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Omdirigering til Radioantenne
 
{{IBrug}} ny - oversat noget fra https://en.wikipedia.org/w/index.php?title=Dipole_antenna&oldid=860472993
Tag: Fjernede omdirigering
Linje 1: Linje 1:
{{IBrug}}
#REDIRECT [[Radioantenne]]
[[File:Half – Wave Dipole.jpg|thumb|UHF-halvbølgedipolantenne.]]
[[File:Dipole radar altimeter antenna.jpg|thumb|Dipolantenne anvendt af [[radar-altimeter]] i en flyvemaskine.]]

[[File:Dipole receiving antenna animation 6 800x394x150ms.gif|thumb|En halvbølgedipolantenne der modtager et radiosignal. Den indkommende [[radiobølge]] ''(hvis [[elektriske felt]] er vist som <span style="color:green;">'''E''', grønne pile</span>)'' inducerer en oscillerende [[elektrisk strøm]] indeni antenneelementer ''(sorte pile)'', vekslende ladning de to sider af antennen positiv (+) og negativ (−). Da antennen kun er en halv bølgelængde lang ved radiobølgens frekvens, spændingen (vist som ''<span style="color:red;">'''V''', røde bånd</span>'') og strøm i antennen giver en [[stående bølge]]. Denne oscillerende strøm formidles fra antennen via ned [[transmissionslinje]]n til [[radioforsats]]en (repræsenteret ved resistor '''R''').]]

Indenfor [[radio]] og [[telekommunikation]] er en '''dipolantenne''' eller '''doublet'''<ref name="Winder">{{cite book |last1=Winder |first1=Steve |last2=Carr |first2=Joseph |author2-link=Joseph Carr |title=Newnes Radio and RF Engineering Pocket Book |edition=3rd |publisher=Newnes |year=2002 |page=4 |url=https://books.google.com/books?id=3b-_InpSowcC&pg=PA4&dq=%22simplest+practical+radiator |isbn=0080497470
}}</ref> den simpleste og mest bredt anvendte klasse af [[radioantenne]]r.<ref>{{cite work |title=Der Dipol in Theorie und Praxis |author=K. Hille (DL1VU)}}</ref><ref name="Basu"/>
Dipolantennen enhver af en klasse af antenner, der producerer et et udstrålingsdiagram som omtrent svarer til en elementær elektrisk dipol med en radioudstrålende struktur med en linjeformet strøm sådan energifødet, at strømmen kun har et punkt i hver ende.<ref name="ieee145">{{cite book |last1=Bodnar |first1=Donald |title=ANSI/IEEE Std 145-1993 IEEE Standard Definitions of Terms for Antennas |date=1993 |publisher=The Institute of Electrical and Electronics Engineers, Inc. |location=New York, NY |page=10 |quote=2.102 dipole antenna. Any one of a class of antennas producing a radiation pattern approximating that of an elementary electric dipole. Syn: doublet antenna.}}</ref>
En dipolantenne består almindeligvis af to udformningsmæssigt identiske elektrisk ledende elementer<ref name="RadioElectronics">{{cite web |title=Dipole Antenna / Aerial tutorial |department=Resources |publisher=Adrio Communications, Ltd. |website=Radio-Electronics.com |year=2011 |url=http://www.radio-electronics.com/info/antennas/dipole/dipole.php |accessdate=29 April 2013}}</ref> såsom [[metaltråd]]e, [[metalrør]] eller [[metalstav]]e.<ref name="Basu">{{cite book |last=Basu |first=Dipak |title=Dictionary of Pure and Applied Physics |edition=2nd |publisher=CRC Press |year = 2010 |page=21 |url=https://books.google.com/books?id=-QhAkBSk7IUC&pg=PA21 |isbn=1420050222}}</ref><ref name="Rouse">{{cite encyclopedia |last=Rouse |first=Margaret |article=Dipole Antenna |title=Online IT Encyclopedia |website=whatis.techtarget.com |year=2003 |url=http://searchmobilecomputing.techtarget.com/definition/dipole-antenna |accessdate=29 April 2013}}</ref><ref name="Balanis3">{{cite book |last=Balanis |first=Constantine A. |title=Modern Antenna Handbook |publisher=John Wiley & Sons |year=2011 |page=2.3 |url=https://books.google.com/books?id=UYpV8L8GNCwC&pg=SA2-PA3 |isbn=1118209753}}</ref>
Den drivende strøm fødes fra [[radiosender]]en - eller for modtagende antenner tages output-signalet fra mellem de to halvdele af antennen, som så formidles til [[radioforsats]]en. Hver side af de to halvdele af antennen forbindes til [[transmissionslinje]]ns ende ende - og den anden ende af transmissionslinjen forbindes til radiosenderen eller [[radiomodtageren]]s antenneindgang.

De fleste anvendte radioantenner indeholder en dipolantenne.{{km}} Selvom dipolantenner kan anvendes alene, anvendes de også som [[drivende element]]er i mere komplekse antennedesign<ref name="Basu" /><ref name="RadioElectronics" /> såsom [[Yagi-Uda-antenne]]n. Dipolantenner (eller design afledt af dem, inklusiv [[monopolantenne]]r) anvendes til at føde [[retningsbestemt antenne|retningsbestemte antenner]] såsom en [[hornantenne]], [[parabolantenna|parabolreflektor]] eller [[hjørnereflektor antenne|hjørnereflektor]].

==Historie==
Den tyske fysiker [[Heinrich Hertz]] var den første, der demonstrerede eksistensen af [[radiobølge]]r i 1887 ved at anvende hvad vi nu kalder en dipolantenne (med kapacitiv endebelastning). På den anden side fandt [[Guglielmo Marconi]] empirisk ud af at han kunne nøjes med jorde radiosenderen (eller den ene side af en transmissionslinje, hvis anvendt) så man kun kunne nøjes med den ene halvdel af antennen, herved var ''vertikalen'' eller [[monopolantenne]]n opfundet.<ref name="Balanis">{{cite book |last1=Balanis |first1=Constantine A. |title=Modern Antenna Handbook |publisher=John Wiley and Sons |date=2011 |pages=2-1 |url=https://books.google.com/books?id=UYpV8L8GNCwC&pg=SA2-PA3#v=onepage&q&f=false |isbn=1118209753}}</ref>
Til langdistance kommunikation anvendte Marconi [[Højfrekvens (3 MHz - 30 MHz)|højfrekvens]] og her blev der anvendt en monopolantenne. Når der skulle kommunikeres via højere frekvenser (især [[VHF]] til FM-radio og TV) var der en fordel at med meget mindre antenner som kunne sættes i toppen af antennetårne og dette var en dipolantenne eller en af dens varianter.

I radioens barndom, blev monopolantennen derfor kaldet en Marconi-antenne - og doublet (dipolantennen) blev opfattet som separate opfindelser. I dag opfattes monopolantennen som et specialtilfælde af dipolantennen{{km}} og hvor monopolantennen har et virtuelt element "under jorden".
<!--
==Dipolantenne varianter==
===Dipolantenner med forskellige længder===
The fundamental resonance of a thin linear conductor occurs at a frequency whose free-space wavelength is ''twice'' the wire's length, i.e. where the conductor is 1/2 wavelength long. Dipole antennas are frequently used at around that frequency and thus termed ''half-wave dipole'' antennas. This important case is dealt with in the next section.

Thin linear conductors of length ''l'' are in fact resonant at any integer multiple of a half wavelength:
: <math>l = n \frac{\lambda}{2}</math>

where ''λ'' = ''c/f'' is the wavelength and ''n'' is an integer. For a center-fed dipole, however, there is a great dissimilarity between ''n'' being odd or being even. Dipoles which are an ''odd'' number of half-wavelengths in length have reasonably low driving point impedances (which are purely resistive at that resonant frequency). However ones which are an ''even'' number of half-wavelengths in length, that is, an integer number of wavelengths in length, have a ''huge'' driving point impedance (albeit purely resistive at that resonant frequency).

For instance, a full-wave dipole antenna can be made with two half-wavelength conductors placed end to end for a total length of approximately ''L''&nbsp;=&nbsp;λ. This results in an additional gain over a half-wave dipole of about 2&nbsp;dB, but the huge feedpoint impedance makes it unsuitable as a stand-alone antenna.

A more practical antenna design is a bit longer. A 5/4-wave dipole antenna has a much lower but not purely resistive feedpoint impedance, which requires a [[matching network]] to the impedance of the transmission line. Its gain is about 3&nbsp;dB greater than a half-wave dipole, the highest gain of any dipole of any similar length.

{| class="wikitable"
|+ Gain of dipole antennas<ref name="Kraus" />
|-
! Length, '''L''', in wavelengths
! [[Directivity|Directive gain]] [[decibel#Antenna measurements|(dBi)]]
! Notes
|-
| ≪0.5
| 1.76
| Poor efficiency
|-
| 0.5
| 2.15
| Most common
|-
| 1.0
| 4.0
| Not used
|-
| 1.25
| 5.2
| Best gain
|-
| 1.5
| 3.5
| Third harmonic
|-
| 2.0
| 4.3
| Not used
|}

Other reasonable lengths of dipole do not offer advantages and are seldom used. However the overtone resonances of a half-wave dipole antenna at odd multiples of its fundamental frequency are sometimes exploited. For instance, [[amateur radio]] antennas designed as half-wave dipoles at 7&nbsp;MHz can also be used as 3/2-wave dipoles at 21&nbsp;MHz; likewise VHF television antennas resonant at the [[Band I|low VHF television band]] (centered around 65&nbsp;MHz) are also resonant at the [[Band III|high VHF television band]] (around 195&nbsp;MHz).

===Half-wave dipole{{anchor|Half-wave antenna}}===
A half-wave dipole antenna consists of two quarter-wavelength conductors placed end to end for a total length of approximately ''L''&nbsp;=&nbsp;λ/2.
[[File:lambdaover2-antenna.svg|right|thumb|The magnitude of current in a standing wave along the dipole.]]
[[File:Dipole xmting antenna animation 4 408x318x150ms.gif|thumb|frame|right|250px|Electric field of a half-wave dipole transmitting antenna.]]

If a half-wave dipole is driven at a point other the center, then the feed point resistance will be higher. The radiation resistance is ''usually'' expressed relative to the maximum current present along an antenna element, which for the half-wave dipole (and most other antennas) is also the current at the feedpoint. However, if the dipole is fed at a different point at a distance ''x'' from a current maximum (the center in the case of a half-wave dipole), then the current there is not I<sub>0</sub> but only I<sub>0</sub> cos(kx). In order to supply the same power, the voltage at the feedpoint has to be similarly ''increased'' by the factor 1/cos(kx). Consequently, the resistive part of the feedpoint impedance Re(V/I) is increased<ref>''Kraus'' p. 227</ref> by the factor 1/cos<sup>2</sup>(kx):
:<math>R_\text{feedpoint} = \frac{R_\text{radiation}}{\cos^2(k x)} = \frac{73.1\ \Omega}{\cos^2(k x)}</math>
This equation can also be used for dipole antennas of other lengths, provided that R<sub>radiation</sub> has been computed relative to the current maximum, which is ''not'' generally the same as the feedpoint current for dipoles longer than half-wave. Note that this equation breaks down when feeding an antenna near a current node, where cos(kx) approaches zero. Indeed, the driving point impedance rises greatly, but is nevertheless limited due to quadrature components of the elements' current which is ignored in the above model for the current distribution.<ref>''Kraus'' p. 228</ref>

===Folded dipole===
{{More citations needed|section|date=March 2018}}

A folded dipole is a half-wave dipole with an additional wire connecting its two ends. If the additional wire has the same diameter and cross-section as the dipole, two nearly identical radiating currents are generated. The resulting far-field emission pattern is nearly identical to the one for the single-wire dipole described above, but at resonance its feedpoint impedance <math>R_{fd}</math> is four times the radiation resistance of a single-wire dipole. This is because for a fixed amount of power, the total radiating current <math>I_0</math> is equal to twice the current in each wire and thus equal to twice the current at the feed point. Equating the average radiated power to the average power delivered at the feedpoint, we may write

The folded dipole is therefore well matched to 300&nbsp;ohm balanced transmission lines, such as twin-feed ribbon cable. The folded dipole has a wider bandwidth than a single dipole. They can be used for transforming the value of input impedance of the dipole over a broad range of step-up ratios by changing the thicknesses of the wire conductors for the fed- and folded-sides.<ref>{{cite journal |first=Yasuto |last=Mushiake |title=An Exact Impedance Step-Up Impedance-Ratio Chart of a Folded Antenna |journal=IRE. Trans. Ant. Prop. |volume=AP-3 |issue=4 |page=163 |date=October 1954 |url=http://www.sm.rim.or.jp/~ymushiak/sub.ire.chart.htm |accessdate=2014-01-10 |doi=}}</ref> Instead of altering thickness or spacing, one can add a third parallel wire to increase the antenna impedance 9&nbsp;times over a single-wire dipole, raising the impedance to 658&nbsp;ohms, making a good match for window line feed cable, and further broadening the resonant frequency band of the antenna.

Half wave folded dipoles are often used for [[FM radio]] antennas; versions made with [[twin lead]] which can be hung on an inside wall often come with FM tuners. The [[T2FD]] antenna is a folded dipole. They are also widely used as [[driven element]]s for rooftop [[Yagi-Uda antenna|Yagi]] [[television antenna]]s.

===Other variants===
There are numerous modifications to the shape of a dipole antenna which are useful in one way or another but result in similar radiation characteristics (low gain). This is not to mention the many [[directional antenna]]s which include one or more dipole elements in their design as [[driven element]]s, many of which are linked to in the information box at the bottom of this page.

* The ''bow-tie antenna'' is a dipole with flaring, triangular shaped arms. The shape gives it a much wider bandwidth than an ordinary dipole. It is widely used in UHF [[television antenna]]s.

[[File:UTR-2 - P3094042 (wiki).jpg|thumb|Cage dipole antennas in the Ukrainian [[Ukrainian T-shaped Radio telescope, second modification|UTR-2]] radio telescope. The 8&nbsp;m by 1.8&nbsp;m diameter galvanized steel wire dipoles have a bandwidth of 8–33&nbsp;MHz.]]
* The ''cage dipole'' is a similar modification in which the bandwidth is increased by using fat cylindrical dipole elements made of a "cage" of wires (see photo). These are used in a few broadband array antennas in the [[medium wave]] and [[shortwave]] bands for applications such as [[over-the-horizon radar|OTH radar]] and [[radio telescope]]s.
* A ''[[halo antenna]]'' is a half-wave dipole bent into a circle.<ref group=lower-alpha>Crucially, a [[halo antenna]] has no electrical connection between the two ends that are bent close together, unlike a [[loop antenna]].</ref> With a horizontal circle, this produces horizontally polarized radiation in a nearly omnidirectional pattern with reduced power wasted toward the sky compared to a bare horizontal dipole.
* A ''[[turnstile antenna]]'' comprises two dipoles crossed at a right angle and feed system which introduces a quarter-wave phase difference between the currents along the two. With that geometry, the two dipoles do not interact electrically but their fields add in the far-field producing a net radiation pattern which is rather close to [[isotropic radiator|isotropic]], with horizontal polarization in the plane of the elements and [[circular polarization|circular]] or elliptical polarization at other angles. Turnstile antennas can be stacked and fed in phase to realize an omnidirectional broadside array or phased for an end-fire array with circular polarization.
* The ''[[batwing antenna]]'' is a [[turnstile antenna]] with its linear elements widened as in a bow-tie antenna, again for the purpose of widening its resonant frequency and thus usable over a larger bandwidth, without re-tuning. When stacked to form an array the radiation is omnidirectional, horizontally polarized, and with increased gain at low elevations, making it ideal for television broadcasting.
* A ‘'''V'''’ (or “Vee”) antenna is a dipole with a bend in the middle so its arms are at an angle instead of co-linear.
* A ''Quadrant'' antenna is a ‘V’ antenna with an unusual overall length of a ''full'' wavelength, with two half-wave horizontal elements meeting at a right angle where it is fed.<ref>{{cite web |url=http://www.virhistory.com/navy/ant/ant-quad-1102-01.JPG |title=Quadrant antenna diagram |series=Navy shore station communication antennas |website=US Navy Radio Communications - 1950s & 1960s}}</ref> Quadrant antennas produce mostly [[horizontal polarization]] at low to intermediate elevation angles and have nearly [[omnidirectional antenna|omnidirectional]] radiation patterns.<ref>{{cite web |url=http://www.mwrs.org.au/wp-content/uploads/2016/05/014_Quadrant_Aerial_v3.pdf |title=Single wire quadrant antenna: Horizontal omnidirectional shortwave aerial comparisons |date=2016-05-13 |author=Ross Beaumont (VK2KRB) |publisher=Manly-Warringah Radio Society |location=Sydney, Australia}}</ref> One implementation uses "cage" elements (see above); the thickness of the resulting elements lowers the high driving point impedance of a full-wave dipole to a value that accommodates a reasonable match to open wire lines and increases the bandwidth (in terms of SWR) to a full octave. They are used for HF band [[Transmission (telecommunications)|transmissions]].
* The ''[[G5RV-antenna]]'' is a dipole antenna fed indirectly, through a carefully chosen length of 300Ω or 450Ω [[twin lead]], which acts as an impedance [[matching network]] to connect (through a [[balun]]) to a standard 50Ω coaxial transmission line.
* The ''[[sloper antenna]]'' is a slanted vertical dipole antenna attached to the top of a single tower. The element can be center-fed or can be end-fed as an unbalanced monopole antenna from a transmission line at the top of the tower, in which case the monopole's "ground" connection can better be viewed as a second element comprising the tower and / or transmission line shield.
* The ''[[Inverted vee antenna|inverted ‘V’ antenna]]'' is likewise supported using a single tower but is a balanced antenna with two symmetric elements angled toward the ground. It is thus a half-wave dipole with a bend in the middle. Like the [[sloper antenna|sloper]], this has the practical advantage of elevating the antenna but requiring only a ''single'' tower.
* The [[Near Vertical Incidence Skywave#AS2259|''AS-2259 Antenna'']] is an inverted-‘V’ dipole antenna used for local communications via [[Near Vertical Incidence Skywave]] (NVIS).

===Feeding a dipole antenna===
Ideally, a half-wave dipole should be fed using a balanced transmission line matching its typical 65&ndash;70&nbsp;Ω input impedance. [[Twin lead]] with a similar impedance is available but seldom used and does not match the balanced antenna terminals of most radio and television receivers. Much more common is the use of common 300&nbsp;Ω twin lead in conjunction with a ''folded dipole''. The driving point impedance of a half-wave folded dipole is 4 times that of a simple half-wave dipole, thus closely matching that 300&nbsp;Ω [[characteristic impedance]].<ref>Practical Wire Antennas 2 (I. Poole, G3YWX)</ref> Most FM broadcast band tuners and older analog televisions include balanced 300&nbsp;Ω antenna input terminals. However twin lead has the drawback that it is electrically disturbed by any other nearby conductor (including earth); it is never used for transmitting.

Many types of [[coaxial cable]] (or "coax") have a characteristic impedance of 75&nbsp;Ω, which would otherwise be a good match for a half-wave dipole. However coax is a [[Single-ended signaling|single-ended]] line whereas a center-fed dipole expects a [[balanced line]] (such as twin lead). By symmetry, one can see that the dipole's terminals have an equal but opposite voltage, whereas coax has one conductor grounded. Using coax regardless results in an unbalanced line, in which the currents along the two conductors of the transmission line are no longer equal and opposite. Since you then have a ''net current'' along the transmission line, the transmission line becomes an antenna itself, with unpredictable results (since it depends on the path of the transmission line).<ref name="w7el">Baluns: What They Do And How They Do It (W7EL) http://www.eznec.com/Amateur/Articles/Baluns.pdf</ref> This will generally alter the antenna’s intended radiation pattern, and change the impedance seen at the transmitter or receiver.

A [[balun]] is required to use coaxial cable with a dipole antenna. The balun transfers power between the single-ended coax and the balanced antenna, sometimes with an additional change in impedance. A balun can be implemented as a [[transformer]] which also allows for an impedance transformation. This is usually wound on a [[ferrite core|ferrite]] [[Toroidal inductors and transformers|toroidal core]]. The toroid core material must be suitable for the frequency of use, and in a transmitting antenna it must be of sufficient size to avoid [[Saturation (magnetic)|saturation]].<ref>Toroid Cores for 1:4 Baluns (DG3OBK) {{cite web |url=http://www.aroesner.homepage.t-online.de/balun.html |title=Archived copy |accessdate=2012-12-29 |deadurl=yes |archiveurl=https://web.archive.org/web/20111222223519/http://www.aroesner.homepage.t-online.de/balun.html |archivedate=2011-12-22 |df= }}</ref> Other balun designs are mentioned below.<ref>Baluns for 88–108 MHz B. Beezely (K6STI) http://www.ham-radio.com/k6sti/balun.htm</ref><ref>http://audiosystemsgroup.com/RFI-Ham.pdf</ref>

{{multiple image
| direction = horizontal
| align = center
| header = Feeding a dipole antenna with coax cable
| width = 150

| image1 = dipolefeedrad.png
| alt1 = Coax and antenna both acting as radiators instead of only the antenna.
| caption1 = Coax and antenna both acting as radiators instead of only the antenna.

| image2 = dipolewidebandbalun.png
| alt2 = Dipole with a current balun.
| caption2 = Dipole with a current balun.

| image3 = Dipolehalfwavebalun.png
| alt3 = A folded dipole (300 Ω) to coax (75 Ω) 4:1 balun.
| caption3 = A folded dipole (300 Ω) to coax (75 Ω) 4:1 balun.

| image4 = dipolesleevebalun.png
| alt4 = Dipole using a sleeve balun.
| caption4 = Dipole using a sleeve balun.

}}
{{clear}}

====Current balun====
A so-called current balun uses a transformer wound on a toroid or rod of magnetic material such as ferrite. All of the current seen at the input goes into one terminal of the balanced antenna. It forms a balun by choking common-mode current. The material isn't critical for 1:1 because there is no transformer action applied to the desired differential current.<ref>{{cite web |title=A Cost Effective Current-mode 1:1 Balun |author=Holland, R. |url=http://www.arising.com.au/people/Holland/Ralph/CMBalun.htm}}</ref><ref>{{cite web |url=http://vk5ajl.com/projects/baluns.php |title=baluns |department=projects}}</ref> A related design involves ''two'' transformers and includes a 1:4 impedance transformation.<ref name="w7el"/><ref>{{cite web |title=A Cost Effective Current-mode 1:4 Balun |author=Holland, R. |url=http://www.arising.com.au/people/Holland/Ralph/CM4Balun.htm}}</ref>

====Coax balun====
A coax balun is a cost-effective method of eliminating feeder radiation, but is limited to a narrow set of operating frequencies.

One easy way to make a balun is to use a length of coaxial cable equal to half a wavelength. The inner core of the cable is linked at each end to one of the balanced connections for a feeder or dipole. One of these terminals should be connected to the inner core of the coaxial feeder. All three braids should be connected together. This then forms a 4:1 balun, which works correctly at only a narrow band of frequencies.

====Sleeve balun====
At [[VHF]] frequencies, a sleeve balun can also be built to remove feeder radiation.<ref>[http://www.w8ji.com/sleeve_baluns.htm Sleeve Baluns]</ref>

Another narrow-band design is to use a ''λ''/4 length of metal pipe. The coaxial cable is placed inside the pipe; at one end the braid is wired to the pipe while at the other end no connection is made to the pipe. The balanced end of this balun is at the end where no connection is made to the pipe. The ''λ''/4 conductor acts as a transformer, converting the zero impedance at the short to the braid into an infinite impedance at the open end. This infinite impedance at the open end of the pipe prevents current flowing into the outer coax formed by the outside of the inner coax shield and the pipe, forcing the current to remain in the inside coax. This balun design is impractical for low frequencies because of the long length of pipe that will be needed.
-->

==Se også==
*[[Isotropisk antenne]]
*[[Rundstrålende antenne]]
*[[Piskantenne]]
*[[Balun]]
*[[Koaksialantenne]]
*[[Amatørradio]]
*[[Kortbølgelytning]]
*[[T-aerial]]

==Kilder/referencer==
{{Reflist}}

Elementære, korte og halvbølge dipolantenner:
{{refbegin|colwidth=33em}}
*{{Citation
|title= Electronic Radio and Engineering
|first= Frederick E.
|last= Terman
|first2= Robert
|last2= Helliwell
|publisher= MacGraw-Hill
|year= 1955
|edition= 4th
|isbn= 978-0-07-085795-7
|doi= }}
*{{Citation
|title=Lectures on Physics
|last=Feynman
|last2= Leighton
|last3= Sands
|publisher= Addison-Wesley
|volume=
|isbn=
|doi= }}
*{{Citation
|title= Classical Electricity and Magnetism
|first= W.
|last= Panofsky
|first2= M.
|last2= Phillips
|publisher= Addison-Wesley
|isbn=
|doi= }}
* http://www.ece.rutgers.edu/~orfanidi/ewa/ Electromagnetic Waves and Antennas, Sophocles J. Orfanidis.
* [http://www.n0hr.com/hamradio/73/10/ham_radio10.htm Wire Antenna Resources for Ham Radio] Wire Antenna Resources including off center fed dipole (OCFD), dipole calculators and construction sites
* https://web.archive.org/web/20060907074441/http://stewks.ece.stevens-tech.edu/sktpersonal.dir/sktwireless/lin-ant.pdf
* https://web.archive.org/web/20070926195106/http://www.nt.hs-bremen.de/peik/asc/asc_antenna_slides.pdf
* [http://farside.ph.utexas.edu/teaching/em/lectures/node94.html The Hertzian dipole]
* {{Citation
|url=http://www.arrl.org/catalog/?category=Antennas,+Transmission+Lines+%26+Propagation#6133
|title= The ARRL Antenna Book
|edition= 21st
|year= 2007
|publisher= The American Radio Relay League, Inc.
|isbn= 0-87259-987-6
|doi=}}
* {{Citation
|url= http://www.arrl.org/catalog/?category=Antennas,+Transmission+Lines+%26+Propagation#7075
|title= ARRL's Wire Antenna Classics - A collection of the best articles from ARRL publications
|volume= 1
|edition= First
|year= 2005
|publisher= The American Radio Relay League, Inc.
|isbn= 0-87259-707-5
|doi= }}
* [https://web.archive.org/web/20050526142614/http://dibinst.mit.edu/DIBNER/DIConferences/OldConferences/Sloan/reflecti.htm Reflections on Hertz and the Hertzian Dipole] [[Jed Z. Buchwald]], MIT and the Dibner Institute for the History of Science and Technology (link inactive February 2, 2007; archive accessed from Wayback, March 13, 2011)
{{refend}}

==Eksterne henvisninger==
*[http://www.emtalk.com/designer_tut_2.htm Dipole Antenna Tutorial] EM Talk
*[http://www.antenna-theory.com/antennas/broaddipole.php Broadband Dipoles] Antenna-Theory.com
*[http://www.ac6v.com/antprojects.htm AC6V's Homebrew Antennas Links]
*[http://www.eham.net/articles/24060 Your First HF Dipole] - simple yet complete tutorial from eham.net
*[https://www.electronics-notes.com/articles/antennas-propagation/dipole-antenna/dipole-antenna-aerial.php Dipole articles] - s series of pages about the dipole in its various forms

[[Kategori:Antennetyper]]

Versionen fra 8. dec. 2018, 23:02

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UHF-halvbølgedipolantenne.
Dipolantenne anvendt af radar-altimeter i en flyvemaskine.
En halvbølgedipolantenne der modtager et radiosignal. Den indkommende radiobølge (hvis elektriske felt er vist som E, grønne pile) inducerer en oscillerende elektrisk strøm indeni antenneelementer (sorte pile), vekslende ladning de to sider af antennen positiv (+) og negativ (−). Da antennen kun er en halv bølgelængde lang ved radiobølgens frekvens, spændingen (vist som V, røde bånd) og strøm i antennen giver en stående bølge. Denne oscillerende strøm formidles fra antennen via ned transmissionslinjen til radioforsatsen (repræsenteret ved resistor R).

Indenfor radio og telekommunikation er en dipolantenne eller doublet[1] den simpleste og mest bredt anvendte klasse af radioantenner.[2][3] Dipolantennen enhver af en klasse af antenner, der producerer et et udstrålingsdiagram som omtrent svarer til en elementær elektrisk dipol med en radioudstrålende struktur med en linjeformet strøm sådan energifødet, at strømmen kun har et punkt i hver ende.[4] En dipolantenne består almindeligvis af to udformningsmæssigt identiske elektrisk ledende elementer[5] såsom metaltråde, metalrør eller metalstave.[3][6][7] Den drivende strøm fødes fra radiosenderen - eller for modtagende antenner tages output-signalet fra mellem de to halvdele af antennen, som så formidles til radioforsatsen. Hver side af de to halvdele af antennen forbindes til transmissionslinjens ende ende - og den anden ende af transmissionslinjen forbindes til radiosenderen eller radiomodtagerens antenneindgang.

De fleste anvendte radioantenner indeholder en dipolantenne.[kilde mangler] Selvom dipolantenner kan anvendes alene, anvendes de også som drivende elementer i mere komplekse antennedesign[3][5] såsom Yagi-Uda-antennen. Dipolantenner (eller design afledt af dem, inklusiv monopolantenner) anvendes til at føde retningsbestemte antenner såsom en hornantenne, parabolreflektor eller hjørnereflektor.

Historie

Den tyske fysiker Heinrich Hertz var den første, der demonstrerede eksistensen af radiobølger i 1887 ved at anvende hvad vi nu kalder en dipolantenne (med kapacitiv endebelastning). På den anden side fandt Guglielmo Marconi empirisk ud af at han kunne nøjes med jorde radiosenderen (eller den ene side af en transmissionslinje, hvis anvendt) så man kun kunne nøjes med den ene halvdel af antennen, herved var vertikalen eller monopolantennen opfundet.[8] Til langdistance kommunikation anvendte Marconi højfrekvens og her blev der anvendt en monopolantenne. Når der skulle kommunikeres via højere frekvenser (især VHF til FM-radio og TV) var der en fordel at med meget mindre antenner som kunne sættes i toppen af antennetårne og dette var en dipolantenne eller en af dens varianter.

I radioens barndom, blev monopolantennen derfor kaldet en Marconi-antenne - og doublet (dipolantennen) blev opfattet som separate opfindelser. I dag opfattes monopolantennen som et specialtilfælde af dipolantennen[kilde mangler] og hvor monopolantennen har et virtuelt element "under jorden".

Se også

Kilder/referencer

  1. ^ Winder, Steve; Carr, Joseph (2002). Newnes Radio and RF Engineering Pocket Book (3rd udgave). Newnes. s. 4. ISBN 0080497470.
  2. ^ Skabelon:Cite work
  3. ^ a b c Basu, Dipak (2010). Dictionary of Pure and Applied Physics (2nd udgave). CRC Press. s. 21. ISBN 1420050222.
  4. ^ Bodnar, Donald (1993). ANSI/IEEE Std 145-1993 IEEE Standard Definitions of Terms for Antennas. New York, NY: The Institute of Electrical and Electronics Engineers, Inc. s. 10. 2.102 dipole antenna. Any one of a class of antennas producing a radiation pattern approximating that of an elementary electric dipole. Syn: doublet antenna.
  5. ^ a b "Dipole Antenna / Aerial tutorial". Resources. Radio-Electronics.com. Adrio Communications, Ltd. 2011. Hentet 29 april 2013.{{cite web}}: CS1-vedligeholdelse: Dato automatisk oversat (link)
  6. ^ Rouse, Margaret (2003). "Dipole Antenna". Online IT Encyclopedia. whatis.techtarget.com. Hentet 29 april 2013.{{cite encyclopedia}}: CS1-vedligeholdelse: Dato automatisk oversat (link)
  7. ^ Balanis, Constantine A. (2011). Modern Antenna Handbook. John Wiley & Sons. s. 2.3. ISBN 1118209753.
  8. ^ Balanis, Constantine A. (2011). Modern Antenna Handbook. John Wiley and Sons. s. 2-1. ISBN 1118209753.

Elementære, korte og halvbølge dipolantenner:

Eksterne henvisninger

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