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RADARRADAR

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What isWhat isRADAR ?RADAR ?

Electromagnetic Device to detect and determine theElectromagnetic Device to detect and determine thevarious parameters of the target .various parameters of the target .

Works on the principle of bouncing back the radioWorks on the principle of bouncing back the radiowaves from the target and the receiver ofRadarwaves from the target and the receiver ofRadarprocesses the required information.processes the required information.

Finds applications in Air Traffic Control, Navigation,Finds applications in Air Traffic Control, Navigation,

Military Surveillance, Ship and Vehicular Movements.Military Surveillance, Ship and Vehicular Movements.

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P

rinciple ofP

rinciple ofOperationOperation The radar device transmits a wave whose band isThe radar device transmits a wave whose band isspread by a PN code from a PN generator, receivesspread by a PN code from a PN generator, receives

the reflected wave.the reflected wave. In this radar device, the received signal is spread to aIn this radar device, the received signal is spread to a

wide range is converted to a lowwide range is converted to a low--frequency bandfrequency bandwhich is easy to be measured by a down converter.which is easy to be measured by a down converter. The RADAR detects correlation between theThe RADAR detects correlation between the

received signal and the PN code.received signal and the PN code.

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RADARRADAR

RARAdiodio DDetectionetectionAAndnd RRanginganging

Radar observables: Target range

Target angles (azimuth & elevation)

Target size (radar cross section)

Target speed (Doppler)

Target features (imaging)

Antenna

Transmitted

Pulse

Target

CrossSection

Propagation

Reflected

Pulse

(echo)

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(http://www.crh.noaa.gov/mkx/radar/part1/slide2.html)(http://www.crh.noaa.gov/mkx/radar/part1/slide2.html)

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(http://www.crh.noaa.gov/mkx/radar/part1/slide3.html)(http://www.crh.noaa.gov/mkx/radar/part1/slide3.html)

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(University of Illinois WW2010 Project)(University of Illinois WW2010 Project)

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(University of Illinois WW2010 Project)

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http://weather.noaa.gov/radar/radinfo/radinfo.html

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Radar Range MeasurementRadar Range Measurement

Target

Target range =cX

2

where c = speed of light

X = round trip time

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How Strong Is It?How Strong Is It?

The strength of the received echo can alsoThe strength of the received echo can alsobe measuredbe measured

This will vary with the distance of theThis will vary with the distance of thetarget, its size, its shape and itstarget, its size, its shape and itscompositioncomposition

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Determining Target LocationDetermining Target Location

Three pieces of informationThree pieces of information

Azimuth angleAzimuth angle

Elevation angleElevation angle

Distance to targetDistance to target

From these data radar can determine exactFrom these data radar can determine exact

target locationtarget location

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Azimuth AngleAzimuth Angle

Angle of beam withAngle of beam withrespect to northrespect to north

(University of Illinois WW2010 Project)

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Elevation AngleElevation Angle

Angle of beam with respect to groundAngle of beam with respect to ground

(University of Illinois WW2010 Project)

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Distance to TargetDistance to Target

D = cT/2D = cT/2

TT || pulsespulses round trip timeround trip time

(University of Illinois WW2010 Project)

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Scanning Strategies 1Scanning Strategies 1

Plan Position Indicator (PPI)Plan Position Indicator (PPI)

Antenna rotates through 360Antenna rotates through 360 sweep at constantsweep at constant

elevation angleelevation angle Allows detection/intensity determination ofAllows detection/intensity determination of

precipitation within given radius from radarprecipitation within given radius from radar

Most commonly seen by general publicMost commonly seen by general public

WSRWSR--88D performs PPI scans over several elevation88D performs PPI scans over several elevationangles to produce 3D representation of localangles to produce 3D representation of localatmosphereatmosphere

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Plan Position IndicatorPlan Position Indicator

Constant elevation angleConstant elevation angle

Azimuth angle varies (antenna rotates)Azimuth angle varies (antenna rotates)

(University of Illinois WW2010 Project)

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D.D. Describe the components of a pulse radarDescribe the components of a pulse radarsystem.system.

1. Synchronizer1. Synchronizer

2. Transmitter2. Transmitter 3. Antenna3. Antenna

4. Duplexer4. Duplexer

5. Receiver5. Receiver

6. Display unit6. Display unit 7. Power supply7. Power supply

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Pulse Radar Block DiagramPulse Radar Block Diagram

Power

Supply

SynchronizerTransmitter

Display

Duplexer

(Switching Unit)

Receiver

Antenna

Antenna Bearing or Elevation

Video

Echo

ATRRF

TR

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24

Detection is based on establishing aDetection is based on establishing athreshold level at the output of thethreshold level at the output of thereceiver. If the receiver output exceeds thereceiver. If the receiver output exceeds thethreshold, a signal is assumed to bethreshold, a signal is assumed to bepresent. This is called threshold detection.present. This is called threshold detection.

Consider the output of a typical radarConsider the output of a typical radarreceiver as a function of time (Fig.).receiver as a function of time (Fig.). This might represent one sweep of theThis might represent one sweep of the

video output displayed on an Avideo output displayed on an A--scope. Thescope. Theenvelope has a fluctuating appearanceenvelope has a fluctuating appearancecaused by the random nature of noise.caused by the random nature of noise.

If a large signal is present such as at A inIf a large signal is present such as at A inFig. , it is greater than the surroundingFig. , it is greater than the surrounding

noise peaks and can be recognized on thenoise peaks and can be recognized on thebasis of its amplitude. Thus, if thebasis of its amplitude. Thus, if thethreshold level were set sufficiently high,threshold level were set sufficiently high,the envelope would not generally exceedthe envelope would not generally exceedthe threshold if noise alone were present,the threshold if noise alone were present,but would exceed it if a strong signal werebut would exceed it if a strong signal werepresent.present.

If the signal were small, however, it wouldIf the signal were small, however, it wouldbe more difficult to recognize its presence.be more difficult to recognize its presence.

The threshold level must be low if weakThe threshold level must be low if weaksignals are to be detected, but it cannot besignals are to be detected, but it cannot beso low that noise peaks cross the thresholdso low that noise peaks cross the thresholdand give a false indication of the presenceand give a false indication of the presenceof targets.of targets.

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