The radar device masking of the jet engine air intake

 

(57) Abstract:

The invention relates to the field of radar technology, and can be used to reduce reverse radar reflections from the inlet jet engine. The technical result is to reduce the level of radar reflections from the channel inlet jet engine when irradiated by a wide range of lengths of waves. The device consists of a solid metallic grid with square cells and form, repeating the cross-sectional profile input window vent. Having docked to the outer edge of each cell of metallized sheets in the form of isosceles triangles allows to reduce by 2 to 4 dB level radar reflections from the air intake in a wide range of wavelengths. 8 Il.

The invention relates to the field of radar technology, and can be used to reduce reverse radar reflections from the inlet jet engine.

Experience of research in radar characteristics of such complex objects, such as aircraft, showed that the greatest contribution to its effective ilocation station, cockpit and several others. Experimentally verified that for angles in the sector nasal angles conventional aircraft from all sources of reflection engines are dominant [1]. Therefore, in the world practice is widespread methods and devices radar camouflage air intake duct of the engine [2]. The closest technical solution to the claimed is a method and apparatus for masking the inlet jet engine [3], which consists in the fact that the air intake box 1 (Fig. 1) is divided into multiple cells or channels of smaller size 2, which prevent the penetration of the incident electromagnetic waves 3 in the intake channel 4, reflecting them in the opposite direction and, practically, do not increase the resistance to air flow. A device that implements this method is a three-dimensional lattice with a square cell with the outer edge 5, is a formed metallic plates 6 width a and thickness h (h << a), with electrical contact at the nodes and form, repeating the cross-sectional profile input window vent. However, this device prevents the penetration of electromagnetic waves inside the substantial limitations when using it in practice. Thus, this device has the following disadvantages:

c a decrease in the length of the electromagnetic wave shielding intake is required to reduce the size of the grid cell to a size smaller wavelength, which, ultimately, will significantly increase the resistance of such grate air flow;

if you build a grid with cell sizes from units of wavelengths and more, its shielding properties will be completely lost, moreover, such a lattice periodic structure will be a good Omni-directional reflector with multi-leaf diagram back reflections with high levels of EPR.

Based on these shortcomings of the existing device can be used effectively only under very limited conditions.

The aim of the present invention is to reduce the level of radar reflections from the channel inlet jet engine when irradiated by a wide range of lengths of waves.

This objective is achieved in that the outer edge of each cell of the lattice pristykovyvayas metallized sheet in the form of an isosceles triangle 7 thickness h, base equal to the edge a, and the other is a 2; h < 0,1; < 60,

where is the wavelength of the radiation.

The presence of metallic triangular plates, paired with the outer edges of the cells of the lattice (triangular ends), provides:

the destruction of the periodic structure of the lattice as Omni-directional radar reflector;

smooth coordination flat front of the incident electromagnetic wave and the absorption in the structure of the lattice as in the fall of waves from the outside and passed through the bars and penetrates in the opposite direction (the effect of "besedovschi");

the possibility of suppression of surface waves generated by the outer edge of the grate and extending along the planar face of each cell in the opposite direction.

Explain each of the allegations.

The outer edge of the metallic plate, forming a lattice-prototype period and when , are complex reflector. The fall of waves on a periodic series of metallic plates in the device prototype will be accompanied by the diffraction of waves on the edges of the plates and the formation of the reflected wave. Due to diffraction at the edges of the plates there is a rather complex field. This field will be present in order to be in phase. Let us consider in more detail the mechanism of scattering. Let the anglei(Fig. 3) indicates the direction of the incident wave. This wave will occur if the line BD is perpendicular to the direction of propagation of the wave, is a wave front, or in other words, the fields at the points b and D are in phase. Field of the incident wave at the points A and C or AC perpendicular to the direction of propagation of the incident wave are in phase. Field at points B and D will be in phase if the difference is equal to an integer number of waves

< / BR>
where a = 0,1,2,3,....

According Fig. 3

< / BR>
therefore,

sini-sins= (/a).

Obviously, growth and (in wavelengths) the number of angles that reflected from the edges of fields are added in phase, will grow. In the end, the reflected field will have a sustainable multi-leaf structure, where the maximum levels of EPR's petals will be determined in the approximation of physical optics [5] , by analogy with the linear lattice of different reflectors, based on the ratio of

< / BR>
where k is the number of cells in the plane orthogonal to ,

= 3,1415926,

h - thickness of the plates,

a - distance between the plates (the edge length of the cell),

- wave length.

The presence of triangular metallic plate, p is the expansion of the structure. As a consequence, the lattice as a whole is fairly smooth transition environment settings from the metal to the free space, so the wave reflected from the boundary between decreases in amplitude. In addition, the perimeter of jagged edges flowing currents of different phase and direction, so the average level of effective excitation of edges in a plane lower than in the rectilinear edge. Accordingly decreases to 5-6 dB level of the diffraction fields associated with the edge, as for reflected waves, and waves that passed inside the channel intake [6].

Smooth coordination flat front incident electromagnetic wave with the structure of the lattice is provided by metallic triangular tip with the angle at the vertex of less than 60o. This design provides multiple reflection of the incident waves between the sloping edges of the triangles. In Fig. 4 shows the course of the rays in the space between the triangular ends. If to characterize reflected from this design electromagnetic wave reflection coefficient power qmthe power flux-density of the reflected wave will be determined from the relation

< / BR>
where n is the number of suusi material triangular ends.

Practical experience shows that for this structure qmcan reach about 20 dB [7].

Along with this, the triangular ends allow you to suppress the level of reflection of surface waves at 32 dB in directions close to the normal of the lattice [8].

The proposed device was tested in the open measuring polygon [9], as evidenced by the "test report".

The substance of the proposed technical solution is illustrated in Fig. 5 - 8.

In Fig. 5 shows the geometry and dimensions of the experimental model of the channel inlet jet engine (hollow metal cylinder, open on one side).

In Fig. 6 - scheme of dimension EPR model channel inlet jet engine device of radar camouflage.

In Fig. 7 shows the dependence of the median values of ESR (0,5dB) model feed intake in 20-degree sectors from a corner location Q at wavelengths: 0,86 cm - b, 3.2 cm - c, 10.7 cm d 17 cm - e,

where:

f - channel model of the air intake with the proposed device masking (a = 7 cm, h = 0.1 cm; = 40);

g - model of the channel inlet with device-prototype (a = 7 cm; 8 presents the integral distribution laws EPR (P()) of a channel model of the air intake in the sector location 30 degrees relative to the normal to the input box, air intake obtained for the respective wavelengths (b, c, d, e) and the above configuration (f, g, i).

The analysis shown in Fig. 7 and 8 results allows to conclude that (Act tests...) that the proposed device masking channel inlet jet engine in comparison with the device of the prototype allows to reduce the median values of EPR in the sector location 30 degrees relative to the normal to the input box intake from 2.3 to 4 dB in the wavelength range from millimeters to decimeters (from 0.86 cm to 17 cm).

The proposed device also provides better than the prototype radar masking channel of the air intake in the areas of location, different from normal. This ensures reduction in the median RCS values from 3 to 10 dB.

Implementation of the claimed device is not difficult. It is obvious that the invention is not limited to the above example of its implementation. Based on its schema can be provided by other variants of its realization, is not beyond the scope of the subject invention. For example, it is obvious that the application of a thin layer of radar absorbing coatings or materials on the surface of the device will improve the="ptx2">

The proposed device should be used in organizations as modernization of existing and development of future aircraft with low radar visibility.

The radar device masking intake of an aircraft engine, which represents a repeating profile input window vent volumetric grid with square cells, with the outer edge, equal and formed of intersecting metallic sheet width and thickness h with electric contact at the nodes, wherein the outer edges of a volume grating docked metallized sheet in the form of an isosceles triangle with thickness h, with base equal to the outside edge, and opposite the base of an acute angle , while the lattice parameters of bulk and isosceles triangles are selected on the basis of ratios

a2; h<0,1<60 ,

where is the wavelength of the radiation.

 

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