Lesson 03 - Radar Principles I

Radar Principles and Radar Principles and SystemsSystems

Part IPart I

Learning ObjectivesLearning Objectives

Comprehend basic operation of a simple Comprehend basic operation of a simple pulse radar system and a simple pulse radar system and a simple continuous wave radar systemcontinuous wave radar systemKnow the following terms: pulse width, Know the following terms: pulse width, pulse repetition frequency, carrier pulse repetition frequency, carrier frequency, peak power, average power, frequency, peak power, average power, and duty cycleand duty cycleKnow the block diagram of a simple pulse Know the block diagram of a simple pulse radar systemradar system

Learning ObjectivesLearning Objectives

Comprehend the concept of Doppler Comprehend the concept of Doppler frequency shiftfrequency shift

Know the block diagram of a simple Know the block diagram of a simple continuous wave radar system (amplifiers, continuous wave radar system (amplifiers, power amplifiers, oscillators, and power amplifiers, oscillators, and waveguides)waveguides)

Comprehend the use of filters in a CW Comprehend the use of filters in a CW radar systemradar system

Two Basic Radar TypesTwo Basic Radar Types

Pulse TransmissionPulse Transmission

Continuous WaveContinuous Wave

Pulse TransmissionPulse TransmissionPulse Width (PW)Pulse Width (PW)– Length or duration of a given pulseLength or duration of a given pulse

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

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

PW determines radar’s PW determines radar’s – Minimum detection rangeMinimum detection range– Maximum detection rangeMaximum detection range

PRF determines radar’s PRF determines radar’s – Maximum detection rangeMaximum detection range

Pulse Radar ComponentsPulse Radar Components

SynchronizerSynchronizer TransmitterTransmitter

Display UnitDisplay Unit ReceiverReceiver

PowerPowerSupplySupply

ANT.ANT.DuplexerDuplexer

RF Out

Ech

o In

Antenna Control

Continuous Wave RadarContinuous Wave Radar

Continual energy transmissionContinual energy transmission

Separate transmit/receive antennasSeparate transmit/receive antennas

Relies on “DOPPLER SHIFT”Relies on “DOPPLER SHIFT”

Doppler Frequency ShiftsDoppler Frequency Shifts

Motion Away: Echo Frequency Decreases

Motion Towards:Echo Frequency Increases

Doppler EffectDoppler Effect

Continuous Wave Radar Continuous Wave Radar ComponentsComponents

Discriminator AMP Mixer

CW RFOscillator

Indicator

OUTOUT

ININ

Transmitter Antenna

Antenna

Pulse Vs. Continuous WavePulse Vs. Continuous Wave

Pulse EchoPulse EchoSingle antennaSingle antenna

Gives range, usually Gives range, usually altitude as wellaltitude as well

Susceptible to jamming Susceptible to jamming

Range determined by Range determined by PW and PRFPW and PRF

Continuous WaveContinuous Wave

Requires 2 antennaeRequires 2 antennae

Range or Altitude infoRange or Altitude info

High SNRHigh SNR

More difficult to jam but More difficult to jam but easily deceivedeasily deceived

Can be tuned to look Can be tuned to look for frequenciesfor frequencies

RADAR Wave ModulationRADAR Wave Modulation

Amplitude Modulation– Vary the amplitude of the carrier sine waveVary the amplitude of the carrier sine wave

Frequency Modulation– Vary the frequency of the carrier sine waveVary the frequency of the carrier sine wave

Pulse-Amplitude Modulation– Vary the amplitude of the pulsesVary the amplitude of the pulses

Pulse-Frequency Modulation– Vary the Frequency at which the pulses occurVary the Frequency at which the pulses occur

AntennaeAntennae

Two basic purposes:Two basic purposes:

– Radiates RF energyRadiates RF energy

– Provides beam forming and energy focusingProvides beam forming and energy focusing

Must be 1/2 the wave length for maximum wave Must be 1/2 the wave length for maximum wave length employedlength employed

Wide beam pattern for searchWide beam pattern for search

Narrow beam pattern for trackingNarrow beam pattern for tracking

Beamwidth Vs. AccuracyBeamwidth Vs. Accuracy

Beamwidth vs Accuracy

Ship A Ship B

Determining Azimuth Angular Determining Azimuth Angular MeasurementMeasurement

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

NShip’s Heading Angle

Target Angle

Determining AltitudeDetermining Altitude

Determining Altitude

Altitude

Angle of Elevation

Altitude = slant range x sin0 elevation

Concentrating Radar Energy Concentrating Radar Energy Through Beam FormationThrough Beam Formation

Linear ArraysLinear Arrays– Uses following principlesUses following principles

Wave summation (constructive interference)Wave summation (constructive interference)

Wave cancellation (destructive interference) Wave cancellation (destructive interference)

– Made up of two or more simple ½ wave antennaeMade up of two or more simple ½ wave antennae– Example – Aegis RadarExample – Aegis Radar

Quasi-opticalQuasi-optical– Uses reflectors and “lenses” to shape the beamUses reflectors and “lenses” to shape the beam

Wave GuidesWave Guides

Used as a medium for Used as a medium for high energy shielding.high energy shielding.

Uses magnetic field to Uses magnetic field to keep energy centered keep energy centered in the wave guide.in the wave guide.

Filled with an inert gas Filled with an inert gas to prevent arcing due to to prevent arcing due to high voltages within the high voltages within the wave guide.wave guide.

Questions?Questions?