RU2711341C1 - Two-dimensional direction finding method - Google Patents

Abstract

FIELD: radio engineering and communications.SUBSTANCE: invention relates to radio engineering and can be used for two-dimensional direction finding of ground and air objects on their radio emissions. Method of two-dimensional direction-finding includes reception of signals of the radiator using vertical dipoles of the antenna array, which is parallel to the earth's surface, measurement of complex amplitudes of the received signals and estimation based on measurement results of the azimuth of the radiator. At that, signals are additionally received with the help of horizontal vibrators, these signals are summed up and complex amplitude of the total signal is measured, results of all measurements are converted in direction of obtained azimuth taking into account amplitude and phase diagrams of directivity of antennae into angular spectrum, by position of maximum of which determining elevation angle of emitter, wherein the horizontal vibrators are located in the plane of the grid, the phase centers are aligned with its center, and the axes are uniformly turned relative to each other. Position of maximum angular spectrum by elevation angle is preliminarily estimated as arctangent of amplitude ratio of total signal normalized to sum of values of directional patterns of horizontal vibrators in direction of zenith and estimated azimuth, to average amplitude of signals of vertical vibrators. Angular spectrum is determined at the point of preliminary evaluation and at points distant from it by the differentiation constant, and the position of the maximum is corrected by the interpolation formula.EFFECT: high accuracy of determining the elevation angle of emitter in 2–6 times.3 cl, 3 dwg

Description

The invention relates to radio engineering and can be used for two-dimensional direction finding of ground and air objects by their radio emissions.

A known method of amplitude two-dimensional direction finding, including receiving a signal with identical antennas with symmetrical radiation patterns relative to the focal axes, whose orientation angles are shifted relative to each other with uniform overlap of the spherical field of view, measuring the amplitudes of the received signals, converting the measurement results taking into account the amplitude radiation patterns of the antennas in the angular spectrum and determining the direction to the emitter as the position of the maximum of the angular spectrum. [RF patent No. 2620130, 2017, G01S 5/04].

The disadvantage of this method is the difficulty of ensuring the necessary degree of identity of the antenna patterns when they are installed on the carrier.

A known method of direction finding, including receiving signals using antennas forming an annular array of vertical vibrators parallel to the earth’s surface and additional antennas located on the normal from its center, measures the complex amplitudes of the received signals, converts phase angles of the measurement antennas into the angular spectrum, and determines from its maximum angles of arrival of radio waves. [RF patent No. 2567850, 2015, G01S 3/00].

The disadvantages of this method are the increase in the dimensions of the antenna-feeder system in the vertical plane due to the installation of additional vertically spaced antennas, which is especially important when direction finding from the aircraft, as well as the low accuracy of determining the elevation angle of air targets by a ground direction finder due to interference of direct and reflected electromagnetic waves with different signs values of the angles of their arrival.

A known method for determining a two-dimensional bearing, including receiving signals using antennas forming an annular equidistant lattice parallel to the earth's surface, measuring the complex amplitudes of the received signals, converting the measurement results into the angular spectrum taking into account phase patterns of the antennas and determining the position of its maximum by the angles of arrival of radio waves in the horizontal , in azimuth, and in vertical, elevation, plane. [RF patent No. 2190236, 2000, G01S 5/04].

The disadvantage of this method is the low accuracy of determining the elevation angle near its zero value.

Of the known methods, the closest to the proposed technical essence is a method that includes receiving emitter signals using vertical vibrators of an antenna array, the plane of which is parallel to the earth’s surface, measuring the complex amplitudes of the received signals and evaluating from the measurement results taking into account phase patterns of the antenna of a two-dimensional bearing. The antenna array includes an annular equidistant array of at least three vibrators and a central antenna located in its center. [RF patent No. 2288481, 2006, G01S 3/00, 5/04].

The determination of a two-dimensional bearing can be carried out by preliminary converting the complex amplitudes to the angular spectrum from its maximum or by determining from the complex amplitudes the phase difference between the signals of the central and other antennas, and calculating the azimuth and elevation phase from these differences.

The disadvantage of this method is the low accuracy of determining the elevation angle, especially near its zero to 20 degrees, when the phase incursions on the lattice elements vary slightly from the elevation angle, and the measurement errors are inversely proportional to the sine of this angle [Dzvonkovskaya A.L., Dmitrienko A.N. Kuzmin A.V. Efficiency of measuring signal arrival angles by direction finders based on the maximum likelihood method. - Radio engineering and electronics, 2001, v. 46, No. 10, p. 1242-1247], and steeply falling radio waves with an incidence angle exceeding 60 degrees, when the reception efficiency of vertical vibrators is sharply reduced.

The technical task of this invention is to improve the accuracy of determining the elevation angle.

The problem is solved due to the fact that in the known method of two-dimensional direction finding, which includes receiving emitter signals using vertical vibrators of an antenna array, the plane of which is parallel to the earth’s surface, measuring the complex amplitudes of the received signals and estimating the emitter’s azimuth from measurements, it’s new that additionally receive signals using horizontal vibrators, summarize these signals and measure the complex amplitude of the total signal, the results of all measurements form in the direction of the estimated azimuth, taking into account the amplitude and phase diagrams of antenna in the angular spectrum of the position of the maximum is determined by the angle transmitter locations, wherein the horizontal vibrators are located in the plane of the grating, the phase centers aligned with its center, and the axes uniformly rotated relative to each other.

The problem is also solved due to the fact that the position of the maximum of the angular spectrum in elevation is previously estimated as the arctangent of the ratio of the amplitude of the total signal, normalized to the sum of the values of the directional patterns of horizontal vibrators in the zenith direction and estimated azimuth, to the average amplitude of the signals of vertical vibrators.

The problem is also solved due to the fact that the angular spectrum is determined at the point of preliminary estimation and at points remote from it by the differentiation constant and the position of the maximum is specified using the interpolation formula

- предварительная оценка угла места, F(θ,β) - угловой спектр,

- оценка азимута, δ - константа дифференцирования.Where

- preliminary estimate of the elevation angle, F (θ, β) is the angular spectrum,

is the azimuth estimate, δ is the differentiation constant.

The solution of this technical problem is based on taking into account differences in signal levels received by vertical and horizontal vibrators. The amplitudes of the received signals are determined by the orientation angles of the electric field vector relative to the antennas. The dependences of the amplitude on the elevation angle of horizontal and vertical vibrators are multidirectional in nature, when receiving electromagnetic waves with linear polarization, they are proportional to the sine and cosine of the elevator angle. By using horizontal vibrators, an increase in the efficiency of reception of steeply falling radio waves at high elevation angles and an increase in the steepness of the discriminatory characteristic in the region of small values with a corresponding increase in accuracy are achieved. The signals of horizontal vibrators are additionally dependent on azimuth. These features lead to the need to take into account jointly phase (prototype method) and amplitude radiation patterns of antennas. The operation of summing the signals of horizontal vibrators with combined phase centers, therefore, with the same initial phase, ensures the formation of only one additional receiving channel relative to the prototype method, and converting it into the angular spectrum in the direction of the obtained azimuth, reducing the required number by preliminary estimation and refining the elevation angle processing operations.

Combining systems of vertical and horizontal vibrators, taking into account the indicated patterns in accordance with the proposed new actions, conditions and the order of their implementation gives the desired effect, allows you to solve the technical problem: to increase the accuracy of determining the angle of the place of arrival of radio waves.

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

In FIG. 1 shows a structural diagram of a direction finder for implementing the inventive method;

in FIG. 2 shows the location of the direction-finding antennas in the horizontal plane with the x, y coordinate axes normalized to the radiation wavelength;

in FIG. 3 - graphs of the dependence of the mean square error of determining the angles of arrival of radio waves from the elevation angle.

The direction finder, FIG. 1, contains: 1.1-1.4 - antennas-vertical vibrators, 2.1-2.3 - antennas-horizontal vibrators, 3 - adder of signals, 4 - radio receiver, 5 - block for determining the azimuth, 6 - block for determining the elevation angle, containing 7 - block preliminary estimates, 8 - angular spectrum analyzer, 9 - refinement unit.

Antennas 1.1-1.4 are connected through a radio receiver 4 to the inputs of the azimuth determination unit 5 and the first inputs of the elevation determination unit 6, the preliminary estimation unit 7 and the angular spectrum analyzer 8. The second inputs of the elevation determination unit 6, the preliminary assessment unit 7 and the angular spectrum analyzer 8 are connected to antennas 2.1-2.3 through a signal adder 3 and a radio receiver 4. The output of the azimuth determination unit 5 is connected to the third input of the elevation determining unit 6, the preliminary estimation unit 7, and the angle analyzer tra 8, whose output is connected to a first input of clarify 9, to the second input and the fourth input of which the angular spectrum analyzer 8 connected to the output of the provisional estimation unit 7.

The outputs of the direction finder are the outputs of the azimuth determination unit 6 and the refinement unit 9 from the composition of the elevation determining unit 6.

Antennas 1.1-1.3 in an amount of at least three - symmetrical vertical vibrators, form an annular lattice, the plane of which is parallel to the earth's surface, are located equidistant around the circumference, a vertical vibrator 1.4 is installed in the center of the lattice. In FIG. 2, these antennas are indicated by dots and are indicated by the capital letters A ₁ -A ₄ . In the following example, the number of grating antennas is N = 3, its radius R is limited from the condition that the phase difference between the signals of the grating antennas and the central vibrator is unambiguous: R <0.5λ, where λ is the radiation wavelength.

Antennas 2.1-2.3 are horizontal vibrators located in the plane of the array, they are shown in FIG. 2 are thick lines and are marked with capital letters a ₁ - a ₃ . The phase centers of the horizontal vibrators are combined with the center of the lattice, and the axes are oriented along the lines "center - vertical vibrator", that is, uniformly in angular distance relative to each other. The number of horizontal vibrators is equal to N for N odd, otherwise half as much.

The adder of signals 3 is made according to one of the known options given, for example, in [Devices for adding and distributing high-frequency oscillation powers. Under. ed. Z.I. Model. - M .: Owls. radio, 1980.]

A radio receiver 4 with the number of channels N + 2 performs filtering and synchronous conversion of the received signals with a digital representation in the form of complex amplitudes (quadrature components), for example, according to the version given in [Poberezhsky KS Digital radio receivers. M., Radio and Communications, 1987, p. 67-68, fig. 3.140]. This measures the complex amplitudes of the received signals. A two-channel version of reception can be used with alternately connecting the array antennas and the adder of signals relative to the central vertical vibrator [Rembovsky A.M., Ashikhmin A.V., Kozmin V.A. Radio monitoring: tasks, methods and tools. - M: Hotline - Telecom, 2006, p. 274-277].

In the blocks for determining the azimuth 5 and elevation angle 6, transformations are implemented by digital signal processing methods.

Two-dimensional direction finding occurs as follows.

The radio emission of the direction finding source is received by antennas 1.1-1.4, 2.1-2.3.

The normalized amplitude directivity pattern of vertical symmetric vibrators is determined by the formula [Belotserkovsky GB Antennas - M: OBORONGIZ, 1962, p. 146]

where β is the elevation angle, L is the length of the vibrator, λ is the radiation wavelength, π = 3.14 ...

The countdown of the positive elevation angle is from the horizon up. The arrow indicates the limit for an elementary vibrator as L / λ → 0.

The pattern of horizontal vibrators, taking into account the rotations of the focal axes of the antennas, is described by the formula

where n '= 0, ..., N'-1 is the number of horizontal vibrators, N' is the number of horizontal vibrators, α '= 2π / N' is the quantum of the angular position of horizontal vibrators, θ is the azimuth with the counting of positive values clockwise from the focal the axis of the vibrator with the number n '= 0.

In the case when the emitter is a vertical vibrator with a radiation pattern G _p (β), the complex amplitudes of the signals at the output of the vertical vibrators are determined by the elevation angle β _{0 of the} emitter

- комплексная амплитуда сигнала всенаправленного излучателя в центре решетки,

- фазовая диаграмма направленности антенн кольцевой решетки, n=0, …, N-1, α=2π/N - квант углового положения ее антенн, R - радиус кольцевой решетки, λ - длина волны излучения, i - мнимая единица.Where

- the complex amplitude of the signal of an omnidirectional emitter in the center of the array,

is the phase diagram of the antenna array of the annular array, n = 0, ..., N-1, α = 2π / N is the quantum of the angular position of its antennas, R is the radius of the annular array, λ is the radiation wavelength, i is the imaginary unit.

The signals at the output of the horizontal vibrators additionally depend on the azimuth θ _{0 of the} emitter:

where n '= 0, ..., N'-1.

In accordance with formulas (3), (4), (1), (2), the amplitude of the signals of vertical and horizontal vibrators in various ways depends on the angle of arrival of radio waves in the vertical plane, in the limit proportional to its cosine and sine. This property is used later for direction finding.

In the adder of signals 3 perform the coherent addition of signals of horizontal vibrators

The total radiation pattern of horizontal vibrators is determined by the formula

- суммарная диаграмма направленности горизонтальных вибраторов в зенитном направлении.Where

- the total radiation pattern of horizontal vibrators in the anti-aircraft direction.

In the radio receiving device 4 measure the complex amplitude of the signals received by the vertical vibrators and the total signal of the horizontal vibrators

- шумы каналов приема.Where

- noise of the reception channels.

According to the results of measurements of the complex amplitudes of the vertical vibrators in block 5, the azimuth to the emitter is determined by one of the known methods, for example, by the method described in [Saidov A.S., Tagilaev A.R., Aliev N.M., Aslanov G.K. Design of phase automatic direction finders. - M.: Radio and Communications, 1997, p. 40] performing transformations of the following form

- разность фаз между сигналами антенн кольцевой решетки и центрального вибратора, arg(⋅) - аргумент (фаза) комплексной величины, охваченной скобками, звездочка - операция комплексного сопряжения.Where

is the phase difference between the signals of the antennas of the annular array and the central vibrator, arg (⋅) is the argument (phase) of the complex quantity enclosed in brackets, the asterisk is the complex conjugation operation.

The results of all measurements in block 6 are converted into an angular spectrum, the maximum of which determines the elevator angle of the emitter.

The angular spectrum is determined according to the well-known rule [Kozmin V.A., Ufaev V.A. Assessment of the quality of bearing calculation in the process of direction finding. Antennas 2009. Issue. 4 (123), p. 71-72], as the ratio of the squared module of the sum of the product of the complex amplitudes of the signals of the receiving channels to their complexly coupled radiation patterns to the sum of the squares of the modules of these radiation patterns, according to the formula

To reduce the number of processing operations to determine the two-dimensional angular spectrum and the position of its maximum, the spectrum values are obtained, firstly, in the direction of the obtained azimuth, and secondly, in the vicinity of the initial elevation angle estimate.

The specified initial assessment is performed in block 7 of the preliminary assessment as the arctangent of the ratio of the amplitude of the total signal, normalized to the sum of the values of the directional patterns of horizontal vibrators in the zenith direction and estimated azimuth, to the average amplitude of the signals of vertical vibrators, according to the formula

This formula directly follows from formulas (3), (4) with limit values of radiation patterns (1), (2).

In the absence of noise and in the limit of a vibrator with a cosine radiation pattern, the initial estimate (10) is accurate. If these conditions are not met, the result is specified. This is carried out using interpolation and determining the correction through the ratio of the first to the second derivative of the angular spectrum at the point of initial estimation. Derivatives are obtained by a numerical method, for which three angular spectrum values are determined in the angular spectrum analyzer 8: at the point of preliminary estimation and at points remote from it by the differentiation constant δ, the recommended value of which is of the order of δ = 0.002 radians.

Clarify the position of the maximum in block 9 refinement according to the interpolation formula [Ufaev VA, Volobuev MF Delay measurement of radio signals using discrete Fourier transforms. Information-measuring and control systems. 2016. No. 3, t. 14, p. 5]

The results of two-dimensional direction finding (8), (11) are given to the consumer.

The effectiveness of the invention is expressed in improving the accuracy of determining the elevator angle of the emitter. The quantitative assessment was performed by simulation, for the following conditions. We studied a direction finder with a ratio of the lattice radius to the radiation wavelength of 0.4 at a ratio of the signal amplitude to the root mean square value of the reception noise equal to 37 for a source located in the horizontal plane, which corresponds to an azimuth measurement error of 0.5 degrees. The radiation from a vertical vibrator with a cosine amplitude radiation pattern was simulated. The number of statistical experiments for each position of the source is 5000. The results of statistical simulation are shown in FIG. 3 in the form of dependences of the mean square errors of two-dimensional direction finding on the elevation angle.

The root-mean-square error σ was determined as the square root of the mean square difference of the measured and true values of the angles of arrival of radio waves. A thin solid line shows the dependence for azimuth, other lines for the elevation angle. A solid line with circles indicates the results provided by the proposed method, a dotted line with rhombuses for the prototype method. Analysis of the presented results shows that in the proposed method, the error in measuring the elevation angle in the range from 0 to 80 degrees is 2-6 times less than for the prototype method. The greatest gain is achieved near the borders of the specified range, up to 20 degrees and over 60 degrees.

The modeling program is developed in the Mathcad system, is available to the authors and the patent holder.

Thus, the proposed technical solution improves the accuracy of determining the elevator angle of the radiator by 2-6 times.

Claims (5)

1. A method of two-dimensional direction finding, including receiving emitter signals using vertical vibrators of an antenna array, the plane of which is parallel to the earth's surface, measuring the complex amplitudes of the received signals and estimating the emitter azimuth from the measurement results, characterized in that they additionally receive signals using horizontal vibrators, summarize these signals and measure the complex amplitude of the total signal, the results of all measurements are converted in the direction of the estimated azimuth, taking into account the amplitudes dnyh and phase diagrams antenna in the angular range, the position of which determines the maximum angle transducer locations, the vibrators disposed in the horizontal plane of the grating, the phase centers aligned with its center axis and uniformly rotated relative to each other. 2. A two-dimensional direction finding method according to claim 1, characterized in that the position of the maximum of the angular spectrum in elevation is previously estimated as the arctangent of the ratio of the amplitude of the total signal normalized to the sum of the values of the directional patterns of horizontal vibrators in the zenith direction and estimated azimuth to the average amplitude of the vertical signals vibrators. 3. The method of two-dimensional direction finding according to claim 1 or 2, characterized in that the angular spectrum is determined at the point of preliminary estimation and at points remote from it by the differentiation constant, and the maximum position is determined using the interpolation formula

, Where

- preliminary estimate of the elevation angle, F (θ, β) is the angular spectrum,

is the azimuth estimate, δ is the differentiation constant.

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