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Focal-plane Array (radio Astronomy)
Focal-plane arrays (FPAs) are widely used in radio astronomy. FPAs are arrays of Receiver (radio), receivers placed at the Focus (geometry), focus of the optical system in a radio-telescope. The optical system may be a Reflecting telescope, reflector or a Lens (optics), lens. 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 feed horns at the Focus (geometry), focus of a radio-telescope. Each feed horn is connected to a receiver to measure the received power and each horn and receiver pair is sensitive to radio waves from a slightly different direction in the sky. A feed array with receivers will increase the survey speed of the telescope by a factor of , making them very powerful sur ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Focal-plane Array
A staring array, also known as staring-plane array or focal-plane array (FPA), is an image sensor consisting of an array (typically rectangular) of light-sensing pixels at the focal plane of a lens. FPAs are used most commonly for imaging purposes (e.g. taking pictures or video imagery), but can also be used for non-imaging purposes such as spectroscopy, spectrometry, lidar, LIDAR, and wave-front sensing. In radio astronomy, the focal-plane array (radio astronomy), FPA is at the Focus (optics), focus of a radio telescope. At optical and infrared wavelengths, it can refer to a variety of imaging device types, but in common usage it refers to two-dimensional devices that are sensitive in the infrared spectrum. Devices sensitive in other spectra are usually referred to by other terms, such as CCD (charge-coupled device) and CMOS image sensor in the visible spectrum. FPAs operate by detecting photons at particular wavelengths and then generating an electrical charge, voltage, or resi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Astronomy
Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest include planets, natural satellite, moons, stars, nebulae, galaxy, galaxies, meteoroids, asteroids, and comets. Relevant phenomena include supernova explosions, gamma ray bursts, quasars, blazars, pulsars, and cosmic microwave background radiation. More generally, astronomy studies everything that originates beyond atmosphere of Earth, Earth's atmosphere. Cosmology is a branch of astronomy that studies the universe as a whole. Astronomy is one of the oldest natural sciences. The early civilizations in recorded history made methodical observations of the night sky. These include the Egyptian astronomy, Egyptians, Babylonian astronomy, Babylonians, Greek astronomy, Greeks, Indian astronomy, Indians, Chinese astronomy, Chinese, Maya civilization, M ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Staring Array
A staring array, also known as staring-plane array or focal-plane array (FPA), is an image sensor consisting of an array (typically rectangular) of light-sensing pixels at the focal plane of a lens. FPAs are used most commonly for imaging purposes (e.g. taking pictures or video imagery), but can also be used for non-imaging purposes such as spectrometry, LIDAR, and wave-front sensing. In radio astronomy, the FPA is at the focus of a radio telescope. At optical and infrared wavelengths, it can refer to a variety of imaging device types, but in common usage it refers to two-dimensional devices that are sensitive in the infrared spectrum. Devices sensitive in other spectra are usually referred to by other terms, such as CCD (charge-coupled device) and CMOS image sensor in the visible spectrum. FPAs operate by detecting photons at particular wavelengths and then generating an electrical charge, voltage, or resistance in relation to the number of photons detected at each pixel. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Amplitude Monopulse
Amplitude-comparison monopulse refers to a common direction finding technique. This method is used in monopulse radar, electronic warfare and radio astronomy. Amplitude monopulse antennas are usually reflector antennas. Approach Two overlapping antenna beams are formed, which are steered in slightly different directions, usually such that they overlap at the half-power point (-3 dB-point) of the beams. By comparing the relative amplitude of the pulse in the two beams, its position in the beams can be determined with an accuracy dependent on the signal-to-noise ratio Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to noise power, often expressed in deci ... (SNR). An accuracy of a tenth of beamwidth can be achieved with an SNR of 10 dB. In most implementations, two signals are formed, one being the sum ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Focal Length
The focal length of an Optics, optical system is a measure of how strongly the system converges or diverges light; it is the Multiplicative inverse, inverse of the system's optical power. A positive focal length indicates that a system Convergence (optics), converges light, while a negative focal length indicates that the system Divergence (optics), diverges light. A system with a shorter focal length bends the Ray (optics), rays more sharply, bringing them to a focus in a shorter distance or diverging them more quickly. For the special case of a thin lens in air, a positive focal length is the distance over which initially Collimated beam, collimated (parallel) rays are brought to a Focus (optics), focus, or alternatively a negative focal length indicates how far in front of the lens a point source must be located to form a collimated beam. For more general optical systems, the focal length has no intuitive meaning; it is simply the inverse of the system's optical power. In mos ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Australian Square Kilometre Array Pathfinder
The ASKAP radio telescope is a radio telescope array located at Inyarrimanha Ilgari Bundara, the CSIRO Murchison Radio-astronomy Observatory in the Mid West region of Western Australia. The facility began as a technology demonstrator for the international Square Kilometre Array (SKA), an internationally planned radio telescope which will be larger and more sensitive. The ASKAP site has been selected as one of the SKA's two central locations. It is operated by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and forms part of the Australia Telescope National Facility. Construction commenced in late 2009 and first light was in October 2012. ASKAP consists of 36 identical parabolic antennas, each in diameter, working together as a single astronomical interferometer with a total collecting area of approximately . Each antenna is equipped with a phased-array feed (PAF), significantly increasing the field of view. This design provides both fast surve ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Westerbork Synthesis Radio Telescope
The Westerbork Synthesis Radio Telescope (WSRT) is an aperture synthesis interferometer built on the site of the former World War II Nazi detention and transit Westerbork transit camp, camp Westerbork, north of the village of Westerbork (village), Westerbork, Midden-Drenthe, in the northeastern Netherlands. Overview The WSRT comprises fourteen radio telescopes deployed in a linear array arranged on a East-West line, of which 10 are in a fixed equidistant position, 2 are nearby on a rail track, and 2 are located eastwards on another rail track. It has a similar arrangement to other radio telescopes such as the One-Mile Telescope, Australia Telescope Compact Array and the Ryle Telescope. Its Equatorial mount is what sets it apart from most other radio telescopes, most of which have an Altazimuth mount. This makes it specifically useful for specific types of science, like polarized emission research as the detectors maintain a constant orientation on the sky during an observat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Beamformer
Beamforming or spatial filtering is a signal processing technique used in sensor arrays for directional signal transmission or reception. This is achieved by combining elements in an antenna array in such a way that signals at particular angles experience constructive interference while others experience destructive interference. Beamforming can be used at both the transmitting and receiving ends in order to achieve spatial selectivity. The improvement compared with omnidirectional reception/transmission is known as the directivity of the array. Beamforming can be used for radio or sound waves. It has found numerous applications in radar, sonar, seismology, wireless communications, radio astronomy, acoustics and biomedicine. Adaptive beamforming is used to detect and estimate the signal of interest at the output of a sensor array by means of optimal (e.g. least-squares) spatial filtering and interference rejection. Techniques To change the directionality of the array when tran ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electromagnetic Field
An electromagnetic field (also EM field) is a physical field, varying in space and time, that represents the electric and magnetic influences generated by and acting upon electric charges. The field at any point in space and time can be regarded as a combination of an electric field and a magnetic field. Because of the interrelationship between the fields, a disturbance in the electric field can create a disturbance in the magnetic field which in turn affects the electric field, leading to an oscillation that propagates through space, known as an ''electromagnetic wave''. The way in which charges and currents (i.e. streams of charges) interact with the electromagnetic field is described by Maxwell's equations and the Lorentz force law. Maxwell's equations detail how the electric field converges towards or diverges away from electric charges, how the magnetic field curls around electrical currents, and how changes in the electric and magnetic fields influence each other. The Lor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phased Array
In antenna (radio), antenna theory, a phased array usually means an electronically scanned array, a computer-controlled Antenna array, array of antennas which creates a radio beam, beam of radio waves that can be electronically steered to point in different directions without moving the antennas. In a phased array, the power from the transmitter is fed to the radiating elements through devices called ''phase shifters'', controlled by a computer system, which can alter the phase or signal delay electronically, thus steering the beam of radio waves to a different direction. Since the size of an antenna array must extend many wavelengths to achieve the high gain needed for narrow beamwidth, phased arrays are mainly practical at the high frequency end of the radio spectrum, in the ultrahigh frequency, UHF and microwave bands, in which the operating wavelengths are conveniently small. Phased arrays were originally invented for use in military radar systems, to detect fast moving pla ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Atacama Pathfinder Experiment
The Atacama Pathfinder Experiment (APEX) is a radio telescope 5,064 meters above sea level, at the Llano de Chajnantor Observatory in the Atacama Desert in northern Chile Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ..., 50 km east of San Pedro de Atacama built and operated by three European research institutes. The main dish has a diameter of 12 m and consists of 264 aluminium panels with an average surface accuracy of 17 micrometres (Root mean square, rms). The telescope was officially inaugurated on September 25, 2005. The APEX telescope is a modified Atacama Large Millimeter Array, ALMA (Atacama Large Millimeter Array) prototype antenna and is at the site of the ALMA observatory. APEX is designed to work at sub-millimetre wavelengths, in the 0.2 to 1.5 mm range — ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
James Clerk Maxwell Telescope
The James Clerk Maxwell Telescope (JCMT) is a submillimetre-wavelength radio telescope at Mauna Kea Observatory in Hawaii, US. The telescope is near the summit of Mauna Kea at . Its primary mirror is 15 metres (16.4 yards) across: it is the largest single-dish telescope that operates in submillimetre wavelengths of the electromagnetic spectrum ( far-infrared to microwave).W.S. Holland et al., SCUBA: a common-user submillimetre camera operating on the James Clerk Maxwell Telescope, Monthly Notices of the Royal Astronomical Society: Letters Volume 303 Issue 4, Pages 659–672, 2002 Scientists use it to study the Solar System, interstellar dust and gas, and distant galaxies. The JCMT started operations in 1987, and was funded until February 2015 by a partnership between the United Kingdom and Canada, and the Netherlands. It was operated by the Joint Astronomy Centre and was named in honour of mathematical physicist James Clerk Maxwell. In March 2015 the operation of the JCM ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
