The Millimetre Receiver Package
The new millimetre receivers system installed on the Australia Telescope Compact Array make use of Monolithic Microwave Integrated Circuit (MMIC) amplifiers. Astronomical signals in the 3mm, 7mm and 12mm bands are first amplified in the cyrogenically coolded, low noise amplifier (LNA) system. The broadband LNAs, use Indium Phosphide (InP) High Electron Mobility Transistor (HEMT) MMICs as the amplifying elements. The LNA's operate a 15 Kelvin in a common vacuum dewar and are cooled by a closed cycle helium regrigerator.
After amplification separate mixer and local oscillator (LO) systems down convert the signal from each polarization to common intermediate frequency (IF) bands. These IF bands match the 4.5 to 6 GHz and 8 to 11 GHz input frequencies of the existing (centimetre) Compact Array receivers. The signals are then processed by the existing Compact Array electronics.
The 12mm, 7mm and 3mm systems have separate feed horns. For this reason it is not possible to observe 2 bands simultaneosly. The selected feed horn is moved to the cassegrain focus of the Compact Array antenna using the rotating positioning system.
Both the 12mm and 7mm systems are equipped with a noise injection system which allows continuous monitoring of system temperatures and polarisation calibration.
For further information refer to the article by Moorey et al. 2002
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