RU2752878C2 - Method of direction finding for broadband signals with increased resolution - Google Patents

Abstract

FIELD: radio technology.

SUBSTANCE: invention relates to radio technology and may be used in radio location, radio navigation and radio communication systems for direction finding of broadband signals and determination of azimuth and angular directions to the radiation sources thereof with increased resolution. The method includes broadband antenna radiators enabling broad band signal reception, wherein the operation frequency range of each radiator is partitioned into K equal frequency intervals, in each of K frequency intervals a frequency of ω_k is determined, a direction finding relief is generated for said frequency and angles θ_i and ϕ_i of each beam of set multi-beam broadband signal is determined by the maximums of the direction finding relief, multi-beam broadband signals are received from these directions and on set frequencies, and for other frequencies of the broadband signals their approximation is conducted by approximation functions and thus the determined broadband signals are retrieved with required accuracy.

EFFECT: possibility of direction finding of broadband radiation sources wherein the angular distance between the sources is lower than the Rayleigh limit.

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Description

The invention relates to radio engineering and can be used in radar, radio navigation and radio communication systems for direction finding of broadband signals and determination of azimuthal and angular directions with increased resolution to their radiation sources.

There is a method [1] for determining the directions to radiation sources, which consists in measuring the signal power at the output of a directional receiving antenna when scanning the survey sector with the antenna directional pattern and determining the directions to the radiation sources along the directions of the AP axis corresponding to the maxima of the measured power values.

The disadvantage of this method is that the accuracy of determining the directions to the radiation sources is limited by the step of changing the directions of the directional pattern axis when scanning the viewing sector at which measurements are taken, and the resolution of closely spaced point sources is determined by the angular width of the directional pattern. Also, this method does not allow to provide direction finding of broadband signals, the angular distance between the sources of which is less than the Rayleigh limit.

There is a known method of determining directions to radiation sources and angular resolution of sources [2], which consists in dividing the viewing sector into resolution elements in a direction, the angular width of which is determined by the required accuracy of determining directions to radiation sources and the angle of resolution of sources and is much smaller in magnitude than the angular width the directional diagram of the receiving antenna, and determining the direction to the radiation sources as the direction of the resolution elements corresponding to the maxima in the power distribution of the radiation sources according to the resolution elements in the viewing sector obtained during the estimation.

The disadvantage of this method is that the method does not provide direction finding of broadband signals, the angular distance between the sources of which is less than the Rayleigh limit.

There is a known method of direction finding with increased resolution [3], including the reception of a multi-beam signal of a source of acoustic or electromagnetic radiation by an antenna array of N elements located evenly around the circumference, and forming an ensemble of signals that depend on the time and number of the antenna element, converting the ensemble of received signals into digital signals, formation of a spatial correlation matrix, describing the amplitudes and phases of mutual signals received by the array elements, transformation of the signal of the spatial correlation matrix into signals of eigenvalues and eigenvectors, comparison of eigenvalue signals with a threshold and when the threshold is not exceeded, the signal of the corresponding eigenvector is identified as an eigenvector signal belonging to the noise subspace, the formation of the matrix of signals of the eigenvectors of the noise subspace, the formation of a two-dimensional signal of the complex phasing function, depending on a given receiving frequency and describing the possible directions of the signal arrival from each potential source. Using the generated matrix of eigenvectors of the noise subspace and the signal of the phasing function, the signal of the angular spectrum is generated, the azimuth and the elevation angle of each beam of the received multipath signal are determined from the maxima of the signal of the angular spectrum. The obtained two-dimensional bearings of the selected rays are displayed on the cartographic background.

The disadvantage of this method is that it can be implemented only for a ring antenna array operating at one frequency, which limits the scope of its application.

The known method [4] direction finding of radio emission sources at one frequency, including the reception of signals by means of a multi-element antenna system, synchronous conversion of the ensemble of received signals, depending on the time and number of the element of the antenna system, into digital signals, conversion of digital signals into an amplitude-phase signal distribution, describing the distribution of amplitudes and phases on the elements of the antenna system, the formation of the amplitudes of complex signals of the amplitude-phase distribution of a system of linear algebraic equations describing the amplitudes of the signals received by the elements of the antenna system. Each line of the system of linear algebraic equations is the sum of the products of the coefficients of the polynomial of exponential functions, and each subsequent equation in the system of formed linear algebraic equations is a shift to the right by one position with respect to the previous equation. Then the roots of the polynomial of exponential functions are determined, which are the parameters of exponential functions, by means of the parameters of exponential functions using the operation of logarithm and arccosine, the bearings of radio emission sources are determined. It makes it possible to estimate the bearings of radio emission sources based on a single synchronous measurement of signals at the outputs of the antenna system elements, that is, by the totality of complex signal amplitudes formed at the outputs of the direction finding channels at a certain moment in time.

The disadvantage of this method is the significant computational complexity and impossibility of direction finding broadband radio sources, the angular distance between which is less than the Rayleigh limit.

There is a known method of direction finding radio emission sources [5], which includes calculating the spatial Fourier spectrum of the signal of the direction finding radio emission source received by the elements of two linear equidistant antenna arrays, and the antenna arrays are located perpendicular to each other, calculating the complex-conjugate spatial Fourier spectrum of the direction finding signal received by the elements the second linear equidistant antenna array, transforming the scales of both calculated spatial spectra of the bearing signal according to the logarithmic law, performing correlation analysis and measuring the relative shift of the transformed spatial spectra of the bearing signal, estimating the angular coordinate (bearing) of the signal source.

The disadvantage of this method is the low accuracy of the assessment of the bearing of the radio emission source and the impossibility of the direction finding of the radio emission sources, the angular distance between which is less than the Rayleigh limit.

There is also known a method [6] direction finding with increased resolution, including

reception of signals from radio emission sources by a multi-element antenna array x _n (t), where n = 0, ..., N-1 is the number of the antenna element,

conversion of received signals into digital form x _n (z), where z is the number of digital sample, formation of a complex covariance matrix from digital signal data

where Z is the total number of digital samples;

H - symbol of complex conjugation and transposition;

formation of direction finding relief according to the formula

where S (θ, ϕ) is the scanning vector of the antenna array at the angles θ and ϕ;

determination of the angles θ _i and ϕ _{i of} each beam of the received multipath signal from the maxima of the direction finding relief P (θ, ϕ).

This method was chosen as a prototype of the proposed solution.

The disadvantage of this method, like the previous analogs, is the impossibility of direction finding broadband radio sources.

The technical result of the proposed invention lies in the possibility of direction finding of broadband radio sources, the angular distance between which is less than the Rayleigh limit.

The specified technical result is achieved by the fact that in the prototype method of direction finding with increased resolution, including the reception of signals from sources of electromagnetic radiation by an antenna array of N elements, the formation of an ensemble of signals that depend on the time and number of the antenna element, synchronous transformation of the ensemble of received signals into digital signals, conversion of digital signals into a signal of a complex spatial covariance matrix describing the amplitudes and phases of mutual signals received by the array elements, formation of the direction finding relief, determination of the angles θ _i and ϕ _{i of} each beam of the received multipath signal from the maxima of the direction finding relief, in addition, emitters are used as elements of the antenna array, allowing to receive signals in a wide frequency band, the frequency band of each radiator is divided into K identical frequency intervals, in each of the K frequency intervals the frequency ω _{k is} determined, for which the bearing relief and determine the angles θ _i and ϕ _{i of} each beam of the received multi-beam broadband signal according to the maxima of the bearing relief, multi-beam broadband signals are received from these directions and at given frequencies, and for other frequencies of broadband signals they are approximated by various approximating functions.

FIG. 1 shows the spectrum of the first broadband direction finding signal coming from the direction θ ₁ = 0 °, φ ₁ = 0 °.

FIG. 2 shows the spectrum of the second broadband direction finding signal coming from the direction θ ₂ = 40 °, φ ₂ = 0 °.

FIG. 3 shows the spectrum of the third broadband direction finding signal coming from the direction θ ₃ = -21 °, φ ₃ = 0 °.

FIG. 4 shows the direction finding relief at a frequency of 0.7 ω ₁ .

FIG. 5 shows the direction finding relief at a frequency of 2.1 ω ₁ .

FIG. 6 shows the direction finding relief at a frequency of 3.5 ω ₁ .

FIG. 7 shows the spectrum of the reconstructed broadband signal at K = 2.

FIG. 8 shows the spectrum of the reconstructed broadband signal at K = 8.

FIG. 9 shows the spectrum of the reconstructed broadband signal at K = 32.

на которой осуществляется прием сигналов от источников радиоизлучения многоэлементной антенной решеткой x_n(t). Далее производится преобразование принятых сигналов в цифровой вид x_n(z) и формирование из цифровых данных сигнала комплексной ковариационной матрицы по формуле (1) для каждой частоты ω_k. На основе полученной комплексной ковариационной матрицы (1) производится для каждой k-ой частоты частотного диапазона функционирования антенной решетки оптимально формируется пеленгационный рельеф для пеленгации составляющих широкополосных сигналов на данной частоте (фиг. 4-6). Пеленгационный рельеф может строиться как на основе метода Кейпона (2), так и на основе метода «теплового шума», который дает более точное разрешениеThe method for direction finding wideband signals with increased resolution is implemented as follows. An additive mixture of broadband signals (Figs. 1-3) arriving from different directions at different frequencies is received by N antenna elements of the antenna array. The bandwidth of each of the N elements of the antenna array is divided into K equal frequency intervals. For each of the K frequency intervals, the frequency is determined

where signals are received from radio emission sources by a multi-element antenna array x _n (t). Next, the received signals are converted into digital form x _n (z) and the signal is formed from the digital data of the complex covariance matrix according to formula (1) for each frequency ω _k . On the basis of the obtained complex covariance matrix (1), for each k-th frequency of the frequency range of operation of the antenna array, the direction finding relief is optimally formed for the direction finding of the components of broadband signals at a given frequency (Figs. 4-6). The direction finding relief can be constructed both on the basis of the Capon method (2), and on the basis of the "thermal noise" method, which gives a more accurate resolution

According to the maxima of the direction finding relief P (θ, ϕ), the angles θ _i and ϕ _{i of} each beam of the received broadband signal are determined (Figs. 4-6). Further, the obtained components of wideband signals are approximated by various approximating functions, for example, a piecewise constant function or a piecewise linear function (Figs. 7-9).

- в случае кусочно-постоянной аппроксимации;where

- in the case of piecewise constant approximation;

ω _k is the average value of the k-th frequency interval;

Δ = (ω ₂ -ω ₁ ) / 2;

ω ₁ , ω ₂ - left and right boundaries of the broadband signal spectrum.

In the case of piecewise linear approximation, expression (4) takes the form

The number of frequencies K for which the direction finding relief is optimally calculated depends on the required accuracy of reconstructing the broadband signal spectrum (Figs. 7-9). In this case, the method on the basis of which the direction finding relief is formed plays a role only at the first stage, when the components of the broadband signals are taken.

The above ratios describe the general case when the AA generates a PR for all signals arriving from different directions, which are covered by the scanning vector, and falling into the operating frequency range of the AA.

Thus, the use of emitters as elements of the antenna array, allowing to receive signals in a wide frequency band, dividing the operating frequency range of each emitter into K identical frequency intervals, determining in each of the K frequency intervals the frequency ω _k , for which the direction finding relief is optimally formed and the angles θ _i and ϕ _{i of} each beam of the received multi-beam broadband signal according to the maxima of the direction finding relief, reception from these directions and at given frequencies of multi-beam broadband signals, the approximation of signal parameters by various approximating functions for the remaining frequencies of broadband signals made it possible to achieve a technical result consisting in the possibility of direction finding of broadband sources radio emissions, the angular distance between which is less than the Rayleigh limit.

Literature

1. Handbook of radar. Ed. M. Skolnik. Per. from English. - M., "Sov. radio ", 1978. T. 1, p. 17.

2. Patent RU No. 2392634, 2010

3. US patent No. 6567034, 2003

4. Patent RU No. 2380719, 2010

5. Patent RU No. 2192651, 2002

6. Keypon J. High-resolution spatial-temporal spectral analysis // TIIER, 1969. V. 57, no. S. 59-69.

Claims (1)

A method for direction finding broadband signals with increased resolution, which consists in receiving signals from sources of electromagnetic radiation by an antenna array of N elements, forming an ensemble of signals that depend on time and the number of an antenna element, synchronously converting the ensemble of received signals into digital signals, converting digital signals into the signal of the complex spatial covariance matrix, which describes the amplitudes and phases of the mutual signals received by the array elements, forms a direction finding relief, determines the angles θ _i and ϕ _{i of} each beam of the received multipath signal from the maxima of the direction finding relief, characterized in that emitters are used as elements of the antenna array, allowing to receive signals in a wide frequency band, the operating frequency range of each emitter is divided into K identical frequency intervals, in each of the K frequency intervals the frequency ω _k is determined, for which the direction finding relief is formed and the angles θ _i and ϕ _{i of} each beam of the received multi-beam broadband signal according to the maxima of the direction finding relief, receive multi-beam broadband signals from these directions and at given frequencies, and for the remaining frequencies of broadband signals, they are approximated by piecewise constant or piecewise linear approximating functions.

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