RU2410712C1 - Method of detecting aerial objects - Google Patents

Abstract

FIELD: physics, radio.

SUBSTANCE: invention relates to radio engineering and can be used in airspace control systems using direct signals and signals reflected from aerial objects, emitted by multiple uncontrolled and controlled transmitters of radio-electronic systems for different purposes. The technical result is achieved due to additional information extracted through identification and picking up a subset of energy-efficient signals reflected from detected aerial objects from a set of received signals and using the picked up subset of signals for selective search, spatial tracking and identification of the type of a wide range of aerial objects.

EFFECT: high efficiency (information content, accuracy and computing efficiency) of searching, spatial tracking and identification of the type of a wide range of aerial objects with one detection-direction finding station under conditions of prior uncertainty of the shape, size and reflecting properties of objects.

3 cl, 9 dwg

Description

The invention relates to radio engineering and can be used in airspace control systems using direct and reflected signals from airborne objects emitted by many uncontrolled and monitored transmitters of various electronic systems.

Achieving high efficiency in the detection, localization and identification of airborne objects is limited by significant a priori uncertainty in size, spatial orientation, reflecting properties and parameters of the movement of objects, as well as the imperfection of known methods for detecting and tracking airborne objects.

The technology of passive detection and tracking of airborne objects, using the natural "illumination" of airborne targets, created at a variety of frequencies by radio emissions from transmitters for various purposes in the ranges of short, meter, decimeter and centimeter waves: broadcast (commercial FM broadcasting, high-definition television), information ( communication) and measuring (control, navigation), has not yet received sufficient distribution, despite the fact that it can significantly increase stealth and efficiency the detection, spatial localization and identification of a wide class of moving objects.

A known method of detecting air objects [1], which consists in the fact that

receive multi-frequency radio signals in the reception band by the antenna array many times greater than the spectrum width of a single radio signal of the transmitter,

form the complex time spectra of the radio signals of each antenna and the power spectrum of the radio signal of the reference antenna,

the power spectrum of the radio signal of the reference antenna detect the signals of the transmitters,

the complex time spectra form the two-dimensional complex angular spectra of the detected transmitters,

azimuthal and elevation bearings of the transmitters are determined from the angular spectra,

and after comparing elevation bearings β with a threshold, the transmitters are divided into ground and air and the oblique range R to the air targets is determined by the formula R = H / sinβ, where H is the known target altitude.

This method provides effective detection of airborne objects equipped with radio signal transmitters. However, in conditions of radio silence, this method loses its effectiveness.

More effective is the method of detecting air objects [2], free from this drawback and selected as a prototype. According to this method:

choose transmitters that emit spread-spectrum radio signals,

synchronously receive an array of antennas at a plurality of search frequencies multipath radio signals, including direct radio signals of the transmitters and the radio signals of these transmitters reflected from objects,

synchronously transform the ensemble of radio signals received by the antennas into digital signals,

at each search frequency, digital and direct reflected signals are generated from digital signals,

comparing selected direct and reflected signals at each search frequency and determining time delays, Doppler shifts and directions of arrival of reflected signals,

by time delays, Doppler shifts and directions of arrival, the detection and spatial localization of air objects are performed.

The prototype method does not require a transmitter emitting radio signals on board a detectable airborne object, since it provides detection and tracking of airborne objects using the natural "illumination" of airborne objects created at multiple frequencies by radio emissions from various transmitters. The effectiveness of the prototype method depends on a number of factors, of which the geometric arrangement of radiation sources, their power, and the effective scattering area of the target are most important.

However, when a wide class of airborne objects is detected under conditions of a priori uncertainty of the shape, size and reflective properties of objects, this method loses its effectiveness.

The loss of efficiency is due to the fact that in the presence of a wide variety of targets (large, medium, small planes and unmanned aerial vehicles, helicopters, rockets, descent vehicles) it is almost impossible to provide an optimal set of factors for their effective detection in advance. This is because the scattering diagram of a complex target, an example of which is, for example, an airplane, significantly depends on the directions of exposure and reception, as well as on the ratio of the characteristic dimensions of the target and the wavelength (frequency) of the exposure. The larger the ratio of the characteristic size of the target to the wavelength, the stronger is the interference character of the dependence of the effective reflecting area of the target on the viewing angle. In this case, a change in the direction of exposure or reception by a fraction of a degree can change the level of the reflected signal by tens of decibels. Similar changes in the level of the reflected signal are observed when the frequency of the irradiating signal changes.

In this regard, the main disadvantage of the prototype method (loss of detection efficiency under conditions of a priori uncertainty of the shape, size and reflective properties of objects) can be eliminated by the use of adaptive processing operations adopted at a plurality of reflected signal search frequencies.

The technical result of the invention is to increase the efficiency (information content, accuracy and computational efficiency) of search, spatial localization and identification of the type of a wide class of airborne objects by one detection-direction finding station under conditions of a priori uncertainty of the shape, size and reflective properties of objects.

The increase in efficiency is achieved due to additional information extracted by identifying and extracting from the set of received signals a subset of the energy-efficient signals reflected from the detected air objects and using the selected subset of signals for selective search, spatial localization and identification of the type of a wide class of air objects.

The technical result is achieved by the fact that in the method of detecting airborne objects, which consists in selecting transmitters emitting spread-spectrum radio signals, synchronously receiving an array of antennas at a plurality of search frequencies, multi-beam radio signals including direct transmitter signals and the signals of these transmitters reflected from objects synchronously they transform the ensemble of signals received by the antennas into digital signals; at each search frequency, digital direct and compressed reflected signals are formed from digital signals According to the invention, at a plurality of search frequencies, the arrival directions of compressed reflected signals are identified, energy-efficient compressed reflected signals and the corresponding reduced set of search frequencies that are used for selective search, spatial localization and identification of a wide class type are extracted and stored from the compressed reflected signals of each direction aerial objects.

Particular cases of the method are possible:

1. Identification of the arrival directions of compressed reflected signals at a set of search frequencies is carried out by forming a set of three-dimensional selective distribution function (WFR) of compressed reflected signals by azimuth, elevation angle and time delay, determining the number of WFR maxima, identifying each WFR maximum as a separate direction the arrival of compressed echoes with azimuth, elevation, and delay corresponding to these maxima.

This increases the information content of the search and spatial localization.

2. The selection of energy-efficient compressed reflected signals of each direction and the corresponding abbreviated set of search frequencies is carried out by forming the amplitude-frequency distribution (AFC) of compressed reflected direction signals, comparing the AFC with a threshold and extracting energy-efficient compressed reflected direction signals and the corresponding reduced set of search frequencies .

This increases the accuracy of subsequent localization and identification of a wide class of objects due to adaptation to fluctuations of the reflected signals, the intensity of which substantially depends on the ratio of the characteristic size of the objects and the wavelength (frequency) of the irradiation, as well as on the directions of irradiation and signal reception.

3. Selective search, spatial localization and identification of the type of a wide class of airborne objects is carried out by averaging over a reduced set of frequencies the values of delay, relative Doppler shift, azimuths and elevation angles of compressed signals of each i-th direction, detection and formation of spatial coordinates of the i-th air object by average values of delay, relative Doppler shift, azimuth and elevation angle of compressed signals of the i-th direction, calculation of the effective reflecting area and (image intensifier) of the i-th object at each frequency of the abbreviated set according to its range, power of the reflected signal of the i-th direction and radiation power of the radio transmitter, identification of the type of the i-th object by the average value of the image intensifier.

This increases the accuracy of spatial localization of objects, as well as the information content and computational efficiency of the search for a wide class of airborne objects.

Thus, due to the additional information extracted by identifying and extracting from the set of received signals a subset of the energy-efficient signals reflected from the detected air objects and using the selected subset of signals for selective search, spatial localization and identification of the type of a wide class of air objects, it is possible to solve the problem with achieving specified technical result.

The operation of the method is illustrated by drawings:

Figure 1. Block diagram of a device that implements the proposed method for detecting air objects;

Figure 2. Functional diagram of a device that implements the proposed method for detecting airborne objects;

Figure 3. Section of the module of a complex two-dimensional cross-correlation function;

Figure 4. Three-dimensional selective distribution function of compressed echoes;

Figure 5. Features of the formation of elements of a three-dimensional selective distribution function;

6. Object scattering diagrams;

7. The allocation scheme of energy-efficient compressed beam signals and the corresponding reduced set of search frequencies;

Fig. 8. The scheme for determining the coordinates of an air object;

Fig.9. The scheme for determining the coordinates of an air object when using one transmitter.

The device (figure 1), which implements the proposed method, contains a series-connected system for receiving and pre-processing 1, a system for modeling and selection of radio transmitters (RPD) 2 and a computer system 3.

, преобразователя частоты 1-k-2, аналого-цифрового преобразователя (АЦП) 1-k-3, формирователя прямого сигнала 1-k-4, формирователя сжатых отраженных сигналов 1-k-5, АЦП 1-k-6, преобразователя частоты 1-k-7 и антенной решетки 1-k-8.In turn, the receiving and preprocessing system 1 includes K receiving and processing devices 1-k, each of which consists of an antenna array 1-k-1,

1-k-2 frequency converter, 1-k-3 analog-to-digital converter (ADC), 1-k-4 direct signal shaper, 1-k-5 compressed reflected signal shaper, 1-k-6 ADC, frequency converter 1-k-7 and antenna array 1-k-8.

Computing system 3 includes an identification device 3-1, a shaper of a reduced set of signals 3-2, a device for detecting, localizing and identifying objects 3-3 and a display device 3-4.

In this case, system 2 is connected to the inputs of devices 3-3 and 3-4, and also has an interface for connecting to an external RPD base. In addition, the device 3 has an output intended for connection to external systems.

Subsystem 1 is an analog-to-digital device and is designed for multichannel reception on a set K of search frequencies and preprocessing of direct transmitter signals and the signals of these transmitters reflected from air objects.

Each 1-k device is designed to receive a multipath radio signal at a separate kth frequency and to generate a digital direct transmitter signal and digital compressed signals of this transmitter reflected from airborne objects from the received radio signal. In this case, the 1-k-1 antenna array, 1-k-2 converter, 1-k-3 ADC and 1-k-4 driver are designed to generate a direct transmitter signal, and the 1-k-8 antenna array, 1-k converter -7, 1-k-6 ADC and 1-k-5 driver are designed to form compressed radio signals of this transmitter reflected from airborne objects.

Note that there may be cases when the radio signal of the transmitter is a priori known. In such cases, a direct transmitter signal can be generated by modeling in system 2. In this case, the receiving and processing channel, including the 1-k-1 antenna array, 1-k-2 converter, 11-k-3 ADC and 1-k- driver 4 can be used to receive and generate compressed reflected signals at an additional search frequency. In this regard, the number of transmitters used and, therefore, simultaneously monitored frequencies can reach 2K.

Devices 1-k of system 1 may be identical. To do this, these devices must be made in ultra-wideband design. A simpler option may be the construction of 1-k devices, in which these devices overlap adjacent subbands of operating frequencies.

. Каждая антенна является направленной и содержит экран для улучшения направленности. Пространственная конфигурация антенной решетки должна обеспечивать измерение азимутально-угломестного направления прихода радиосигналов и может быть произвольной пространственной конфигурации: плоской прямоугольной, плоской кольцевой или объемной, в частности конформной. Для улучшения различения сигналов не только по пространству, но и по поляризации требуется существенное различие поляризационных откликов антенн решетки, то есть антенная решетка должна быть неоднородной (гетерогенной), то есть должна иметь антенные элементы с отличающимися векторными диаграммами направленности.Antenna arrays 1-k-1 and 1-k-8 consist of N antennas with numbers

. Each antenna is directional and contains a screen to improve directivity. The spatial configuration of the antenna array should provide measurements of the azimuthal elevation direction of arrival of the radio signals and can be of any spatial configuration: flat rectangular, flat circular or surround, in particular conformal. To improve the distinction of signals not only in space, but also in polarization, a significant difference in the polarization responses of the array antennas is required, that is, the antenna array must be heterogeneous (heterogeneous), that is, it must have antenna elements with different vector radiation patterns.

Frequency converters 1-k-2 and 1-k-7 are N-channel, are made with a common local oscillator and with the bandwidth of each channel, variable in accordance with the width of the spectrum of the received radio signal. A common local oscillator provides multi-channel coherent signal reception.

The 1-k-3 and 1-k-6 ADCs are also N-channel and are synchronized by the reference oscillator signal (for simplicity, the reference oscillator is not shown in the diagram).

If the resolution and speed of the ADC are sufficient for direct analog-to-digital conversion of the input signals, as, for example, in the KB range, then frequency selective bandpass filters and amplifiers can be used instead of frequency converters 1-k-2 and 1-k-7. In addition, each frequency converter 1-k-2 and 1-k-7 provides the connection of one of the antennas instead of all the antennas of the array to periodically calibrate the channels using an external signal source in order to eliminate their amplitude-phase non-identity. Calibration by internal signal source is possible. In this case, a noise generator can be used, the output of which is also connected instead of all antennas for periodic calibration of channels.

Shapers 1-k-4 and 1-k-5 are computing devices and are designed to generate respectively direct and compressed reflected digital signals.

Subsystem 2 is a computing device and is designed to identify, select, and periodically update a set of transmitters that irradiate a given region of airspace with spread spectrum radio signals, as well as generate model signals of selected transmitters.

Computing system 3 is intended to identify the directions of arrival of the reflected signals or, in other words, to divide the entire set of reflected signals into groups that differ in the directions of arrival of the signals. In addition, the system 3 is designed to generate an abbreviated set of energy-efficient compressed echoes of each direction, detect airborne objects using an abbreviated set of energy-efficient compressed echoes, generate spatial coordinates and identify the type of detected airborne objects.

An enlarged diagram of the functioning of the device that implements the proposed method for detecting air objects is presented in figure 2. The scheme includes four transmitters RPD1, ..., RPD4 emitting spread-spectrum radio signals at the set of frequencies f _{k = 1} , ..., f _{k = 4} , as well as a detection-direction finding (SOP) station. The radio signals of the transmitters RPD 1, ..., RPD4 are propagated by the earth wave, which is received by the detection-direction-finding station in the form of direct radio signals, and also by the direct wave irradiating a given area of the airspace, received by the detection-direction-finding station in the form of radio signals reflected from the airborne object.

In the detection-direction finding station, a direct signal is generated at each frequency f _k , which is used as a reference signal in the correlation division of the multipath signal into separate beams, i.e. when forming compressed signals reflected from air objects. From the reflected signals, energy-efficient compressed reflected signals and the corresponding reduced set of search frequencies that are used for detection, spatial localization and identification of airborne objects are distinguished.

Transmitters RPD1, ..., RPD4 can be conditionally divided into two classes: uncontrolled (uncontrolled) and controlled (managed). For example, if the RPD1, RPD2, and RPD4 transmitters were not specifically created to work together with a detection-direction finding station and do not have communication lines with a detection-direction-finding station, they can be considered as uncontrolled (uncontrolled). As uncontrolled transmitters, any systems or devices emitting in the short, meter, decimeter, and centimeter wavelength ranges can be selected with spread spectrum radio signals and satisfying the following requirements: spatial placement providing direct visibility between the transmitter and the detection system (if the radio signal parameters are accurate to synchronization is a priori known, then direct visibility between the transmitter and the detection system is not required); type, frequency and power of the emitted radio signal; lack of mutual interference interference at the operating frequency of the transmitter. Examples of uncontrolled transmitters are broadband digital radio and television transmitters, cellular transmitters and repeaters, as well as an ever-increasing number of broadband transmitters for information and measurement radio systems. If the RPDZ transmitter is specially designed to solve the problem of detecting airborne objects together with a detection-direction finding station, then this transmitter can be classified as controlled (controlled). At the same time, to control its operating modes, a communication line is provided with a detection-direction finding station (see Fig. 2).

The device operates as follows.

In system 2, based on the data of the external base of the radio transmitters, as well as data on the detected transmitters coming from the shapers 1-k-4, using the modeling software, a set of transmitters emitting spread-spectrum radio signals is identified, selected and periodically updated. During the simulation, possible coverage areas, detection probabilities, and achievable localization and identification accuracy of airborne objects of various classes are estimated, which can be provided with different types of placement of transmitters relative to a detection-direction finding station. In addition, model 2 transmitter signals are generated in system 2, which can be used instead of real direct transmitter signals with a priori known synchronization parameters.

The parameters of the selected set of transmitters (number j = 1, ..., J, carrier frequency, spectral width, shape and power of the emitted signal, coordinates or distance and angular position relative to the SOP) are stored in subsystem 2, fed to devices 3-3 and 3-4 , and are also used to configure the converters 1-k-2 and 1-k-7. In order to simplify the control circuit of the converters are not shown.

According to the signal of system 2, each pair of frequency converters 1-k-2 and 1-k-7 is tuned to a given reception frequency f _k .

. При этом обеспечивается одновременный прием радиосигналов выбранного множества J=K передатчиков.Multipath radio signals, including direct signals of spread spectrum transmitters and the signals of these transmitters reflected from objects, are synchronously received by K pairs of antenna arrays 1-k-1 and 1-k-8 at the set of search frequencies f _k ,

. This ensures the simultaneous reception of radio signals of the selected set of J = K transmitters.

The time-dependent radio signal x _kn (t) received by each antenna element with number n of each antenna array 1-k-1 and 1-k-8 is filtered by frequency and transferred to a lower frequency in each converter 1-k-2 and 1 -k-7.

The ensemble of radio signals x _kn (t) formed in the converters 1-k-2 and 1-k-7 is synchronously converted using the 1-k-3 and 1-k-6 ADCs into an ensemble of digital signals x _kn (z), where z is the number of the time reference of the signal that goes to the shapers 1-k-4 and 1-k-5.

In each shaper 1-k-4 from digital signals x _kn (z), a digital direct signal of the j-th transmitter emitting at a frequency f _k is generated, and the parameters of the generated signal are determined.

The digital direct signal of the transmitter can be generated in various ways, for example, by adaptive spatial filtering of digital signals x _kn (z) [3, p. 7].

The generated digital direct signal of the j-th transmitter enters the shaper 1-k-5. In addition, the digital direct signal and its parameters (frequency f _k , azimuthal elevation direction of arrival and signal level) are received in system 2, where they are stored.

In each shaper 1-k-5, digital compressed signals reflected from objects at a frequency are formed from digital signals x _kn (z) and the digital direct transmitter signal received from the shaper 1-k-4.

между принятым каждой n-й антенной решетки цифровым многолучевым сигналом x_kn(z) и сформированным в формирователе 1-k-4 цифровым прямым сигналом, усреднения модулей комплексных ДКФВ

определения по максимумам усредненной ДКФВ

числа сжатых сигналов и фиксации значений задержки по времени τ_kp и абсолютного доплеровского сдвига F_kp каждого p-го сжатого сигнала, идентификации соответствующих отдельному максимуму усредненной ДКФВ

составляющих комплексных ДКФВ

как сжатый по времени и частоте p-й сигнал, выделения и запоминания значений идентифицированных составляющих комплексных ДКФВ

а также значений задержки по времени τ_kp и абсолютного доплеровского сдвига F_kp каждого p-го сжатого сигнала.The generation of compressed reflected signals and the determination of their parameters (time delay τ _kp , absolute Doppler shift F _kp , azimuthal α _kp and elevation β _kp direction of arrival, amplitude α _kp , where p is the number of the generated compressed signal at a frequency f _k ) can be made different methods of cross-correlation processing of direct and multipath signals. For example, following [4], in the 1-k-5 shaper, the extraction of compressed reflected signals can be carried out by generating at the frequency f _k, depending on the time τ and frequency F shifts of complex two-dimensional cross-correlation functions (DCF) -

between the digital multipath signal x _kn (z) received by each nth antenna array and the digital direct signal generated in the 1-k-4 shaper, averaging the integrated DKFV modules

determination by the maxima of the averaged DKFV

the number of compressed signals and fixing the values of the time delay τ _kp and the absolute Doppler shift F _{kp of} each p-th compressed signal, identifying the corresponding individual maximum of the averaged DKFV

components of complex DKFV

as the pth signal compressed in time and frequency, isolating and storing the values of the identified components of complex DKFV

as well as the values of the time delay τ _kp and the absolute Doppler shift F _{kp of} each p-th compressed signal.

между принятым каждой n-й антенной решетки цифровым многолучевым сигналом x_kp(z) и сформированным в системе 2 цифровым модельным прямым сигналом, синхронизированным с облучающим сигналом.Note that in those cases when the radio signal of the transmitter is a priori known, the extraction of compressed reflected signals can be carried out by generating time-dependent τ and frequency F offsets of complex DVKF

between the digital multipath signal x _kp (z) received by each nth antenna array and the digital direct model signal generated in system 2 synchronized with the irradiating signal.

Figure 3 shows, as an example, three cross sections for the delay τ _kp (range) for various Doppler shifts F _{kp of} the complex DVKF module, depending on the frequency and time shifts of the three-beam, p = 1, 2, 3, radio signal received by the nth antenna array 1-k-8 at a frequency f _k . It can be seen that the first compressed signal has zero absolute Doppler shift and the smallest value of the time delay. The less powerful second and third compressed signals differ from the first signal in the values of time delays and absolute Doppler shifts. Physically, this may correspond to the case of receiving at the frequency f _{k the} direct signal of the transmitter and two signals reflected from two air objects moving relative to the detection-direction-finding station at different ranges and with different radial speeds.

синтезируется комплексный двумерный угловой спектр, по максимумам модуля которого определяется азимутально-угломестное направление прихода (α_kp, β_kp) p-го сжатого сигнала.When determining the azimuthal elevation directions of arrival of compressed reflected signals in the shaper 1-k-5, for example, using the method [5] using the selected values of the pth identified components of complex DKFV

a complex two-dimensional angular spectrum is synthesized, the maximum modulus of which determines the azimuthal elevation direction of arrival (α _kp , β _kp ) of the pth compressed signal.

а также определены временная задержка τ_kp, абсолютный доплеровский сдвиг F_kp, азимутально-угломестное направление прихода (α_kp, β_kp) и амплитуда

каждого p-го сжатого сигнала.Thus, at this stage, in the shapers 1-k-5 at each frequency f _{k of the} selected set of search frequencies f _{k = 1} , ..., f _{k = K} , compressed echoes are generated and extracted

and also determined the time delay τ _kp , the absolute Doppler shift F _kp , the azimuthal elevation direction of arrival (α _kp , β _kp ) and the amplitude

every p-th compressed signal.

Formed at the given search frequencies f _{k = 1} , ..., f _{k = K, the} compressed reflected signals and their parameters are input to the device 3-1, where they are stored.

In the device 3-1, the arrival directions of the compressed reflected signals are identified at a plurality of search frequencies.

In order to increase the information content, the identification of the arrival directions of compressed reflected signals at the set of search frequencies is carried out as follows:

- a three-dimensional selective distribution function (VGF) of the compressed reflected signals is generated in the set of search frequencies in azimuth α, elevation angle β, and time delay τ;

- the number of WFR maxima is determined;

- each VFR maximum is identified as a separate direction of arrival of the compressed reflected signals with the corresponding azimuth values α _i , elevation angle β _i, and time delay τ _i , where i is the number of the identified direction of arrival of the compressed reflected signals.

- номер элемента (ячейки) ВФР по азимуту,

- номер элемента ВФР по углу места,

- номер элемента ВФР по задержке, а [Δα; Δβ; Δτ] - размер элементов объема по азимуту, углу места и задержке соответственно.As the event used in the formation of three-dimensional VFR, the event is selected consisting in getting estimates of the azimuth α _kp , elevation angle β _kp and delay τ _{kp of the} compressed reflected signals in the three-dimensional volume element [α _ν , α _ν + Δα; β _µ , β _µ + Δβ; τ _l , τ _l + Δτ], where

- the number of the element (cell) WFR in azimuth,

- the number of the element VFR in elevation,

is the number of the VGF element by delay, and [Δα; Δβ; Δτ] is the size of the volume elements in azimuth, elevation and delay, respectively.

The size of the WFR element (cell) is determined on the basis of the required resolution in azimuth α, elevation angle β, and delay τ.

In the most typical situation, the cell sizes are equal: in azimuth and elevation, respectively, 3 and 5 degrees, and in the delay of 1-5 μs, depending on the frequency range.

Figure 4 presents a three-dimensional VGF for the case of the arrival of reflected signals in five directions: 1 - (α = 60 °, β = 10 °); 2 - (α = 60 °, β = 50 °); 3 - (α = 230 °, β = 40 °); 4 - (α = 30 °, β = 15 °); 5 - (α = 290 °, β = 15 °).

Figure 5 shows the features of the formation of elements of a three-dimensional selective distribution function over the set of search frequencies f _{k = 1} , ..., f _{k = K.} In this case, on the azimuth-delay plane (Fig. 5a), four directions of arrival of reflected signals are observed, which differ in azimuths. Two directions α = 30 ° and α = 290 ° contain signals that coincide in a delay equal to τ _k = 8 μs. On the other hand, on the plane "elevation angle - delay" (figb) also there are four directions that differ in elevation angles. The signals of the two directions coincide in a delay equal to τ _k = 1 μs. However, from a joint consideration of FIGS. 5a and 5b, it follows that on the set of search frequencies f _{k = 1} , ..., f _{k = 5,} there are five directions of arrival of the reflected signals: for τ _k = 1 μs - (α = 60 °, β = 10 °) and (α = 60 °, β = 50 °); for τ _k = 4 μs - (α = 230 °, β = 40 °); for τ _k = 8 μs - (α = 30 °, β = 15 °) and (α = 290 °, β = 15 °).

Physically, this corresponds to the case when at the range corresponding to the delay τ _k = 4 μs, one object is present, and at ranges corresponding to the delays τ _k = 1 μs and τ _k = 8 μs, there are two targets, in the first case coinciding in azimuth , and in the second case coinciding in elevation.

и их параметры (множество частот поиска f_k=1,…,f_k=K, временная задержка

, абсолютный доплеровский сдвиг

и азимутально-угломестное направление прихода

и амплитуда

каждого p-го сжатого сигнала) поступают в формирователь 3-2.The identified directions of arrival of the compressed reflected signals (azimuth α _i and elevation angle β _i ) and the corresponding values of the time delays τ _i , as well as the compressed reflected signals of each direction

and their parameters (the set of search frequencies f _{k = 1} , ..., f _{k = K} , time delay

absolute doppler shift

and azimuthal elevation direction of arrival

and amplitude

each p-th compressed signal) enter the shaper 3-2.

In the shaper 3-2 of the compressed reflected signals of each i-th direction are selected and stored energy-efficient compressed reflected signals and the corresponding reduced set of search frequencies.

To increase the signal-to-noise ratio in the shaper 3-2, the selection of energy-efficient compressed reflected signals of each direction and the corresponding reduced set of search frequencies is carried out as follows:

- the amplitude-frequency distribution (AFC) of the compressed reflected direction signals is formed;

- the AChP is compared with the threshold and when the threshold is exceeded, the energy-efficient compressed reflected directional signals and the corresponding reduced set of search frequencies are allocated.

The threshold is selected based on minimizing the probability of missing the target.

Figure 6 presents typical scattering patterns of an air object, simultaneously obtained at two frequencies. From Fig.6 it follows that the level of the reflected signal received at different frequencies f ₁ and f ₂ at the location of the SOP, can significantly (by 10 dB or more) differ. This implies the need to eliminate weak reflected signals and highlight energy-efficient signals for each direction of arrival and the corresponding reduced set of search frequencies.

7 is a diagram of the allocation of energy-efficient reflected signals and their corresponding abbreviated set of search frequencies. The selection of these energy-efficient signals provides improved localization accuracy of airborne objects. In addition, this makes it possible to reduce the set of search frequencies by about 2 times and, as a result, increase the computational efficiency of subsequent detection and localization of airborne objects by about 2 times.

Thus, at this stage, the energy-efficient reflected signals of each direction and the corresponding reduced set of search frequencies are allocated in the shaper 3-2. This gives the station detecting direction finding of air objects adaptability to fluctuations of the reflected signal. The fluctuations of the reflected signal significantly depend on the ratio of the characteristic dimensions of the object and the wavelength (frequency) of the irradiation, as well as on the directions of irradiation and signal reception.

These operations are key to improving the quality of subsequent detection, spatial localization and identification of a wide class of airborne objects.

The energy-efficient reflected signals, their parameters and the corresponding reduced set of search frequencies are supplied to the device 3-3.

In device 3-3, the energy-efficient compressed directional signals and the corresponding reduced set of search frequencies are used for selective search, spatial localization, and identification of the type of a wide class of airborne objects.

To increase efficiency in the device 3-3, selective search, spatial localization and identification of the type of a wide class of air objects is carried out as follows:

относительного доплеровского сдвига

азимутов

и углов места

сжатых сигналов каждого i-го направления;- the delay values are averaged over the reduced set of search frequencies K ⁽ⁱ⁾

relative doppler shift

azimuths

and elevation

compressed signals of each i-th direction;

относительного доплеровского сдвига

азимута

и угла места

сжатых сигналов i-го направления.- the i-th air object is detected and its spatial coordinates are determined by the averaged delay values

relative doppler shift

azimuth

and elevation

compressed signals of the i-th direction.

The following actions are performed:

и угла места

, сигналов i-го направления и при превышении порога принимаются решения об обнаружении i-го воздушного объекта.1) the average values of the absolute Doppler shift are compared with the threshold

and elevation

, signals of the i-th direction and when the threshold is exceeded, decisions are made to detect the i-th air object.

The threshold is selected based on minimizing the probability of missing an object;

2) the absolute delay of the signal reflected from the i-th object is determined.

i-го направления.Moreover, if the synchronization parameters of the signal of the j-th transmitter are a priori known, then the absolute delay of the signal of the j-th transmitter reflected from the i-th object is equal to the average value of the delay

i-th direction.

If the synchronization parameters of the signal of the j-th transmitter are a priori unknown, then the following actions are performed:

i-ых направлений выбирается задержка с минимальным значением;a) from the average values of the delays

i-th directions, a delay with a minimum value is selected;

прямого сигнала j-го передатчика;b) the value of the selected delay is identified as the value of the delay

direct signal of the j-th transmitter;

c) the relative delays for each i-th direction are determined

где r_j - расстояние между СОП и j-м передатчиком, а c - скорость света;d) the absolute delay of the signal reflected from the i-th object is determined by the following formula:

where r _j is the distance between the SOP and the jth transmitter, and c is the speed of light;

3) for each pair of “SOP - j-th transmitter” an ellipsoid of equal delays is constructed as the geometric place of points in space, the sum of the propagation delays to which (from the j-th transmitter to the i-th object and from the i-th object to SOP) equal to the found value of the absolute delay τ _ij ;

4) at the intersection of the set j = 1, ..., J of ellipsoids of equal delays, the geographical coordinates of the i-th detected object are determined.

Fig. 8 shows, by way of example, a diagram for determining the coordinates of a low-flying object when ellipsoids in space can be replaced by ellipses on the earth's surface.

For the unambiguous determination of the coordinates of the i-th detected object in the described manner, at least three transmitters located on more than one line are required.

Unambiguous determination of the coordinates of the i-th detected object is possible when using only one transmitter.

When determining the geographical coordinates of the i-th detected object using one transmitter in the device 3-3, the following actions are performed:

1) the pair signal “SOP - jth transmitter” corresponding to the most effective reflected from the i-th object is selected;

2) the value of the absolute delay of the signal τ _ij determines the apparent distance to the i-th object D _i = τ _ij c,

и угла места

сигналов i-го направления, например, в соответствии с [6].3) the spatial coordinates of the i-th detected object are determined by the apparent range D _i and the average azimuth values

and elevation

signals of the i-th direction, for example, in accordance with [6].

и угол места

) прихода отраженных сигналов определяются географические координаты i-го обнаруженного объекта.Moreover, for the selected pair “SOP - the jth transmitter”, an ellipsoid of equal apparent distances corresponding to the geometrical place of points in space is constructed, the sum of the distances to which (from the jth transmitter to the i-th object and from the i-th object to SOP) equal to the found value of the apparent range D _i . At the intersection of the ellipsoid of equal apparent distances and the average value of the i-th direction (azimuth

and elevation

) the arrival of the reflected signals determines the geographical coordinates of the i-th detected object.

Figure 9 as an example shows a diagram for determining the coordinates of an air object using a single transmitter.

After that, the following operations are performed in device 3-3:

- calculates the effective reflective area (EOC) of the i-th object at each k-th frequency of the reduced set according to the following formula:

- мощность сигнала на выходе антенной решетки СОП, отраженного на частоте f_k от i-го объекта; r_1i - расстояние от j-го передатчика до i-го объекта; r_2i - расстояние от i-го объекта до СОП; λ_k=300/f_k - длина волны; G_1i и G_2i - значения диаграмм направленности по мощности j-го передатчика и СОП в направлении на i-й объект соответственно. Расстояния r_1i и r_2i рассчитываются по пространственным координатам i-го объекта и СОП, поступившим от системы 2;where P _1k is the power radiated by the jth transmitter at a frequency f _k ;

- signal power at the output of the SOP antenna array, reflected at a frequency f _k from the i-th object; r _1i is the distance from the j-th transmitter to the i-th object; r _2i is the distance from the i-th object to the SOP; λ _k = 300 / f _k is the wavelength; G _1i and G _2i are the radiation pattern values for the power of the j-th transmitter and SOP in the direction to the i-th object, respectively. The distances r _1i and r _{2i are} calculated according to the spatial coordinates of the i-th object and SOP received from system 2;

- values of the image intensifier of the i-th object are averaged over the frequency

.- the type of the i-th object is identified by the average value of the image intensifier

.

Identification of the type of the i-th object is carried out as follows:

i-го объекта с порогами σ₀ и σ₀<σ₁.- compares the average value of the image intensifier

of the ith object with thresholds σ ₀ and σ ₀ <σ ₁ .

The thresholds σ ₀ and σ ₁ are selected on the basis of the experimental values of the image intensifier of airborne objects of three classes: a small-sized object, a medium-sized object, and a large-sized object;

- a decision is made to detect a small object, if

- a decision is made to detect a medium-sized object if

.- a decision is made to detect a large-sized object if

.

The results of detection, spatial localization and identification of airborne objects arrive at device 3-4, where they are displayed to increase information content.

From the above description, it follows that the application in the proposed method of extracting energy-efficient signals (the difference in signal-to-noise ratios received at different frequencies of the reflected signals can reach more than 10 dB) and the corresponding reduced set of search frequencies, as well as averaging operations on a reduced set of frequency values delay, relative Doppler shift and azimuth-elevation direction of arrival of energy-efficient signals increases the quality of detection of airborne objects ht and accuracy of measuring spatial coordinates and evaluating the effective reflective area of an object. In other words, the proposed method provides improved search efficiency, spatial localization and identification without increasing the size of the receiving antennas and transmitter power.

Thus, due to additional information extracted by identifying and extracting from a set of received signals a subset of energy-efficient signals reflected from detected air objects, an increase in information content, accuracy and computational search efficiency, spatial localization and identification of the type of a wide class of air objects by one detection-direction finding station is achieved .

Information sources

1. RU, patent, 2158002, cl. G01S 13/14, 2000

2. US patent 7012552 B2, class. G08B 21/00, 2006

3. Ratynsky M.V. Adaptation and superresolution in antenna arrays. M .: Radio and communication. 2004.

4. RU, patent, 2319976, cl. G01S 5/04, 2008

5. RU, patent, 2190236, cl. G01S 5/04, 2002

6. US Patent, 5,719,584 B2, class. G01S 003/02, 1998

Claims (3)

1. A method for detecting airborne objects, which consists in selecting transmitters that emit spread-spectrum radio signals, synchronously receiving an array of antennas at a plurality of search frequencies, multi-beam radio signals, including direct transmitter signals and the signals of these transmitters reflected from objects, synchronously transform the ensemble of signals received by the antennas into digital signals, at each search frequency, digital direct and compressed reflected signals are generated from digital signals, characterized in that The search directions identify the arrival directions of the compressed reflected signals, the energy-efficient compressed reflected signals and the corresponding abbreviated set of search frequencies that are used for selective search, spatial localization and identification of the type of a wide class of aerial objects by averaging over the shortened one are extracted and stored from the compressed reflected signals of each direction set of frequencies of delay values, relative Doppler shift, azimuths and elevation angles of compressed signals each of the i-th direction, detection and formation of spatial coordinates of the i-th air object from the averaged values of the delay, relative Doppler shift, azimuth and elevation angle of the compressed signals of the i-th direction, calculating the effective reflective area (EOC) of the i-th object at each frequency abbreviated set according to its range, power of the reflected signal of the i-th direction and radiation power of the radio transmitter, identification of the type of the i-th object by comparing the average value of the image intensifier

of the i-th object with thresholds σ ₀ and σ ₁ , σ ₀ <σ ₁ , selected on the basis of the experimental values of the image intensifier of airborne objects of three classes — a small-sized object, a medium-sized object, and a large-sized object, and the decision to detect a small-sized object is made if

, the decision to detect a medium-sized object is made if

and the decision to detect a large-sized object is made if

. 2. The method according to claim 1, characterized in that the directions of arrival of the compressed reflected signals at a plurality of search frequencies are identified by generating, by a plurality of search frequencies, a three-dimensional selective distribution function (VGF) of the compressed reflected signals in azimuth, elevation and time delay, determining the number VFR maxima, identification of each VFR maximum as a separate arrival direction of compressed reflected signals with azimuth, elevation and delay corresponding to these maxima. 3. The method according to claim 1, characterized in that the selection of energy-efficient compressed reflected signals of each direction and the corresponding reduced set of search frequencies is carried out by forming the amplitude-frequency distribution (ACP) of the compressed reflected direction signals, comparing the ACP with a threshold and isolating energy-efficient compressed reflected directional signals and the corresponding reduced set of search frequencies.

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