Introduction to Radar

Presented By

Doddipalli Srinivas

DT13ECE055

SupervisorDr. A.G.KothariElectronics dept.

Functions of Radar

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

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.

History of Radar

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.

Weather RadarNSSL's first

Doppler Weather Radar

located in Norman,

Oklahoma. 1970's research using this radar

led to NWS NEXRAD WSR-

88D radar network.

The expensive radar equipment is protected by

the sphere shaped cover. On the inside it looks similar to

this:

Two Basic Radar Types

Pulse Transmission

Continuous wave

Pulse Transmission

PRFPRF

PWPW

RestingRestingTimeTime

CarrierCarrierWaveWave

Pulse Width

Determines the range resolution.Determines the minimum detection range.Can also determine the maximum range of radar.The narrower the pulse, the better the range resolution.

Pulse Power

High peak power is desirable to achieve maximum ranges.

Low power means smaller and more compact radar units and less power required to operate.

Pulse Radar Components

SynchronizerSynchronizer TransmitterTransmitter

Display UnitDisplay Unit ReceiverReceiver

PowerPowerSupplySupply

ANT.ANT.DuplexerDuplexer

RF Out

Ech

o In

Antenna Control

Pulse TransmissionPulse Width (PW)

Length or duration of a given pulse

PW determines radar’s Minimum detection range Maximum detection range

Pulse Repetition Time (PRT=1/PRF) Time from beginning of one pulse to the next Inverse of PRF

Pulse Repetition Frequency (PRF) Frequency at which consecutive pulse are transmitted

PRF determines radar’s Maximum detection range

Continuous Wave Radar

Employs continual RADAR transmission

Relies on the “DOPPLER EFFECT”

Doppler Frequency Shifts

Motion Away

Motion Towards

Echo Frequency Decreases

Echo Frequency Increases

Continuous Wave Radar Components

Discriminator AMP Mixer

CW RFOscillator

Indicator

OUTOUT

ININ

Transmitter Antenna

Antenna

Pulse Vs. Continuous Wave

Pulse EchoSingle AntennaGives Range & Alt.Susceptible To JammingPhysical Range Determined By PW and PRF.

Continuous WaveRequires 2 AntennaeNo Range or Alt. InfoHigh SNRMore Difficult to Jam But Easily DeceivedAmp can be tuned to look for expected frequencies

Target Range

time

t = 2 x range / speed of lightmeasure t, then determine Range

Example: t = .001 secSpeed of light = c = 3x108 meters/secondRange = .001 x 3x108 / 2 = 150,000 m = 150 km

TxRx

Classification by Primary Radar Mission

Search radars and modes• Surface search• Air search • Two-dimensional search radars• Three-dimensional search radars

Tracking radars and modesTrack-while-scan

AN/FPS-24 Search Radar

Azimuth Angular Measurement

Azimuth Angular MeasurementRelative Bearing = Angle from ship’s heading.True Bearing = Ship’s Heading + Relative Bearing

NShip’s Heading Angle

Target Angle

Determining Altitude

Determining Altitude

Altitude

Angle of Elevation

Altitude = slant range x sin0 elevation

Tracking RadarTracking 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.

Antenna

Two Basic Purposes:

Radiates RF Energy

Provides Beam Forming and Focus

Must Be 1/2 of the Wave Length for the maximum wave length employed

Wide Beam pattern for Search, Narrow for Track

Types of Antennas

Introducing two types of antenna

reflector mirror antenna

array antenna

Reflector Antenna

Parabolic Reflector

Basic paraboloid reflector; Truncated paraboloid;Orange-peel paraboloid;Cylindrical paraboloid

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.

An Example of Array Antenna

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.

Other Factors Affecting Performance

Scan Rate and Beam Width Narrow beam require slower antenna rotation rate.

Pulse Repetition Frequency Determines radars maximum range(tactical factor).

Carrier Frequency Determines antenna size, beam directivity and

target size.

Radar Cross Section (What the radar can see(reflect))

Determines target size, shape, material, angle and carrier frequency.

Reference

www.fas.org/man/dod-01/sys/ac/equip/http://www.tpub.com/neets/book11/46a.htmhttp://www.tpub.com/neets/book18/79j.htmetc.

Thank You