User manual

ILX34-AENWG ♦ Point I/O Platform Reference
Wireless POINT I/O Adapter User Manual
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ProSoftTechnology,Inc. Page187of209
September19,2011
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6.5 Antennas
Whenyouarereadytoconnectantennastotheradio,seeConnectingantennas.
Youmustalsoconsiderthreeimportantelectricalcharacteristicswhenselectingantennas:
 Antennapattern(page187)
 Antennagain(page188)
 Antennapolarity(page188)
 Antennalocation,spacing,andmounting(page192)
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6.5.1 Antenna Pattern
Informationbetweentwowirelessdevicesistransferredviaelectromagneticenergyradiatedby
oneantennaandreceivedbyanother.Theradiatedpowerofmostantennasisnotuniforminall
directionsandhasvaryingintensities.Theradiatedpowerinvariousdirectionsiscalledthe
patternoftheantenna.Eachantennashouldbe
mountedsothatitsdirectionofstrongest
radiationintensitypointstowardtheotherantennaorantennaswithwhichitwillexchange
signals.
Completeantennapatternsarethree‐dimensional,althoughoftenonlyatwo‐dimensionalslice
ofthepatternisshownwhenalltheantennasofinterestarelocatedinroughly
thesame
horizontalplane,alongthegroundratherthanaboveorbelowoneanother.
Aslicetakeninahorizontalplanethroughthecenter(orlookingdownonthepattern)iscalled
theazimuthpattern.Aviewfromthesiderevealsaverticalplaneslicecalledtheelevation
pattern.
Anantenna
patternwithequalornearlyequalintensityinalldirectionsisomnidirectional.Intwo
dimensions,anomnidirectionalpatternappearsasacircle(inthreedimensions,an
omnidirectionalantennapatternwouldbeasphere,butnoantennahastrueomnidirectional
patterninthreedimensions).Anantennaisconsideredomnidirectionalifone
ofitstwo
dimensionalpatterns,eitherazimuthorelevationpattern,isomnidirectional.
Beamwidthisanangularmeasurementofhowstronglythepowerisconcentratedinaparticular
direction.Beamwidthisathreedimensionalquantitybutcanbebrokenintotwo‐dimensional
slicesjustliketheantennapattern.Thebeamwidthofan
omnidirectionalpatternis360degrees
becausethepowerisequalinalldirections.
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