RU2616586C1 - Device for measuring the effective area of scattering of radar objects - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: operation of the device based on the measurement values of the effective area of the scattering diffraction maxima signals reflected from the grating composed of these objects, and comprises a transmitting and receiving unit coupled to the registrar, musculoskeletal swivel unit on which the rotational axis in parallel are fixed equidistantly apart linear equidistant lattice of identical and identically oriented radar objects, forming a two-dimensional lattice, and the change is carried out by a certain law step placement of objects in the line of equidistant arrays.

EFFECT: improved accuracy of measurement of ultra-low values of the effective area of scattering radar objects.

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Description

The claimed invention relates to the field of radar technology and can be used to measure the effective scattering area (EPR) of various objects of radar, comparable and shorter wavelengths.

A known method of measuring EPR using a pulsed location, including placing the object under study in a field emitted by a pulsed locator, measuring the dissipated power and comparing it with the power dissipated by the reference reflectors (Mayzels E.N., Torgovanov V.A. Measuring the dispersion characteristics of radar targets. - M .: “Sov. Radio”, 1972, p. 166-174). However, this method allows you to measure the EPR only in cases where the power of the useful signal is higher than the power of background reflections, i.e. The ESR of the investigated object is higher than the ESR of the background.

There are methods and devices that can solve this problem. A known method based on the irradiation of a linear equidistant lattice (LER), composed of the same and equally oriented objects, and the reception of the signal scattered on it, which is used to judge the EPR of an individual object (Kobak V.O. Radar reflectors. - M .: “Sov Radio ”, 1975, p. 219).

The closest technical solution to the proposed invention is a known device for measuring the EPR of radar objects (SU, copyright certificate No. 491111, MKI G01R 29/10, 1975 - prototype). The design of this device is illustrated in FIG. 1. The device comprises a transmitting unit 1, a receiving unit 2, connected to the recorder 3, a support-rotary unit 4, on which an LER 6 is fixed from the same and equally oriented measured radar objects 5 with a step d ₀ , while the normal to the grating, normal to the flat front of the electromagnetic wave emitted by the transmitting unit and the normal to the flat front of the wave reflected from the grating lie in the same plane.

The advantage of this device is the provision of the possibility of high-precision EPR measurements of radar objects, comparable and shorter wavelengths. It is believed that at the maximums of reflection from the LER, its EPR is close to the EPR of a solitary object, multiplied by the square of their number. The level of excess of the power of the reflected signal over the background required for ESR measurements with a given accuracy is achieved by increasing the number of objects in the array.

However, the known device has a significant drawback. It does not allow measuring the EPR of radar objects with ultra-low reflection levels with the required accuracy: in this case, a grating with such a large number of objects is necessary that its linear size will exceed the size of the measurement zone.

The objective of the present invention is to improve the accuracy of measuring ultra-small values of the effective scattering area of radar objects, the size of which is comparable or less than the wavelength.

The technical result that provides the solution of this problem is to increase the power of the signal reflected by the laser, the size of which is limited by the size of the measurement zone, as well as an increase in the signal-to-background ratio during ESR measurements.

The specified task and obtaining the claimed technical result are achieved due to the fact that in the device for measuring the effective scattering area of radar objects, containing the transmitting unit 1, the receiving unit 2, connected to the recorder 3, the slewing-rotary unit 4, on which, according to the invention, the original LER 6 composed of M measurement objects 5 with a step of d ₀ , is supplemented by parallel to the original lattice at a distance h from each other, in the plane formed by the original LER and the axis of rotation 7, with additional N LER 8 (Fig. 2), each of which consists of M measurement objects with a step d _n , which is selected based on the ratio:

d _n = (1 + 0,1⋅n) ⋅d ₀ , for λ≥d ₀ ≥λ / 2

or

d _n = (1,5-0,1⋅n) ⋅d ₀ , for d ₀ > λ,

where n is the serial number of the additional LER, n = 1, 2, ... N; N≈10;

d ₀ is the step of placing M measurement objects in the original LER;

h is the distance between the electron beam, h≥λ;

λ is the wavelength of the measurement setup.

From the methodology for constructing the LER for measuring ultra-low ESR levels of objects with specified accuracy (Kovalev S.V., Nesterov S.M., Skorodumov I.A. // RE, 1995. T. 40. No. 9. P. 1346) the dependence is known EPR measurement error δ ₁ from the ratio of the size of the measurement zone to the linear size of the electron beam in the direction of maximum reflection:

Where

π = 3.1415926 ...;

L is the linear size of the LER;

R is the location range;

θ _0.5 is the width of the Gaussian antenna pattern at half power level.

It follows from (1) that an increase in the power of the maximum reflection of the electron beam due to an increase in the linear dimensions of the electron beam leads to unacceptable errors in measuring the extremely small EPR values of a single object.

A larger number of M objects in the electron beam with a restriction on its size can be achieved by replacing the linear lattice (Fig. 3a) with a two-dimensional square or rectangular lattice (Fig. 3b). However, its back reflection diagram (DOE) is formed with a high level of side lobes (BL), like that of a linear grating, which does not contribute to an increase in the signal-to-background ratio (Fig. 6, j and f).

To overcome this problem, we will use methods known in the theory of antennas to reduce the level of interference and side lobes in the radiation pattern of phased antenna arrays (PAR). For example, in (Yu.V. Krivosheev, VV Denisenko, AV Shishlov. Suppression of interference maxima in aperiodic phased antenna arrays composed of periodic sublattices // Antennas. 2011. No. 2 (165). P. 26 -39) ways to reduce the BL level in discharged headlights due to the nonequidistant arrangement of emitters are considered. These methods make it possible to reduce the BL level of the antenna array multiplier to -10 ... -12 dB relative to the level of the main lobe (GL), however, their use for measuring the ESR of small objects with a given accuracy is technically difficult.

From the publication (Antenna-feeder and optoelectronic devices. Edited by Prof. BC Verba, Prof. A.P. Kurochkin. - M .: Radio Engineering, 2014, p. 83-89) it is known that to obtain the factor of the PAR with the BL level of the order of -20 dB, the method of line-column arrangement of emitters is used. Reductions in the BL level in it are achieved by changing the distance between the emitters from one horizontal row to another, while in each individual horizontal row the emitters are located equidistantly, i.e. form LER (Fig. 3, c). Distances are chosen so that the GL directions from different horizontal lines, as well as the BLs accompanying them, do not coincide. As a result, when overlapping diagrams in space, the interference lobe of the PAR factor is “blurred” in a wide angular sector.

This method is applicable to justify the scheme and principle of operation of the proposed device for measuring the EPR of objects. Let us compare the DOO of two-dimensional gratings, consisting in the first case of an electron beam with different steps (Fig. 3c) and in the second with the same (Fig. 3b). Note that the BL level (A _BL ) in the horizontal section of the DOO decreases N times based on the ratio A _BL ≈20 log (1 / N), where N is the number of LERs with different steps between the objects. From the ratio it follows that to ensure A _BL = -20 dB, it is sufficient to use at least 10 LERs with different steps between the measured objects. In FIG. Figure 4 shows the dependence of A _BL on the number of LERs with different steps. It follows that the requirement for the level A _BL = -20 dB is fulfilled starting from N≈10.

To estimate the decrease in _{BL BL} , taking into account the partial overlap of BL, we calculated the multiplier of a flat two-dimensional lattice, consisting of measuring objects much smaller than the wavelength, according to the following formula (Antenna-feeder and optoelectronic devices. Edited by Prof. V.S. Verba, Prof. A.P. Kurochkina. - M: Radio Engineering, 2014, p. 83-89):

Where

- множитель решетки для n-й ЛЭР;

is the lattice factor for the nth LER;

λ is the wavelength;

M - the number of measurement objects in the LER;

- координаты фазовых центров объектов в ЛЭР - (kd_n - изменение шага объектов измерения от n-й ЛЭР к соседней, k - коэффициент отличия шага, n - порядковый номер ЛЭР, при этом фазовый центр каждой ЛЭР находится в точке x_m=0).

- coordinates of the phase centers of objects in the LER - (kd _n - change in the step of the measurement objects from the n-th LER to the neighboring, k - step difference coefficient, n - serial number of the LER, while the phase center of each LER is at the point x _m = 0) .

In the calculation process, it was assumed that the dimensions of the measurement objects were much smaller than the wavelength λ, and for x _m the inequality x _m ≤ L was verified, where L was limited by condition (1).

The operability of the considered method of reducing _{BL BL} was estimated by calculation in relation to a lattice of 15 LER (M = 10, l = λ / 6 (size of the measurement object), d ₀ = λ; h = λ), where the discreteness of the step change of the measurement objects (kd _n ) was 0.01. In FIG. Figure 5 shows the dependence of the _BL on the difference coefficient of step k. It follows from it that a significant decrease in _BL is observed with an increase in k to 0.15. A further increase in k does not lead to a significant decrease in A _BL .

With limited dimensions of the measurement zone (the linear size of the LER is limited), the minimum value of the step difference coefficient (k _min ), at which A _BL can have extremely low values, is of interest. Consider the LER of M measurement objects placed with step d. Suppose that the step change for each individual LER in a two-dimensional lattice obeys a linear law. When it is irradiated with a plane front of an electromagnetic wave, the BL width according to a probability level of -3 dB can be estimated as Δθ _0.5 = λ / dM. The angle between the axes of the GL and the first BL in the horizontal section of the DOO is θ _bl = λ / d.

The minimum difference coefficient k _{min of} step d in two neighboring LERs can be found based on the condition that:

(λ / d) - (λ / kd) = λ / dM,

whence we have k _min = M / (M-1) ≈ (1 / M).

From those given in (Yu.D. Krivosheev, VV Denisenko, AV Shishlov. Suppression of interference maxima in aperiodic phased antenna arrays composed of periodic sublattices // Antennas. 2011. No. 2 (165). P. 32 ) of the results it follows that the minimum coefficient of difference (increment) of the step k _min ≈1.1, i.e. the absolute increment of the step from one LER to another is ≈ 0.1 steps. With the same number of measurement objects M = 10 in each LER, due to their shifts relative to each other, overlapping in the antiphase of the BL DOO LER is ensured, which ultimately leads to their “out-of-phase”. Optimization of the geometry of a planar two-dimensional lattice, built on the basis of the above arguments, shows that a 10% change in the step of the measurement objects in two neighboring LERs ensures a decrease in the level of side lobes below -20 dB.

Thus, the approach known in the theory of antennas is applicable to the proposed measurement device with a given accuracy of ultra-low ESR levels of objects. Let us consider the options for supplementing the initial LER to a planar two-dimensional lattice with additional LER, the limiting dimensions of which are limited by the dimensions of the measurement zone. It is known (Radar characteristics of objects. Research methods. Edited by S. M. Nesterov. - M .: Radio engineering, 2015, p. 138-160) that, to exclude mutual influence of objects, the LER step is set based on the condition d≥λ / 2 , i.e. the minimum step of the original LER (d ₀ ) or additional LER (d _n ) is λ / 2.

Two options are proposed for constructing a two-dimensional flat lattice for a device for measuring the EPR of radar objects.

1st option: if λ> d ₀ ≥λ / 2, additional N≈10, LER are formed with step d _n during the sequential increment of step d ₀ by the coefficient k = (1 + 0,1⋅n), i.e. . d _n = (1 + 0,1⋅n) ⋅d ₀ , where n is the serial number of the additional LER, n = 1, 2, ... Ν;

2nd option: if d ₀ ≥λ, additional Ν≈10, LER are formed with step d _n during the sequential reduction of step d ₀ by a factor k = (1.5-0.1⋅n), i.e. d _n = (1,5-0,1⋅n) ⋅d ₀ , where n is the serial number of the additional LER, n = 1, 2, ... N.

For both variants, the initial LER is supplemented with parallel additional N LERs parallel to it, at the same distance h between them. The distance h is chosen so that the directional coefficient of the two-dimensional lattice remains maximum: h≈0.96⋅λ (Kovalev S.V., Nesterov S.M., Skorodumov I.A. // RE, 1995. T. 140. No. 9. C. 1346). To satisfy condition (1), we can assume that h≥λ. A variant of the proposed flat two-dimensional lattice is shown in FIG. 3, p.

The principle of operation of the device is based on the following. Composed of identical measurement objects, a two-dimensional lattice containing the source one with increments d ₀ and N of additional LER with different increments d _{n is} placed in the radar field at an angle to the measuring installation (Fig. 2):

where λ is the wavelength;

d _n - step of the n-th additional LER d _n ;

θ _i is the angle of incidence of the electromagnetic wave emitted by the transmitter on the plane of the two-dimensional lattice;

θ _s is the angle of reflection of the electromagnetic wave from the grating in the direction of the receiver;

n = 1, 2, ... N; N≈10;

θ is the angle between the normal to the grating and the bisector of the separation angle of the receiving and transmitting antennas.

The power dissipated by the grating at an angle θ = 0 is determined by comparing it with the standard of its ESR, and then the ESR of the object under study is calculated by dividing the measured value by the number of elements in the grid squared.

The use of N additional LERs with different spacing d _n composed from the initial LER into a flat two-dimensional lattice allows, in the directions specified by expression (2), due to shifts of BL DOO of each individual LER relative to each other, they are added in antiphase, thereby reducing the amplitude Fields scattered by separate objects in the angular sector adjacent to the GL DOE. At the same time, at θ = 0 deg, due to the in-phase addition of the GL DOE N LER, increase the useful signal scattered by the measurement objects to a value exceeding the background level of the measurement setup used.

In FIG. 1 is a diagram of a known device for measuring the EPR of radar objects, FIG. 2 is a diagram of the proposed device for measuring the EPR of radar objects.

A device for measuring the effective scattering area of radar objects works as follows. A flat two-dimensional lattice of the same and equally oriented radar objects of measurement is placed in a radar field and rotated around its vertical axis so that it is normal to the axis of rotation and to the original electron beam, normal to the plane front of the electromagnetic wave emitted by the transmitting unit and normal to the plane front reflected from this the wave gratings lie in one plane (Fig. 2). The radio waves emitted by the transmitting unit are scattered on a two-dimensional array composed of the source and N additional LERs and are registered by the registrar through the receiving unit.

When radio waves are scattered by the studied objects in the initial (d ₀ ) and N additional LERs, the following occurs. The difference in the course of waves incident on neighboring objects is:

Δ _i = d _n sin θ _i ;

for waves scattered by the same objects:

Δ _s = d _n sinθ _s ;

and the total will be:

Δ _i + Δ _s = d _n (sinθ _i + sinθ _s ).

If the phase difference is an integer number of periods, i.e.:

d _n (sinθ _i + sinθ _s ) = nλ,

then the amplitudes of the fields scattered from all the measurement objects are added up, and the useful signal in the direction θ increases in power by a factor of M ² . At d≥λ / 2, more than one main diffraction lobe (GL-1, GL-2, etc.) is formed in the DOE of the nth LER. In addition, when this condition is fulfilled, the effect of rereflections between objects on the ESR of the GL of the lattice is small, and it is close to the ESR of a solitary object σ _i times the number of objects squared (M ² ). Since d ₀ ≠ d ₁ ≠ d ₂ ≠ ... ≠ d _n , the reflected signals in the directions θ of the GL of different LERs, as well as the BLs accompanying them, do not coincide and add up with a different phase. As a result, there is a “blurring” of the interference lobe of the factor of the entire lattice in a wide angular sector. At the same time, in the direction θ = 0 deg, the reflected signals in the GL direction of the source and N additional LER are added in phase, and the useful signal increases in power ((Ν + 1) × M) ² times. Thus, using a two-dimensional lattice composed of identical measurement objects placed in separate LERs with different steps, it is possible to measure the EPR of the studied objects with a level lower than the level of background reflections.

Verification of the proposed technical solution was carried out on the basis of numerical electrodynamic mathematical modeling using the CST program (Radar characteristics of objects. Research methods. Edited by S.M. Nesterov.- M.: Radiotekhnika, 2015, p. 126-136). For this, models of a linear, rectangular, and also a flat two-dimensional lattice were formed (Fig. 3, a, b, c), consisting of the same measurement objects in the form of conductive microspheres with dimensions l, which includes the initial LER and 10 additional ones with the following parameters:

M = 10, l = λ / 6, d ₀ = λ; h = λ, d _n = (1.5-0.1⋅n) ⋅λ, where n is the serial number of the additional LER, n = 1, 2, ... 10.

The wavelength (λ) of the radio emission was 3.1 cm. The results of mathematical modeling are shown in FIG. 6.

Calculated DOE of the original LER (Fig. 3, a), a two-dimensional rectangular lattice of 11 LER with the same pitch between the objects (Fig. 3, b), as well as the proposed two-dimensional lattice consisting of the original and 10 additional LER with the same number of measurement objects but placed with different steps (Fig. 3, c) are presented respectively in FIG. 6, j, f, g.

A feature of the proposed device for measuring the EPR of objects from the prototype is that the measured value is the value of the GL level, i.e. reflections normal to the plane of the two-dimensional lattice. Only in the vicinity of the GL, according to the presented arguments, in a wide sector of angles can the BL be “blurred”, thereby increasing the signal-to-background ratio. Given this fact, in order to reduce background reflections, it is proposed that the flat base of the two-dimensional lattice, on which the measurement objects are mounted, be made in the form of a plane-parallel dielectric plate with a thickness that is a multiple of a quarter of the wavelength of the measurement setup, or in the form of a plate of a radar absorbing material with radiophysical characteristics providing a reflection coefficient Normal is no worse than -25 dB. Suitable materials for RPM are materials of the type ALVU-4, VRP-4, List-51 or their analogues. In FIG. Figure 7 shows the DOO plates measured at a wavelength of 3.1 cm at a size of 70 × 70 cm from foamed freonoma (foam) type PE-6 (Fig. 7, w) and RPM type VRP-4 (Fig. 7, z). The s and t levels correspond to the median values of the EPR of the plates in the sector 0 ± 30 °. The analysis of DOE shows that reflections along the normal to the plates will not worsen the predicted (calculated) maximum values of the GL level (region s-t in Fig. 6).

An analysis of the results (Fig. 6) showed that the excess of the useful signal over the background reflections (the level of the first side lobes) in the first case is 19.3 dB, in the second - 35.6 dB. This result, based on the dependence of the maximum measurement error of the EPR of the object on the background level (Mayzels EN, Torganov VA, Measurement of the scattering characteristics of radar targets. - M .: Sov. Radio, 1972, p. 190), provides reduction of measurement error from 1.2 dB to 0.4 dB.

Technical result achieved: increased power of the signal reflected by an equidistant array, the size of which is limited by the size of the measurement zone, and increased the signal-to-background ratio.

The objective of the invention is solved: the claimed device for measuring the effective dispersion area of radar objects allows to increase the accuracy of measuring ultra-small values of the effective dispersion area of radar objects, the size of which is comparable and less than the wavelength.

The implementation of the inventive device is not difficult, because it consists in replacing one lattice with another or in changing the step of placing measurement objects in the same lattice.

Claims (8)

A device for measuring the effective dispersion area of radar objects, comprising a transmitting unit, a receiving unit connected to a recorder, a rotary support unit on which an initial linear equidistant array (LER) is fixed from the same and equally oriented measured radar objects, while normal to the array, the normal to the flat front of the electromagnetic wave emitted by the transmitting unit and the normal to the flat front of the electromagnetic wave reflected from the grating lie in the same plane, different yuscheesya in that the initial LER composed of M objects of measurement in steps d _0, complement disposed parallel initial lattice at a distance h from each other, in the plane defined by the initial LER and the axis of rotation, additional N LER, each of which consists of M objects measurements with a step d _n , which is selected based on the ratio: d _n = (1 + 0,1⋅n) ⋅d ₀ , for λ≥d ₀ ≤λ / 2 or d _n = (1,5-0,1⋅n) ⋅d ₀ , for d ₀ > λ, where n is the serial number of the additional LER, n = 1, 2, ... N; N≈10; d ₀ is the step of placing M measurement objects in the original LER; h is the distance between the electron beam, h≥λ; λ is the wavelength of the measurement setup.

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