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~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 ofτ<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.
基金
the support of NAOC Astronomical Technology Center
support of the Ministry of Science and Technology(MOST)grant(2012AA121701)
supported by MOST grant(2016YFE0100300)
the National Natural Science Foundation of China(NSFC,Grant Nos.11633004 and 11473044)
the Chinese Academy of Sciences(CAS)grant(QYZDJ-SSW-SLH017)
partially supported by the MOST grant(2018YFE0120800)
National Key R&D Program 2017YFA0402603
the CAS Interdisciplinary Innovation Team(JCTD-2019-05)
Part of the computations are performed on the Tianhe-2 supercomputer(with the support of the NSFC grant U1501501)
partially supported by NSF Award(AST-1616554)
partial support from CNRS(IN2P3&INSU)
Observatoire de Paris
Irfu/CEA。