|
Search over 100 encyclopedias and dictionaries: |
Research categories | Follow us on Twitter |
Research categories
View all topics in the newsView all reference sources at Encyclopedia.com |
|||
antenna
antenna , in electronics, system of wires or other conductors used to transmit or receive radio or other electromagnetic waves (see radio ); sometimes called an aerial. The idea of using an antenna was developed by Guglielmo Marconi (c.1897). In a transmitting antenna, the signal from an electronic circuit causes electrons in the antenna to oscillate; these moving electric charges generate electromagnetic radiation, which is transmitted through the air and space. Distribution of the waves depends on the design of the antenna; the transmitting antennas of a radio station might be designed to emit waves in all directions, while an antenna used for radar or space communications would be designed to focus the waves in a single direction. In a receiving antenna electromagnetic waves cause the electrons to oscillate, inducing a signal that can be detected by an electronic circuit. The antenna has a characteristic frequency related to its physical dimensions; a wire of a given length may be inherently tuned to radio waves whose wavelengths are simple fractions or multiples of the length of the wire. In general, a longer antenna is used to transmit or receive signals of longer wavelength. Although theoretically, the same antenna can be used both for sending and receiving signals, in many instances transmitting antennas are designed differently from receiving antennas, especially if they must handle very high power loads. Any straight vertical conductor may serve as an antenna and will transmit to or receive from all directions. A horizontal antenna radiates or intercepts energy principally at right angles to itself; the use of horizontal antennas enables transmitters to concentrate or beam their signals into desired areas and enables receivers to select one of several signals having the same frequency but arriving with different polarizations. The dish-shaped microwave antenna is highly directional; it uses a parabolic reflector to focus received signals on a small antenna element. Phased array antennas, used for long range radar and radio astronomy, are composed of large groupings of individual antennas; they may be electronically aimed by changing the relative phase of the signal at each element. |
|
|
Cite this article
"antenna." The Columbia Encyclopedia, 6th ed.. 2011. Encyclopedia.com. 26 May. 2012 <http://www.encyclopedia.com>. "antenna." The Columbia Encyclopedia, 6th ed.. 2011. Encyclopedia.com. (May 26, 2012). http://www.encyclopedia.com/doc/1E1-antenna.html "antenna." The Columbia Encyclopedia, 6th ed.. 2011. Retrieved May 26, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1E1-antenna.html |
|
Antenna
AntennaAn antenna is a device used to transmit and receive electromagnetic waves, such as radio waves and microwaves. Antennas are found in a great variety of communication devices, including radios and television sets, weather radar systems, satellite communications systems, and radio astronomy research centers. Your local radio station uses an antenna to transmit the programs it broadcasts. Words that are spoken or music that is played within the station are converted to electrical signals. These signals are then transmitted to an antenna in the form of an electric current. Electrons inside the antenna vibrate back and forth with the same frequency as the incoming electric current. The vibration is characteristic of the sounds produced within the station. As these electrons vibrate, they create an electromagnetic wave in the air around the antenna. That wave spreads out and travels in all directions from the antenna. The frequency of the wave is the same as the frequency of the electron vibration in the antenna and of the sounds spoken in the station. An antenna placed in the path of these waves reverses the above process. Electromagnetic waves in the air cause electrons in the receiving antenna to begin vibrating. The frequency of vibration is the same in the receiving antenna as it is in the wave. The vibrating electrons are converted into an electrical current, which travels into your radio receiver and is converted back into sound. Antennas come in all sizes and shapes, from the tiny units found in miniature transistor radios to the massive structures used to transmit messages to and receive messages from outer space. [See also Microwave communication; Radar; Radio ] |
|
|
Cite this article
"Antenna." UXL Encyclopedia of Science. 2002. Encyclopedia.com. 26 May. 2012 <http://www.encyclopedia.com>. "Antenna." UXL Encyclopedia of Science. 2002. Encyclopedia.com. (May 26, 2012). http://www.encyclopedia.com/doc/1G2-3438100049.html "Antenna." UXL Encyclopedia of Science. 2002. Retrieved May 26, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1G2-3438100049.html |
|
antenna
antenna A device used in radio astronomy to detect radio waves; also known as an aerial. In an antenna, radio waves induce an oscillating electric current in a conductor. The simplest antenna is a dipole antenna, which is a simple metal rod. More complex antennas, such as the Yagi antenna, may consist of a dipole or folded dipole (the driven element) with other conducting rods (parasitic elements) which direct or reflect the waves on to the dipole and so increase the antenna's directivity and gain. The most powerful radio telescopes, especially at high frequencies, use parabolic (dish) antennas to collect waves and bring them to a focus. Large numbers of antennas may be combined in an array to achieve high resolution. Antennas may also be used to transmit radio waves.
|
|
|
Cite this article
"antenna." A Dictionary of Astronomy. 1997. Encyclopedia.com. 26 May. 2012 <http://www.encyclopedia.com>. "antenna." A Dictionary of Astronomy. 1997. Encyclopedia.com. (May 26, 2012). http://www.encyclopedia.com/doc/1O80-antenna.html "antenna." A Dictionary of Astronomy. 1997. Retrieved May 26, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O80-antenna.html |
|
antenna
an·ten·na / anˈtenə/ • n. 1. Zool. (pl. -ten·nae / -ˈtenē/ ) either of a pair of long, thin sensory appendages on the heads of insects, crustaceans, and some other arthropods. ∎ (antennae) fig. the faculty of instinctively detecting and interpreting subtle signs: he has the political antennae of a party whip. 2. (pl. -ten·nas ) a rod, wire, or other device used to transmit or receive radio or television signals. DERIVATIVES: an·ten·nal / -ˈtenl/ adj. (in sense 1). an·ten·na·ry / -ˈtenərē/ adj. (in sense 1). |
|
|
Cite this article
"antenna." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. 26 May. 2012 <http://www.encyclopedia.com>. "antenna." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. (May 26, 2012). http://www.encyclopedia.com/doc/1O999-antenna.html "antenna." The Oxford Pocket Dictionary of Current English. 2009. Retrieved May 26, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O999-antenna.html |
|
antenna
antenna A long whiplike jointed mobile paired appendage on the head of many arthropods, usually concerned with the senses of smell, touch, etc. (see sensillum). In insects, millipedes, and centipedes they are the first pair of head appendages and are specialized and modified in many insects. In crustaceans they are the second pair of head appendages, the first pair (the antennules) having the sensory function, while the antennae are modified for swimming and for attachment.
|
|
|
Cite this article
"antenna." A Dictionary of Biology. 2004. Encyclopedia.com. 26 May. 2012 <http://www.encyclopedia.com>. "antenna." A Dictionary of Biology. 2004. Encyclopedia.com. (May 26, 2012). http://www.encyclopedia.com/doc/1O6-antenna.html "antenna." A Dictionary of Biology. 2004. Retrieved May 26, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O6-antenna.html |
|
antenna
antenna One of a pair of sensory structures which grow from the head of an invertebrate animal. Antennae may be long and filiform as in cockroaches, feathery as in male moths, or club-shaped as in some Diptera. The antenna is richly supplied with nerves and is covered with a battery of sense organs, including various types of mechanoreceptors and chemoreceptors. The antenna is a dead-end space, but haemolymph is circulated through it by means of a pump or heart.
|
|
|
Cite this article
MICHAEL ALLABY. "antenna." A Dictionary of Zoology. 1999. Encyclopedia.com. 26 May. 2012 <http://www.encyclopedia.com>. MICHAEL ALLABY. "antenna." A Dictionary of Zoology. 1999. Encyclopedia.com. (May 26, 2012). http://www.encyclopedia.com/doc/1O8-antenna.html MICHAEL ALLABY. "antenna." A Dictionary of Zoology. 1999. Retrieved May 26, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O8-antenna.html |
|
antenna
antenna horn or feeler of insects. XVII. — L. antenna, prop. antemna sail-yard, used in pl. (XV) to tr. Aristotle's keraioi ‘horns’ of insects.
|
|
|
Cite this article
T. F. HOAD. "antenna." The Concise Oxford Dictionary of English Etymology. 1996. Encyclopedia.com. 26 May. 2012 <http://www.encyclopedia.com>. T. F. HOAD. "antenna." The Concise Oxford Dictionary of English Etymology. 1996. Encyclopedia.com. (May 26, 2012). http://www.encyclopedia.com/doc/1O27-antenna.html T. F. HOAD. "antenna." The Concise Oxford Dictionary of English Etymology. 1996. Retrieved May 26, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O27-antenna.html |
|
antenna
antenna See aerial
|
|
|
Cite this article
"antenna." World Encyclopedia. 2005. Encyclopedia.com. 26 May. 2012 <http://www.encyclopedia.com>. "antenna." World Encyclopedia. 2005. Encyclopedia.com. (May 26, 2012). http://www.encyclopedia.com/doc/1O142-antenna.html "antenna." World Encyclopedia. 2005. Retrieved May 26, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O142-antenna.html |
|
antenna
antenna
•Alana, Anna, bandanna, banner, Branagh, canna, canner, Diana, fanner, Fermanagh, Guyana, Hannah, Havana, hosanna, Indiana, Joanna, lanner, Louisiana, manna, manner, manor, Montana, nana, planner, Pollyanna, Rosanna, savannah, scanner, spanner, Susanna, tanner
•Abner • Jaffna • Patna • caravanner
•Africana, Afrikaner, Americana, ana, banana, Botswana, bwana, cabana, caragana, Christiana, Dana, darner, Edwardiana, garner, Georgiana, Ghana, Gloriana, Guiana, gymkhana, Haryana, iguana, Lana, lantana, liana, Lipizzaner, Ljubljana, Mahayana, mana, mañana, marijuana, nirvana, Oriana, pacarana, piranha, prana, Purana, Rosh Hashana, Santayana, Setswana, sultana, Tatiana, Tijuana, Tirana, tramontana, Tswana, varna, Victoriana, zenana
•Gardner • partner
•antenna, Avicenna, duenna, henna, Jenna, Jenner, Morwenna, Ravenna, senna, Siena, sienna, tenner, tenor, Vienna
•Edna • interregna • Etna • Pevsner
|
|
|
Cite this article
"antenna." Oxford Dictionary of Rhymes. 2007. Encyclopedia.com. 26 May. 2012 <http://www.encyclopedia.com>. "antenna." Oxford Dictionary of Rhymes. 2007. Encyclopedia.com. (May 26, 2012). http://www.encyclopedia.com/doc/1O233-antenna.html "antenna." Oxford Dictionary of Rhymes. 2007. Retrieved May 26, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O233-antenna.html |
|
|
Search over 100 encyclopedias and dictionaries:
HighBeam™ Research, Inc. © Copyright 2012. All rights reserved.
The Encyclopedia.com advertising network includes:
