RU2571957C1 - Method for experimental verification of information and identification capabilities of doppler portraits of aerial objects - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: result is achieved by employing an additional radar station in full-scale experiments with real aerial objects, said additional radar station having a carrier frequency different from the frequency of the main radar station used in the experiments. Both radar stations are switched to automatic tracking mode on angular coordinates and range, and after identification of marks from the aerial object, signals reflected by the aerial object are synchronously detected using a double-channel analogue-to-digital converter and then stored in a storage device in the form of general arrays of amplitude-phase reflections. From general arrays with parameters of reflected signals, partial samplings of reflections which are synchronous and have an equal number of elements (duration of the corresponding inverse synthesizing interval) are selected, from which complex spectral vectors of the Doppler portraits of the aerial object are generated by discrete Fourier transform, and envelopes thereof are selected, which enable to compare the behaviour of evolution of the structure of Doppler portraits obtained in radar station with different frequency.

EFFECT: high quality of verifying identification capabilities of Doppler portraits of aerial objects.

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Description

The invention relates to radar methods and is intended to conduct a thorough and high-quality verification of the identification capabilities of vector single-frequency signs of identification (identification) of objects, which, in particular, include Doppler portraits.

The use of vector signs of classification (determining the class of an object) and identification (determining the type of an object) of objects is currently generally accepted and is described, for example, in [1-6]. However, the features of identification (distinguishing) of the objects proposed in them are most often formed by the method of mathematical or physical modeling and do not pass a thorough check for stability under various conditions, as a result of which additional errors occur that reduce the efficiency of identifying objects using these signs. The above problem of checking signs for repeatability and stability as an example is discussed in [3 p. 275-276]. Therefore, signs of a vector type that are critical to the formation conditions and parameters of radar devices must undergo a global rigorous experimental test of stability and repeatability using various methods and methods. Such methods are known, but they do not always provide high quality verification of signs, which include the Doppler portrait [5-8].

There is a method of experimental verification of the information and identification capabilities of Doppler portraits (DP) of air objects (VO), implemented in compliance with the principles of electrodynamic scale modeling in an anechoic chamber [1, 2, 9-15]. The method consists in the fact that the test object is made in a reduced size, and the scaling factor is chosen so that the model of the object allows it to be placed in an anechoic chamber (BC) and mounted on a rotary device. The wavelength λ _{backing of the} transmitting radar device BC is selected from the conditions for fulfilling the requirements of electrodynamic similarity according to the formula

λ _backing = λ _radar L _mod / L _rev = λ _radar / K _mod ,

, где В - коэффициент пропорциональности, причем В>1 [10 с. 29; 16 с. 12]. Этот выбор обеспечивает плоский фронт падающей электромагнитной волны (ЭМВ) в точке расположения модели объекта. Для более качественного получения плоского фронта волны в области масштабной модели дополнительно используют коллиматор (радиолинзу). Излучают в направлении масштабной модели объекта (ММО) радиолокационные сигналы и принимают с помощью радиоприемной системы, расположенной также внутри БЭК, отраженные моделью объекта сигналы. Изменяя азимутальное (курсовое) положение ММО с низкой угловой скоростью, последовательно записывают параметры принимаемых отраженных сигналов в запоминающее устройство (ЗУ). Одновременно с записью параметров отраженных сигналов проводят фиксацию и запись углового положения ММО. Проводят согласованную корреляционно-фильтровую обработку принятых сигналов от ММО, усиливают их, разделяют на фазовом детекторе на квадратурные (синусную и косинусную) составляющие и записывают их значения в ЗУ, формируя генеральный массив квадратурных составляющих для всех значений азимута β ММО, т.е. при изменении β вкруговую. Повторяют запись отраженных сигналов и их квадратурных составляющих при изменении азимута ММО от 0 до 360° несколько раз. Последовательно выбирают из массива записанных квадратурных составляющих N смежных пар этих составляющих, соответствующих изменению азимутального положения ММО на единицы градусов, проводят с ними операцию дискретного (по возможности - быстрого) преобразования Фурье (ПФ) для получения доплеровского портрета ММО и сохраняют в ЗУ сформированный доплеровский портрет ММО в виде массива или вектора квадратурных составляющих комплексных чисел, модульные значения которых представляют огибающую ДП ММО, соответствующего вполне конкретному угловому (азимутальному) положению объекта. Огибающую комплексного спектрального вектора ДП в большинстве исследовательских коллективов и считают непосредственным доплеровским портретом объекта. Интервал времени, в течение которого были последовательно записаны очередные N отраженных сигналов, называют интервалом синтезирования. Сформированный из N отраженных сигналов ДП считают соответствующим азимутальному положению ММО в середине интервала синтезирования, используемого для записи этих N сигналов. Сравнивая полученные в разное время, но при одинаковом азимутальном положении ММО, доплеровские портреты между собой по мере их сходства между собой, а также по мере их сходства с ДП реального объекта, полученного на том же азимуте (если такие данные имеются), определяют степень устойчивости, повторяемости и информационности ДП объекта, а также его идентификационные возможности. Считают при этом, что идентификационные возможности тем выше, чем сильнее мера сходства ДП, полученных из отраженных сигналов, отраженных объектом при одинаковых условиях, но в разное время, т.е. на разных этапах экспериментальных исследований.where λ _radar is the wavelength of a real radar station in the interests of which research is being carried out [16], L _mod is the size of the model of the object, L _rev is the size of the real object, K _mod = L _rev / L _mod is the coefficient or scale of the simulation. The model of the object is made of a material whose reflective properties correspond to the reflective properties of a real object. The object model is placed on a rotary radar absorbing platform, the angular position of which is fixed at any time by a special recorder with high accuracy (accuracy, as a rule, is not worse than 0.01 °). The removal of the R _{backing of the} turntable from the transmitting antenna inside the BEC is chosen taking into account the inequality $$R_{b\mathrm{uh}\mathrm{to}}\ge 2L_{m\mathrm{about}d}^{2}B/{\lambda }_{b\mathrm{uh}\mathrm{to}}$$

where B is the coefficient of proportionality, with B> 1 [10 p. 29; 16 sec 12]. This choice provides a flat front of the incident electromagnetic wave (EMW) at the location of the object model. In order to obtain a better plane wave front in the region of the scale model, a collimator (radio lens) is additionally used. Radar signals are emitted in the direction of the object’s scale model (IMO) and signals received by the object model are received using a radio receiving system located also inside the BEC; Changing the azimuthal (course) position of the IMO with a low angular velocity, the parameters of the received reflected signals are sequentially recorded in a storage device (memory). Simultaneously with the recording of parameters of the reflected signals, fixation and recording of the angular position of the IMO is carried out. A consistent correlation and filter processing of the received signals from the IMO is carried out, amplified, divided into quadrature (sine and cosine) components on the phase detector, and their values are recorded in the memory, forming a general array of quadrature components for all azimuth values of β IMO, i.e. when β changes in a circular fashion. Repeat the recording of reflected signals and their quadrature components when the azimuth of the IMO changes from 0 to 360 ° several times. Sequentially select from the array of recorded quadrature components N adjacent pairs of these components corresponding to a change in the azimuthal position of the IMO by units of degrees, perform a discrete (if possible fast) Fourier transform (PF) operation to obtain a Doppler portrait of the IMO and save the formed Doppler portrait to the memory IMO in the form of an array or vector of quadrature components of complex numbers, the modular values of which represent the envelope of the IMO IM corresponding to a very specific global (azimuthal) position of the object. The envelope of the complex spectral vector of the DP in most research teams is considered a direct Doppler portrait of the object. The time interval during which the next N reflected signals were successively recorded is called the synthesis interval. The DP formed from N reflected signals is considered to correspond to the azimuthal position of the IMO in the middle of the synthesis interval used to record these N signals. Comparing obtained at different times, but with the same azimuthal position of the IMO, Doppler portraits among themselves as they resemble each other, and also as they resemble the DP of a real object obtained at the same azimuth (if such data are available), determine the degree of stability , repeatability and informational content of the object's object, as well as its identification capabilities. It is believed that the identification possibilities are the higher, the stronger the similarity measure of DP obtained from the reflected signals reflected by the object under the same conditions, but at different times, i.e. at different stages of experimental research.

The described method of experimental verification of information and identification capabilities of DP is not effective, since it has the following disadvantages:

- in the manufacture of IMO can not be taken into account all the features of structural elements, and especially their individual reflective properties;

- upon receipt of the AP in BEC, it is impossible to correctly adequately take into account the different elevation angles of the object (air object);

- all measurements are carried out at the same radiation frequency, and the dependence of the DP as a sign of identification on the frequency is not checked, i.e. this dependence (if any) is neglected;

- there is no accounting for reflections from rotating elements of propulsion systems that can distort the glider reflective characteristic (OH) of an air object;

- the reflective characteristics of the IMO are obtained at a constant angular velocity of rotation, which in real conditions of tracking the HE is extremely rare (with the exception of space objects).

There is another way to experimentally verify the information and identification capabilities of the DP of airborne objects, implemented under conditions of radiation of radar signals in free space, but also when using IMO [17]. The method consists in the fact that MMOs with a scaling factor of not more than a few units together with a rotary support device (OPU) are suspended using cables and extensions in free space at a height of several tens of meters above the ground. Cables of radiolucent material holding MMOs with OPU are fixed on towers located at a distance at which these towers go beyond the directional characteristics of the antenna of the transceiver radar station. As an experimental radar, a typical radar with pulse sensing and isolation of a transmitting and receiving device or radar with a separate transmitting and separately located receiving device is used. This type of experiment is considered to be semi-natural [1]. The angle between the directions from the attachment point of the IMO to the receiving and transmitting antennas is chosen to be of the order of units of degrees (in [17] it is 6 °). The distance from the radar to the IMO is chosen equal to 5 × 10 ⁴ wavelengths, i.e. about 1.5 km, which at a wavelength of λ = 3 cm ensures the fulfillment of the conditions of the far zone. To rotate the MMOs, they use an OPU with a reducer reducing the angular velocity, providing the angular velocity of rotation of the IMO in azimuth γ = 4.3 ± 0.2 ° / s. Sounding signals are emitted in the direction of the MMO and receive reflected MMO signals, amplify them and compensate for the stray reflections from local objects, the control tower and towers by a special method (compensation method). MMO-holding cables mounted on towers are placed perpendicular to the line of sight of the object under study. The IMO is rotated in azimuth (heading relative to the radar) and with a time discretization step Δt = 30 ms, which corresponds to the azimuth discretization step δβ = 8 arc minutes, the amplitude, phase, and arrival (reception) time of the reflected MMO radar are recorded using a special recording device signals, as well as using a chart recorder, record the change in time of the course (azimuth β) of the IMO. The choice of the sampling step in azimuth is carried out for reasons that it is less than the width of the lobe of the secondary scattering diagram, equal to the value of λ / L _modes , where L _mode is the maximum transverse size of the model of the largest overall object. The size of the receiving and transmitting antennas is chosen equal to 37λ, thereby ensuring the width of the directivity ΔΘ _0.5p ≈1.5 °. The amplitudes A, phases φ, times t, and angular positions β are recorded after the amplitudes and phases ix of the samples are converted into a complex form of the form A _i exp (j (φi) is carried out on a magnetic medium of a computer. After recording the parameters of the reflected signals for of all azimuthal IMO positions (i.e., circular), relying on the data on the times of reception of the reflected signals, select from the general general array (GM) of data on the reflected signals private samples (CV) of the data on the amplitudes and phases of the signals obtained at a predefined interval x inverse synthesizing (IMS). For all IMS formed CV value is selected and the corresponding change in the same azimuth MMO 1-2 °. Given the invariance of the repetition period T _{and the} radiated signals obtained in each of the FT M complex numbers expressing reflection parameters of signal IMO Private samples are formed with a shift by one GM element.With the number X of complex samples in the GM and the number M of complex samples-elements in the FW, (X-M + 1) private samples are extracted from the general array. Each FW is considered appropriate to its IIS. A discrete PF operation is performed with an array of complex amplitude-phase samples of each FW [18, 19], as a result, for each IMS (for each FW) a spectral complex array (vector) of samples is formed, the envelope of which is considered the Doppler portrait of the IMO corresponding in time to the middle of this IIS, i.e. the time of reception of the reflected signal recorded in the middle of the used FW [20, 21]. The envelopes indicated above are distinguished, graphical forms of the obtained DPs are built, and they are compared with DPs obtained for similar objects by other methods, as well as with DPs formed by the indicated method, but in previous cycles of experiments. Based on the results of the coincidence of the parameters of the DP of the same course angle (azimuth) between themselves, a decision is made on the reliability and corresponding informativeness of the obtained DP. And according to the results of the difference in DP obtained at the same course angles, but from different objects, they conclude that the identification capabilities of the DP.

This method also cannot be considered effective, as it has the following disadvantages:

- in the manufacture of IMO can not be taken into account all the features of structural elements, and especially their individual reflective properties;

- when receiving a DP from models suspended on ropes, it is impossible to correctly adequately take into account the different elevation angles of the object (air object);

- all measurements are carried out on the same sounding carrier frequency, the dependence of the DP as a sign of identification on the frequency is not checked, i.e. this dependence (if any) is neglected;

- accounting for reflections from the rotating elements of the propulsion systems of the object, which may distort the glider OH of the air object, is absent or does not have adequacy;

- the reflective characteristics of the IMO are obtained at a constant angular velocity of rotation, which in real conditions of tracking the HE is extremely rare;

- the principles of electrodynamic similarity are not fulfilled, since the models are made to scale, and the locators have a standard wavelength.

Another (the most adequate and reliable) method of experimentally verifying the information and identification capabilities of Doppler portraits of airborne objects [22] is known and tested in practice, namely, in the direction of a real object (which can be an air object) using a real radar with a wave range from units to tens of centimeters emit microwave pulses of the same frequency, and then receive the signals reflected by the object, amplify them at a high frequency, spend their hour filtering, transfer to the intermediate frequency, carry out the main amplification at the intermediate frequency, conduct intra-period (within the pulse repetition period) coordinated processing of the received signals by convolution with a probing signal to isolate the peaks of their responses, at the peak points of the responses of the reflected signals, their amplitude, phase and exact time of reception, record these parameters for all in turn repetition periods on a magnetic medium (in [22] it is magnetic tape) in the form of a general data array (GM) of data, s containing amplitudes, phases and signal reception times [23], the IMS T _c value (which is called the accumulation interval) is selected based on the necessary spectral resolution according to the formula T _c = 1 / δf _p , where δf _p is the necessary resolution in the frequency domain, from the general array of data on amplitudes, phases and reception times, a private sample (FW) corresponding to the investigated IMS is converted to the amplitude A _s and phase φ _{s of} each s-th sample (the signal number and the corresponding parameters are called a sample) using an analog-digital pre of the educator (ADC) into digital form and then into the complex form of the form A _s exp (jφ _s ), where A _s and φ _s are the amplitude and phase of the response peak of the s-th reflected signal, respectively, carried out with data from a private sample of complex reflections from the object operation of discrete Fourier transform (PF) and form as a result a spectral complex array expressing with its envelope the Doppler portrait of an air object. The envelope of the complex spectral vector is isolated and called its Doppler portrait of VO. Consistently shifting in time within the interval of data recording in the general array selected by the duration of the IMS, i.e. moving from the beginning to the end of the general array of FWs, a corresponding Doppler portrait is formed for each IMS using the discrete PF method and envelope extraction, the generated Doppler portraits are recorded in a storage device and transmitted digitally to an analysis device (for example, to an object identification device), which compares the obtained DPs with their counterparts formed in advance by similar or other methods. The results of comparison or the results of identification determine the stability and informational properties (correspondence to analogues obtained by a different method or at other times) of Doppler portraits corresponding to a particular object with a certain azimuthal position, on the basis of which a decision is made on the identification capabilities of Doppler portraits.

In [22], information is provided that when identifying five different ground objects, according to the structure of the Doppler portraits (referred to as spectra in [22]) described by the structure taking into account the known azimuths of objects, estimates of the correct solution for identification of the order of 0.9 or erroneous are obtained solutions not exceeding 10%.

This method is more effective in terms of assessing the identification properties of the DP HE, as it relies on the use of real HE, uses real sounding signals at real radar ranges, i.e. adequate radiation and reception conditions. However, even this method is not without drawbacks, namely:

- the azimuthal position of the VO moving in a turbulent atmosphere with trajectory instabilities (VT) of the flight is not determined accurately, in view of which, a methodological error is introduced in comparing the DP with its analogs due to errors in the measurement of the heading angle;

- a constant radiation frequency of microwave signals is used and the indifference of the DP to a change in the carrier frequency is not checked, which does not allow to objectively select signs of identification of objects and to state the degree of their information content.

The objective of the invention is to improve the experimental method for verifying the identification capabilities of DP VO, providing the best possible account of the dependence of the structure of the DP on the heading angle (azimuth), a qualitative assessment of the indifference of the DP to the radiation frequency of the signals and the possibility of a reasonable allocation of integral signs of object identification from the structure of the DP.

To solve this problem, it is proposed to organize experimental studies involving two radars (radar1 and radar2) of the same range. In this case, the radiation frequencies in radar1 and radar2 must be different and the principle of electromagnetic compatibility of these radars, which is expressed in the absence of the influence of one radiating radar on the results of signal processing in another and vice versa, must be satisfied. Electromagnetic compatibility should be performed primarily with the mutual emission of radar and radar radar1. It is proposed to place two radars on an even position at a distance d of about 15-30 meters from each other (see drawing). The line of the pair involved in the radar experiments should be perpendicular to the main direction of the VO observation. It is proposed to choose the distance to the HE in the experiments for reasons that the difference Δγ of the angles of the HE from the radar location points does not exceed units of angular minutes, for example, Δγ≤4 ′. Since for small values of Δγ the expression Δγ≈d / R _H ≈d / R _{g is} valid, where R _n and R _g are the inclined and horizontal ranges to the VO, respectively, it is advisable to choose the range of ordered VO flights taking into account the inequality R _n ≥d / Δγ. For example, for d = 30 m and Δγ = 4 ′, a range of R _n ≥30 km should be recommended. It is proposed that the registration of reflected signals and the formation of DP VO from them be performed during VO flights “on a parameter”, i.e. with lateral angles, when the heading angle is close to π / 2. Under this condition, the angular velocity of rotation of the aircraft relative to the line of sight of the object, due to the rotation of the glider in strictly rectilinear motion without VT, is maximum. After the detection of an airborne object, radar station 1 and radar station 2 should be identified by comparing its angular coordinates and range, as well as the motion parameters measured in radar station 1 and radar station 2. After identifying the airborne object detected by both radars, it is necessary to ensure that the radar station 1 and radar station 2 are in automatic tracking (AS) mode in angular coordinates and range. The transfer of the radar station 1 and radar station 2 into the AC mode can occur at different points in time. Therefore, radar operators should be able to control the operating modes of the neighboring radar, for which it is necessary to provide for the presence of voice or other communication between the radar operators. In addition, it is necessary to ensure good quality speakers, i.e. absence of breakdowns of escort during the first 1-2 seconds of being in AC mode. When exchanging information, it is necessary to notify the operators of the adjacent radar used in the experiments of the absence of disruptions, which indicates acceptable quality of support for the experiments for experiments. In one of the radars (for example, in radar 1) it is proposed to place the equipment for recording the reflected signals in the form of a computer with a built-in two-channel analog-to-digital shaper (ADC).

Recording the parameters of the reflected signals should be carried out only after the transition of both radars to AC mode. For mutual control and exchange of information about the operating modes and coordinates of the HE, as already mentioned above, voice or other communication between radar station 1 and radar station 2 should be organized. After the transition of both radars to the AC mode in angular coordinates and range, the operator switches on the registration mode, which consists in digitizing and recording the parameters of the reflected signals in the computer memory. The two-channel ADC provides almost synchronous registration of the signals of both radars. It is proposed to transmit signals to the ADC of the computer via a coaxial cable from the output of the intermediate-frequency pre-amplifiers [24]. In this case, the reflected signals of the main radar are proposed to be digitized by the first ADC channel, and the reflected signals of the second radar - by the second ADC channel. The duration of registration of reflected signals should be tens of seconds (for example, 20 seconds or more). After receiving and storing the parameters of the reflected signals in digital form in a storage device, similarly to the method described in [22, 23], they should be coordinated filter processing in each repetition period, ie Convolve the received reflected VO signal of a certain sounding period with a digitized complex conjugate sounding signal of the same sounding period to obtain a response of a matched digital filter and extract the amplitude and phase of the reflected signal at the peak of the response of the matched filter. The parameters of the probe signal for consistent filtering are extracted from the initial region of each repetition period, where the probe signal of the next period seeps from the transmitting path.

From the amplitudes and phases of the response peaks of the signals reflected by the same VO on a magnetic carrier used in computer experiments with ADCs, reflection arrays M1 and M2 are formed [23], called general data arrays. Each GM data expresses a complex reflective characteristic of the VO formed for the corresponding radar (M1 for radar1, M2 for radar2). After selecting the IMS values, similar to [22], it is proposed to extract from the generated general data arrays M1 and M2 time-synchronized FW parameters of the reflected signals corresponding to the duration of the IMS, to carry out a discrete PF operation with the vectors of complex data of two time-synchronized FV recordings [23], to form As a result of such a transformation, two synchronous spectral complex DP vectors (assuming that they were obtained in two different radars at the same time points), select the envelopes of these vectors s, take them for Doppler portraits of VO and compare the parameters and structure of the DP between themselves. If the structure obtained in two different radar stations coincides, the information and identification properties of the radiation carriers should be considered resistant to changes in the wavelength λ, and in the case of a difference in the structure of the radiation waves, determine the degree of mismatch by special criteria, for example, by the difference in the central frequencies of the components with the same number in the radio frequency [ 20, 21], by the difference in the number of components, by the difference in the amplitudes of the same number components, etc.

It is further proposed to sequentially shift the extracted FW by 1 count within the corresponding arrays M1 and M2, and for each FW extraction option, generate the corresponding DF VOs, thus obtaining a sequence of DFs generated from radar signals 1 and RLS2. In total, from each GM with the number of complex elements X with the number of complex elements in the FW equal to M, (X-M + 1) offset from 1 sample of private samples will be extracted. And after conducting a discrete PF for each radar (each GM), (X-M + 1) complex spectral vectors of Doppler portraits of the HE will be formed. For each complex spectral vector of the DP, its envelope is formed (a sequence of modular values of complex numbers is distinguished), considering it to be its graphical image of the DP or just a Doppler portrait. The simplest way to compare the DP of different radars is to compare the structures of the DP of the same synchronous IMS. To do this, it is proposed to number all the formed RPs of the first and second radars and compare them in pairs, i.e. match DP of the same numbers. The more pairs of DPs turn out to be identical, the better should be recognized the information and identification capabilities of DPs. In addition, it is possible to subsequently analyze the dynamics of changes in the RP of VO obtained from the signals of RLS1, and the similar dynamics of changes in the DP for RLS2. By analyzing the dynamics of changes in the structure over time for both radars, it will be possible to determine the time moments corresponding to an increase and decrease in the number of components in the DP. A comparison of these moments corresponding to the reflective characteristics of the VO recorded in the arrays M1 and M2 allows us to establish the degree of identity of the behavior of the DP obtained in radars with different wavelengths of the probing signal. For greater evidence of the experimental results obtained during processing, it is advisable to carry out a series of similar experiments with various HEs and when changing the parameters of their motion, i.e. at different heading angles.

As can be seen from the description, the proposed method for experimental verification of the information and identification capabilities of DP VO differs from its prototype in the increased reliability of the results and absolute adequacy to the real conditions for the formation of identification signs contained in the structure of the DP. The synchronization of data recording and the behavior of VOs that are identical with respect to RLS1 and RLS2 allow more confidence in the results of such verification of the information and identification capabilities of DP VOs. The frequencies in the involved radars and even the radars themselves can be changed, thereby forming a more representative statistical database of experimental data.

поворота объекта, а в меньшей степени - длиной волны излучения [25, 26]. И поскольку угловая скорость поворота планера ВО $$\dot{\gamma }$$

при его полете в турбулентной атмосфере изменяется, причем это изменение нелинейно [27] (является квазимаятниковым), то сопоставлять ДП реальных ВО, полученные в разное время, даже при записях прецизионной аппаратурой, некорректно и нецелесообразно, так как поведение самолетов в турбулентности непредсказуемо и случайно. Следовательно, случайной является и истинная угловая скорость поворота ВО в конкретный момент времени. А ее величина определяет структуру ДП. Поэтому для корректного соотнесения структур ДП, полученных на разных частотах излучения, необходима только синхронная регистрация.The essence of the invention lies in the fact that, according to theoretical justification, the structure of the object's DP is largely determined by the size of the object, the magnitude of the IMS and the angular velocity $$\dot{\gamma }$$

rotation of the object, and to a lesser extent - the radiation wavelength [25, 26]. And since the angular velocity of rotation of the airframe VO $$\dot{\gamma }$$

when it is flying in a turbulent atmosphere, it changes, and this change is non-linear [27] (it is quasimaterial), then it is incorrect and impractical to compare the DPs of real HEs obtained at different times, even when recorded with precision equipment, since the behavior of aircraft in turbulence is unpredictable and random . Therefore, the true angular velocity of rotation of the VO at a particular moment in time is also random. And its value determines the structure of the DP. Therefore, for the correct correlation of the structures of the DP obtained at different radiation frequencies, only synchronous registration is necessary.

On the other hand, the analytical expressions for describing the structure of the DP indicate that in the same wavelength range the structure of the DP with the identical external conditions and parameters of the VO motion should be relatively stable, i.e. suitable for using DP in recognition systems. This should be confirmed experimentally. But only such a full-scale experiment can be recognized as correct, when the registration of signals reflected by the VO and belonging to radar probes of different frequencies is carried out synchronously.

To confirm the possibility of obtaining identical radios in the structure of different radars, one should turn to the materials of [2, 5, 20, 21, 28, 29], which contain expressions for describing the radar and analyze the internal structure of the formed airborne radar. In particular, in [5, 28] it was shown that the DP is a set of spectral components from the local scattering centers (RCs) of the HE surface. The reflected signal received by the locator according to the principle of superposition of reflections in the Fraunhofer zone [30-32] can be written as

where m = 1 ... M is the number of the RC on the surface of VO; U _m - the amplitude of the signal reflected by the m-th RC surface VO; ω = 2πf is the circular frequency; R _m (f) is the slant range from the phase center [30] of the mth RC to the radar; Ψ _m is the phase shift that occurs when a wave is reflected from the phase center of the mth RC; C is the propagation velocity of electromagnetic waves.

The frequency spectral resolution of the RC in the DP during the implementation of the inverse synthesis principle is achieved due to the periodic change in the phase difference of the signals reflected by different RCs when the latter move. The received signal after coherent quadrature processing upon transition to the local effective scattering areas σ _m mx RC will be equal to

where C is a coefficient depending on the amplifying and filtering properties of the radar system.

Using the expansion of the range function in a series and convolution with the Dirichlet window function, as a result of the analysis of the monochromatic reflected VO signal with a good pairwise transverse resolution of the RC, it is possible to form the VO DP in the form of a module of the amplitude-frequency spectrum

- относительная круговая частота сигнала, отраженного m-м РЦ; $$R_m^{\text{'}}\left(t_0\right)$$

- производная функции наклонной дальности до m-го РЦ по времени; Sinc(x) - арочная функция вида Sin(x)/x; Т_c - величина ИИС.Where $${\Omega }_m\left(t_0\right)=\mathrm{four}\pi R_m^{\text{'}\text{'}}\left(t_0\right)/\lambda$$

- the relative circular frequency of the signal reflected by the mth RC; $$R_m^{\text{'}\text{'}}\left(t_0\right)$$

- derivative of the function of the slant range to the m-th RC in time; Sinc (x) - arch function of the form Sin (x) / x; T _c - the value of the IMS.

Expression (3) shows that the position of the spectral components in the DP with amplitudes proportional to the reflective abilities of the corresponding RCs depends on the flight speed of the HE, the angle of location and the spatial position of the RC relative to the center of tracking of the object (CCO). The central frequencies of the spectral components of the RC in the DC are proportional to the distance from the corresponding RC to the plane formed by the axis of rotation and the line of sight of the object.

The continuous function of changing the range to the RC corresponds to a continuous monochromatic signal, which is not used in modern radars. In real radars, quasimonochromatic signals are used. Therefore, it is more correct to conduct analytical studies for pulsed sounding. So when using coherent addition in the inverse synthesis of K reflected pulses, the i-th element of the envelope of the DP is described by the expression [28]

где

- относительная поперечная дальность m-го РЦ относительно ЦСО, измеренная в единицах поперечного разрешения δR_⊥; $$\dot{\gamma }$$

- угловая скорость изменения ракурса локации ВО.

Where

- the relative transverse range of the mth RC relative to the DSS, measured in units of transverse resolution δR _⊥ ; $$\dot{\gamma }$$

- the angular velocity of the change in the angle of location of VO.

. Второй член суммы в фигурных скобках в (4) представляет собой интерференционную составляющую, которой вследствие малости ее амплитуды чаще всего пренебрегают.The main contribution to the structure of the DP is made by the term containing

. The second term in curly brackets in (4) is the interference component, which due to the smallness of its amplitude is most often neglected.

и длины волны λ. Угловая скорость и величина ИИС для привлекаемых к экспериментам РЛС одинаковы. Поэтому несоответствия в структуре ДП может быть вызвано только несовпадением длин волн.From (4) it can also be seen that the relative position of the RC harmonics in the DP depends on the transverse distance of these RCs from the CCO, as well as on the magnitude of the IIS T _c and the angular velocity $$\dot{\gamma }$$

and wavelength λ. The angular velocity and IMS value for the radars involved in the experiments are the same. Therefore, discrepancies in the structure of the DP can be caused only by mismatch of wavelengths.

радиальную скорость V_rm этого m-го РЦ относительно радиальной скорости ЦСО (центра масс ВО) $$V_{rm}=R_{\perp m}\dot{\gamma }$$

. Это, в свою очередь, определяет вторичную доплеровскую частоту m-го РЦThe transverse removal of the m-th RC from the TSS determines $$\dot{\gamma }$$

the radial velocity V _{rm of} this m-th RC relative to the radial velocity of the central pressure vessel (center of mass of VO) $$V_{rm}=R_{\perp m}\dot{\gamma }$$

. This, in turn, determines the secondary Doppler frequency of the mth RC

It is the difference in the secondary Doppler frequencies of the RC, i.e. in the central frequencies of the secondary Doppler components of the RC in the object's DP, it is possible to distinguish between them according to the structure of their DP.

Let us estimate the degree of possible component displacement in the DP due to a change in the wavelength. The difference in carrier frequencies in modern radars of the same range, ensuring their electromagnetic compatibility at a small distance, is not more than hundreds of megahertz. With an increase in the carrier frequency of EMF radiation by 400 MHz, the wavelength λ of a typical radar changes from 3.7 to 3.5 cm. Then, the Doppler frequency of the RC remote from the DSS in the transverse direction by 5 meters changes according to (5) from 4.74 Hz up to 5.01 Hz. When the recommended value for aerodynamic IN IMS ≈0,5 T _c with the frequency resolution of the order of 2 Hz. This means that even such a significant change in the carrier frequency (400 Hz) cannot significantly affect the mutual position of the components from the RC in the DP VO. Thus, the Doppler portraits formed by two similar, but not coincident in radar frequency, should coincide in structure and can be compared, which is the purpose of the experiment.

As can be seen from the description and examples given, the proposed method for experimental verification of information and identification capabilities of DP VO meets the requirements that are presented to it by the task of the invention. The method is easily implemented in polygon and park conditions and can be recommended to research teams studying the signs of object identification generated by the inverse aperture synthesis method.

Information sources

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Claims (1)

A method of experimentally verifying the information and identification capabilities of Doppler portraits of airborne objects, which consists in emitting microwave pulses of the same frequency in the direction of an airborne object using a main radar station with a wavelength range from units to tens of centimeters, and then receiving signals reflected by the object, amplifying them at a high frequency, carry out their frequency filtering, transfer to an intermediate frequency, conduct the main gain at the intermediate to the weakening frequency, an inter-period matched correlation-filter processing of the received signals is carried out by convolution with probing signals to select the response peaks of the signals reflected by the object, their amplitude, phase and exact time of reception are recorded at the peak points of the reflected signals, these parameters are recorded for all repetition periods in turn magnetic carrier in the form of a general data array containing the amplitudes, phases, and signal reception times, select the value of the inverse synthesis interval T _s to On the basis of the necessary spectral resolution according to the formula T _c = 1 / δf _p , where δf _p is the necessary resolution in the frequency domain, a private sample corresponding to the inverse synthesis interval under study is extracted from the general array of data on amplitudes, phases and reception times, and data are samples of complex reflections from an air object, the discrete Fourier transform operation and, as a result, form a complex spectral array expressing the complex vector of the Doppler portrait of the air of the object, successively shifting in time within the interval of data recording into the general array, the inverse synthesis interval selected for the duration, form for each of the inverse synthesis intervals using the discrete Fourier transform the corresponding complex vector of the Doppler portrait, write the formed complex vectors of Doppler portraits into a storage device, select their envelopes, calling these envelopes Doppler portraits of an air object, I transmit t Doppler portraits in digital form into an analysis device in which the obtained Doppler portraits are compared with their analogues formed in advance, the stability and informational properties of Doppler portraits corresponding to a specific aerial object with a certain course angle or a certain azimuthal position are determined by the results of comparison decide on the identification capabilities of Doppler portraits of aerial objects, characterized in that at the same time as By using the main radar station, a second radar station of the same range is additionally similarly used, the carrier frequency of the signals of which differs from the carrier frequency of the main radar station by hundreds of megahertz, it is checked that the two radar stations involved in the experiments do not negatively affect each other while functioning and broadcasting, have a second radar station at a distance of 15-30 meters from the main line, perpendicular yarnoy main viewing direction of air objects, slant range R _n custom aircraft objects is selected for experimentation inequality R _n ≥d / Δγ, where Δγ = 4 '- maximum allowable difference of the angles of the air exchange object from two points of location used radar, d - the distance between the radar stations, for synchronous registration by two radar stations of the signals reflected by the airborne object, the registration equipment is placed in one of the radar stations Trapped signals in the form of an electronic computer with a built-in two-channel analog-to-digital converter, establish and provide communication between radar stations for mutual control about the air object selected for tracking and research, after the air object is detected and identified by its location and movement coordinates both radar stations in the automatic tracking mode by angular coordinates and range, by changing the coordinates of the air volume In the course of time, its heading angle relative to radar stations is measured, making sure that the automatic tracking of the airborne object is stable, synchronous recording of the parameters of the reflected signals in the storage device of the electronic computer begins, for which the signals reflected by the airborne object at an intermediate frequency from the primary and secondary radar stations with equal points of the receiving path are sent via coaxial cables to the corresponding inputs of the two-channel analog o-digital converter, convert the signals reflected by the aerial object into digital form using a two-channel analog-to-digital converter, the reflected signals of the main radar station being digitized by the first channel of the two-channel analog-to-digital converter, and the reflected signals of the second radar station by the second channel of the two-channel analog-to-digital converter , the total time of continuous registration of the reflected signals is set at least 20 seconds, the agreed processing is received signals are carried out in digital form by the method of intraperiodic convolution with a complex conjugate probing signal that seeps into the receiving path of the radar station at the beginning of each repetition period, after extracting the values of amplitudes and phases at the peak locations of the responses of the reflected signals, a general array of data on the amplitude, phase and time receiving signals separately for each radar station, sequentially allocate private samples shifted by 1 count within the general data array with ex amplitude-phase parameters of the reflected signals corresponding to the set inverse synthesis interval, i.e. private samples are distinguished by the same position, duration, and also the number of elements from both general data arrays, and the private samples sequentially allocated from each general data array are numbered, private samples are obtained for each general array (X-M + 1), where X is the total number of complex elements in the general array, M is the number of complex elements in a private sample, from each private sample of both general arrays form a complex spectral method of the discrete Fourier transform the vector of the Doppler portrait of an air object, by directly extracting envelopes from the complex spectral vectors of Doppler portraits, they directly form Doppler portraits of the air object, compare the parameters of the structures of Doppler portraits obtained for the same number of private samples extracted from different general datasets, based on the results of sequential pairwise comparison of Doppler structures portraits more reliably determine the identification capabilities of Doppler portraits.

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