Post on 20-Jan-2016
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Introduction to Radar
Presented By
Doddipalli Srinivas
DT13ECE055
SupervisorDr. A.G.KothariElectronics dept.
Functions of Radar
RADAR is a method of using electromagnetic waves to remote-sense the position, velocity and identifying characteristics of targets.
History of Radar
Radar was developed for military purposes during W. W. II. The British and US Military used radar to locate ships and airplanes.
History of Radar
History of Radar
During the war, radar operators found annoying blips continually appearing on the radar screen. Scientists had not known that radar would be sensitive enough to detect precipitations.Today, radar is an essential tool for predicting and analyzing the weather.
Weather RadarNSSL's first
Doppler Weather Radar
located in Norman,
Oklahoma. 1970's research using this radar
led to NWS NEXRAD WSR-
88D radar network.
The expensive radar equipment is protected by
the sphere shaped cover. On the inside it looks similar to
this:
Two Basic Radar Types
Pulse Transmission
Continuous wave
Pulse Transmission
PRFPRF
PWPW
RestingRestingTimeTime
CarrierCarrierWaveWave
Pulse Width
Determines the range resolution.Determines the minimum detection range.Can also determine the maximum range of radar.The narrower the pulse, the better the range resolution.
Pulse Power
High peak power is desirable to achieve maximum ranges.
Low power means smaller and more compact radar units and less power required to operate.
Pulse Radar Components
SynchronizerSynchronizer TransmitterTransmitter
Display UnitDisplay Unit ReceiverReceiver
PowerPowerSupplySupply
ANT.ANT.DuplexerDuplexer
RF Out
Ech
o In
Antenna Control
Pulse TransmissionPulse Width (PW)
Length or duration of a given pulse
PW determines radar’s Minimum detection range Maximum detection range
Pulse Repetition Time (PRT=1/PRF) Time from beginning of one pulse to the next Inverse of PRF
Pulse Repetition Frequency (PRF) Frequency at which consecutive pulse are transmitted
PRF determines radar’s Maximum detection range
Continuous Wave Radar
Employs continual RADAR transmission
Relies on the “DOPPLER EFFECT”
Doppler Frequency Shifts
Motion Away
Motion Towards
Echo Frequency Decreases
Echo Frequency Increases
Continuous Wave Radar Components
Discriminator AMP Mixer
CW RFOscillator
Indicator
OUTOUT
ININ
Transmitter Antenna
Antenna
Pulse Vs. Continuous Wave
Pulse EchoSingle AntennaGives Range & Alt.Susceptible To JammingPhysical Range Determined By PW and PRF.
Continuous WaveRequires 2 AntennaeNo Range or Alt. InfoHigh SNRMore Difficult to Jam But Easily DeceivedAmp can be tuned to look for expected frequencies
Target Range
time
t = 2 x range / speed of lightmeasure t, then determine Range
Example: t = .001 secSpeed of light = c = 3x108 meters/secondRange = .001 x 3x108 / 2 = 150,000 m = 150 km
TxRx
Classification by Primary Radar Mission
Search radars and modes• Surface search• Air search • Two-dimensional search radars• Three-dimensional search radars
Tracking radars and modesTrack-while-scan
AN/FPS-24 Search Radar
Azimuth Angular Measurement
Azimuth Angular MeasurementRelative Bearing = Angle from ship’s heading.True Bearing = Ship’s Heading + Relative Bearing
NShip’s Heading Angle
Target Angle
Determining Altitude
Determining Altitude
Altitude
Angle of Elevation
Altitude = slant range x sin0 elevation
Tracking RadarTracking radars dwell on individual targets and follow their motion in azimuth, elevation,range and Doppler.Most tracking radars can follow only a single target.A few radars can track multiple targets simultaneously. An electronically steered array antenna is used so that beam positions can be moved quickly from one target to another.
Antenna
Two Basic Purposes:
Radiates RF Energy
Provides Beam Forming and Focus
Must Be 1/2 of the Wave Length for the maximum wave length employed
Wide Beam pattern for Search, Narrow for Track
Types of Antennas
Introducing two types of antenna
reflector mirror antenna
array antenna
Reflector Antenna
Parabolic Reflector
Basic paraboloid reflector; Truncated paraboloid;Orange-peel paraboloid;Cylindrical paraboloid
Array Antenna
An array antenna is composed of multiple element arrays for example, linear array, area array or nonformal array. The element antennas are half-wavelength dipoles, microstrip patches and wave guide slot. The advantages of array antenna are to enable beam scanning without changing the looking angle of each array antenna and to generate an appropriate beam shaping by selective excitation of current distribution of each element.
An Example of Array Antenna
AN/FPS-115 PAVE PAWS Early Warning Radar Array Antenna
PAWS stands for Phased Array Warning System. The radar is used primarily to detect and track sea-launched and intercontinental ballistic missiles. It can search over long distance(to 5000 km or more). Each system has two array faces 72.5 feet in diameter with 2677 element positions.To provide surveillance across the horizon, the building is constructed in the shape of a triangle. The two building faces supporting the arrays, each covering 120 degrees, will monitor 240 degrees of azimuth.
Other Factors Affecting Performance
Scan Rate and Beam Width Narrow beam require slower antenna rotation rate.
Pulse Repetition Frequency Determines radars maximum range(tactical factor).
Carrier Frequency Determines antenna size, beam directivity and
target size.
Radar Cross Section (What the radar can see(reflect))
Determines target size, shape, material, angle and carrier frequency.
Reference
www.fas.org/man/dod-01/sys/ac/equip/http://www.tpub.com/neets/book11/46a.htmhttp://www.tpub.com/neets/book18/79j.htmetc.
Thank You