The document discusses various topics related to naval stealth technology including radar cross section (RCS) reduction techniques. It provides information on radar frequencies and functions, radar working principles, RCS prediction methods, and examples of stealth ships. Key points covered include how shaping, radar absorbing materials, and passive/active cancellation can be used to reduce the RCS and vulnerability of detection of naval vessels. Prediction software, instrumentation systems, and examples of reduced RCS for components like gun barrels are also summarized.

1. 03/24/18 1
RADAR CROSS SECTION

2. 03/24/18 2
NAVAL STEALTH
A TECHNOLOGY FOR
REDUCING SIGNATURES SUCH
AS RCS, MAGNETIC, ELFE,
ACOUSTICS , IR ETC. THEREBY
REDUCING VULNERABILITY OF
DETECTION BY ENEMY

3. 03/24/18 3
FREQUENCY BAND DESIGNATION TYPICAL SERVICE
3-30k Hz Very low frequency(VLF) Navigation, sonar
30-300k Hz Low frequency (LF) Radio beacons , navigational aids
300-3,000k Hz Medium frequency (MF) AM broadcasting, maritime
radio,coast guard communication
3-30M Hz High frequency (HF) Telephone, telegraph & facsimile;
SW broadcasting, ship-to-coast &
ship-to-aircraft communication
30-300M Hz Very high frequency (VHF) TV,FM broadcast,air traffic
control,police taxicab mobile radio,
navigational aids
300-3,000M Hz Ultra high frequency
(UHF)
Television satellite communication,
surveillance radar, navigational aids
3-30G Hz Super high frequency
(SHF)
Airborne radar, microwave links,
mobile communication, satellite
communication
30-300G Hz Extreme high frequency
(EHF)
Radar, experimental
INTERNATIONALLY ACCEPTED
Frequency band designation

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FREQUENCY OLD NEW
500-1,000 M Hz VHF C
1- 2 GHz L D
2- 3 G Hz S E
3- 4 G Hz S F
4- 6 G Hz C G
6- 8 G Hz C H
8-10 G Hz X I
10-12.4 G Hz X J
12.4-18 G Hz Ku J
18- 20 G Hz K J
20- 26.5 G Hz K K
26.5- 40 G Hz Ka K
MICROWAVE FREQUENCY BAND DESIGNATION
INDUSTRY STANDARDS

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RADAR WORKING PRINCIPLE

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Illustration of Radar Operation
X
range / time
ground range
height
cross-section
of fan beam
main lobe
elevation
azimuth
xmit
pulse
xmit
pulse
xmit
pulse
target
echoes
target
echoes
pulse repetition interval (pri)
Antenna Beam Pattern
Sidelobes Main Lobe
Targets
slant range
Radar
Location

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RADAR BLOCK DIAGRAM
Receiver Detector
Signal
Processor
Data
Processor Display
T / R
Scanner
Transmitter
RF
Source

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300 MHz30 MHz 1 GHz 2 GHz 4 GHz 8 GHz 12GHz 16 GHz 40 GHz
Early warning Radar
Long Rang Surveillance
Acquisition Radar
Multifunction Radar
Weapon Locating Radar
Short Range Surveillance
Tracking Radar
Radar
Function
Frequency
RADAR FUNCTIONS ACROSS FREQUENCY SPECTRUM

9. 03/24/18 9
RADAR CROSS SECTION
 RCS is a measure of power scattered in
a given direction when a target is
illuminated by a incident wave. The
received power is normalized with the
incident power with the incident power at
the target so that RCS does not depend
on the distance between the target and
the illuminating source.

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RCS is function of
 Frequency or wavelength
 Target geometry
 Material composition
 Aspect angle

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RCS to be reduced for
 To make the ships less vulnerable for
enemy radar detection
 To increase the effectiveness of chaff
 To make classification of our ship difficult
for enemy

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RADAR CROSS SECTION
 PREDICTION
RCSPT (Radar Cross Section Prediction Tool)
 REDUCTION TECHNIQUES
Shaping. Using RAM, RAP
 MEASUREMENT
Using Radar

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RCS s/w prediction
methods
Low frequency methods
 Method of Moments (MoM)
 Finite Difference Time Domain (FDTD)
High frequency methods
 Geometrical Optics (GO)
 Physical Optics (PO)
 Physical Theory of Diffraction (PTD)
 Shooting and Bouncing Ray method
(SBR)

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Low frequency methods
For electrically small scatterers
i.e., objects of order 1λ to 10λ
Less accurate results
High frequency methods
For electrically large scatterers
i.e., objects of order >10 λ
For more accurate results

18. 03/24/18 18
Low frequency methods

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Method of Moment
 Versatile & powerful
 Can be applied to linear,planar &
3D problems
Eg: Metallic cylinder

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Finite Difference Time Domain
method
 Finite difference format is based on
1D Taylor series expansion
 Permits spatial variation of intrinsic
parameters of media
 Employs rectangular co-ordinate
system
Eg: Metallic cylinder,
Metallic plate

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High frequency methods

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Geometrical Optics (GO)
Assumptions
 Frequency is infinite.(λ →0)
 Field behavior is local
 Wave front is always a plane wave
 Specular reflection
Disadvantages
 Breaks down at edges
 Fails to predict away from specular
reflection
Eg: Surfaces with planar shapes

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Physical Optics(PO)
 Based on Huygen’s principle.
 Assumes scatterer to be electrically
large.
 E po = E direct +E induced
Eg: Planar surfaces
Cubes shadowed by extended flat
plate

24. 03/24/18 24
Physical Theory of diffraction(PTD)
 Proposed by Ufimstev
 Assumed that PO induced current
is a part pf total current.
 Current induced in the edges are
considered.
 J PTD = J PO + J edge
Eg: Flat plate
Edges

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Shooting and Bouncing Ray(SBR)
method
 Can treat cavities of arbitrary cross
section and material loading
 Low computational requirement
Eg: Gun barrels

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PREDICTION
EM MESH OF BOLLARD

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Image plot at azimuth 0°
Image Plot at azimuth 90°

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CAD MODEL OF HULL AND DECKS

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RCS OF FEW TARGETS AT 10G Hz

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RCS of some more targets
Small open boat 0.02
Fishing vessel 6
Wooden mine
sweeper 80
Patrol boat 100
Small cargo ship 140
Surfaced submarine 10-200
Tanker 2,230
Cargo ship 100-106
Navy cruiser 14,000

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BASIC METHODS OF
RCS REDUCTION
1. SHAPING
2. DISTRIBUTED LOADING
3. PASSIVE CANCELLATION
4. ACTIVE CANCELLATION

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SHAPING
THE OBJECTIVE OF SHAPING IS TO
ORIENT THE TARGET’S
SURFACES AND EDGES TO
DEFLECT THE SCATTERED
ENERGY IN THE DIRECTION
AWAY FROM THE RADAR.

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RADAR ABSORBING
MATERIALS (RAM)
RAM REDUCE THE ENERGY
REFLECTED BACK TO THE RADAR
BY MEANS OF ABSORPTION AND
REDIRECTION OF EM ENERGY.

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PASSIVE
CANCELLATION
RESISTIVE SHEETS ARE PLACED
OVER SCATTERING CENTERS TO
MODIFY THE SURFACE
IMPEDENCE IN ORDER TO
CANCEL THE REFLECTIONS

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ACTIVE
CANCELLATION
ACTIVE DEVICES ARE
EMPLOYED TO SENSE THE
INCIDENT RADAR WAVE AND
SEND OUT SIGNALS TO CANCEL
THE ECHOS FROM THESE
POINTS.

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APPLICATIONS OF SHAPING

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APPLICATIONS OF
RADAR
ABSORBING PAINT

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RCS of flat plate with and without RAP

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RCS With & without RAP
RCS With & without RAP

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Cylindrical
supporting columns
Non-cylindrical
supporting columns

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RCS of cylindrical and non-cylindrical supporting columns

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SOLID MODEL OF FRONT GUN

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HOT SPOT LOCATION AND DETAILS OF
SHAPING AND PAINTING FOR FRONT GUN
Azim –0
Azim –70
Azim – 90
2
3
1
4
5
Painting
and
shaping
( 2 deg.
Outside)
1,2,3
Painting
Only.
4,5
Painting/s
haping
Surfaces

52. 03/24/18 52
Mark Angle RCS RCS
WITHOUT WITH
RAP RAP
( degrees) ( dBsm) (dBsm)
1. 0 52.12 40.38
2. 75 49.72 38.27
3. 90 48.66 37.2
4. 180 33.83 21.32
2
3
4
1

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Mark Angle RCS RCS
WITHOUT WITH
SHAPING SHAPING
( degrees) ( dBsm) (dBsm)
1. 0 52.12 34.37
2. 75 49.72 29.09
3. 90 48.66 29.55
1
2
3

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INSTRUMENTATION RADAR SYSTEM

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CHAFF LAUNCHER
RCS MEASUREMENT OF CHAFF

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Few stealth ships

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VISBY (Swedish)
Type : Corvette
Power plant: Diesel
electric
Length : 72m
Beam : 10.4 m
Crew : 105

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MEKO (Germany)
Type :
Corvette/Frigate
Length : 82.8-121m
Beam : 11.8-16.34 m
Crew : 93 -120

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SEA SHADOW (US)
Type : Technology
demonstrator
Power plant: Diesel
electric
Length : 164 ft
Beam : 68 ft
Crew : 10

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SMYGE (Swedish)
Type : Test platform
Power plant: Diesel
electric water jets

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SEA WRAITH (Britain)
Type : Corvette
Power plant: Diesel
electric
Length : 377 ft
Beam : 51 ft
Crew : 105

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HIGH SPEED CRAFT
Type : Trimaran
Power plant: Gas turbines
Length : various
Beam : various
Crew : various

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CLICK FORMAGNETIC STEALTH