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 non-smoothness 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 S-parameters, 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

National Astronomical Observatories,Chinese Academy of Sciences,Beijing 100101,China;University of Chinese Academy of Sciences,Beijing 100049,China;Department of Physics,University of Wisconsin Madison,1150 University Ave,Madison WI 53703,United States of America;IJC Lab,CNRS/IN2P3&UniversitéParis-Saclay,15 rue Georges Clémenceau,F-91405 Orsay,France;The 54th Research Institute,China Electronics Technology Group Corporation,Shijiazhuang,Hebei 050051,China;Fermi National Accelerator Laboratory,P.O.Box 500,Batavia IL 60510-5011,United States of America;School of Mechanical Engineering,Hangzhou Dianzi University,Hangzhou 310017,China;Department of Physics,College of Sciences,Northeastern University,Shenyang 110819,China;Center of High Energy Physics,Peking University,Beijing 100871,China

天文和天体物理学研究

[1]Shijie Sun;Jixia Li;Fengquan Wu;Peter Timbie;Reza Ansari;Jingchao Geng;Huli Shi;Albert Stebbins;Yougang Wang;Juyong Zhang;Xuelei Chen-.The Electromagnetic Characteristics of the Tianlai Cylindrical Pathfinder Array)[J].天文和天体物理学研究,2022(06):234-255

Tianlai,pathfinder

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