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Proceedings Paper

Far sidelobes measurement of the Atacama Cosmology Telescope
Author(s): Rolando Dünner; Patricio Gallardo; Ed Wollack; Fernando Henriquez; Carlos Jerez-Hanckes
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Paper Abstract

The Atacama Cosmology Telescope (ACT) is a 6m telescope designed to map the Cosmic Microwave Background (CMB) simultaneously at 145GHz, 220 GHz and 280 GHz. Its off-axis Gregorian design is intended to minimize and control the off-axis sidelobe response, which is critical for scientific purposes. The expected sidelobe level for this kind of design is less than -50 dB and can be challenging to measure. Here we present a measurement of the 145GHz far sidelobes of ACT done on the near-field of the telescope. We used a 1mW microwave source placed 13 meters away from the telescope and a chopper wheel to produce a varying signal that could be detected by the camera for different orientations of the telescope. The source feed was designed to produce a wide beam profile. Given that the coupling is expected to be dominated by diffraction over the telescope shielding structure, when combined with a measurements of the main beam far field response, these measurement can be used to validate elements of optical design and constrain the level of spurious coupling at large angles. Our results show that the diffractive coupling beyond the ground screen is consistently below -75 dB, satisfying the design expectations.

Paper Details

Date Published: 24 September 2012
PDF: 12 pages
Proc. SPIE 8452, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy VI, 845225 (24 September 2012); doi: 10.1117/12.926631
Show Author Affiliations
Rolando Dünner, Pontificia Univ. Católica de Chile (Chile)
Patricio Gallardo, Pontificia Univ. Católica de Chile (Chile)
Ed Wollack, NASA Goddard Space Flight Ctr. (United States)
Fernando Henriquez, Pontificia Univ. Católica de Chile (Chile)
Carlos Jerez-Hanckes, Pontificia Univ. Católica de Chile (Chile)


Published in SPIE Proceedings Vol. 8452:
Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy VI
Wayne S. Holland, Editor(s)

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