RU2329520C1 - Selector of low-altitude air and ground target in on-board radio detection and ranging - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: invention relates to on-board radio detection and ranging system at (ObRDR) air-crafts. The result is achieved by the claimed instrument, which includes receiver of ObRDR sum channel and non-coherent detector in sum channel, receiver of differential elevation channel, slope inclination detector, five logic elements "AND", logic element "OR", calculator, functional angle transmitter of relief point-height, three memory units and two threshold units, expected value and relief altitude dispersion estimator interconnected in a certain manner.

EFFECT: possibility to distinguish low-altitude air and ground targets if they are detected by means of non-coherent monopulse ObRDR system or coherent ObRDR instruments in non-coherent modes.

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Description

The invention relates to radar technology, in particular, to airborne radar stations (RLS) of aircraft (fighters, helicopters), and can be used to distinguish detected low-altitude air targets, including hovering helicopters, and ground targets in incoherent radars and incoherent modes of coherent radar .

Known radar (G. Morris. L. Harkness, Airbom Pulsed Doppler Radar, Artech House, 1996, p. 116, 296; Handbook on radar under the editorship of M. Skolnik, t.3, chap. 7, "Soviet Radio", Moscow, 1977), intended, in particular, for the detection of air targets (CC) against the background of the underlying surface with various types of ground (surface) objects or targets (SC) located on it. The selection of the CC in the main beam of the radar antenna pattern is achieved due to spatial selection and due to differences in echo signals from them in delay and Doppler frequency relative to the NC. However, if these radar stations are incoherent or, being coherent, use the incoherent mode of signal processing, then there is no possibility to distinguish between CC and SC by the magnitude of the Doppler shift. Therefore, existing methods of selection based on differences in Doppler frequencies, for example, spatial-velocity selection (Dudnik P.I. A method for detecting and isolating low-flying targets against the background of the Earth based on the use of periodic oscillations of the position of the phase front of the field, which is the result of interference from radar scattered by the target and reflections from underlying surface, Military Radio Electronics, 1970, 1 (318), p. 3), are not applicable.

Of the known technical solutions, the closest is the device described in US patent No. 4862177, MKI G01S 13/52; 13/58; US 342/160 (Sung Y. Wong Processor for discriminating between ground and airborn moving targets), based on the analysis of the output signal of the elevation channel of a coherent single-pulse radar. This device contains a receiver for the sum channel of a monopulse radar and a multichannel (in terms of the number of range gates) pulse detector in the sum channel, a receiver for a difference elevation channel, similar to a receiver for a sum channel, and an angular discriminator for extracting the error signal according to the elevation angle. Its work is based on the fact that in each element of the range scanning range of interest, the difference between the values of the output signal of the elevation discriminator is determined when a spectral count of the echo signal reflected from the underlying surface and a spectral count of the echo signal from the detected moving object are applied to its input. If the absolute value of the difference does not exceed the selected tolerance, then a decision is made on the detection of the SC, otherwise - the CC.

The disadvantage of the prototype is that to obtain comparable estimates of the elevation angle of the CC and SC it requires Doppler information that is not available in incoherent radar.

The objective of the invention is to provide the ability to distinguish between low-altitude air and ground targets when they are detected using incoherent monopulse radar or in incoherent modes of coherent radar.

The problem is achieved in that in a device containing a range-gated receiver of the total channel of a monopulse radar and an N-channel (N is the number of range gates that cover the range of expected delays of the echo signals of the targets) an incoherent detector of a pulse signal in the total channel, a receiver of a difference elevation channel similar to the receiver of the total channel and connected to the N-channel incoherent detector of the pulse signal in the total channel, angular disc an inator for isolating the error signal according to the elevation angle, the first, second, third and fourth logical elements (LEs) “I”, the logical element “OR”, a computing device, an elevator is additionally connected in series with the functional converter — elevation of the terrain, the first storage device , a unit for estimating the mathematical expectation and variance of the elevation of the terrain in a two-dimensional sliding window, the first threshold device and the fifth logical element "And", as well as the second and third storage device wa, shadow detector, second threshold device.

Figure 1 shows a block diagram of a device for selecting low-altitude air and ground targets in radar, figure 2 - two-dimensional sliding window, figure 3 is a drawing explaining the geometric relationships for the problem.

The device for selecting low-altitude air and ground targets in the radar contains (Fig. 1) a range-gated receiving device 1 of the total channel of a single-pulse radar, N-channel (N is the number of range gates covering the range of expected delays of the echo signals of the targets) incoherent detector of pulse signals 2, receiving differential angle channel device 3, similar to the gated receiving device 1, the gating input of which is connected to the first output of the N-channel incoherent pulse detector 2 ala in the total channel, angular discriminator 4, elevator - elevation of elevation 5, the first storage device (ZU-1) 6 for forming a sliding window, the unit for estimating the mathematical expectation and dispersion of elevation of terrain 7 in a sliding two-dimensional window, the first threshold device 8 for detecting high-altitude targets, a second memory device (ZU-2) 9 for forming a sliding shadow window, a shadow detector according to the logic "k of n" 10, the fifth logic element (LE) "And" 11, the second threshold device 12 for registering the presence of reflections from the underlying surface, the third storage device (ZU-3) 13, the first, second, third, and fourth LE "I" 14, 15, 16 and 17, respectively, with the third LE "I" 16 having a second input, and at the fourth LE “I” 17 the second and third inputs are inverted, the LE “OR” 18, the computing device 19 connected to the output of the functional converter elevation - elevation 5. From the on-board sensors of the aircraft to the second input of the functional converter elevation - elevation of terrain 5, and also n a first input of the calculation unit 19 receives data of N altitude, angle of attack α carrier radar and an elevation equisignal direction of the antenna system β _PCH, on two second memory-1 6 ZU-September 2 (control) inputs, memory 3 13 - azimuth data of the optical axis of the antenna in the form of numbers of the current j and the analyzed j0 positions of the scanning sector.

A range-gated receiving device 1 of the total channel of a monopulse incoherent radar (Fig. 1) is designed to receive echo signals in N range gates, an N-channel incoherent pulse signal detector 2 connected to its output is used to establish the presence or absence of a target in each of N range gates with the formation of a sign of the presence of a target in the i-th gate (PNC (1)) and transmitting it to the gating input of the receiving device of the differential elevation channel 3 and to the signal input ZU-2 9 (first exit e detector 2), for transmitting (broadcasting) the signal of the receiver of the total channel to the angular discriminator 3 (second output of the detector 2) and the module of this signal to the threshold device 12 to establish the fact of the presence of reflections from the underlying surface of the required level (third output of the detector 2) .

The receiving device 3 of the differential elevation channel is similar to the receiving device 1 of the total channel, except that it is gated by range gates with those numbers that are determined by the range elements with signals detected in the total channel, for which the signal of the presence of the target of the PNC (i) is used, which is received at its second input (gating input).

The angular discriminator 4, connected by one input to the second output of the detector 2 and another input - with the output of the receiving device 3 of the differential elevation channel, serves to generate a signal of angular mismatch in the elevation angle of the detected echo signal relative to the equal-signal direction (RSN) of the monopulse radar antenna system. Functional converter 5 is designed to convert the angular error signal in the range element to the height of the detected object, taking into account the position in the vertical plane of the optical axis of the antenna and the distance to this object, thereby forming a high-altitude "profile" of the detected objects along the range scan for each position of the antenna beam in azimuth (scanning sectors) j (see formulas (1), (2)).

The first storage device (ZU-1) 6 is used to record along the scan along the range of the height samples of the detected objects obtained in the functional converter 5 and store them for several consecutive during the ongoing review of the antenna beam positions in azimuth (scanning sectors) j. The combination of these provisions determines the azimuthal length of the two-dimensional “follow-up window” selected for obtaining elevation elevation estimates of the underlying surface associated with the resolution element being analyzed (for the notion of “follow-up window” see, for example, Y.D. Shirman, V.N. Manzhos. Theory and technique of processing radar information against the background of interference, "Radio and communications", Moscow, 1981, p. 316). The length of the sliding window in range of 2 · L (L is the number of elements in each half of the ZU-1 window) is determined from compromise considerations that take into account both the need to obtain a statistically stable estimate of the height of the terrain in the analyzed range gate and the possibility of heterogeneity in the range of this relief . The set of output signals in each of these memory elements forms the output signal at the first output of the memory device ZU-1, and the signal of the central window element containing the information of the analyzed range gate i0 forms a signal at the second output of the first memory device ZU-1. The total number of azimuthal positions for which the altitude "profile" of the relief is memorized is M. Part of this number may relate to the azimuthal directions probed after passing through the controlled airspace of the analyzed direction j0. In this case, the selection results are issued with a delay relative to the transit time of the analyzed beam position in azimuth. Memory ZU-1 6 is divided into blocks (pages), each of which contains information of one azimuthal direction, located within a sliding window.

The evaluation unit 7 of the mathematical expectation and variance of the elevation of the terrain (altitude distribution parameters) is used to obtain sample mean and variance of the obtained height readings of the objects surrounding the analyzed resolution element. Algorithms for calculating sample mean and variance values of random variables, which are samples of the height of the terrain, are known from the literature (see formulas (4) - (6) below).

The first threshold device 8 is designed to calculate the difference in the values of the height of the detected object h _c (formula (1)) and the selected average elevation of the relief (formula (4)) in the vicinity of this object, and then compare this difference with the threshold value, which is determined by the product of the mean square height (formula (5)) in a sliding window (neighborhood of the analyzed element) by a threshold coefficient.

The second memory device (ZU-2) 9 is used to store signals for exceeding the threshold (signs of the presence of the PNC target (i, j)) from the output of the N-channel incoherent pulse signal detector 2 (here i is the number of the range element, j is the number of the angular sector) . The memory allocation in ZU-2 9 is similar to the memory allocation in ZU-16.

The shadow detector according to the logic "k of n" 10 is designed to register radar shadow from a high-rise structure on the ground. Here k is the number of sampled signal values that exceeded the threshold from a sample of signals of volume n fed to the detector input. The principle of shadow detection is based on the assumption that there are no signals exceeding the threshold in the range scan range, which is adjacent to the analyzed element and has a finite length equal to n. The fifth logical element (LE) "AND" 11 is used to select a decision regarding an identifiable detected object based on the presence or absence of a shadow: a high-rise ground object (having a shadow) or an air object (without a shadow).

The second threshold device 12 with a fixed threshold is designed to establish the fact of the presence in the element of the range of the signal reflections from the underlying surface with the desired level. In the third storage device 13, the memory in which is distributed in the same way as in the first two, the signs of the presence of a reflection signal from the underlying surface of the required level P _PP (i) are stored.

The purpose of the LE "I" 14, 15, 16, 17, as well as the LE "OR" 18, as in the prototype, is to select only those marks (signals) of the target for which the conditions for the selection of the CC / SC are met: detection of the signal from the underlying surface (sign П _ПП (i) = 1) within the allowable range of ranges, i.e. zones of permitted selection (attribute P _RS (i) = 1) - the first LE "I" 14, the decision to detect a ground target - the second LE "I" 15, the decision to detect an air target when the conditions for discrimination of the CC / SC are met - the third LE “I” 16, making a decision to detect an air target in cases when these conditions are not fulfilled - the fourth LE “I” 17, the formation of a joint decision to detect an air target - the LE “OR” 18.

The computing device WU 19, as in the prototype, is part of the radar computing system. It determines what is necessary for the functioning of the inventive device for the selection of the CC / SC number n = n _m - the length of the window in the shadow detector 10 - according to the formula:

,

,

where ΔR is the length of the range resolution element,

H is the height of the radar carrier;

R _i0 is the distance to the range element in which the object (target) is detected;

h _c - the calculated value of the height of the detected object,

as well as the near R _bg and far R _dg boundaries of the allowed selection zone according to well-known formulas using the values of the antenna deflection angle β _RSN from the on-board sensors relative to the horizontal plane, the flight height of the carrier H, the radar antenna beam width in the vertical plane Δβ:

,

, 0<k<1,

,

, 0 <k <1,

where the parameter k determines the width of the zone of allowed selection, and the formation of the sign of the location of the target signal in the zone of allowed selection P _RS (i)

The values of R _bg and R _{dg are} calculated with an accuracy determined by the accuracy of the on-board sensors.

The shape of the sliding window is shown in Fig.2. Unlike commonly used tracking windows for signal detectors, this window is two-dimensional to obtain a local estimate of the level of interference at the signal location. Given the possible fragmentation of the echo signal between adjacent elements of the range and the angular positions of the beam, neighboring elements in the tracking window are not included.

Figure 3 presents a figure explaining the operating conditions of the radar and the meaning of the quantities included in the formula. The following notation is introduced: α is the angle of attack of the radar carrier (the angle between the carrier’s construction axis and the horizontal plane), β _RSN is the elevation angle of the equal-signal direction (RSN) of the antenna system relative to the carrier’s construction axis, Δε is the angle of the mismatch between the direction to the target and the RSN in the elevation plane , R _i0 is the distance to the range element in which the target is present.

The inventive device operates as follows. When probing the controlled space using radar during azimuth scanning, the output of the N-channel incoherent detector of pulse signals 2 in the total channel shows signs of exceeding the threshold of the PNC (i), indicating the detection of an echo signal with intensity A _Σ in the element of range (strobe) i i) (A _Σ (i) is the signal module S _Σ (i) in gate i; the echo signals S _Σ and S _Δ arrive at the inputs of the receivers of the total and difference elevation channels from the antenna unit) that exceeds the threshold value. Next, the signal S _Σ (i) for gate i of the receiving device 1 of the total channel together with the output signal S _Δ (i) of the receiving device 3 of the difference elevation channel for the same gate are fed to the angular discriminator 4 to extract the error signal at the elevation angle Δε (i) directions to the detected object and RSN in the vertical plane. After that, in the functional converter 5, the height of the detected object h _c (i) is calculated using the relations valid for the case of a flat Earth (it is easy to obtain similar relations when taking into account the sphericity of the Earth):

where f ^-1 (U _beats ) is the function inverse to the direction-finding characteristic of the elevation channel U _beats = f (Δε);

H is the height of the radar carrier;

α is the angle of attack of the radar carrier (values of the angle of attack a and the height of the carrier of the radar N come from on-board sensors);

R _i0 is the distance to the range element in which the target is present (the distance to the detected object is determined by the product of the number of the corresponding range gate i ₀ coming from the detector 2 and the range resolution element ΔR);

Δε is the angle of mismatch between the direction to the target and the RSN in the elevation plane;

β _rsn - _elevation angle of the _equal - _signal direction of the antenna system relative to the construction axis of the carrier.

In particular, for the linear portion of the direction-finding characteristic of the elevation channel f (Δε), the angular mismatch can be defined as

where S _beats is the steepness of the direction-finding characteristic of the elevation channel.

Then, the calculated elevation values are entered for recording in the first memory 1-6, where they are stored in cells with numbers i equal to the number of range gates for which the height is calculated on page j associated with the corresponding position of the antenna beam in azimuth. Since writing to the memory unit 1 and reading data from it for subsequent processing is performed on a sliding window, after filling all M pages and obtaining statistical characteristics of the altitude profile of the neighborhood of the analyzed element, all data is shifted by one page in the direction of lower numbers to make room for records of newly received data.

и среднеквадратических

значений распределения высот в окрестности анализируемого элемента дальности с использованием известных формул (С.А.Айвазян, И.С.Енюков, Л.Д.Мешалкин. Прикладная статистика, гл.8, "Финансы и статистика", М., 1983, стр.248)The next processing step, which is performed in the evaluation unit 7 on the basis of the data received at its first input from the first output of the memory unit 1 6, is to obtain, upon filling out the entire sliding window, selective averages

and rms

values of the distribution of heights in the vicinity of the analyzed range element using well-known formulas (S.A. Ayvazyan, I.S. Enyukov, L.D. Meshalkin. Applied Statistics, Ch. 8, "Finances and Statistics", M., 1983, p. .248)

In these expressions, Si ₀ j ₀ is the set of window elements attached to the analyzed element (i ₀ , j ₀ ), where i ₀ is the number of the range gate (element), j ₀ is the number of the angular sector with the analyzed element, Zi ₀ j ₀ - a subset of the elements of the set Si ₀ j ₀ for which the sign of exceeding the detection threshold (sign of the presence of a target) PNC (i, j) = 0.

In the calculations that are performed in the evaluation unit 7, only those range elements are involved in which there are signals that have exceeded the detection threshold. To do this, the stored values of the detection signs of the CSC (i, j) are sent to the second input of the evaluation unit 7 from the memory-2 6. After the formation of estimates of the mathematical expectation and the rms value of the heights in the vicinity of the analyzed element in the first threshold device 8, the threshold for it is calculated and the height value of the detected object is compared with this threshold. In case of exceeding the threshold at the output of the threshold device 8, the sign of altitude П _h (i, j) of the detected object is assigned the value 1, otherwise, the value 0.

Along with the sign of altitude П _h (i, j) of the detected object for it, on the basis of the data stored in the memory-2 9, a sign of the presence of the radar shadow P _ten (i0, j0) is formed in the shadow detector using the logic "k of n" 10. For this, each range element with detected objects is assigned a logical value of 0 or 1, depending on the result of the analysis of a sequence of adjacent range elements with numbers following the number of the analyzed range element. The length of the sequence n _m is determined by the formula

where ΔR is the length of the range resolution element,

in the computing device 19, which is part of the computer. If there is no signal in all elements of this sequence, then the attribute П _ten (i0, j0) is assigned a logical value 0 (the shadow is present), otherwise - the logical value 1 (no shadow).

Then, after comparing both the formed features (the altitude П _h (i0, j0) and the shadow П _пн (i0, j0)) with the help of the fifth LE "I" 11, a preliminary decision is made on the nature of the detected target. The preliminary decision "high-rise object without a shadow"("presumably aerial target") with assigning the value of P _{CC / SC} (i ₀ , j ₀ ) to 1 is taken if both of the above signs are equal to 1, otherwise a preliminary decision is made that it is detected " high-rise object with a shadow "with assignment of П _{ВЦ / НЦ} (i ₀ , j ₀ ) to 0.

The final stage of data processing is to verify that the preliminary decision regarding the selection of the CC / SC at the output of the fifth LE "I" is made for the allowed zone, i.e. within the range of ranges limited by the near R _BG and far R _RG boundaries (P _pc (i ₀ , j ₀ ) = 1), and subject to the presence of reflections from the underlying surface P _pp (i ₀ , j ₀ ) = 1 (the result of this verification is formed at the output of the first LE "I" 14). Further, in the case of logical 1, at the output of the first LE And "14 second LE" And "15 forms a sign of detection of a ground target NC = 1, and if at the output of the first LE And 14 - logical 0, then the third LE And 16 forms a conditional a sign of detecting an air target when the selection conditions are met This last in the LE OR 18 logically combines with the conditional sign of detecting an air target if the selection conditions are not met (at the output of the fourth LE And 17 logical value 1), to form a common detection sign aerial targets at the exit of the EC = 1.

To perform the inventive device can be used, for example, domestic microcircuits on MOS transistors series K156, K561, K566, etc. or foreign analogues: microcircuits of series 4000, MAX300, etc., as well as microprocessor sets of suitable series. A part of the memory of the onboard computer system can also be used as a memory.

The use of the invention will allow to distinguish between low-altitude airborne objects, including hovering helicopters, using incoherent radars or in incoherent modes of coherent radar.

Claims (1)

A device for selecting low-altitude air and ground targets in an airborne radar station (NLS) containing a range-gated N gates (N is the number of range gates covering the range of expected delays of target echo signals) a receiving device for a single-channel radar, the N-channel output of which is connected to the corresponding the inputs of the N-channel incoherent detector of pulse signals, the receiver of the differential elevation channel, the gating input of which is connected to the first output detector, angular discriminator, the first input of which is connected to the second output of the said detector, and the second input - to the output of the said receiving device of the differential elevation channel, the first logic element (LE) "I", the output of which is connected to the second input of the second LE "I" designed to make a decision to detect a ground target, and the inverted (second) input of the third LE "I", LE "OR", designed to make a joint decision to detect aerial target, the first input of which is connected with the output of the third LE "I", and the second input with the output of the fourth LE "I", a computing device that generates a sign of the target echo in the area permitted by the data from the on-board sensors supplied to its first input from the aircraft’s flight altitude and antenna tilt angle selection, which from its first output goes to the third input of the first LE "I" and the second (inverted) input of the fourth LE "I", characterized in that it also introduced a functional converter elevation - elevation, first zap a detecting device, a unit for estimating the mathematical expectation and the rms value of the height distribution on a sliding window, and a first threshold device, a second and third storage device, a shadow detector according to the logic “k from n”, a second threshold device, a fifth logic element “AND” so that the output the angular discriminator is connected to the first input of the said functional converter, the output of which is connected to the second input of the computing device and to the signal input of the first storage device, the first the output of which is connected to the first input of the unit for estimating the mathematical expectation and the mean square value of the distribution of heights on a sliding window, and the second output is connected to the first input of the first threshold device, the second and third inputs of which receive signals for evaluating the mathematical expectation and the mean square value of the height of the terrain, respectively, from the first and the second outputs of the evaluation unit, the output of the first threshold device is connected to the first input of the fifth LE "I", the second input of which is connected to the output of of the shadow expander according to the logic “k from n”, and the output of the fifth LE “AND” is connected to the inverted (first) input of the first LE “I”, the signal input of the second storage device is connected to the first output of the said N-channel incoherent pulse signal detector, and its the output is connected to the first input of the shadow detector by the logic "k of n", with the second input of the evaluation unit, with the first inputs of the second LE "I", the third LE "I" and the fourth LE "I", the input of the second threshold device is connected to the third output the mentioned detector, and the output is with a signal input ohm of the third storage device, the output of which is connected to the second input of the first LE "I" and the inverted (third) input of the fourth LE "I", the second output of the computing device is connected to the second input of the shadow detector by the logic "k from n", and the data from the onboard sensors about the flight altitude and the angle of attack of the carrier, as well as the angle of inclination of the antenna, additionally go to the second input of the aforementioned functional converter elevation angle - elevation of the terrain, azimuth data of the optical axis of the radar antenna in the form of numbers of the current j and a aliziruemogo j0 sector angular scanning positions supplied to the control inputs of the first, second and third memory devices.

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