Stealth technology also known as LOT (Low Observability Technology) is a sub-discipline of electronic countermeasures 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. Electronic Countermeasures ( ECM') are a subsection of Electronic warfare which includes any sort of electrical or electronic device designed to trick Stealth aircraft are Aircraft that use Stealth technology to make it harder to be detected by radar and other means than conventional aircraft by employing a 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 A missile (see also pronunciation differences) is a self-propelled explosive Projectile used as a weapon towards a target Radar is a system that uses electromagnetic waves to identify the range altitude direction or speed of both moving and fixed objects such as Aircraft, ships Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of

The concept of stealth is not new: being able to operate without the knowledge of the enemy has always been a goal of military technology and techniques. However, as the potency of detection and interception technologies (radar, IRST, surface-to-air missiles etc. Radar is a system that uses electromagnetic waves to identify the range altitude direction or speed of both moving and fixed objects such as Aircraft, ships An infra-red search and track ( IRST) system (sometimes known as infra-red sighting and tracking) is a method for detecting and tracking objects which give off A surface to air missile ( SAM) or ground-to-air missile ( GTAM) is a Missile designed to be launched from the ground to destroy Aircraft ) has increased, so too has the extent to which the design and operation of military vehicles have been affected in response. A 'stealth' vehicle will generally have been designed from the outset to have reduced or controlled signature. It is possible to have varying degrees of stealth. The exact level and nature of stealth embodied in a particular design is determined by the prediction of likely threat capabilities and the balance of other considerations, including the raw unit cost of the system.

A mission system employing stealth may well become detected at some point within a given mission, such as when the target is destroyed, but correct use of stealth systems should seek to minimize the possibility of detection. Attacking with surprise gives the attacker more time to perform its mission and exit before the defending force can counter-attack. If a surface-to-air missile battery defending a target observes a bomb falling and surmises that there must be a stealth aircraft in the vicinity, for example, it is still unable to respond if it cannot get a lock on the aircraft in order to feed guidance information to its missiles. A surface to air missile ( SAM) or ground-to-air missile ( GTAM) is a Missile designed to be launched from the ground to destroy Aircraft

Contents 1 Stealth principles 1.1 Radar cross-section (RCS) reductions 1.1.1 Vehicle shape 1.1.1.1 Propulsion subsystem shaping 1.1.2 Non-metallic airframe 1.1.3 Radar absorbing material 1.1.4 Radar stealth countermeasures and limitations 1.1.4.1 Low frequency radar 1.1.4.2 Multiple transmitters 1.2 Acoustics 1.3 Visibility 1.4 Infrared 1.5 Reducing radio frequency (RF) emissions 2 Measuring stealth 3 Stealth tactics 4 See also 5 References 6 External links

Stealth principles

Stealth technology (often referred to as "LO", for "low observability") is not a single technology but 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 specifically:

Radar cross-section (RCS) reductions

Almost since the invention of radar, various techniques have been tried to minimize detection. Radar cross section (RCS is a measure of how detectable an object is with a Radar. Acoustic signature is used to describe a combination of acoustic emissions of ships and submarines Infrared homing refers to a passive missile guidance system which uses the emission from a target of Electromagnetic radiation in the Infrared Radar is a system that uses electromagnetic waves to identify the range altitude direction or speed of both moving and fixed objects such as Aircraft, ships Rapid development of radar during WWII led to equally rapid development of numerous counter radar measures during the period; a notable example of this was the use of chaff. This is a List of World War II Electronic warfare equipment and code words and tactics derived directly from the use of electronic equipment Chaff, originally called Window by the British, and Düppel by the World War II era German Luftwaffe, is a

The term 'Stealth' in reference to reduced radar signature aircraft became popular during the late eighties when the F-117 stealth fighter became widely known. The first large scale (and public) use of the F-117 was during the Gulf War in 1991. Year 1991 ( MCMXCI) was a Common year starting on Tuesday (link will display full calendar of the Gregorian Calendar. However, F-117A stealth fighters were used for the first time in combat during Operation Just Cause, the United States invasion of Panama in 1989. The United States invasion of Panama, codenamed Operation Just Cause, was the Invasion of Panama by the United States in December 1989 The United States invasion of Panama, codenamed Operation Just Cause, was the Invasion of Panama by the United States in December 1989 Since then it has become less effective due to developments in the algorithms used to process the data received by radars, such as Bayesian particle filter methods. In Mathematics, Computing, Linguistics and related subjects an algorithm is a sequence of finite instructions often used for Calculation Debt AIDS Trade in Africa (or DATA) is a Multinational non-government organization founded in January 2002 in London by U2 's Particle filters, also known as sequential Monte Carlo methods (SMC are sophisticated model Estimation techniques based on Simulation. Increased awareness of stealth vehicles and the technologies behind them is prompting the development of techniques for detecting stealth vehicles, such as passive radar arrays and low-frequency radars. Passive radar systems (also referred to as passive coherent location and passive covert radar) encompass a class of Radar systems that detect and track Low Frequency Radar is the use of Radars which use frequencies lower than 1 GHz as opposed to the usual Radar bands which can range from the X band at 8-12 GHz Many countries nevertheless continue to develop low-RCS vehicles because low RCS still offers advantages in detection range reduction as well as increasing the effectiveness of decoys against radar-seeking threats.

Vehicle shape

The possibility of designing aircraft in such a manner as to reduce their radar cross-section was recognized in the late 1930s, when the first radar tracking systems were employed, and it has been known since at least the 1960s that aircraft shape makes a very significant difference in how well an aircraft can be detected by a radar. The Avro Vulcan, a British bomber of the 1960s, had a remarkably small appearance on radar despite its large size, and occasionally disappeared from radar screens entirely. WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout A bomber is a Military aircraft designed to attack ground and sea targets primarily by dropping Bombs on them It is now known that it had a fortuitously stealthy shape apart from the vertical element of the tail. On the other hand, the Tupolev 95 Russian long range bomber (NATO reporting name 'Bear') appeared especially well on radar. WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout NATO reporting names are unclassified Code names for military equipment of the Eastern Bloc ( Soviet Union and other nations of the Warsaw pact It is now known that propellers and jet turbine blades produce a bright radar image; the Bear had four pairs of large (5. A propeller is essentially a type of fan which transmits power by converting Rotational motion into Thrust for propulsion of a vehicle such as an 6 meter diameter) contra-rotating propellers. Contra-rotating propellers, also referred to as coaxial contra-rotating propellers, apply the maximum power of a single piston or Turboprop engine

Another important factor is the internal construction. Behind the skin of some aircraft are structures known as re-entrant triangles. Radar waves penetrating the skin of the aircraft get trapped in these structures, bouncing off the internal faces and losing energy. This approach was first used on SR-71. WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout

The most efficient way to reflect radar waves back to the transmitting radar is with orthogonal metal plates, forming a corner reflector consisting of either a dihedral (two plates) or a trihedral (three orthogonal plates). A corner reflector is a Retroreflector consisting of three mutually perpendicular intersecting flat surfaces which reflects Electromagnetic waves back towards the This configuration occurs in the tail of a conventional aircraft, where the vertical and horizontal components of the tail are set at right angles. Stealth aircraft such as the F-117 use a different arrangement, tilting the tail surfaces to reduce corner reflections formed between them. The most radical approach is to eliminate the tail completely, as in the B-2 Spirit. WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout

In addition to altering the tail, stealth design must bury the engines within the wing or fuselage, or in some cases where stealth is applied to an existing aircraft, install baffles in the air intakes, so that the turbine blades are not visible to radar. WING "ESPN 1410" is a commercial AM radio station in Dayton Ohio operating with 5000 watts at 1410 kHz with studios offices and transmitter located on David The fuselage (from the French fuselé "spindle-shaped" is an Aircraft 's main body section that holds crew and passengers or Cargo A stealthy shape must be devoid of complex bumps or protrusions of any kind; meaning that weapons, fuel tanks, and other stores must not be carried externally. Any stealthy vehicle becomes un-stealthy when a door or hatch is opened.

Planform alignment is also often used in stealth designs. A planform or Plan view is a vertical Orthographic projection of an object on a horizontal plane like a Map. Planform alignment involves using a small number of surface orientations in the shape of the structure. For example, on the F-22A Raptor, the leading edges of the wing and the tail surfaces are set at the same angle. Careful inspection shows that many small structures, such as the air intake bypass doors and the air refueling aperture, also use the same angles. The effect of planform alignment is to return a radar signal in a very specific direction away from the radar emitter rather than returning a diffuse signal detectable at many angles.

Stealth airframes sometimes display distinctive serrations on some exposed edges, such as the engine ports. Airframe means the mechanical structure of an Aircraft and as generally used does not include the engines The YF-23 has such serrations on the exhaust ports. WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout This is another example in the use of re-entrant triangles and planform alignment, this time on the external airframe.

Shaping requirements have strong negative influence on the aircraft's aerodynamic properties. The F-117 has poor aerodynamics, is inherently unstable, and cannot be flown without computer assistance. Some modern anti-stealth radars target the trail of turbulent air behind it instead, much like civilian wind shear detecting radars do. Wind shear, sometimes referred to as windshear or Wind gradient, is a difference in Wind speed and direction over a relatively

Ships have also adopted similar techniques. The Visby corvette was the first stealth ship to enter service, though the earlier Arleigh Burke class destroyer incorporated some signature-reduction features [1]. History Much of the design was based on the experiences learned from the experimental ship HMS Smyge. Characteristics The Arleigh Burke class are among the largest and most powerful destroyers ever built both larger and more heavily armed than many previous cruisers Other examples are the French La Fayette class frigate, the USS San Antonio amphibious transport dock, and most modern warship designs. French version Context In the late 1980s the Marine Nationale started the studies for frigates adapted to low-intensity conflicts in the post-Cold War era Metric system Wherever possible the LPD 17 class was designed using the Metric system, specifying millimeters for linear dimensions and other parameters

Propulsion subsystem shaping

Now in research, fluidic nozzles for thrust vectoring with aircraft jet engines, and ships, will have lower RCS, due to being less complex, mechanically simpler, with no moving parts or surfaces, and less massive (up to 50% less). Fluidics (also known as Fluidic logic) is the use of a Fluid or compressible medium to perform analog or Digital operations similar to those Thrust vectoring is the ability of an Aircraft or other vehicle to direct the Thrust from its main Engine (s in a direction other than parallel to specific --->A jet engine is a Reaction engine that discharges a fast moving jet of Fluid to A ship /ʃɪp/ is a large vessel that floats on water Ships are generally distinguished from Boats based on size They will likely be used in many unmanned aircraft, and 6th generation fighter aircraft. A fighter aircraft is a Military aircraft designed primarily for air-to-air combat with other Aircraft, as opposed to a Bomber, which is designed Fluidic nozzles divert thrust via fluid effects[2][3][4]. Tests show that air forced into a jet engine exhaust stream can deflect thrust up to 15 degrees.

Non-metallic airframe

Dielectric composites are relatively transparent to radar, whereas electrically conductive materials such as metals and carbon fibers reflect electromagnetic energy incident on the material's surface. A dielectric is a nonconducting substance ie an insulator. The term was coined by William Whewell in response to a request from Michael Faraday. The M acro E xpansion T emplate A ttribute L anguage complements TAL, providing macros which allow the reuse of code across Composites used may contain ferrites to optimize the dielectric and magnetic properties of the material for its application.

Radar absorbing material

Radar absorbent material (RAM), often as paints, are used especially on the edges of metal surfaces. Radar absorbent material, or RAM, is a class of materials used in Stealth technology to disguise a vehicle or structure from radar detection One such coating, also called iron ball paint, contains tiny spheres coated with carbonyl iron ferrite. Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26 Radar waves induce alternating magnetic field in this material, which leads to conversion of their energy into heat. Early versions of F-117A planes were covered with neoprene-like tiles with ferrite grains embedded in the polymer matrix, current models have RAM paint applied directly. Neoprene or polychloroprene is a family of synthetic Rubbers that are produced by Polymerization of Chloroprene. The paint must be applied by robots because of problems of solvent toxicity and tight tolerances on layer thickness.

Similarly, coating the cockpit canopy with a thin film transparent conductor (vapor-deposited gold or indium tin oxide) helps to reduce the aircraft's radar profile because radar waves would normally enter the cockpit, bounce off something random (the inside of the cockpit has a complex shape), and possibly return to the radar, but the conductive coating creates a controlled shape that deflects the incoming radar waves away from the radar. A cockpit is the area usually near the front of an Aircraft, from which a pilot controls the aircraft Physical vapor deposition (PVD is a variety of vacuum deposition and is a general term used to describe any of a variety of methods to deposit Thin films by the condensation Gold (ˈɡoʊld is a Chemical element with the symbol Au (from its Latin name aurum) and Atomic number 79 Uses ITO is mainly used to make transparent conductive coatings for Liquid crystal displays Flat panel displays Plasma displays touch panels The coating is thin enough that it has no adverse effect on the pilot's vision.

Radar stealth countermeasures and limitations

Low frequency radar

Shaping does not offer stealth advantages against low-frequency radar. If the radar wavelength is roughly twice the size of the target, a half-wave resonance effect can still generate a significant return. However, low-frequency radar is limited by lack of available frequencies which are heavily used by other systems, lack of accuracy given the long wavelength, and by the radar's size, making it difficult to transport. A long-wave radar may detect a target and roughly locate it, but not identify it, and the location information lacks sufficient weapon targeting accuracy. Noise poses another problem, but that can be efficiently addressed using modern computer technology; Chinese "Nantsin" radar and many older Soviet-made long-range radars were modified this way. It has been said that "there's nothing invisible in the radar frequency range below 2 GHz". [5]

Multiple transmitters

Much of the stealth comes from reflecting the transmissions in a different direction other than a direct return. Therefore detection can be better achieved if the sources are spaced from the receivers and multiple, and proposals exist to even use reflections from sources such as civilian radio transmitters.

Acoustics

Acoustic stealth plays a primary role in submarine stealth as well as for ground vehicles. A submarine is a Watercraft that can operate independently below water as distinct from a Submersible that has only limited underwater capability Submarines have extensive usage of rubber mountings to isolate and avoid mechanical noises that could reveal locations to underwater passive sonar arrays. Sonar (which started as an Acronym for sound navigation and ranging) is a technique that uses Sound propagation (usually underwater to navigate

Early stealth observation aircraft used slow-turning propellers to avoid being heard by enemy troops below. Surveillance aircraft are military Aircraft used for monitoring enemy activity usually carrying no armament Stealth aircraft that stay subsonic can avoid being tracked by sonic boom. The term sonic boom is commonly used to refer to the shocks caused by the Supersonic flight of an aircraft The presence of supersonic and jet-powered stealth aircraft such as the SR-71 Blackbird indicates that acoustic signature is not always a major driver in aircraft design, although the Blackbird relied more on its extremely high speed and altitude. WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout Acoustic signature is used to describe a combination of acoustic emissions of ships and submarines

Visibility

Most stealth aircraft use matte paint and dark colors, and operate only at night. List of optical topics Gloss is an Optical property which is based on the interaction of light with physical characteristics of a surface Lately, interest on daylight Stealth (especially by the USAF) has emphasized the use of gray paint in disruptive schemes, and it is assumed that Yehudi lights could be used in the future to mask shadows in the airframe (in daylight, against the clear background of the sky, dark tones are easier to detect than light ones) or as a sort of active camouflage. Yehudi lights are lamps placed on the underside of an Aircraft to raise Luminance, to disguise the aircraft against the background sky Airframe means the mechanical structure of an Aircraft and as generally used does not include the engines Active camouflage or adaptive camouflage, is a group of Camouflage technologies which allow an object to blend into its surroundings by use of panels or coatings capable The B-2 has wing tanks for a contrail-inhibiting chemical, alleged by some to be chlorofluorosulphonic acid[6], and mission planning also considers altitudes where the probability of their formation is minimized.

Infrared

An exhaust plume contributes a significant infrared (IR) signature. Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of One means of reducing the IR signature is to have a non-circular tail pipe (a slit shape) in order to minimize the exhaust cross-sectional volume and maximize the mixing of the hot exhaust with cool ambient air. Often, cool air is deliberately injected into the exhaust flow to boost this process. Sometimes, the jet exhaust is vented above the wing surface in order to shield it from observers below, as in the B2 Spirit, and the unstealthy A-10 Thunderbolt II. WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout To achieve infrared stealth, the exhaust gas is cooled to the temperatures where the brightest wavelengths it radiates on are absorbed by atmospheric carbon dioxide and water vapor, dramatically reducing the infrared visibility of the exhaust plume. [7] Another way to reduce the exhaust temperature is to circulate coolant fluids such as fuel inside the exhaust pipe, where the fuel tanks serve as heat sinks cooled by the flow of air along the wings.

Reducing radio frequency (RF) emissions

In addition to reducing infrared and acoustic emissions, a stealth vehicle must avoid radiating any other detectable energy, such as from onboard radars, communications systems, or RF leakage from electronics enclosures. The F-117 uses passive infra-red and "low light level TV" sensor systems to aim its weapons and the F-22 Raptor has an advanced LPI radar which can illuminate enemy aircraft without triggering a radar warning receiver response.

Measuring stealth

The size of a target's image on radar is measured by the radar cross section or RCS, often represented by the symbol σ and expressed in square meters. Radar cross section (RCS is a measure of how detectable an object is with a Radar. This does not equal geometric area. A perfectly conducting sphere of projected cross sectional area 1 m² (ie a diameter of 1. 13 m) will have an RCS of 1 m². Note that for radar wavelengths much less than the diameter of the sphere, RCS is independent of frequency. Conversely, a square flat plate of area 1 m² will have an RCS of σ = 4π A² / λ² (where A=area, λ=wavelength), or 13,982 m² at 10 GHz if the radar is perpendicular to the flat surface. ^[1] At off-normal incident angles, energy is reflected away from the receiver, reducing the RCS. Modern stealth aircraft are said to have an RCS comparable with small birds or large insects, though this varies widely depending on aircraft and radar.

If the RCS was directly related to the target's cross-sectional area, the only way to reduce it would be to make the physical profile smaller. Rather, by reflecting much of the radiation away or absorbing it altogether, the target achieves a smaller radar cross section. [8]

Stealth tactics

Stealthy strike aircraft such as the F-117, designed by Lockheed Martin's famous SkunkWorks, are usually used against heavily defended enemy sites such as Command and Control centers or surface-to-air missile (SAM) batteries. Command and control can be defined as the exercise of Authority and Direction by a properly designated Commander over assigned and attached Forces Enemy radar will cover the airspace around these sites with overlapping coverage, making undetected entry by conventional aircraft nearly impossible. Stealthy aircraft can also be detected, but only at short ranges around the radars, so that for a stealthy aircraft there are substantial gaps in the radar coverage. Thus a stealthy aircraft flying an appropriate route can remain undetected by radar. Many ground-based radars exploit Doppler filter to improve sensitivity to objects having a radial velocity component with respect to the radar. A doppler radar is a Radar using the Doppler effect of the returned echoes from targets to measure their Radial velocity. Mission planners use their knowledge of the enemy radar locations and the RCS pattern of the aircraft to design a flight path that minimizes radial speed while presenting the lowest-RCS aspects of the aircraft to the threat radar. In order to be able to fly these "safe" routes, it is necessary to understand the enemy's radar coverage (see Electronic Intelligence). Mobile radars such as AWACS can complicate matters.

See also

• Stealth aircraft
  • Military flying saucers
  • F-117 Nighthawk
  • B-2 Spirit bomber
  • F-22 Raptor
  • F-35 Lightning II
  • PZL-230 Skorpion
• Stealth ship
  • La Fayette class frigate
  • Formidable class frigate
  • Sea Shadow (IX-529)
  • Visby class corvette
  • Shivalik class frigate
  • Sachsen class frigate
  • De Zeven Provinciën class frigate
  • Braunschweig class corvette
  • Skjold class patrol boat
  • Hamina class missile boat
• Radar
• Plasma stealth

References

• Sequential Monte Carlo Methods in Practice, by A Doucet, N de Freitas and N Gordon. Published by Springer.
• Countering stealth
• How "stealth" is achieved on F-117A
• Ufimtsev, Pyotr Ya. , "Method of edge waves in the physical theory of diffraction," Moscow, Russia: Izd-vo. Sov. Radio [Soviet Radio Publishing], 1962, pages 1-243.

External links

• Grant R, The Radar Game - Understanding Stealth and Aircraft Survivability, Iris Independent Research
• The Advent, Evolution and New Horizons of United States Stealth Aircraft
• What is Stealth Technology?
• Stealth design used for military aircraft?
• Stealth Satellites
• Anti-Stealth Technology
• STEALTH IN STRIKE WARFARE
• STEALTH TECHNOLOGY
• The Paradigm Shift in Air Superiority (Stealth)
• Stealth Technology
• USAF Stealth Fighters briefing
• Pyotr Ufimstev biography
• Advancement of Plasma antennas in stealth

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