|Cosmic Background Imager|
Left: a face-on view of the CBI antenna platform showing one possible configuration of the 13 antennas.
Right: the CBI at elevation 50░.
The antenna platform is an irregular hexagon ~ 6.5 m in diameter and 0.6 m thick. It is a space-frame structure with 52 1-m triangular cells, each with four antenna locations. This allows many different array configurations, including baselines that are not simply integer multiples of 1 m. The pointing and stiffness requirements for the CBI antenna platform are driven by mosaicing. A visibility phase error of 1░ at wavelength 1 cm corresponds to a 1'' pointing error on a 6-m baseline or a displacement of 28 Ám in the surface of the antenna platform. The azimuth and platform rotation bearings in the CBI have ~ 2'' axial errors and the worst-case gravitational deformation in the platform is ~ 50 Ám. Thus, the worst-case visibility phase error on any CBI baseline will be ~ 5░.
The CBI mount on its concrete foundation in Chile, prior to installation of the antennas, electronics, and dome (August 1999).