Stealth technology has been one of the most discussed topics in recent years. Despite the fact that the first aircraft with their use appeared more than thirty years ago, disputes about their effectiveness and practical benefits are still ongoing. For each argument pro there is a contra, and this happens all the time. At the same time, the aviation industry of developed countries seems to have made their choice in favor of the use of stealth technologies. At the same time, unlike earlier projects, new aircraft are made taking into account a decrease in radar and thermal visibility, but no more. Stealth is no longer an end in itself. As shown by the not very successful experience of operating the Lockheed F-117A aircraft, it is necessary to put aerodynamics and flight performance at the forefront, not stealth. Therefore, the designers of radar stations and anti-aircraft systems have small "clues" for detecting and attacking stealthy aircraft.
Despite a long history of research and development in the field of stealth, the number of techniques that can be applied in practice is not so great. So, to reduce the likelihood of detecting an aircraft using radar, it should have specific hull and wing contours that minimize the reflection of the radio signal towards the radiating antenna, and, if possible, absorb part of this signal. In addition, due to the development of materials science, it became possible to use radio-transparent materials that do not reflect radio waves in the structure. With regard to stealth in the infrared, then in this area all solutions can be counted on one hand. The most popular method is to create a custom engine nozzle. Due to its shape, such a unit is able to significantly cool reactive gases. As a result of the application of any of the existing methods of reducing the signature, the detection range of the aircraft is significantly reduced. In this case, complete invisibility in practice is unattainable, only a decrease in the reflected signal or radiated heat is possible.
It is the remnants of radio and thermal radiation that are the "clues" that can make it possible to detect an aircraft made with the use of stealth technologies. In addition, there are techniques that allow you to increase the visibility of a stealth aircraft without resorting to very complex technological solutions. For example, it is often proposed to use against stealth aircraft their own main feature - the scattering of incident radio waves. In theory, it is possible to separate the transmitter and receiver of the radar at a sufficiently large distance. In this case, the "distributed" radar station will be able to record the reflected radiation without much difficulty. However, despite its simplicity, this method has a number of serious disadvantages. First of all, it is the complexity of ensuring the operability of a radar with a transmitter and a receiver separated by a considerable distance. A certain communication channel is required that connects different blocks of the station and has sufficient characteristics of speed and reliability of data transmission. In addition, in this case, special difficulties will be caused by the great complexity or even impossibility of making two rotating antennas, synchronizing the operation of systems, etc.
All the complexities of the spaced apart radar equipment do not allow the use of such systems in practice. Nevertheless, a similar principle is used in electronic reconnaissance systems, which can also be used to detect enemy aircraft. Last year, the European concern EADS announced the creation of the so-called. passive radar, which works only for reception and processes incoming signals. The principle of operation of such a system is based on receiving signals from third-party emitters - television and radio towers, cellular substations, etc. Some of these signals can be reflected from a flying aircraft and hit the antenna of a passive radar, the equipment of which analyzes the received signals and calculates the location of the aircraft. The main difficulty in designing this system, reportedly, was the creation of an algorithm for the computing complex. The electronics of the passive radar is designed to extract the required signal from all available radio noise and then process it. There is information about the creation of a similar system in our country. The arrival of passive radars in the troops should be expected no earlier than 2015. At the same time, the prospects for these systems are not yet fully understood, although manufacturers, in particular the EADS concern, are already not shy about making loud statements about the guaranteed detection of any inconspicuous flying equipment.
An alternative to new and daring solutions like antenna diversity or passive radar is a method that is effectively a throwback to the past. The physics of propagation and reflection of radio waves is such that with an increase in wavelength, the main indicator of the object's visibility increases - its effective scattering surface. Thus, by going back to the old long-wave emitters, it is possible to increase the likelihood of detecting a stealth aircraft. It is noteworthy that the only confirmed case of the destruction of an unobtrusive aircraft at the moment is associated with just such a technique. On March 27, 1997, an American attack aircraft F-117A was shot down over Yugoslavia, discovered and attacked by a crew of an S-125 anti-aircraft missile system. One of the main factors that led to the destruction of the American aircraft was the operating range of the detection radar, which worked in conjunction with the C-125 complex. The use of VHF waves did not allow the aircraft's stealth technologies to prove themselves, which led to the subsequent successful attack by anti-aircraft gunners.
Invisible F-117A stealth was shot down over Yugoslavia, about 20 km from Belgrade, near the Batainice airfield, by the ancient C-125 air defense system with a radar missile guidance system
Of course, the use of meter waves is far from a panacea. Most modern radar stations use shorter wavelengths. The fact is that with an increase in the wavelength, the range of action increases, but the accuracy of determining the coordinates of the target decreases. As the wavelength decreases, the accuracy increases, but the detection range decreases. As a result, the centimeter range was recognized as the most convenient for use in radar, giving a reasonable combination of detection range and target location accuracy. Thus, a return to older radars with a longer wavelength will necessarily affect the accuracy of determining the coordinates of the target. In some cases, this feature of long waves can be useless or even harmful to a particular radar or air defense system. When changing the operating range of the radar, it is also worth considering the fact that promising stealth aircraft, most likely, will henceforth be created taking into account possible countermeasures to the most common radar stations. Therefore, such a development of events is possible when the designers of the radar will change the radiation range, trying to maintain a balance between range, accuracy and requirements for countering the stealth decisions of aircraft designers, and they, in turn, will change the design and appearance of aircraft in accordance with current trends in development of means of detection.
The experience of previous years clearly shows that to protect any object, several anti-aircraft systems and several detection means are required. There is a concept of the so-called. integrated radar system, which, as conceived by its authors, is capable of providing reliable protection of covered objects from air attacks. An integrated system implies the "overlap" of the same area by several radar stations operating at different ranges and frequencies. Thus, an attempt to fly unnoticed by the radar of the integrated system will result in failure. Part of the reflected signal from some of these stations can get to others, or the plane will give out its lateral projection, which, for obvious reasons, is poorly adapted for scattering the radio signal. This technique makes it possible to detect stealth aircraft using fairly simple methods, but at the same time it has a number of disadvantages. For example, tracking and attacking targets becomes difficult. For effective missile guidance, it will be necessary to create an effective data transmission system from the "lateral" radar to the control systems of the air defense missile system. This need persists when using radio command-guided missiles. The use of missiles with a radar seeker - active or passive - also has its own characteristic features, partially making it difficult to carry out an attack. For example, effective target acquisition with a homing head is possible only from a number of angles, which does not increase the missile's combat effectiveness.
Finally, the integrated air defense system, as well as other systems using radio waves, are susceptible to attacks by anti-radar missiles. To prevent the destruction of the station, a short-term activation of the transmitter is usually used in order to have time to detect the target and prevent the rocket from targeting itself. However, another method of countering anti-radar missiles is also possible, associated with the absence of any radiation. In theory, the detection and tracking of a stealth aircraft can be carried out using systems that detect the infrared radiation of the engine. However, such systems, firstly, have a limited detection range, which also depends on the direction to the target, and secondly, they significantly lose efficiency when the radiation level is reduced, for example, when using special engine nozzles. Thus, optical radar stations can hardly be used as the main means of detection with the required efficiency of existing and future aircraft made with the use of stealth technologies.
Thus, at present, several technical or tactical solutions can be considered as a countermeasure to stealth technologies. Moreover, they all have pros and cons. Due to the lack of any means capable of guaranteed finding stealth aircraft, the most promising option for the further development of all detection technologies is the combination of various techniques. For example, a system of integral structure, in which radars of both centimeter and meter ranges, will be employed, will have good opportunities. In addition, the further development of optical-location systems or combined complexes looks quite interesting. The latter can combine several principles of detection, for example, radar and thermal. Finally, recent work in the field of passive location allows us to hope for the imminent appearance of practically applicable complexes operating on this principle.
In general, the development of systems for detecting air targets does not stand still and is constantly moving forward. It is quite possible that in the near future any country will present a completely new technical solution designed to counter stealth technologies. However, one should expect not revolutionary new ideas, but the development of existing ones. As you can see, the existing systems have room for development. And the development of air defense means will necessarily entail the improvement of technologies for concealing aircraft.
