Monopole Antenna Project

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MONOPOLEANTENNA Page[2] HashemiteUniversity|DepartmentofElectricalandComputerEngineering MonopoleAntenna Analysis,DesignandSimulationusingComputer Supervisor: Dr.OmerAlSaraereh Students: AbdulKaremA.AlSbeeh AimanS.Resiq AhmadH.Zaid IbrahimM.Hruob MohammedHisham IsmailAbdelRazzaq YazeedSulaiman JaafarH.AbuRaad 2007 DepartmentofElectricalandComputerEngineering HashemiteUniversity 2007

Transcript of Monopole Antenna Project

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MONOPOLE�ANTENNA Page�[2]�

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

����

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

Supervisor:�

Dr.Omer�Al�Saraereh��Students:�Abdul�Karem��A.Al�Sbeeh��Aiman�S.Resiq��Ahmad�H.Zaid�Ibrahim�M.Hruob�Mohammed�Hisham�Ismail�Abdel�Razzaq��Yazeed�Sulaiman�Jaafar�H.AbuRaad�

2007

Department�of�Electrical�and�Computer�Engineering�Hashemite�University�

2007�

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

���������������������������Fig.1:�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�

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

����������������� ��Fig.2:�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�

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

Fig.3:�Azimuthally�Plan

fraction� of� a� wavelength� to� many� wavelengths.� Therefore,� it� is� desirable� to� know� how� the� input� impedance� and�radiation�pattern�of�the�antenna�change�as�the�dimensions�of�the�monopole�element�and�the�ground�plane�vary.�The�directivity� on� or� near� the� radio� horizon� (the� ground� plane� is� assumed� to� be� horizontal)� is� of� particular� interest�because�the�maximum�operational�range�of�a�communication�system�often�depends�on�the�directivity�on�the�radio�horizon.���The�broadband�monopole�antenna� is�vertically�polarized,�has�a� low�angle�radiation�pattern�and�is�used�for�short�range�circuits�by�ground�wave�and�medium�to�long�range�circuits�by�sky�wave.�The�antenna�is�broadband,�Omni�directional�and�conical.�The�broadband�frequency�capability� does� not� require� tuning.� The� radiation� pattern� in� the�azimuth� plane� is� essentially� unidirectional,� while� the� elevation�pattern�varies�with�frequency.�The�support�structure�is�a�guyed�mast�supported� on� a� base� insulator.� The� radiator� comprises� a� bi�conical�cage�of�wire.�Monopole�antennas�require�a�radial�ground�screen�for�specified� performance.� The� ground� screen� consists� of� wire�conductors�laid�out�radially�from�the�tower�base�and�terminated�at�the�outer�end.��The�monopole�Antenna�is�commonly�used�in�radio�broadcasting,�the�radio� frequency� power� from� the� broadcasting� transmitter� is� fed�across� the� base� insulator� between� the� tower� and� a� ground� system.� The� ground� system� normally� comprises� 120�buried� copper� or� phosphor� bronze� radial� wires� at� least� one�quarter� wavelength� long� and� a� ground�screen� in� the�immediate�vicinity�of�the�tower.�All�the�ground�system�components�are�bonded�together,�usually�by�brazing�or�using�coin�silver�solder�to�help�reduce�corrosion.�Monopole�antennas�that�use�guy�wires�for�support�are�called�masts� in�some� countries.� In� the� United� States,� the� term� “mast”� is� not� generally� used� to� relate� to� antennas,� so� both� self�supporting�and�guyed�radio�antennas�are�simply�called�monopoles�if�they�stand�alone.�If�used�in�numbers�to�control�the�direction�of�radio�frequency�propagation,�they�are�called�directional�antenna�arrays.�

Examples�of�monopole�antennas�are:�

1. The�whip�antenna�.�

2. The�radio�mast���when�isolated�from�the�ground�and�bottom�fed.��

��

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

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.��

�������

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:� In�addition�to�the�constraint�on�I(z)�given�by�Eq.�(1),�assume�that�the�return�current�Ir(z)�on�the�outside�of�the�coaxial�line’s�outer�conductor�is�given�by:�

………………………………………………………………..�(Eq.1)�

………………………………………………………………..�(Eq.2)�

………………………………………………………………..�(Eq.3)�

………………………………………………………………..�(Eq.4)

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

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:��

��Where���������������������������is�the�current�on�the�bottom�of�the�ground�plane�at�a�radius�equal�to�that�of�the�outer�conductor� �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. � Where: 2.1.2�CONCEPT�OF�A�GROUND�PLANE�OF�ZERO�EXTENT��Consider�a�monopole�antenna�excited�by�a�coaxial�line�with�an�outer�conductor�of�radius�b1�that�is�terminated�by�free�space,�rather�than�by�a�ground�plane.�The�ground�plane�for�such�an�antenna�is�denoted�as�being�of�zero�extent.��

………………………………………………………………..�(Eq.5)�

………………………………………………………………..�(Eq.6)�

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

The�coaxial�line�excitation�may�be�replaced�by�an�equivalent�magnetic�current�(frill)�M��sitting�on�top�of�a�thick�ground�plane�of�radius�P=�b1�.For�sufficiently�lossy�ferrite�toroids�along�the�outside�of�the�coaxial�line,�the�current�on�the�exterior�of�the�coaxial�line’s�outer�conductor�may�be�neglected.�The�magnetic�frill�may�be�removed�from�the�circuit�without�appreciably�affecting�the�results�because�kb1<<1�for�the�assumed�sinusoidal�current�distribution�on�the�monopole�element.�Finally,�the�ground�plane�of�radius�b1�may�be�removed�from�the�circuit�without�appreciably�affecting�the�results�because�a�finite�current�on�an�electrically�small�conductor�does�not�radiate�an�appreciable�amount�of�power�compared�with�that�radiated�by�a�monopole�element�of�length�hqb1:�The�circuit�idealization�of�a�monopole�antenna�with�a�ground�plane�of�zero�extent�is�therefore�an�electrically�thin�monopole�element�with�no�ground�plane.��The�near�fields,�far�fields,�and�input�impedance�of�an�electrically�thin�monopole�element�are�derived�and�summarized�in�the�later�section.�The�input�impedance�is�derived�by�way�of�the�induced�EMF�method.���2.1.3�NEAR�FIELDS� Consider�a�monopole�element�of�length�h�with�a�sinusoidal�current�distribution��������������������������������������������������������������������������������������������������������������������������������������On�the�surface�of�the�element�(Fig.�2.3)�for�an�electrically�thin�element�with�a�known�current�distribution,�the�fields�at�arbitrary�points�P(X,�Y,�Z)�external�to�the�element�may�be�determined�almost�exactly�by�approximating�the�source�points�to�lie�on�the�element�axis�that�is�for�the�current�waveform,�the�magnetic�vector�potential�A�is�given�by:���� ���������������������������������������������������������������������������������������������������������������������Fig.4:�Monod�pole�Antenna�far�and�near�filed�region�

��

�Exact�closed�form�expressions�of�A,�H,�E,�and�radiation�resistance�were�first�obtained�for�an�infinitely�thin�element�by�Brillouin�[7]�and�are�summarized�by�Stratton�[8].�The�magnetic�and�electric�fields�are�given�by���

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

����2.1.4�FAR�FIELDS� Consider�a�field�point�P�at�a�sufficiently�large�radial�distance�r,�which�satisfies�both�the�far�radiation�zone�and�Fraunhofer�diffraction�conditions�given�by:�

�For�the�far�radiation�zone�conditions,�and����For�the�Fraunhofer�diffraction�condition�for�these�conditions,�we�write���������

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

��Reduce�to�the�far�fields�given�by:��

�������

��The�radiation�resistance�R,�referred�to�the�base�current,�is�given�for�an�infinitely�thin�element�by:��

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

The�result�given�for�the�definite�integral�of�in�section�3�is�readily�obtained�by�Letting�t�=�Cos���and�noting�that���

��The�numeric�directivity�d�(�)�is�given�by��

� For electrically short monopole elements and for

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

Directivity�and�input�impedance At a far-field observation point the numeric directivity of the antenna is defined as the ratio of its radiated power density to its radiated power density averaged over all directions. The radiated power density averaged over all directions is equivalent to the power density radiated by a hypothetical “isotropic” (ideal) antenna. Accordingly, the directivity expressed in spherical coordinates with the origin at the antenna, is given by: Table�1�:�Spherical,�Cylindrical,�and�Oblate�Spheroidal�Coordinates�

Coordinates� Spherical�r�(R,�,�)� Cylindrical�(p,Z,�)� Oblate�Spheroidal�(�,�,�)�Radius� R� P�=r�Sin(�)�Elevation� �� Z�=�r�Cos(�)�Azimuth� �� �� ��

��The�total�time�averaged�radiated�power�Ptotal�of�the�antenna�is�given�by�

�The�antenna�radiation�resistance�Rrad,�referred�to�the�complex�amplitude�I�(Z=0)�of�the�antenna�base�current,�is�defined�by:�

��After�substituting�equations�above:�

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

Where�Rohmic�is�the�ohmic�loss�resistance�of�the�antenna�for�finite�conductivity�of�either�the�monopole�element�or�the�ground�plane�Here,�Rohmic�=�0�because�the�monopole�element�and�ground�plane�are�assumed�to�be�of�infinite�conductivity.�Accordingly,�

�����

Antenna�Gain� It�is�of�interest�to�determine�the�antenna�gain�(including�mismatch�loss)�on�the�radio�horizon���as�a�function�of����������������������������������������������������������Ground�plane�radius�for�the�same�tuning�words�that�are�selected�when�the�monopole�element�is�mounted�on�the�reference�ground�plane.�The�antenna�gain,�G�(�/2)�(decibels�relative�to�isotropic�(dBi)),�on�the�radio�horizon�is�given�by�

��The�radiation�efficiency,��,�is�given�by�

��

��

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

�Although� the� mismatch� gain� M� is� determined� by� specifying� the� voltage� reflection� coefficient� r,� it� may� also� be�determined� by� specifying� the� equivalent� voltage� standing� wave� ratio� (VSWR)� that� would� be� measured� along� a�transmission� line� between� the� source� generator� and� the� impedance�matching� network.� The� VSWR,� r,� and� M� are�related�by:�

����The�analytical�model�does�not� include�the�effect�of�any� impedance�pad�that�might�be�placed�between�the�source�generator�and�the�impedance�matching�network.�A�two�port�impedance�pad�between�the�source�generator�and�the�impedance�matching�network�does�not�improve�the�mismatch�gain�of�the�antenna�but�does�help�protect�the�source�generator�from�being�damaged�by�the�reflected�power�from�the�antenna.�The�impedance�pad�reduces�the�amount�of� power� reflected� back� to� the� source� generator� but� also� reduces� the� antenna� gain� by� an� amount� equal� to� the�insertion�loss�L�(dB)�of�the�pad�(for�a�pad�whose�input�and�output�impedances�are�equal�to�the�source�impedance�when�the�opposite�port�is�terminated�in�the�source�impedance).�For�example,�a�pad�of�3�dB�insertion�loss�will�ensure�a�VSWR�<3:1�between�the�generator�and�the�pad�for�any�load�impedance�at�the�output�of�the�pad.�However,�the�antenna�gain�will�be�reduced�by�3�dB�since�the�voltage�reflection�coefficient�of�the�input�to�the�impedance�matching�network�will�be�unchanged�by�the�presence�of�the�pad�and�the�power�delivered�to�the�antenna�will�be�reduced�by�3�dB.�For�this�reason,�impedance�pads�are�generally�not�used�in�high�power�transmitting�antennas.�

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

TMn0�Spherical�Wave�Modes� The�solution�of�the�vector�Helmholtz�equation�in�spherical�co�ordinates,�subject�to�the�constraints�of�vertical�polarization,�outward�traveling�waves,�and�an�Omni�directional�pattern�in�the�azimuthally�direction,�is�a�set�of�orthogonal�TMn0�spherical�wave�modes.�The�resulting�fields�evaluated�at�a�radius�r�=�ro�are�given��

���

���The�radial�wave�impedance�Zn0(P)�of�the�Poynting�vector�in�the�outward�radial�direction�for�each�mode�is�defined�as���

���The�Poynting�vector�is�not�sufficient�to�characterize�the�mode�Qn0�because�its�imaginary�part�is�proportional�to�the�difference�(rather�than�the�sum)�of�electric�and�magnetic�stored�energies.�The�radial�wave�impedance�and�all�its�derivatives�with�respect�to�frequency�are�sufficient�but�not�convenient�to�characterize�Qn0�of�the�TMn0�mode.�������������������Fig.5:�Radiating�regions.��

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

Design�and�Simulation�an�Monopole�antenna�“Using�CST�2006B�software�” Chapter�

III��

�Monopole�Antenna�Configurations: 4.1�Type�One:�

� Soled�Monopole�with�feeding�from�origin.�

Fig.6�Monopole�Antenna�soled�

Fig.7�Monopole�Antenna�Feeding�

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

Fig.8�Port�Signal�������

Fig.9�Energy�Signal�

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

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Fig.10�Power�Flow����

������

Fig.11�Far�filed�Region�radiation�

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

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�����

Fig.12�Far�filed�Region�radiation�of��������

Fig.13�Far�filed�Region�radiation�of�axial�Ratio�

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

4.2�Type�Two:�� Soled�Monopole�with�feeding�from�origin�but�with�Y�axis�Orientation.�

��

��

Fig.14�Monopole�Antenna�with�center�Feeding�

Fig.15�center�Feeding�

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

����������������������

Fig.16�Port�Signal��������������

���������������������������������������������������

�Fig.17�Energy�Signal�

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

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�����

Fig.18�Power�Flow���

���������������������� Fig.19�Far�field�region�radiation��

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

�����

��

Fig.20�Far�field�region�radiation�of����4.3�Type�three:�

� Cylindrical�Monopole�with�feeding�from�origin.��

Fig.21�Cylindrical�Monopole�Antenna��

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

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���

Fig.22�Monopole�Antenna�Feeding����

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Fig.23�Port�Signal�

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

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��

Fig.24�Energy�Signal��������������������������

Fig.25�Power�Flow�

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

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Fig.26�Far�field�region�radiation�����

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Fig.27�Far�field�region�radiation�of����������

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

Conclusions Chapter�

IV��

Double�parameter�and�single�parameter�tuning�of�an�electrically�short�monopole�antenna�are�investigated�above�to�determine� the� range� of� ground�plane� radii� for� which� the� same� tuning� words� can� be� utilized� in� maintaining� a�specified�antenna�gain�over�the�30–150MHz�frequency�band.���In�double�parameter�tuning,� the� tuning�words�are�chosen�by�varying�two� inductances�of� the� impedance�matching�network� to�provide�a�perfect� impedance�match�at�each� frequency�of� interest�when� the�antenna� is�mounted�on�a�reference�ground�plane�of�4� ft� in� radius.� In� single�parameter� tuning,� the� tuning�words�are�chosen�by�varying�one�inductance�to�provide�a�perfect� impedance�match�at�30�MHz�and�zero�input�reactance�at�other�frequencies�when�the�antenna�is�mounted�on�a�ground�plane�of�4�ft�in�radius.��Edge� diffraction� by� the� circular� ground� plane� significantly� alters� the� antenna� input� impedance� so� that� it� is� not�possible� to�utilize� the� same� tuning�words� to�provide�a�good� impedance�match� for�ground�plane� radii� appreciably�different� from�the�radius�of� the�reference�ground�plane�and,� in� the�case�of� single�parameter� tuning,�even� for� the�reference�ground�plane.��The�maximum�antenna�gain�on�the�horizon�as�a�function�of�ground�plane�radius�is�generally�greater�with�double�parameter�tuning�than�with�single�parameter�tuning.�The�range�of�ground�plane�radii�for�which�the�gain�is�within�3�dB�of�the�maximum�gain,�however,�is�generally�not�significantly�increased�with�double�parameter�tuning.��The�maximum�antenna�gain�on�the�horizon�as�a�function�of�ground�plane�radius�generally�decreases�with�increasing�ohmic�resistance�Rohmic�of�the�antenna�circuit,�whereas�the�range�of�ground�plane�radii�for�which�the�gain�is�within�3�dB�of�the�maximum�gain�generally�increases�with�increasing�values�of�Rohmic.��The�antenna�gain�on�the�horizon�as�a�function�of�ground�plane�radius�is�a�maximum�at�30MHz�for�any�given�ground�plane� except� the� reference� ground� plane.� For� example,� the� antenna� gain� is� 40–100� dB� less� at� 30� MHz� than� at�150MHz�for�ground�plane�radii�much�less�or�greater�than�the�radius�of�the�reference�ground�plane.�Obviously,�such�large�mismatch�losses�are�not�olerable,�either�for�a�transmitting�antenna�or�for�a�receiving�system�whose�external�noise�factor�is�comparable�to�or�less�than�the�mismatch�loss.�At�3�MHz�the�antenna�gain�on�the�horizon�as�a�function�of�ground�plane�radius�is�a�maximum�for�ground�plane�radii�approximately�equal�to�the�radius�of�the�reference�ground�plane�with�gains�of�2,��6,�and��12�dBi�for�Rohmic�=�0,�1.7,�and�7.8V,�respectively.�At�30�MHz,�the�range�of�ground�plane�radii�a,�for�which�the�horizon�gain�is�within�3�dB�of�the�maximum�horizon�gain,�is����������������������������������������������������������ft�for�Rohmic�¼�0,�1.7,�and�7.8V,�respectively.�It�is�concluded�that�it�may�not�be�possible�to�use�the�same�tuning�words�for�all�ground�planes�of�interest�without�a�substantial�loss�in�antenna�gain�because�of�mismatch�loss�at�some�frequencies,�particularly�at�the�lower�end�of�the�band.�Therefore,�it�may�be�necessary�to�have�different�tuning�words�for�different�ground�planes.�Different�tuning�words�for�different�ground�planes�may�be�implemented�by�utilizing�more�than�one�antenna�configuration�or�by�sensing�in�real�time�the�impedance�mismatch�and�then�modifying�the�tuning�word�at�a�given�frequency�to�minimize�the�impedance�mismatch.��The�latter�method�is�preferable,�because�it�would� 1. Eliminate�the�difficult�logistics�problem�of�having�to�field�several�antenna�configurations�for�different�ground�

planes.�

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2. Solve�the�problem�of�tuning�instabilities�arising�from�environmental�changes�in�humidity�and�temperature�in�addition�to�that�of�ground�plane�size.��

3. Improve�the�antenna�radiation�efficiency,�since�it�would�not�be�necessary�to�load�the�antenna�circuit�with�antenna�loss�in�order�to�provide�tuning�stability.�

�An�alternative�to�the�implementation�of�different�tuning�words�for�different�platforms�might�be�to�utilize�a�different�antenna�element,�such�as�a�dipole,�whose�input�impedance�might�not�be�as�sensitive�to�ground�plane�size�as�that�of�a�monopole.�However,�even�if�such�an�element�would�prove�to�have�better�tuning�stability�with�varying�ground�plane�size�and�to�have�the�desired�gain�pattern�characteristics,�it�is�not�clear�how�such�an�alternative�would�solve�the�problem�of�tuning�instabilities�arising�from�changes�in�humidity�and�temperature�without�having�to�load�the�antenna�circuit�with�antenna�loss�in�order�to�provide�tuning�stability.��Consequently,�implementation�of�different�tuning�words,�by�sensing�in�real�time,�the�impedance�mismatch�and�then�modifying�the�tuning�word�at�a�given�frequency�to�minimize�the�impedance�mismatch,�is�a�preferable�design�objective.��Such�an�objective�has�been�realized�at�HF�frequencies�and�for�a�radio�frequency�(RF)�power�level�of�400W�with�sensing�and�tuning�times�of�approximately�20msec�and�1�sec,�respectively,�by�a�circuit�comprising�a�directional�coupler,�digital�processor,�and�electromechanical�switches.�The�substitution�of�p�type/�intrinsic�type/n�type�(PIN)�diode�switches�for�the�electromechanical�switches�might�prove�to�be�a�feasible�technique�for�achieving�such�an�objective�with�a�tuning�time�of�less�than�1�msec,�provided�that�the�inter�modulation�products�generated�by�the�use�of�such�switches�are�not�excessive�for�the�intended�application.��Electronically�tunable�helical�elements�utilizing�PIN�diode�switches�have�been�successfully�designed�and�tested�in�an�open�loop�mode�with�an�RF�power�level�of�10Wat�VHF�frequencies�and�400Wat�HF�frequencies.�Closed�loop�operation�is�compatible�with�the�fast�tuning�capability�of�PIN�diode�switches�but�its�realization�has�not�yet�been�reported�in�the�open�literature.���We�can�see�from�design�an�monopole�antenna�in�chapter�3�that�monopole�antenna�made�from�cylindrical�materials�that�produce�radiation�Pattern�more�better�than�in�monopole�Antenna�made�from�soled�materials.�See�the�figures��

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

References Chapter�V

Books:��

1. JH�Richmond.�Monopole�Antenna�on�Circular�Disk.�Technical�Report�711639�1.�Electro�Science�Laboratory,�July�1979.�See�also�IEEE�Trans�Antennas�Propagation�AP�32(12):1282�1287,�1984.�

2. A�Leitner,�RD�Spence.�The�oblate�spheroidal�wave�functions.�Franklin�Inst�J�249(4):299–321,�1950.�3. JE�Storer.�The�impedance�of�an�antenna�over�a�large�circular�screen.�J�Appl�Phys�22(Aug):1058–

1066,�1951.�See�also�Techical�Report�No�119,�Cruft�Laboratory,�Harvard�University,�Nov�1950.�4. KH�Awadalla,�TSM�Maclean.�Monopole�antenna�at�the�center�of�a�circular�ground�plane:�Input�

impedance�and�radiation�pattern.�IEEE�Trans�Antennas�Propagation�AP�27(2):151–153,�1979.�5. RS�Elliot.�Antenna�Theory�and�Design.�Englewood�Cliffs,�NJ:�Prentice�Hall,�1981,�pp�290–291.�6. CA�Balanis.�Antenna�Theory:�Analysis�and�Design.�New�York:�Harper�and�Row,1982,�p�315.�7. L�Brillouin.�Origin�of�radiation�resistance.�Radioelectricite�3:147–152,�1922.�8. JA�Stratton.�Electromagnetic�Theory.�New�York:�McGraw�Hill,�1941,�pp�454–457.�9. Printed�circular�disc�monopole�antenna�for�ultra�wideband�applications�J.�Liang,�C.C.�Chiau,�X.�Chen�

and�C.G.�Parini.�

���Word�Wide�Web�(WWW):��

1. http://www.antennex.com/preview/monopole.htm�2. http://antennasystems.com/saber/monopoles/monopoles.html�3. http://www.mwjournal.com/Journal/article.asp?HH_ID=AR_689�4. http://www.antenna.be/vm.htm�5. Wikipedia,�the�free�encyclopedia.com�