Index Lens Antennas for Wireless Communications

The trend in wireless communication is moving towards higher frequencies, offering increased data rates and broader spectrum availability. However, these benefits come with the challenge of higher path loss, necessitating antenna systems with highly directional beams. Consequently, antennas require high gain, greater than 20 dBi, but with narrow beamwidths, making beam scanning capabilities essential to cover wide fields-of-view, exceeding ±50°. Additionally, a broad operational bandwidth ($>$50\%) is preferred to support various applications.

This dissertation aims to design a high-gain antenna with wide-angle beam scanning across a broadband. Considering the need for massive deployment, the proposed antenna should also be low-cost and energy-efficient. Gradient Refractive Index (GRIN) antennas present a promising solution, meeting performance and constraint requirements. However, improvement in beam scanning range and scan loss is needed.

To address these challenges, this dissertation introduces a novel lens impedance matching structure and a lens ray tracing simulation technique. Both designs then enable two types of beam scanning lenses. By reformulating taper theory, the impedance matching tapers achieve broadband matching from 8 to 78 GHz with a uniform physical layer length. The ray tracing solver incorporates the complex electrical field, allowing evaluation of lens radiation patterns within a minute for lenses with arbitrary shapes and permittivity profiles.

Using these tools, a 3D compound lens was designed with a fast hybrid optimization workflow involving three solvers, conducting over 50,000 simulations in four days. The resulting lens design achieves an average scan loss exponent of $n_s = 2.17$ within ±55° across the Ka-Band. Additionally, a proposed phased array fed lens (PAFL) demonstrates improved beam scanning capabilities by using a small number of feeds with nonuniform amplitude and phase excitation. Two PAFL designs were developed: one with a 0.7$\lambda$ spacing feed array, requiring around half the feeds compared to the standard 0.7$\lambda$ spacing, which reduces cost and power consumption while improving $n_s$ from 5 to 3.6 at 29 GHz, and another with a broadband feed array that achieves beam scanning improvements from 15 GHz to 50 GHz.

无线通信的发展趋势正逐渐向高频段转变，这一转变带来了数据传输速率的提升和频谱可用性的拓宽。然而，这一进步伴随着路径损耗增加的挑战，这就要求天线系统具备高度定向的波束。因此，天线需要具备超过20 dBi的高增益，同时拥有狭窄的波束宽度，这使得波束扫描能力成为覆盖广泛视场角（超过±50°）的必要条件。此外，宽工作带宽（>50%）更为理想，以支持多样化的应用需求。

本论文旨在设计一款宽带范围内具有广角波束扫描能力的高增益天线。鉴于大规模部署的需求，所提出的天线应具备低成本和高效能的特点。梯度折射率（GRIN）天线作为一种有前景的解决方案，能够满足性能和约束要求。然而，在波束扫描范围和扫描损耗方面仍有待改进。

为了应对这些挑战，本论文引入了一种新型的透镜阻抗匹配结构和透镜光线追踪仿真技术。这两种设计使得两种类型的波束扫描透镜得以实现。通过重新阐述渐变理论，阻抗匹配渐变实现了从8 GHz到78 GHz的宽带匹配，且物理层长度均匀。光线追踪求解器包含复杂的电场，允许在短时间内评估任意形状和介电常数分布的透镜辐射模式。

利用这些工具，通过快速混合优化工作流程，设计了一款3D复合透镜，该流程涉及三个求解器，在四天内进行了超过50,000次模拟。最终透镜设计在Ka波段内，±55°范围内实现了平均扫描损耗指数$n_s = 2.17$。此外，提出的相控阵馈电透镜（PAFL）通过使用少量具有非均匀幅度和相位激励的馈电，展示了改进的波束扫描能力。两种PAFL设计得到开发：一种是0.7λ间距的馈电阵列，与标准0.7λ间距相比，所需馈电数量减少约一半，从而降低了成本和功耗，同时将29 GHz处的$n_s$从5降低到3.6；另一种是宽带馈电阵列，从15 GHz到50 GHz实现了波束扫描性能的提升。