Stealth aircraft are designed to avoid radar detection by relying on special paint and body design to absorb and deflect radio waves, reducing radar cross-section. Yet stealth aircraft can be detected by certain radars: low-frequency radar can penetrate stealth, and multistatic radar detect some stealth aircraft better than conventional monostatic radars by circumventing stealth blind spots and triangulating weak echoes from several antennas.
Expert behind this article
Jim Goodrich
Jim Goodrich is a pilot, aviation expert and founder of Tsunami Air.
Can radar detect stealth aircraft?
No, radar usually cannot detect stealth aircraft. Stealth aircraft reduce echo by deflecting radar energy, so traditional radar, which sends out electromagnetic waves and interprets their echoes, often fails to track them. The F-117 Nighthawk, for example, presents less than 0.01 m (0.108 ft) to the beam. Because first-generation stealth technology increases RCS in other directions, passive radars that monitor other directions can provide cuing for antiair weapons systems, exploiting speed rather than reflectivity also aids detection. Thus, stealth aircraft are not invisible but merely hard targets, and radar can still classify, measure range, velocity and motion vector, track, and optionally illuminate for missile lock if enough energy is caught by the receiving antenna.
Which planes cannot be detected by radar?
Planes that cannot be detected by radar include the Horten Ho 229 flying-wing fighter-bomber; it was built with a lack of vertical surfaces and its shape made it less detectable than other aircraft when it flew at high speeds and low altitudes. If an F-22 turns off its transponder, air-traffic-control radar does not detect it.
Radar coverage has a limit below which an aircraft will not be picked up by a system, and mountains or other terrain block radar signals; going too low in a mountainous area therefore takes you out of radar coverage. Apart from altitude, drones are too small for traditional radar and the signals do not tell them apart from birds. Private airplanes routinely drop off radar en route.
How is a plane invisible to radar?
Stealth technology allows an airplane to become invisible to radar. The first element is the plane's radar-absorbent surface. Aircraft structure is covered with Radar Absorbing Materials (RAM). RAM absorbs electromagnetic waves and consists of conductive and non-conductive materials like carbon and iron oxide. Special radar-absorbent paints and coatings help reduce the radar cross-section. Composites absorb radar signals.
The second element in radar invisibility is the plane's shape. Stealth airplanes are designed so that radar signals are reflected away from radar equipment. The B-2's unique ‘flying wing’ design helps scatter and deflect radar waves away from the transmitting source. B-2's design has no tail, sharp edges, or vertical surfaces. Flattened, less vertical surface creates minimal radar cross-section. Stealth designs avoid the use of large flat surfaces, sharp curves, concavities, and right angles. Most conventional aircraft have a rounded shape which creates a very efficient radar reflector.
Stealth designs must contain the engines within the wing or fuselage. The A-12 included special fuel to reduce the signature of the exhaust plume. Stealth aircraft use different engine exhaust nozzle designs, heat-absorbing coatings, and thermal management systems to minimize IR emissions. ECM pods can jam enemy radar signals and confuse tracking systems. An F-35 has an RCS of less than 0.005 m (0.054 ft) on the frontal axis, whereas a conventional aircraft like the Su-30 has an RCS of around 4 to 10 m (43.1 to 107.6 ft ). B-2 computers calculate best position relative to enemy radar to keep signature low.
What radar can detect stealth aircraft?
Low-frequency radar can detect stealth aircraft. Low-frequency radar is used for early warning and can penetrate radar-absorbing coatings. VHF radar, operating with frequencies from 30-300 MHz and wavelengths of 1-10 m (3.28-32.8 ft), offers counter-stealth capability. The P-18 radar is a ground-based VHF radar with such capability. Meter-wave radars like the JY-27V have longer wavelengths and require thicker and more intricate RAM to be effectively shielded. CETC unveiled the JY-27V radar at the World Radio Detection and Ranging Expo, describing it as a ‘master artist’ in detecting stealth targets, and China has unveiled over 100 advanced radar systems including the YLC-8E. Dual-band radars are more effective against stealth, and receiver offset Doppler radar can reveal stealth movements. Quantum radars send out photons and will prove to be a game changer. Advanced low-frequency radio detection and ranging working in the VHF and UHF wavebands possess a larger possibility to sense stealth aircraft, because the lengthier wavelengths are less absorbed or deflected by the fleet's form and materials. These systems can lighten up stealth aircraft from sudden slants or at big remoteness.
