Focal-plane array (radio astronomy)

. Traditional radio-telescopes have only one receiver at the focus of the telescope, but radio-telescopes are now starting to be equipped with focal plane arrays, which are of three different types: multi-beam feed arrays, bolometer arrays, and the experimental phased-array feeds.

Multi-beam feed arrays

Multi-beam feed arrays consist of a small array of

.

Bolometer arrays

Bolometer arrays are arrays of bolometer receivers which measure the energy of incoming radio photons. They are typically used for astronomy at millimeter wavelengths. Examples include the SCUBA receiver on the James Clerk Maxwell Telescope and the LABOCA ^[4] instrument on the APEX telescope.

Phased array feeds

Phased Array Feeds are an experimental type of focal plane array using

with appropriate weights to synthesise several discrete beams. They are currently being developed for the Apertif ^[5] upgrade to the Westerbork Synthesis Radio Telescope, and for the Australian Square Kilometre Array Pathfinder radio telescope.

Switched array feeds

A switchable array of feed antennas in the focal plane is referred to as a switchable FPA. With this configuration, it is possible to switch between a set of beams directed in different directions. This makes the system steerable in the switching sense, thus creating a multi-beam system. In a switched FPA, the distance between feeding elements are chosen following ^[6]

${\displaystyle \Delta d=F\lambda /D,}$

where F is the focal length of the optical system, D is the diameter of the optical system and λ is the wavelength.

Monopulse feeds

The angle to the observed target (e.g. a meteor in meteor studies) can be estimated using

. In such a configuration, three signals are collected from four feed elements. These signals are the elevation difference signal, the azimuth difference signal and the sum signal.

See also

• Staring array

References