Download - Radar Basic Introduction
RADAR
Today We are going to know something about RADAR.
RADAR-Radio Detection and Ranging
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 RadarWeather Surveillance Radar, designed in 1957. It became the primary radar for the weather service for nearly 40 years.
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 Diagram
PRFPRF
PWPW
RestingRestingTimeTime
CarrierCarrierWaveWave
Pulse Radar Components
SynchronizerSynchronizer TransmitterTransmitter
Display UnitDisplay Unit ReceiverReceiver
PowerPowerSupplySupply
ANT.ANT.DuplexerDuplexer
RF Out
Echo
In
Antenna Control
Pulse TransmissionPulse Repetition Time (PRT=1/PRF)Pulse Width (PW) Length or duration of a given pulse PRT is time from beginning of one pulse to the
beginning of the next PRF is frequency at which consecutive pulses are
transmitted.PW can determine the radar’s minimum range resolution.PRF can determine the 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
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
AN/SPS-49 Very Long Range Air Surveillance Radar
AN/TPS-43The AN/TPS-43 radar system, with a 200 mile range, was the only Air Force tactical ground based long range search and warning radar for nearly two decades. Most of the AN/TPS-43 radars are being modified to the AN/TPS-75 configuration.
3-D Air Search Radar
AN/TPS-75
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.
Radar Performance and Frequency Bands
BandwidthThe bandwidth determines the range resolution and frequency agility capabilities of the radar.
AntennaFor a given gain, low frequency antennas are larger than high frequency. Low frequency are favored for long-range
search applications, because of the larger effective area associated with a given gain, allowing more effective capture of echoes.
TransmitterIn general, more radio frequency power can be produced at low frequency than at high.
ReceiverThere is no clear choice between high and low frequencies.
PropagationThe attenuation at high frequency is dramatic. A given raindrop has over three orders of magnitude more scattering
cross-section at X-band(10 GHz) than at L-band(1.3 GHz), producing far more clutter and signal at the higher frequency.
TargetsIf the wavelength is long compared to the target extent, targets are Rayleigh scatterers, and have small, non-fluctuating
RCS.
SummaryIn general, the longer the range at which the radar must detect targets, the lower the frequency of the
radar.