Radar communication
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Transcript of Radar communication
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PRESENTED BY:
M.A.ARAVINDLAL
R.NANDHA KUMAR
P.S.PRASAANTH
P.RAJU
S.SARAVANAN
M.MESHAKPRABHAKARAN
S.BALAJI
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1. Introduction to radar
2. History
3. Components & range
4. atmospheric effects
5. Radar classification.
6. Advantages&disadvantages
7. conclusion
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Radar observables:
• Target range
• Target angles (azimuth & elevation)
• Target size (radar cross section)
• Target speed (Doppler)
• Target features (imaging)
Antenna
Transmitted
Pulse
Target
Cross
Section
Propagation
Reflected
Pulse
(“echo”)
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Bats use a basic form of radar
They send sound waves that reflect off of an
object just as electric radar systems do
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The first form of radar created by humans
was the telemobiloscope
It was mainly used to detect ships to avoid
collisions
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Radar was kept fairly secret during world
war II
Following the war, it was published that the
United States used radar to measure the
distance to the moon
It was later discovered that Hungary had
done this two years earlier than the U.S.
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Radar Frequencies
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The components of a radar system.
1. Transmitter
2. Antenna
3. Receiver
4. Display unit
5. Power supply
6. Duplexer( improved radar).
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Distance from the
radar
Measured from time
delay between
transmitted pulse and
returned signal
received
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Remember, in general v=d/t and d=vt
The range is just a distance
Since radio waves travel at the speed of
light (v = c = 300,000 km/sec )
range = c•time/2Why divided by 2?
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The “2” is because the measured time is for
a round trip to and from the target. To
determine the range, you only want the time
to the object, so you take half!
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Target
• Target range = ct
2
where c = speed of light
t = round trip time
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• Atmospheric attenuation
• Reflection off of earth’s
surface
• Over-the-horizon
diffraction
• Atmospheric refraction
Radar beams can be attenuated, reflected and
bent by the environment
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that the Doppler effect is the change in
frequency that occurs when a source and a
target are in relative motion.
The Doppler affect can be used in a CW radar
in order to determine velocity.
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Fd = 2Vr
λ
Fd = doppler shift
Vr = relative velocity of target with respect to
radar.
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Motion Away:
Echo Frequency Decreases
Motion Towards:
Echo Frequency Increases
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Pulse Transmission
Continuous Wave
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Employs continual
RADAR transmission
Separate transmit and
receive antennas
Relies on the
“DOPPLER SHIFT”
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Continuous wave (CW) radars typically
determine target velocity, and can achieve
considerable ranges without the high peak
power. These radars are typically simpler,
more compact and less costly.
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Discriminator AMP Mixer
CW RF
Oscillator
Indicator
OUT
IN
Transmitter Antenna
Antenna
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An unmodulated CW radar is incapable of
detecting range, as there is no reference
point in the transmitted or returned signal
for measuring elapsed time.
By frequency modulating the CW signal,
differences between the transmitted and
received frequencies can be used to
estimate range.
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Pulse EchoSingle Antenna
Comparitively low SNR
Susceptible To Jamming
Physical Range Determined By PW.
Continuous Wave
Requires 2 Antennae
High SNR
More Difficult to Jam But Easily Deceived
Amp can be tuned to look for expected frequencies
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Penetration Capability
Uses electromagnetic wave so it require no
medium
Less susceptible to weather conditions
Flexible – can be used in number of ways
Beam spread can incorporate many targets
Reliable
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Time factor
Wide beam spread
Larger targets can saturate receiver
Possibility of falsify readings
Interference sources
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Airplanes use radar to avoid collisions and to
coordinate landings
Operators visually watch the radar outputs
and relay the information to pilots
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Police officers use radar to detect people
who drive over the speed limit
Their radar units are compact for easy
portability and fast, accurate use
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Ground mapping radar is often used in
construction settings
They drag the unit across the ground to
determine if there are any objects or
unstable soil where they plan on building
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The military use radar to detect enemy
artillery as well as their own machinery
They can show where their vehicles and
soldiers are in relation to enemy machines
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Used to study the Earth's ionosphere and its
interactions with the upper atmosphere, the
magnetosphere, and the solar wind .
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Electrons in ionosphere
are radar targets
These electrons can
scatter radio waves
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The strength of the echo received from the
ionosphere measures the number of
electrons able to scatter radio waves or what
we call electron.
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Some electrons are moving due to heat - In this case the echo is scattered
The echo will contain a range of frequency close to the transmitter frequency
As the temperature increases, the electrons move faster
So radar can act like a thermometer and measure the temperature of the ionosphere
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When an electron is removed from an atom, the remaining charged atom is called an ion
The ion gas can have a different temperature from the electron gas
The electron/ion mixture is known as a plasma and is usually in motion (like our wind)
So incoherent scatter radar can also measure wind speed
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The US Military is currently using
groundbreaking radar
This radar allows soldiers to see objects and
people through walls
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Technology will continue to grow, and radar
will advance with it
Growth of radar technologies will be
accompanied by a wider variety of
applications
Radar in the future will most likely be as
common as cell phone applications are today
LIDAR is advanced type of radar which uses
visible light from laser.
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REFERENCES
M. Kulkarni, “Microwave and Radar
Engineering”, 3rd edition, Umesh
Publication, 2003, pp. 493 – 536
Merri.I.skolnik, “Intoduction to Radar
System”, 3rd edition, Tata McGraw
Hill, 2003
“Types of Radar”, Engineers
Garage,2012[online]. Available:
http://www.engineersgaragee.
com/articles/type-of-radars
[accessed: September 2012]
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