Editing Very Small Array (section)

== Design ==
[[File:Teide Observatory 2018 116.jpg|thumb|right|The ground shield that used to hold the VSA]]
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,<ref name="cam" /> based on an [[NRAO]] design).<ref name="jbo_dev" /> The separate elements are combined using a correlator to form an [[aperture synthesis]] array.<ref name="jbo_dev" /> 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.<ref name="cam" />

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.<ref name="cam" /> While the compact array has antennas 143{{nbsp}}mm in diameter, the extended array uses 322{{nbsp}}mm diameter antennas.<ref name="grainge" /> 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.<ref name="jbo_techspecs" /> The extended array is also a factor of 5 more sensitive than the compact array.<ref name="grainge" /> The super-extended array will be able to measure multipoles up to 3000,<ref name="dickinson" /> and has 550{{nbsp}}mm antenna mirrors. The front-end amplifiers were also upgraded.<ref name="cleary" />

The telescope can be tuned to frequencies between 26 and 36&nbsp;GHz, with 1.5&nbsp;GHz bandwidth, meaning that the telescope can carry out observations at different frequencies.<ref name="taylor" />

It also includes two 3.7{{nbsp}}m radio telescopes, also working at 30&nbsp;GHz,<ref name="jbo_sources" /> which are dedicated to monitoring foreground sources.<ref name="watson" /> 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.<ref name="grainge" />

Both the source subtractor dishes, and the VSA itself, are surrounded by large metal ground shields.<ref name="jbo" />

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.<ref name="jbo" /><ref name="scott" />