Radar cross-section (RCS) in one number
An aircraft's RCS is the area of a perfect metal sphere that would return the same energy. A B-52 has an RCS of about 100 m². An F-15 is around 10 m². An F-35 is reportedly 0.005 m². The B-2 is rumoured below 0.0001 m². Radar detection range scales with the fourth root of RCS — cutting RCS by a factor of 10,000 only cuts detection range by a factor of 10.
Where the returns come from
Flat surfaces perpendicular to the radar give huge returns — like a mirror to a flashlight. Edges, gaps, right angles between surfaces (corner reflectors), and protruding shapes all contribute. The F-117 was made of flat panels because in 1975 nobody could simulate curved-surface RCS yet. The B-2 used curves once computing caught up. Both work; they're different decades of the same physics.
Radar-absorbent material (RAM)
RAM is a thin coating that converts incoming radio energy to heat. It works best at the frequency it was tuned for. F-22 and F-35 surfaces use a different RAM than the B-2. Maintenance is expensive — sweat, rain, exhaust and bird strikes all degrade RAM. Stealth aircraft spend more time in dehumidified hangars than in the air.
Why low-frequency radar still sees stealth
Stealth is optimised for X-band (around 10 GHz) — the band used by most fighter radars. Drop to VHF (30-300 MHz) and the wavelength becomes comparable to aircraft features, which destroys the RCS reduction. Russian and Chinese OTH and VHF early-warning radars are designed exactly for this. They can detect that a stealth aircraft exists, but they can't track it precisely enough for a missile.
The challenge of heat: Infrared signatures
While shaping and coatings manage microwave reflections, they do nothing to hide a jet's thermal footprint. Jet engines operate at extreme temperatures, and their exhaust plumes are visible to infrared search and track (IRST) sensors from dozens of miles away. To combat this, stealth aircraft like the F-22 and B-2 use specialized nozzle designs. By flattening the exhaust into thin ribbons and mixing it with cooler ambient air, the thermal intensity is diluted. Furthermore, the exhaust is often shielded by the aircraft’s fuselage or 'beaver tail' to prevent a direct line-of-sight from ground-based sensors to the hottest internal turbine components.
Internal heat management is equally critical. Stealth aircraft cannot use traditional high-friction cooling vents because every hole in the skin acts as a massive radar reflector. Instead, they often use their fuel as a heat sink, cycling it through internal heat exchangers before it reaches the engines. This 'thermal management' is a hidden layer of stealth technology that complicates the engineering significantly. If the skin of the aircraft heats up too much from air friction at supersonic speeds, it glows in the long-wave infrared spectrum, rendering the RCS-reduction efforts moot against modern optoelectronic detection systems.
Plasma stealth and active cancellation
Beyond passive shaping and coatings, research into active stealth methods has persisted since the Cold War. One theoretical approach is plasma stealth, where a layer of ionized gas is generated around the aircraft. This plasma layer can theoretically absorb or refract radar waves, effectively cloaking a conventional airframe without the need for complex faceted geometry. While the Soviet Union reportedly experimented with this on the 3M25 Meteorit missile in the late 1970s, the power requirements or 'blooming' effect—where the plasma itself becomes a detectable beacon at certain frequencies—have kept it out of widespread operational use in Western designs.
A more modern digital approach is active cancellation, often referred to as 'anti-radar' or electronic stealth. This involves the aircraft’s onboard sensors analyzing an incoming radar pulse and immediately broadcasting an identical signal exactly 180 degrees out of phase. When these two signals meet, they undergo destructive interference, resulting in a zero return to the enemy receiver. This requires extreme processing speeds and precise timing, as a delay of even a few nanoseconds would render the technique ineffective. While largely classified, it represents the next logical step in the cat-and-mouse game, moving stealth from passive geometry into the domain of real-time signal processing.
The role of edge alignment and planform
In modern low-observable design, edge alignment is as critical as RAM. Engineers align the leading and trailing edges of wings, tail fins, and even access panels to a specific set of narrow angles. This technique, called planform alignment, ensures that any radar energy not absorbed by the skin is reflected in a few very narrow 'spikes' rather than being scattered in all directions. If the radar transmitter is not positioned exactly on one of those few lines of reflection, the return signal never reaches the receiver. This is why the F-22 and F-35 have jagged, sawtooth patterns on their landing gear doors and engine nozzles.
Total concealment is impossible; the goal is to minimize the duration of the return. By concentrating reflections into narrow lobes, a stealth aircraft appears to a radar operator as a momentary, erratic blip that the software filters out as atmospheric noise or a bird. This 'glint' is insufficient for a tracking radar to achieve a weapons-grade lock. Consequently, the aircraft remains tactically invisible even if it is technically detectable. To maintain this geometry, stealth aircraft must store all weapons and fuel internally, as a single protruding missile rail would increase the RCS by several orders of magnitude.
Bistatic radar and the geometry of detection
Traditional radar is monostatic, meaning the transmitter and receiver are in the same location. Stealth design exploits this by reflecting waves away from the source. However, bistatic radar systems separate the transmitter from the receiver by tens or hundreds of kilometers. When a stealth aircraft passes between these two points, it can unintentionally reflect energy directly toward the off-site receiver. While this concept was understood as early as the 1930s, the computing power required to synchronize multiple receivers and triangulate a fast-moving target has only recently become mobile and cost-effective for field deployment.
Despite this vulnerability, bistatic systems face significant operational hurdles. They require precise timing and high-bandwidth communication between nodes that are often vulnerable to jamming. Furthermore, while a bistatic system might detect an aircraft's presence, it rarely provides the localized accuracy needed to guide a surface-to-air missile. The cat-and-mouse game has thus shifted toward 'passive' detection, where sensors listen for the subtle disruption of ambient signals like FM radio or cellular towers caused by an aircraft’s passage, a technique known as Passive Coherent Location (PCL).