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Ultra-Gaussian Horns for ClOVER - a B-Mode CMB Experiment

Authors:
P.A. Ade, R. J. Wylde, J. Zhang
Abstract:
ClOVER is a UK funded experiment to be based in the Atacama Desert to measure the B-mode polarization of the Cosmic Microwave background between multipoles of 20 and 1000 down to foreground limited sensitivities. One of two telescopes will operate large focal plate arrays at 150 and 225 GHz, using TES bolometers. The feeds to these bolometers utilise corrugated horns with novel features which meet with two important performance requirements: very low sidelobes, to avoid uncontrolled signal contamination and high pass filtering to control the fields presented to the Radial Probe detectors. The former is provide by a design, developed by Graham Smith in St. Andrews, to deliberately excite HE12 higher order modes in a sine-square profile section of the horn, followed by an extended parallel section designed to bring the HE12 mode into phase with the dominate HE11 mode. Surprisingly wide bandwidths - at the 30% level - with sidelobes well below minus 35dB are achieved. Analysis shows that close to 99.88% of the transmitted power (in a time reversed view) is in the fundamental Gaussian free space mode - hence the term, Ultra-Gaussian horn. The later is provide by a filter section close to the transition into the detector module. The suppression of leaks well below the nominal HE11 cut-off provided an interesting computational and experimental challenge, requiring significant modelling effort in both HFSS and more traditional Mode Matching programs. Special attention has been applied to the production engineering of these horns - given budgetary constraints and the large number required (100 in each band).
Categories:
Applications, Components
Year:
2009
Session:
T4
Full-text:
Download a PDF of this paper.
Page Number(s):
128-137