Design
The telescope consists of 14 elements (yielding 91 baselines), each of which have a horn reflector antenna focusing astrophysical signals into individual receivers (pseudomorphic HFET amplifiers, with a system temperature around 25 K and a physical temperature of 12 K, based on an NRAO design). The separate elements are combined using a correlator to form an aperture synthesis array. The elements are mounted on a tip-table, which is capable of tracking the sky and can tilt up to 35 degrees from the zenith.
The telescope has been used in three different configurations – "compact", "extended" and "super-extended", each of which differ in the separation distance between the elements (the difference between compact and extended is a factor of 2.25), and the size of the antennas. While the compact array has antennas 143mm in diameter, the extended array uses 322mm diameter antennas. This means that the compact array has a primary beam of 4.5 degrees, and a resolution of 30 arcminutes (multipoles between 100 and 800), while the extended array has a primary beam of 2 degrees, a resolution of 12 arcminutes and can hence observe multipoles between 250 and 1500. The extended array is also a factor of 5 more sensitive than the compact array. The super-extended array will be able to measure multipoles up to 3000, and has 550mm antenna mirrors. The front-end amplifiers were also upgraded.
The telescope can be tuned to frequencies between 26 and 36 GHz, with 1.5 GHz bandwidth, meaning that the telescope can carry out observations at different frequencies.
It also includes two 3.7m radio telescopes, also working at 30 GHz, which are dedicated to monitoring foreground sources. These source subtraction dishes were upgraded to more accurate ones following the first series of observations, to allow the monitoring of much weaker sources than previously.
Both the source subtractor dishes, and the VSA itself, are surrounded by large metal ground shields.
As the VSA is an interferometer, it directly measures the angular power spectrum of the CMB, rather than having to construct a map of the sky first.
Read more about this topic: Very Small Array
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