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 ∼142 ns is most clearly identified which is produced in the 15-meter feed cable. We also identify 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.

在 21 cm 强度映射中，利用前景的光谱平滑度将其与弱得多的 21 cm 信号分开。然而，仪器的非平滑频率响应使这个过程复杂化。反射和驻波对频率响应产生调制。在这里，我们报告了对天来圆柱阵列信号通道带通中驻波的分析。通过傅里叶将带通变换到延迟时域，我们发现望远镜上产生了各种驻波。在 15 米长的馈电电缆中产生的时延约为 142 ns 的驻波被最清楚地识别出来。我们还在更短的τ延迟处确定了一个强峰值< 50 ns，这可能是反射器和馈源之间的驻波以及 4 m 中频 (IF) 电缆上的驻波的混合。我们还表明，通过去除反射感应调制可以部分恢复更平滑的频率响应。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大的挑战。