RU2407034C1 - Method of resolving group target - Google Patents

Abstract

FIELD: physics. ^ SUBSTANCE: quadrature components of the complex envelope of a signal received by an antenna are picked up, in each quadrature component, the signal is converted to digital form, within intervals (strobes) equal to duration of a probing pulse, digital readings are summed up, in each strobe N readings obtained during summation undergo amplitude weighing, filter processing is performed on an algorithm of N-point fast Fourier transformation, the modulus of the complex envelope of the signal at the output of Doppler filters is calculated, in the range strobe, a set of adjacent Doppler filters is selected, a first Doppler frequency f1 from said set of adjacent Doppler filters is determined as frequency of the filter jmax1 with maximum signal amplitude, a vector Z composed of complex amplitude values of signals of all range strobes in the filter with frequency jmax1 is multiplied by a predefined inverse autocorrelation matrix, the modulus of elements of the vector E obtained from the multiplication is compared with threshold values which are set based on the required probability values for erroneous solutions, presence of a signal of a separate target in a group with range corresponding to the i-th strobe is indicated by the i-th element of vector E exceeding the threshold. ^ EFFECT: possibility of determining the number and distance to separate targets in a group target. ^ 5 dwg

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. 2106653 of 03/10/1998, IPC G01S 7/292]. In this method, the task of detecting a group target is solved based on the phenomenon of mutual suppression of overlapping signals when they are compressed after limitation. This result is achieved by the fact that in the known method of processing a radar signal based on the weight processing of the received oscillation and comparing it with the threshold U ₀ , additionally carry out the weight processing of the oscillation after its limitation. The decision to detect a group target is made if the signal level after the main processing reaches the value U _0i , and after the additional one — below the level U _d1 corresponding to the value U _0i .

The disadvantage of this method is that in order to make a decision on the detection of a group target, an additional processing channel is necessary, which complicates the technical implementation of the method. In addition, it provides for signal processing in a limited mode, which leads to additional losses, distortion of the phase structure of the received signal and a decrease in the probability of detecting a group target.

A known method for detecting a group target [US Patent No. 4536764 from 08.20.85, IPC G01S 7/28, 13/52]. The essence of the method lies in the fact that within the intervals equal to the duration of the probe pulse (range gates), the digital samples are added up, the N samples obtained as a result of the summation are subjected to amplitude weighting, filter processing is performed according to the N-point fast Fourier transform (FFT) algorithm, in the range strobe, a plurality of adjacent Doppler filters is selected, the first Doppler frequency f ₁ is determined from the named set of adjacent Doppler filters as filter frequency j max1 with the 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 , obtain the value of the first threshold by multiplying the signal amplitude of the first Doppler frequency f ₁ with the first factor less than unity in the first subset of the set of adjacent Doppler filters R ₁ , determine the group of amplitudes of the signals exceeding the first threshold, divide the obtained group of amplitudes of the signals into clusters, the width of which is three Doppler filter, count the number of clusters to obtain the first count C ₁ , attenuate by blanking the amplitudes of the signals of the first Doppler frequency f ₁ and the group of Doppler frequencies located close to, determine the second Doppler frequency f ₂ as the filter frequency jmax2 with the maximum signal amplitude among the underexposed signals from the first subset adjacent Doppler filters R _1, selecting a second subset of adjacent Doppler filters R ₂ centered about the selected second Doppler frequency f ₂ are prepared led second threshold rank by multiplying the signal amplitude of the second Doppler frequency f ₂ to the second multiplier when the first tab C ₁ is less than or equal to one, or by multiplying the signal amplitude of the second Doppler frequency f ₂ to the first multiplier when the first tab C ₁ greater than unity, then in second subset of the plurality of adjacent Doppler filters R ₂ group is determined signal amplitudes that exceed the second threshold, the received signals are separated into clusters amplitudes group whose width is three Doppler filter podschity ayut number of clusters to obtain a C ₂ of the second account is calculated intermediate score according to the mathematical expression

C = C ₁ - | C ₂ -C ₁ | +1,

Further, the final score is equated to the intermediate score C, if the received intermediate score C is greater than or equal to one, or the final score is equal to one, if the received intermediate score C is less than one, a decision is made to detect a group target in the range gate if the received final score is greater than one .

The disadvantage of this method is the low probability of detecting a group target for which the Doppler frequencies of the signals of its individual elements coincide. This is due to the fact that the resolution of the method is determined by the width of the group of adjacent Doppler filters, which in principle cannot be less than the width of one or three Doppler filters. Thus, if the Doppler frequencies of the signals of a group target coincide, then when performing the operation of blanking the amplitudes of the signals of a group of adjacent Doppler frequencies, information that the target is a group can be lost. This is the reason for the low probability of detecting a group target, the Doppler frequencies of the signals of which practically coincide.

к амплитуде сигнала в фильтре jmax1 строба kmax

:The closest technical solution is a method for detecting a group target [RF Patent No. 2298806 (priority from 10/10/2005) 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 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, in the range strobe select a set of adjacent Doppler filters, determine the first Doppler frequency f ₁ from the specified set of adjacent Doppler filters as the filter frequency jmax1 with the maximum signal amplitude, for all other range gates, determine the ratio of the signal amplitude b _k in the filter jmax1 of the kth gate

to the signal amplitude in the filter jmax1 strobe kmax

:

,

,

,

, равного разностям модулей соответствующих квадратурных составляющих сигнала в фильтре jmax1 k-го строба и произведений, найденных отношений амплитуд сигналов b_k на модули соответствующих квадратурных составляющих сигнала в фильтре jmax1 строба kmax:find the quadrature components of the voltage

,

equal to the differences between the modules of the corresponding quadrature components of the signal in the filter jmax1 of the kth gate and the products of the found ratios of the amplitudes of the signals b _k to the modules of the corresponding quadrature components of the signal in the filter jmax1 of the strobe kmax:

,

,

,

,

, величина которой характеризует состав цели (одиночная или групповая) какget voltage amplitude

, the value of which characterizes the composition of the target (single or group) as

,

,

с амплитудой напряжения η, характеризующей порог обнаружения, который устанавливают исходя из требуемого значения вероятности ложного обнаружения групповой цели, при превышении порога принимают решение об обнаружении групповой цели в стробе дальности.compare the obtained voltage amplitude

with a voltage amplitude η characterizing the detection threshold, which is set based on the required value of the probability of false detection of the group target, when the threshold is exceeded, a decision is made to detect the group target in the range gate.

The disadvantages of the prototype method are the inability to determine the number and ranges to individual targets in the group when the Doppler frequencies of their echo signals practically coincide, and there is no resolution in range and angular coordinates.

The invention solves the problem: after detecting a group target according to the prototype method, provide the ability to determine the number and range of individual targets in the group, including when the Doppler frequencies of the signals of individual targets are within the same Doppler filter of an N-point FFT and there is no resolution in range and angular coordinates.

The solution to the problem is that after determining the first Doppler frequency f ₁ as the filter frequencies jmax1 with the maximum signal amplitude, multiply the vector Z composed of the complex amplitudes of the signals of all range gates in the filter with the frequency jmax1 and calculate the inverse autocorrelation matrix in advance, and compare the modules of the elements obtained in the result of multiplying the vector E with threshold values, which are set based on the required values of the probabilities of false decisions, when the threshold is exceeded by the ith element of the vector and E decide whether a signal is present separate targets as part of a group with a range corresponding to the i-th strobe.

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, 9 - phase shifter 90 °. 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 ability to determine the proposed method and the number and range of individual targets in the group, including in the case when the Doppler frequencies signals of individual targets are within the same Doppler filter of the N-point FFT, and there is no resolution in range and angular coordinates. Figure 3-5 shows the results of processing according to the proposed method for long-range strobe filter angles 1. Figure 3 shows the results of signal processing for single-purpose situations, figure 4 for dual-purpose and figure 5 for triple. In this case, the bearings of individual targets are equal, the Doppler frequencies of individual targets are f ₁ , and for multi-purpose situations, the distance between individual targets is ten times less than the range of range resolution.

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 coherent-pulse radar, is a superposition of responses to each effect. That is, the response of the correlation filter processing scheme to a mixture of echoes of individual targets from a group is nothing more than the sum of the responses to the echo of each individual target. The response in the range gates of the filter jmax1 of the correlation-filter processing scheme to an echo of a single target is the autocorrelation function of the probe signal shifted by the delay time multiplied by the complex amplitude of the echo signal.

Having performed the inverse linear transformation of the output signal of the range filter gates at the angles jmax1, the values of the complex amplitudes of the echo signals of individual targets from the group at all ranges corresponding to the generated gates are determined. The delay times of the echo signals of real individual targets correspond to certain range gates. In these gates, after the above inverse linear conversion, the complex amplitudes of these echo signals are formed. In the remaining gates, zeros are formed, since there are no echoes of real targets with corresponding ranges.

In the presence of observation noises in those range gates where there are no real echo signals, values close to zero will be obtained. By comparing the modules of the obtained estimates of the amplitudes with the thresholds established on the basis of the required values of the probabilities of false decisions, the number and range of individual targets from the group are estimated. In this case, the potential resolution is determined by the relative position of the range gates, which is proposed to be set smaller than the classical range of range resolution.

To obtain a specific relationship linking the amplitudes of the echoes of individual targets from the group structure with the output signal of the range filter gates jmax 1, we introduce a number of notation.

Let D ₁ , D ₂ , D ₃ = ... = D _{n the} distance to the targets corresponding to the filter gates jmax1 (D ₂ -D ₁ = D ₃ -D ₂ = ... = D _n -D _n-1 = ΔD). Of the signals at the output of the filter gates jmax1, a vector Z = [Z ₁ Z ₂ ... Z _n ] ^{T is formed} , T is the transpose operator.

Assigning to each range gate an 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 ranges corresponding to all filter gates jmax1, 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 targets, the individual elements of the vector E are actually zero.

If in the processed implementation there is only a target echo at a distance D ₁ with a complex amplitude E 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

,

,

where ξ (D) is the autocorrelation function of the probe signal.

Similarly, in the case when in the processed implementation there are all n targets corresponding to all the strobe of the filter jmax1, 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) as 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 noise, as a result of calculating E according to (4), complex amplitudes of echo signals of real targets are formed in the gates corresponding to their ranges. The remaining elements of the vector E are equal to zero. In real radar systems there are observation noises, this 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, in order to make a decision about the number and ranges to 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 by the mutual arrangement of the range gates ΔD, i.e. may be significantly shorter than the classic range resolution range. A decrease in ΔD will reduce the instrumental component of errors in estimating the number and ranges of individual targets.

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 is carried out within intervals equal to the duration of the probe pulse (range gates).

согласно выражениям (1)-(4), характеризующая отличия наблюдаемых откликов стробов от откликов сигнала одиночной цели, в предлагаемом способе вычисляют непосредственно оценку вектора комплексных амплитуд составляющих сигнала групповой цели E, для чего умножают вектор Z на заранее рассчитанную согласно формуле (2) обратную автокорреляционную матрицу Q^-1. Сравнивают модули элементов полученного в результате умножения вектора E с пороговыми значениями, которые устанавливают исходя из требуемых значений вероятностей ложных решений. При превышении порога i-м элементом вектора E принимают решение о наличии сигнала отдельной цели в составе групповой с дальностью, соответствующей i-му стробу.All further signal processing takes place in the signal processing processor 8. Fig. 2 is a diagram explaining the signal conversion sequence in the signal processing processor 8. The samples obtained by summing in each gate are subjected to amplitude weighting and are filtered by the FFT algorithm. Then calculate the module of the complex envelope of the signal at the output of the Doppler filters. Next, in the kmax range gate, 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 a maximum signal amplitude. Of the complex amplitudes of the signals at the outputs of all range gates in the filter with a frequency jmax1, vector Z is made up. Then, in contrast to the prototype method, in which for each range gate the value is calculated

according to expressions (1) - (4), characterizing the differences between the observed responses of the gates from the responses of a signal of a single target, in the proposed method, the estimate of the vector of complex amplitudes of the components of the signal of the group target E is directly calculated, for which the vector Z is multiplied by the inverse calculated in advance according to formula (2) autocorrelation matrix Q ^-1 . 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. If 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 with a range corresponding to the i-th gate.

Confirmation of the receipt of 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.

Figures 3-5 show diagrams demonstrating the possibility of estimating the number and ranges of individual targets in the group as a proposed method, including when the Doppler frequencies of the signals of individual targets are within the same Doppler filter of an N-point FFT and there is no resolution in range and angular coordinates. 4-5, the distance between the targets is one tenth of the standard range of range resolution. The true values of the ranges to 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 range to individual targets from the group to the accuracy of the distance between the gates in range ΔD. Moreover, the ΔD value is limited mainly 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 resolution to resolve individual targets in a group in the absence of resolution in angular coordinates, range and Doppler frequency.

Claims (1)

The method for resolving a group target, which consists in isolating the quadrature components of the complex envelope of the received antenna signal, in each quadrature component, the signal is converted into digital form, within the intervals (gates) equal to the duration of the probe pulse, the digital samples are added up, in each gate subjected to the summation of N samples in amplitude weighting, carry out filter processing according to the algorithm of N-point fast conversion Fourier, calculate the modulus of the complex envelope of the signal at the output of the Doppler filters, select a number of adjacent Doppler filters in the range gate, 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, characterized in that it is composed of complex the amplitudes of the signals of all range gates in the filter with a frequency jmax1, the vector Z is multiplied by a pre-calculated inverse autocorrelation matrix, the element modules are compared Acquiring a result of multiplication of the vector E with the threshold values, which establish, on the basis of the desired values of the probabilities of false solutions, in excess of the threshold i-th element of the vector E decide on the presence of a signal in a single target composed of a group with a range corresponding to the i-th strobe.

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