AI 中文总结
针对全局21厘米信号测量的校准难题，推导校准方程并协调不同文献的表达式，基于莫比乌斯几何给出校准源阻抗选择条件，解决了宽带测量下开关策略不足的问题。
AI 中文摘要
全局21厘米信号观测因所需测量的绝对特性，带来了一系列独特的校准挑战。由于无法利用天空上的差分测量来观测全局信号，通常使用多个具有不同噪声温度和源阻抗的校准源，以确定放大链的四个噪声参数和功率增益。由于测量的宽带特性，天线阻抗随频率的变化方式与校准源不同，因此最简单的三路Dicke开关策略并不适用。我们对校准方程进行了完整且明确的推导，协调了早期全局21厘米观测文献中的表达式与电气工程文献中常用的放大器噪声表示形式得到的结果。我们还根据复Γ（或Z）平面上的莫比乌斯几何，给出了定义校准源阻抗选择所需的条件。
英文摘要
21cm global signal observations present a unique set of calibration challenges owing to the absolute character of the required measurement. Since differential measurements on the sky cannot be used for observing the global signal, typically a number of calibration sources with differing noise temperatures and source impedances are used to determine the four noise parameters and the power gain of the amplification chain. Because of the broadband nature of the measurement, the antenna impedance varies with frequency in a manner different from the calibration sources, so that the simplest three-way Dicke switching strategy is not adequate. We present a self-contained and explicit derivation of the calibration equations and reconcile expressions from the early global 21cm observation literature with the results obtained following the amplifier noise representation formalism commonly used in the electrical engineering literature. We also present a condition in terms of Möbius geometry on the complex $Γ$- (or $Z$-) plane defining the choice of calibration source impedances required.
CommentsLaTeX, 7 pages with 4 figures
