RADAR Presentation Ppt

Presentation On

RADAR

Presented by

Laishram Rajita Chanu

ECE Department

NIT Manipur

Saturday, April 8, 2023 1

IntroductionWorking overviewRadar equationWorking principleComponents of radarElectromagnetic spectrumRadar frequency bandsThe rangeRange measurementTypes and usesApplicationsFactors affecting radar beamReference

Outline


Introduction

RADAR (Radio Detection And Ranging) is a way to detect and study far off targets by transmitting a radio pulse in the direction of the target and observing the reflection of the wave.


Working overview

Radar observables:• Target range• Target angles (azimuth & elevation)• Target size (radar cross section)• Target speed (Doppler)• Target features (imaging)

Antenna

TransmittedPulse

TargetCross

Section

Propagation

ReflectedPulse

(“echo”)


The heart of the principle of radar is the radar equation

Pr: Average power returned to the radar from a target. Pt: Peak power transmitted by the radar. G: Antenna gain of the radar. θ : Angular beamwidth of the radar. H: Pulse Length of the radar. K: This is a physical constant. L: This is the loss factor of the radar. Z: This is the reflectivity factor of the precipitate. R: This is the target range of the precipitate. λ : This is the wavelength of the transmitted energy.

Radar equation


Radar is capable of detecting the presence shape and motion of ships, aircraft land vehicles and people at distances ranging up to hundreds and thousands of miles, depending on the conditions.

Radar is based on the principle that high frequency RF signals are reflected by conductive targets. The most usual targets are airplanes, missiles, ships and automobiles. In a radar system, a signal is transmitted toward the target.

The reflected signal is picked by receiver in a radar unit. The reflected or returned radio signal is called an echo.The radar unit can then determined the distance to the target. Its direction or azimuth, and in some cases, its elevation or distance above the ground.

Working principle


Transmitter The radar transmitter produces the short duration high-power rf pulses of energy

that are into space by the antenna. Duplexer The duplexer alternately switches the antenna between the transmitter and receiver

so that only one antenna need be used. This switching is necessary because the high-power pulses of the transmitter would destroy the receiver if energy were allowed to enter the receiver.

Receiver The receivers amplify and demodulate the received RF-signals. The receiver

provides video signals on the output. Radar Antenna The Antenna transfers the transmitter energy to signals in space with the required

distribution and efficiency. This process is applied in an identical way on reception. Indicator The indicator should present to the observer a continuous, easily understandable,

graphic picture of the relative position of radar targets.The radar screen (in this case a PPI-scope) displays the produced from the echo signals bright blibs. The longer the pulses were delayed by the runtime, the further away from the center of this radar scope they are displayed. The direction of the deflection on this screen is that in which the antenna is currently pointing.

Components of radar


Radar FrequenciesSaturday, April 8, 2023 8

Radar Frequency Bands

Frequency

Wavelength 1 mm1 km 1 m 1 mm 1 nm

1 MHz 1 GHzIR UV

109 Hz

0 1 2 3 4 5 6 7 8 9 10 11 12

30 20 10 8 6 5 4 39 7

Allocated Frequency (GHz)

Wavelength (cm)

X-BandC-BandS-BandL-BandUHF

VHF

Visible

1012 Hz

Ku K Ka W


The Range Distance from the radar Measured from time delay between transmitted pulse and returned signal

received Since radio waves travel at the speed of light (v = c = 300,000 km/sec)

range = c•time/2 The “2” is because the measured time is for a round trip to and from the

target. To determine the range, we only want the time to the object, so you take half!

The range and the direction of the target determine its location, which is what is needed for many radar applications such as air traffic control.

The strength of the received echo can also be measured This will vary with the distance of the target, its size, its shape and its

composition


Range Measurement

Transmitted

Pulse

Reflected

Pulse

Range

Target

• Target range = ct2

where c = speed of lightt = round trip time


Types and uses of Radar Search radars scan a large area with pulses of short radio waves

Targeting radars use the same principle but scan a smaller area more often

Navigational radars are like search radar, but use short waves that reflect off hard surfaces. They are used on commercial ships and long-distance commercial aircraft

Mapping radar scans a large regions for remote sensing and geography applications

Wearable radar which is used to help the visually impaired

Air traffic control uses radar to reflect echoes off of aircraft

Weather radar uses radar to reflect echoes off of clouds

Weather radars use radio waves with horizontal, dual (horizontal and vertical), or circular polarization

Some weather radars use the Doppler effect to measure wind speeds


Applications Pressure measurement The strength of the echo received from the ionosphere

measures the number of electrons able to scatter radio waves or what we call electron pressure

Temperature measurement Some electrons are moving due to heat - In this case

the echo is scattered.The echo will contain a range of frequencies 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

Wind speed measurement 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


Atmospheric Effects


Atmospheric attenuation

Reflection off of earth’s surface

Over-the-horizon diffraction

Atmospheric refraction

Factors affecting Radar beams


References

http://www.radartutorial.eu/01.basics/rb04.en.html

http://www.radarpages.co.uk/theory/theoryindex.htm

http://en.wikipedia.org/wiki/Category:Radar_theory

http://www.bom.gov.au/australia/radar/about/what_is_radar.shtml

http://www.radartheory.8m.com/basics.html


Thanks everyone Have a pleasant moment


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RADAR Presentation Ppt