SEMINAR REPORT ON MECHANICAL ASPECTS IN STEALTH TECHNOLOGY
CONTENTS
1.
LIST OF FIGURES ……………………………………………………………...1
INTRODUCTION .................................................................................................. 2
2.
STEALTH TECHNOLOGY .................................................................................. 3
3.
2.1.
Stealth Principle ............................................................................................... 3
2.2.
The term “Signature” of a Vehicle ................................................................... 3
2.3.
What is the need for Stealth?............................................................................ 3
2.4.
The Key Features of Stealth ............................................................................. 4
2.5.
Detection Method & There Field ..................................................................... 4
RADAR................................................................................................................... 5
3.1.
4.
Radar (RADIO DETECTION AND RANGING) ........................................... 5
3.1.1.
ECHO ........................................................................................................ 5
3.1.2.
Doppler Shift ............................................................................................. 5
3.2.
Why Radio waves and not sounds waves? ....................................................... 6
3.3.
Distance Measurement ..................................................................................... 6
3.4.
Frequency Modulation ..................................................................................... 7
3.5.
Speed Measurement ......................................................................................... 7
3.6.
Size Measurement ............................................................................................ 7
STEALTHSHIP ...................................................................................................... 8
4.1.
Shaping ............................................................................................................. 8
5.
RADAR ABSORBENT SURFACES..................................................................... 9
6.
RADAR ABSORBING MATERIAL ................................................................... 10
7.
METHODS OF AVOIDING DETECTION ......................................................... 11
8.
9.
7.1.
Visual stealth .................................................................................................. 11
7.2.
Infrared stealth................................................................................................ 12
7.3.
Acoustic stealth .............................................................................................. 13
7.4.
Radar stealth ................................................................................................... 13
7.5.
Absorption ...................................................................................................... 13
7.6.
Deflection ....................................................................................................... 14
ADVANTAGES AND DISADVANTAGES OF STEALTH .............................. 15
8.1.
Advantages of Stealth Technology ................................................................ 15
8.2.
Disadvantages of Stealth Technology ............................................................ 15
CONCLUSION ..................................................................................................... 17
REFERENCES ............................................................................................................. 18
MECHANICAL ASPECTS IN STEALTH TECHNOLOGY
LIST OF FIGURES
Figure 2-1: Anti-Aircraft Turret [1] ------------------------------------------------------------- 4
Figure 3-1: ECHO Effect ------------------------------------------------------------------------ 5
Figure 3-2: Audio Example of Doppler Shift [1] ---------------------------------------------- 6
Figure 4-1: STEALTHSHIP [3]------------------------------------------------------------------ 8
Figure 5-1: Comparing Conventional Vs. Stealth Aircraft [8] ------------------------------ 9
Figure 6-1: Incident Radar Beam Dissipated in RAM Coating ---------------------------10
Figure 7-1: VISUAL STEALTH PLANE-HAWK GB [11] --------------------------------11
Figure 7-2: Thermal infrared image - US Military F117 Stealth [6]-----------------------12
Figure 7-3: ACOUSTIC STEALTH AIRCRAFT [6] ---------------------------------------13
Figure 7-4: DEFLECTIN OF RADAR BECAUSE OF THE STEALTH DESIGN [13]
------------------------------------------------------------------------------------------------------14
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1. INTRODUCTION
Stealth technology also known as LOT (Low Observability Technology) is a technology
which covers a range of techniques used with aircraft, ships and missiles, in order to
make them less visible (ideally invisible) to radar, infrared and other detection methods.
From the late years of World War II to today's computer enabled design changes, stealth
has been a major factor in the improvement of reconnaissance and attack aircraft. The
term "stealth", is thought to have been coined in 1966 by Charles E. "Chuck" Myers,
combat pilot and later an exec at Lockheed. When we think of stealth today, immediately
images of the B-2 bomber or the F-117A Nighthawk fighter come to mind.
In simple terms, stealth technology allows an aircraft to be partially invisible to Radar
or any other means of detection. This doesn't allow the aircraft to be fully invisible on
radar. Stealth technology cannot make the aircraft invisible to enemy or friendly radar.
All it can do is to reduce the detection range or an aircraft. This is similar to the
camouflage tactics used by soldiers in jungle warfare. Unless the soldier comes near
you, you can't see him. Though this gives a clear and safe striking distance for the
aircraft, there is still a threat from radar systems, which can detect stealth aircraft.
Stealth technology is expanded into each of those areas which seek to detect the aircraft,
ships & missiles. Thus it is essential to develop visual, infrared acoustic and radar
stealth. However, many countries have announced that they have developed counterstealth techniques that allow them to negate stealth.
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2. STEALTH TECHNOLOGY
The concept behind the stealth technology is very simple. As a matter of fact, it is totally
the principle of reflection and absorption that makes aircraft "stealthy". Deflecting the
incoming radar waves into another direction and thus reducing the number of waves
does this, which returns to the radar. Another concept that is followed is to absorb the
incoming radar waves totally and to redirect the absorbed electromagnetic energy in
another direction. Whatever may be the method used, the level of stealth an aircraft can
achieve depends totally on the design and the substance with which it is made of.
2.1. Stealth Principle
Stealth technology (or LO for "Low Observability") is not a single technology. It is a
combination of technologies that attempt to greatly reduce the distances at which a
vehicle can be detected; in particular radar cross section reductions, but also acoustic,
thermal, and other aspects.
2.2. The term “Signature” of a Vehicle
Signature - Any unique indicator of the presence of certain materiel or troops; especially
the characteristic electronic emissions given off by a certain type of vehicle, radar, radio,
or unit. Thus Signature can be concluded as any activity or radiation or the characteristic
of the body that helps to revile its presence at a particular point.
All the detection methods used that be in military and civil systems are by detecting
the signature of the body. This signature is called by different names in different
contexts. Radar Signature is called Radar Cross Section or RCS and so on. Thus
signature can be rightly called as Observability of an object and stealth vehicles can be
called as low-observable vehicles or low-signature vehicles.
2.3. What is the need for Stealth?
There is one application of radar that pushed stealth technology into existence. That
application is of the radar guided anti-aircraft systems. There are several different
varieties to these systems. One system is to guide a turret to hit an enemy aircraft with
a bullet. Such a system is shown in Figure 1.
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Figure 2-1: Anti-Aircraft Turret [1]
Another system is to fire radar fused shells into the air. These shells emit their own
radar signal and then determine the distance to planes around it. When it is close enough
to a plane it explodes launching fragments in every direction. With these two types of
systems, it became very dangerous to use aircraft to penetrate an enemy controlled area.
[1]
2.4. The Key Features of Stealth
 Unusual Design
 Outer Paint
 Reduce Heat Exhaust Signatures
 Eliminate High Altitude Contrails
 Eliminate Brown Exhaust
2.5. Detection Method & There Field
 RCS: - Aircrafts, Missiles, Ships, Land Vehicles...
 Infrared signature:-Aircrafts, Missiles, Ships, Land Vehicles, Submarines.
 Acoustic Signature: - Predominantly for Submarines (SONAR), Ships,
Aircrafts
 Visible Signature: - Predominantly for Land Vehicles, Aircrafts, and Ships.
 Laser Cross Section:-Aircrafts, Missiles, Ships, Land Vehicles.
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3. RADAR
3.1. Radar (RADIO DETECTION AND RANGING)
RADAR is the acronym for Radio Detection and Ranging. Radar is an object-detection
system that uses radio waves to determine the range, altitude, direction, or speed of
objects. Radar is something that is in use all around us, although it (radio waves) is
normally invisible. RADAR basically works on two major principles.
3.1.1. ECHO
As the name suggest it is related to the sound waves it occurs
because some of the sound waves in your shout reflect off of a
surface (either the water at the bottom of the well or the canyon
wall on the far side) and travel back to your ears. A mirror is an
example of light waves being reflected back at one’s self. Light
from an external source hits a body and bounces off in several
directions. Some light waves propagate towards the mirror and
then reflect off of the mirror back to that person’s eyes. This same
exact principle applies to radio waves. Radio waves are simply
non-visible forms of light. The idea behind radar is to transmit a
radio wave and then receive the reflection from an aircraft. The
amount of time between the transmission and the reception can be
used with a very accurate number for the speed of light to
Figure 3-1: ECHO Effect
determine how far away the plane is from the radar station.
3.1.2. Doppler Shift
Doppler shift occurs when sound is generated by, or reflected off of, a moving object.
Doppler shift in the extreme creates sonic booms. This effect is more commonly felt for
sound. The sound that you hear as a vehicle is approaching you is at a higher pitch or a
higher frequency than the sound you hear when the vehicle is moving away from you.
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Figure 3-2: Audio Example of Doppler Shift [1]
This property when applied to radar can be used to determine the speed of the object.
The frequency of the reflected wave can be the same, greater or lower than the
transmitted radio wave. If the reflected wave frequency is less than this means that the
target is moving away from the transmitter and if higher then moving close to the
transmitter and if constant then the target is not moving like a helicopter hovering at a
point. This can be used to predict the speeds of the target too.
3.2. Why Radio waves and not sounds waves?
Although the above said principles are applicable to sound waves radio waves are
used for detection and ranging due to the following reasons. The speeds of the radio
waves are comparable with that of light and are much higher than that of sound. Sound
waves cannot travel as far as light in the atmosphere without significant attenuation.
And finally, electromagnetic echo is much easier to detect than a sound echo. [1]
3.3. Distance Measurement
One way to measure the distance to an object is to transmit a short pulse of radio signal
(electromagnetic radiation), and measure the time it takes for the reflection to return.
The distance target is one half the product of the time taken by the radiated signal to
travel to the target and back to the receiver and the speed of the signal radiated.
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3.4. Frequency Modulation
Another form of distance measuring radar is based on frequency modulation. Frequency
comparison between two signals is considerably more accurate, even with older
electronics, than timing the signal. By changing the frequency of the returned signal and
comparing that with the original, the difference can be easily measured.
3.5. Speed Measurement
Speed is the change in distance to an object with respect to time. Speed measurement is
done by using the technique of Doppler Effect. The radar beam is fired at the moving
target. As it recedes from the radar source, each successive wave has to travel further to
reach the car, before being reflected and re detected near the source. As each wave has
to move further the gap between each wave increases. This shows a change in the
spectrum of the waves. [2]
3.6. Size Measurement
The size of targets image on radar is measured by the radar cross section (RCS)
measured in Square meters. This does not equal geometric area. A perfectly Conducting
sphere of projected cross-sectional area 1 m2. RADAR wavelength much less than the
diameter of the sphere. RCS is independent of frequency, Conversely, a flat plate of area
1 m2 will have an RCS of almost 14000 m2 at 10GHz if the radar is perpendicular to the
flat surface since it will reflect the signal right back to the radar antenna from where it
came. By reflecting much of the radiation away from the antenna or absorbing it
altogether, the target achievers smaller radar cross section. [2]
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4. STEALTHSHIP
A stealth ship is a ship which employs stealth technology construction techniques in an
effort to ensure that it is harder to detect by one or more of radar, visual, sonar, and
infrared methods. These techniques borrow from stealth aircraft technology, although
some aspects such as wake and acoustic signature reduction are unique to stealth ships'
design.
Reduction of radar cross section (RCS), visibility and noise is not unique to stealth ships;
visual masking has been employed for over two centuries and RCS reduction traces back
to American and Soviet ships of the Cold War. One common feature is the inwardsloping tumblehome hull design that significantly reduces the RCS. [3]
Figure 4-1: STEALTHSHIP [3]
4.1. Shaping
In designing a ship with reduced radar signature, the main concerns are radar beams
originating near or slightly above the horizon (as seen from the ship) coming from
distant patrol aircraft, other ships or sea-skimming anti-ship missiles with active radar
seekers. Therefore, the shape of the ship avoids vertical surfaces, which would perfectly
reflect any such beams directly back to the emitter. Retro-reflective right angles are
eliminated to avoid causing the cat's eye effect. A stealthy ship shape can be achieved
by constructing the hull and superstructure with a series of slightly protruding and
retruding surfaces. This design was developed by several German shipyards, and is thus
extensively applied on ships of the German Navy. [5]
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5. RADAR ABSORBENT SURFACES
RAS or Radar absorbent surfaces are the surfaces on the aircraft, which can deflect the
incoming radar waves and reduce the detection range. RAS works due to the angles at
which the structures on the aircraft's fuselage or the fuselage itself are placed. These
structures can be anything from wings to a refuelling boom on the aircraft. The extensive
use of RAS is clearly visible in the F-117 "Night Hawk". Due to the facets (as they are
called) on the fuselage, most of the incoming radar waves are reflected to another
direction. Due to these facets on the fuselage, the F-117 is a very unstable aircraft. [1]
Figure 5-1: Comparing Conventional Vs. Stealth Aircraft [8]
The concept behind the RAS is that of reflecting a light beam from a torch with a mirror.
The angle at which the reflection takes place is also more important. When we consider
a mirror being rotated from 0o to 90o, the amount of light that is reflected in the direction
of the light beam is more. At 90o, maximum amount of light that is reflected back to
same direction as the light beam's source. On the other hand when the mirror is tilted
above 90o and as it proceeds to 180o, the amount of light reflected in the same direction
decreases drastically. This makes the aircraft like F-117 stealthy. [1]
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6. RADAR ABSORBING MATERIAL
Radar absorbent surfaces absorb the incoming radar waves rather than deflecting it in
another direction. ‘Radar absorbent Material’ totally depends on the surface of the
aircraft is made. Though the composition of this material is a top secret. The F-117
extensively uses RAM to reduce its radar signature or its radar cross section. [1]
The RAS is believed to be silicon based inorganic compound. The RAM coating over
the B-2 is placed like wrapping a cloth over the plane. When radar sends a beam in the
direction of the B-2, the radar waves are absorbed by the plane’s surface and are
redirected to another direction after it is absorbed. This reduces the radar signature of
the aircraft. A Jaumann absorber or Jaumann layer is a radar absorbent device. The Foam
absorber is applied to the chamber walls with the tips of the pyramids pointing inward
or toward the radar. As a radar wave strikes a pyramid, it experiences a gradual transition
from free space at the tip of the pyramid to absorbing foam at the base. [1]
Figure 6-1: Incident Radar Beam Dissipated in RAM Coating
The idea behind RAM paint is to absorb the energy of the radio waves transmitted by
the radar antenna. RAM contains carbonyl iron ferrite as the active ingredient. When
radar waves hit the RAM coating a magnetic field is produced in the metallic elements
of the coating. The magnetic field has alternating polarity and dissipates the energy of
the signal. The energy that is not dissipated by the individual carbonyl iron ferrite
elements is reflected to other elements as shown in Figure 6-2.
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7. METHODS OF AVOIDING DETECTION
Design for stealth requires the integration of many techniques and materials. The types
of stealth that a maximally stealthy aircraft & ships seeks to achieve can be categorized
as visual, infrared, acoustic, and Radar.
7.1. Visual stealth
Low visibility is desirable for all military aircraft and is essential for stealth aircraft. It
is achieved by colouring the aircraft so that it tends to blend in with its environment. For
instance, reconnaissance planes designed to operate at very high altitudes, where the sky
is black, are painted black. (Black is also a low visibility colour at night, at any altitude.)
Conventional daytime fighter aircraft are painted a shade of blue known as "airsuperiority blue-grey”, to blend in with the sky. Stealth aircraft are flown at night for
maximum visual stealth, and so are painted black or dark grey. Chameleon or "smart
skin" technology that would enable an aircraft to change its appearance to mimic its
background is being researched. [9]
Figure 7-1: VISUAL STEALTH PLANE-HAWK GB [11]
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7.2. Infrared stealth
Another important factor that influences the stealth capability of an aircraft is the IR (i.e.
Infrared, electromagnetic waves in the. 72–1000 micron range of the spectrum)
signature given out by the plane. Usually planes are visible in thermal imaging systems
because of the high temperature exhaust they give out. This is a great disadvantage to
stealth aircraft as missiles also have IR guidance system. The IR signatures of stealth
aircraft are minute when compared to the signature of a conventional fighter or any other
military aircraft.
Figure 7-2: Thermal infrared image - US Military F117 Stealth [6]
Engines for stealth aircraft are specifically built to have a very low IR signature. Another
main aspect that reduces the IR signature of a stealth aircraft is to place the engines deep
into the fuselage. This is done in stealth aircraft like the B-2, F-22 and the JSF. The IR
reduction scheme used in F-117 is very much different from the others. The engines are
placed deep within the aircraft like any stealth aircraft and at the outlet; a section of the
fuselage deflects the exhaust to another direction. This is useful for deflecting the hot
exhaust gases in another direction. [10]
Infrared radiation are emitted by all matter above absolute zero; hot materials, such as
engine exhaust gases or wing surfaces heated by friction with the air, emit more infrared
radiation than cooler materials. Heat-seeking missiles and other weapons zero in on the
infrared glow of hot aircraft parts. Infrared stealth, therefore, requires that aircraft parts
and emissions, particularly those associated with engines, be kept as cool as possible. [9]
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7.3. Acoustic stealth
Although sound moves too slowly to be an effective locating signal for antiaircraft
weapons, for low-altitude flying it is still best to be inaudible to ground observers.
Several ultra-quiet, low-altitude reconnaissance aircraft, such as Lockheed's QT-2 and
YO-3A, have been developed since the 1960s. Aircraft of this type are ultra-light, run
on small internal combustion engines quieted by silencer-suppressor mufflers, and are
driven by large, often wooden propellers. They make about as much sound as gliders
and have very low infrared emissions as well because of their low energy consumption.
The U.S. F-117 stealth fighter, which is designed to fly at high speed at very low
altitudes, also incorporates acoustic-stealth measures, including sound-absorbent linings
inside its engine intake and exhaust cowlings. [9]
Figure 7-3: ACOUSTIC STEALTH AIRCRAFT [6]
7.4. Radar stealth
Radar stealth or invisibility requires that a craft absorbs incident radar pulses, actively
cancel them by emitting inverse waveforms, deflect them away from receiving antennas,
or all of the above. Absorption and deflection treated below are the most important
prerequisites of radar stealth. [9]
7.5. Absorption
Metallic surfaces reflect RADAR; therefore, stealth aircraft parts must either be coated
with RADAR-absorbing materials or made out of them to begin with. The latter is
preferable because an aircraft whose parts are intrinsically RADAR-absorbing derives
aerodynamic as well as stealth function from them, whereas a RADAR-absorbent
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coating is, aerodynamically speaking, dead weight. The F-117 stealth aircraft is built
mostly out of a RADAR-absorbent material termed Fibaloy, which consists of glass
fibers embedded in plastic, and of carbon fibbers, which are used mostly for hot spots
like leading wing-edges and panels covering the jet engines. [9]
7.6. Deflection
Most RADAR are mono static, that is, for reception they use either the same antenna
as for sending or a separate receiving antenna collocated with the sending antenna;
deflection therefore means reflecting RADAR pulses in any direction other than the one
they came from. This in turn requires that stealth aircraft lack flat, vertical surfaces that
could act as simple RADAR mirrors. [9]
Figure 7-4: DEFLECTIN OF RADAR BECAUSE OF THE STEALTH DESIGN [13]
RADAR can also be strongly reflected wherever three planar surfaces meet at a corner.
Planes such as the B-52 bomber, which have many flat, vertical surfaces and RADARreflecting corners, are notorious for their RADAR-reflecting abilities; stealth aircraft, in
contrast, tend to be highly angled and streamlined, presenting no flat surfaces at all to
an observer that is not directly above or below them. The B-2 bomber, for example, is
shaped like a boomerang. [10]
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8. ADVANTAGES AND DISADVANTAGES OF STEALTH
8.1. Advantages of Stealth Technology
1. A smaller number of stealth vehicles may replace fleet of conventional attacks
vehicles with the same or increased combat efficiency. Possibly resulting in
longer term savings in the military budget.
2. A Stealth vehicles strike capability may deter potential enemies from taking
action and keep them in constant fear of strikes, since they can never know if the
attack vehicles are already underway.
3. The production of a stealth combat vehicles design may force an opponent to
pursue the same aim, possibly resulting in significant weakening of the
economically inferior party.
4. Stationing stealth vehicles in a friendly country is a powerful diplomatic gesture
as stealth vehicles incorporate high technology and military secrets.
5. Decreasing causality rates of the pilots and crew members.
8.2. Disadvantages of Stealth Technology
1. Stealth technology has its own disadvantages like other technologies. Stealth
aircraft cannot fly as fast or is not manoeuvrable like conventional aircraft. The
F-22 and the aircraft of its category proved this wrong up to an extent. Though
the F-22 may be fast or manoeuvrable or fast, it can't go beyond Mach 2 and
cannot make turns like the Su-37.
2. Another serious disadvantage with the stealth aircraft is the reduced amount of
payload it can carry. As most of the payload is carried internally in a stealth
aircraft to reduce the radar signature, weapons can only occupy a less amount of
space internally. On the other hand a conventional aircraft can carry much more
payload than any stealth aircraft of its class.
3. Whatever may be the disadvantage a stealth vehicles can have, the biggest of all
disadvantages that it faces is its sheer cost. Stealth aircraft literally costs its
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weight in gold. Fighters in service and in development for the USAF like the B2 ($2 billion), F-117 ($70 million) and the F-22 ($100 million) are the costliest
planes in the world. After the cold war, the number of B-2 bombers was reduced
sharply because of its staggering price tag and maintenance charges.
4. The B-2 Spirit carries a large bomb load, but it has relatively slow speed,
resulting in 18 to 24 hour long missions when it flies half way around the globe
to attack overseas targets. Therefore advance planning and receiving intelligence
in a timely manner is of paramount importance.
5. Stealth aircraft are vulnerable to detection immediately before, during and after
using their weaponry. Since reduced RCS bombs and cruise Missiles are yet not
available; all armament must be carried internally to avoid increasing the radar
cross section. As soon as the bomb bay doors opened, the planes RCS will be
multiplied.
6. Another problem with incorporating "stealth" technology into an aircraft is a
wing shape that does not provide the optimum amount of lift. The resulting
increase in drag reduces flight performance. "Stealth" shapes, such as the
"faceting" found on Lockheed's F-117 "stealth" fighter, also tend to be
aerodynamically destabilizing. This is brought under control only through the
use of highly sophisticated computers that serve to electronically balance the
aircraft in flight through its autopilot and control system. All of these
modifications, however, hurt the plane's performance, adding weight, affecting
aerodynamics, and altering the structure of the aircraft.
The advantages of stealth technology must always be weighed against its
disadvantages impossible.
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9. CONCLUSION
Till date stealth aircraft have been used in several low and moderate intensity conflicts,
including operation Desert Storm. Undoubtedly, Stealth technology is the Future of
Military Combat and at Present is one of the best technology to make things invisible as
far as possible. But, the main problem with stealth is its very high cost and because of
this, not all nations can adopt this technology. So as we know the material used in stealth
aircraft having high cost so we can use the composite material or smart material while
the using of costly material. That reduces the cost of the material. An advance in one
field, such as materials or aerodynamics, must be accompanied by advances in other
fields, such as computing or electromagnetic theory. The second lesson is that
sometimes trial and error techniques are insufficient and advances in mathematical
theory are necessary in order to achieve significant advances. Finally, stealth teaches the
lesson that technology is never static-a "stealth breakthrough" may only last for a few
years before an adversary finds a means of countering it. Finally we conclude that the
future of the stealth technology is not only in air, it perform under the water as well as
on the land also which helps to increase the strength of the nation in defence sector.
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REFERENCES
[1] Justin Wilson (2004); Electromagnetic Stealth: The Fight Against Radar
[2] V.K. Saxena (2012): Stealth and Counter-stealth Some Emerging Thoughts and
Continuing Debates, Journal of Defence Studies, Vol-6, Issue-3.pp- 19-28.
[3] Ki-Yeon Park, Sang-Eui Lee, Chun-Gon Kim and Jae-Hung Han (2006);
“Fabrication and Electromagnetic Characteristics of Electromagnetic, v.66
no.3/4, pp.576-584
[4] Vinoy KJ, Jha RM. Radar absorbing materials from theory to design and
characterization. Boston: Kluwer Academic Publishers 1996.
[5] Konstantinos Zikidis (Maj, HAF) (2014); Low Observable Principles, Stealth
Aircraft and Anti-Stealth Technologies, Journal of Computations & Modelling,
vol.4, no.1, 2014, 129-165.
[6] Gaylor, K. “Radar Absorbing Materials - Mechanisms and Materials,” DSTO
Materials Research Laboratory, 1989
[7] Oh, J-H. et al., 2004, “Design of radar absorbing structures using glass/epoxy
composite containing carbon black in X-band frequency ranges”, Composites
Part B: Engineering, Vol. 35, No. 1, pp. 49-56.
[8] Paul Saville (2005); Review of Radar absorbing material; DRDC Atlantic.
[9] Hayt, W. H., Buck, J. A., Engineering Electromagnetics, 6th ed., McGraw-Hill,
1958.
[10]Howe, D. Introduction to the Basic Technology of Stealth Aircraft: Part 2-
Illumination by the Enemy - (Active Considerations). The American Society of
Mechanical Engineers. June 11-14, 1990.
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