RU2273924C1 - Radar antenna reflector - Google Patents

Abstract

FIELD: antenna assemblies; passive reflecting beacons or radar-target reflected signal simulators.

SUBSTANCE: radar antenna reflector has cylindrical mirror and additional reflector in the form of linear lattice of greater number of cophasal dipoles whose axes are disposed on same straight line and at equal distance from mirror; equations for selecting distance from linear lattice axis to cylindrical mirror and size of linear lattice dipoles relative to wavelength are given in description of invention. In addition, dipoles can be made of two different-length parts, and disposition of these parts is also stipulated in description of invention.

EFFECT: enlarged effective dissipation area.

3 cl, 5 dwg

Description

The invention relates to antenna devices.

The radar antenna reflector is a two-mirror antenna system used in the reradiation mode of the incident plane wave / 1 /. The main task that he must solve is to provide a larger effective scattering area than with an equal flat reflecting plate / 2 /.

A known antenna, which may be a reflector, consists of a mirror in the form of a parabolic cylinder and a linear irradiator and is used when it is necessary to obtain a back reflection (DOO) diagram, narrow enough in one plane and wide in another, perpendicular to the first. The closest in technical solution is a radar antenna reflector (figure 1), containing a cylindrical mirror 1 and an additional reflector 2 in the form of a linear array of a large number of in-phase vibrators 3, whose axes are located along a straight line at the same distance f from the mirror / 3 /. It is quite obvious that for such an antenna, which can be a reflector at the same time, they primarily try to construct a linear array of vibrators in such a way that the main lobe of the radiation pattern has the required width and the level of side lobes is minimal. Compliance with these requirements contradicts the conditions that ensure an increase in the effective scattering area of the antenna as a radar reflector and is its main drawback.

The purpose of the invention is to increase the effective scattering area.

This goal is achieved provided that in a known antenna with a mirror in the form of a parabolic cylinder, the distance from the axis of the linear array to the cylindrical mirror f, the number of vibrators n located with step d in the linear array and wavelength λ will be related by the relation

λ / 2π≤f <{2 [(n-1) d] ² } / λ,

where d> λ, π = 3,1415926 ....

It is known that an example of an additional reflector is a linear array of a large number of in-phase vibrators whose axes are located on one straight line. With a sufficiently long linear reflector, we can assume that in a limited region of space the field reflected from it has the character of cylindrical waves, neglecting the field distortions that inevitably occur near the first and last element (vibrator) of the additional reflector. At a very large distance from the linear reflector, the reflected field has the character of spherical waves. It follows that the region where the cylindrical mirror should be in relation to the linear reflector is determined by the distance, much larger compared to the wavelength, but less than the distance to the wave (far) zone, where the field has the nature of spherical waves (figure 2 ) If the length of the linear reflector is represented as (n-1) d, where n and d are the number of vibrators and the step length in the grating, respectively, and f is the distance from the axis of the linear reflector to the mirror (in a plane perpendicular to the cylinder generatrix), then all possible f values must be within

λ / 2π≤f <{2 [(n-1) d] ² } / λ,

otherwise the mirror will be outside the region of cylindrical waves. When reflected from a parabolic cylinder, the front of the cylindrical wave becomes flat, therefore, such a reflector can be considered as a reflector with a rectangular opening and in-phase distribution of the field. In this case, the monostatic effective scattering area (EPR) of a cylindrical radar reflector irradiated along the normal to the aperture is determined by the expression σ _m = ΩS ² / λ ² , where Ω is the angle of the solid cylindrical segment expressed in steradians with a vertex on the axis of the linear grating and bounded by the edges of the mirror , S = hd (n-1). If a plane wave falls on a cylindrical opening at a certain angle θ, then the value of the monostatic EPR decreases rapidly, and the expression for a cylindrical antenna can be written in approximate form as

σ (θ) = σ _m [F (θ)] ² ,

where F (θ) is the normalized antenna radiation pattern in power in the radiation (reception) mode. In order that the value of the monostatic EPR of the reflector with a change in the angle θ does not decrease rapidly, it is proposed to create conditions that would ensure that a large number of diffraction maxima appear in the plane coinciding with the axis of the linear grating (azimuthal plane). Their formation occurs when d> λ. In this case, the number of diffraction maxima i per unit of azimuthal angle is determined by the lattice spacing and is approximately equal to i≈ (4d / λ) cos ((rad ^-1 ) / 1 /.

The reflector works as follows. A plane electromagnetic wave is incident on the reflector along the normal to its opening. The wave is focused by the cylindrical mirror 1. The cylindrical wave is reflected normally to the vibrators 3 of the linear array 2, located at a given distance from the mirror, excites them and is reflected back to the mirror in the form of a cylindrical wave. Obviously, the part of the wave scattered by the linear lattice after the second reflection from the mirror in the form of a plane wave will return in the direction of the incoming wave. So reflects the in-phase aperture, approximately equal to the area of the cylindrical aperture. When a plane electromagnetic wave is incident on the reflector from directions other than normal, the linear array of vibrators together with the reflector will form a complex multilobe diffraction pattern in a wide sector of viewing angles.

Obviously, the EPR value of each diffraction maximum σ _I will depend on the EPR value of a single vibrator σ _n and their number n in the linear lattice. For example, for a half-wave vibrator (0.5λ), the value of its EPR in the case of the polarization of the incident electromagnetic wave coinciding with the vibrator axis is approximately equal to σ _n ≈λ ² . Thus, the diffraction peak value of the ESR will be given by σ _i ≈ (nλ) ^2/1 /. The choice of the d / λ ratio provides the required number of diffraction maxima in a wide sector of the angles of the azimuthal plane. The presence of a cylindrical mirror allows, due to repeated reflections from it, to additionally increase the EPR value of diffraction maxima by about an order of magnitude.

In the case of a normal incidence of a plane electromagnetic wave on a half-wave vibrator, its DOE has a width in the azimuthal plane not exceeding 0 ± 30 ° (Fig. 3), this in turn leads to a decrease in the EPR values of diffraction maxima formed at angles θ> 30 °. To form diffraction maxima with constantly high EPR values, the DOO of an individual vibrator should be expanded. For this, it is proposed that each vibrator in the linear array be made of two parts of different lengths and separated by a distance of 0.01λ: the first part should be equal to half the wavelength, the second should be equal to five-fourth of the wavelength and positioned in relation to neighboring vibrators so that from the side part of a small length was part of a larger length of the adjacent vibrator, and on the part of the part of large length was part of a shorter length of the neighboring vibrator and so on along the entire length of the linear array. Most of the vibrator with a length of five fourth wavelengths has a petal DOO (Fig. 3) / 4 /, therefore, a combination of two parts of different lengths allows you to form the total DOO of the vibrator, wider (up to 0 ± 60 °) than the DOO of the half-wave vibrator .

The essence of the proposed technical solution is illustrated by figures 1-5, which shows the radar antenna reflector and the results of its experimental studies in the conditions of the Reference radar measuring complex 2 Central Research Institute of the Ministry of Defense of the Russian Federation / 5 /.

Figure 1 shows a General view of the radar antenna reflector.

Figure 2 - geometry of the formation of cylindrical waves.

Figure 3 shows the normalized DOO vibrators with a length of 0.5λ and 1.25λ in free space.

Figure 4 shows the DOO of the same size radar antenna reflectors (mirror size 4λ × 100λ) in the sector of viewing angles 0 ± 90 °:

k - with a reflector in the form of a linear array of identical vibrators 0.25λ long each, separated by a gap of 0.01λ (prototype);

q - with a reflector in the form of a linear lattice with a period of d = 2λ from the same vibrators with a length of 0.5λ each.

Figure 5 shows the EPR histograms (upper part of Fig. 5) and the distribution function of the EPR values (lower part of Fig. 3) in the sector of viewing angles 0 ± 60 ° for the corresponding radar antenna reflectors (k) and (q).

An analysis of the results shown in FIGS. 4 and 5 allows us to conclude (Test report ...) that the proposed radar antenna reflector in comparison with the prototype reflector allows to increase the median EPR values (by probability level 0.5) in the location sector 0 ± 60 ° relative to the normal to the opening of the mirror to 11.7 dB.

The implementation of the inventive reflector is not difficult. Obviously, the invention is not limited to the foregoing example of its implementation. Based on its scheme, other options may be provided that improve its radar characteristics and do not go beyond the scope of the subject invention.

The proposed radar reflector is advisable to use as a passive reflector-beacon or a simulator of the radar signal reflected from the target.

Information sources

1. Kobak V.O. Radar reflectors. M .: "Sov. Radio". 1975.P.211.

2. Radar antenna reflector according to AS USSR No. 1646017, IPC: H 01 Q 15/16, 1991.

3. Eisenberg G.Z., Yampolsky V.G., Tereshin O.N. Antennas of ultrashort waves. M .: "Communication". Part 1. 1977. S. 371-376. (Prototype).

4. Ruck G.T., Barrick D.E., Stuart W. D., Krichbaum C.K. Radar cross section handbook. V.1-2, N.Y. London, "Plenum Press", 1970, p. 298.

5. Sumin A.S. and others. Control for "invisible". AVIA panorama. No. 6. 1997. S. 30.

Claims (3)

1. Radar antenna reflector containing a cylindrical mirror and an additional reflector in the form of a linear array of a large number of in-phase vibrators whose axes are located on one straight line at the same distance from the mirror, characterized in that the distance from the axis of the linear array to the cylindrical mirror f, the number of vibrators n located with a step d in the linear lattice, and the wavelength λ are related by the relation λ / 2π≤f <{2 [n-1) d] ² } / λ, where d> λ; π = 3.1415926 ... 2. The device according to claim 1, characterized in that the length of each vibrator in the linear array is equal to half the wavelength. 3. The device according to claim 1, characterized in that each vibrator in a linear array is made of two parts of different lengths, separated by a distance of 0.01λ, the first part equal to half the wavelength, the second to five fourth wavelengths, and is located in relation to neighboring vibrators in such a way that on the part of the small length is part of the larger length of the adjacent vibrator, and on the part of the long length is part of the smaller length of the adjacent vibrator and so on along the entire length of the linear array.

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