RU2293349C1 - Mode of detection of a group target - Google Patents

Abstract

FIELD: the invention refers to radiolocation and may be used in on-board, on-land and on-ship radars for establishment of the fact of availability of a group target in impulse volume.

SUBSTANCE: the technical result is increasing probability of detection of a group target, whose Doppler frequency signals are in the limits of one-three Doppler filters. The mode of detection of a group target is in that they single out quadrature components of an envelope line of the signal received by the antenna, in each quadrature component they execute transformation of the signal in digital form in the limits of the interval equal to duration of a sounding impulse, make summing up of digital readings, subject the N readings received in the result of summing up to amplitude weighting , execute filter processing in accordance with the algorithm of N- dot quick transformation of Fourier filters different the more so that for all N Doppler filters the signal in the j-filter is multiplied on value

where i - an imaginary unit, N - quantity of Fourier filters, j - a number of Doppler filter

calculate the modules of complex envelope signals at the output of Doppler filters, in the distance strobe choose a large number of adjacent Doppler filters, define Doppler frequency f1 out of named large number of adjacent Doppler filters, define Doppler frequency f1 out of named magnitude of adjacent Doppler filters as the frequency of the filter jmax1 with maximum amplitude of the signal, choose subset multitude of adjacent Doppler filters R1 with the center near chosen Doppler frequency f_1, for all filters of subset R1 calculate coefficient b_j, equal relatively to the amplitude of the signal of the j-filter

to founded maximum amplitude of the signal in the filter jmax1

:

calculate values

,

equal to differences of the modules of corresponding quadrature components of the signal of the j-filter and products of found coefficients b_j in the modules corresponding to quadrature components of the signal of the filter with maximum amplitude:

calculate index

as

, compare received index

with the threshold of detection η, which is installed proceeding from demanded meaning of probability of false detection of a group target, at exceeding the threshold at least in one filter the decision about detection of a group target is taken.

EFFECT: increases probability of detection of a group target.

5 dwg

Description

The invention relates to radar and can be used in airborne, ground and ship radar stations (radar) to establish the fact of the presence of a group target in the pulse volume.

A known method of detecting a group target [RF Patent No. 2157550 from 10.10.2000, IPC G 01 S 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 Handbook / 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 root-mean-square value of the angular noise of a group target is 0.5 × L (L is the largest size of a group target) [Radar Handbook. / 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 from 12/27/99, IPC G 01 S 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.

The closest technical solution is a method for detecting a group target [US Patent No. 4536764 from 08.20.85, IPC G 01 S 7/28, 13/52]. The essence of the method lies in the fact 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, the 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 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 , 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 a number of 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 band and Doppler frequencies located near define a second Doppler frequency f ₂ as jmah2 filter frequency with the maximum amplitude signal among Neos ablennyh signals from a first subset of adjacent Doppler filters R _1, selecting a second subset of adjacent Doppler filters R ₂ about the selected second Doppler frequency center f ₂ gave a second threshold value by multiplying the amplitude of the signal 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 amplitude of the signal of the second Doppler frequency f ₂ with the first factor, if the first count C _{1 is} more than one, then in the second subset of _two 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 the prototype 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.

The invention solves the problem: to increase the probability of detecting a group target whose Doppler signal frequencies are within the same Doppler filter, and there is no resolution in range and angular coordinates.

, где i - мнимая единица, N - количество фильтров БПФ, j - номер доплеровского фильтра

, вычисляют модули комплексных огибающих сигналов на выходах доплеровских фильтров, выбирают множество смежных доплеровских фильтров, определяют доплеровскую частоту f₁ из названного множества смежных доплеровских фильтров, как частоту фильтра j_max1 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 solution to the problem is that after filtering by the N-point FFT algorithm, for all N Doppler filters, the signal in the jth filter is multiplied by

where i is the imaginary unit, N is the number of FFT filters, j is the number of the Doppler filter

the modules of the complex envelopes of the signals at the outputs of the Doppler filters are 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 j _max1 with the maximum signal amplitude, a subset of the set of adjacent Doppler filters R ₁ with a center of about 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.

, на фиг.4 - при относительном рассогласовании сигналов целей по частоте

и на фиг.5 - при относительном рассогласовании сигналов целей по частоте

.The invention is illustrated by drawings. Figure 1 shows a structural diagram of a device that implements the proposed method for detecting 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 showing changes in the detection efficiency of a group target when using the proposed method compared to the prototype method, where P ₁₁ is the probability of correct detection of a single target, P ₁₂ - probability of false detection of a group target, P ₂₁ - probability of missing a group target, P ₂₂ - probability of correct detection of a group target, Δ _f - signal mismatch frequency of targets, ΔF is the width of the Doppler filter. Figure 3 presents the dependence of performance indicators on the signal-to-noise ratio with relative mismatch of target signals in frequency

, figure 4 - with the relative mismatch of the signals of the targets in frequency

and figure 5 - with a relative mismatch of the signals of the targets in frequency

.

The essence of the invention is that in the case when the target is single, the coefficients b _j calculated according to (1) are equal to the ratios of the frequency response modules jx of the filters to the filter characteristic module jmax1 at the Doppler frequency of the target:

- комплексная амплитуда сигнала цели;Where

- the complex amplitude of the target signal;

- значение комплексной частотной характеристики доплеровского фильтра с номером j на частоте f;

- the value of the complex frequency response of the Doppler filter with number j at a frequency f;

- значение комплексной частотной характеристики доплеровского фильтра с номером jmах1 на частоте f;

- the value of the complex frequency response of the Doppler filter with the number jmax1 at a frequency f;

f is the Doppler frequency of the target signal.

. Для устранения этого смещения и получения вещественных характеристик доплеровских фильтров, выходные сигналы после алгоритма БПФ необходимо домножать на величины

. В результате частотные характеристики фильтров БПФ становятся вещественными:

и

. C учетом выполненного умножения квадратурные составляющие сигналов на выходах доплеровских фильтров j и jmах1 описываются следующими выражениями:It is known that the characteristics of Doppler filters obtained using FFT are complex. The phase shift for the jth filter is

. To eliminate this bias and obtain the material characteristics of Doppler filters, the output signals after the FFT algorithm must be multiplied by

. As a result, the frequency characteristics of the FFT filters become real:

and

. Taking into account the performed multiplication, the quadrature components of the signals at the outputs of the Doppler filters j and jmax1 are described by the following expressions:

Substitution of (5) - (9) into (2) and (3) allows us to obtain

в случае одиночной цели равно нулю. Важно, что в случае групповой (например, парной) цели значение коэффициента b_j зависит не только от доплеровских частот сигналов f₁, f₂, но и от их комплексных амплитуд

,

:As follows from (4), (10), (11), the value

in the case of a single target is zero. Importantly, in the case group (e.g., steam) target value of the coefficient b _j depends not only on the Doppler frequency signals f _1, f _2, but also of their complex amplitudes

,

:

и

в общем случае отличны от нуля:Accordingly, the values

and

generally nonzero:

является показателем для принятия решения об обнаружении групповой цели. При наличии внутреннего шума приемника для принятия решения необходимо величину

сравнивать с порогом η, который устанавливают исходя из требуемого значения вероятности ложного обнаружения групповой цели, например, в соответствии с выражениемThus, the quantity

is an indicator for making a decision on the detection of a group target. In the presence of internal noise of the receiver, a value is necessary for making a decision

compare with the threshold η, which is set based on the desired value of the probability of false detection of a group target, for example, in accordance with the expression

where μ is a constant coefficient;

μ ₀ - threshold level of detection of a single target.

Implement the proposed method of processing is possible in a pulse-Doppler radar. One of the possible structural diagrams of a device that implements the proposed method for detecting a group target is shown in FIG. 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 performed within an interval equal to the duration of the probe pulse.

.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 as a result of summation are subjected to amplitude weighting, filter processing is performed according to the FFT algorithm, and for all N Doppler filters, the signal in the jth filter is multiplied by

.

Then, the modules of the complex envelopes of the signals at the outputs of the Doppler filters are calculated. 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.

,

и рассчитывают показатель

согласно (4). Затем показатель

сравнивают с порогом η, который вычисляют в процессоре обработки сигналов 8 по формуле (15). При превышении порога хотя бы в одном фильтре принимают решение об обнаружении групповой цели.For all filters of the subset R _{1, the} coefficient b _{j is} calculated according to relation (1). Next, in the signal processor 8 in accordance with the expressions (2) and (3) calculate the values

,

and calculate the indicator

according to (4). Then indicator

compare with the threshold η, which is calculated in the signal processing processor 8 according to the formula (15). If the threshold is exceeded, at least one filter decides to detect a group target.

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

As an indicator of the effectiveness of the proposed method, a matrix P of the probabilities of the outcomes of signal processing is introduced. The element P _{nm of the} matrix P is the probability that in the presence of a single (n = 1) or group (n = 2) target, a decision will be made whether there is a single (m = 1) or group (m = 2) target. The probabilities P ₁₁ and P ₂₂ are the probabilities of making the right decisions, and P ₁₂ and P ₂₁ are the wrong decisions.

.Figure 3-5 shows the estimates of the values of the elements of the matrix P when using the proposed processing method and the prototype method for single and dual-purpose situations, various signal-to-noise ratios and relative mismatches of target signals in frequency

.

(фиг.5), вероятность правильного обнаружения P₂₂ для предлагаемого способа в зависимости от отношения сигнал/шум составляет 0,2-0,9, а для способа-прототипа - не превышает 0,1.Analysis of the graphical dependencies shown in Fig.3-5, allows us to conclude that the probability of correct detection of the group target P ₂₂ when using the proposed method in comparison with the prototype method is 2-10 times depending on the signal-to-noise ratio. The greater the gain, the higher the signal-to-noise ratio. For example, in the most difficult conditions for detecting a group target, when the relative mismatch of the target signals in frequency

(figure 5), the probability of correct detection of P ₂₂ for the proposed method depending on the signal-to-noise ratio is 0.2-0.9, and for the prototype method it does not exceed 0.1.

The use of the invention in airborne, ground and ship radars will not require a change in their construction principles, operating modes, significant computational costs and will make it possible to detect with high reliability a group target whose signals are within the same Doppler filter in the absence of resolution of individual targets in the group by angular coordinates and range.

Claims (1)

A method for detecting 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 an interval equal to the duration of the probe pulse, digital samples are added up, N samples obtained from the summation are subjected to amplitude weighing, filtering is performed according to the N-point fast Fourier transform (FFT) algorithm, characterized in that for all N Doppler filters the signal in j-th filter is multiplied by the value

where i is the imaginary unit, N is the number of FFT filters, j is the number of the Doppler filter

the modules of the complex envelopes of the signals at the outputs of the Doppler filters are 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

:

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:

calculate indicator

as

compare the result

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

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