Changes

==Origin==

==Origin==

Medieval Latin, from Latin, sail yard

Medieval Latin, from Latin, sail yard

*[http://en.wikipedia.org/wiki/17th_century 1646]

*[https://en.wikipedia.org/wiki/17th_century 1646]

==Definitions==

==Definitions==

*1:plural ''an·ten·nae'' : one of a pair of slender movable segmented [[sensory]] organs on the head of insects, myriapods, and crustaceans  

*1:plural ''an·ten·nae'' : one of a pair of slender movable segmented [[sensory]] organs on the head of insects, myriapods, and crustaceans  

An '''antenna''' (or aerial) is an [[electrical]] device which converts [[electric]] currents into [[radio]] waves, and vice versa. It is usually used with a radio transmitter or radio receiver. In transmission, a radio transmitter applies an oscillating radio [[frequency]] electric current to the antenna's terminals, and the antenna [[radiates]] the energy from the current as [[electromagnetic]] [[waves]] (radio waves). In reception, an antenna intercepts some of the [[power]] of an electromagnetic wave in order to produce a tiny voltage at its terminals, that is applied to a receiver to be amplified. An antenna can be used for both transmitting and receiving.

An '''antenna''' (or aerial) is an [[electrical]] device which converts [[electric]] currents into [[radio]] waves, and vice versa. It is usually used with a radio transmitter or radio receiver. In transmission, a radio transmitter applies an oscillating radio [[frequency]] electric current to the antenna's terminals, and the antenna [[radiates]] the energy from the current as [[electromagnetic]] [[waves]] (radio waves). In reception, an antenna intercepts some of the [[power]] of an electromagnetic wave in order to produce a tiny voltage at its terminals, that is applied to a receiver to be amplified. An antenna can be used for both transmitting and receiving.

Antennas are essential components of all equipment that uses [[radio]]. They are used in systems such as [http://en.wikipedia.org/wiki/Radio_broadcasting radio broadcasting], [http://en.wikipedia.org/wiki/Broadcast_television broadcast television], two-way radio, communications receivers, radar, cell phones, and [[satellite]] communications, as well as other devices such as garage door openers, wireless microphones, [http://en.wikipedia.org/wiki/Bluetooth bluetooth] enabled devices, wireless computer networks, baby monitors, and [http://en.wikipedia.org/wiki/RFID_tag RFID tags] on merchandise.

Antennas are essential components of all equipment that uses [[radio]]. They are used in systems such as [https://en.wikipedia.org/wiki/Radio_broadcasting radio broadcasting], [https://en.wikipedia.org/wiki/Broadcast_television broadcast television], two-way radio, communications receivers, radar, cell phones, and [[satellite]] communications, as well as other devices such as garage door openers, wireless microphones, [https://en.wikipedia.org/wiki/Bluetooth bluetooth] enabled devices, wireless computer networks, baby monitors, and [https://en.wikipedia.org/wiki/RFID_tag RFID tags] on merchandise.

Typically an antenna consists of an arrangement of metallic [http://en.wikipedia.org/wiki/Conductor_(material) conductors] ("elements"), electrically connected (often through a transmission line) to the receiver or transmitter. An oscillating current of [[electrons]] forced through the antenna by a transmitter will create an oscillating [[magnetic]] field around the antenna elements, while the charge of the electrons also creates an oscillating electric field along the elements. These time-varying fields [[radiate]] away from the antenna into [[space]] as a moving [[electromagnetic]] field wave. Conversely, during reception, the oscillating electric and magnetic fields of an incoming radio wave exert force on the electrons in the antenna elements, causing them to move back and forth, creating oscillating currents in the antenna.

Typically an antenna consists of an arrangement of metallic [https://en.wikipedia.org/wiki/Conductor_(material) conductors] ("elements"), electrically connected (often through a transmission line) to the receiver or transmitter. An oscillating current of [[electrons]] forced through the antenna by a transmitter will create an oscillating [[magnetic]] field around the antenna elements, while the charge of the electrons also creates an oscillating electric field along the elements. These time-varying fields [[radiate]] away from the antenna into [[space]] as a moving [[electromagnetic]] field wave. Conversely, during reception, the oscillating electric and magnetic fields of an incoming radio wave exert force on the electrons in the antenna elements, causing them to move back and forth, creating oscillating currents in the antenna.

Antennas may also contain reflective or directive elements or surfaces not connected to the transmitter or receiver, such as parasitic elements, [http://en.wikipedia.org/wiki/Parabolic_antenna parabolic reflectors] or horns, which serve to direct the [[radio]] waves into a beam or other desired [[radiation]] [[pattern]]. Antennas can be [[designed]] to transmit or receive radio waves in all [[directions]] equally ([http://en.wikipedia.org/wiki/Omnidirectional_antenna omnidirectional antennas]), or transmit them in a beam in a particular [[direction]], and receive from that one direction only (directional or [http://en.wikipedia.org/wiki/High_gain_antenna high gain antennas]).

Antennas may also contain reflective or directive elements or surfaces not connected to the transmitter or receiver, such as parasitic elements, [https://en.wikipedia.org/wiki/Parabolic_antenna parabolic reflectors] or horns, which serve to direct the [[radio]] waves into a beam or other desired [[radiation]] [[pattern]]. Antennas can be [[designed]] to transmit or receive radio waves in all [[directions]] equally ([https://en.wikipedia.org/wiki/Omnidirectional_antenna omnidirectional antennas]), or transmit them in a beam in a particular [[direction]], and receive from that one direction only (directional or [https://en.wikipedia.org/wiki/High_gain_antenna high gain antennas]).

The first antennas were built in 1888 by German physicist [http://en.wikipedia.org/wiki/Heinrich_Hertz Heinrich Hertz] in his pioneering [[experiments]] to prove the existence of [[electromagnetic]] waves predicted by the [[theory]] of [http://en.wikipedia.org/wiki/James_Clerk_Maxwell James Clerk Maxwell]. Hertz placed dipole antennas at the [[focal point]] of [http://en.wikipedia.org/wiki/Parabolic_reflector parabolic reflectors] for both transmitting and receiving. He published his work in ''[http://en.wikipedia.org/wiki/Annalen_der_Physik_und_Chemie Annalen der Physik und Chemie]'' (vol. 36, 1889).

The first antennas were built in 1888 by German physicist [https://en.wikipedia.org/wiki/Heinrich_Hertz Heinrich Hertz] in his pioneering [[experiments]] to prove the existence of [[electromagnetic]] waves predicted by the [[theory]] of [https://en.wikipedia.org/wiki/James_Clerk_Maxwell James Clerk Maxwell]. Hertz placed dipole antennas at the [[focal point]] of [https://en.wikipedia.org/wiki/Parabolic_reflector parabolic reflectors] for both transmitting and receiving. He published his work in ''[https://en.wikipedia.org/wiki/Annalen_der_Physik_und_Chemie Annalen der Physik und Chemie]'' (vol. 36, 1889).

[[Category: Physics]]

[[Category: Physics]]