天来圆柱阵的反射波和驻波
Reflections and Standing Waves on the Tianlai Cylinder Array
摘要：
在21~cm强度映射中，利用前景的光谱平滑性将其与弱得多的21~cm信号分离。然而，仪器的非平滑频率响应使该过程复杂化。反射和驻波对频率响应产生调制。本文分析了天来圆柱阵信号通道带通中的驻波。通过傅立叶变换的带通到延迟时间域，我们发现各种驻波产生的望远镜。最清楚地识别出在15米馈电电缆中产生的具有约142 ns的时间延迟的驻波。我们还发现在较短的延迟$τ< 50 \ns$，这可能是一个混合的驻波之间的反射器和饲料，和驻波的4米中频（IF）电缆的强峰值。我们还表明，一个平滑的频率响应可以部分恢复通过消除反射诱导的调制。然而，天线上的驻波是方向相关的，这对高精度校准提出了更困难的挑战。
英文摘要：
In 21~cm intensity mapping, the spectral smoothness of the foreground is exploited to separate it from the much weaker 21~cm signal. However, the non-smooth frequency response of the instrument complicates this process. Reflections and standing waves generate modulations on the frequency response. Here we report the analysis of the standing waves in the bandpass of the signal channels of the Tianlai Cylinder Array. By Fourier transforming the bandpass into the delay time domain, we find various standing waves generated on the telescope. A standing wave with time delay at about 142 ns is most clearly identified which is produced in the 15 meter feed cable. We also find a strong peak at a shorter delay of $τ< 50 \ns$, which may be a mix of the standing wave between the reflector and feed, and the standing wave on the 4 m intermediate frequency (IF) cable. We also show that a smoother frequency response could be partially recovered by removing the reflection-inducted modulations. However, the standing wave on the antenna is direction-dependent, which poses a more difficult challenge for high precision calibration.
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