Abstract
The history of radio astronomy is very much a history of the pursuit of higher resolution. The angular scale of cosmic radio emission ranges from tens of degrees in the continuum emission of our Galaxy down to submilliarc-second structure in the cores of distant radio galaxies and quasars. Single apertures observing at centimeter wavelengths can only provide resolution of a few arc-minutes. Radio astronomers quickly turned to interferometer arrays to study the more compact cosmic radio sources [1-6].