Stealth Technology 372017

STEALTH TECHNIQUES FOR RADAR SUBMITTED BY: SUSHMITHA.H.N(1SG12EC105)

Mrs.AGALYA .P ASSOCIATE PROFESSOR

Ms. PREETHI.T.S ASSISTANT PROFESSOR

STEALTH TECHNIQUES FOR RADAR

INTRODUCTION 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 combination of features to reduce visibility in the visual, audio, infrared and radio frequency (RF) spectrum. Well known examples include the United States' F-117 Nighthawk (1980s-2008), the B-2 Spirit "Stealth Bomber," and the F-22 Raptor.

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STEALTH TECHNIQUES FOR RADAR

The idea is for the radar antenna to send out a burst of radio energy, which is then reflected back by any object it happens to encounter. The radar antenna measures the time it takes for the reflection to arrive, and with that information can tell how far away the object is. The metal body of an airplane is very good at reflecting radar signals, and this makes it easy to find and track airplanes with radar equipment. The goal of stealth technology is to make an airplane invisible to radar.

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STEALTH TECHNIQUES FOR RADAR The goal of stealth technology is to make an airplane invisible to radar. There a different ways to create invisibility: ive stealth technology: •The airplane can be: • shaped so that it reflects any radar signals; • covered by materials that absorb radar signals; • constructed so as to reduce its infrared radiation; • constructed so as to reduce its visual detection. •use of fiber radio optical (Active Radar Cancellation System); • the body of the aircraft can be cloaked with real time cloud of plasma. • •

Most conventional aircraft have a rounded shape. This shape makes them aerodynamic, but it also creates a very efficient radar reflector. The round shape means that no matter where the radar signal hits the plane, some of the signal gets reflected back

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STEALTH TECHNIQUES FOR RADAR

A stealth aircraft, on the other hand, is made up of completely flat surfaces and very sharp edges. • When a radar signal hits a stealth plane, the signal reflects away at an angle •Surfaces on a stealth aircraft can be treated so they absorb radar energy. •The overall result is that a stealth aircraft like an F-117A can have the radar signature of a small bird rather than an airplane.

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STEALTH TECHNIQUES FOR RADAR

RADAR REFLECTIVITY

A certain amount of electromagnetic energy is transmitted through a directional antenna, which focuses it into a conical beam. When a reflective target blocks part of the beam, that part of the beam is reflected in many different directions, or "scattered." If the scattering is fairly random, as is usually the case, some energy will be reflected in the direction of the radar antenna. Most radar transmits this energy in pulses, thousands of them every second. In the gaps between the pulse transmissions, the radar becomes a receiver, and the gaps are carefully chosen to be just long enough for the signal to make its way to the target and back at the speed of light. The time interval between the transmission and reception of the pulse gives the range from the radar to the target. The radar only "sees" the energy that is reflected toward it. The radar can detect a target ONLY when its antenna captures enough energy to rise above the electronic noise that is invariably present in the receiver. The factors that affect it are - The strength of the outgoing signal - The width of the beam -The size of the antenna - The reflectivity, or RCS, of the target. ELECTRONICS AND COMMUNICATION,SCE

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STEALTH TECHNIQUES FOR RADAR

RCS The size and ability of a target to reflect radar energy can be summarized into a single term, σ, known as the radar crosssection, which has units of m². The target radar cross sectional area depends of: •Size •Material used •Smooth surfaces •shape, directivity and orientation The use of stealth technology to reduce radar cross section increases the survivability and decreases the target detection of military aircraft.

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STEALTH TECHNIQUES FOR RADAR

•The sphere has essentially same RCS in almost all directions i.e. 360 degree. •The flat plane has has almost no RCS except when aligned directly towards radar i.e. 90 degree The corner reflector has an RCS almost high as flat plane over a wider angle i.e. 60 degree

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STEALTH TECHNIQUES FOR RADAR

GEOMETRICAL DESIGN CONSIDERATIONS Conventional aircraft use round shape cone as it principle of aerodynamics. •The stealth aircraft is made up of flat surface and very sharp edges •Radar signal heating the stealth plane are scattered in all directions by this. • Metallic surfaces generally reflect the radar signals. The stealth aircraft should be coated with radar absorbent materials. Which deflect and absorbed incoming radar waves and reduce the detection range •Another trick, similar but antipodal to the first one inprinciple,is to shape the airframe in such way that, instead of having the reflected energy scatter in all directions (and thus a portion of it being always picked-up by the enemy radar), it will bounce back on a very limited number of directions, maybe only one or two.

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STEALTH TECHNIQUES FOR RADAR

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RAM Radiation-absorbent material, usually known as RAM, is a material which has been specially designed and shaped to absorb incident RF radiation as effectively as possible, from as many incident directions as possible. The more effective the RAM, the lower the resulting level of reflected RF radiation.

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STEALTH TECHNIQUES FOR RADAR

RAS •A properly configured RAS layer can also reduce the radar reflection by ive cancellation. The way this works is that the external skin may reflect back part of the energy pulse (E1), but the rest will be redirected through refraction into the internal of the airframe and then bounced blackout against the exactly opposite phase (E2). Thus hopefully the two radar returns will cancel each other out. •Another popular structure that follows the gradual absorption principle is extensively used on the leading and trailing edges of stealthy airframes. The idea is that the external skin is composed of a high-frequency ferrite absorber, while the interior begins with a low-absorption layer and thickens back into gradually deeper and more absorbent layers.

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STEALTH TECHNIQUES FOR RADAR

ACTIVE CANCELLATION

•The original incoming signal from the radar will be reflected from many spots on the aircraft's body. Each spot will produce an individual reflection with its own unique amplitude and phase. The amplitude of the reflection would depend on many factors, such as incidence angle, particular type of material, geometrical form of a certain location on the aircraft's body that produced the reflection and some other factors. •The phase shift will be dictated by the wavelength of the radar signal and the location (and geometrical form) of the particular spot that produced the reflection in question. The enemy radar does not, however, receive all of the reflected variations of the original signal as separate entities. It either selects the strongest return signal, or averages several strongest reflections. This simplification can be used to the advantage of the aircraft, since it will only need two antennas to transmit a simulated return signal averaged over the length of the aircraft. The return signal, picked Up by the radar, would look somewhat chaotic, consisting of background noise and the main return spikes.

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STEALTH TECHNIQUES FOR RADAR

PLASMA STEALTH •Plasma stealth technology is what can be called as “Active stealth technology” in scientific . This technology was first developed by the Russians. It is a milestone in the field of stealth technology. The technology behind this not at all new. The plasma thrust technology was used in the Soviet / Russian space program. Later the same engine was used to power the American Deep Space 1 probe. •In plasma stealth, the aircraft injects a stream of plasma in front of the aircraft. The plasma will cover the entire body of the fighter and will absorb most of the electromagnetic energy of the radar waves, thus making the aircraft difficult to detect .

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STEALTH TECHNIQUES FOR RADAR

INFRARED STEALTH

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. Embedding jet engines inside the fuselage or wings is one basic design step toward infrared stealth. Other measures include extra shielding of hot parts, mixing of cool air with hot exhausts before emission; splitting of the exhaust stream by ing it through parallel baffles so that it mixes with cooler air more quickly; directing of hot exhausts upward, away from ground observers; and the application of special coatings to hot spots to absorb and diffuse heat over larger areas. Active countermeasures against infrared detection and tracking can be combined with ive stealth measures; these include infrared jamming and the launching of infrared decoy flares. Combat helicopters, which travel at low altitudes and at low speeds, are particularly vulnerable to heat-seeking weapons and have been equipped with infrared jamming devices for several decades.

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