Measuring phased-array antenna beampatterns with high dynamic range for the Murchison Widefield Array using 137MHz ORBCOMM satellites

A. R. Neben, R. F. Bradley, J. N. Hewitt, G. Bernardi, Judd Bowman, F. Briggs, R. J. Cappallo, A. A. Deshpande, R. Goeke, L. J. Greenhill, B. J. Hazelton, M. Johnston-Hollitt, D. L. Kaplan, C. J. Lonsdale, S. R. McWhirter, D. A. Mitchell, M. F. Morales, E. Morgan, D. Oberoi, S. M. OrdT. Prabu, N. Udaya Shankar, K. S. Srivani, R. Subrahmanyan, S. J. Tingay, R. B. Wayth, R. L. Webster, A. Williams, C. L. Williams

Research output: Contribution to journalArticle

29 Scopus citations

Abstract

Detection of the fluctuations in a 21cm line emission from neutral hydrogen during the Epoch of Reionization in thousand hour integrations poses stringent requirements on calibration and image quality, both of which necessitate accurate primary beam models. The Murchison Widefield Array (MWA) uses phased-array antenna elements which maximize collecting area at the cost of complexity. To quantify their performance, we have developed a novel beam measurement system using the 137MHz ORBCOMM satellite constellation and a reference dipole antenna. Using power ratio measurements, we measure the in situ beampattern of the MWA antenna tile relative to that of the reference antenna, canceling the variation of satellite flux or polarization with time. We employ angular averaging to mitigate multipath effects (ground scattering) and assess environmental systematics with a null experiment in which the MWA tile is replaced with a second-reference dipole. We achieve beam measurements over 30dB dynamic range in beam sensitivity over a large field of view (65% of the visible sky), far wider and deeper than drift scans through astronomical sources allow. We verify an analytic model of the MWA tile at this frequency within a few percent statistical scatter within the full width at half maximum. Toward the edges of the main lobe and in the sidelobes, we measure tens of percent systematic deviations. We compare these errors with those expected from known beamforming errors.

Original languageEnglish (US)
Pages (from-to)614-629
Number of pages16
JournalRadio Science
Volume50
Issue number7
DOIs
StatePublished - Jul 1 2015

Keywords

  • antenna arrays
  • antennas
  • radio astronomy

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Earth and Planetary Sciences(all)
  • Electrical and Electronic Engineering

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    Neben, A. R., Bradley, R. F., Hewitt, J. N., Bernardi, G., Bowman, J., Briggs, F., Cappallo, R. J., Deshpande, A. A., Goeke, R., Greenhill, L. J., Hazelton, B. J., Johnston-Hollitt, M., Kaplan, D. L., Lonsdale, C. J., McWhirter, S. R., Mitchell, D. A., Morales, M. F., Morgan, E., Oberoi, D., ... Williams, C. L. (2015). Measuring phased-array antenna beampatterns with high dynamic range for the Murchison Widefield Array using 137MHz ORBCOMM satellites. Radio Science, 50(7), 614-629. https://doi.org/10.1002/2015RS005678