RU2713235C1 - Method to increase accuracy of direction finding of radio-frequency sources by detector-direction finder with multiscale antenna system - Google Patents

Abstract

FIELD: radio equipment.

SUBSTANCE: invention relates to radio engineering and can be used in multichannel monopulse detectors-direction finders of radio monitoring systems for solving problems of direction finding radio-frequency sources. For this purpose, multiple reception of radio signals involves accumulation of time-based realizations of spectral signal readings for each signal, which enables to increase efficiency of direction-finding due to higher output signal-to-noise ratio. At that, deciding function of direction finding is valid in case of antenna system with arbitrary structure and antenna elements directivity characteristics, and is also adaptive to mutual effects of antenna elements on each other, which enables to use the disclosed method in real conditions of operation of the detector-direction finder.

EFFECT: high efficiency and accuracy of determining azimuthal and elevation bearings on a signal source by taking into account mutual correlation links between spatial-amplitude-phase distribution of spectral densities within the frequency band.

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Description

The invention relates to the field of radio engineering and can be used in multi-channel monopulse detectors-direction finders (OP) of radio monitoring systems for solving problems of direction finding of radio emission sources (IRI).

Improving the efficiency and accuracy of determining azimuthal and elevation bearings to the signal source is achieved by taking into account mutual correlation between the spatial-amplitude-phase distribution of spectral densities in the redistribution of the frequency band. In the case of multiple reception of radio signals, accumulation of time realizations of spectral readings for each signal is used, which makes it possible to increase direction-finding efficiency indicators by increasing the output signal-to-noise ratio and distinguishing against the background noise of wide-band pseudorandom signals with a low power spectral density. The decisive direction finding function is valid in the case of an antenna system (AS) with an arbitrary structure and directivity characteristics of antenna elements (AE), and is also adaptive to the mutual influences of antenna elements on each other, which makes it possible to use the proposed method under real operating conditions of a detector-direction finder.

A known method of direction finding of radio signals [1], which consists in the following:

1. Reception of radio signals by an antenna array (AR) consisting of N elements (N> 2) located in the direction-finding plane; identical non-directional antennas are used as elements of the antenna array.

2. Conversion of signals (including the reference signal) by a multichannel receiver with a common local oscillator for all channels. Conversion of signals by a multichannel receiver is performed sequentially in time from a pair of elements, while the signal from one element not included in this pair is used as a reference signal. Consistently in time, the signals from the following pairs of elements are converted, while the signal from one element not included in the next pair is used as a reference signal. In this way, signals from all possible pairs of elements of the antenna array are converted in the number of P groups of pairs formed for the N element antenna array, and in each group of the pairs, the signals are converted from elements with the same distance between them.

3. Obtaining the spectral characteristics of the signals of each channel by measuring in equal time intervals the complex spectra of the signals of each channel and dividing them into selected frequency subbands.

4. Comparison of the complex spectral characteristics of the signals in each frequency subband by storing P groups of pairs of signal spectra.

5. The definition of convolution of complex conjugate spectra for each frequency range. In this case, an additional determination of the convolution of complex conjugate signal amplitudes for P signal pairs is performed; complex amplitudes of P signal pairs are obtained. The complex signal amplitudes for each channel and frequency subband are obtained using the Fourier transform of all channels.

6. Two-dimensional Fourier transforms are performed for all complex amplitudes of the signal pairs for each of the P groups, the components of the two-dimensional angular spectrum are obtained, which form the two-dimensional angular spectrum corresponding to the radio signal for the selected frequency subband.

7. By multiplying the P components, the maximum modulus of the two-dimensional angular spectrum is determined. The value of the bearing is determined from the value of the argument of the maximum modulus of the angular spectrum.

The disadvantages of this method are as follows:

- to implement this method of direction finding, an N-element antenna array and a multi-channel radio receiving device that receives signals from each pair of antenna elements sequentially in time are used. The distance between the antenna elements should be the same, which imposes strict requirements on the configuration of the antenna array;

- the method does not imply the implementation of the procedure of accumulating temporary realizations for each spectral component, which does not allow increasing the efficiency of the direction finding process of the IRI by increasing the amount of information.

A known method for determining estimates of the direction to the source of radio emission [2], involving the calculation of the mutual spectrum of the spectral components of the signal for all possible combinations of antenna pairs. This method involves the following:

1. Synchronous (coherent) reception of temporary implementations from the outputs of all N (where N> 2) elements of the antenna system in the spatial channels of the detector-direction finder, simultaneously falling into the current reception (analysis) band.

2. Coherent transfer (heterodyning) to a lower frequency and synchronous conversion of temporary implementations into digital form.

3. Calculation of samples of the Fourier transform of the digitized implementation in each spatial channel of the detector-direction finder. For each spectral report of the fast Fourier transform of temporary realizations, channel amplitudes and energies are calculated.

4. The formation of the decisive function is the assessment of the complex amplitude of the signals.

5. Maximization of the squared modulus of the complex angular spectrum by the possible angles of arrival of the wave in horizontal and vertical planes.

6. Assessment of the direction of arrival and elevation of the source of radio emission.

The disadvantages of this method are as follows:

- the decisive function of the analogue is obtained for the case of receiving one temporary implementation. Performing independent direction finding by spectral readings of each received implementation provides a decrease in direction-finding efficiency indicators compared to the case when, in order to increase the signal-to-noise ratio, energy is accumulated for each spectral readout;

- the decisive function of the analog is valid when the antennas of the detector-direction finder are identical and non-directional, and their radiation patterns have a unit amplitude that does not depend on the direction of arrival of the IRI radio wave. In the general case, in the presence of mutual influences in the antenna system of the detector-direction finder, as well as in the case of using antenna elements of a different type, the decisive function becomes unfair, which leads to a deterioration in the performance indicators of the analogue.

Closest to the proposed method is the direction finding of radio sources with a correlation interferometer with two receiving channels [3], adopted further as a prototype and involving the following steps:

1. Obtaining time-synchronous samples of the direction-finding radio signal received by two antenna elements.

2. Display of the received signal samples from the time domain to the frequency domain (performing the Fourier transform on the received samples).

3. The calculation of complex convolutions between the spectral components with the same numbers for a pair of antenna elements and obtaining the interference vector of a pair of signals by the formula:

, $${\dot{A}}_{{\mathrm{<figure-callout\; id="1"\; label="n"\; filenames="00000021.png,00000022.png"\; state="\{\{state\}\}">n</figure-callout>}}_1,{\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="00000021.png"\; state="\{\{state\}\}">n</figure-callout>}}_2}={\displaystyle \sum _i{\dot{S}}_c\left(k,i,n_1\right){\dot{S}}_o{}^{\ast }\left(k,i,n_2\right)}$$

,

– комплексные отсчеты спектра сигнала сигнального тракта,Where $${\dot{S}}_c\left(k,i,n_1\right)$$

- complex samples of the signal spectrum of the signal path,

– комплексные отсчеты спектра сигнала опорного тракта, $${\dot{S}}_o\left(k,i,n_2\right)$$

- complex samples of the spectrum of the signal of the reference path,

k - radio channel number, 1 ≤ k ≤ k _max ,

i is the number of the spectrum reference in the channel, i = 0, 1, K, q-1,

n ₁ , n ₂ - numbers of elements of the AP, n ₁ ≠ n ₂ .

4. Repeat steps 1-3 for all direction finding pairs.

всех пеленгационных пар, формируемых путем последовательного перемножения измеренного интерференционного вектора на вектор опорного (теоретического) пространственного сигнала, варьируемого по пространственным угловым координатам.5. The calculation of partial radiation patterns $${\dot{D}}_p\left(\theta ,\beta \right)$$

all direction-finding pairs formed by sequentially multiplying the measured interference vector by the vector of the reference (theoretical) spatial signal, varying in spatial angular coordinates.

For an equidistant annular antenna array (ECAR), the partial radiation patterns have the form:

, $${\dot{D}}_p\left(\theta ,\beta \right)={\dot{A}}_{{\mathrm{<figure-callout\; id="1"\; label="n"\; filenames="00000021.png,00000022.png"\; state="\{\{state\}\}">n</figure-callout>}}_1,{\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="00000021.png"\; state="\{\{state\}\}">n</figure-callout>}}_2}\cdot \exp \left\{-\frac{2\pi R}{\lambda }\left(\cos \left(\theta -{\alpha }_{n_1}\right)\sin \beta -\cos \left(\theta -{\alpha }_{n_2}\right)\sin \beta \right)\right\}$$

,

where R is the radius of the ring,

λ is the received wavelength,

α _n - the location angle of the n-th element of the AR, counted counterclockwise from the x axis,

θ, β are the variable angular coordinates.

6. The synthesis of radiation patterns of the antenna array according to the formula:

. $${\dot{D}}_A\left(\theta ,\beta \right)={\displaystyle \sum _p{\dot{D}}_p\left(\theta ,\beta \right)}$$

.

.7. Calculation of the bearing to the source as an argument of the maximum synthesized radiation pattern $${\dot{D}}_A\left(\theta ,\beta \right)$$

.

The disadvantages of this method are as follows:

- when receiving a signal, it is not taken into account that for each switching pair of channels the realization of noise and the complex amplitudes of the signals are different;

- the direction finding method presented in the prototype does not imply the implementation of the procedure for accumulating temporary realizations for each spectral component, which does not allow increasing the efficiency of the IR direction finding procedure by increasing the amount of information accumulation.

The problem to which this invention is directed is to increase the efficiency of direction finding of radio emission sources.

The technical result that can be obtained by implementing the method is to increase the accuracy of direction finding by the IR detector-direction finder with multi-scale antenna system.

The technical result is achieved due to the fact that in the method of direction finding of radio emission sources by a direction finding detector with a multiscale antenna system, each signal is a set of spectral samples of the Fourier transform of time realizations. Each temporal realization is a complex amplitude of temporal realizations in the elementary frequency channel (ECH). The bandwidth of the ECH is inversely proportional to the duration of the temporary implementation, characterized by frequency proximity and information about the direction of arrival of the signal of each component. The signal component of each spectral reference characterizes the distribution of the amplitude and phase of the field of the radio wave of the IRI over the opening of the antenna of the detector-direction finder. The components of the noise and noise components in spatially separated receiving points have random amplitudes and phases that are not caused by the fall of a certain radio wave.

Using the accumulation of time realizations of the spectral samples of the signal for each signal allows to increase the efficiency of the method by increasing the output signal-to-noise ratio.

The use of the developed most plausible Iranian direction finding algorithm in special software of the radio reconnaissance and radio monitoring subsystems will increase the efficiency of processing the results of reconnaissance through the use of more complete information about the signal.

The proposed method for improving the accuracy of direction finding of radio emission sources of a detector-direction finder using a multiscale antenna system involves the following procedures.

1. Multiple sequential in time obtaining synchronous samples of the direction-finding radio signal received by two antenna elements - direction-finding pair.

2. Display of the received signal samples from the time domain to the frequency domain (performing the Fourier transform).

взаимных энергий, накопленной по серии из R > 1 измерений для ПП:3. The calculation of the matrix $${\dot{Q}}^{\left(p\right)}$$

mutual energies accumulated over a series of R> 1 measurements for PP:

, (1)

– двухмерный вектор наблюдаемых данных, элементами которого являются комплексные амплитуды напряжений на выходе n₁, n₂ элементах АР, $$n_1\ne n_2$$

, сформированные по всем измерениям серии:Where $${\dot{U}}_r^{\left(p\right)}$$

Is a two-dimensional vector of the observed data, the elements of which are the complex amplitudes of the voltages at the output n ₁ , n ₂ elements of the AR, $${\mathrm{<figure-callout\; id="1"\; label="n"\; filenames="00000021.png,00000022.png"\; state="\{\{state\}\}">n</figure-callout>}}_1\ne {\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="00000021.png"\; state="\{\{state\}\}">n</figure-callout>}}_2$$

formed by all measurements of the series:

$${\dot{U}}_r^{\left(n\right)}=\left(\begin{array}{c}{\dot{S}}_c\left(k,i,n_1\right)\\ {\dot{S}}_0\left(k,i,n_2\right)\end{array}\right)\cdot$$

– комплексные отсчеты спектра сигнала сигнального тракта, $${\dot{S}}_c\left(k,i,n_1\right)$$

- complex samples of the signal spectrum of the signal path,

– комплексные отсчеты спектра сигнала опорного тракта, $${\dot{S}}_o\left(k,i,n_2\right)$$

- complex samples of the spectrum of the signal of the reference path,

k - radio channel number, 1 ≤ k ≤ k _max ,

i is the number of the spectrum reference in the channel, i = 0, 1, K, q-1,

n ₁ , n ₂ - numbers of elements of the AP, n ₁ ≠ n ₂ .

4. Repeat steps 1-3 for all p direction finding pairs (PP).

всех ПП:5. The calculation of partial DN $${\dot{D}}_p\left(\theta ,\beta \right)$$

all PP:

, $$D_p=\frac{{\dot{H}}^{\left(p\right)}{\left(\theta ,\beta \right)}^{\text{H}}{\dot{K}}_p^{-1}{\dot{Q}}^{\left(p\right)}{\dot{K}}_p^{-1}{\dot{H}}^{\left(p\right)}\left(\theta ,\beta \right)}{{\dot{H}}^{\left(n\right)}{\left(\theta ,\beta \right)}^{\text{H}}{\dot{K}}_p^{-1}{\dot{H}}^{\left(p\right)}\left(\theta ,\beta \right)}$$

,

– двухмерный комплексный вектор, элементы которого являются коэффициентами пропорциональности между амплитудой $${\dot{E}}_r^{\left(q\right)}$$

напряженности поля пеленгуемой волны в энергетическом центре АС и напряжением на ее нагрузке,Where $${\dot{H}}^{\left(p\right)}\left(\theta ,\beta \right)$$

Is a two-dimensional complex vector whose elements are proportionality coefficients between the amplitude $${\dot{E}}_r^{\left(q\right)}$$

the field strength of the direction-finding wave in the AC energy center and the voltage at its load,

– обратная матрица ковариации шума в приемных каналах р-й пеленгационной пары. $${\dot{K}}_p^{-1}$$

- the inverse matrix of noise covariance in the receiving channels of the r-th direction finding pair.

представим следующим образом:For an equidistant annular antenna array (ECAR) of radius R with a radio wave length λ, the vector $${\dot{H}}^{\left(p\right)}\left(\theta ,\beta \right)$$

imagine as follows:

. $${\dot{H}}^{\left(p\right)}\left(\theta ,\beta \right)=\left(\begin{array}{c}\exp \left\{\frac{2\pi R}{\lambda }\left(\cos \left(\theta -{\alpha }_{n_1}\right)\sin \beta \right)\right\}\\ \exp \left\{\frac{2\pi R}{\lambda }\left(\cos \left(\theta -{\alpha }_{n_2}\right)\sin \beta \right)\right\}\end{array}\right)$$

.

6. The synthesis of radiation patterns of antenna arrays according to the formula:

. $$M\left(\theta ,\beta \right)={\displaystyle \sum _p{\dot{D}}_p\left(\theta ,\beta \right)}$$

.

. 7. Calculation of the bearing to the source as an argument of the maximum of the synthesized radiation pattern $$M\left(\theta ,\beta \right)$$

.

The proposed method for improving the accuracy of direction finding of radio sources by a detector-direction finder with a multi-scale antenna system is devoid of the above disadvantages of the prototype, namely:

- in the formation of the decisive direction finding function, it is taken into account that for each direction finding pair of noise realization channels, the complex amplitudes of the received signals are different and different;

- the method involves the procedure of accumulating temporary realizations for each spectral component, this allows, by accumulating information about the direction of arrival of the radio wave over the spectral components of the signal of the same IRI, to increase the efficiency of the direction finding procedure of the IRI.

In FIG. 1 shows a structural diagram of a device that implements the proposed method:

1 - serial connection of the antenna array with the switch;

2 - antenna switch;

3 - two-channel coherent receiver (3.1 - the first receiver, 3.2 - the second receiver);

4 - block of analog-to-digital signal processing (4.1 - first analog-to-digital converter, 4.2 - second analog-to-digital converter, 4.3 - block of digital signal processing);

5 - electronic computer.

The two-channel coherent receiver 3 has two inputs: the first is signal, and the second is the reference. Antenna switch 2 sequentially connects to the inputs of a two-channel receiver pairs of elements of the antenna array, selected according to the direction finding algorithm. The main functions of the two-channel receiver: frequency conversion of the received radio signal and primary filtering by side channels of reception, that is, the function of preparing the received radio signal for conversion to digital form. In the block of analog-to-digital processing 4, the basic computational operations by the digital processing algorithm are performed. The computer performs control functions, and also displays the results.

The device operates as follows.

A superposition of radio signals from various sources of radio emission is received by the elements of AP 1 and fed to the input of the switch, which passes signals from the selected pair of AE to two inputs of the receiver 3. From a pair of receiver outputs, the intermediate frequency signals are fed to the ADC inputs, where they are synchronously converted to digital signals, in the analog-to-digital signal processing unit 4, using the discrete Fourier transform for each signal from each direction-finding pair, complex signal samples of the signal and reference path spectrum are obtained , a matrix of mutual energies is formed, a partial radiation pattern is synthesized. Based on the totality of all direction-finding pairs, a directional relief is formed, the maximum value of which determines the direction of arrival (bearing) of the signal.

The reception method with a two-channel radio receiving channel is applicable in a number of practical cases (for example, in order to reduce the mass-dimensional characteristics of the equipment). The proposed method, without changing the sequence of actions and their functional purpose, allows to increase the efficiency of direction finding IRI due to the correct statement of the direction finding problems and the use of the correct statistical optimal decision statistics - two-dimensional angular spectrum, namely:

- accumulation of spectral components, which allows to increase the accuracy and reliability of direction finding;

- adaptability of the algorithm to unknown noise intensity;

- the validity of the decisive direction finding function in the case of speakers with an arbitrary structure and directional characteristics of antenna elements;

- a statistically optimal expression for the angular spectrum (both partial and total);

- the decisive direction finding function, allowing you to use the proposed method in the real conditions of the operation of the OP, when there are mutual effects of the antennas on each other.

IMPLEMENTATION

Statistical modeling of performance indicators of a method for improving the accuracy of direction finding of radio sources by a direction finding detector with a multi-scale antenna system was carried out in the Matlab mathematical modeling package. In FIG. Figures 2 and 3 present the results of statistical modeling (measured bearings and their histograms) for direction finding of radio waves using a direction finding detector with a seven-element ECAR. The neighboring antenna elements of the antenna array were used as pairs participating in direction finding.

The plane wave incidence in the azimuthal direction of 180 degrees was simulated with a ratio of the ECAR radius to the wavelength of 1.4, the signal-to-noise ratio is 12 dB. In statistical modeling, the number of statistical tests was chosen equal to 10 ⁸ , the number of accumulations of the mutual spectra of the signals was assumed to be 3. Additive noise was assumed to be Gaussian with the same intensity in the channels of the detector-direction finder. In FIG. 2a shows the result of direction finding in accordance with the proposed method, and in FIG. 2b - in accordance with the prototype.

In FIG. Figure 3 shows the dependence of the mean square error (RMS) of direction finding on the ratio of the ECAR radius to the wavelength. The solid line corresponds to the direction finding results of the proposed method, the dashed line corresponds to the prototype method.

The simulation results confirmed that the proposed method for improving the accuracy of direction finding by a direction finding detector with a multi-scale antenna system provides improved direction finding efficiency (reducing the likelihood of anomalous and variance of normal direction finding errors).

SOURCES OF INFORMATION

1. RF patent for the invention No. 2144200 “Method of direction finding of radio signals and multichannel direction finder” / Ashikhmin A.V., Vinogradov A.D., Kondrashchenko V.N., Rembovsky A.M., 1999.

2. Radzievsky V.G., Ufaev V.A. Primary signal processing in digital panoramic direction finders. - Radio engineering, 2003, No. 7, p. 26 - 31.

3. Rembovsky A.M., Ashikhmin A.V., Kozmin V.A. Radio monitoring: tasks, methods, tools / Edited by A.M. Rembovsky. M .: hot line-Telecom, 2006 - 492 p.

Claims (1)

A method for improving the accuracy of direction finding of radio emission sources by a direction finder with a multi-scale antenna system, including obtaining time-synchronous samples of a direction-finding radio signal received by two antenna elements - a direction-finding pair of a multi-element antenna array, displaying the received signal samples from the time domain into the frequency domain - performing Fourier transform on the received samples , calculation of partial radiation patterns for each direction finding pair, synthesis of n directivity of the antenna array as the sum of the partial radiation patterns, calculation of the estimate of the direction to the source as an argument to the maximum of the synthesized radiation pattern of the antenna array, characterized in that the time-synchronous samples of the direction-finding radio signal received by the direction-finding pair are produced repeatedly sequentially in time, partial radiation patterns are calculated as the ratio of two products: the product of the matrices of Hermitian conjugate two-dimensional complex vector Inverse covariance matrix of the noise in the receiver channels, the matrix of accumulated energy mutual inverse covariance matrix of the noise in the receiver channels, the two-dimensional complex vector and the Hermitian conjugate matrix product dimensional complex vector inverse covariance matrix of noise in the receiver channels, the two-dimensional complex vector.

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