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Radar cross section (RCS) describes the extent to which an object reflects an incident Electromagnetic wave. It is a measure of the strength of the radar signal backscattered from a "target" object for a given incident wave power. DEFINITIONS An object's RCS depends on its size, reflectivity of its surface, and the '''directivity''' of the radar reflection caused by the object's geometric shape. Radar cross section (RCS) = Geometric cross section × Reflectivity × Directivity RCS () can also be represented as:http://www.aerospaceweb.org/question/electronics/q0168.shtml where the power that is reflected toward the radar is ''Pbackscatter'', and the power intercepted by the object is ''Pintercepted'', both of which depend on the Radar Wavelength and the Angle Of Incidence of the Radio wave relative to the object. When the object's size spans several wavelengths, the RCS of a target object is equal to the Cross-section al area of a Perfectly Conducting Sphere that would produce the same magnitude of reflection as that observed from the target object.http://www.ccrs.nrcan.gc.ca/glossary/index_e.php?id=2827 The usual definition or RCS differs by a factor of (4π) from the standard Geometric definition of Cross Section at 180 degrees. Bistatic radar cross section is defined similarly for other angles. The RCS is integral to the development of radar Stealth Technology , particularly in applications involving Aircraft and Ballistic Missile s. RCS data for current military aircraft are almost all classified. MEASUREMENT Measurement of a target's RCS is performed at a radar Reflectivity Range or Scattering Range . 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. CALCULATION Quantitatively, the RCS is an effective surface area that intercepts the incident wave and that scatters the energy Isotropically in space. For the RCS, is defined in three-dimensions as : Where is the RCS, is the incident Power Density measured at the target, and is the scattered power density seen at a distance away from the target. In electromagnetic analysis this is also commonly written as |
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