EC 09 RADIATION AND PROPAGATIONEC 09 RADIATION AND PROPAGATION

AJAL.A.J Assistant Professor –Dept of ECE,

UNIVERSAL ENGINEERING COLLEGE   Mob: 8907305642   MAIL: ec2reach@gmail.com

VLF/VLF/ LFLF/ MF/ MF Antennas Antennas

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Antenna SystemsAntenna Systems

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Instrument Configuration

IDPU: Instrument Data Processor UnitSPB : Spin Plane Booms (4x)AXB : Axial Booms (2x)SST : Solid State Telescope (2x)ESA : Electrostatic Analyzer FGM : Fluxgate MagnetometerSCM : Search Coil Magnetometer

5

Fuel Tank

ESA

EFI SPB

Thruster T1

EFI Axial Booms (2, Stowed)

BatteryBAU

Repress Tank

Miniature Sun Sensor

Transponder

Thruster T2

IDPU

Fuel Tank

Antenna

EFI SPB

EFI SPB

Thruster A1

Thruster A2

AEB

Gyros

Probe Configuration

EM SpectrumEM Spectrum

Propagation characteristics are different in each frequency band

UV

1 MHz1 kHz 1 GHz 1 THz 1 PHz 1 EHz

infrared visible

X raysGamma rays

AM ra

dio

S/W ra

dio

FM ra

dio

TV TV cellu

lar

LF HF VHF UHF SHF EHFMF

30kHz 300kHz 3MHz 30MHz 300MHz 30GHz 300GHz

10km 1km 100m 10m 1m 10cm 1cm 100mm

3GHz

902 – 928 Mhz

2.4 – 2.4835 Ghz

5.725 – 5.785 Ghz

ISM band

7

RADIO IR VISIBLE UV X-RAYS GAMMA RAYS

VLF LF MF HF VHF UHF SHF EHF

3k 30k 300k 3M 30M 300M 3G 30G 300GHz

VLF: Very Low Frequency LF: Low FrequencyMF: Medium Frequency HF: High FrequencyVHF: Very High Frequency UHF: Ultra High FrequencySHF: Super High Frequency EHF: Extremely High Frequency

Frequency Band Allocations

RADIO

VLF, LF long waves MF medium waves HF, VHF short waves UHF, SHF microwaves

EHF millimeter waves

Above microwave region, only certain windows of frequencies propagate freely through air, rain, etc.

Infrared and visible light will not penetrate walls X-rays and gamma rays interact with matter

8

Wavelengths of Frequency Bands

c

fmeters sec

cycles secmeters

cycle

Propagate well beyond line of sight

The distance the signal travels Decreases as the frequency increases

R=100 m

RX

TX

VLF AntennasVLF Antennas• They operates on VLF Band.They operates on VLF Band.

• They are electrically small. This simplifies analysis.They are electrically small. This simplifies analysis.

• They They are physically large structuresare physically large structures..

– GGenerally have a number of towers 200-300 m highenerally have a number of towers 200-300 m high..– GGenerally cover areas of up to a square kilometer or more. enerally cover areas of up to a square kilometer or more.

• Support worldwide communicatipn.Support worldwide communicatipn.

• The principal objective is The principal objective is to radiate specified amount of power over to radiate specified amount of power over a sufficient bandwidth of frequency.a sufficient bandwidth of frequency.

Problems with VLF AntennasProblems with VLF Antennas

1.1. Bandwidth is less than 200 Hz. Bandwidth is less than 200 Hz.

2.2. Small radiation resistanceSmall radiation resistance..

3.3. They are expensive structures.They are expensive structures.

4.4. Antenna system covers a large area.Antenna system covers a large area.

5.5. Designing an efficient transmitting antenna is Designing an efficient transmitting antenna is difficult.difficult.

6.6. High power levels are needed for transmission.High power levels are needed for transmission.

Vertical Electric Monopole AntennaVertical Electric Monopole Antenna-Antenna Model--Antenna Model-

Vertical Electric Monopole AntennaVertical Electric Monopole Antenna-E and H Fields--E and H Fields-

Assume a uniform vertical electric current I along a monopole of effective Assume a uniform vertical electric current I along a monopole of effective

height hheight hee

rms vertical electric field

rms tangentical 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 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 sufficient bandwidthssufficient bandwidths::

Huge antenna systems can be built.Huge antenna systems can be built.

oror

SeveralSeveral small multiple-tuned elements can be small multiple-tuned elements can be usedused. .

Multiple Tuned VLF AntennasMultiple Tuned VLF Antennas

Ground 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 elements can Instead of one and vulnerable antenna, several and smaller elements can achieve the same bandwidth-efficiencyachieve the same bandwidth-efficiency product.product.

If one element is shunt off servicing, the others still can be operated.If one element is shunt off servicing, the others still can be operated.

The effective ground loss with multiple-tuning will be less than for a The effective ground loss with multiple-tuning will be less than for a single elementsingle element..

Tuning and retuning after the system is disturbed is difficult.Tuning and retuning after the system is disturbed is difficult.

Each antenna has to be matched to a transmitter. Each antenna has to be matched to a transmitter.

Multiple Tuned VLF AntennasMultiple Tuned VLF Antennas

Goliath Antenna

Some Applications of VLF AntennaSome Applications of VLF Antenna

1.1.Submarine:Submarine: Requires EM Wave at VLF because of skin effect.Requires EM Wave at VLF because of skin effect.

Propagation in sea water is almost vertical so only electric and magnetic Propagation in sea water is almost vertical so only electric and magnetic type of dipoles can be used.type of dipoles can be used.

Transmitted wave will be attenuated in the sea-water so output power must Transmitted wave will be attenuated in the sea-water so output power must be high enough to reach receiver.be high enough to reach receiver.

Some Applications of VLF Antenna (II)Some Applications of VLF Antenna (II)

2.2.Underground Mine Communication:Underground Mine Communication:

Especially it is designed for the event of mine disaster.Especially it is designed for the event of mine disaster.

Provide wireless communication between earth’s surface and miner.Provide wireless communication between earth’s surface and miner.

Normal radio frequency get attenuated rapidly so VLF Band is used.Normal radio frequency get attenuated rapidly so VLF Band is used.

VLF Loop antenna can be used for this purpose.VLF Loop antenna can be used for this purpose.

Some Other ApplicationsSome Other Applications

Water resource exploration.Water resource exploration. Geological mapping.Geological mapping. Human bodyHuman body SAR detection SAR detection..

Simplified VLF Transmitting AntennaSimplified VLF Transmitting Antenna

PicturesPicturesTriatic Type AntennaTriatic Type Antenna

Maine Antenna Installation Maine Antenna Installation

Goliath AntennaGoliath Antenna

Goliath Antenna (2)Goliath Antenna (2)

Goliath AntennaGoliath Antenna

ConclusionConclusion@@

VLF bandVLF band

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 BandLF Band

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

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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 (1/4 length) copper wires120 buried (1/4 length) copper wires• Extending radially outwardExtending radially outward• 120-180 cm depth is sufficient120-180 cm depth is sufficient• Individual ground systems are Individual ground systems are

required for each tower of the required for each tower of the array. array. • Copper-mesh ground system may also be Copper-mesh ground system may also be

used.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:

Ship’s Antenna ArrangementShip’s Antenna Arrangement

Ship’s Antenna ArrangementShip’s Antenna Arrangement

RDF loop

Radar

Scanner

VHF TX/RX

Navtex RXLoran RX

VHF DSC TX

MF/HF Radio Telephone

VHF T/RX no. 2

DSC RX

E.B. Saturn 35 Radome

VHF DSC RX

Watch keeping RX

F2-layer

Day

D-layer

Night

F1-layerE-layer

TX RXDirect Wave

Reflected Wave

VHFVHF

TX RX

Reflected Wave

Ground Wave

MFMF

TX

HFHF

8 Mhz 16 Mhz

TX

E- Layer’s EffectE- Layer’s Effect

E - Layer

F - Layer

DAY

TX

E- Layer’s EffectE- Layer’s Effect

E - Layer

F - Layer

NIGHT

TX

E- Layer’s EffectE- Layer’s Effect

E - Layer

F - Layer