# Monopole Antenna Project

July 26, 2017 | Author: Akram Sarrawy | Category: Antenna (Radio), Wavelength, Radio Technology, Telecommunications, Physics & Mathematics

#### Description

2007

MONOPOLEANTENNA

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MonopoleAntenna Analysis,DesignandSimulationusingComputer          

Supervisor:

Dr.OmerAlSaraereh  Students:

DepartmentofElectricalandComputerEngineering HashemiteUniversity 2007 HashemiteUniversity|DepartmentofElectricalandComputerEngineering

MONOPOLEANTENNA

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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.  Fig.1:MonopoleAntenna 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 HashemiteUniversity|DepartmentofElectricalandComputerEngineering

MONOPOLEANTENNA

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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

HashemiteUniversity|DepartmentofElectricalandComputerEngineering

MONOPOLEANTENNA

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Thewhipantenna.

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HashemiteUniversity|DepartmentofElectricalandComputerEngineering

MONOPOLEANTENNA

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Monopoleantenna 

ChapterII

ElectricandMagneticfieldinnearandfarfiledregions 2.1.1BOUNDARYCONDITIONS Thecurrentamplitudes,I(z)andI(r),onthemonopoleelementandgroundplane,respectively,aregenerally complexandinitiallyunknownquantities.Considernowthecasewherethecurrentdistributiononthemonopole elementisassumedtobesinusoidal.

………………………………………………………………..(Eq.1) ………………………………………………………………..(Eq.2)

        Althoughasinusoidaldistributionofcurrentisnotpossible,evenforaninfinitelythinantenna,ismostlikelyafair approximationtothecurrentifthemonopoleelementissufficientlythinelectricallyandnottoolong[13].Fora centerfeddipoleofradiusbandtotallength2,Elliot[5]givesexampleswherethecurrentdistributionis approximatelysinusoidalandofapproximatelyconstantargumentfor Elliotdemonstratesthatthecurrentdistributionisno longersinusoidalnearthecenterofthedipole,noris(argz)approximatelyconstant.Balanis[6]shows ThecurrentdistributionisnotsinusoidalnearthecenteroftheDipole. Thecurrentdistributionisneithersinusoidal,norofconstantphase,andthatthedeviationsfromEq.(1)and(2) increasewithincreaseinvaluesofh/andb/.Onthebasisoftheaboveresults,itappearsthatEq.(1)and(2)are approximatelyvalidfortheconditions:

………………………………………………………………..(Eq.4)

HashemiteUniversity|DepartmentofElectricalandComputerEngineering

MONOPOLEANTENNA

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 TheconstraintofEq.(4)correspondstotheidealizedconditionthattheferritetoroidshavea1/ecurrent attenuationdistanceh1,givenby:  Thecurrentconstraintsonthemonopoleantennaaregivenby: 

………………………………………………………………..(Eq.5)

 ForthecurrentconstraintsofaboveequationsthetotalmagneticandelectricfieldintensitiesH(total),E(total)atan arbitraryfieldpointP(X,Y,Z)externaltotheelementexcitationsourcepointsaresimplythevectorsumofthefields resultingfromtheelementcurrentandthecurrentinducedonthegroundplanebythefieldsincidentbythe element. 

………………………………………………………………..(Eq.6) Where: