  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 wide-field 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.
