Monopole Antenna Project

  MONOPOLEANTENNA Page[2]  HashemiteUniversity|DepartmentofElectricalandComputerEngineering      MonopoleAntenna Analysis,DesignandSimulationusingComputer  Supervisor: DrOmerAlSaraereh  Students: AbdulKaremAAlSbeehAimanSResiqAhmadHZaidIbrahimMHruobMohammedHishamIsmailAbdelRazzaqYazeedSulaimanJaafarHAbuRaad 2007 DepartmentofElectricalandComputerEngineeringHashemiteUniversity2007  MONOPOLEANTENNA Page[3]  HashemiteUniversity|DepartmentofElectricalandComputerEngineering    Fig1 :MonopoleAntenna   Introduction   ChapterI   OverviewaboutmonopoleAntenna   Nowdays,wirelesscommunicationsystemsarebecomingincreasinglypopularHowever,thetechnologiesforwirelesscommunicationstillneedtobeimprovedfurthertosatisfythehigherresolutionanddataraterequirementsInthecommunicationsystemthemorethingsislooktoisthecoastandlowpowerdeviceanditisthemonopolewhichpreviousthingisusedandstillbeimproveforthecommunicationsystemMonopoleisatypeoftheradioantennaformedbyreplacingonehalfofadipoleantennawithagroundplaneatrightanglestotheremaininghalfIfthegroundplaneislargeenough,themonopolebehavesexactlylikeadipole,asifitsreflectioninthegroundplaneformedthemissinghalfofthedipoleThisstudyisrestrictedtoamonopolegeometryconsistingofaverticalcylindricalelementatthecenterofaperfectlyconducting,infinitelythin,circulargroundplaneinfreespaceThisgeometryisofinterestbecauseitsradiationpatternisuniformintheazimuthdirectionandbecauseitselectricalcharacteristicsareprimarilyafunctionofonlythreeparameters,namely,theelementlength,theelementradius,andthegroundplaneradius,wheneachisnormalizedtotheexcitationwavelengthTherefore,thisgeometryisconducivetoanalysis,experimentalverification,andstandardizationAtypicalfeedforthemonopoleantennaisacoaxiallinewithitsinnerconductorconnectedthroughaholeinthegroundplanetotheverticalmonopoleelementanditsouterconductorconnectedbymeansofaflangetothegroundplaneTypically,theinnerconductor’sdiameterisequaltothemonopoleelement’sdiameterandtheouterconductor’sdiameterisequaltothegroundplaneholediameterUnlessstatedotherwise,suchafeedwillbeassumedinthisstudyTheratioofthecoaxialline’soutertoinnerconductordiametersaffectstheantenna’sinputimpedance,butonlysignificantlyforarelativelythickmonopoleelementonaverysmallgroundplaneFortheidealizedcaseofagroundplaneofinfiniteextentandinfiniteconductivity,themonopoleantennamaybemodeledbythemethodofimagesasadipolewithonehalftheinputimpedanceanddoublethepeakdirectivityofthedipoleTheinfinitegroundplanepreventsmonopoleradiationintothehemispherebelowthegroundplane,butallowsaradiationpatternidenticaltothatofthedipoleintheupper  MONOPOLEANTENNA Page[4]  HashemiteUniversity|DepartmentofElectricalandComputerEngineering    Fig2 :MonopoleBroadcasting   hemisphereHowever,foramonopoleelementmountedonagroundplaneoffiniteextent,theouteredgeofthegroundplanediffractsincidentradiationinalldirections,andconsequentlymodifiesthecurrentsonthegroundplaneandtheverticalelementfromthoseofaninfinitegroundplaneAttheouteredgeofthegroundplane,thecurrentsonitstopandbottomfacesareequalinmagnitudebutoppositeindirectionbecausethenetcurrentmustbezeroattheedgeOuteredgediffractionbecomesincreasinglysignificantwithdecreasingsizeofthegroundplanebecauseoftheincreasingmagnitudeofthecurrentsonthegroundplanefacesattheouteredgeEdgediffractioncanaltertheinputimpedancebymorethan3dBanddirectivityintheplaneofthegroundplanebymorethan6dBfromthevaluesforagroundplaneofinfiniteextentTheoreticalmodelsexistforpredictingtheeffectsofdiffractionbytheouteredgeofthegroundplaneTheexistingmodelsmaybeclassifiedintotwocategories,distinguishedbywhetherthecurrentdistributiononthemonopoleelementisinitiallyknownorunknownWhenthemonopoleelementisverythinandnottoolong,itscurrentdistributionisapproximatelysinusoidalandindependentoftheradiusofthegroundplaneConsequently,theelement’scurrentdistributioncanbeinitiallyspecifiedandwendedonlydeterminethegroundplane’scurrentdistributionForthiscategoryofmonopoles,thetheoreticalmodelsreportedintheliteratureessentiallyconsistofBardeen’sintegralequationmethodforagroundplaneradiusthatissmallcomparedtoawavelength[1],Richmond’smethodofmoments(groundplaneonly)foragroundplaneradiusthatisnottoolargecomparedtoawavelength[2],LeitnerandSpence’smethodofoblatesphericalwavefunctionsforagroundplaneradiusthatiscomparabletoawavelength[3–5],Tang’sscalartheoryofdiffractionandthegeometrictheoryofdiffraction(GTD)foragroundplaneradiusthatislargecomparedtoawavelength,andStorer’svariationmethodforagroundplaneradiusthatisverylargecomparedtoawavelength[3]Whenthemonopoleelementisrelativelythick,itscurrentdistributionisnolongersinusoidal,andthecurrentdistributiononboththemonopoleelementandthegroundplaneconsequentlyneedtobedeterminedasafunctionofthegroundplaneradiusForthiscategoryofmonopoles,thetheoreticalmodelsreportedintheliteratureessentiallyconsistofRichmond’smethodofmomentsforgroundplaneradiusthatisnottoolargecomparedtoawavelength[4]andAwadallaMaclean’smethodofmoments(monopoleelementonly)combinedwiththegeometrictheoryofdiffractionforgroundplaneradiusthatislargeorcomparabletoawavelength[9,10]ThieleandNewhousehavealsoreportedamodelthatcombinesthemethodofmomentswiththegeometrictheoryofdiffraction,buttheircomputerprogramisunavailable  Applicationsofmonopoleantenna   MonopoleantennasarecommonlyemployedinairborneandgroundbasedcommunicationsystemsatawiderangeoffrequenciesTheelectricalpropertiesofsuchantennasaredependentuponthegeometryofboththemonopoleelementandthegroundplaneTypically,themonopoleelementmaybeelectricallyshort(lengthismuchlessthanaquarterwavelength)ornearresonant(lengthapproximatelyaquarterwavelength),anditmaybethin(lengthtoradiusratioismuchgreaterthan104)orrelativelythick(lengthtoradiusratioof101to104)Inaddition,thegroundplanedimensionsmayvaryfroma