radar communication

PRESENTED BY:

M.A.ARAVINDLAL

R.NANDHA KUMAR

P.S.PRASAANTH

P.RAJU

S.SARAVANAN

M.MESHAKPRABHAKARAN

S.BALAJI

1. Introduction to radar

2. History

3. Components & range

4. atmospheric effects

5. Radar classification.

6. Advantages&disadvantages

7. conclusion

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”)

Bats use a basic form of radar

They send sound waves that reflect off of an

object just as electric radar systems do

The first form of radar created by humans

was the telemobiloscope

It was mainly used to detect ships to avoid

collisions

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.

Radar Frequencies

The components of a radar system.

1. Transmitter

2. Antenna

3. Receiver

4. Display unit

5. Power supply

6. Duplexer( improved radar).

Distance from the

radar

Measured from time

delay between

transmitted pulse and

returned signal

received

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?

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!

Target

• Target range = ct

2

where c = speed of light

t = round trip time

• 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

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.

Fd = 2Vr

λ

Fd = doppler shift

Vr = relative velocity of target with respect to

radar.

Motion Away:

Echo Frequency Decreases

Motion Towards:

Echo Frequency Increases

Pulse Transmission

Continuous Wave

Employs continual

RADAR transmission

Separate transmit and

receive antennas

Relies on the

“DOPPLER SHIFT”

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.

Discriminator AMP Mixer

CW RF

Oscillator

Indicator

OUT

IN

Transmitter Antenna

Antenna

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.

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

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

Time factor

Wide beam spread

Larger targets can saturate receiver

Possibility of falsify readings

Interference sources

Airplanes use radar to avoid collisions and to

coordinate landings

Operators visually watch the radar outputs

and relay the information to pilots

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

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

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

Used to study the Earth's ionosphere and its

interactions with the upper atmosphere, the

magnetosphere, and the solar wind .

Electrons in ionosphere

are radar targets

These electrons can

scatter radio waves

The strength of the echo received from the

ionosphere measures the number of

electrons able to scatter radio waves or what

we call electron.

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

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

The US Military is currently using

groundbreaking radar

This radar allows soldiers to see objects and

people through walls

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.

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]