Editing Radar cross section (section)

==Measurement==
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. This does not equal geometric area. A perfectly conducting sphere of projected cross sectional area 1 m<sup>2</sup> (i.e. a diameter of 1.13 m) will have an RCS of 1 m<sup>2</sup>. For radar wavelengths much less than the diameter of the sphere, RCS is independent of frequency. Conversely, a square flat plate of area 1 m<sup>2</sup> will have an RCS of <span style="white-space:nowrap">σ = 4π ''A''<sup>2</sup> / ''λ''<sup>2</sup></span> (where ''A''=area, ''λ''=wavelength), or 139.62 m<sup>2</sup> at 1&nbsp;GHz if the radar is perpendicular to the flat surface.<ref name=":0">{{cite book | last=Knott | first=Eugene |author2=Shaeffer, John |author3=Tuley, Michael | title=Radar Cross Section, 2nd ed | publisher=Artech House, Inc. | year=1993 | pages=231 | isbn=978-0-89006-618-8 }}</ref> At off-normal [[angle of incidence (optics)|incident angle]]s, 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,<ref>[http://www.globalsecurity.org/military/systems/aircraft/f-22-stealth.htm F-22 Raptor Stealth] GlobalSecurity.org</ref> 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 by absorbing it, the target achieves a smaller radar cross section.<ref>Bill Sweetman, [http://www.airspacemag.com/issues/2008/december-january/stealth.php Unconventional Weapon: What we learned about stealth technology from the combat career of the F-117], Smithsonian Air & Space Magazine, 01 January 2008</ref>

Measurement of a target's RCS is performed at a radar [[reflectivity range]] or [[scattering range]].{{citation needed|date=December 2020}} The first type of range is an outdoor range where the target is positioned on a specially shaped low RCS pylon some distance down-range from the transmitters. Such a range eliminates the need for placing radar absorbers behind the target, however multi-path interactions with the ground must be mitigated.

An [[anechoic chamber]] is also commonly used. In such a room, the target is placed on a rotating pillar in the center, and the walls, floors and ceiling are covered by stacks of radar absorbing material. These absorbers prevent corruption of the measurement due to reflections. A compact range is an anechoic chamber with a reflector to simulate far field conditions.

Typical values for a centimeter wave radar are:<ref>[http://www.sbfisica.org.br/rfai/Vol15/Num1/v15_24.pdf Radar Cross Section Measurements (8-12 GHz)]</ref><ref>[http://www.mar-it.de/Radar/RCS/Ship_RCS_Table.pdf Ship RCS Table]</ref>

* Insect: 0.00001 m<sup>2</sup>
* Bird: 0.01 m<sup>2</sup>
* [[Stealth aircraft]]: <0.1 m<sup>2</sup> (e.g. [[Lockheed F-117 Nighthawk|F-117A]]: 0.001 m<sup>2</sup>)
* [[Surface-to-air-missile]]: ≈0.1 m<sup>2</sup> 
* Human: 1 m<sup>2</sup>
* small combat aircraft: 2–3 m<sup>2</sup>
* large combat aircraft: 5–6 m<sup>2</sup>
* Cargo aircraft: up to 100 m<sup>2</sup>
* [[Coastal trading vessel]] (55 m length): 300–4000 m<sup>2</sup>
* [[Corner reflector]] with 1.5&nbsp;m edge length: ≈20,000 m<sup>2</sup><ref>[http://www.radartutorial.eu/01.basics/Radar%20Cross%20Section.en.html www.radartutorial.eu (Radar Cross Section (RCS))]</ref><ref>M. Skolnik: ''Introduction to radar systems.'' 2nd Edition, McGraw-Hill, Inc., 1980, p. 44</ref>
* [[Frigate]] (103 m length): 5000–100,000 m<sup>2</sup>
* [[Container ship]] (212&nbsp;m length): 10,000–80,000 m<sup>2</sup>