Editing Directional antenna (section)

{{Short description|Radio antenna which has greater performance in specific alignments}}
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[[File:Patch antenna pattern.gif|thumb|Patch antenna gain pattern]]

A '''directional antenna''' or '''beam antenna''' is an [[antenna (electronics)|antenna]] that radiates or receives greater radio wave power in specific directions. Directional antennas can radiate [[radio wave]]s 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 [[Interference (communication)|interference]] from unwanted sources.  This contrasts with [[omnidirectional antenna]]s such as [[dipole antenna]]s 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 [[radiation pattern]], is concentrated in one direction is measured by a parameter called [[antenna gain]]. A '''high-gain antenna''' ('''HGA''') is a directional antenna with a focused, narrow [[beam width]], permitting  more precise targeting of the radio signals.<ref>{{cite book |title=Proceedings of the 11th National Technical Seminar on Unmanned System Technology 2019: NUSYS'19 |author1=Zainah Md Zain |author2=Hamzah Ahmad |author3=Dwi Pebrianti |author4=Mahfuzah Mustafa |author5=Nor Rul Hasma Abdullah |author6=Rosdiyana Samad |author7=Maziyah Mat Noh |publisher=Springer Nature |year=2020 |isbn=978-981-15-5281-6 |page=535 |url=https://books.google.com/books?id=t_LvDwAAQBAJ}} [https://books.google.com/books?id=t_LvDwAAQBAJ&pg=PA535 Extract of page 535]</ref> Most commonly referred to during [[space missions]],<ref>{{cite book |title=Encyclopedia of Space and Astronomy |author1=Joseph A. Angelo |edition= |publisher=Infobase Publishing |year=2014 |isbn=978-1-4381-1018-9 |page=364 |url=https://books.google.com/books?id=VUWno1sOwnUC}} [https://books.google.com/books?id=VUWno1sOwnUC&pg=PA364 Extract of page 364]</ref> these antennas are also in use all over [[Earth]], most successfully in flat, open areas where there are no mountains to disrupt radiowaves.{{citation needed|date=December 2019}}

In contrast, a '''low-gain antenna''' ('''LGA''') is an [[omnidirectional antenna]], 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 [[spacecraft]] as a backup to the ''high-gain antenna'', which transmits a much narrower beam and is therefore susceptible to loss of signal.<ref>{{cite encyclopedia |title=Low-gain antenna |encyclopedia=Oxford Reference (oxfordreference.com) |url=http://www.oxfordreference.com/view/10.1093/oi/authority.20110803100116961}}</ref>

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{{citation needed|date=December 2019}}
* the [[Yagi–Uda antenna]],
* the [[log-periodic antenna]], and
* the [[corner reflector antenna]].
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 [[TV antenna]]s. [[Cellular repeater]]s often make use of external directional antennas to give a far greater signal than can be obtained on a standard [[cell phone]]. [[Satellite television]] receivers usually use [[parabolic antenna]]s. For long and medium [[wavelength]] [[frequencies]], [[tower array]]s are used in most cases as directional antennas.