Radio Interferometers with wide bandwidths

The Australia Telescope Compact Array and the Very Large Array are currently being upgraded to operate with wide bandwidths; interferometers dedicated to the measurement of cosmic microwave background anisotropies are being designed with large instantaneous bandwidths for high sensitivity. Interferometers with wide instantaneous bandwidths that do not operate with correlators capable of decomposing the bands into narrow channels suffer from ‘bandwidth smearing’ effects in widefield imaging. The formalism of mosaic imaging is extended here to interferometers with finite bandwidths to examine the consequences for the imaging of wide fields if very wide instantaneous bandwidths are used. The formalism presented here provides an understanding of the signal processing associated with wide-band interferometers: mosaicing may be viewed as decomposing visibilities over wide observing bands and, thereby, avoiding ‘bandwidth smearing’ effects in wide-field imaging. In particular, the formalism has implications for interferometer measurements of the angular power spectrum of cosmic microwave background anisotropies: mosaic-mode observing with wide-band radio interferometers decompose wide-band data and synthesize narrow filters in multipole space.