Stealth TechnologyAnkit Kumar Parashar 9109ECE I A

StealthOverviewStealth PrinciplesCounter MeasuresList of Stealth Aircrafts & ShipsProgress in India

What is Stealth?Literal meaning : secret, clandestine, or surreptitious procedure. Now used to infer to a particular technique of warfare.Lots of money every year is spent on developing stealth techniques but only a few countries have economically been able to do it.

Stealth PrinciplesRadar cross-section (RCS) reductionsVehicle shapeNon-metallic airframeRadar absorbing material

RCS ReductionReduced signature design improves platforms' overall survivability through the improved effectiveness of its radar counter-measures. The distance at which a target can be detected for a given radar configuration varies with the fourth root of its RCS.

As a rule, the larger an object, the stronger its RADAR reflection and thus the greater its RCS. Also, RADAR of one band may not even detect certain size objects. For example. 10cm (S-band RADAR) can detect rain drops but not clouds whose droplets are too small. wherePt= power transmitted by the radar (watts)Gt=gainof the radar transmit antenna (dimensionless)r= distance from the radar to the target (meters)= radar cross section of the target (meters squared)Aeff= effective area of the radar receiving antenna (meters squared)Pr= power received back from the target by the radar (watts)

F 117 Nighthawk

Vehicle ShapeThe most efficient way to reflect radar waves back to the transmitting radar is with orthogonal metal plates, forming acorner reflectorconsisting of either a dihedral (two plates) or a trihedral (three orthogonal plates). A more radical approach is to eliminate the tail completely, as in theB-2 Spirit.

Corner Reflector

B 2 Spirit Stealth Bomber

Non-metallic AirframeDielectriccompositesare more transparent to radar, whereas electrically conductive materials such asmetalsandcarbon fibersreflect electromagnetic energy incident on the material's surface. Composites may also containferritesto optimize the dielectric and magnetic properties of the material for its application.

Radar absorbing materialRadar absorbent material, orRAM, is a class of materials used instealth technologyto disguise a vehicle or structure from radar detection. A material's absorbency at a given frequency of radar wave depends upon its composition. A radar absorbent material can significantly reduce an object's radar cross sectionin specific radar frequencies, but it does not result in "invisibility" on any frequency.

Radar Absorbents

Counter MeasuresLow frequency radar Shaping does not offer stealth advantages againstlow-frequency radar. If the radarwavelengthis roughly twice the size of the target, a half-wave resonanceeffect can still generate a significant return.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, known asbistatic radar, and proposals exist to use reflections from sources such as civilianradio transmitters, includingcellular telephone radio towers.

List of Stealth Aircrafts & ShipsF-35 Lightning II

Sukhoi PAK FA

K32 HMS Helsingborg

Medium Combat Aircraft

Progress In IndiaMaterials scientists at the Indian Institute of Technology in Roorkee (IIT-R) have developed microwave absorbing nanocomposite coatings that could make aircraft almost invisible to radar. Its developers have said that the nanocomposite coating on the aluminum sheet absorbed 89 per cent of incident microwaves at 15 GHz - the frequency normally used by radars - reflecting only 11 per cent. A stealth aircraft should ideally absorb all the incident radiation and reflect nothing.

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