Measuring HERA's Primary Beam in Situ: Methodology and First Results

Nunhokee, Chuneeta D.; Parsons, Aaron; Kern, Nicholas S.; Nikolic, Bojan; Pober, Jonathan C.; Bernardi, G.; Carilli, C. L.; Abdurashidova, Zara; Aguirre, James E.; Alexander, Paul; Ali, Zaki S.; Balfour, Yanga; Beardsley, Adam P.; Billings, Tashalee S.; Bowman, Judd D.; Bradley, Richard F.; Burba, Jacob; Cheng, Carina; DeBoer, David R.; Dexter, Matt; deLeraAcedo, Eloy; Dillon, Joshua S.; Ewall‐Wice, Aaron; Fagnoni, Nicolas; Fritz, Randall; Furlanetto, Steve R.; Gale‐Sides, Kingsley; Glendenning, Brian; Gorthi, Deepthi; Greig, Bradley; Grobbelaar, Jasper; Halday, Ziyaad; Hazelton, B. J.; Hewitt, Jacqueline N.; Jacobs, Daniel; Julius, Austin; Kerrigan, Joshua; Kittiwisit, Piyanat; Kohn, Saul A.; Kolopanis, Matthew; Lanman, Adam; LaPlante, Paul; Lekalake, Telalo; Liu, Adrian; MacMahon, David; Malan, Lourence; Malgas, Cresshim; Maree, Matthys; Martinot, Zachary E.; Matsetela, Eunice; Mesinger, Andrei; Molewa, Mathakane; Morales, M. F.; Mosiane, Tshegofalang; Neben, Abraham R.; Patra, Nipanjana; Pieterse, Samantha; Razavi-Ghods, N.; Ringuette, Jon; Robnett, James; Rosie, Kathryn; Sims, Peter; Smith, Craig; Syce, Angelo; Thyagarajan, Nithyanandan; Williams, Peter K. G.; Zheng, Haoxuan

doi:10.3847/1538-4357/ab9634

Cited by 18 publications

(12 citation statements)

References 55 publications

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“…Those measurements are quite challenging and are the focus of other work (e.g. Jacobs et al 2017;Nunhokee et al 2020). However, given the statistical understanding we have developed in Section 4.1 of the imprint of non-redundancy on redundant-baseline calibration's gains, it is reasonable to ask whether that structure is reproducible in a relatively simple simulation.…”

Section: Explaining Temporal Structure In Terms Of Non-redundancymentioning

confidence: 99%

Redundant-baseline calibration of the hydrogen epoch of reionization array

Dillon

Lee

Ali

et al. 2020

Monthly Notices of the Royal Astronomical Society

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In 21 cm cosmology, precision calibration is key to the separation of the neutral hydrogen signal from very bright but spectrally-smooth astrophysical foregrounds. The Hydrogen Epoch of Reionization Array (HERA), an interferometer specialized for 21 cm cosmology and now under construction in South Africa, was designed to be largely calibrated using the self-consistency of repeated measurements of the same interferometric modes. This technique, known as redundant-baseline calibration resolves most of the internal degrees of freedom in the calibration problem. It assumes, however, on antenna elements with identical primary beams placed precisely on a redundant grid. In this work, we review the detailed implementation of the algorithms enabling redundant-baseline calibration and report results with HERA data. We quantify the effects of real-world non-redundancy and how they compare to the idealized scenario in which redundant measurements differ only in their noise realizations. Finally, we study how non-redundancy can produce spurious temporal structure in our calibration solutions—both in data and in simulations—and present strategies for mitigating that structure.

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Section: Explaining Temporal Structure In Terms Of Non-redundancymentioning

confidence: 99%

Redundant-baseline calibration of the hydrogen epoch of reionization array

Dillon

Lee

Ali

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…Lastly, Nunhokee et al (2020) has measured the HERA radiation pattern in-situ using bright radio sources, and compared that with our simulated beams. The measured and simulated gains do agree well up to a level of -20 dB relative to the peak gain.…”

Section: Validation Of the Models With Measurementsmentioning

confidence: 99%

Understanding the HERA Phase I receiver system with simulations and its impact on the detectability of the EoR delay power spectrum

Fagnoni

Acedo

DeBoer

et al. 2020

Monthly Notices of the Royal Astronomical Society

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The detection of the Epoch of Reionization (EoR) delay power spectrum using a ”foreground avoidance method” highly depends on the instrument chromaticity. The systematic effects induced by the radio-telescope spread the foreground signal in the delay domain, which contaminates the EoR window theoretically observable. Applied to the Hydrogen Epoch of Reionization Array (HERA), this paper combines detailed electromagnetic and electrical simulations in order to model the chromatic effects of the instrument, and quantify its frequency and time responses. In particular, the effects of the analogue receiver, transmission cables, and mutual coupling are included. These simulations are able to accurately predict the intensity of the reflections occurring in the 150-m cable which links the antenna to the back-end. They also show that electromagnetic waves can propagate from one dish to another one through large sections of the array due to mutual coupling. The simulated system time response is attenuated by a factor 104 after a characteristic delay which depends on the size of the array and on the antenna position. Ultimately, the system response is attenuated by a factor 105 after 1400 ns because of the reflections in the cable, which corresponds to characterizable k∥-modes above 0.7 $h\,\,\rm {Mpc}^{-1}$ at 150 MHz. Thus, this new study shows that the detection of the EoR signal with HERA Phase I will be more challenging than expected. On the other hand, it improves our understanding of the telescope, which is essential to mitigate the instrument chromaticity.

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“…Methods to estimate primary beams include electromagnetic simulations of radio antennas using software packages e.g. or (Fagnoni et al 2021;Mahesh et al 2021), holographic beam mapping techniques (Berger et al 2016;Iheanetu et al 2019;Asad et al 2021), beam mapping using bright radio sources transiting through the sky (Baars et al 1977;Nunhokee et al 2020) as well as artificial sources e.g. satellites (Neben et al 2016;Line et al 2018), and more recently using artificial radio sources mounted on Unmanned Aerial Vehicles (e.g.…”

Section: Effect Of Inaccurate Primary Beammentioning

confidence: 99%

Effects of model incompleteness on the drift-scan calibration of radio telescopes

Gehlot

Jacobs

Bowman

et al. 2021

Monthly Notices of the Royal Astronomical Society

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Precision calibration poses challenges to experiments probing the redshifted 21-cm signal of neutral hydrogen from the Cosmic Dawn and Epoch of Reionization (z ∼ 30 − 6). In both interferometric and global signal experiments, systematic calibration is the leading source of error. Though many aspects of calibration have been studied, the overlap between the two types of instruments has received less attention. We investigate the sky based calibration of total power measurements with a HERA dish and an EDGES style antenna to understand the role of auto-correlations in the calibration of an interferometer and the role of sky in calibrating a total power instrument. Using simulations we study various scenarios such as time variable gain, incomplete sky calibration model, and primary beam model. We find that temporal gain drifts, sky model incompleteness, and beam inaccuracies cause biases in the receiver gain amplitude and the receiver temperature estimates. In some cases, these biases mix spectral structure between beam and sky resulting in spectrally variable gain errors. Applying the calibration method to the HERA and EDGES data, we find good agreement with calibration via the more standard methods. Although instrumental gains are consistent with beam and sky errors similar in scale to those simulated, the receiver temperatures show significant deviations from expected values. While we show that it is possible to partially mitigate biases due to model inaccuracies by incorporating a time-dependent gain model in calibration, the resulting errors on calibration products are larger and more correlated. Completely addressing these biases will require more accurate sky and primary beam models.

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Measuring HERA's Primary Beam in Situ: Methodology and First Results

Cited by 18 publications

References 55 publications

Redundant-baseline calibration of the hydrogen epoch of reionization array

Redundant-baseline calibration of the hydrogen epoch of reionization array

Understanding the HERA Phase I receiver system with simulations and its impact on the detectability of the EoR delay power spectrum

Effects of model incompleteness on the drift-scan calibration of radio telescopes

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