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| 1 | Reflections and standing waves on the Tianlai cylinder array显示文摘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. | Ji-Xia Li Feng-Quan Wu Shi-Jie Sun Zi-Jie Yu Shi-Fan Zuo Ying-Feng Liu You-Gang Wang Cong Zhang Reza Ansari Peter Timbie Xuelei Chen | 2021 | Research in Astronomy and Astrophysics2021，21，3： | 1 |
| 2 | The Tianlai Cylinder Pathfinder array: System functions and basic performance analysis显示文摘The Tianlai Cylinder Pathfinder is a radio interferometer array designed to test techniques for 21 cm intensity mapping in the post-reionization Universe,with the ultimate aim of mapping the large scale structure and measuring cosmological parameters such as the dark energy equation of state.Each of its three parallel cylinder reflectors is oriented in the north-south direction,and the array has a large field of view.As the Earth rotates,the northern sky is observed by drift scanning.The array is located in Hongliuxia,a radio-quiet site in Xinjiang,and saw its first light in September 2016.In this first data analysis paper for the Tianlai cylinder array,we discuss the sub-system qualification tests,and present basic system performance obtained from preliminary analysis of the commissioning observations during 2016-2018.We show typical interferometric visibility data,from which we derive the actual beam profile in the east-west direction and the frequency band-pass response.We describe also the calibration process to determine the complex gains for the array elements,either using bright astronomical point sources,or an artificial on site calibrator source,and discuss the instrument response stability,crucial for transit interferometry.Based on this analysis,we find a system temperature of about 90 K,and we also estimate the sensitivity of the array. | JiXia Li ShiFan Zuo FengQuan Wu YouGang Wang JuYong Zhang ShiJie Sun YiDong Xu ZiJie Yu Reza Ansari YiChao Li Albert Stebbins Peter Timbie YanPing Cong JingChao Geng Jie Hao QiZhi Huang JianBin Li Rui Li DongHao Liu YingFeng Liu Tao Liu John PMarriner ChenHui Niu Ue-Li Pen Jeffery BPeterson HuLi Shi Lin Shu YaFang Song HaiJun Tian GuiSong Wang QunXiong Wang RongLi Wang WeiXia Wang Xin Wang KaiFeng Yu Jiao Zhang BoQin Zhu JiaLu Zhu XueLei Chen | 2020 | Science China(Physics,Mechanics & Astronomy)2020，63，12： | 0 |
| 3 | The Electromagnetic Characteristics of the Tianlai Cylindrical Pathfinder Array显示文摘A great challenge for 21 cm intensity mapping experiments is the strong foreground radiation which is orders of magnitude brighter than the 21 cm signal.Removal of the foreground takes advantage of the fact that its frequency spectrum is smooth while the redshifted 21 cm signal spectrum is stochastic.However,a complication is the nonsmoothness of the instrument response.This paper describes the electromagnetic simulation of the Tianlai cylinder array,a pathfinder for 21 cm intensity mapping experiments.Due to the vast scales involved,a direct simulation requires a large amount of computing resources.We have made the simulation practical by using a combination of methods:first simulate a single feed,then an array of feed units,finally with the feed array and a cylindrical reflector together,obtain the response for a single cylinder.We studied its radiation pattern,bandpass response and the effects of mutual coupling between feed units,and compared the results with observation.Many features seen in the measurement result are reproduced well in the simulation,especially the oscillatory features which are associated with the standing waves on the reflector.The mutual coupling between feed units is quantified with Sparameters,which decrease as the distance between the two feeds increases.Based on the simulated S-parameters,we estimate the correlated noise which has been seen in the visibility data,and the results show very good agreement with the data in both magnitude and frequency structures.These results provide useful insights on the problem of 21 cm signal extraction for real instruments. | Shijie Sun Jixia Li Fengquan Wu Peter Timbie Reza Ansari Jingchao Geng Huli Shi Albert Stebbins Yougang Wang Juyong Zhang Xuelei Chen | 2022 | Research in Astronomy and Astrophysics2022，22，6： | 0 |
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