  Here we describe the Compact Array Broadband Backend (CABB) and present first
results obtained with the upgraded Australia Telescope Compact Array (ATCA).
The 16-fold increase in observing bandwidth, from 2 x 128 MHz to 2 x 2048 MHz,
high bit sampling, and addition of 16 zoom windows (each divided into a further
2048 channels) provide major improvements for all ATCA observations. The
benefits of the new system are: (1) hugely increased radio continuum and
polarization sensitivity as well as image fidelity, (2) substantially improved
capability to search for and map emission and absorption lines over large
velocity ranges, (3) simultaneous multi-line and continuum observations, (4)
increased sensitivity, survey speed and dynamic range due to high-bit sampling,
and (5) high velocity resolution, while maintaining full polarization output.
The new CABB system encourages all observers to make use of both spectral line
and continuum data to achieve their full potential.
  Given the dramatic increase of the ATCA capabilities in all bands (ranging
from 1.1 to 105 GHz) CABB enables scientific projects that were not feasible
before the upgrade, such as simultaneous observations of multiple spectral
lines, on-the-fly mapping, fast follow-up of radio transients (e.g., the radio
afterglow of new supernovae) and maser observations at high velocity resolution
and full polarization. The first science results presented here include
wide-band spectra, high dynamic-range images, and polarization measurements,
highlighting the increased capability and discovery potential of the ATCA.

Instrumentation and Methods for Astrophysics;Cosmology and Nongalactic Astrophysics;Astrophysics of Galaxies;Solar and Stellar Astrophysics