Military & Aerospace

Countering Stealth Technology in Military Aviation
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Issue Vol. 38.1, Jan-Mar 2023 | Date : 02 May , 2023

The unveiling of the B-21 ‘Raider’ by the United States Air Force (USAF) and Northrop Grumman Corporation (NGC) on 02 December at the USAF’s classified Air Force Plant 42 in Palmdale, California, signified a leap forward in the now raging battle between stealth and counter-stealth technologies. Part of the USAF’s Long-Range Strike Bomber Programme, the B-21 is a long-range, strategic stealth bomber and is slated to complement and later replace its low-observable predecessor, the Northrop Grumman B-2 ‘Spirit’, which has been used to lethal effect in operations commencing from Kosovo and over Libya and Afghanistan.

The press release by NGC stated that the $700-million B-21, the world’s first aircraft with ‘sixth-generation’ characteristics, has been designed against the backdrop of ‘stiff’ stealth/counter-stealth technology competition being pursued by China and Russia. The B-21 also represents an effective means to penetrate and defeat the Anti-Access Area-Denial (A2AD) strategy practiced by rival countries.

While the B-21 embodies a paradigm shift in aviation stealth technology, it also represents a challenge for rival countries to add further impetus to develop their respective counter-stealth capabilities. Apropos, this article will concentrate on developments in sixth-generation stealth technology and commensurate extant/developing global counter-stealth capabilities.

What are the likely Contours of Sixth-Generation Aircraft Stealth Technology?

Multiple Sixth Generation Fighter Aircraft (SGFA) programmes (the term SGFA/FGFA is being used for convenience and covers all stealth military aircraft) are being pursued as under:–

    • The USAF is pursuing the Next Generation Air Dominance Programme with the F-X SGFA as a successor to the F-22 Raptor, as also the ‘Penetrating Counter Air’ (PCA) fighter-escort aircraft to operate alongside its stealth bombers. The US Navy is pursuing its Fighter/Attack F/A-XX Programme, intended to replace the F/A-18E/F Super Hornet and complement the F-35C Lightning-II.
    • Germany, France and Spain are jointly developing the New Generation Fighter (NGF), as part of Europe’s Future Air Combat System (FCAS) Programme, aimed at replacement of the F/A-18E/F, Dassault Rafale and Eurofighter Typhoon in service respectively with these countries.
    • UK, Sweden and Italy are invested in developing BAE System’s Tempest, slated to enter service in the next decade to replace the Eurofighter Typhoon.
    • Russia is developing the ‘MiG-41’ SGFA Interceptor to replace the MiG-31.
    • Post successful induction of the J-20 Fifth Generation Fighter Aircraft (FGFA), China plans to complete development of its SGFA by mid-2030s.
    • India plans to commence production of the Advanced Medium Combat Aircraft (AMCA) Mark-I FGFA in 2028, with the Mark-II incorporating Sixth-Generation characteristics.

 True stealth capability and not just partial stealth characteristics separate FGFA programmes like the US F-35/F-22, the Chinese J-20/under-development J-31 and Russia’s SU-57/under-development Su-75 from their predecessors. FGFA stealth design incorporates suitable visual camouflage, full-body stealth construction with low reflectivity composite materials to diminish Radar Cross-Section (RCS), flush fuselage, internal weapon bays, minimum external projections/non-perpendicular faceted surfaces (akin to a gemstone face, without curves) to reduce radar reflectivity, exhaust design to minimise acoustic/heat signature and incorporation of passive sensors to reduce Electromagnetic (EM) emissions- in short, stealth across all detection mediums.

As the principal subset of sixth-generation technology, SGFA stealth would include the stealth technologies of FGFA, with additional measures to mitigate pan-medium detection, and could include the following:–

    • Active Flow Control (AFC). US Defence Advanced Research Projects Agency (DARPA) is working on AFC as part of its X-Plane ‘Control of Revolutionary Aircraft with Novel Effectors’ (CRANE) Programme. AFC eliminates the need for moving flight control surfaces/projections, improves aircraft performance by reducing weight/aerodynamic drag and enhances stealth since such surfaces represent a chink in the stealth profile. Technologies being considered include fuselage vents to channel exhaust for thrust vector control and electrodes mounted on wings/fuselage to produce electrical discharge to heat the surrounding air, thus altering air density and influencing the aircraft’s flight profile.
    • Stealthy Fuselage and Inlets. SGFA would sport sharply chiselled nose-cones/fuselage or angular airframe design to minimise direct reflection and cause inaccuracies in location detection. Divertless Supersonic Inlets (DSI-also used in FGFA) and conformal engine ‘nacelles’ will improve the SGFA’s stealth characteristics by eliminating the requirement to divert air from the air-intake hitherto fore required since the aircraft cannot directly handle intake of supersonic air. Additionally, the “bumped” surface of the DSI shields the engine (a major source of reflectivity) from radar exposure. Reduced stealth due to opening of bomb-bays/landing-gear (a bugbear in current stealth technology) would be overcome by trapezoidal/serrated or sliding doors. Another standard facet (existing in the B-2/B-21), would be the ‘flying wing’ or ‘all-wing’ ‘planform’ design, referring to a tailless aerodynamic shape with no clearly defined distinction between the wings/fuselage, thus eliminating surfaces which can reflect back radar waves. Dovetailing control surfaces such as ailerons/elevators directly into the wing to reduce RCS, is also being explored.
    • High Durability Radar-Absorbent Composite Material. Use of electrically conductive radar-absorbent polymers/ablative (degradable) aircraft paint with embedded metal spheres/carbon nano-fibres to coat leading edges of the airframe and coating the canopy with transparent conductor coating to increase radar transparency, would be standard features. The high durability of these coatings would allow SGFA to undertake multiple, protracted missions without the need for regular/ extensive maintenance between sorties, thus reducing operational turnaround time. Use of a narrow frequency band in the aircraft’s radar (most combat aircraft radars operate in the X Band) and the use of ‘band-pass’ radar coating which is only transparent to desired frequencies, will further enhance stealth. ‘Fibre Mat’ coating used in the F-35, provides depth to the stealth coating, thus reducing attenuation of the latter and preventing consequent degradation of RCS.
    • Airborne Next-Generation (NG) Jammers/Spoofers/Low-Power Emitters. NG Jammers would not only attempt to degrade detection capability of ground-based emitters, but would also be able to infuse inaccuracies by invading networks. Spoofing technolog y present in the B-21, wherein SGFA could ‘spoof’ adversary radars by firing targeted radar emissions/modulating ambient emissions to disguise itself as a different object, will also be a feature. Use of Metasurface coating (slender meta-material layers that allow/inhibit propagation of EM waves in desired directions) will aid in Low-Observability (LO). Plasma-stealth technique will use ionised gas plumes (plasma) to create a plasma cloud around the aircraft to deflect/absorb incident radar waves. Low-Probability-Intercept Radars which do not trigger radar emission warnings in the adversary’s airborne/ground-based receivers, passive IR sensors and Low-Light TV would find favour as onboard sensors to reduce aircraft EM emissions. The use of ‘unmanned wingmen’, where an Unmanned Aerial System (UAS) is controlled from the stealth platform to act as a sensor and seamlessly relay information to the stealth platform’s onboard computer, thus reducing the need for aircraft emissions, will also be a feature.
    • Infra-Red (IR) Obscurators. SGFA will incorporate IR obscuring features in engines/exhausts to reduce/dissipate raised body temperature due to exhaust/skin friction due to movement of air over wings/fuselage. These include ceramic tile-coated exhausts, altered tail-pipe shape/exhaust vents to dissipate the exhaust plume, pre-mixing of exhaust gases with cold intake air to lower exhaust temperature and thermal conductor coating/vapour vents to conduct heat away from the surrounding air and dissipate it in different directions. Wing-mounted/embedded engines/over-wing exhausts, as in the B-2/B-21, which obscure engines/exhaust from ground observation, would be a standard feature, as would be routing of fuel circuits in a manner to allow the fuel tanks themselves to act as heat sinks for absorbing a portion of exhaust heat.
    • Visual Obfuscation. Visual identification can be the hardest to evade, but is only effective at short ranges, usually leaving no time for ground-based sensors/vectors to react and therefore may not be as critical to SGFA operation. Nevertheless, use of mimetic paints/patterns, in which the surface resembles the ambient background (e.g. the B-2 is black, since most operations are envisaged at night), grey disruptive patterns, anti-glint canopies, contrail (vapour-trail) reducing chemicals admixed in fuel, cockpit-contrail sensors to alert the pilot to change altitude to obviate a vapour trail and anti-contrast shading. Painting traditional shadow areas with lighter shades to mask contrast, would also be features.

Counter-Stealth Technology (CST)

In today’s world of stealth combat aircraft dominance, a robust, persistent and at-par counter-stealth system with suitable detection/engagement means, would necessarily be integrated into a Nation’s Defensive Counter-Air Operations, as one of the first responders in what is described by Air Forces the world over as a ‘kill-chain’ (Detect-Identify-Target-Carry out Post Strike Damage Assessment) against an adversary’s stealth aircraft attempting to degrade own combat air power and/or in support of an adversary’s ground/maritime /pan-domain operations.

Traditionally, CST has played follow-up to developments in stealth capability. However, the race is now much closer than ever before, with major players like Russia and China focussing on A2AD strategies to safeguard/deny air/maritime/overland space to a potential adversary, thus making them increasingly sensitive to stealth-aided incursions. Extant/emerging CST is profiled below.

Radar-Based CST

Stealth aircraft are configured for LO in the X-Band, where small, high frequency (HF)/low wavelength airborne/ground-based radar emitters achieve high accuracies for ‘weapons-grade’ lock-on required for intercepting such aircraft. Modern stealth aircraft such as the F-35 and larger stealth planes such as the B-2 and B-21 would show LO characteristics across large spectrum swathes, from Ku (12-16 GhZ/1.67-2.5 cm) to L (1-2 GhZ/15-30 cm) Bands. However, towards the higher wavelengths, the LO shape tends to lose relevance as the wavelength tends to equal the Radar Cross Section (RCS), causing increase in spectral (regular)/non-spectral (diffused) reflection from the general shape of the aircraft, thus compromising stealth. Unfortunately, higher wavelengths mean low accuracy for weapons-grade track and large emitter size, which need to be addressed by dovetailed use of EM band radars/other means.

Multiple high-power emitters, with separate receivers (bi/multi-static radars), where the emitters and receivers are separated by a distance comparable to anticipated detection ranges, will invariably pick up an aspect of the aircraft and achieve detection with the help of multi-sensor data fusion (MSDF).This is because stealth aircraft, including the F-35, are designed for optimum stealth/minimum RCS from a frontal aspect/against X-Band, with other viewing angles/radar frequencies presenting degraded/larger RCS which allows detection by a multi-static radar array.

Multi-static radars can also use an aircraft’s jamming frequency to work out its location. The Russian 55Zh6M Nebo-M, designed as an Air Defence (AD) surveillance radar and for integration with the S-400 Triumf Integrated AD System (which has a stated targeting range of 150km against stealth targets) is a multi-static array of four VHF Active Electronically Scanned Array (AESA) radar systems, capable of detecting aircraft and hypersonic vectors at ranges up to 600km.

The Nebo-Mis is also a multi-band radar system that uses two low-frequency radar arrays-the Nebo SVU in the VHF-band and the Protivnik-G in the L-band, to detect stealth aircraft on approach, while the Gamma-S1 array, broadcasting in the S/X-bands, provides an effective means of tracking/targeting detected stealth aircraft.

The Nebo-M, therefore, could be considered a variant of a Multiple Input-Multiple Output (MIMO) radar, described below. As a counter to the Nebo-M, China has developed the JY-27A VHF AESA long-range air surveillance and guidance radar system, which claims to be able to detect the F-22 and the F-35, albeit with very low accuracy. It has a stated maximum detection range of 500km.

Satellite images reveal that China has installed a MIMO Synthetic Impulse and Aperture Radar (SIAR) on the Subi Reef in the South China Sea. The radar array consists of three concentric rings of emitter/receiver antennae and operates in the VHF Band. Each of the transmitters simultaneously emits a unique, coded pulse which is received by a dedicated receiver. Impulse synthesis of these signals is then carried out along with aperture synthesis of doppler inputs of the movement of the stealth aircraft relative to the array. The fusion of impulse synthesis and aperture synthesis yields a 3D track: range, bearing and elevation, as well as the target’s speed, thus overcoming deficiency of a single VHF receiver to provide a weapons-grade track.

Wavelength Manoeuver is a fallout technique of multi-static radar technology, wherein lower frequency radars are used to detect/track a stealth aircraft, followed by cueing a different emitter viz. an AESA radar to fire multiple, multi-directional UHF beams over a narrow field-of-view to penetrate aircraft stealth and generate target-engagement data.

Over-The-Horizon Radars (OTHR) are able to detect/track aerial targets beyond line-of-sight, using HF (3-30 MHz/10-100m) radar waves. The ‘Skywave’ type of OTHR uses refraction from the ionosphere to reflect/refract transmitted radar waves back to the earth’s surface. In doing so, some reflected waves from a stealth aircraft’s surface reach the receiver, enabling detection at ranges up to 4,000km. The ‘Surface Wave’ type of OTHR uses reflection from the ocean surface to similarly detect aircraft/ships, albeit at lower ranges of up to 300km. While engagement accuracies may not be possible with OTHR, these radars provide early warning and can cue other vectors/radars toward the target. The French Nostradamus is a mono-static Skywave OTHR with 360ºcoverage which, as per available literature, can detect a B-2 at over 3000km, but with a very low accuracy of approximately five kilometre, making the mating of such radars with a weapons-track capable radar imperative for effective counter-stealth operations.

Another CST involves Passive Anti-Stealth (PAS) radars (akin to multi-static radar deployment), wherein accurate location is achieved by computing the ‘time difference on arrival’ of an emitted (EM) signal from the aircraft. Since these systems do not actively transmit EM waves, they fall under the ambit of Electronic Support Measures (ESM) systems and are difficult to neutralise. The Czechoslovak Tamara KRTP-91 Trash-Can and the Thales Ground Alerter-100 Multi-Static Passive Radar are examples.

Infra-Red Search and Track (IRST)

Airborne and some land-based IRST systems can be used to detect IR signature of stealth aircraft. While internal emissions of modern stealth aircraft would be considerably muted due to technologies described above, some amount of emission and heat due to skin friction is unavoidable, which can be picked up by a sensitive, multi-channel passive IRST system against the backdrop of cold, ambient air. Typically, airborne IRST mounted on modern multi-role fighters such as the US F-35, the Russian MiG-35 or the French Rafale. The IRST systems that would form part of the under-development PCA, FCAS, Tempest or the MiG-41, would be capable of picking up a non-afterburning aerial target almost up to BVR engagement ranges. The AN/AAQ-37 Electro-Optical Distributed Aperture System (DAS) is a new-generation IRST system on the F-35, consisting of six high-resolution IR sensors around the F-35’s airframe capable of long-range detection of even LO aircraft. The SU-57 mounts the advanced 101KS-V (OLS-50M) IRST which works on ‘Quantum Well Imaging Photodetector’ technology, providing a wider spectral bandwidth to detect minimal IR signatures from even ‘very cool’ stealth targets. The EORD-31 (3rd Generation) IRST developed for the Chinese J-20/J-31stealth fighters, claims an IR detection range of 150km for the B2 and 110km for the F-22. The Rafale mounts the Optronique Secteur Frontal (OSF) EO/IRST which has proved effective against the F-22 in many aerial exercises.

Emerging Technologies

Light Detection and Ranging (LIDAR) Technology involves using directed LASER beams in the near-IR portion of the EM spectrum to generate weapons-grade track, once the stealth target has been detected and its approximate inbound track localised. LIDAR can be grouped within multi-static radar arrays for this purpose. Options of multiple LIDARs aboard airborne platforms to create a LASER ‘mesh’ to detect stealth aircraft ingress are also being researched. Problems of atmospheric attenuation however, would need to be addressed. A private vendor in the US has reportedly successfully demonstrated detection of an F-35 from air-to-air/ground-to-air LIDAR at a distance/altitude of five kilometre/15,000 feet respectively.

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Cellphone Radar (CELLDAR) is an emerging PAS technology conceptualised by a private research group in the UK and being developed in collaboration with BAE Systems, as per reports. The concept involves detection of reflected cellular/radio/TV signals off an inbound stealth aircraft, by deployed cellular radars. MSDF then builds tracking data for detection/collation. The system may also incorporate acoustic detectors over a widespread network to detect an aircraft’s aural signature. These inputs, when collated and fused, would serve to provide an inbound track of a stealth aircraft and could be used for cueing other EM emitters to obtain weapons-grade track for engagement.

China claims to have developed a multi-purpose anti-stealth radar based on quantum technology, supposedly capable of ground/aircraft-based IRST detection of stealth aircraft at 100/300km respectively. The system also incorporates LIDAR technology, with high-sensitivity receivers capable of ‘single-photon’ detection, which will be able to pick up even minute reflection of LASER light, to detect a stealth aircraft. China Electronics Technology Group Corporation had unveiled a prototype of the YLC-8E3D anti-stealth radar at the Ninth World Radar Expo, held in Nanjing in April 2021. The radar works in the UHF, L, S and C bands and is capable of bombarding the stealth target with a high-energy ‘EM Storm’, ensuring at least some amount of reflected signal is received back, thus aiding detection at long ranges. China has also claimed to be developing ‘ghost-imaging’ satellite-based detectors, that would use the principle of ‘quantum entanglement‘ to produce an image of a stealth aircraft on which the LASER beam from the satellite is directed. These claims, however, require corroboration.


The duel amongst stealth and counter-stealth capabilities promises to push the envelope of disruptive technologies in these fields further and faster than ever before, in a race where one leverages cutting-edge technology to defeat ever-developing facets of the other. Global competition seems to be narrowing down to key players seeking to achieve pan-domain dominance in an increasingly stealthy battlefield in a contest that promises to get even more intense in the times ahead.

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The views expressed are of the author and do not necessarily represent the opinions or policies of the Indian Defence Review.

About the Author

Brig Arvind Dhananjayan

has Commanded an Operational Brigade and has been Brigadier-in-Charge Administration in a Premier Training Facility. He has had exposure abroad on deputation to Botswana, Southern Africa as member of an Indian Army Training Team.

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