Radar cross-section

radar cross sectionradar signatureRCSradar cross-section (RCS)radar signaturesCross-Sectionradardifficult to detect on radarlow observabilitylow radar cross-section
Radar cross-section (RCS) is a measure of how detectable an object is by radar.wikipedia
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Stealth aircraft

stealthstealth fighterstealth bomber
For example, a stealth aircraft (which is designed to have low detectability) will have design features that give it a low RCS (such as absorbent paint, flat surfaces, surfaces specifically angled to reflect the signal somewhere other than towards the source), as opposed to a passenger airliner that will have a high RCS (bare metal, rounded surfaces effectively guaranteed to reflect some signal back to the source, lots of bumps like the engines, antennas, etc.).
These are usually combined with active measures such as carefully planning all mission maneuvers in order to minimize the aircraft's radar cross-section, since common actions such as hard turns or opening bomb bay doors can more than double an otherwise stealthy aircraft's radar return.

Lockheed SR-71 Blackbird

SR-71SR-71 BlackbirdLockheed SR-71A Blackbird
The SR-71 Blackbird and other planes were painted with a special "iron ball paint" that consisted of small metallic-coated balls.
The shape of the SR-71 was based on the A-12 which was one of the first aircraft to be designed with a reduced radar cross-section.

Stealth technology

stealthstealthystealthier
RCS is integral to the development of radar stealth technology, particularly in applications involving aircraft and ballistic missiles.
Equations outlined in the paper quantified how a plane's shape would affect its detectability by radar, its radar cross-section (RCS).

Radar

radar stationradarsradar system
Radar cross-section (RCS) is a measure of how detectable an object is by radar.
The extent to which an object reflects or scatters radio waves is called its radar cross section.

Radiation-absorbent material

radar-absorbent materialradar absorbent materialiron ball paint
The SR-71 Blackbird and other planes were painted with a special "iron ball paint" that consisted of small metallic-coated balls. This could arise from open bomb-bays, engine intakes, ordnance pylons, joints between constructed sections, etc. Also, it can be impractical to coat these surfaces with radar-absorbent materials.
A radar-absorbent material can significantly reduce an object's radar cross-section in specific radar frequencies, but it does not result in "invisibility" on any frequency.

Bomb bay

weapons baybomb-bayweapons bays
This could arise from open bomb-bays, engine intakes, ordnance pylons, joints between constructed sections, etc. Also, it can be impractical to coat these surfaces with radar-absorbent materials.
Military fighters are now designed to have the smallest possible radar cross-section, which has decreased very substantially since attention was paid to this feature.

Lockheed F-117 Nighthawk

F-117F-117 NighthawkF-117A Nighthawk
The surfaces of the F-117A are designed to be flat and very angled.
Ufimtsev demonstrated that he could calculate the radar cross-section across a wing's surface and along its edge.

Sigma

Σlunate sigma
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.
a target's radar cross-section (RCS) in radar jamming or electronic warfare

Northrop Grumman B-2 Spirit

B-2B-2 SpiritB-2 stealth bomber
The B-2 Spirit stealth bomber benefited from increased computing power, enabling its contoured shapes and further reduction in RCS.
In 1974, DARPA requested information from U.S. aviation firms about the largest radar cross-section of an aircraft that would remain effectively invisible to radars.

Chi-squared target models

Swerling Target Modelschi-square
Statistical models include chi-square, Rice, and the log-normal target models.
Swerling models were introduced by Peter Swerling and are used to describe the statistical properties of the radar cross-section of complex objects.

Frigate

frigatesguided missile frigatearmored frigate
Frigate (103 m length): 5000–100,000 m²
Frigate shapes are designed to offer a minimal radar cross section, which also lends them good air penetration; the maneuverability of these frigates has been compared to that of sailing ships.

Lockheed Martin F-35 Lightning II

F-35F-35 Lightning IIF-35B Lightning II
The F-22 Raptor and F-35 Lightning II continue the trend in purpose shaping and promise to have even smaller monostatic RCS.
The F-35 has external hardpoints to carry missiles, bombs, and drop tanks at the expense of increased radar cross-section, and thus reduced stealth.

Corner reflector

radar reflectorcorner cubecorner-cube
The relief of a surface could contain indentations that act as corner reflectors which would increase RCS from many orientations.
This effect was put to use on the ADM-20 Quail, a small missile which had the same radar cross section as a B-52.

Plasma stealth

Plasma stealth is a proposed process to use ionized gas (plasma) to reduce the RCS of an aircraft.
Plasma stealth is a proposed process to use ionized gas (plasma) to reduce the radar cross-section (RCS) of an aircraft.

Salisbury screen

Resonant but somewhat 'lossy' materials are applied to the reflecting surfaces of the target. The thickness of the material corresponds to one-quarter wavelength of the expected illuminating radar-wave (a Salisbury screen). The incident radar energy is reflected from the outside and inside surfaces of the RAM to create a destructive wave interference pattern. This results in the cancellation of the reflected energy. Deviation from the expected frequency will cause losses in radar absorption, so this type of RAM is only useful against radar with a single, common, and unchanging frequency.
It was first applied to ship radar cross section (RCS) reduction.

Computational electromagnetics

computational electrodynamicselectromagnetic modelingelectromagnetic simulation
The field of solving Maxwell's equations through numerical algorithms is called computational electromagnetics, and many effective analysis methods have been applied to the RCS prediction problem.
It typically involves using computationally efficient approximations to Maxwell's equations and is used to calculate antenna performance, electromagnetic compatibility, radar cross section and electromagnetic wave propagation when not in free space.

Lockheed Martin F-22 Raptor

F-22 RaptorF-22F-22A Raptor
The F-22 Raptor and F-35 Lightning II continue the trend in purpose shaping and promise to have even smaller monostatic RCS.
Measures to reduce radar cross-section include airframe shaping such as alignment of edges, fixed-geometry serpentine inlets that prevent line-of-sight of the engine faces from any exterior view, use of radar-absorbent material (RAM), and attention to detail such as hinges and pilot helmets that could provide a radar return.

System Planning Corporation

System Planning Corporation
SPC designed and fabricated one of the first specialized radar cross section (RCS) measurement radars used to validate the low observable signatures of stealthy vehicles.

Aircraft

heavier-than-airflying machineheavier-than-air flight
RCS is integral to the development of radar stealth technology, particularly in applications involving aircraft and ballistic missiles.

Ballistic missile

ballistic missilesthrow-weightballistic
RCS is integral to the development of radar stealth technology, particularly in applications involving aircraft and ballistic missiles.

Wavelength

wavelengthsperiodsubwavelength
the relative size of the target (in relation to the wavelength of the illuminating radar);

Angle of incidence (optics)

angle of incidencenormal incidencegrazing incidence
the incident angle (angle at which the radar beam hits a particular portion of the target, which depends upon the shape of the target and its orientation to the radar source);

Isotropic radiator

isotropic antennaisotropicisotropically
Somewhat less informally, the RCS of a radar target is an effective area that intercepts the transmitted radar power and then scatters that power isotropically back to the radar receiver.

Gain (electronics)

gainvoltage gaincurrent gain
G_t = gain of the radar transmit antenna (dimensionless)