The ABS telescope imaged the sky at a frequency of 145 GHz (2 mm wavelength), in the microwave region of the electromagnetic spectrum, where the CMB emission is at its maximum.

[2] The optics consisted of two 60 cm mirrors that were kept at a temperature of 4 K. At the frequencies relevant for measuring the CMB, emission from water vapor in the atmosphere can be a strong contaminant.

Inflationary models generically predict that a gravitational-wave background (GWB) would have been produced along with the density perturbations that seed large-scale structure formation.

[5][6] Based on an analysis of data from a 2400 deg2 primary observing patch (roughly 6% of the full sky), the ABS experiment measured the expected polarization of the CMB from density perturbations in the early universe, but found no evidence for a GWB from inflation.

[7] The ABS experiment also demonstrated the ability to use a half-wave plate as a fast, front-end polarization modulator for measurement stability[3] and control of systematic errors.