Radar Cross Section is a measure of how detectable an object is by radar. It is the electromagnetic signature of an object, expressed as the power scattered from a target toward the radar when the target is illuminated by electromagnetic radiation. Radar Cross Section is the hypothetical area required to intercept the transmitted power density at the target; is the area intercepting that amount of power which, if radiated isotropically, produces the same received power in the radar.
Expert behind this article
Jim Goodrich
Jim Goodrich is a pilot, aviation expert and founder of Tsunami Air.
What is the radar cross section in aircraft?
Radar cross-section (RCS) is a measure of how detectable an object is by radar, and it is the area intercepting that amount of power which, if radiated isotropically, produces the same received power in the radar. The radar cross section indicates an effective area that captures the incoming wave and re-radiates it into space.
Radar cross-section (RCS) is the hypothetical area that intercepts the incident power at the target, and if this power were then scattered isotropically, the same echo power that the actual target produces appears at the radar. RCS is not the physical area of the aircraft but a comparison of the scattered power density that the receiver sees with the incident power density that strikes the target.
Because the aircraft is an electrically large body much further from the radar than a wavelength and rotated in evaluation measurement, its RCS is composed of the sum of many small partial powers located at different points of the reflecting object. These partial powers arise from several scattering mechanisms: specular surface reflection, edge diffraction, tip diffraction, creeping wave, traveling wave return, and curvature discontinuities created by doubly curved surfaces, singly curved surfaces, and flat plates that are perpendicular to the line of sight. Propulsion components like inlets and exhaust also contribute, so RCS is an aircraft-specific quantity that depends on many factors and describes the ability of the target to capture energy from the radar and reradiate it back toward the radar.
What is a radar signature of an aircraft?
A radar signature of an aircraft, alternatively called radar cross-section (RCS), is a measure of how detectable an object is by radar. This radar signature consists of information about characteristic echo signals of a reflecting object, and it does not only concern aspect-dependent amplitude changes of the Radar Cross-Section. The radar signature contains information about the effective reflection surface of the target. Radar signature is like a fingerprint, a way to determine the type of target. It includes aspect-dependent amplitude changes of Radar Cross-Section, the spectrum of Doppler frequencies, and characteristic modulation or harmonics in the echo signal.
Because an object reflects only a limited amount of radar energy back to the source, detectability is affected by geometry, materials, and onboard systems. Target signature contains structural, propulsion, and avionics contributors: body shape, control surfaces, wings, fuselage, engines, inlets, exhaust, seekers, communication antennas, GPS, and altimeters. Scattering mechanisms - specular reflection, leading-edge diffraction, trailing-edge diffraction, creeping wave, and standing wave - together with induced surface currents determine the scattered field.
The viewing direction, radar frequency, polarization, waveform, and bandwidth strongly affect signature features. Radar signature is determined empirically and collected in databases. Accurate estimation draws upon measurement and prediction tools like Xpatch and method-of-moments codes.
RCS measurement is vital for evaluating and minimizing the radar signature. Stealth platforms minimize RCS to evade defenses. In military radar equipment, radar signatures play a major part in target characterization, allowing threat systems to control transmit power, gain, losses, dwell time, and spread factors while still risking detection when external auxiliary fuel tanks under the wings make the aircraft light up a radar screen.
What are the radar cross section values of various aircraft?
The radar cross section values of various aircraft are given in the table below.
| Aircraft | RCS (m ) |
|---|---|
| F-4 | 6 |
| Modern stealth | <0.0002 |
| Large combat | 5-6 |
| Small combat | 2-3 |
| B-2 (widely) | -40 dBm |
| B-2 (head-on) | -20 dBm |
| B-2 (approx.) | 0.75 |
| B-2 (bumble bee) | 0.0001 |
| B-52 | 100 |
| F-22 Raptor | 0.0001-0.0005 |
| MIG-21 | 3 |
| F-35 Lightning II | 0.0015-0.005 |
| F-16 | 5 |
| F-117A | 0.001 |
| B-1 bomber | 10 |
| J-10C | 0.5-1 |
| SU-34/35 | 1 |
| A-12/SR-71 | 0.01 |
| B-26 (certain angles) | >3100, 35 dBm |
| Cargo aircraft | up to 100 |
| F/A-18 Hornet | 1 |
| Chinese J-20 | 1 |
| Stealth aircraft | <0.1 |
| Frigate (103 m) | 5000-100,000 |
| Container ship (212 m) | 10,000-80,000 |
| Coastal trading vessel (55 m) | 300-4000 |
| Bird | 0.01 |
| Human | 1 |
| Insect | 0.00001 |
What aircraft has the smallest radar cross section?
Among operational and soon-to-enter-service types, the aircraft that presents the smallest radar cross section is China's carrier-capable Shenyang J 35: its design yields an RCS smaller than a human palm, a figure that translates to something on the order of 5-15 square centimeters. The U.S. Air Force's forthcoming B-21 Raider bomber, now being built by Northrop Grumman, is in the same class: while still in flight-test, factory data claims the bomber ‘shows up about the size of a mosquito’ to common threat radars and is virtually invisible in the UHF/VHF bands, giving it a frontal RCS estimated at well below one hundredth of a square meter.
Both designs beat the long-serving B-2 Spirit, whose very small cross section was the benchmark of the 1990s, and they outperform the older F-117 Nighthawk whose flat faceting was state-of-the-art in the 1980s. Among fighters already in squadron service, the F-22 Raptor and the 5G F-35 each manage a golf-ball-sized signature (4.27 cm) on frontal aspects, while the Russian Su-57, the Turkish Bayraktar Kızılelma UCAV and China's ground-based J-20 are next in line, though their designs and coating choices leave them detectably larger than the J-35 and B-21. Thus, measured in raw size, the palm-sized echo of the J-35 and the mosquito-sized return of the B-21 set the present low-water mark for radar visibility.
