introduction to radar mit l1
TRANSCRIPT
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Introduction-1AG 6/18/02
MIT Lincoln Laboratory
Introduction to Radar Systems
Dr. Robert M. ODonnell
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MIT Lincoln LaboratoryIntroduction-2
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Disclaimer of Endorsement and Liability
The video courseware and accompanying viewgraphs presented on this server were prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, nor the Massachusetts Institute of Technology and its Lincoln Laboratory, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, products, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government, any agency thereof, or any of their contractors or subcontractors or the Massachusetts Institute of Technology and its Lincoln Laboratory.
The views and opinions expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or any of their contractors or subcontractors
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Introduction-3AG 6/18/02
MIT Lincoln Laboratory
Introduction to Radar Systems
Introduction
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MIT Lincoln LaboratoryIntroduction-4
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Acknowledgement
Developers of Tutorial Material
Dr. Eric D. Evans Dr. Andrew D. Gerber Dr. Robert M. ODonnell
Dr. Robert G. Atkins Dr. Pamela R. Evans Dr. Robert J. Galejs Dr. Jeffrey S. Herd Dr. Claude F. Noiseux Dr. Philip K. W. Phu Dr. Nicholas B. Pulsone Dr. Katherine A. Rink Dr. James Ward Dr. Stephen D. Weiner And many others
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Background on the Course
One of Many Radar Courses Presented at the Laboratory
Relatively Short 10 lectures 40 to 60 minutes each
Introductory in Scope Basic Radar Concepts Minimal Mathematical Formalism
Prerequisite A College Degree Preferred in Engineering or Science, but not Required
More Advanced Issues Dealt with in Other Laboratory Radar Courses
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MIT Lincoln LaboratoryIntroduction-6
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Outline
Why radar?
The basics
Course agenda
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MIT Lincoln LaboratoryIntroduction-7
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What Means are Available for Lifting the Fog of War ?
The Invasion of Normandy
D-Day + 1
D-Day
Courtesy of National Archives.
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MIT Lincoln LaboratoryIntroduction-8
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What Means are Available for Lifting the Fog of War ?
Iwo Jima1945
Courtesy of National Archives.Courtesy of National Archives.
Courtesy of US Marine Corp, History Division.
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MIT Lincoln LaboratoryIntroduction-9
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Military Means of Sensing
Sonar Blast detection Troop movement
detection
Ground surveillance/ reconnaissance/ID
Laser targeting Night vision Space surveillance Missile seekers
Chem/Bio Radiological
Surveillance Tracking Fire control Target ID/
discrimination Ground surveillance/
reconnaissance Ground mapping Moving target detection Air traffic control Missile seekers
Optical/IR Radar Acoustic Other
A
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Long range All-weather Day/night 3-space target location Reasonably robust against
countermeasures
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MIT Lincoln LaboratoryIntroduction-10
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Early Days of Radar Chain Home Radar, Deployment Began 1936
Chain Home Radar Coveragecirca 1940
(21 Early Warning Radar Sites)
Sept 2006 Photograph of Three Chain Home
Transmit Towers, near Dover
Courtesy of Robert Cromwell.Used with permission.
DoverRadar Site
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MIT Lincoln LaboratoryIntroduction-11
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Chain Home Radar System
Frequency 20-30 MHz
Wavelength 10-15 m
Antenna Dipole Array on
Transmit Crossed Dipoles on
Receive Azimuth Beamwidth
About 100o Peak Power
350 kW Detection Range
~160 nmi on German Bomber
Radar ParametersTypical Chain Home Radar Site
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MIT Lincoln LaboratoryIntroduction-12
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Chain Home Transmit & Receive Antennas
360'
240'215'
95'
45'
0'
/2
/2
MainAntenna
Gap FillerAntenna
Two Transmitter Towers
One Receiver Tower
Transmit Antenna Receive Antenna
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MIT Lincoln LaboratoryIntroduction-13
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Radar and The Battle of Britain
The Chain Home Radar British Force Multiplier
during the Battle of Britain Timely warning of direction
and size of German aircraft attacks allowed British to
Focus their limited numbers of interceptor aircraft
Achieve numerical parity with the attacking German aircraft
Effect on the War Germany was unable to
achieve Air Superiority Invasion of Great Britain
was postponed indefinitely
Chain Home Radar Coveragecirca 1940
(21 Early Warning Radar Sites)
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Surveillance and Fire Control Radars
Courtesy of Raytheon. Used with permission.
Courtesy of Raytheon. Used with permission.
Courtesy of Raytheon. Used with permission.Courtesy of Raytheon.Used with permission.
Courtesy of Raytheon.Used with permission.
Photo courtesy Photo courtesy of ITT of ITT
Corporation.Corporation.Used with Used with
permission.permission.
Courtesy of Global Security.Used with permission.
Courtesy of US Navy.
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Airborne and Air Traffic Control Radars
Courtesy Lincoln Laboratory.
Courtesy of Northrop Grumman.Courtesy of Northrop Grumman.Used with permission.Used with permission.
Courtesy of Boeing Used with permission
Courtesy of US Navy. Courtesy of US Air Force.
Courtesy of US Air Force. Courtesy of US Air Force.
Courtesy of US Air Force.
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MIT Lincoln LaboratoryIntroduction-16
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Instrumentation Radars
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MIT Lincoln LaboratoryIntroduction-17
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Outline
Why radar?
The basics
Course agenda
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MIT Lincoln LaboratoryIntroduction-18
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RADAR RAdio Detection And Ranging
Radar observables: Target range Target angles (azimuth & elevation) Target size (radar cross section) Target speed (Doppler) Target features (imaging)
Antenna
TransmittedPulse
TargetCross
Section
Propagation
ReflectedPulse
(echo)
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Electromagnetic Waves
Radar Frequencies
Courtesy Berkeley National Laboratory
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MIT Lincoln LaboratoryIntroduction-20
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Properties of Waves Relationship Between Frequency and Wavelength
Speed of light, cc = 3x108 m/sec
= 300,000,000 m/sec
Frequency (1/s) =Speed of light (m/s)Wavelength
(m)
Examples: Frequency Wavelength100 MHz 3 m
1 GHz 30 cm3 GHz 10 cm
10 GHz 3 cm
1, 2, 3,
Figure by MIT OCW.
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MIT Lincoln LaboratoryIntroduction-21
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Properties of Waves Phase and Amplitude
Amplitude (volts)
)sin(A
)sin(A o90
Phase,
90 phase offset
A
Amplitude (volts)
Phase,
A
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Properties of Waves Constructive vs. Destructive Addition
Constructive(in phase)
Destructive(180 out of phase)
Partially Constructive(somewhat out of phase)
Non-coherent signals(noise)
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MIT Lincoln LaboratoryIntroduction-23
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Polarization
x
yElectric Field
Magnetic Field
Electromagnetic Wave
x
y
zE
Horizontal Polarization
Electric Field
Magnetic Field
Electromagnetic Wave
x
y
z
E
Vertical Polarization
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MIT Lincoln LaboratoryIntroduction-24
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Radar Frequency Bands
Frequency
Wavelength 1 mm1 km 1 m 1 m 1 nm
1 MHz 1 GHzIR UV
109 Hz
0 1 2 3 4 5 6 7 8 9 10 11 12
30 20 10 8 6 5 4 39 7
Allocated Frequency (GHz)
Wavelength (cm)
X-BandC-BandS-BandL-BandUHFVHF
Visible
1012 Hz
KuKKa
W
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IEEE Standard Radar Bands (Typical Use)
HF 3 30 MHz
VHF 30 MHz300 MHz
UHF 300 MHz1 GHz
L-Band 1 GHz2 GHz
S-Band 2 GHz4 GHz
C-Band 4 GHz8 GHz
X-Band 8 GHz12 GHz
Ku-Band 12 GHz18 GHz
K-Band 18 GHz27 GHz
Ka-Band 27 GHz40 GHz
W-Band 40 GHz 100+ GHz
SearchRadars
Search &Track Radars
Fire Control &Imaging Radars
MissileSeekers
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Radar Block Diagram
Transmitter
PulseCompression
Recording
Receiver
Tracking &ParameterEstimation
Console /Display
Antenna
PropagationMedium
TargetCross
Section DopplerProcessingA / D
WaveformGenerator
Detection
Signal Processor
Main Computer
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MIT Lincoln LaboratoryIntroduction-27
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Radar Range Equation
R
Transmitted Pulse
Received Pulse
Received SignalEnergy
TransmitPower
TransmitGain
SpreadFactor
TargetRCS
SpreadFactor
ReceiveAperture
DwellTime
Target Cross Section Antenna Aperture ATransmit Power PT
PT4A2 4R2
1 4R2
1 A
Losses
L1
=
Figure by MIT OCW.
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MIT Lincoln LaboratoryIntroduction-28
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Signal-to-Noise Ratio
SNR = Received Signal Energy
Noise Energy
Received Signal
Noise
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MIT Lincoln LaboratoryIntroduction-29
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What the #@!*% is a dB?
Signal-to-noise ratio (dB) = 10 log 10Signal PowerNoise Power
ScientificFactor of: Notation dB
10 101 10100 102 201000 103 30...
1,000,000 106 60
Example:
The relative value of two things, measured on a logarithmic scale, is often expressed in deciBels (dB)
0 dB = factor of 1 -10 dB = factor of 1/10-20 dB = factor of 1/100
3 dB = factor of 2-3 dB = factor of 1/2
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Pulsed Radar Terminology and Concepts
P
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Duty cycle =
Average power = Peak power * Duty cycle
P
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Time
Pulse length
Pulse repetition interval(PRI)
Pulse lengthPulse repetition interval
Pulse repetition frequency (PRF) = 1/(PRI)
Continuous wave (CW) radar: Duty cycle = 100% (always on)
TargetReturn
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Pulsed Radar Terminology and Concepts
P
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Duty cycle =
Average power = Peak power * Duty cycle
P
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k
p
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Time
Pulse length
Pulse repetition interval(PRI)
Pulse lengthPulse repetition interval
Pulse repetition frequency (PRF) = 1/(PRI)
Continuous wave (CW) radar: Duty cycle = 100% (always on)
TargetReturn
1 MW
100 kW
10%
100 sec
1 msec
1 kHz
1 W
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Brief Mathematical Digression Scientific Notation and Greek Prefixes
109 1,000,000,000 Giga GHz106 1,000,000 Mega MHz, MW103 1,000 kilo km101 10 - -100 1 - -10-3 0.001 milli msec10-6 0.000,001 micro sec
ScientificNotation
StandardNotation
GreekPrefix
RadarExamples
MHz = MegahertzMW = Megawatt
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MIT Lincoln LaboratoryIntroduction-33
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Radar Waveforms
Waves?
or Pulses?
Waves, modulatedby on-off action of
pulse envelope
What do radars transmit?
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Radar Waveforms (contd.)
Pulse at single frequency
LinearFrequency-Modulated
(LFM)Waveform
Time
F
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c
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Pulse with changing frequency
Time
F
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c
y
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MIT Lincoln LaboratoryIntroduction-35
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Radar Range Measurement
Transmi
tted
Pulse
Reflecte
d
Pulse
Range
Target
Target range = c2where c = speed of light
= round trip timeCourtesy of Raytheon. Used with permission.
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Antenna Gain
R
Isotropic antenna
G = antenna gain
.
Directional antenna
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MIT Lincoln LaboratoryIntroduction-37
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Propagation Effects on Radar Performance
Atmospheric attenuation
Reflection off of earths surface
Over-the-horizon diffraction
Atmospheric refraction
Radar beams can be attenuated, reflected and bent by the environment
Radar beams can be attenuated, reflected and bent by the environment
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MIT Lincoln LaboratoryIntroduction-38
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Radar Cross Section (RCS)
Incident Power Density
(Watts/m2)
ReflectedPower(Watts)
(m2)
x =
RCS
Radar Cross Section (RCS, or s) is the effective cross-sectional area of the target as seen by the radar
measured in m2, or dBm2
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MIT Lincoln LaboratoryIntroduction-39
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Signal Processing Pulse Compression
MatchedFilter
1 msec c2
x = 150 km
Problem: Pulse can be very long; does not allow accurate range measurement
Solution: Use pulse with changing frequency and signal process using matched filter
Uncompressed pulse Compressed pulse
?Figure by MIT OCW.
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Bandwidth
Time
F
r
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q
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c
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Time
F
r
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q
u
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c
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NarrowbandWaveform
WidebandWaveform
CompressedPulse
LowRange
ResolutionBandwidth
Bandw
idth
HighRange
Resolution
c2BR =
CompressedPulse
Range
Range
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Why Bandwidth is Important.
Relative Range (m)
High(X 10)
Medium(X 3)
Low
P
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Very High (X 30)
Bandwidth
Wideband Target Profile
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Detection of Signals in Noise
RMSNoiseLevel
DetectionThreshold
Detected Target
FalseAlarm
MissedTarget
Range
P
o
w
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r
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Coherent Integration
0
V
o
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t
a
g
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Signal buried in Noise
(SNR < 0 dB)
0
P
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Signal integrated out of Noise
(SNR increases by N)
Pulse 1
+ Pulse 2
+ Pulse 3
+ Pulse N
...
Signals are same each time; add coherently (N2)
Noise is different each time; doesnt add coherently (N)
|x|2
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Doppler Effect
Figure by MIT OCW.
Observer A Observer B
Driver Hears
Observer A Hears Observer B Hears
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Doppler Shift Concept
c v
= cfc v
f = c
c
f = f
(2v/) Dopplershift
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Why Doppler is Important
Clutter returns are much larger than target returns
Note: if youre moving too, you need to take that into account.
however, targets move, clutter doesnt.
Surface Radar Airborne Radar
Doppler lets you separate things that are moving from things that arentDoppler lets you separate things that are moving from things that arent
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Clutter Doppler Spectra
0 50 100 150 200
-20
-10
0
10
20
30
40
50
60
70
Land
Velocity (m/s)
R
e
l
a
t
i
v
e
P
o
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(
d
B
)
SeaRainChaffBirds
Target
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Radar Block Diagram
Transmitter
PulseCompression
Recording
Receiver
Tracking &ParameterEstimation
Console /Display
Antenna
PropagationMedium
TargetCross
Section DopplerProcessingA / D
WaveformGenerator
Detection
Signal Processor
Main Computer
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MIT Lincoln LaboratoryIntroduction-49
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Outline
Why radar?
The basics
Course agenda
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MIT Lincoln LaboratoryIntroduction-50
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Introduction to Radar Systems Tutorial Agenda
Introduction Radar Equation Propagation Effects Target Radar Cross Section Detection of Signals in Noise & Pulse Compression Radar Antennas Radar Clutter and Chaff Signal Processing-MTI and Pulse Doppler Tracking and Parameter Estimation Transmitters and Receivers
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References
Skolnik, M., Introduction to Radar Systems, New York, McGraw-Hill, 3rd Edition, 2001
Nathanson, F. E., Radar Design Principles, New York, McGraw-Hill, 2nd Edition, 1991
Toomay, J. C., Radar Principles for the Non-Specialist, New York, Van Nostrand Reinhold, 1989
Buderi R., The Invention That Changed the World, New York, Simon and Schuster, 1996
Introduction to Radar Systems Disclaimer of Endorsement and LiabilityIntroduction to Radar Systems IntroductionAcknowledgementBackground on the CourseOutlineWhat Means are Available for Lifting the Fog of War ?What Means are Available for Lifting the Fog of War ? Military Means of SensingEarly Days of RadarChain Home Radar, Deployment Began 1936Chain Home Radar SystemChain Home Transmit & Receive AntennasRadar and The Battle of BritainSlide Number 14Slide Number 15Slide Number 16OutlineRADARRAdio Detection And RangingElectromagnetic WavesProperties of WavesRelationship Between Frequency and WavelengthProperties of WavesPhase and AmplitudeProperties of WavesConstructive vs. Destructive AdditionPolarizationRadar Frequency Bands IEEE Standard Radar Bands (Typical Use)Radar Block DiagramRadar Range EquationSignal-to-Noise RatioWhat the #@!*% is a dB?Pulsed RadarTerminology and ConceptsPulsed RadarTerminology and ConceptsBrief Mathematical DigressionScientific Notation and Greek PrefixesRadar WaveformsRadar Waveforms (contd.)Radar Range MeasurementAntenna GainPropagation Effects on Radar PerformanceRadar Cross Section (RCS)Signal ProcessingPulse CompressionBandwidthWhy Bandwidth is ImportantDetection of Signals in NoiseCoherent IntegrationDoppler EffectDoppler Shift ConceptWhy Doppler is ImportantClutter Doppler SpectraRadar Block DiagramOutlineIntroduction to Radar Systems TutorialAgendaReferences