The Australia Telescope Compact Array (ATCA) is a radio interferometer situated at the Paul Wild Observatory, near Narrabri in New South Wales, Australia. It is operated by the Australia Telecope National Facility (ATNF), a branch of CSIRO (the Commonwealth Scientific and Research Organization), which also operates the Mopra and Parkes observatories.

ATCA comprises six individual 22-m radio antennae (or ‘elements’) arranged primarily along a 6-km East-West track; towards the middle of this there is also a short North-South track or ‘spur’. The ATCA’s antennae can be moved along its tracks to change the beam size or resolution available at each observing frequency.

Five of the six antennas of the Australian Telescope Compact Array (ATCA) arranged on the main East-West track and the North spur (the latter is the horizontal track shown in this image).
Credit: ATNF/CSIRO

The ATCA operates in the millimetre and centimetre wavebands, specifically those centred around 20-, 13-, 6-, 3-, 1.2-, 0.7- and 0.3-cm.

The ATCA is a National Facility, which means it is open for use by everybody via a peer-review process. Applications are accepted biannually for semesters that span April-September and October-March. The winter semester is favoured for millimetre-wavelength observations, as the colder atmosphere is more stable for short-wavelength observing.