RU2316788C9 - Mode of detection by a pulsed-doppler radar of a group target - Google Patents

Abstract

FIELD: the invention refers to radiolocation and may be used for determination of the fact of availability of a group target in a pulsed volume.

SUBSTANCE: the achieved technical result is increasing probability of determination of a group or a single targets taking into account a turbo-propeller effect. As the base for the mode one can use the principle of compensation of the signal if it is formed by a single target at availability only of an echo-signal from the airframe and appearance of uncompensated residues, if the echo-signal is formed by a group target or a single target taking into account the reflections as of the airframe so of the turbine blades or the propellers of a flying vehicle. For this it is necessary to execute a correlation-filter processing of the signal received by an antenna in strobes of distance and Doppler filters. The difference in complex amplitudes is found out by way of comparison of weight coefficients of complex amplitudes of signals on Doppler frequencies in each current strobe of distance. The decision about correct detection of a target is taken if differences of these coefficients prevail some threshold value.

EFFECT: increases reliability of detection of an air target.

10 dwg

Description

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

A known method for detecting a group target according to the patent of the Russian Federation No. 2157550 dated 10.10.2000, IPC G01S 5/04, 3/72. The method is based on the fact that various methods of direction finding a group target give diverging bearings. To this end, direction finding of the target is carried out simultaneously by several known methods of direction finding. For example, single-channel and monopulse, in the direction of receiving emissions of on-board electronic equipment and single-channel or also monopulse method. If the scatter of the received bearing values, measured simultaneously by different direction finding methods, exceeds a threshold value, then a decision is made about the presence of a group target.

The disadvantage of this method is that the probability of detecting a group target decreases significantly with increasing range to it.

There is also another method for detecting a group target according to the patent of the Russian Federation No. 2143706 dated 12/27/99, IPC G01S 3/22. The method consists in the fact that in the process of viewing the radar space in azimuth α, they measure direction-finding error signals in azimuth U ' _α and elevation angle U' _β , convert them into a direction-finding error signal, the magnitude and sign of which are associated with angular mismatch in the elevation coordinate β the ratio

U _β = U ' _β cosγ-U' _α sin sin,

where γ is the angle between the scanning plane of the radar antenna beam and the direction-finding plane, the direction-finding error signal U _β is fixed at the beginning of U _βn and at the end of U _{βk of the} total signal packet, the difference module ΔUβ of the signals U _βн and U _{βк is formed} , which serves to detect a group target

ΔU _{β is} compared with a set threshold value corresponding to the radar hardware error U _n , when exceeded which a decision is made to detect a group target.

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 according to US patent No. 4536764 from 08.20.85, IPC G01S 7/28, 13/52. The method is based on the analysis of the amplitudes of the Doppler frequency signals in a pulse-Doppler radar. The essence of the method lies in the fact that in the strobe in which the target is detected (accompanied), several signals of adjacent Doppler frequencies are selected. The selected Doppler frequency signals are processed in two passes, and each pass includes the steps of searching, threshold detection and counting the number of targets C ₁ and C _2, respectively. Then calculate the intermediate score C in accordance with the expression

and then equate the final score C ₀ to the interim account C (C ₀ = C) if the resulting interim account C is greater than or equal to one (C≥1), or equate the final score C ₀ to one (C ₀ = 1) if received interim account C is less than one (C <1). If the final score C ₀ obtained is greater than unity (C ₀ > 1), then a decision is made to detect a group target.

The disadvantage of the prototype method is the low probability of detecting group or single targets in the presence of intense signals in their spectrum of Doppler frequencies due to the turboprop effect (echo signals from screws, turbine blades, etc.). In the prototype method, signals due to the presence of this effect, like signals from a glider (“glider component”), can fall into the analyzed set of Doppler frequency signals and be taken as a set of separate group or single targets, which leads to a low probability of detecting group or solitary goals.

The objective of the invention is to provide detection of group or single targets, taking into account the presence in their spectrum of Doppler frequencies of signals due to the turboprop effect (echo signals from screws, turbine blades, etc.).

и

T_n - период повторения зондирующих импульсов, Δt - интервал дискретизации), формируют стробы дальности

,

(K - скважность зондирующих импульсов) путем суммирования цифровых отсчетов сигналов в пределах интервалов, равных длительности τ_зи зондирующего импульса, подвергают полученные в результате суммирования сигналы амплитудному взвешиванию, осуществляют фильтровую обработку сигналов по алгоритму БПФ, вычисляют модуль

(J - количество сигналов доплеровских частот на выходе фильтров БПФ) комплексной огибающей сигналов доплеровских частот на выходе фильтров БПФ. Выбирают далее сигнал с наибольшим значением модуля комплексной огибающей U_{kj max} и определяют соответствующий ему k-й строб дальности и сигнал доплеровской частоты jmax. Для всех сигналов доплеровских частот выбранного k-го строба дальности определяют коэффициенты ослабления

комплексных амплитуд сигналов по частотам, равные отношению комплексных амплитуд сигналов j-х частот

к максимальной комплексной амплитуде сигнала частоты jmax

A method for detecting a group target of a pulse-Doppler radar is to isolate the quadrature cosine S ^c (t) and sinus S ^s (t) components of the complex envelope of the received radar antenna signals reflected from the target, in each quadrature component, the signals are converted to digital form

and

T _n is the repetition period of the probe pulses, Δt is the sampling interval), form the range gates

,

(K - porosity probing pulses) by summing the digital samples of signals within intervals of equal duration τ _{communication} probe pulse, is subjected to the resultant summation signal amplitude weighting, The filter processing performed by the FFT algorithm signal, calculating module

(J is the number of Doppler frequency signals at the output of the FFT filters) the complex envelope of the Doppler frequency signals at the output of the FFT filters. Next, the signal with the highest value of the modulus of the complex envelope U _{kj max} is selected and the corresponding kth range gate and the Doppler frequency signal jmax are determined. For all the Doppler frequencies of the selected k-th range gate, the attenuation coefficients are determined

complex amplitudes of signals in frequencies equal to the ratio of complex amplitudes of signals of j frequencies

to the maximum complex amplitude of the frequency signal jmax

формируют разность амплитуд сигналов Δ_j между комплексными амплитудами сигналов доплеровских частот и произведения максимальной комплексной амплитуды сигнала частоты jmax на соответствующие коэффициенты ослабления

видаin the adjacent k-th range gate using the calculated coefficients

form the difference in the amplitudes of the signals Δ _j between the complex amplitudes of the Doppler frequency signals and the product of the maximum complex amplitude of the frequency signal jmax by the corresponding attenuation coefficients

kind of

comparing the obtained signal amplitude difference Δ _{j with a} threshold amplitude value η, which is set based on the desired probability of false detection of a group target, if the threshold value η is exceeded, at least one value of the signal amplitude difference Δ _j decides to detect a group target.

Let us explain in more detail the essence of the invention. For the single-target option, the complex amplitude of the reflected signal in the kth range gate and jth frequency filter in the absence of noise can be written as

- комплексная амплитуда сигнала на выходе доплеровского фильтра, обусловленная суммарным воздействием комплексных амплитуд планерной и турбинных составляющих сигнала цели на частотную характеристику j-го фильтра;Where

- the complex amplitude of the signal at the output of the Doppler filter, due to the total effect of the complex amplitudes of the glider and turbine components of the target signal on the frequency response of the j-th filter;

F _k - a value equal to the number of discrete samples of the target signal attributable to the k-th range gate.

комплексной амплитуды сигнала по частотам, вычисленные в k-м стробе дальности, согласно (1), равныAt the same time, attenuation coefficients

the complex amplitude of the signal in frequency, calculated in the k-th range gate, according to (1), are

It can be seen from expression (4) that in the case of a single target, the obtained coefficients are determined by the ratio of the complex amplitudes of the signals at the output of the Doppler filters and do not depend on which range gate they are received in. In the adjacent range gate, for example, (k + 1) -m, using the calculated coefficients (4) we find the differences between the complex signal amplitudes in accordance with expression (2)

It can be seen from expression (5) that the differences in the signal amplitudes Δ _j in this case will be zero, since for a single target in any range gate, the complex signal amplitudes in the Doppler filters are compensated. Thus, for the single-target option, in the absence of noise, the signal amplitude differences Δ _j will be zero.

In the case of a group target, the expression for the signal in the kth range gate and jth frequency filter in the absence of noise can be written as

- комплексная амплитуда сигнала на выходе доплеровского фильтра, обусловленная суммарным воздействием комплексных амплитуд планерной и турбинных составляющих сигнала n-й цели на частотную характеристику j-го фильтра;Where

- the complex amplitude of the signal at the output of the Doppler filter, due to the total effect of the complex amplitudes of the glider and turbine components of the signal of the nth target on the frequency response of the jth filter;

F _kn - a value equal to the number of discrete samples of the signal of the nth target falling on the k-th range gate;

N - the number of single targets in the group.

комплексной амплитуды сигнала по частотам, вычисленные в k-м стробе дальности, согласно (1), равныAt the same time, attenuation coefficients

the complex amplitude of the signal in frequency, calculated in the k-th range gate, according to (1), are

From the expression (7) it can be seen that in the case of a group goal, the obtained coefficients are determined by a rather complex dependence. In particular, they now depend on the relative position of the nth reflected signal of the group target relative to the kth range gate.

In the adjacent (k + 1) th range gate, using the calculated coefficients (7), we find the differences between the complex signal amplitudes in accordance with expression (2)

It can be seen from expression (8) that the differences in the signal amplitudes Δ _j in this case will not be zero, since the dependence of the coefficients on the relative position of the nth reflected group target signal relative to the kth range gate does not allow to compensate for the complex signal amplitudes at the output of Doppler filters . Thus, for the group target option, in the absence of noise, the signal amplitude differences Δ _j will not be zero. This is a hallmark of group and single goals.

The invention is illustrated by drawings in figures 1-10. Figure 1 shows the structural diagram of a pulse-Doppler radar 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 - local oscillator, 8 - signal processor.

Figure 2 presents the algorithm explaining the sequence of signal conversion in the signal processor 8.

Figure 3-10 shows a diagram of experimental data proving the efficiency of the method.

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. In the pulse-Doppler radar diagram, the antenna system 5 is connected in series with the signal receiver 6. The output signal of the receiver 6 is divided into two quadrature channels by two phase detectors 1, a local oscillator 7, and a phase shifter 90 ° 9. Each quadrature channel contains a phase detector 1 connected in series, a low-pass filter 2, an ADC 3 and an adder 4. The outputs of the quadrature channels, i.e. adders 4, are connected to the signal processing processor 8. The signal processing processor 8 operates in accordance with a pre-programmed program.

и

T_n - период повторения зондирующих импульсов, Δt - интервал дискретизации). Далее формируются стробы дальности

,

(K - скважность зондирующих импульсов) путем суммирования отсчетов сигналов в сумматорах 4. Суммирование производится в пределах интервалов, равных длительности τ_зи зондирующего импульса РЛС.The detection of a group target of a pulse-Doppler radar occurs as follows. The signals received by antenna 5 are fed to the input of receiver 6. To ensure coherent processing, the signals from the output of receiver 6 using two phase detectors 1, a local oscillator 7, a 90 ° phase shifter, and two low-pass filters 2 are separated into quadrature cosine S ^c (t) and sinus S ^s (t) components. In the analog-to-digital converters 3 the formation of a sequence of digital samples of the quadrature component signals

and

T _n is the repetition period of the probe pulses, Δt is the sampling interval). Next, range gates are formed

,

(K - porosity probing pulses) by summing the signal samples in the adders 4. The summation is within the interval of duration τ _{communication} probing radar pulse.

,

(J - количество сигналов доплеровских частот на выходе фильтров БПФ). Далее выбирают сигнал с наибольшим значением модуля комплексной огибающей U_{kj max} и определяют соответствующий ему k-й строб дальности и сигнал доплеровской частоты jmax. В процессоре обработки сигналов 8 для всех сигналов доплеровских частот выбранного k-го строба дальности определяют коэффициенты ослабления

комплексных амплитуд сигналов по частотам, в соответствии с выражением (1). Затем в смежном стробе дальности (например, k+1-м) при помощи вычисленных коэффициентов ослабления амплитуды сигнала

формируют разности амплитуд сигналов Δ_j по формуле (2). Полученные разности амплитуд сигналов Δ_j сравнивают с пороговым значением амплитуды сигнала η, которое устанавливают исходя из требуемого значения вероятности ложного обнаружения групповой цели. При превышении порогового значения η хотя бы одной разностью амплитуд сигналов Δ_j принимают решение об обнаружении групповой цели.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 signals obtained from the summation are subjected to amplitude weighting and are filtered by the FFT algorithm, and then the complex envelope module is calculated Doppler frequency signals at the output of FFT filters

,

(J is the number of Doppler frequency signals at the output of the FFT filters). Next, select the signal with the highest value of the modulus of the complex envelope U _{kj max} and determine the corresponding kth range gate and the Doppler frequency signal jmax. In the signal processing processor 8, for all signals of the Doppler frequencies of the selected k-th range gate, the attenuation coefficients are determined

complex amplitudes of signals in frequencies, in accordance with expression (1). Then, in an adjacent range gate (for example, k + 1-m) using the calculated attenuation coefficients of the signal amplitude

form the difference in the amplitudes of the signals Δ _j according to the formula (2). The resulting signal amplitude differences Δ _{j are} compared with a threshold signal amplitude η, which is set based on the desired value of the probability of false detection of a group target. If the threshold value η is exceeded by at least one difference in signal amplitudes Δ _j , a decision is made 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 according to experimental data (Fig.3-10).

определялись, согласно соотношению (1), по сигналам доплеровских частот одиночной цели в k-м стробе дальности. Из фиг.5 видно, что разности амплитуд сигналов Δ_j ниже порогового значения амплитуды η.Figure 3 presents the signals of the Doppler frequencies of a single target in the k-th range gate. Figure 4 shows the signals of the Doppler frequencies of the same single target in the (k + 1) -th range gate. Figure 5 shows the differences in the amplitudes of the signals A, calculated by the formula (2) in the (k + 1) -th range gate. The presented differences in the signal amplitudes Δ _j were calculated for the signals of the Doppler frequencies of a single target, presented in figure 3, 4. The attenuation coefficients of the complex signal amplitude in frequency

were determined, according to relation (1), from the signals of the Doppler frequencies of a single target in the k-th range gate. From figure 5 it is seen that the difference in the amplitudes of the signals Δ _j below the threshold amplitude η.

Therefore, in accordance with the proposed method, a decision will be made to detect a single target, which is true.

To verify the operability of the method in the presence of a group target, the signals of the single-target Doppler frequencies shown in Figs. 6 and 7 with the signals of the single-target Doppler frequencies shown in Figs. 3 and 4 in the kth and in (k + 1) were combined programmatically -th range gates, respectively. The signals of the Doppler frequencies of the group (pair) target obtained in such a combination in the kth and in the (k + 1) -th range gates are shown in Figs. 8, 9, respectively. The difference in signal amplitudes Δ _j calculated by formula (2) in the (k + 1) -th range gate is shown in Fig. 10. Figure 10 shows that one of the differences in the signal amplitudes Δ _j exceeded the threshold value of the amplitude η, therefore, in accordance with the proposed method, a decision will be made to detect a group target, which also corresponds to reality.

The use of the invention in airborne, ground-based and ground-based pulse-Doppler radars will not require a change in their construction principles, operating modes, as well as significant computational costs and will make it possible to detect group or single targets in the presence of signals due to the turboprop effect in their spectrum of Doppler frequencies (echo signals from screws, turbine blades, etc.).

Claims (1)

A method for detecting a group target by a pulse-Doppler radar station (radar), which consists in extracting the quadrature cosine S ^s (t) and sine S ^s (t) components of the complex envelope of the received radar antenna of the signals reflected from the target, in each quadrature component they transform digital signals

and

,

T _n - the repetition period of the probe pulses, Δt - sampling interval), form the range gates

,

(K -skvazhnost probing pulses) by summing the digital samples of signals within intervals of equal duration τ _{communication} probe pulse, is subjected to the resultant summation signal amplitude weighting, The filter signal processing performed by the algorithm of fast Fourier transform (FFT), calculating module

,

(J is the number of Doppler frequency signals at the output of the FFT filters) of the complex envelope of Doppler frequency signals at the output of the FFT filters, characterized in that the signal with the highest value of the complex envelope modulus U _{kjmax is selected} and the corresponding kth range gate and the Doppler frequency signal jmax , for all signals of the Doppler frequencies of the selected k-th range gate, the attenuation coefficients are determined

complex amplitudes of signals in frequencies equal to the ratio of complex amplitudes of signals of j frequencies

to the maximum complex amplitude of the frequency signal jmax

in the adjacent k-th range gate using the calculated coefficients

form the difference in the amplitudes of the signals Δ _j , of the form

between the complex amplitudes of the Doppler frequency signals and the product of the maximum complex amplitude of the frequency signal jmax by the corresponding attenuation coefficients

, the obtained difference in the amplitudes of the signals Δ _{j is} compared with a threshold value of the amplitude η, which is set based on the required value of the probability of false detection of a group target; if the threshold value η is exceeded, at least one value of the difference in the amplitudes of the signals Δ _j decides to detect a group target.

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