AI 中文总结
研究21厘米宇宙学实验中天线相互耦合问题，提出直接主波束校正框架减轻耦合，通过电磁模拟验证其有效性，应用于模拟观测发现对功率谱分析有影响，指出全天空校正或分离主旁瓣贡献对稳健恢复EoR窗口的必要性。
AI 中文摘要
天线之间的相互耦合已成为密集孔径阵列中主要的方向相关干扰，在亚兆赫兹空间和频谱结构上留下明显印记，破坏了用于分离微弱21厘米信号的时间选通和前景分离策略。本文介绍了直接主波束校正，这是一个与领域无关的框架，通过对堆叠琼斯矩阵进行正则化、方向加权线性反演来重建相对于任意参考的远场辐射方向图，从而消除相互耦合等方向相关失真。利用SKA-Low的全波电磁模拟，证明该框架在适当条件下的视场内可将辐射方向图重建到数值本底噪声水平，重建精度由正则化反演和基础波束模型的保真度决定。将该框架应用于122 - 134 MHz频段EoR0场的4小时模拟观测，发现对21厘米功率谱分析有两个主要影响。一是仅校正主瓣和近旁瓣是不够的，色光栅瓣贡献会继续污染EoR窗口。二是相互耦合引起的污染在时间上是相干的，不会因跟踪EoR场而在各快照间平均掉。因此，直接主波束校正提供了一种计算高效的减轻相互耦合的方法；然而，要稳健恢复EoR窗口，需要进行全天空校正或在功率谱估计前明确分离主瓣和旁瓣贡献。
英文摘要
Mutual coupling between antennas has emerged as the dominant direction-dependent corruption in dense aperture arrays, imprinting pronounced sub-MHz spatial and spectral structure that compromises the time-gating and foreground-separation strategies used to isolate the faint 21-cm signal. In this work, we introduce \textit{Direct Primary Beam Correction}, a domain-agnostic framework for reconstructing the far-field radiation pattern relative to an arbitrary reference via a regularised, direction-weighted linear inversion of stacked Jones matrices, thereby enabling the removal of direction-dependent distortions such as mutual coupling. Using full-wave electromagnetic simulations of SKA-Low, we demonstrate that this framework reconstructs the radiation pattern down to the numerical noise floor within a suitably conditioned field of view, with the reconstruction accuracy governed by the regularised inversion and the fidelity of the underlying beam model. Applying the framework to a simulated 4-hour observation of the EoR0 field in the $122$--$134$~MHz band, we identify two principal implications for 21-cm power-spectrum analysis. First, restricting the correction to the main lobe and near sidelobes is inadequate: chromatic grating lobe contributions, whether left insufficiently or entirely uncorrected, continue to contaminate the EoR window. Second, mutual-coupling-induced contamination is temporally coherent and, being anchored to the fixed array geometry, does not average down across snapshots as the EoR field is tracked. Direct primary beam correction, therefore, provides a computationally efficient means of mitigating mutual coupling; however, robust recovery of the EoR window necessitates either full-sky correction or explicit separation of main-beam and sidelobe contributions prior to power-spectrum estimation.
Comments18 pages, 10 figures, submitted to Monthly Notices of the Royal Astronomical Society
