 | | - The optical depth of the atmosphere,
 , becomes important. - Up to now, no low-noise amplifiers were used in front of the mixers. The ATCA is the first interferometer to make use of this new technology.
- This is because
 is important in the mm regime. - Consideration of field-of-view vs. collecting surface area: Maximising the antenna surface area A, which makes the telescope sensitive, decreases at the same time the field of view of an interferometer. Especially in the millimetre regime, but in general for imaging of extended sources on scales of the primary beam or larger, one ideally should have as many as possible moderate-size antennae.
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