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Contrary to the latest trends in the Russian language, we still decided to use the English term "stele" - "secret", "secret" in thetitle of our report, primarily because he had already taken root in our literature and is widely used in our press and in a foreign,including in non-English speaking countries. Under the stealth technology now mean a set of technical solutions that result inreduced levels of the signals coming from the military facility to the receiving system, trying to locate and destroy. These signalsare transferred to the acoustic and electromagnetic waves in a wide frequency spectrum. We shall deal here only one task,namely to reduce the signal level resulting from the reflection object electromagnetic waves emitted radar. Radar stations - themost "long-range" means detection and guidance, and the first boom in the press about the stealth technology has been associatedwith the emergence of an American F-117 aircraft that was created in the first place to successfully overcome the Soviet air defense system, equipped with powerful radars.Ben Rich, former head of the plants of the company "Lockheed", in his memoirs about the creation of the F-117 is the story of stealth technology in 1975, linking it to start with this plane. In fact, the first steps were made in Germany at the end of theSecond World War. As a result of night attacks British planes, equipped with radar, soared loss of German submarines. It wasthen that they began to render radio-cutting and coating technology was developed serial production of fine ferromagnetic fillersused in coatings. Since then, the problem of reducing the radar cross section of different objects of weapons and militarytechnology has attracted serious attention in industrialized countries.The main characteristic that determines the properties of the aircraft as reflecting electromagnetic radiation of the object, is theradar cross section. It characterizes the ability to convert incident electromagnetic wave into the scattered wave propagating inthe direction of the receiver. In the future, we will consider the single station location where the receiver and transmitter arelocated in one place. The effective surface cross section (RCS) is defined as:
σ =πR 40S s/ Si,
where R
0
- the distance between the transmitter and the object;
S s
- the energy flux density of the scattered wave near thereceiver; S
i
- the energy flux density of the incident wave near the body.ESR value depends on the orientation of the object relative to the beam and radar wavelength of electromagnetic radiation. For physicists, the best analogy EPR - is the differential scattering cross section is back. If we consider the frequency dependence of the EPR metal sphere (Fig. 1), in the wavelength range of low ESR coincides with the area of its cross-section. At wavelengthscomparable to the size of the ball, having diffraction minima and maxima.
Fig.
1.
Frequency dependence of the effective scattering surface of ametallic sphere
a - radius of the sphere,
λ
- Wavelength
Figure 2 shows the EPR cylinder depending on the angle of incidence of the electromagnetic waves to the wave vector in the plane which passes through the axis of the cylinder, Figure 3 - EPR modern aircraft for different directions of incidence of theelectromagnetic waves in the horizontal plane passing through the axis of the aircraft. Because of the complex shape of theobject to its ESR showed significant fluctuations in value at a very small change in the angle of incidence of the electromagneticwave. Such a situation arises due to diffraction phenomena and the subsequent interference of electromagnetic waves reflectedfrom various parts of the aircraft with a corresponding phase delay of each reflecting element.
Fig.
2.
The angular dependence of the effective scatteringsurface of the cylinder
D and L - the diameter and length of the cylinder,
θ
-the angle of incidence of the electromagnetic wave,the arrow shows the direction of its fall
Fig.
3.
"Facet" model of the Su-27 (top) and a diagram of the effectivesurface scattering plane
depending on the viewing angle in the horizontal plane (bottom)
The solid line corresponds to the scatter plot of the real plane, dotted - aircraft with a reduced radar signature, 1, and2 - averaged over a range of angles of ± 30 °, the values of the EPR Naturally, in practice, the values of interest in EPR averaged over a relatively small range of angles, due to the unavoidablevibrations because the trajectory is determined average level of the signal processed in the receiver. The task of the steletechnology is the maximum possible reduction of the EPR aircraft. For example, a qualitative leap in the capabilities of combataircraft would occur in the case if, instead of EPR shown in Figure 3 by a solid line, it was possible to obtain the ESR as shownin phantom in the same figure.Stealth technology includes the following main areas: the theory of diffraction on complex bodies, the development and study of radar absorbing materials, coating technology and, finally, Radio Physics experiment is used to control each of these areas.Currently stealth technology begins with the mathematical modeling of electromagnetic wave scattering at the facility, radar signature which has to be reduced. This step is of fundamental importance for the preliminary assessment of the achievableresults and to optimize the shape and electrical characteristics of the object. Mathematical and computational models are basedon the solution of boundary value problems of electromagnetic waves on bodies of complex shape, having in its composition,special materials and coatings. Capabilities of modern computers allow you to create software for the simulation of electromagnetic wave scattering even for complex objects such as aircraft and ships, taking into account the diversity of rigginghardware, cracks, hatches, and many other seemingly minor details of construction.On the world market offers several software packages that are suitable for such modeling. All of them are used in thedevelopment of "facet" object model, which will be mentioned below, and the method of the physical theory of diffraction. For well-known reasons, due to closeness of such works, until recently in the national press (as opposed to the foreign press) werenot published details of a particular application of mathematical modeling of scattering objects of weapons and militaryequipment. However, the analysis of scientific literature on the theory of diffraction of specialists in the field of electrodynamicswas not difficult to assess the level of development of the industry.The contribution of Russian scientists in the theory of diffraction is not only significant, but also in many important areas of basic. Suffice it to mention the names of Academician VA Fock, professors EN Vasilyev and PY Ufimtseva. VA Fok is notonly the first to formulate the integral equation for the current on the surface of the irradiated metal body, but the proposedapproximate solution for the phone with a large radius of curvature. Pioneering work was E. Vasiliev on the numerical solutionof integral equations in electromagnetic excitation of metal. PY Ufa - the founder of the method of edge waves in the physicaltheory of diffraction, which is of paramount importance in the development of stealth action recognized by the internationalscientific community. That numerical methods for solving the problems of scattering on the basis of integral equations,evaluation of the scattering properties of the method of boundary waves, and the combination of these techniques have been used by us in numerous electrodynamic models of objects with low radar signature.Employees of the Institute of Theoretical and Applied Electrodynamics, Russian Academy of Sciences for many yearsdeveloping numerical methods, building on the achievements of both Russian and foreign schools of diffraction theory.Application of asymptotic and hybrid algorithms requires a clear understanding of the physical phenomena which lead to theformation of the scattered field in each case: specular reflection, diffraction at the edges, traveling waves, multiple reflections
within the cavities, etc. Accounting mirror images of real objects is realized through the development of "facet" models, wherethe surface of the object is represented as a large number of individual flat areas of simple shape (see Fig. 3).In the calculation of the EPR large (in wavelengths) of compound bodies is essential that at relatively high frequencies candistinguish the individual fragments of the structure of objects that at a given angle are the main contributors to the formation of the scattered field. This makes it possible to perform calculations of scattering centers independently of one another, if appropriate taking into account their reciprocal influence on the subsequent stages. Accuracy of calculation of the characteristics of the scattering centers is of particular importance in the analysis of subtle detail, so much attention has been paid to the development and improvement of relevant electrodynamic models. The classical model of this kind is considered to be a wedge(edge). In this model, the infinite boundaries are accounted for using the results of the physical theory of diffraction, and thefields and currents in a finite region of space near the edges are determined by numerically solving the equations of the electromagnetic field. The allocation of individual scattering centers can also analyze specific diffraction phenomena peculiar to this structure, and to identify their dependence on a small number of local parameters.Role of numerical methods is extremely high, when the characteristic dimensions of the object fragments much larger than the wavelength, but because of high diffraction approximation processes do not provide the desired accuracy. In this fragment,creating the main contribution to the scattered field in the front hemisphere of the aircraft, powerplant is the air intake system of the engine inlet vanes. Using a hybrid approach allows independent consider the passage of electromagnetic waves via the air intake system and diffracted by the blades. However, the calculation of the scattering wave at the inlet of the engine having a transverse dimension of tens of wavelengths, and consisting of a plurality of elements of complex shape - an independent task that requires the use of rigorous methods and their efficient numerical implementation. The developed software allows you to perform the necessary calculations with sufficient accuracy (Fig. 4).
Fig.
4.
Model inlet plane (a) and the effective surface of the scattering diagram inlet (b)
Comparison of the calculated and experimental data shows good accuracy of the software Creating adequate electrodynamic model of such a complex object, like an airplane, requires a combination of methods physics,electrodynamics, computational mathematics, signal processing. As a result of extensive experience in programming,computational tasks and the effective use of the technology of modern computing. In particular, the importance of the integration of specialized software: the computational core, designed to determine the scattering properties, and engineering design systems, with which the transfer of the design documentation (in electronic form), the preparation and modification of the data on the form and structure of the object, the analysis output data. A widespread system of AutoCAD, from which data are transmitted in electromagnetic simulation models through a special interface.In the short-term progress in the development of methods for calculating the scattering properties of complex objects is largely due to the good organization of work, raising the necessary specialists, good information and technical support, as it seems to us,many of the fundamental issues that existed previously in this area have been resolved.Applied to the various elements of the aircraft radio-absorbing coatings are different from those used 10-15 years ago. Modern coating to have a variable thickness profile, a complex structure with varying values of permittivity and permeability as the thickness of (normal to the surface), and along the skin surface. Solving the fundamental problems associated with the passage of electromagnetic waves through a heterogeneous environment, studying the behavior of heterogeneous mixtures near the percolation threshold, the researchers learned how to create a substance with any frequency behavior of the real and imaginary parts of the dielectric constant, of course, within the framework of the principle of the Kramers-Kronig relations. Creating materials with an arbitrary behavior of the magnetic permeability is associated with some additional restrictions. Modern designer to optimize the ESR of a fragment of the plane and picking up for this purpose permittivity and magnetic permeability of the material, its thickness distribution over the surface of the fragment can be sure that in the future technology will reproduce the required parameters. Note also that the conduct of the relevant optimization requires considerable prior experience, because it is necessary continually to find a compromise between the desire for minimum reflection, the thickness of the material, its strength and, finally, the aerodynamic properties of a movie.Coating use very different technologies. Most of the aircraft surface is covered by paint technology. Despite the apparent simplicity of this technique is most responsible, because of its contribution to the quality depends EPR one major plane of the scattering element - its inlet, moreover, the adhesion to the air inlet cover may cause damage to the aircraft. Multilayer radioabsorbing coatings are deposited using a robotic systems in series production aircraft, or manually when creating experimental models of equipment.A daunting task is the production of fine ferromagnetic fillers with the given values of the magnetic permeability. Currently,using special technology, it is possible within a wide range of ferromagnetic fillers to modify the spectra in the microwave region. Combining ferromagnetic inclusions with inclusions of other types, create the desired set of broadband radar absorbing coatings. Their further development is not possible without addressing many fundamental questions
Fig.
5.
Scheme reflection of electromagnetic waves from the cowl to thesemiconductor controlled screen (a), the change in resistance of semiconductor films, depending on the light conditions (b) and the scheme of the reflection of electromagnetic waves from the fairing with a controlled display (c)
On the chart: dark rectangle corresponds to the conductivity of thefilms, providing transparency screen, gray rectangle - the level of conductivity, providing metallization surface fairing, 1 - theresistance of existing semiconductor films, 2 - resistance hypotheticalfilms that will realize the idea of a semiconductor managed ScreenGenerally speaking, the resistance of semiconductor doped CdS films CdSn or change by many orders of magnitude at quitereasonable levels of illumination (curve 1 in Fig. 5b). However, they are not suitable for implementing the above-describedtechnical solutions. Required film to other dynamic properties (curve 2 in Fig. 5b), but how to make it, is not very clear.Another technical solution - to the locator installation screen on the surface of which has the so-called frequency-selectivestructure - the system some form of periodic apertures that are configured so that they freely passed in either direction of theelectromagnetic wave in a narrow band radar eigenfrequencies and fully reflect the electromagnetic wave other frequencies.Introducing these specially organized aperture, which substantially represent open resonators semiconductor control system can,if desired, to "close" the screen, making it opaque to all frequencies.The problem of frequency-selective surfaces is an extensive literature from which to draw conclusions about the features of their application. We have developed numerical methods for calculation of frequency-selective screens possess appropriatetechnology and built working models of managed screens. Depending on the antenna design can be used as a frequency-selective screen, and plasma. It is mounted inside the shroud in same manner as the frequency-selective screen, but its operation principle somewhat different. In the absence of a control signal, which can be supplied to the aircraft or the pilot station to detectthe external irradiation, the screen is turned off and is transparent at all frequencies. When a signal voltage is applied to thescreen, it collisional low temperature plasma is ignited as a result of radiation is partially reflected from the screen in thedirections shown in Figure 5 in, and partially absorbed in the screen. Effective screen to electromagnetic radiation of frequencylower than the plasma. Meaning plasma frequency in such systems can be very large. Long-term studies of processes in low-temperature plasma, allowed to find the optimal parameters for the composition of gases produced by the plasma, and optimizehigh-speed plasma generation system needed to respond to the rapidly changing external environment. Flight tests demonstratethe high efficiency of the proposed solutions to reduce the radar cross antenna cover.Control of many radio physical and electrical parameters of the individual layers that make up the coat, and the results of optimization of individual fragments of the aircraft is carried out in the course of radio-physical experiments. To study themacroscopic properties of substances of the behavior of the frequency dispersion of dielectrics, ferromagnetic materials, fine particles made from ferromagnetic alloys, semi-transparent thin island films used laboratory equipment that must satisfy all therequirements of modern physics laboratories involved in the electrodynamics of continuous media. In addition, you need specialMaterials Research and chemical equipment for the study of the properties of composites developed.Fragments of the aircraft covered by radar absorbing and dissipating coatings investigated in the so-called anechoic chambers.They simulate the conditions realized in the real space in the situation in which the object falls flat and there is electromagneticwave reflections from the underlying surface. Create anechoic chambers with low noise requires skillful work, skills whichRussian scientists hold to the extent that these cameras are exported to industrialized countries. Once the main pieces of theaircraft will be tested in an anechoic chamber, made technological amendments, if necessary, and implemented a fulltechnological cycle of work on the plane. In the process it is a continuous monitoring of Radio.All of the above technological development is carried out in our country and in leading foreign countries. We demonstrate theglobal trend of the radar signature of supersonic maneuverable aircraft (Fig. 6). If in the 1980s, aircraft such as the F-15 had anESR of more than 10 m
2
then upgraded aviation complex EPR is 1-1.5 m
2,
while the prospective fifth-generation aircraft systemssuch as the F-22, JSF, - 0.3 m
2
. An even smaller value of the EPR in the modernized Russian MiG-21.
Fig.
6.
Trends in the radar signature of supersonic aircraft
Measures to reduce the visibility of the aircraft should be coordinated with the capabilities and requirements of electroniccountermeasures. Reduction of visibility, of course, reduces the power consumption of electronic countermeasures, but moreimportantly, the use of electronic counter-stealth aircraft provides a significant advantage in the air.In the foreign literature it is possible to find estimates of the probability of loss of aircraft depending on the EPR (Fig. 7).Reducing the EPR 10-15 m
2
- values typical for heavy fourth-generation fighter, to 0.3 m
2
enables fundamentally reduce the lossof aircraft in combat. This effect is enhanced by simultaneously using aircraft having a low ESR, use modern means of electronic countermeasures (Fig. 8).
Fig.
7.
Losses in overcoming aircraft defense according to their effective surface scattering
Fig.
8.
Effect of combined application of anti-radar equipment and toreduce the radar signature of loss of aircraft
It should be remembered that at the first stage of the construction of the new aircraft must be addressed if we are ready to put inas a task number 1 may receive a small value of the EPR to the detriment of many other properties of the aircraft or will strive tomaintain a good aerodynamics of the aircraft when it reaches the level of its small radar signature. Examples of the firstapproach - this aircraft F-117 and B-2, the shape of which is optimized to achieve low ESR to the detriment of their aerodynamic properties, examples of the second approach - this aircraft F-22, JSF, and others.Obviously, when you create a new aircraft with low ESR values required design and technology activities to optimize the shapeof an airplane: to ensure a smooth transition between the elements of the airframe, the exclusion of the outer suspension arms -carry weapons inside the fuselage. In turn, this requires the fuselage longitudinal stiffness, entering into the construction of additional hydromechanical units start and reset safety arms and even changes targeting algorithms.One of the technological methods that reduce the visibility of the aircraft - the use of large-size panels of complex shape aselements of the fuselage structure (Fig. 9). Installing a panel can be reduced significantly by joints on the surface skins of aircraft riveting and bolting elements that are reflected in the forward hemisphere at different angles.
Technological processes of manufacture and assembly of aircraft must meet the minimum clearances between the elements andthe units located on the outer surface: doors, hatch covers, etc. Complex technological problem is the creation of besperepletnycockpit canopy to avoid the connecting arcs, degrade visibility of the aircraft.When all the measures aimed at reducing the radar signature is required optimization of complex avionics. Telltale signs caused by his work, becomes important against the background of reduced radar signature aircraft. It is envisaged to minimize the timeof the onboard equipment in raioelektronnogo radar radiation, the use of bistatic radar mode. Wanted secretive methods of liaison aircraft in the group. Two planes are paired, and one of them emits a signal and the second operates in passive mode andis not detected by the locator opponent. Using computational power of the onboard equipment, maps and a variety of other techniques can determine the mode-locked position of the aircraft and combat missions.You need to ensure the effectiveness of all the activities. Naturally, the most objective criterion of effectiveness would beinvolved in a real conflict, which, fortunately, has recently been trying to avoid most of the countries. However, the process of testing aircraft from the point of view of studying their radar signature is required and has a number of specific features. The probability of detection is proportional to the EPR, is a statistical value and depends on many factors, including the weather and,of course, of course the aircraft with respect to the radar.Flight tests precede the ground when the aircraft shall be observed from different angles. Land measuring system (Figure 10)allows you to get a pie chart of the EPR in a wide range of wavelengths. Measurements can be made with the engine running, itis important to determine the EPR in the rear hemisphere. It is also possible to estimate the contribution of individual elementsin the plane of the EPR. Then the ESR is measured in terms of aircraft flying with simultaneous evaluation of detection range.For a set of statistics to a large number of experiments on the ground and in flight. In particular, during the works to reduce theradar signature of the fourth-generation aircraft such as the Su-27 for a set of statistics required more than 100 hours of continuous operation of radar stations on the ground and stand more than 30 hours - in flight. In some cases, comparativeevaluations were paired flights, which involved nearly invisible and conventional aircraft.
Fig.
10.
Aircraft on a turntable ground measuring complex
To summarize, we can say that as a result of research and development addressed a number of fundamental and applied problems of the stele technology: developed computational and experimental methods, and complex technology to reduce thevisibility, refined and tested a fourth-generation aircraft such as the Su-27, proposed radio-absorbing materials not is inferior tothe best foreign models. We believe that this area needs further development in order to strengthen the country's defense. Stealthtechnology can be used in the modernization of aircraft were in service, and development of advanced aircraft systems.
https://www.scribd.com/document/152376871/Fundamental-and-Applied-Problems-STEALTH-TECHNOLOGY
σ =πR 40S s/ Si,
where R
0
- the distance between the transmitter and the object;
S s
- the energy flux density of the scattered wave near thereceiver; S
i
- the energy flux density of the incident wave near the body.ESR value depends on the orientation of the object relative to the beam and radar wavelength of electromagnetic radiation. For physicists, the best analogy EPR - is the differential scattering cross section is back. If we consider the frequency dependence of the EPR metal sphere (Fig. 1), in the wavelength range of low ESR coincides with the area of its cross-section. At wavelengthscomparable to the size of the ball, having diffraction minima and maxima.
Fig.
1.
Frequency dependence of the effective scattering surface of ametallic sphere
a - radius of the sphere,
λ
- Wavelength
Figure 2 shows the EPR cylinder depending on the angle of incidence of the electromagnetic waves to the wave vector in the plane which passes through the axis of the cylinder, Figure 3 - EPR modern aircraft for different directions of incidence of theelectromagnetic waves in the horizontal plane passing through the axis of the aircraft. Because of the complex shape of theobject to its ESR showed significant fluctuations in value at a very small change in the angle of incidence of the electromagneticwave. Such a situation arises due to diffraction phenomena and the subsequent interference of electromagnetic waves reflectedfrom various parts of the aircraft with a corresponding phase delay of each reflecting element.
Fig.
2.
The angular dependence of the effective scatteringsurface of the cylinder
D and L - the diameter and length of the cylinder,
θ
-the angle of incidence of the electromagnetic wave,the arrow shows the direction of its fall
Fig.
3.
"Facet" model of the Su-27 (top) and a diagram of the effectivesurface scattering plane
depending on the viewing angle in the horizontal plane (bottom)
The solid line corresponds to the scatter plot of the real plane, dotted - aircraft with a reduced radar signature, 1, and2 - averaged over a range of angles of ± 30 °, the values of the EPR Naturally, in practice, the values of interest in EPR averaged over a relatively small range of angles, due to the unavoidablevibrations because the trajectory is determined average level of the signal processed in the receiver. The task of the steletechnology is the maximum possible reduction of the EPR aircraft. For example, a qualitative leap in the capabilities of combataircraft would occur in the case if, instead of EPR shown in Figure 3 by a solid line, it was possible to obtain the ESR as shownin phantom in the same figure.Stealth technology includes the following main areas: the theory of diffraction on complex bodies, the development and study of radar absorbing materials, coating technology and, finally, Radio Physics experiment is used to control each of these areas.Currently stealth technology begins with the mathematical modeling of electromagnetic wave scattering at the facility, radar signature which has to be reduced. This step is of fundamental importance for the preliminary assessment of the achievableresults and to optimize the shape and electrical characteristics of the object. Mathematical and computational models are basedon the solution of boundary value problems of electromagnetic waves on bodies of complex shape, having in its composition,special materials and coatings. Capabilities of modern computers allow you to create software for the simulation of electromagnetic wave scattering even for complex objects such as aircraft and ships, taking into account the diversity of rigginghardware, cracks, hatches, and many other seemingly minor details of construction.On the world market offers several software packages that are suitable for such modeling. All of them are used in thedevelopment of "facet" object model, which will be mentioned below, and the method of the physical theory of diffraction. For well-known reasons, due to closeness of such works, until recently in the national press (as opposed to the foreign press) werenot published details of a particular application of mathematical modeling of scattering objects of weapons and militaryequipment. However, the analysis of scientific literature on the theory of diffraction of specialists in the field of electrodynamicswas not difficult to assess the level of development of the industry.The contribution of Russian scientists in the theory of diffraction is not only significant, but also in many important areas of basic. Suffice it to mention the names of Academician VA Fock, professors EN Vasilyev and PY Ufimtseva. VA Fok is notonly the first to formulate the integral equation for the current on the surface of the irradiated metal body, but the proposedapproximate solution for the phone with a large radius of curvature. Pioneering work was E. Vasiliev on the numerical solutionof integral equations in electromagnetic excitation of metal. PY Ufa - the founder of the method of edge waves in the physicaltheory of diffraction, which is of paramount importance in the development of stealth action recognized by the internationalscientific community. That numerical methods for solving the problems of scattering on the basis of integral equations,evaluation of the scattering properties of the method of boundary waves, and the combination of these techniques have been used by us in numerous electrodynamic models of objects with low radar signature.Employees of the Institute of Theoretical and Applied Electrodynamics, Russian Academy of Sciences for many yearsdeveloping numerical methods, building on the achievements of both Russian and foreign schools of diffraction theory.Application of asymptotic and hybrid algorithms requires a clear understanding of the physical phenomena which lead to theformation of the scattered field in each case: specular reflection, diffraction at the edges, traveling waves, multiple reflections
within the cavities, etc. Accounting mirror images of real objects is realized through the development of "facet" models, wherethe surface of the object is represented as a large number of individual flat areas of simple shape (see Fig. 3).In the calculation of the EPR large (in wavelengths) of compound bodies is essential that at relatively high frequencies candistinguish the individual fragments of the structure of objects that at a given angle are the main contributors to the formation of the scattered field. This makes it possible to perform calculations of scattering centers independently of one another, if appropriate taking into account their reciprocal influence on the subsequent stages. Accuracy of calculation of the characteristics of the scattering centers is of particular importance in the analysis of subtle detail, so much attention has been paid to the development and improvement of relevant electrodynamic models. The classical model of this kind is considered to be a wedge(edge). In this model, the infinite boundaries are accounted for using the results of the physical theory of diffraction, and thefields and currents in a finite region of space near the edges are determined by numerically solving the equations of the electromagnetic field. The allocation of individual scattering centers can also analyze specific diffraction phenomena peculiar to this structure, and to identify their dependence on a small number of local parameters.Role of numerical methods is extremely high, when the characteristic dimensions of the object fragments much larger than the wavelength, but because of high diffraction approximation processes do not provide the desired accuracy. In this fragment,creating the main contribution to the scattered field in the front hemisphere of the aircraft, powerplant is the air intake system of the engine inlet vanes. Using a hybrid approach allows independent consider the passage of electromagnetic waves via the air intake system and diffracted by the blades. However, the calculation of the scattering wave at the inlet of the engine having a transverse dimension of tens of wavelengths, and consisting of a plurality of elements of complex shape - an independent task that requires the use of rigorous methods and their efficient numerical implementation. The developed software allows you to perform the necessary calculations with sufficient accuracy (Fig. 4).
Fig.
4.
Model inlet plane (a) and the effective surface of the scattering diagram inlet (b)
Comparison of the calculated and experimental data shows good accuracy of the software Creating adequate electrodynamic model of such a complex object, like an airplane, requires a combination of methods physics,electrodynamics, computational mathematics, signal processing. As a result of extensive experience in programming,computational tasks and the effective use of the technology of modern computing. In particular, the importance of the integration of specialized software: the computational core, designed to determine the scattering properties, and engineering design systems, with which the transfer of the design documentation (in electronic form), the preparation and modification of the data on the form and structure of the object, the analysis output data. A widespread system of AutoCAD, from which data are transmitted in electromagnetic simulation models through a special interface.In the short-term progress in the development of methods for calculating the scattering properties of complex objects is largely due to the good organization of work, raising the necessary specialists, good information and technical support, as it seems to us,many of the fundamental issues that existed previously in this area have been resolved.Applied to the various elements of the aircraft radio-absorbing coatings are different from those used 10-15 years ago. Modern coating to have a variable thickness profile, a complex structure with varying values of permittivity and permeability as the thickness of (normal to the surface), and along the skin surface. Solving the fundamental problems associated with the passage of electromagnetic waves through a heterogeneous environment, studying the behavior of heterogeneous mixtures near the percolation threshold, the researchers learned how to create a substance with any frequency behavior of the real and imaginary parts of the dielectric constant, of course, within the framework of the principle of the Kramers-Kronig relations. Creating materials with an arbitrary behavior of the magnetic permeability is associated with some additional restrictions. Modern designer to optimize the ESR of a fragment of the plane and picking up for this purpose permittivity and magnetic permeability of the material, its thickness distribution over the surface of the fragment can be sure that in the future technology will reproduce the required parameters. Note also that the conduct of the relevant optimization requires considerable prior experience, because it is necessary continually to find a compromise between the desire for minimum reflection, the thickness of the material, its strength and, finally, the aerodynamic properties of a movie.Coating use very different technologies. Most of the aircraft surface is covered by paint technology. Despite the apparent simplicity of this technique is most responsible, because of its contribution to the quality depends EPR one major plane of the scattering element - its inlet, moreover, the adhesion to the air inlet cover may cause damage to the aircraft. Multilayer radioabsorbing coatings are deposited using a robotic systems in series production aircraft, or manually when creating experimental models of equipment.A daunting task is the production of fine ferromagnetic fillers with the given values of the magnetic permeability. Currently,using special technology, it is possible within a wide range of ferromagnetic fillers to modify the spectra in the microwave region. Combining ferromagnetic inclusions with inclusions of other types, create the desired set of broadband radar absorbing coatings. Their further development is not possible without addressing many fundamental questions
Fig.
5.
Scheme reflection of electromagnetic waves from the cowl to thesemiconductor controlled screen (a), the change in resistance of semiconductor films, depending on the light conditions (b) and the scheme of the reflection of electromagnetic waves from the fairing with a controlled display (c)
On the chart: dark rectangle corresponds to the conductivity of thefilms, providing transparency screen, gray rectangle - the level of conductivity, providing metallization surface fairing, 1 - theresistance of existing semiconductor films, 2 - resistance hypotheticalfilms that will realize the idea of a semiconductor managed ScreenGenerally speaking, the resistance of semiconductor doped CdS films CdSn or change by many orders of magnitude at quitereasonable levels of illumination (curve 1 in Fig. 5b). However, they are not suitable for implementing the above-describedtechnical solutions. Required film to other dynamic properties (curve 2 in Fig. 5b), but how to make it, is not very clear.Another technical solution - to the locator installation screen on the surface of which has the so-called frequency-selectivestructure - the system some form of periodic apertures that are configured so that they freely passed in either direction of theelectromagnetic wave in a narrow band radar eigenfrequencies and fully reflect the electromagnetic wave other frequencies.Introducing these specially organized aperture, which substantially represent open resonators semiconductor control system can,if desired, to "close" the screen, making it opaque to all frequencies.The problem of frequency-selective surfaces is an extensive literature from which to draw conclusions about the features of their application. We have developed numerical methods for calculation of frequency-selective screens possess appropriatetechnology and built working models of managed screens. Depending on the antenna design can be used as a frequency-selective screen, and plasma. It is mounted inside the shroud in same manner as the frequency-selective screen, but its operation principle somewhat different. In the absence of a control signal, which can be supplied to the aircraft or the pilot station to detectthe external irradiation, the screen is turned off and is transparent at all frequencies. When a signal voltage is applied to thescreen, it collisional low temperature plasma is ignited as a result of radiation is partially reflected from the screen in thedirections shown in Figure 5 in, and partially absorbed in the screen. Effective screen to electromagnetic radiation of frequencylower than the plasma. Meaning plasma frequency in such systems can be very large. Long-term studies of processes in low-temperature plasma, allowed to find the optimal parameters for the composition of gases produced by the plasma, and optimizehigh-speed plasma generation system needed to respond to the rapidly changing external environment. Flight tests demonstratethe high efficiency of the proposed solutions to reduce the radar cross antenna cover.Control of many radio physical and electrical parameters of the individual layers that make up the coat, and the results of optimization of individual fragments of the aircraft is carried out in the course of radio-physical experiments. To study themacroscopic properties of substances of the behavior of the frequency dispersion of dielectrics, ferromagnetic materials, fine particles made from ferromagnetic alloys, semi-transparent thin island films used laboratory equipment that must satisfy all therequirements of modern physics laboratories involved in the electrodynamics of continuous media. In addition, you need specialMaterials Research and chemical equipment for the study of the properties of composites developed.Fragments of the aircraft covered by radar absorbing and dissipating coatings investigated in the so-called anechoic chambers.They simulate the conditions realized in the real space in the situation in which the object falls flat and there is electromagneticwave reflections from the underlying surface. Create anechoic chambers with low noise requires skillful work, skills whichRussian scientists hold to the extent that these cameras are exported to industrialized countries. Once the main pieces of theaircraft will be tested in an anechoic chamber, made technological amendments, if necessary, and implemented a fulltechnological cycle of work on the plane. In the process it is a continuous monitoring of Radio.All of the above technological development is carried out in our country and in leading foreign countries. We demonstrate theglobal trend of the radar signature of supersonic maneuverable aircraft (Fig. 6). If in the 1980s, aircraft such as the F-15 had anESR of more than 10 m
2
then upgraded aviation complex EPR is 1-1.5 m
2,
while the prospective fifth-generation aircraft systemssuch as the F-22, JSF, - 0.3 m
2
. An even smaller value of the EPR in the modernized Russian MiG-21.
Fig.
6.
Trends in the radar signature of supersonic aircraft
Measures to reduce the visibility of the aircraft should be coordinated with the capabilities and requirements of electroniccountermeasures. Reduction of visibility, of course, reduces the power consumption of electronic countermeasures, but moreimportantly, the use of electronic counter-stealth aircraft provides a significant advantage in the air.In the foreign literature it is possible to find estimates of the probability of loss of aircraft depending on the EPR (Fig. 7).Reducing the EPR 10-15 m
2
- values typical for heavy fourth-generation fighter, to 0.3 m
2
enables fundamentally reduce the lossof aircraft in combat. This effect is enhanced by simultaneously using aircraft having a low ESR, use modern means of electronic countermeasures (Fig. 8).
Fig.
7.
Losses in overcoming aircraft defense according to their effective surface scattering
Fig.
8.
Effect of combined application of anti-radar equipment and toreduce the radar signature of loss of aircraft
It should be remembered that at the first stage of the construction of the new aircraft must be addressed if we are ready to put inas a task number 1 may receive a small value of the EPR to the detriment of many other properties of the aircraft or will strive tomaintain a good aerodynamics of the aircraft when it reaches the level of its small radar signature. Examples of the firstapproach - this aircraft F-117 and B-2, the shape of which is optimized to achieve low ESR to the detriment of their aerodynamic properties, examples of the second approach - this aircraft F-22, JSF, and others.Obviously, when you create a new aircraft with low ESR values required design and technology activities to optimize the shapeof an airplane: to ensure a smooth transition between the elements of the airframe, the exclusion of the outer suspension arms -carry weapons inside the fuselage. In turn, this requires the fuselage longitudinal stiffness, entering into the construction of additional hydromechanical units start and reset safety arms and even changes targeting algorithms.One of the technological methods that reduce the visibility of the aircraft - the use of large-size panels of complex shape aselements of the fuselage structure (Fig. 9). Installing a panel can be reduced significantly by joints on the surface skins of aircraft riveting and bolting elements that are reflected in the forward hemisphere at different angles.
Technological processes of manufacture and assembly of aircraft must meet the minimum clearances between the elements andthe units located on the outer surface: doors, hatch covers, etc. Complex technological problem is the creation of besperepletnycockpit canopy to avoid the connecting arcs, degrade visibility of the aircraft.When all the measures aimed at reducing the radar signature is required optimization of complex avionics. Telltale signs caused by his work, becomes important against the background of reduced radar signature aircraft. It is envisaged to minimize the timeof the onboard equipment in raioelektronnogo radar radiation, the use of bistatic radar mode. Wanted secretive methods of liaison aircraft in the group. Two planes are paired, and one of them emits a signal and the second operates in passive mode andis not detected by the locator opponent. Using computational power of the onboard equipment, maps and a variety of other techniques can determine the mode-locked position of the aircraft and combat missions.You need to ensure the effectiveness of all the activities. Naturally, the most objective criterion of effectiveness would beinvolved in a real conflict, which, fortunately, has recently been trying to avoid most of the countries. However, the process of testing aircraft from the point of view of studying their radar signature is required and has a number of specific features. The probability of detection is proportional to the EPR, is a statistical value and depends on many factors, including the weather and,of course, of course the aircraft with respect to the radar.Flight tests precede the ground when the aircraft shall be observed from different angles. Land measuring system (Figure 10)allows you to get a pie chart of the EPR in a wide range of wavelengths. Measurements can be made with the engine running, itis important to determine the EPR in the rear hemisphere. It is also possible to estimate the contribution of individual elementsin the plane of the EPR. Then the ESR is measured in terms of aircraft flying with simultaneous evaluation of detection range.For a set of statistics to a large number of experiments on the ground and in flight. In particular, during the works to reduce theradar signature of the fourth-generation aircraft such as the Su-27 for a set of statistics required more than 100 hours of continuous operation of radar stations on the ground and stand more than 30 hours - in flight. In some cases, comparativeevaluations were paired flights, which involved nearly invisible and conventional aircraft.
Fig.
10.
Aircraft on a turntable ground measuring complex
To summarize, we can say that as a result of research and development addressed a number of fundamental and applied problems of the stele technology: developed computational and experimental methods, and complex technology to reduce thevisibility, refined and tested a fourth-generation aircraft such as the Su-27, proposed radio-absorbing materials not is inferior tothe best foreign models. We believe that this area needs further development in order to strengthen the country's defense. Stealthtechnology can be used in the modernization of aircraft were in service, and development of advanced aircraft systems.
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