MotRadar System Principles

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By: Motuma Muktar

Radar System Principles

andApplications


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Outline

Definition Historical Background

Radar Basics Radar Equation

Doppler Effect

Polarization Limiting Factors

Radar Sets and Devices

Components of Radar System

Advantages Applications

Summary

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Definition

Radar: acronym for Radio Detection and Ranging.

an electronic and electromagnetic system that uses radio waves to detect

and locate objects.

It operates by transmitting a particular kind of radio

frequency waveform and detecting the nature of the reflected

echo.

When radio waves strike an object, some portion is reflected,

and some of this reflected energy is returned to the radar

set, where it is detected.



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Historical Background

In 1886, Heinrich Hertz showed that radio waves could bereflected from solid objects.

The German Christian Huelsmeyer was the first to use

radio waves to detect "the presence of distant metallic

objects". In 1904 he demonstrated the feasibility ofdetecting a ship in dense fog, but not its distance.

After passing through many stages, full radar evolved as a

pulsed system, and the first such elementary apparatus was

demonstrated in December 1934 by the American RobertM. Page, working at the Naval Research Laboratory.

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Radar Basics

A radar system has a transmitter that emits radio wavescalled radar signals in predetermined directions.

When these come into contact with an object they are

usually reflected and/or scattered in many directions.

Radar signals are reflected especially well by materials ofconsiderable electrical conductivity.

If the object is moving either closer or farther away, there is

a slight change in the frequency of the radio waves, due to

the Doppler Effect.



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Cont

Radar receivers are usually, but not always, in the samelocation as the transmitter.

Although the reflected radar signals captured by the

receiving antenna are usually very weak, these signals can

be strengthened by the electronic amplifiers. The weak absorption of radio waves by the medium

through which it passes is what enables radar sets to detect

objects at relatively-long range.



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Cont

Radar waves scatter in a variety of ways depending on thesize (wavelength) of the radio wave and the shape of the

target.

If the wavelength is much shorter than the target's size, the wave

will bounce off in a way similar to the way light is reflected by amirror.

If the wavelength is much longer than the size of the target, the

target may not be visible due to poor reflection.



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Radar Equation

The power Prreturning to the receiving antenna is given by

Pt = transmitter power

Gt = gain of the transmitting antenna

Ar= effective aperture (area) of thereceiving antenna

= radar cross section, or scattering

coefficient, of the target

F = pattern propagation factor

Rt = distance from the transmitter to the

targetRr= distance from the target to the receiver.



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Doppler Effect The apparent frequency (f) of the wave changes with the relative

position of the target. Doppler equation is stated as:

The change in phase of the return signal is often used instead of thechange in frequency.

Only the radial component of the speed is available. when a target is moving at right angle to the radar beam, it has no velocity

one parallel to it has maximum recorded speed

vobs= the radial speed of

the observer

vs= the radial speed ofthe targetf0 =frequency of wave :



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Polarization

In the transmitted radar signal, the electric field isperpendicular to the direction of propagation. This direction

of the electric field is the polarization of the wave.

Radars use horizontal, vertical, linear and circular

polarization to detect different types of reflections. E.g. Circular polarization is used to minimize the interference caused by

rain.

Linear polarization returns usually indicate metal surfaces.

Random polarization returns usually indicate a fractal surface, such

as rocks or soil, and are used by navigation radars.



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Limiting Factors

Beam path and range

Noise

Interference

Clutter

Jamming



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Limiting Factors

Beam path and range

Noise

Interference

Clutter

Jamming

The radar beam would follow

linear path in vacuum

curved path in the

atmosphereMaximum range limiting factors

LOS

The maximum non-

ambiguous range

Radar sensitivity and

power of the returned signal



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Limiting Factors

Beam path and range

Noise

Interference

Clutter

JammingNoise is generated by:

Electronic components

natural thermal radiation

of the background scene



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Limiting Factors

Beam path and range

Noise

Interference

Clutter

Jamming

The ability of the radar system to

overcome these unwantedsignals defines its signal-to-noise

ratio (SNR).

A higher system's SNR is

required .



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Limiting Factors

Beam path and range

Noise

Interference

Clutter

Jamming

Includes ground returns, sea

returns, weather, buildings, birds

and insects.

It depends on the function of the

radar.

Types of Clutter:

Surface clutter

Volume clutter

Point clutter



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Limiting Factors

Beam path and range

Noise

Interference

Clutter

Jamming

It refers to radio frequency signals

originating from sources outside the

radar, transmitting in the radar's

frequency

mask targets of interest.

It is problematic to radar because the jamming signal only

needs to travel one-way

the radar echoes travel two-

ways

Therefore radar signal is

significantly reduced in powerby the time they return to the

radar receiver



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Radar Sets and Devices



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Classification of Radar System Based on Technology



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Cont

Based on the Designed use



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Radar Signal Processor



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Components of Radar System



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Advantage of Radar

It provides superior penetration capability through any type ofweather condition

It can be used in the day or night time.

It uses electromagnetic wave that does not require a medium

like Sonar (that uses water) so can be used in space and air. Radar can be long range and the wave propagate at the speed of

light rather than sound (like with sonar).

It is less susceptible to weather conditions compared with

Lasers.



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Applications

Military purposes: to locate air, ground and sea targets.

Aviation : to warn from obstacles in or approaching their

path and give accurate altitude readings.

Marine radars are used to measure the bearing and distance

of ships to prevent collision with other ships

Meteorologists use radar to monitor precipitation

Geologists use specialized ground-penetrating radars to

map the composition of the Earth's crust.



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Summary

The transmission and reception of radio waves is thefundamental operation of radar waves.

Many properties and phenomena of radio waves are crucial

to the operation of the radar system.

The Earths atmosphere plays a central role in radaroperation, as it is the medium of propagation for the radio

waveforms.

The Doppler Effect also plays a vital role in practical radar

systems. Radar has numerous applications including air traffic

control, meteorology, and military applications.



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References

Wikipedia http://en.wikipedia.org/wiki/Radar

http://www.radartutorial.eu/

Michael O. Kolawole,Radar System, Peak Detection and Tracking,

1st Edition, 2003

Lav Varshney, Technical Report,Radar System Components and

System Design, November 22, 2002

Reintjes, J. Francis and Godfrey T. Coate, Principles of Radar. New

York: McGraw-Hill, 1952.

Skolnik, Merrill I.,Introduction to Radar Systems. New York:

McGraw-Hill, 1980. Thomas, Daniel, Signal Processing. Radar 101 Lecture Series.

Syracuse Research Corporation, Syracuse. 31 Oct. 2001.



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