Use of many dishes together, forming an interferometer array, allows astronomers to provide a more complete picture of objects.
Many sources have complicated shape, both with large and small-scale structure. Better
quality images of the observed sources can be formed if more than two radio-telescope-dishes
are used. Furthermore, with the advent of more powerful computers, signals from several
dishes can be combined electronically. In order to do so, it is important that the computer
should be used to carefully coordinate the movements of each dish. Thus, each dish can be
combined as a pair with every other dish to maximize the number of possible spacings between
the two dishes. This, in turn, maximizes the size-scales measured within the source, and
hence, information on the source. In addition, the rotation of the Earth further changes the
distances from the source to each dish, adding to the information on the source. The
interference pattern is generated by a special purpose computer called a correlator, which
electronically merges/multiplies the signal from each pair forming multiple fringe
patterns.
(Ref : Introduction to Radio Interferometry,
http://www.atnf.csiro.au/education/interferometry/introduction/index.html).