[论文解读] Electrical and electromagnetic co-simulations of the HERA Phase I receiver system including the effects of mutual coupling, and impact on the EoR window

Nicolas Fagnoni, Eloy de Lera Acedo+68 more|arXiv (Cornell University)|Aug 6, 2019

Radio Astronomy Observations and Technology被引用 17

一句话总结

本文提出了一种协同仿真框架，整合了HERA Phase I的天线、射频接收机、电缆以及互耦效应，以模拟系统色散性。研究发现，150米电缆引起强烈的反射，而互耦效应使信号能在阵列中传播，导致1400纳秒后系统响应衰减10⁴–10⁵，这限制了在150 MHz频率下高于0.7 h Mpc⁻¹的可观测EoR模式，使得EoR探测比以往假设更具挑战性。

ABSTRACT

The detection of the Epoch of Reionization (EoR) delay power spectrum using a avoidance highly depends on the instrument chromaticity. The systematic effects induced by the radio-telescope spread the foreground signal in the delay domain, which contaminates the EoR window theoretically observable. Therefore, it is essential to understand and limit these chromatic effects. This paper describes a method to simulate the frequency and time responses of an antenna, by simultaneously taking into account the analogue RF receiver, the transmission cable, and the mutual coupling caused by adjacent antennas. Applied to the Hydrogen Epoch of Reionization Array (HERA), this study reveals the presence of significant reflections at high delays caused by the 150-m cable which links the antenna to the back-end. Besides, it shows that waves can propagate from one dish to another one through large sections of the array because of mutual coupling. In this more realistic approach, the simulated system time response is attenuated by a factor $10^{4}$ after a characteristic delay which depends on the size of the array and on the antenna position. Ultimately, the system response is attenuated by a factor $10^{5}$ after 1400 ns because of the reflections in the cable, which corresponds to characterizable ${k_\parallel}$-modes above 0.7 $h m{Mpc}^{-1}$ at 150 MHz. Thus, this new study shows that the detection of the EoR signal with HERA Phase I will be more challenging than expected. On the other hand, it improves our understanding of the telescope, which is essential to mitigate the instrument chromaticity.

研究动机与目标

• 理解由电缆和互耦引起的仪器色散性如何影响HERA Phase I的EoR延迟功率谱。
• 建模包含射频组件、电缆和全阵列互耦效应的完整接收链路的联合频域与时域响应。
• 量化这些效应对EoR信号可观测性的影响，特别是对延迟功率谱的影响。

提出的方法

• 使用电磁场与电路模型对HERA Phase I接收系统进行协同仿真。
• 纳入150米传输电缆的频率相关响应和阻抗不连续性。
• 通过全波电磁仿真建模相邻天线之间的互耦效应。
• 从S参数数据中提取时域响应，以评估系统色散性。
• 采用延迟谱分析将系统响应映射到可观测的k∥-模式。
• 通过与EoR窗口污染的理论预期对比，验证结果的可靠性。

实验结果

研究问题

• RQ1 150米电缆中的反射如何影响系统的时域响应和EoR可观测性？
• RQ2 天线之间的互耦在多大程度上实现了信号在阵列中的跨区域传播？
• RQ3 由于色散效应，系统响应在何种特征延迟后显著衰减？
• RQ4 电缆反射与互耦效应共同作用，如何限制EoR功率谱中可观测的k∥-模式范围？
• RQ5 在1400纳秒之后，系统响应衰减程度如何，其对EoR探测的影响是什么？

主要发现

• 150米电缆引入了显著的反射，导致系统响应在特征延迟后衰减10⁴倍，该延迟取决于阵列尺寸和天线位置。
• 互耦效应使波能在阵列的大范围区域中传播，导致系统响应尾部延长。
• 由于电缆反射，1400纳秒后系统响应衰减10⁵倍，限制了可观测的EoR模式。
• 该衰减对应于在150 MHz频率下，k∥-模式高于0.7 h Mpc⁻¹的部分被抑制，降低了EoR窗口的动态范围。
• 电缆反射与互耦效应的共同作用增加了系统色散性，使得EoR探测比以往估计更具挑战性。
• 本研究为HERA Phase I仪器响应提供了更真实的模型，对减轻EoR实验中的系统效应至关重要。