RU2535174C1 - Method of two-dimensional direction finding of air object - Google Patents

Abstract

FIELD: radio, communication.

SUBSTANCE: signals of the object transmitter are received using the antennas forming an annular grid located parallel to the earth's surface, according to the received signals the azimuth of the object is measured, the signals are received with at least two additional antennas located on the central axis of the annular grid orthogonally to its plane, the received signals are converted to the angular range on the angles of the place of the direct signal and the signal reflected from the earth's surface in the direction of the measured azimuth of the object, at that the angular spectrum is converted into an angular spectrum of the second order, and the object site angle is determined by one-parameter maximization of the angular spectrum of the second order.

EFFECT: improving accuracy of measurement of the object site angle and reduction of the time of direction finding.

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Description

The invention relates to radio engineering, in particular to direction finding, and can be used to determine the location of airborne objects from the radio emissions of their transmitters.

There is a method of two-dimensional direction finding, including receiving signals from the airborne transmitter of an airborne object using antennas forming an annular array, measuring the phases of the received signals, reconstructing them by eliminating the cyclic phase measurements, and calculating the azimuth and elevation angle from the reconstructed phases (Saidov A.S., Tagilaev A .R., Aliev N.M., Aslanov GK Design of phase automatic direction finders. M: Radio and communications, 1997, chap. I, II, p. 10, p. 51-52).

A limitation of the method is the low accuracy of measuring the elevation angle when the energy center of the rays with significant fluctuations is direction finding. In addition, the phase incursions in the antennas are proportional to the cosine of the elevation angle and, with its values close to zero, for shallow radio waves, they differ slightly. Another disadvantage is the difficulty of performing the phase reconstruction operation.

A known method of direction finding, including receiving a signal using omnidirectional antennas forming an annular array, measuring the phase difference between signals in two groups, vectors connecting pairs of antennas in which are collinear, and using the combination of phase differences in groups using multiscale measurements, evaluate unique ones at a distance of the diameter of the array phase incursions by which the azimuth and elevation angle are calculated (RU, No. 2251707).

In this method, the phase reconstruction operation is excluded, but the main disadvantage of the previous analogue (low accuracy of measuring the elevation angle) is not eliminated.

A known method for determining a two-dimensional bearing, including receiving radio signals using a central antenna and antennas forming an N element ring array with a total number of antennas of at least three, synchronous measurement of the complex amplitudes of the received radio signals, converting them in the nodes of the grid pointing the lattice into an angular spectrum and determining the coordinates of the maximum its module (RU, No. 2288481).

The introduction of a central antenna allows you to increase the maximum allowable radius of the array and thereby increase the accuracy of direction finding in the horizontal plane, i.e. azimuth. However, the main drawback - the low accuracy of measuring the elevation angle - persists for the reasons mentioned above.

Of the known methods, the closest to the proposed technical essence is the method of two-dimensional direction finding of an air object, which consists in receiving the signals of the transmitter of the object using antennas forming an annular array located parallel to the earth's surface, measuring the azimuth of the object from the received signals, and converting the received signals to angular spectrum at elevation angles (Saidov A.S., Tagilaev A.R., Aliev N.M., Aslanov G.K. Design of phase automatic direction finders. M: Radio and communications, 1997, chapter II, p. 47- 48 )

In this method, the received signals are converted into a two-dimensional angular spectrum according to possible azimuths and elevation angles of the object, and a two-dimensional bearing is determined as the position of the maximum square of the modulus of this spectrum. Moreover, the conversion into a two-dimensional angular spectrum is performed by multiplying the received signals by complex conjugate two-dimensional radiation patterns in the direction of the possible position of the object and averaging the results of multiplication over the totality of the array antennas.

In this method, the potential accuracy and extreme sensitivity of the azimuth measurement are achieved, but the main disadvantage of the analogues is preserved - the insufficient accuracy of measuring the elevation angle of the object. An additional complication is the performance of operations of two-dimensional conversion of signals into an angular spectrum for a set of antennas of a ring array, which complicates the processing and increases the time of direction finding.

The problem solved by the invention is the improvement of technical and operational characteristics.

Achievable technical result of the invention is to improve the accuracy of measuring the elevation angle of the object and reduce the direction finding by reducing the number of processing operations of the received signals.

To solve the problem with the achievement of the specified technical result in the known method of two-dimensional direction finding of an air object, which consists in the fact that the signals of the transmitter of the object are received using antennas that form an annular array located parallel to the earth's surface, the azimuth of the object is measured from the received signals, the received signals are converted to the angular spectrum at elevation angles according to the invention receives signals by at least two additional antennas located on the central axis of tsevoy grating orthogonally to its plane, convert the received signals into the angular range of elevation angles of direct and reflected from the earth's surface a signal in the direction of the measured azimuth of the object, the angular spectrum is converted into the angular range of the second order, and the angle of the object space is determined by the one-parameter maximizing the angular spectrum of the second order.

It is advisable that the conversion to the angular spectrum of the second order was carried out in accordance with the mathematical expression

,

- угловой спектр принятых сигналов в направлении измеренного азимута объекта по углам места β и -β прямого и отраженного от земной поверхности сигнала соответственно,

, N' - общее число антенн, n - порядковый номер антенны,

,

- соответственно комплексная амплитуда принятого n-й антенной сигнала и ее комплексная диаграмма направленности в направлении измеренного азимута

объекта, звездочка * сверху и справа у

означает операцию ее комплексного сопряжения,

- весовая функция.Where

,

- the angular spectrum of the received signals in the direction of the measured azimuth of the object at the elevation angles β and -β of the direct and reflected signal from the earth’s surface, respectively,

, N 'is the total number of antennas, n is the serial number of the antenna,

,

- respectively, the complex amplitude of the received nth antenna signal and its complex radiation pattern in the direction of the measured azimuth

object, asterisk * above and to the right of

means the operation of its complex conjugation,

- weight function.

- соответственно комплексная амплитуда принятого n-й антенной сигнала и ее комплексная диаграмма направленности в направлении измеренного азимута

объекта для отраженного от земной поверхности сигнала. Однопараметрическая максимизация углового спектра второго порядка осуществляется только по параметру измеренного азимута

объекта, а по максимуму F(β) судят об истинном угле места

объекта.For reflected signal

- respectively, the complex amplitude of the received nth antenna signal and its complex radiation pattern in the direction of the measured azimuth

object for the signal reflected from the earth's surface. One-parameter maximization of the angular spectrum of the second order is carried out only by the measured azimuth parameter

object, and the maximum F (β) judge the true elevation

object.

The solution of the stated technical problem is based on two-direction finding of the direct and reflected waves from the earth’s surface, which come from one azimuth, but are mirror symmetric in elevation, in the upper and lower half-planes of the annular lattice, with elevation angles equal in magnitude but with different signs. Taking this regularity into account is ensured by obtaining the angular spectrum additionally at possible elevation angles of the beam reflected from the earth's surface. However, in this case, only antennas of the annular array, in which the phase incursions are even, are proportional to the cosine of the elevation angle, for two-beam direction finding. Necessary conditions: the presence of additional antennas in a vertical plane with an odd (proportional to sine) dependence of phase incursions, and in an amount of at least two. The reception of signals in at least three (together with the array antennas) vertical levels provides the necessary conditions for the separation of rays, since taking into account the amplitude and phase of the received vibrations for three levels, the system describing them contains six equations with exactly six unknowns: amplitude, phase, angle of arrival of the direct and reflected beam.

Under these conditions, the second-order angular spectrum obtained from the aggregate of signals of all N 'antennas (ring arrays and additional ones) has a maximum in the vicinity of a true two-dimensional bearing with a decrease in measurement error. The axial symmetry of the antenna system is also significant: an annular array and additional antennas. This makes it possible to determine the azimuth by one of the known methods from the received signals of the annular lattice, and the elevation angle by one-parameter maximization of the angular spectrum of the second order in the direction of the measured azimuth. The last step excludes the procedure for determining and maximizing the two-dimensional angular spectrum, as in the closest analogue, which leads to a reduction in the number of signal processing operations and, as a result, to a decrease in the time of two-dimensional direction finding.

Accounting for these patterns in accordance with the proposed new actions, conditions and the order of their implementation, allows to achieve the specified technical result: to increase the accuracy of measuring the elevation angle and the speed of direction finding.

These advantages, as well as features of the present invention are illustrated by a variant of its implementation with reference to the accompanying figures.

Figure 1 presents the structural diagram of the direction finder for implementing the inventive method;

figure 2 shows the angular spectra;

figure 3 - dependence of the measured elevation angles from the distance to the object;

figure 4 - dependence of the error of measurement of elevation angles from the distance to the object.

The direction finder for implementing the claimed method (Fig. 1) contains antennas 1.0-1.N'-1 connected to the inputs 0-N'-1 of the radio receiving device 2, outputs 0-N-1 connected to the inputs of the same name of the azimuth determination unit 3 and the analyzer 4 angular spectrum. The inputs N-N'-1 of the angular spectrum analyzer 4 are connected to the outputs of the radio receiver 2 of the same name, and the input N 'is connected to the output of the azimuth determination unit 3, the output of which is connected to the input of the weight function calculation unit 5 and to the first input of the indicator 8. Converter 6 the angular spectrum, the minimum determining device 7 and the indicator 8 are connected in series. The first and second output of the angular spectrum analyzer 4 are respectively connected to the first and second input of the angular spectrum converter 6, and its third input is connected to the output of the weight function calculation unit 5.

All antennas 1.0-1.N'-1 can be made identical, omnidirectional in the horizontal plane, for example, a type of symmetrical vibrator. Antennas 1.0-1.N-1 form an annular array (equidistant) with the number of antennas N> 3 in it. To ensure further unambiguous phase measurements, the radius ρ of the annular array is selected from the condition that the distance between the nearest antennas 1.0-1.N-1 of the annular array of half the radiation wavelength does not exceed. The annular array is oriented by the reference antenna 1.0 to the north. The phase centers of the antennas of the annular array are located in one horizontal plane at a height h above the earth's surface, of the order of several tens of meters. Additional antennas 1.N-1.N'-1 in an amount of at least two are installed on the normal to the plane of the array from its center, for example, with a constant pitch δh relative to the plane of the antenna array at a height Δh _n , determined by the formula Δh _n = δh- (n + 1-N), where n = N, ..., N'-1 is the serial number of the additional antenna, N, N 'is the number of antennas of the ring array and the total number of antennas, respectively.

A multi-channel radio receiver 2 with the number of channels equal to the total number of antennas N 'performs filtering and synchronous conversion of the received signals with digital measurement and presentation in the form of complex amplitudes (quadrature components).

, где

- мгновенные значения напряженности поля, ξ_n - шумы приема, n=0, …, N'-1.Direction finding of an air object is as follows. The radiation of the airborne transmitter is received by antennas 1.0-1.N'-1 and their complex amplitudes are measured in the radio receiver 2

where

- instantaneous field strengths, ξ _n - receiving noise, n = 0, ..., N'-1.

, принимаемого антеннами радиопеленгатора, определяются соотношениемA direct and reflected wave from the earth's surface arrives at the direction-finding point from the onboard transmitter of the airborne object. Moreover, according to the method of mirror image instantaneous field strength

received by the direction finding antennas are determined by the ratio

,

- комплексная амплитуда напряженности поля прямого и отраженного сигнала в центре кольцевой решетки,

- диаграммы направленности антенн для прямого сигнала,

- то же, для отраженного сигнала, θ, β - азимут и угол места.Where

,

- the complex amplitude of the field strength of the direct and reflected signal in the center of the ring lattice,

- antenna patterns for the direct signal,

- the same for the reflected signal, θ, β - azimuth and elevation.

The positive values of elevation angles β are counted from a line parallel to the earth’s surface to the zenith, azimuth θ from the reference antenna (with serial number n = 0) in a clockwise direction.

The radiation patterns of antennas in free space are determined, respectively, for an annular array (n = 0, ..., N-1) and additional antennas (n = N, ..., N'-1), according to the formulas

where i is the imaginary unit, k = 2π / λ is the wave number, λ is the radiation wavelength, α = 2π / N is the quantum of the angular position of the antennas of the annular array, ρ is the radius of the annular array, Δh _n is the height of the additional antennas.

The unknown parameters are the azimuth θ and elevation angle β of the object, and also, due to the uncertainty of the electrical parameters of the earth's surface in the reflection region, the complex amplitudes of the rays. Subsequent actions on the signals are aimed at overcoming this a priori uncertainty.

, где

- аргумент комплексного числа, заключенного в скобки (фаза вектора),

- комплексная амплитуда принятого n-й антенной сигнала, звездочка * сверху и справа у

означает операцию ее комплексного сопряжения, ⊕ - операция сложения по модулю N, и рассчитывают азимут объектаIn block 3 of determining the azimuth from the results of measurements of the complex amplitude of the grating signals received at the inputs 0-N-1 from the same outputs of the radio receiving device 2, the phase differences Δφ _n between the signals of the nearest antennas of the ring grating are estimated by the formula:

where

- argument of a complex number enclosed in brackets (vector phase),

- the complex amplitude of the received nth antenna signal, an asterisk * above and to the right of

means the operation of its complex conjugation, ⊕ is the addition operation modulo N, and the azimuth of the object is calculated

Assessment of the bearing by formula (4) does not require two-dimensional conversion of signals into the angular spectrum, as is done in the closest analogue, which reduces the number of processing operations of the received signals, reduces the time of direction finding, and simplifies the technical implementation of the claimed method.

If the distance between the nearest antennas of the annular array is half the wavelength of the radiation, the use of the method of multiscale measurements of phase differences can be recommended.

In the analyzer 4 of the angular spectrum convert the received signals arriving at the inputs 0-N'-1 from the same outputs of the radio receiving device 2, in the angular spectrum. This conversion is performed by multiplying the received signals by complex conjugate antenna patterns [in accordance with mathematical expressions (2), (3)] and averaging the results of multiplication over the set of antennas in the direction of the obtained azimuth [in accordance with the mathematical expression (4)] of the object, arriving at the input N 'of the analyzer 4 from the output of block 3, according to the formula

Transformation (5) is performed at the possible elevation angles of the object β of the direct signal (beam) and the reflected signal (ray) -β, that is, for positive and negative elevation angles.

поступают на первый выход анализатора 4 углового спектра, а симметричные им для отрицательных значений

по второму выходу.Results for positive elevation

the angular spectrum analyzer 4 arrives at the first output of the analyzer, and symmetric them for negative values

on the second exit.

At the same time, in the calculation block 5, the weight function is determined, also in the azimuth direction (4) and at the possible elevation angles of the object:

Transformation (6) is similar to operation (5), but the input quantities for it are the radiation patterns of the antennas in the field of positive (direct signal) and negative (reflected signal) elevation values.

In the Converter of the angular spectrum 6 according to the results of (5), (6) determine the angular spectrum of the second order by the formula

The second-order angular spectrum (7) differs from the angular spectrum of the closest analogue by the presence of the second term, which takes into account the presence of both a direct signal and a signal reflected from the earth's surface.

в соответствии с выражением (5). Спектры нормированы на максимальное значение и получены для истинного угла места объекта, равного 2,8 градуса. Видно, что максимум углового спектра второго порядка F(β) находится в окрестности истинного значения угла места. Этот спектр сосредоточен в существенно меньшей области возможных углов места, чем квадрат модуля

углового спектра сигналов антенн кольцевой решетки, что повышает точность измерения истинного угла места

в присутствии шумов.A typical view of the angular spectrum of the second order in accordance with the mathematical expression (7) is shown in figure 2 by a dashed line with circles. For comparison, the dots show the square of the module of the angular spectrum of the signals of the array antennas

in accordance with the expression (5). The spectra are normalized to the maximum value and obtained for the true elevation angle of the object, equal to 2.8 degrees. It is seen that the maximum of the angular spectrum of the second order F (β) is in the vicinity of the true value of the elevation angle. This spectrum is concentrated in a significantly smaller region of possible elevation angles than the square of the module

the angular spectrum of the signals of the antennas of the annular array, which increases the accuracy of measuring the true elevation angle

in the presence of noise.

объекта (вход 2) отражаются на индикаторе 8.In the device for determining the maximum 7 determine the elevation angle of the object as the position of the maximum angular spectrum of the second order. The results of the determination of the bearing θ (input 1 of indicator 8) and the true elevation angle

object (input 2) are reflected in indicator 8.

Thus, as shown above, it is possible to achieve an increase in the accuracy of measuring the elevation angle of the object and reduce the time of direction finding by simplifying the processing of the received signals.

Quantitative assessment was carried out by simulation method for the following conditions.

We studied a direction finder located above the sea surface with a relative permittivity of 75 and a conductivity of 3 Ohm / m and containing a 3-element antenna array with a radius of 0.25 m raised to a height of 15 m and two additional antennas mounted above the plane of the array to a height of 1 and 2 m. The maximum sensitivity of direction finding is set to 2 μV / m. The height of the airborne object is 1000 m, the transmitter power is 10 W, the radiation wavelength is 1 m. The simulation program is developed in the Mathcad system.

и погрешности измерений Δβ от дальности d до объекта для ближайшего аналога кружками, а для заявленного способа решения - точками. Истинные значения угла места указаны на фиг.3 тонкой сплошной линией.The simulation results are shown in figure 3, 4 in the form of the dependence of the measured elevation angles

and measurement errors Δβ from the range d to the object for the nearest analogue circles, and for the claimed method of solution - points. The true elevation values are indicated in FIG. 3 by a thin solid line.

It can be seen that the measurement errors in the proposed method at a distance to the object greater than 1 km are approximately an order of magnitude smaller and do not exceed one degree in absolute value at a distance of up to 100 km. The maximum value of the range for the closest analogue at the specified level of error is limited to about 15 km. Improving the accuracy of measuring the elevation angle of the proposed method allows you to simplify, make more reliable and safe escort of the aircraft to non-equipped navigation installations airfields or, for example, drilling sites, construction sites, agricultural land, etc.

The most successfully claimed method of two-dimensional direction finding of an air object is industrially applicable for direction finding of aircraft (airplanes, helicopters, airships) with high accuracy in a complex electronic environment.

Claims (2)

1. The method of two-dimensional direction finding of an airborne object, which consists in receiving signals from the transmitter of the object using antennas forming an annular array parallel to the earth’s surface, measuring the azimuth of the object from the received signals, converting the received signals into an angular spectrum at elevation angles, characterized in that they receive signals by at least two additional antennas located on the central axis of the annular array orthogonal to its plane, convert the received signals into an angular spectrum along In terms of the direct and reflected beam from the earth’s surface in the direction of the measured azimuth of the object, the angular spectrum is converted into a second-order angular spectrum, and the object’s elevation angle is determined from the one-parameter maximization of the second-order angular spectrum, which is obtained by taking into account both direct and reflected from the earth’s surface beam, as well as the number of antennas used, their complex radiation patterns and complex amplitudes of the signals received by the antennas. 2. The method of two-dimensional direction finding of an air object according to claim 1, characterized in that the second-order angular spectrum is obtained
by conversion formula

Where

,

- the angular spectrum of the received signals in the direction of the measured azimuth of the object at the elevation angles β of the direct and reflected β from the earth's surface of the beam,

N ′ is the total number of antennas, n is the serial number of the antenna,

,

- respectively, the complex amplitude of the received nth antenna signal and its complex radiation pattern in the direction of the measured azimuth

object, an asterisk * above and to the right of the value means the operation of its complex conjugation,

- weight function.

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