EEE 4190 Introduction to Modern Radar

Yap Hap Lun, DSO Ng Boon Poh, NTU Tan Shen Hsiao, TL@NTU

2RFCircuits

Antennae

Digital Circuits

Signal Processing

Data Processing

Complex System!Rides on top of the

standalone concepts you have learnt

Radio Detection and Ranging

Its all aboutTRADE-OFFS

A brief history

3

Major developments in the preludebefore WW2

Chain Home Air Defence (early in WW2)

Airborne interception Radar Mk VIIon the British Beaufighter

Radio Detection and Ranging

4

AM Radio Broadcast RadioContinuous waves in this example

Radio Detection and Ranging

5

Pulse moving at the speed of light

Range, RTime, R/c

Take-away: 1s delay is equivalent to 150m

Only need to listen for return echoes at the ranges we are interested in!

Pulse-widths and resolution

6

2 point targetsseparated by c/4

Radar location

First target at range, R

Pulsewidth,

Range axis

Received signal, t = 0

t = R/c

t = 2R/c Time axis

Pulse-widths and resolution

7

2 point targetsseparated by c/4

Radar location

First target at range, R

Pulsewidth,

Range axis

Received signal, t = 0

t = R/c

Time axist = 2R/c

/4

Pulse-widths and resolution

8

2 point targetsseparated by c/4

Radar location

First target at range, R

Pulsewidth,

Range axis

Received signal, t = 0

t = R/c

Time axist = 2R/c

/2

Pulse-widths and resolution

9

2 point targetsseparated by c/4

Radar location

First target at range, R

Pulsewidth,

Range axis

Received signal, t = 0

t = R/c

Time axist = 2R/c

Overlapping return signal

Pulse-widths and resolution

10

2 point targetsseparated by c/4

Radar location

First target at range, R

Pulsewidth,

Range axis

Received signal, t = 0

t = R/c

Time axist = 2R/c

5/4

Pulse-widths and resolution

11

2 point targetsseparated by c/4

Radar location

First target at range, R

Pulsewidth,

Range axis

Received signal, t = 0

t = R/c

Time axist = 2R/c

3/2

The 2 targets cannotbe resolved (i.e. looks like single target)

Pulse-widths and resolution

12

2 point targetsseparated by c/2

Radar location

First target at range, R

Pulsewidth,

Range axis

Received signal, t = 0

t = R/c

t = 2R/c Time axis

Pulse-widths and resolution

13

2 point targetsseparated by c/2

Radar location

First target at range, R

Pulsewidth,

Range axis

Received signal, t = 0

t = R/c

Time axist = 2R/c

/2

Pulse-widths and resolution

14

2 point targetsseparated by c/2

Radar location

First target at range, R

Pulsewidth,

Range axis

Received signal, t = 0

t = R/c

Time axist = 2R/c

Pulse-widths and resolution

15

2 point targetsseparated by c/2

Radar location

First target at range, R

Pulsewidth,

Range axis

Received signal, t = 0

t = R/c

Time axist = 2R/c

3/2

Signal from both targetsjust begin to be separated

Pulse-widths and resolution

16

2 point targetsseparated by c/2

Radar location

First target at range, R

Pulsewidth,

Range axis

Received signal, t = 0

t = R/c

Time axist = 2R/c

2

Signal from both targetsjust begin to be separated

Take-away: Range resolution = or

The basic radar equation

17

The idea behind it... if we send out a pulse with power, Pt, what is the power we receive, Pr, after it is reflected back from a target?

Pt Target

Power density at target

Antenna Gain, Gt

Supplement - Terms & Notations

18

Pr : Power received in watts (W) Pt : Power transmitted in watts (W) Gt : Gain of transmit antenna, dBi Gr : Gain of receive antenna, dBi : wavelength of transmitted signal in meters (m) : radar cross-section in square meters (m2) R : Range to target in meters (m)

Supplement - Terms & Notations

19

The decibel or dB

- Logarithmic ratio of power- Power ratio in dB = 10 log10 (P2/P1)- It has no units on its own (i.e. dimensionless)- For example, the difference between 1000 W and 10 W is 10 log10 (1000/10) or 20 dB

dBW is power relative to 1 W or 10 log10 (P2/1)eg. 1 kW = 10 log10 (1000/1) = 30 dBW

dBm is power relative to 1 mW or 10 log10 (P2/0.001)eg. 1 kW = 10 log10 (1000/0.001) = 60 dBm

dBsm is area relative to 1 m2 or 10 log10 (A/1)eg. 50 m2 = 10 log10 (50/1) = 17 dBsm

Lets put some numbers in

20

Transmit power Pt 1 kW 30 dBWTransmit antenna gain Gt 30 dBReceive antenna gain Gr 30 dBTransmit wavelength 3 cm -30.5 dB

Target RCS 100 m2 20 dBRange R 100 km 200 dB(4)3 33 dB

Noise bandwidth B 100 MHz

Pr = 30 + 30 + 30 - 30.5 + 20 - 33 - 200 dBW = -153.5 dBW or -123 dBm or 5 10-16 W

Band-limited thermal noise = kTB = -94 dBm

Take-away: Signal from a single pulse is usually below noise (negative SNR)

More numbers ...

21

A little twist to the radar equation

22

Receiver with noise figure, F and bandwidth, B

FilterLNA...

Target (or signal) + noise

ADC

Signal-to-noise ratio

How can we improve this?

23

Increase the power?12 dB more power needed to double the rangeIncrease antenna gain?Bigger aperture... can you afford the space?Lower the frequency?You lose antenna gain...

Look beyond the equation

24

So far, weve only discussed the power returned from a single pulse...But theres no reason to limit ourselves to just one pulse

Multiple pulses or integration

25

Take-away: Integrating multiple pulses gives you SNR gain to help overcome the poor hardware/RF power

budget (Coherent SNR gain (dB) = 10log10N)

When integration breaks...

26

Fast moving target, say 800km/h or 222m/sLarge range cell/resolution, say 10mA reflecting surface on the target stays within the same resolution cell for at most 45msDe-correlation occurs after this!Sometimes use about half this time (22.5ms) for designing the systemThis time is commonly known as the Coherent Integration Interval (CIT) or sometimes the Dwell Time.

Shoot as many pulses as we can with the CIT?

PRF and range ambiguity

27

1000 s or 150 km

666 s or 100 km 1 kHz pulse repetition frequency

2 kHz pulse repetition frequency

PRF < 1/Time to furthest target

Radar Frequency Bands

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IEEE Band Frequency

HF 3 30 MHz

VHF 30 300 MHz

UHF 300 1000 MHz

L 1 2 GHz

S 2 4 GHz

C 4 8 GHz

X 8 12 GHz

Ku 12 18 GHz

K 18 27 GHz

Ka 27 - 40 GHz

83

Choice of RadioFrequency

1. Portion of electromagnetic spectrum used for radar.

Aprimary consideration in the design of virtuallyevery radar is the frequency of the transmittedradio wavesthe radars operating frequency.How close a radar may come to satisfying manyof the requirements imposed on itdetection range, angu-lar resolution, doppler performance, size, weight, cost,etc.often hinges on the choice of radio frequency. Thischoice, in turn, has a major impact on many importantaspects of the design and implementation of the radar.

In this chapter, we will survey the broad span of radiofrequencies used by radars and examine the factors whichdetermine the optimum choice of frequency for particularapplications.

Frequencies Used for Radar

Today, radars of various kinds operate at frequenciesranging from as low as a few megahertz to as high as300,000,000 megahertz (Fig. 1).

At the low end are a few highly specialized radars:sounders that measure the height of the ionosphere, aswell as radars that take advantage of ionospheric reflectionto see over the horizon and detect targets thousands ofmiles away.

At the high end are laser radars, which operate in thevisible region of the spectrum and are used to provide theangular resolution needed for such tasks as measuring theranges of individual targets on the battlefield.

Most radars, however, employ frequencies lying some-where between a few hundred megahertz and 100,000megahertz.

To make such large values more manageable, it is cus-tomary to express them in gigahertz. One gigahertz, you

Stimson George W, Introduction to Airborne Radar, 2nd edition

The HF Band (3 30 MHz)

29

Wavelength 10 - 100m Over-the-Horizon (OTH) radars

Surface wave or skywave propagation Very long range detection possible for ships Land-based due to huge amount of space needed for antennas Accuracy is low but traded off for range Australian Jindalee or French Nostradamus

The VHF Band (30 300 MHz)

30

Wavelength 1 - 10m Specialty applications

Chain Home works here Accuracy better than HF, smaller antennas Line-of-sight more important than HF Still good against stealth by materials and shape Good FOliage PENetration (FOPEN) Passive radar using FM/TV (Lockheed Martins Silent Sentry) For more information, contact:Joe Kurian

Manager, PCL/Silent Sentry Programs(301) 240-7267joe.kurian@lmco.comLockheed Martin is an Equal Opportunity Employer. Lockheed Martin Corporation, 2005.LOCKHEED MARTIN, LOCKHEED and the STAR DESIGN[and any other marks used in the body of document] are eitherregistered marks in the U.S. Patent and Trademark Officeand/or other countries throughout the world, or are trademarksand servicemarks of Lockheed Martin Corporation in theU.S. and/or other countries.Silent Sentry is a registered trademark ofLockheed Martin CorporationPrinted in the United States of America 06/05. All Rights Reserved.

PerformanceSurveillance Volume Azimuth: Up to 360 degrees Elevation: 60 degrees Continuous SearchRange Typically 0 to 150 nmi within FOV Depends on antenna usedTargets 100+ simultaneously Aircraft, missiles, vehicles, shipsAccuracy (FM) 150 m horizontal position 1000 m vertical position < 2 m/s horizontal velocity Better positional accuracy with HDTVData Output Silent Sentry track format or OTH Gold Link 16 (planned) XML (planned)PortabilityConfigurations Installation on fixed

or mobile platforms

Form Factor: VME rack 2' x 2' transit cases Easy to ship or transportDeployment 1-2 person setupSurvivabilityOperating Environment Room temperature Shelter protected 1.5 kw 120V powerReliability COTS product based No moving parts All-weather capableDetectability Covert when operating with

indigenous illumination

Principles of OperationRF energy already existing in theenvironment from broadcast radio andTV transmitters is scattered from a targetand collected by the Silent Sentry receiver,which then compares the scattered waves tothe direct signal to determine the locationand velocity of the target.

Silent Sentrys Passive Coherent Location (PCL) technology provides precise, real-time, all-weatherdetection and tracking ideal for air surveillance, missile tracking and homeland security applica-tions. Silent Sentrys innovative approach is totally passive, allowing targets to be tracked withoutgenerating any RF energy by using existing broadcast signals from FM radio and TV (analog anddigital) transmitters across the globe. This virtually undetectable surveillance system has no safetyor environmental impact. With no moving parts and a commercial off-the-shelf (COTS) approach,Silent Sentry is less expensive to acquire, operate and maintain than traditional radar systems.Silent Sentry systems provide covert, robust performance featuring three-dimensional trackingwith highly accurate horizontal position and velocity measurements. A modular, flexible,network-ready COTS design facilitates integration with legacy and emerging systems. SilentSentry systems are compact, easily deployed, and configurable for a variety of surveillanceapplications.

Capabilities

Innovative Technology forPassive, Persistent Surveillance

The UHF Band (300 1000 MHz)

31

Wavelength 0.3 - 1m Long range air surveillance

Accuracy better than VHF, smaller antennas Still good against stealth by materials and shape Fair FOliage PENetration (FOPEN) Good compromise of range/accuracy in volume search Medium Extended Air Defense System (MEADS), early generation Airborne Early Warning (AEW)

L-band Air Traffic Control Radar Antenna SystemThe ASC Signal L-band Radar Antenna and Pedestal System is a well-proven off-the-shelf design. The system has been installed and in operation in major airports throughout the world.

The antennas and pedestals are manufactured in accordance with ISO9001 Quality Assurance to stringent specifications and perform to the exacting standards demanded of them. ASC Signal has invested in extensive manufacturing tooling to ensure repeatability in production.

The ASC Signal Corporation L-bandPrimary Surveillance Radar Antenna System is a widely deployed advanced antenna and pedestal with a proven record of performance and reliability. Drawing on its renowned advanced antenna and pedestal design, ASC Signal fabricates these surveillance radar antenna systems with proven performance advantages. Choose the ASC Signal Advantage for your next Radar System. Complete system solution with rotary joint, control unit and ancillary equipment are also available.

Antenna Features

High gain

High and low radiating beams

Low sidelobes

Enhanced high angle performance

Instantaneous polarization switching

Weather channel

Pedestal Features

Type tested for operation in extreme environment

Developed from FAA approved base design

Versatile and rugged

Dual helical gearbox

Selectable rotation speed

Optional control unit and rotary joint

The system has been installed and in operation in major airports throughout the world.

P R O D U C TS P E C I F I C A T I O N S

The L-Band (1 2 GHz)

32

Wavelength 0.15 - 0.3m Long range air surveillance

No longer very useful for FOPEN Long range air surveillance for air traffic management, more recent generations of AEW

L-band Air Traffic Control Radar Antenna System

S P E C I F I C AT I O N S

Mechanical Performance

Feed Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Prime focus offset feed system Reflector Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Modified Parabola, Aluminum ConstructionTilt Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -7 to +9Weight, net . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2,598 kgDimensions (l x w x h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.3 m x 13 m x 6.7 m

Electrical Performance

Frequency Band . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.25 1.35 GHz

Low BeamGain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 dBi minVSWR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1:1.35Isolation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 dB minPolarizer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Switchable circular/linearICR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 dB

Beamwidth . . . . . . . . . Az . . . . . . . . . . . . . . . . . . . . . 1.2 El . . . . . . . . . . . . . . . . . . . . . 3.8

Radiation Pattern . . . . . . . . . Az . . . . . . . . . . . . . . . . . . . . . 26 dB max, typ. 29 dB El . . . . . . . . . . . . . . . . . . . . . Modified Cosecant Sq.

High BeamGain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 dBi minVSWR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1:1.55Polarizer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Swichable circular/linearICR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 dB

Beamwidth . . . . . . . . . Az . . . . . . . . . . . . . . . . . . . . . 1.25 El . . . . . . . . . . . . . . . . . . . . . 5.5

Radiation Pattern . . . . . . . . . Az . . . . . . . . . . . . . . . . . . . . 26 dB max El . . . . . . . . . . . . . . . . . . . . . Modified Cosecant Sq.

Pedestal Performance

Dual Drive Motors, HP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Rotation Rate, rpm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4, 5, 6, 7.5, 10, 12, 15Peak Torque, ft-lb (dual drive) . . . . . . . . . . . . . . . . . . . . . . . . 4,200Motor Frequency, Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50/60Motor Voltage, volts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208/380/415Weight, net . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2727 kgDimensions (l x w x h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.9 m x 1.7 m x 1.7 m

Evironmental (Antenna and Pedestal)

Operating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50C to +50CNon-operating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -50C to +65CRadiation Pattern . . . . . . . . Az . . . . . . . . . . . . . . . . . . . . . 26 dB maxHumidity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . up to 98% at 40COperation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . in a radome

Available Options

Rotary JointLadder Kit

Shipping Information

AntennaWeight, gross . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5010 kgDimensions (l x w x h)8 skids (each) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.7 m x 2.3 m x 2.3 m1 skid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 m x 2.3 m x 1.5 m1 crate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. 6 m x 1.8 m x 2.0 mTransportable via five closed ISO containers

Pedestal Weight, gross . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3182 kgDimensions (l x w x h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 m x 2.1 m x 1.6 mTransportable in a single closed ISO container.

8.7 m

1.1 m

13.6 m

Call today for pricing and interface details for your application. ASC Signal also supplies custom design, system integration, field installation, and test services.

ISO9001

CERTIFIEDFIRM

ASC Signal Corporation620 North Greenfield ParkwayGarner, NC 27529 USA

Telephone: +1-919-329-8700Fax: +1-919-329-8701

Internet: www.ascsignal.com

All designs, specifications and availabilities of products and services presented in this bulletin are subject to change without notice.ASC-MGR3 2007 ASC Signal Corporation

The S-Band (2 4 GHz)

33

Wavelength 7.5 - 15cm Shorter range air traffic management

Weather radars start from this band Marine navigation radar (less affected by rain than X-band), big ships carry both

Gyro Log GPS AIS

Interswitched X & S-Band SystemInterswitched Dual Transceiver / Display System

Features & System

s

MCIControl Panel

Chair Mounted Ergopod Console Display

Control/Display Options

Interswitch Unit

10kW X -Band 30kW S -Band

425

415

630

Dimensions and Weights

2.5m X Band 20kg

1.9m X Band 14kg

High Speed X Band

Soft Start Units

Mk VII X Band25kW

Mk VII S Band30kW

10kW X Band 25kW X Band 30kW/SharpEye S-Band

305

482

90

273

368

170

418

570

230

300

540

210

Radar Interswitch Unit

Transmitter Interface Unit1.3m X Band 10kg

3.7m S Band 70kg

Displays/Processors

Antennas/Transceivers/Ancillaries

718

595

520

485

520 300

420

520125 102650

525

500

650 786

595

700

1200

650 786 520

1120

750

720 720

420 250420 250

20"26"

20"26"

20"26"

5.5kg

270

Weight: 99kg Weight: 78kg

Weight: 32kgWeight: 38kg

Weight: 28kg Weight: 20kg Weight: 32kg Weight: 25kg

270415

630

7kg

10kg

7kg

370

290

290

410570

250

310

406 418

474

480

540

23kg 40kg 100kg

30kg 35kg

The C-Band (4 8 GHz)

34

Wavelength 3.75 - 7.5cm Portability begins to come into play mainly

because of antenna size Battlefield or mobile radars for short to medium range (artillery locating) Majority of weather radars are in this band

The X-Band (8 12 GHz)

35

Wavelength 2.5 - 3.75cm Antenna size becomes small enough for combat

aircraft Most fighter aircraft nose radar are in this band Weather radar for commercial aircraft Most marine navigation radars carry at least the X-band version Missile seekers and police speed radars (the older ones) start here

The Ku-Band (12 - 18 GHz)

36

Wavelength 1.6 - 2.5cm Radar for smaller platforms

Most fighter aircraft nose radar are in this band Weather radar for commercial aircraft Most marine navigation radars carry at least the X-band version Many missile seekers operate in this band especially AAM.

The K-Band (18 27 GHz)

37

Wavelength 1.1 - 1.6cm Hand-held radars!

Sports radar (tennis, golf, etc) Miniature missile seekers of the future ISM band @ 24 GHz for automotive applications Surface movement

The Ka-Band (27 - 40 GHz)

38

Wavelength 7.5 - 11mm Police paradise

Almost all police speed radars are now here 35 GHz for cloud radars

Radar displays: A- and B-Scope

39

Amplitude versus time

Range or time

The earliest displays1

Range versus angle

1 Not in common use these days

Radar displays: PPI

40

Plan Position IndicatorPolar plot of range and angle

SAR Images

41

UHF

A comparison with ...

42