VLF LF MF and HF VLF LF MF and HF ANTENNASANTENNAS
CLASSIFICATION ACCORDING TO CLASSIFICATION ACCORDING TO
FREQUENCY BANDSFREQUENCY BANDS
VLF/LF Antennas and VLF/LF Antennas and Antenna SystemsAntenna Systems
VLF BandVLF Band
EMEM waves penetrate well in waves penetrate well intoto the sea water the sea water.. (Communications with submerged submarines)(Communications with submerged submarines)
Low atmospheric attenuationLow atmospheric attenuation..
Appropriate for long range communication.Appropriate for long range communication.
VLF AntennasVLF Antennas
• Ground and Sky wavesGround and Sky waves
• Frequeny range: 3-30 KHzFrequeny range: 3-30 KHz
• Antennas : very largeAntennas : very large
• Power: kW levels and even morePower: kW levels and even more
Some Problems Associated with VLF Some Problems Associated with VLF Antenna SystemsAntenna Systems
• Small Small Bandwidth Bandwidth (usually (usually less than 200 Hzless than 200 Hz))
• Small radiation resistanceSmall radiation resistance..
• High cost.High cost.
• Antenna system covers a large area.Antenna system covers a large area.
• Need for very high Need for very high power levels for transmission.power levels for transmission.
LF AntennasLF Antennas
Ground and Sky wavesGround and Sky waves
Frequeny range: 30-300 KHzFrequeny range: 30-300 KHz
Antennas: largeAntennas: large
Power: kW levels and even morePower: kW levels and even more
Some DisadvantagesSome Disadvantages
High cosHigh costt
Large Large DimensionsDimensions
TTroublroublee with efficiency with efficiency, power capacity, , power capacity, bandwidthbandwidth
VLF and LF antennas are VLF and LF antennas are “electrically small” antennas“electrically small” antennas : :
problem: high capacitive reactance and problem: high capacitive reactance and small antenna radiation resistancesmall antenna radiation resistance
remedy: top loadingremedy: top loading
Top-loadingTop-loading
Top-loadingTop-loading
increases gain bandwidth (by decreasing reactance)increases gain bandwidth (by decreasing reactance)
In VLF large top-loadingIn VLF large top-loading
supported by towerssupported by towers
A simple VLF/LF Transmitting A simple VLF/LF Transmitting AntennaAntenna
VLF / LF Ground SystemsVLF / LF Ground Systems
Radial-wire:Radial-wire:
radial wires buried in the groundradial wires buried in the ground
Multiple-star:Multiple-star:
small radial-wire systems forming a star topologysmall radial-wire systems forming a star topology
Basic Theory: The Basic Theory: The Vertical Electric Vertical Electric Monopole AntennaMonopole Antenna
Vertical Electric Monopole AntennaVertical Electric Monopole AntennaAssume uniform electric current I along a vertical monopole of Assume uniform electric current I along a vertical monopole of
effective height heffective height he :e :
electric field
magnetic field
Vertical Electric Monopole AntennaVertical Electric Monopole Antenna-Radiated Power--Radiated Power-
The vertical electric field in terms of radiated power is:
Vertical Electric Monopole AntennaVertical Electric Monopole Antenna-Equivalent Antenna Circuit--Equivalent Antenna Circuit-
Vertical Electric Monopole AntennaVertical Electric Monopole Antenna(Radiation Efficiency)(Radiation Efficiency)
where and
Effective power = (power capacity of the transmitter) x (antenna system efficiency)
antenna total loss resistance
Vertical Electric Monopole AntennaVertical Electric Monopole Antenna-Antenna Bandwidth--Antenna Bandwidth-
The 3 dB bandwidth The 3 dB bandwidth bb in (c/s) for a single resonant circuit is in (c/s) for a single resonant circuit is::
f : resonant frequency
Q: the circuit reactance resistance ratio X/R0
R0: Total series resistance
Multiple Tuned VLF AntennasMultiple Tuned VLF Antennas
To have To have sufficientsufficiently largely large bandwidths bandwidths::
Huge antenna systems must be built.Huge antenna systems must be built.
oror SeveralSeveral small multiple-tuned elements small multiple-tuned elements must must
bebe be used be used. .
Multiple Tuned VLF AntennasMultiple Tuned VLF Antennas
Multiple Tuned VLF AntennasMultiple Tuned VLF AntennasGround losses are reduced.Ground losses are reduced.
Radiation resistance and efficiency are increased.Radiation resistance and efficiency are increased.
Instead of one and vulnerable antenna, several and smaller Instead of one and vulnerable antenna, several and smaller elements can achieve the same bandwidth-efficiencyelements can achieve the same bandwidth-efficiency product.product.
If one element is If one element is out of serviceout of service, the others , the others can can still operate.still operate.
The effective ground loss with multiple-tuning will be less than The effective ground loss with multiple-tuning will be less than for a single elementfor a single element..
Tuning and retuning the system is difficult.Tuning and retuning the system is difficult.
eeach antenna has to be matched to ach antenna has to be matched to thethe transmitter. transmitter.
Triatic Type AntennaTriatic Type Antenna
Cutler, Maine Cutler, Maine Antenna InstallationAntenna Installation
Goliath AntennaGoliath Antenna
Goliath Antenna Goliath Antenna
ReferencesReferences
(1) “VLF Radio Engineering”, A. D. Watt, Perg. Press, 1967(2) “High Power Very Low Frequency/Low Frequency Transmitting Antennas”, P Hansen, Military Communications Conf., 1990. MILCOM '90, Conference Record, 'A New Era'. 1990 IEEE, 30Sept.-3Oct.1990 Pages:1091 - 1096 vol.3(3) Technology Conference, 1991.IMTC-91.Conference Record. ,8th IEEE , 14-16 May 1991 Pages:330 - 334(4) “Multiple Tuned VLF Antennas”, Manfred Schopp, IEEE Transactions
on Broadcasting, Vol. 39, No.4, Dec. 1993. References for the photos & figuresReferences for the photos & figures::
[1] http://hawkins.pair.com/nss.shtml[2] http://www.tpub.com/neets/book17/77.htm
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MFMF ANTENNAS & ANTENNAS & ANTENNA SYSTEMS ANTENNA SYSTEMS
INTRODUCTIONINTRODUCTION
• Usually: Usually: Vertical radiators operating in Vertical radiators operating in the the MF band (300-3000 kHz)MF band (300-3000 kHz)..
• The towers may be guyed or self-The towers may be guyed or self-supportingsupporting..
APPLICATION AREASAPPLICATION AREAS
• AM BroadcastingAM Broadcasting
• Maritime RadioMaritime Radio
• Coast Guard CommunicationCoast Guard Communication
• Direction FindingDirection Finding
CHARACTERISTICS OF CHARACTERISTICS OF RADIATORSRADIATORS
• Maximum radiation in the horizontal planeMaximum radiation in the horizontal plane• Antennas Antennas taller than one-half wavelength have a taller than one-half wavelength have a
minor lobeminor lobe
Characteristics of the Characteristics of the RadiatorsRadiators
Requirement for metallic ground plane to Requirement for metallic ground plane to
minimize lossesminimize losses
Vertical polarization is preferred due to Vertical polarization is preferred due to
superior propagation characteristicssuperior propagation characteristics
Other features of the Other features of the radiatorsradiators• Shunt fed radiatorsShunt fed radiators
• Top loaded radiatorsTop loaded radiators• Sectionalized Sectionalized radiatorsradiators
Circuits for MF antenna systemsCircuits for MF antenna systems• Antenna tuning units for matching purposesAntenna tuning units for matching purposes• Phase shifter networks for directional antenna systemsPhase shifter networks for directional antenna systems• Power dividing networksPower dividing networks
ANTENNA TUNING
UNIT T-LINE
ANTENNA TUNING
UNIT PHASE CONTROL
NETWORK T-LINE
POWER DIVIDER
NETWORK
FROM TRASMITTER
PHASE CONTROL NETWORK
Ground SystemsGround Systems
• 120 buried (/4 length) copper wires120 buried (/4 length) copper wires• Extending radially outwardExtending radially outward• 120-180 cm depth is sufficient120-180 cm depth is sufficient• Individual ground systems are required Individual ground systems are required
for each tower of the for each tower of the array. array. • Copper-mesh ground system may also Copper-mesh ground system may also
be used.be used.
Ground SystemsGround SystemsA typical groundA typical ground system for a two-element directional system for a two-element directional
antenna antenna
HF Antennas & HF Antennas & Antenna SystemsAntenna Systems
HF Antennas and Antenna HF Antennas and Antenna SystemsSystems
Frequency Range: 3 to 30 MHz Frequency Range: 3 to 30 MHz
( ( 10 to 100 meters; in wavelength10 to 100 meters; in wavelength) )
For medium- and long- distance For medium- and long- distance communications and broadcoastingcommunications and broadcoasting
Characteristics of HF Antennas:Characteristics of HF Antennas:
Signals are distorted as the ionosphere is neither Signals are distorted as the ionosphere is neither regular nor smooth.regular nor smooth.
High powers and high antenna gains may be High powers and high antenna gains may be needed for communication.needed for communication.
Types of HF Antennas:Types of HF Antennas:
Non-Resonant HF AntennasNon-Resonant HF AntennasLong-wire AntennaLong-wire AntennaVee AntennaVee AntennaRhombic AntennaRhombic Antenna
Resonant HF AntennasResonant HF AntennasMonopole AntennaMonopole AntennaDipoles and Slot Dipoles and Slot AntennasAntennasLoop AntennasLoop Antennas
Log Periodic HF AntennasLog Periodic HF AntennasEarly Log-Periodic AntennaEarly Log-Periodic AntennaLogarithmic Dipole AntennaLogarithmic Dipole Antenna
Directional HF AntennasDirectional HF AntennasEnd-fire ArraysEnd-fire ArraysBroadside ArraysBroadside ArraysCircular ArraysCircular Arrays
Non-Resonant HF Antennas:Non-Resonant HF Antennas:
• wave propagates along the radiator in one wave propagates along the radiator in one direction onlydirection only
• remaining power is absorbed in a matched load remaining power is absorbed in a matched load
TYPESTYPES
Long-wire AntennaLong-wire Antenna Vee AntennaVee Antenna Rhombic AntennaRhombic Antenna
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Long-wire AntennaLong-wire Antenna
A long terminated wire radiatorA long terminated wire radiator
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Vee AntennaVee Antenna Single mast (one wire radiator terminated in a resistive loadSingle mast (one wire radiator terminated in a resistive load
at the far end).at the far end). Radiation pattern exhibits large side lobes near the main beam.Radiation pattern exhibits large side lobes near the main beam. The efficiency is low (almost half of the total input power may be The efficiency is low (almost half of the total input power may be
exhausted in the matched load.exhausted in the matched load.
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Rhombic AntennaRhombic Antenna• 4 radiating wires of equal length mounted on four masts4 radiating wires of equal length mounted on four masts• one of the wires are load-matched.one of the wires are load-matched.• high directivity high directivity • the large rhombics are used for long-range communications.the large rhombics are used for long-range communications.
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Resonant HF Antennas:Resonant HF Antennas:
Monopole AntennaMonopole Antenna• Elevated-feed MonopoleElevated-feed Monopole• Double-cone MonopoleDouble-cone Monopole• Inverted-L and –T AntennaInverted-L and –T Antenna
Dipoles and Slot AntennasDipoles and Slot Antennas
Loop AntennasLoop Antennas
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Monopole AntennasMonopole AntennasOutside half-wave resonance, elevation pattern breaks up into main Outside half-wave resonance, elevation pattern breaks up into main lobes as input impedance becomes very high. Efficiency decreaseslobes as input impedance becomes very high. Efficiency decreases
Dipole AntennasDipole Antennas
Loop AntennasLoop Antennas
Usully used for reception and direction findingUsully used for reception and direction finding..
The Log-Periodic AntennaThe Log-Periodic Antenna Fed from the vertex.Fed from the vertex. Signal travells along the structure until reaches its resonant region.Signal travells along the structure until reaches its resonant region. The signal radiates from the resonant regionThe signal radiates from the resonant region
Directional HF Antennas:Directional HF Antennas:
End-fire ArraysEnd-fire Arrays• Horizontal Array of DipolesHorizontal Array of Dipoles• RCA Fishborne AntennaRCA Fishborne Antenna• Series Phase ArraySeries Phase Array
Broadside ArraysBroadside Arrays• Broadside Dipole ArrayBroadside Dipole Array• Wide-Band Curtain ArrayWide-Band Curtain Array
Circular ArraysCircular Arrays
End-fire ArraysEnd-fire Arrays
Higher directivity.Higher directivity. Provide increased directivity in Provide increased directivity in
elevation and azimuth planes.elevation and azimuth planes. Generally used for reception.Generally used for reception. Impedance match difficulty in Impedance match difficulty in
high power transmissions.high power transmissions. Variants are:Variants are:
Horizontal Array of DipolesHorizontal Array of Dipoles RCA Fishborne AntennaRCA Fishborne Antenna Series Phase ArraySeries Phase Array
Broadside ArraysBroadside Arrays
Beam steering by phase variation is possible.Beam steering by phase variation is possible.
Circular ArraysCircular Arrays Used for direction finding.Used for direction finding. Consists of 30 – 100 elements, with equi-spaced and fed Consists of 30 – 100 elements, with equi-spaced and fed
from a central source – goniometer.from a central source – goniometer. Band-width seperation is possible:Band-width seperation is possible:
ReferencesReferences
JASIK, H.: Antenna Engineering Handbook; Mc Graw Hill, JASIK, H.: Antenna Engineering Handbook; Mc Graw Hill, 19611961
Y.T., LEE S.W.: Antenna Handbook; Van Nostrand Reinhold, Y.T., LEE S.W.: Antenna Handbook; Van Nostrand Reinhold, 19881988..
RUDGE, A.W., MILNE K., OLVER A.D., KNIGHT P.: Handbook RUDGE, A.W., MILNE K., OLVER A.D., KNIGHT P.: Handbook of Antenna Design (Volume 2); Peter Peregrinus, 1983.of Antenna Design (Volume 2); Peter Peregrinus, 1983.