Directional antenna

A directional antenna or beam antenna is an <a href="/facts/Antenna_(electronics)/pGlcXBvc">antenna</a> that radiates or receives greater radio wave power in specific directions. Directional antennas can radiate <a href="/facts/Radio_wave/XmB6WPpF">radio waves</a> in beams, when greater concentration of radiation in a certain direction is desired, or in receiving antennas receive radio waves from one specific direction only. This can increase the power transmitted to receivers in that direction, or reduce <a href="/facts/Interference_(communication)/BVce5g8d">interference</a> from unwanted sources. This contrasts with <a href="/facts/Omnidirectional_antenna/6h21xRge">omnidirectional antennas</a> such as <a href="/facts/Dipole_antenna/GYWgnX72">dipole antennas</a> which radiate radio waves over a wide angle, or receive from a wide angle. 
The extent to which an antenna's angular distribution of radiated power, its <a href="/facts/Radiation_pattern/5t0QU2mv">radiation pattern</a>, is concentrated in one direction is measured by a parameter called <a href="/facts/Antenna_gain/ke1y0LcM">antenna gain</a>. A high-gain antenna (HGA) is a directional antenna with a focused, narrow <a href="/facts/Beam_width/rxCGx8q8">beam width</a>, permitting more precise targeting of the radio signals. Most commonly referred to during <a href="/facts/Space_missions/2eKXYVdq">space missions</a>, these antennas are also in use all over <a href="/facts/Earth/HLLmDfj0">Earth</a>, most successfully in flat, open areas where there are no mountains to disrupt radiowaves.
In contrast, a low-gain antenna (LGA) is an <a href="/facts/Omnidirectional_antenna/6h21xRge">omnidirectional antenna</a>, with a broad radiowave beam width, that allows the signal to propagate reasonably well even in mountainous regions and is thus more reliable regardless of terrain. Low-gain antennas are often used in <a href="/facts/Spacecraft/YQqQaUw0">spacecraft</a> as a backup to the high-gain antenna, which transmits a much narrower beam and is therefore susceptible to loss of signal.
All practical antennas are at least somewhat directional, although usually only the direction in the plane parallel to the earth is considered, and practical antennas can easily be omnidirectional in one plane. The most common directional antenna types are

<ul><li>the <a href="/facts/Yagi%25E2%2580%2593Uda_antenna/lu6FNjcl">Yagi–Uda antenna</a>,</li>
<li>the <a href="/facts/Log-periodic_antenna/aHDbIHY7">log-periodic antenna</a>, and</li>
<li>the <a href="/facts/Corner_reflector_antenna/PV8KHzCn">corner reflector antenna</a>.</li></ul>
These antenna types, or combinations of several single-frequency versions of one type or (rarely) a combination of two different types, are frequently sold commercially as residential <a href="/facts/TV_antenna/0NWmdAIR">TV antennas</a>. <a href="/facts/Cellular_repeater/VYTFwYJY">Cellular repeaters</a> often make use of external directional antennas to give a far greater signal than can be obtained on a standard <a href="/facts/Cell_phone/H3EcqD9h">cell phone</a>. <a href="/facts/Satellite_television/UxytxnPW">Satellite television</a> receivers usually use <a href="/facts/Parabolic_antenna/8EpLcN6q">parabolic antennas</a>. For long and medium <a href="/facts/Wavelength/kcJU0ymz">wavelength</a> <a href="/facts/Frequencies/QUSbPaW8">frequencies</a>, <a href="/facts/Tower_array/Xv3BwKSb">tower arrays</a> are used in most cases as directional antennas.

Directional antenna open-in-new

Directional antenna