Menu
Home
People
Places
Arts
History
Plants & Animals
Science
Life & Culture
Technology
Reference.org
Antenna (radio)
open-in-new
<p>In <a href="/facts/Radio-frequency_engineering/fpFFb036">radio-frequency engineering</a>, an antenna or aerial (<a href="/facts/British_English/ymJR5Rnd">British English</a>) is an electronic device that converts an <a href="/facts/Alternating_current/qxICS3xa">alternating electric current</a> into <a href="/facts/Radio_wave/XmB6WPpF">radio waves</a> (transmitting), or radio waves into an electric current (receiving). It is the interface between radio waves <a href="/facts/Radio_propagation/80y1JV4M">propagating</a> through space and electric currents moving in metal <a href="/facts/Electrical_conductor/BSuyupLP">conductors</a>, used with a <a href="/facts/Transmitter/nFYghtKv">transmitter</a> or <a href="/facts/Receiver_(radio)/5olDTxkg">receiver</a>. In <a href="/facts/Transmission_(telecommunications)/33zk8a0A">transmission</a>, a radio transmitter supplies an electric current to the antenna's <a href="/facts/Terminal_(electronics)/CwbKGSuB">terminals</a>, and the antenna radiates the energy from the current as <a href="/facts/Electromagnetic_radiation/Ynx7ujCW">electromagnetic waves</a> (radio waves). In <a href="/facts/Receiver_(radio)/5olDTxkg">reception</a>, an antenna intercepts some of the power of a radio wave in order to produce an electric current at its terminals, that is applied to a receiver to be <a href="/facts/Amplifier/pnRgxncC">amplified</a>. Antennas are essential components of all <a href="/facts/Radio/XFr909M2">radio</a> equipment. </p><p>An antenna is an array of <a href="/facts/Conductor_(material)/BSuyupLP">conductor segments</a> (<a href="/facts/Driven_element/hzuNIeLB">elements</a>), electrically connected to the receiver or transmitter. Antennas can be designed to transmit and receive radio waves in all horizontal directions equally (<a href="/facts/Omnidirectional_antenna/6h21xRge">omnidirectional antennas</a>), or preferentially in a particular direction (<a href="/facts/Directional_antenna/oLesxknQ">directional</a>, or high-gain, or "beam" antennas). An antenna may include components not connected to the transmitter, <a href="/facts/Parabolic_antenna/8EpLcN6q">parabolic reflectors</a>, <a href="/facts/Horn_antenna/kVroJAmN">horns</a>, or <a href="/facts/Passive_radiator/6Yn8zvel">parasitic elements</a>, which serve to direct the radio waves into a beam or other desired <a href="/facts/Radiation_pattern/5t0QU2mv">radiation pattern</a>. Strong <a href="/facts/Directivity/ELvBJQu6">directivity</a> and good efficiency when transmitting are hard to achieve with antennas with dimensions that are much smaller than a half <a href="/facts/Wavelength/kcJU0ymz">wavelength</a>. </p><p>The first antennas were built in 1886 by German physicist <a href="/facts/Heinrich_Hertz/sbL2MSpM">Heinrich Hertz</a> in his pioneering experiments to prove the existence of electromagnetic waves predicted by the 1867 electromagnetic theory of <a href="/facts/James_Clerk_Maxwell/jtYyze61">James Clerk Maxwell</a>. Hertz placed <a href="/facts/Dipole_antenna/GYWgnX72">dipole antennas</a> at the focal point of <a href="/facts/Parabolic_reflector/uTkv4pJF">parabolic reflectors</a> for both transmitting and receiving. Starting in 1895, <a href="/facts/Guglielmo_Marconi/U7HXnDnq">Guglielmo Marconi</a> began development of antennas practical for long-distance <a href="/facts/Wireless_telegraphy/g1p5PaPA">wireless telegraphy</a> and opened a factory in <a href="/facts/Chelmsford/R08HBTn4">Chelmsford</a>, England, to manufacture his invention in 1898. </p> <a href="/facts/Half-wave_dipole/GYWgnX72">Half-wave dipole</a> antenna receiving a radio wave: The electric field (E) of the incoming wave pushes the electrons in the rods back and forth, and oscillating currents (black arrows) flow through the receiver.Antenna radiating radio waves: The transmitter applies an alternating current (red arrows) to the rods, which charges them alternately positive and negative, emitting loops of electric field. The arrows of the loops get reversed each time the current changes polarity.