Introduction to Radar

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Introduction to Radar

• Shaohua Li
• Graduate Student
• Department of Electrical and Computer Engineering

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Functions of Radar

• RADAR is a method of using electromagnetic waves
  to remote-sense the position, velocity and
  identifying characteristics of targets.

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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.

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History of Radar
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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.

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Weather Radar

• Weather Surveillance Radar, designed in 1957. It
  became the primary radar for the weather service
  for nearly 40 years.

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Weather Radar

• NSSL's first Doppler Weather Radar located in
  Norman, Oklahoma. 1970's research using this
  radar led to NWS NEXRAD WSR-88D radar network.

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The expensive radar equipment is protected by the
sphere shaped cover. On the inside it looks
similar to this
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Two Basic Radar Types

• Pulse Transmission
• Continuous Wave

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Pulse Diagram
PRF
Resting Time
Carrier Wave
PW
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Pulse Radar Components
Synchronizer
Transmitter
RF Out
Power Supply
ANT.
Duplexer
Echo In
Display Unit
Receiver
Antenna Control
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Pulse Transmission

• Pulse Repetition Time (PRT1/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 radars minimum range
  resolution.
• PRF can determine the radars maximum detection
  range.

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Continuous Wave Radar

• Employs continual RADAR transmission
• Relies on the DOPPLER EFFECT

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Doppler Frequency Shifts
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Continuous Wave Radar Components
Transmitter
Antenna
CW RF Oscillator
OUT
IN
Discriminator
Mixer
AMP
Antenna
Indicator
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Pulse Vs. Continuous Wave

• Pulse Echo
• Single Antenna
• Gives Range Alt.
• Susceptible To Jamming
• Physical Range Determined By PW and PRF.

• Continuous Wave
• Requires 2 Antennae
• No Range or Alt. Info
• High SNR
• More Difficult to Jam But Easily Deceived
• Amp can be tuned to look for expected frequencies

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Classification by Primary Radar Mission

• Search radars and modes
• Surface search
• Air search
• Two-dimensional search radars
• Three-dimensional search radars
• Tracking radars and modes
• Track-while-scan

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AN/FPS-24 Search Radar
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AN/SPS-49 Very Long Range Air Surveillance Radar
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AN/TPS-43
The 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
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AN/TPS-75
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Tracking Radar

• Tracking 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.

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AN/APG-66 in the F-16
http//www.tpub.com/neets/book18/79j.htm
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Types of Antenna

• Introducing two types of antenna
• reflector mirror antenna
• array antenna

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Reflector Antenna
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Parabolic Reflector
Basic paraboloid reflector Truncated
paraboloidOrange-peel paraboloidCylindrical
paraboloid
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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.

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An Example of Array Antenna
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Edgewall Slot Array-AN/APY-2 on E-3D Aircraft
The E-3 Sentry is an airborne warning and control
system (AWACS) aircraft that provides all-weather
surveillance, command, control and communications
needed by commanders of U.S. and NATO air defense
forces. As proven in Desert Storm, it is the
premier air battle command and control aircraft
in the world today.
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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.
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Radar Performance and Frequency Bands

• Bandwidth
• The bandwidth determines the range resolution and
  frequency agility capabilities of the radar.
• Antenna
• For 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.
• Transmitter
• In general, more radio frequency power can be
  produced at low frequency than at high.
• Receiver
• There is no clear choice between high and low
  frequencies.
• Propagation
• The 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.
• Targets
• If the wavelength is long compared to the target
  extent, targets are Rayleigh scatterers, and have
  small, non-fluctuating RCS.
• Summary
• In general, the longer the range at which the
  radar must detect targets, the lower the
  frequency of the radar.

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Reference

• www.fas.org/man/dod-01/sys/ac/equip/
• http//www.tpub.com/neets/book11/46a.htm
• http//www.tpub.com/neets/book18/79j.htm
• etc.