Focal Plane Arrays
Encyclopedia
Focal Plane Arrays are arrays of receivers placed at the focus
of a radio-telescope. 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.
receivers, each with its own feed horn
, in a small array at the focus
of the radio-telescope. A feed array with n receivers will increase the survey speed of the telescope by a factor n, making them very powerful survey instruments. Because radio wavelengths are large, the resulting feed arrays are amongst the largest radio-astronomy receivers ever built. Examples include the multi-beam arrays
on the Parkes Observatory
, and the ALFA
array at Arecibo Observatory
, both of which have been used for major pulsar
and Hydrogen line
studies, such as HIPASS
.
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
instrument on the APEX
telescope.
technology in which heterodyne
receivers are closely spaced so that they do not act independently, but instead act as sensors of the electromagnetic field across the array of the incoming radio waves. The outputs of the receivers can then be combined to synthesise the effect of several discrete beams. They are currently being developed for the Apertif
upgrade to the Westerbork Synthesis Radio Telescope
, and for the Australian Square Kilometre Array Pathfinder
radio telescope. Phased array systems are widely used in medical ultrasound
where a phased array digitally focuses on one axis, and a conventional cylindrical acoustic lens focuses on the other.
Focus
Focus, FOCUS, or foci may refer to:In science, mathematics or computing:*Focus , selectively concentrating on one aspect of the environment while ignoring other things...
of a radio-telescope. 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 incorporate several distinct Superheterodyne receiverHeterodyne
Heterodyning is a radio signal processing technique invented in 1901 by Canadian inventor-engineer Reginald Fessenden where high frequency signals are converted to lower frequencies by combining two frequencies. Heterodyning is useful for frequency shifting information of interest into a useful...
receivers, each with its own feed horn
Feed horn
In satellite dish and antenna design, a feedhorn is a small horn antenna used to convey radio waves between the transmitter and/or receiver and the reflector, particularly in parabolic antennas...
, in a small array at the focus
Focus
Focus, FOCUS, or foci may refer to:In science, mathematics or computing:*Focus , selectively concentrating on one aspect of the environment while ignoring other things...
of the radio-telescope. A feed array with n receivers will increase the survey speed of the telescope by a factor n, making them very powerful survey instruments. Because radio wavelengths are large, the resulting feed arrays are amongst the largest radio-astronomy receivers ever built. Examples include the multi-beam arrays
on the Parkes Observatory
Parkes Observatory
The Parkes Observatory is a radio telescope observatory, 20 kilometres north of the town of Parkes, New South Wales, Australia. It was one of several radio antennas used to receive live, televised images of the Apollo 11 moon landing on 20 July 1969....
, and the ALFA
array at Arecibo Observatory
Arecibo Observatory
The Arecibo Observatory is a radio telescope near the city of Arecibo in Puerto Rico. It is operated by SRI International under cooperative agreement with the National Science Foundation...
, both of which have been used for major pulsar
Pulsar
A pulsar is a highly magnetized, rotating neutron star that emits a beam of electromagnetic radiation. The radiation can only be observed when the beam of emission is pointing towards the Earth. This is called the lighthouse effect and gives rise to the pulsed nature that gives pulsars their name...
and Hydrogen line
Hydrogen line
The hydrogen line, 21 centimeter line or HI line refers to the electromagnetic radiation spectral line that is created by a change in the energy state of neutral hydrogen atoms. This electromagnetic radiation is at the precise frequency of 1420.40575177 MHz, which is equivalent to the vacuum...
studies, such as HIPASS
HIPASS
The HI Parkes All Sky Survey was an astronomical survey for neutral atomic hydrogen . Data was taken between 1997 and 2002 using the Parkes Observatory. HIPASS covered 71% of the sky and identified 5317 sources emitting HI's signature wavelength...
.
Bolometer Arrays
Bolometer arrays are arrays of bolometerBolometer
A bolometer is a device for measuring the power of incident electromagnetic radiation via the heating of a material with a temperature-dependent electrical resistance. It was invented in 1878 by the American astronomer Samuel Pierpont Langley...
receivers which measure the energy of incoming radio photons. They are typically used for astronomy
Astronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
at millimeter wavelengths. Examples include the SCUBA
Scuba
Scuba is an acronym for self-contained underwater breathing apparatus. It may also refer to:* Scuba diving, the use of a self-contained breathing set to stay underwater for periods of time* Scuba set, the equipment used to do scuba diving...
receiver on the James Clerk Maxwell Telescope
James Clerk Maxwell Telescope
The James Clerk Maxwell Telescope is a submillimetre-wavelength telescope at Mauna Kea Observatory in Hawaii. Its primary mirror is 15 metres across: it is the largest astronomical telescope that operates in submillimetre wavelengths of the electromagnetic spectrum...
and the LABOCA
instrument on the APEX
Atacama Pathfinder Experiment
The Atacama Pathfinder Experiment is a radio telescope located at 5,100 meters above sea level, at the Llano de Chajnantor Observatory in the Atacama desert, in northern Chile, 50 kilometers to the east of San Pedro de Atacama. The main dish has a diameter of 12 meters and consists of 264...
telescope.
Phased Array Feeds
Phased Array Feeds are an experimental type of focal plane array using Phased arrayPhased array
In wave theory, a phased array is an array of antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions.An antenna array...
technology in which heterodyne
Heterodyne
Heterodyning is a radio signal processing technique invented in 1901 by Canadian inventor-engineer Reginald Fessenden where high frequency signals are converted to lower frequencies by combining two frequencies. Heterodyning is useful for frequency shifting information of interest into a useful...
receivers are closely spaced so that they do not act independently, but instead act as sensors of the electromagnetic field across the array of the incoming radio waves. The outputs of the receivers can then be combined to synthesise the effect of several discrete beams. They are currently being developed for the Apertif
upgrade to the Westerbork Synthesis Radio Telescope
Westerbork Synthesis Radio Telescope
The Westerbork Synthesis Radio Telescope is an aperture synthesis interferometer near camp Westerbork, north of the village of Westerbork, Midden-Drenthe, in the northeastern Netherlands. It consists of a linear array of 14 antennas with a diameter of 25 metres arranged on a 2.7 km East-West line...
, and for the Australian Square Kilometre Array Pathfinder
Australian Square Kilometre Array Pathfinder
The Australian Square Kilometre Array Pathfinder, or ASKAP, is CSIRO’s new radio telescope currently under construction at the Murchison Radio-astronomy Observatory in Mid West region of Western Australia...
radio telescope. Phased array systems are widely used in medical ultrasound
Medical ultrasonography
Diagnostic sonography is an ultrasound-based diagnostic imaging technique used for visualizing subcutaneous body structures including tendons, muscles, joints, vessels and internal organs for possible pathology or lesions...
where a phased array digitally focuses on one axis, and a conventional cylindrical acoustic lens focuses on the other.