What is Stealth Technology, Threats and Counter-Threat Measures?

Stealth and/or low visibility has become the magic word in contemporary weapon systems and especially in aircraft. Contemporary work on stealth has its roots in long-standing efforts to reduce the visibility of military aircraft through camouflage paint schemes. However, as electronic sensors have replaced pilots' eyes as the primary means of tracking other aircraft, more sophisticated means of defense have been needed.

Often thought of simply as the use of special materials to make an aircraft invisible to radar, stealth is actually a complex design philosophy that reduces the ability of an attacking system's sensors to detect, track and attack an aircraft (or other platforms such as warships). Since a variety of sensors will be used in this process, the design of a stealthy air, sea or land vehicle requires careful trade-offs between different techniques.

The great secrecy surrounding stealth programs is designed to protect the choice and mix of techniques used in a given system, not just to protect a particular stealth technology. Various technologies can be combined to make a platform "invisible-invinsible" to radar.

These technologies include a smooth surface, a "flying wing" design, radar absorbent materials (RAM), engines concealed in the airframe, and electronic countermeasures (ECM). Each of these features contributes to the attempt to deceive and/or blind enemy air defense systems.

The aircraft's low radar cross section (RCS) reduces the range at which ground-based and airborne radars can detect the aircraft. Radar Absorbent Material (RAM) absorbs most of a radar signal, and the aircraft's wing-shaped and rounded design directs most of the remaining power away from the radar source. The engines are embedded in the fuselage with air intake and exhaust ducts placed on top of the aircraft to reduce the heat signature and hide the jet engine's compressor blades from radar detection.

Electronic Countermeasures ECM is a last-ditch attempt to confuse the radar operator through jamming and ghost imaging. The benefits of stealth technology are inherently obvious, especially since 70 percent of Soviet-style air defense systems use radar detection and tracking modes.  However, in terms of limitations, the other IR, EO, Electro-Optical and visual elements of air defense detection and tracking must also be circumvented if an aircraft is to be truly "stealthy-stealthy".

Limitations:

There is no perfect stealth design; instead, as each mission requirement requires an appropriate mix of techniques, it is necessary to design as optimally as possible. The application of stealth is not without penalties. Some of the stealth-enhancing equipment used requires specialized and costly maintenance. The maneuverability of an aircraft can be limited, reduced or even made almost unwieldy by the application of stealth design features. 

As with the F-117A, the B-2's low observable characteristics require frequent structural and maintenance activities, so each B-2 bomber will have its own closed maintenance facility.

Stealth requires not only design compromises, but also operational compromises. The sensors used to locate targets pose a particular problem for stealth aircraft. The large radars used by conventional aircraft would clearly compromise the position of a stealth aircraft. Air-to-air combat will rely on infrared tracking as well as passive detection of transmissions by enemy aircraft. However, these techniques have marginal effectiveness against other stealthy aircraft, which explains the limited application of stealth to the Advanced Tactical Fighter.

Aircraft attacking ground targets face a similar problem. FLIR-Forward-Looking Infrared Systems can be used to accurately aim at targets of known general location, but are not well suited to searching for targets over a large area. Using a radar on board to scan for potential targets can jeopardize the aircraft's position. Stealth aircraft could rely on an airborne laser radar to locate targets, but such a sensor would only be of limited use in bad weather. A more promising approach would be to use data transmitted directly from reconnaissance satellites.

Yes, there are limits to the use of stealth techniques. Because the radar cross section of an aircraft depends on the angle at which it is viewed, an aircraft will have a much smaller RCS (Radar Cross Section) when viewed from the front or rear than when viewed from the side or above. In general, stealth aircraft are designed to minimize their front RCS. However, it is not possible to contour the surface of an aircraft to reduce RCS equally in all directions, and reductions in frontal RCS can lead to a larger RCS from above. Therefore, an invisible aircraft may be difficult to track to a ground-based radar or when flying towards another aircraft at the same altitude, while it would be easier for a high-altitude weather radar or space-based radar to track it.

Like sound waves, radar waves reflect off some things better than others. With a smaller RCS, radars cannot detect a stealth aircraft until it is much closer than a non-stealth aircraft. 

With a 172 ft wingspan, the B-2 Spirit is about 6 times larger than the F-16, but has a smaller radar cross section (RCS). 

Countermeasures against Stealth Technology:

Passive (Bi-Static) Radars:

Passive radar is also known as passive coherent location, passive stealth radar, and passive bi-static radar.

Another limitation of stealth aircraft is their vulnerability to detection by bi-static radars. 

The contour of a stealth aircraft is designed to prevent a monostatic radar signal from reflecting directly back in the direction of the radar transmitter. However, the transmitter and receiver of a bi-static radar are separate, in fact a single transmitter can be used by radar receivers scattered over a wide area. This greatly increases the probability that at least one of these receivers will pick up a reflected signal. If the radar transmitter is space-based and therefore sees the aircraft from above, which is the direction of the largest radar cross-section, the likelihood of stealth aircraft being detected by bi-static radar is even greater.

Passive radar can perform detection, localization and tracking functions as well as target acquisition.

Basic stealth techniques will be less effective than before against passive radar systems that exploit bi-static geometry and the use of waveforms to counter stealth.

IRST Systems:

Several analysts claim that stealth aircraft such as the F-22 will be vulnerable to detection by Infrared Search and Track Systems (IRST). The natural heating of an aircraft's surface makes it visible to such systems. The faster the plane flies, the hotter it gets and thus the easier it is to be detected by infrared means. "If an aircraft deviates from its surroundings by only one degree Celsius, you will be able to detect it at militarily useful ranges," says one expert. 

In fact, both the Russian MiG-29 and Su-27 carry IRST devices, suggesting that the Russians have long seen it as a potential anti-secrecy system, aiming to turn stealth's weakness against IRST systems into an advantage in the air.

In conclusion, neither passive radar nor stealth technology is magic. The truth is that the side with the best spellbook has the best chance of winning the air wars of the future, not the best magic.

Ladar (Laser Radar):

Stealth aircraft are even more vulnerable to multiple sensors used in succession. Superior data is provided by using an IRST (Infrared Search and Track Systems) to track the target and a Ladar (laser radar) or narrow beam, high power radar to paint the target.

The main potential limitation of stealth is its vulnerability to visual detection. Since the F-22 is, for example, 25-30 percent larger than the F-15 and 40 percent larger than the F-18, it will be much easier to detect visually from ranges of 10 miles. Given that stealth capabilities will greatly reduce the effectiveness of various types of guided air-to-air missiles, fighter dogfights are likely to return to the realm of visual range. In this context, an F-22 that could be unwieldy in a dogfight would be at a distinct disadvantage.

What is the Future of Stealth?

In conclusion, neither passive radar, nor IRST, nor ladar, nor stealth technologies are magic, they are known and practiced technologies. The truth is that the side with the best spellbook is not the side with the best magic, but the side with the best chance of winning the air wars of the future.

The US introduced stealthy air platforms with the F-117A, followed by the B-2, F-22, F-35 and B-21. In fact, this feature became the defining characteristic of the 5th generation jet fighters. The 6th generation jet fighters will also be stealthy (see Ref.-1 for detailed information).

The US is followed by China with the J-20 and J-31 and Russia with the Su-57.

Korea with the KAI KF-21 Boramae and Turkey with the TF-23 KAAN will also have stealth capability, having designed and started manufacturing their own 5th generation jet fighters. In this case, we see that stealth detection systems have not yet been able to eliminate the extraordinary "force multiplier" effect that stealth adds to air warfare.

Neither stealth nor countermeasures technologies will stop evolving. If a threat is being developed, countermeasures against that threat will also be developed.

References:

1. Jet Fighter Development/Jet Fighter Generations

https://strasam.org/savunma/havacilik-ve-uzay-sanayii/jet-savas-ucagi-gelisimi-jet-savas-ucagi-nesilleri-1197