RU2379704C1 - Method of multiple target resolution - Google Patents

Abstract

FIELD: radiolocation.

SUBSTANCE: invention relates to radiolocation and can be used for isolation of separate targets from multiple targets in pulsed mode. Proposed method comprises isolating quadrature components of complex envelope of signal received by antenna, and converting, within every quadrature component, of the signal into digital form. Digital countdowns are summed within the interval equal to probing pulse duration. Obtained, by summation, N countdowns are supplemented by zeroes to produce sequence of M countdowns, where M=2ⁿ>N (n is integer). Obtained M countdowns are subjected to amplitude weighing. Filter processing by algorithm of M-point fast Fourier conversion (FFC) is effected. Module of signal complex envelope at the DDC algorithm output is determined. Multiple adjacent Doppler filters are selected. Doppler frequency f₁ is determined from said multiple adjacent Doppler filters as filter frequency jmax1 maximum signal amplitude with the center nearby selected Doppler frequency f_1. Vector Z made up of complex amplitudes of signals of subset R₁ is multiplied by inverse autocorrelation matrix. Moduli of the elements of vector E resulted from multiplication are compared with threshold values. If i-th element of vector E exceeds the threshold, decision made about the presence of separate target signal in multiple targets with Doppler frequency corresponding to i-th filter of subset R₁.

EFFECT: increased multiple target resolution.

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Description

The invention relates to radar and can be used in airborne, ground and ship radar stations (radar) to resolve individual targets from the group in the pulse volume.

A known method for detecting a group target [RF Patent No. 2157550 IPC G01S 5/04, 3/72]. The solution to the problem is based on the fact that various direction finding procedures for a group target extended along angular coordinates produce diverging bearings. For this, direction-finding is carried out simultaneously on the basis of two or more known procedures (single-channel, single-pulse, in the direction of receiving emissions from on-board electronic equipment) and a decision is made on the presence of a group target if the spread of the received bearing values exceeds a threshold.

The disadvantage of this method is that the probability of detecting a group target with an increase in the range to it is significantly reduced.

Indeed, the physical basis for the operability of the method is the angular noise of the target. The angular error of radar direction-finding caused by angular noise is determined by the expression σ = σ _usd / r (σ _ush is the rms value of the angular noise expressed in linear units; r is the distance to the group target) [Radar Reference. Ed. M. Skolnik. T.1. M .: Sov. Radio, 1979, p. 409]. Since angular errors caused by angular noise are inversely proportional to range, the effect of this noise affects mainly medium and short ranges [Radar Handbook. Ed. M. Skolnik. T.1. M .: Sov. Radio, 1979, p. 409]. So, if the direction finder provides an accuracy of 0.1 × Θ (Θ is the width of the radiation pattern of the radar antenna), then with a beam width of 1 ° the direction finding error will be 1.7 × 10 ^-3 rad. The maximum rms angular noise of a group target is 0.5 × L (L is the largest group target size) [Radar Reference. Ed. M. Skolnik. T.1. M .: Sov. Radio 1979, p. 411]. Then, for a group target with a size L equal to 100 m, the angular error will be 2.5 × 10 ^-3 rad and 5 × 10 ^-4 rad at ranges of 20 and 100 km, respectively. As can be seen from the above calculations, at large ranges, the error caused by angular noise is significantly less than the error of the direction finder itself, which reduces the probability of detecting a group target in this way.

A known method for detecting a group target [RF Patent No. 2143706, IPC G01S 3/22]. The essence of the method lies in the fact that they evaluate the increment of the direction-finding error signal, for example, in the elevation plane ΔU _ε , and compare it with a set threshold corresponding to the radar equipment error. To increase the likelihood of correct detection of a group target, the direction-finding error signal U _{ε is} fixed at the beginning (U _εн ) and at the end of the packet (U _εк ) of the total signal, and the angle γ between the scanning plane of the radar antenna beam and the direction-finding plane is also taken into account. When this form the output signal ΔU _ε = | U _εn -U _εk |, which serves to detect a group target. If there is a single target, the values of U _ε at the beginning of U _εн , and at the end of the pack U _εк remain unchanged U _ε = U _εн = U _εк , and in the presence of a group goal they change in accordance with the shift of the energy center, i.e. depend on its angular dimensions.

The disadvantage of the method, as previously discussed, is the dependence of the probability of the correct detection of a group target on the range to it.

A known method for detecting a group target [US Patent No. 4536764, IPC G01S 7/28, 13/52]. The essence of the method is that the quadrature components of the complex envelope of the received signal antenna are extracted, the signal is converted into digital form in each quadrature component, within the interval equal to the duration of the probe pulse, digital samples are added up, N samples obtained from the summation are subjected to amplitude weighting filtering is carried out according to the N-point fast Fourier transform (FFT) algorithm, the complex og modulus is calculated the signal at the output of the Doppler filters, select a set of adjacent Doppler filters, determine the first Doppler frequency f ₁ from the above set of adjacent Doppler filters, as the filter frequency jmax1 with a maximum signal amplitude, select the first subset of the set of adjacent Doppler filters R ₁ centered around the selected first Doppler frequency f ₁ , the value of the first threshold is obtained by multiplying the amplitude of the signal of the first Doppler frequency f ₁ with the first factor less than unity in the first sub After many adjacent Doppler filters R ₁ , the signal amplitude groups exceeding the first threshold are determined, the obtained signal amplitude groups are divided into clusters whose width is three Doppler filters, the number of clusters is calculated to obtain the first C ₁ count, and weakened by blanking the signal amplitudes of the first Doppler frequency f ₁ and groups of nearby Doppler frequencies determine the second Doppler frequency f ₂ as the filter frequency jmax2 with the maximum signal amplitude among non- abnormal signals from the first subset of adjacent Doppler filters R ₂ , select the second subset of the set of adjacent Doppler filters R ₂ centered around the selected second Doppler frequency f ₂ , obtain the value of the second threshold by multiplying the amplitude of the signal of the second Doppler frequency f ₂ with a second factor, if the first count C _{1 is} less than or equal to one, or by multiplying the amplitude of the signal of the second Doppler frequency f ₂ with the first factor, if the first count C _{1 is} greater than one, then in the second subset of adjacent Doppler filters R ₂ , determine the group of signal amplitudes that have exceeded the second threshold, divide the obtained group of signal amplitudes into clusters, the width of which is three Doppler filters, count the number of clusters to obtain a second C ₂ count, calculate the intermediate count in accordance with the mathematical expression

C = C ₁ - | C ₂ -C ₁ | +1,

Further, the final score is equated to the interim account C, if the received interim account C is greater than or equal to one, or the final score is equal to one, if the received interim account C is less than one, a decision is made to detect a group target if the resulting final score is more than one.

The disadvantage of this method is the low probability of detecting a group target whose Doppler signal frequencies are within the same cluster, i.e. The resolution of the prototype method is determined by the width of the cluster, which in principle cannot be less than the width of one or three Doppler filters.

, вычисляют модуль комплексной огибающей сигнала на выходе доплеровских фильтров, выбирают множество смежных доплеровских фильтров, определяют доплеровскую частоту f₁ из названного множества смежных доплеровских фильтров, как частоту фильтра jmax1 с максимальной амплитудой сигнала, выбирают подмножество множества смежных доплеровских фильтров R₁ с центром около выбранной доплеровской частоты f₁, для всех фильтров подмножества R₁ вычисляют коэффициент b_j, равный отношению амплитуды сигнала j-го фильтра

к найденной максимальной амплитуде сигнала в фильтре jmах1

:The closest technical solution is a method for detecting a group target [RF Patent No. 2293349 (priority from 05/18/2005) IPC G01S 13/04, 13/56]. The essence of the method is that the quadrature components of the complex envelope of the received signal antenna are extracted, the signal is converted into digital form in each quadrature component, within the interval equal to the duration of the probe pulse, digital samples are added up, N samples obtained from the summation are subjected to amplitude weighting filtering is performed according to the N-point FFT algorithm; for all Doppler filters, the signal in the jth filter is multiplied by value

the module of the complex envelope of the signal at the output of the Doppler filters is calculated, the set of adjacent Doppler filters is selected, the Doppler frequency f ₁ is determined from the above set of adjacent Doppler filters as the filter frequency jmax1 with the maximum signal amplitude, the subset of the set of adjacent Doppler filters R ₁ with the center near the selected Doppler frequency f ₁ , for all filters of the subset R ₁ calculate the coefficient b _j equal to the ratio of the amplitude of the signal of the j-th filter

to the found maximum signal amplitude in the filter jmax1

:

равные разностям модулей соответствующих квадратурных составляющих сигнала j-го фильтра и произведений найденных коэффициентов b_j на модули соответствующих квадратурных составляющих сигнала фильтра с максимальной амплитудой:calculate values

equal to the differences between the modules of the corresponding quadrature components of the jth filter signal and the products of the found coefficients b _j by the modules of the corresponding quadrature components of the filter signal with the maximum amplitude:

какcalculate indicator

as

с порогом обнаружения η, который устанавливают исходя из требуемого значения вероятности ложного обнаружения групповой цели, при превышении порога хотя бы в одном фильтре принимают решение об обнаружении групповой цели.compare the result

with a detection threshold η, which is set based on the required value of the probability of false detection of a group target, when the threshold is exceeded, at least one filter decides to detect a group target.

The disadvantages of the prototype method are the inability to determine the number and Doppler frequencies of individual targets in the group, as well as the inability to resolve the group target, the Doppler frequencies of the signals of which are within the same N-point FFT filter, i.e. The potential resolution of the prototype method is determined by the width of one Doppler filter of an N-point FFT.

The invention solves the problem: after detecting a group target according to the prototype method, it is possible to determine the number and frequencies of Doppler echoes of individual targets as part of a group, including when Doppler frequencies of signals of individual targets are within the same Doppler filter of an N-point FFT and are absent resolution in range and angular coordinates.

The solution to the problem is that after the summation of the digital samples is completed, the sequence of N samples obtained by summing is supplemented with zeros to a sequence of M samples, where

M = 2 ⁿ > N (n is an integer), the obtained M samples are subjected to amplitude weighing, filtering is performed according to the M-point FFT algorithm, the module of the complex envelope of the signal at the output of the FFT algorithm is calculated, the set of adjacent Doppler filters is selected, the Doppler frequency f is determined ₁ of the above set of adjacent Doppler filters, as the filter frequency jmax1 with the maximum signal amplitude, select a subset of the set of adjacent Doppler filters R ₁ centered around the selected Doppler frequency f ₁ , derived from the complex amplitudes of the filter signals of the subset R _{1, the} vector Z is multiplied by a pre-calculated inverse autocorrelation matrix, the modules of the elements obtained as a result of the multiplication of the vector E are compared with threshold values, which are set based on the required values of the probability of false decisions, when the threshold is exceeded by the ith element of the vector E decide on the presence of a single target signal as part of a group signal with a Doppler frequency corresponding to the ith filter of the subset R ₁ .

The invention is illustrated by drawings. Figure 1 shows a structural diagram of a device that implements the proposed method for resolving a group target, where 1 is a phase detector, 2 is a low-pass filter, 3 is an analog-to-digital converter, 4 is an adder, 5 is an antenna, 6 is a receiver, 7 is a local oscillator , 8 - signal processing processor. Figure 2 presents a diagram explaining the sequence of signal conversion in the signal processing processor 8. Figure 3-5 shows diagrams that demonstrate the possibility of determining the proposed method and the number and frequency of the Doppler echo signals of individual targets in the group, including in the case when the Doppler the signal frequencies of individual targets are within the same Doppler filter of the N-point FFT. In FIGS. 3-5, the initial sequence of N samples is padded with zeros to M samples so that M = 4N. Therefore, the filter spacing along the frequency axis in the subset R ₁ obtained from the results of the M-point FFT is four times smaller than the filter spacing (width) in the N-point FFT. Figure 3 presents the results of signal processing for a single-purpose situation, in Fig. 4 for a dual-purpose and in Fig. 5 for a tri-purpose. In Fig. 4 and Fig. 5, the Doppler frequency spacing of the target echoes corresponds to half the filter width of the N-point FFT.

The essence of the invention is as follows. It is known that the response to the sum of input actions for linear systems, which include the FFT algorithm, is a superposition of responses to each effect. That is, the response of the FFT algorithm to the mixture of echoes of individual targets from the group is nothing more than the sum of the responses to the echo of each individual target. The response of the FFT algorithm to the echo of an individual target is the autocorrelation function of the weight window shifted by the Doppler frequency multiplied by the complex amplitude of the echo. Having inverse linear transformation FFT output signal on a subset of R _1, determined values of the complex amplitudes of the echoes from the individual targets group at all frequencies corresponding FFT points subset R _1. The echoes of real individual targets are "located" only at certain points on the frequency axis corresponding to the Doppler frequencies of the echoes of these targets. At these points from the subset R ₁ after the above inverse linear transformation, the complex amplitudes of these echo signals are formed. At the remaining points of the subset R ₁ zeros are formed, since there are no echo signals of real targets with such Doppler frequencies. In the presence of observation noises at points of the frequency axis, where there are no real echo signals, values close to zero will be obtained. By comparing the modules of the amplitude estimates obtained on the subset R ₁ with the thresholds established on the basis of the observation noise level, the number and Doppler frequencies of the echo signals of individual targets from the group are estimated. In this case, the potential resolution is determined by the frequency removal of the filters of the M-point FFT.

To obtain a specific relationship linking the amplitudes of the echo signals of individual targets from the group to the output signal of the FFT algorithm, we introduce a number of notation.

Let F ₁ , F ₂ , F ₃ = ... = F _{n the} points of the frequency axis corresponding to the FFT points of the subset R ₁ (F ₂ -F ₁ = F ₃ -F ₂ = ... = F _n -F _n-1 = ΔF) . From the signals at the output of the FFT algorithm at the points of the subset R ₁ the vector Z = [Z ₁ Z _{2 ...} Z _n ] ^{T is formed} , T is the transpose operator.

Putting in correspondence with each point of the frequency axis some amplitude of the echo of an individual target from the group, that is, formally assuming that the processed signal contains echoes of individual targets with Doppler frequencies corresponding to all points of the frequency axis from the subset

R ₁ , we write the vector of complex amplitudes of these echo signals: E = [E ₁ E ₂ ... E _n ] ^T. Since the composition of a real group goal may contain a different number of single goals, the individual elements of the vector E are actually zero.

If in the processed implementation there is only a target echo with a complex amplitude E ₁ and Doppler frequency F ₁ , and the amplitudes of the other targets are zero (E ₂ = E ₃ = ... = E _n = 0), then the vector Z in the absence of observation noise takes the form

Z = [1ξ (F ₂ -F ₁ ) ... ξ (F _n -F ₁ ) ^T E ₁ = [1ξ (ΔF) ... ξ ((n-1) ΔF)] ^T E ₁ ,

where ξ (F) is the autocorrelation function of the weight window, the specific form of which depends on the weighting function used.

Similarly, in the case when in the processed implementation there are all n goals corresponding to the points of the subset R ₁ , then:

Formula (1) takes into account the fact that the value of the autocorrelation function for a negative value of an argument is complex conjugate (operator ( ^* )).

Denoting by the variable Q the matrix of values of the autocorrelation function (autocorrelation matrix):

we write formula (1) in the form of a linear matrix equation with an unknown vector E:

To find E from equation (3), we multiply both its parts on the left by the matrix Q ^-1 , the inverse of Q:

In the absence of observation noises, as a result of calculating E according to (4), complex amplitudes of echo signals of real targets are formed at points corresponding to their Doppler frequencies. The remaining elements of the vector E are equal to zero. In real radar systems, there are observation noises, which means that the vector Z in (1) will be somewhat distorted, and the elements of the vector E are also calculated with some error. Therefore, to decide on the number and frequency of the Doppler echo signals of individual targets from the group, it is necessary to compare the modules of the elements of the vector E with threshold values. The latter are selected based on the required values of the probabilities of false decisions.

The potential resolution of the radar when implementing the proposed method and increasing the signal-to-noise ratio depends on the distance in frequency ΔF of the FFT points. To reduce the ΔF value after summing the digital samples of the input signal within the interval equal to the duration of the probe pulse, the sequence of N samples obtained by summing should be supplemented with zeros to the M-sequence, where M = 2 ⁿ > N (n is an integer). After that, it is possible to perform an M-point FFT on the input signal. Since the number of FFT points in the initial frequency range increases, the distance between the points on the frequency axis is M / N times smaller compared to the N-point FFT [Marple ml. S.L. Digital spectral analysis and its applications. Per. from English - M .: Mir, 1990, p.65].

The proposed method of processing in a pulse-Doppler radar. One of the variants of the structural diagram of a device that implements the proposed method for detecting a group target, is presented in figure 1. The signal received by antenna 5 is fed to the input of receiver 6. To ensure coherent processing, the signal from the output of receiver 6 using two phase detectors 1, a local oscillator 7, a 90 ° 9 phase shifter, and two low-pass filters 2 is divided into quadrature components. In analog-to-digital converters 3 the formation of a sequence of digital samples of the quadrature components of the signal. Further, in the adders 4, the summation of the digital samples of the quadrature components of the signal. Summation, as in the prototype method, is carried out within the interval equal to the duration of the probe pulse.

All further signal processing occurs in the signal processing processor 8. FIG. 2 is a diagram explaining the signal conversion sequence in the signal processing processor 8. The sequence of N samples obtained by summing is supplemented with zeros to the M-sequence, where M = 2 ⁿ > N ( n is an integer). The obtained M samples are subjected to amplitude weighting, and filter processing is performed according to the M-point FFT algorithm. Then calculate the module of the complex envelope of the signal at the output of the FFT algorithm. Next, a plurality of adjacent Doppler filters are selected. From the selected set of adjacent Doppler filters, the Doppler frequency f ₁ is determined as the filter frequency jmax1 with the maximum signal amplitude, and a subset of the set of adjacent Doppler filters R ₁ with a center near the selected Doppler frequency f _{1 is} selected. The vector Z composed of the complex amplitudes of the filter signals of the subset R _{1 is} multiplied by the inverse autocorrelation matrix Q ^-1 previously calculated according to formula (2). The modules of the elements obtained by multiplying the vector E are compared with threshold values, which are set based on the required values of the probabilities of false decisions. When the threshold is exceeded by the i-th element of the vector E, they decide on the presence of a signal of an individual target in the group signal with a Doppler frequency corresponding to the i-th filter of the subset R ₁ .

Confirmation of the possibility of obtaining the above technical result in the implementation of the proposed method was carried out using mathematical modeling.

Three situations were simulated: in the processed signal there are echo signals of one (figure 3), two (figure 4) and three (figure 5) targets with equal amplitudes. In each situation, the signal was subjected to amplitude weighting with a rectangular window (the amplitudes of the samples did not change), followed by the calculation of the vector Z using the M-point FFT. Then, according to formula (4), the vector E.

Figures 3-5 show diagrams demonstrating the possibility of estimating the number and frequency of the Doppler echo signals of individual targets as part of a group one, including when the Doppler frequencies of the signals of individual targets are within the same Doppler filter of an N-point FFT. In FIGS. 3-5, the initial sequence of N samples is padded with zeros to M samples so that M = 4N. Therefore, the filter spacing along the frequency axis in the subset R ₁ obtained from the results of the M-point FFT is four times smaller than the filter spacing (width) in the N-point FFT. The true values of the Doppler frequencies of the echo signals of the targets in FIGS. 3-5 are indicated by vertical arrows.

Figure 3-5 shows that a comparison of the moduli of the elements of the vector E with threshold values will determine the quantitative composition of the group target and measure the Doppler frequency of the echo signals of individual targets from the group with an accuracy of up to one M-point FFT filter. Moreover, the value of M is limited only by the computing capabilities of the radar computer.

The use of the invention in airborne, ground and ship radars does not require a change in their construction principles, operating modes, significant computational costs and will allow high-performance resolution of a group target in the absence of resolution of individual targets in a group by angular coordinates and range.

Claims (1)

A method for resolving a group target, which consists in isolating the quadrature components of the complex envelope of the received antenna of the signal, converting the signal into digital form in each quadrature component, within the interval equal to the duration of the probe pulse, summing up the digital samples, characterized in that they complement the received as a result of summation, the sequence of N samples by zeros to the sequence of M samples, where M = 2 ⁿ > N (n is an integer), the obtained M from amplitude weighting accounts, carry out filtering according to the M-point fast Fourier transform (FFT) algorithm, calculate the complex envelope module of the signal at the output of the FFT algorithm, select the set of adjacent Doppler filters, determine the Doppler frequency f ₁ from the specified set of adjacent Doppler filters as the filter frequency jmax1 with the maximum signal amplitude is selected subset of adjacent Doppler filters R ₁ centered about the selected doppler frequency f ₁ composed of compl ksnyh amplitudes R ₁ subset filter signal vector Z multiplied by the calculate in advance an inverse autocorrelation matrix compared modules elements obtained by the multiplication of the vector E with a threshold value which is set based on the required value of false solutions probability when exceeding the threshold i-th element of the vector E take a decision on the presence of a signal of an individual target as part of a group with a Doppler frequency corresponding to the ith filter of the subset R ₁ .

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