Uncrewed Aerial Vehicles (UAVs) serving as Aerial Base Stations (ABSs) are expected to extend 6G millimeter-Wave (mmWave) coverage and improve link reliability in urban areas. However, UAV-based Air-to-Ground (A2G) channels are highly dependent on height and urban geometry. This paper proposes an ABS height-dependent mmWave channel model and investigates whether urban geometry, beyond the standard built-up parameters, significantly affects LoS probability (PLoS) and Large-Scale Fading (LSF). Using MATLAB ray tracing at 26 GHz, we simulate approximately 10K city realizations for four urban layouts that share identical built-up parameters but differ in their spatial organization. We extract elevation-based PLoS using a sigmoid model and derive height-dependent Path-Loss Exponents (PLEs) and shadow-fading trends using exponential fits. Results show that PLE for Non-Line-of-Sight (NLoS) decreases toward 2.5-3 at high altitudes, Line-of-Sight (LoS) PLE remains near 2, and shadow fading reduces with height. We also find that geometric layout introduces a modest but consistent change in PLE (+/- 0.2), even when built-up parameters are fixed. The proposed unified model aligns well with ray-tracing statistics and offers a practical, height-dependent LSF model suitable for ABS planning in complex urban scenarios.

翻译：作为空中基站（ABS）的无人机（UAV）有望在6G毫米波（mmWave）系统中扩展城市区域的覆盖范围并提升链路可靠性。然而，基于无人机的空对地（A2G）信道高度依赖于飞行高度和城市几何结构。本文提出了一种与ABS高度相关的毫米波信道模型，并探究了除标准建筑参数外，城市几何布局是否显著影响视距概率（PLoS）和大尺度衰落（LSF）。通过在26 GHz频段使用MATLAB射线追踪仿真，我们对四种城市布局进行了约10,000次城市场景模拟，这些布局具有相同的建筑参数但空间结构不同。我们采用Sigmoid模型提取基于高度的PLoS，并通过指数拟合推导出高度相关的路径损耗指数（PLE）及阴影衰落趋势。结果表明：非视距（NLoS）的PLE在高空下降至2.5-3范围内，视距（LoS）的PLE保持在2附近，阴影衰落随高度增加而减弱。研究还发现，即使建筑参数固定，几何布局仍会引入适度但一致的PLE变化（±0.2）。所提出的统一模型与射线追踪统计结果高度吻合，为复杂城市场景中的ABS规划提供了一个实用且高度相关的大尺度衰落模型。