RU2510863C1 - Inter-scanning device for mapping passive jamming using chirp signals - Google Patents

Abstract

FIELD: physics, navigation.

SUBSTANCE: invention relates to radar and can be used in radar stations to improve detection of radar signals on the background of passive jamming. The prototype device, which includes a signal detector, two AND logic elements, two range gating expanding devices, a target counter and a threshold device, also includes random-access memory, a delay line, a third AND logic element, a ranging device, a multiplier and a second threshold device with respective connections.

EFFECT: preventing generation of a false mapping signal on two (or more) nearby targets while maintaining the quality of mapping passive jamming.

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Description

The invention relates to radar and can be used in radar stations to improve the detection of radar signals against a background of passive interference.

As you know, the work of any radar station occurs against the background of interfering reflections - natural (underlying surface, clouds, hydrometeors) and artificial (dipole anti-radar reflectors) passive interference. The intensity of passive interference can be hundreds of times higher than the level of the useful signal and prevent its detection.

Protection against them is traditionally carried out using a broadband notch filter. To eliminate the zones of "blind" speeds in the amplitude-speed characteristic of the notch filter, sounding is performed with wobble of the pulse repetition period [1, 2].

It should be noted that in any amplitude-speed characteristic there are dips that can lead to a significant weakening of the spectral components of the targets. At long ranges (~ 200-300 km), the level of target echoes is low, so introducing additional losses into these echo signals will lead to their skipping (non-detection). Thus, the use of a notch filter to protect against passive interference is advisable only in those areas of space where this interference is present. The detection (mapping) of passive interference is carried out using mapping devices.

Known inter-review device for mapping passive interference [3], containing a signal detector and inter-review comparison circuit, which generates mapping signals in the presence of stationary or slowly moving objects.

Interference and target signals from the detector output are recorded in the corresponding cells of the storage device if they are detected in two adjacent surveys in the same space elements.

The disadvantage of this device is poor-quality interference when it is located on the cell edge of the inter-review memory device, since even small changes in the spatial position of the interference can cause it to appear in other cells of the memory device. The efficiency of the device is further reduced by mapping passive interference moving under the influence of wind.

This disadvantage was partially eliminated in the device [4], which uses two jamming maps, displaced in coordinates one relative to another by half of the selected spatial element, to map slowly moving noise reflections.

This device carries out identification of signals using, as an identification criterion, the amount of displacement of an object in space during the analysis time, which exceeds the time of one survey.

The disadvantage of this device is the false mapping of low-speed single targets.

In addition, it is known inter-device interference mapping [5], designed to highlight the spatial areas affected by the interference, using speed and energy differences between the interference signals and targets. This device comprises a signal detector, a recording control circuit, a first AND gate, a write register, an inter-review memory, a segment counter, an azimuth counter, an azimuth adder, a read register, a first range strobe extension device consisting of an auxiliary memory and a standby multivibrator, the second device for expanding the gate in range, consisting of a delay line and a waiting multivibrator, range counter, rev counter, range adder, control circuit a address, target counter, threshold device, read register and the second logical element "AND".

We choose this device as a prototype, because it is the closest in technical essence to the claimed device.

The principle of operation of the prototype device is based on speed and energy differences between the echo signals of targets and passive interference. The separation of moving passive interference is realized by comparing the current information in each spatial element with an expanded, compared with the space element, strobe formed around each mark from the signal from the previous review. The dimensions of the strobe are selected such that the signal from an object moving at a speed less than a given one during one review does not go beyond the strobe and is identified as a passive interference. The above comparison in the prototype device is carried out in the first logical element "And", and the expanded strobe is formed by the second device to expand the strobe in range.

Additionally, a scheme is provided that eliminates the formation of a mapping signal for low-speed targets by counting and comparing with the threshold value the number of range elements (quanta) affected by the interference. If the number of such elements is greater than the threshold value, then a decision is made about the presence of passive interference in this period. Counting quanta affected by interference is carried out in the target counter, and comparison with a threshold is performed in a threshold device.

Modern radar stations use solid-state transmitting devices. As probing signals, the most widely used are signals with linear frequency modulation (LFM). In addition, to normalize the dynamic range of noise and protect radar stations from impulse noise in the optimal signal processing, a nonlinear device - an amplitude limiter [6] is used, therefore the channel of optimal processing in the signal detector is nonlinear.

The use of chirp signals will lead to the formation of a false mapping signal for two (or more) closely located targets in the prototype device. This is explained by the fact that at the output of the signal detector there will be marks not only from the targets, but also from satellite signals arising from the optimal processing of the LFM signals in a nonlinear channel [6]. Additional marks increase the value of the target counter, which leads to exceeding the threshold value in the threshold device and the false formation of the mapping signal.

Thus, the main disadvantage of the prototype device when using chirp signals in radar stations is the formation of a false mapping signal for two (or more) closely spaced targets.

The technical result of the invention is to eliminate the specified disadvantage of the prototype device while maintaining the quality of mapping passive interference.

The specified result is achieved by the fact that in the prototype device containing a signal detector, the first output connected to the first input of the first logical element "I", the second input of which is connected to the output of the second gate expansion device in range, the first gate expansion device in range connected to the first the input of the second logical element "And", the second input of which through the first threshold device is connected to the output of the target counter, the output of the second logical element "And" is the output of the whole device, random access memory is introduced, connected to the input of the second strobe extension device by the output, and input to the first output of the signal detector, the second output of which is connected through the ranking device, the multiplier and the second threshold device with the second input of the third logical element "I", the first input which, like the input of the first strobe extension device, is connected through the delay line to the output of the first logical element “I”, and the output to the input of the target counter.

Figure 1 shows the structural diagram of the inventive device, where the following notation:

1 - signal detector;

2, 4, 10 - the first, second and third logical elements of "AND";

3, 5 - the first and second devices for expanding the gate in range;

6 - goal counter;

7, 13 - the first and second threshold devices;

8 - random access memory;

9 - delay line;

11 - ranking device;

12 - multiplier.

As can be seen from figure 1, the inventive device includes a signal detector 1, three logical elements "And" 2, 4, 10, two devices for expanding the strobe in range 3, 5, target counter 6, two threshold devices 7, 13, operational storage device 8, delay line 9, ranking device 11 and multiplier 12.

The first output of the signal detector 1 is connected to the first input of the first logical element "And" 2, as well as through random access memory 8 and the second device to expand the gate in range 5 with the second input of the first logical element "And" 2, the output of which is connected to the input of the line delay 9, the output connected to the first input of the third logical element "And" 10, as well as through the first device for expanding the gate in range 3rd the first input of the second logical element "And" 4.

The second output of the signal detector 1 through the ranking device 11, the multiplier 12 and the second threshold device 13 is connected to the second input of the third logical element "And" 10, the output of which through the target counter 6 and the first threshold device 7 is connected to the second input of the second logical element "And" four.

The output of the second logical element "AND" 4 is the output of the entire device.

The principle of operation of the claimed device is as follows. The received radar signals are sent to signal detector 1, in which they are first limited (to normalize the dynamic range of the noise and protect the radar station from impulse noise), then, by inter-period and inter-period processing, they are separated from the external and intrinsic noise of the radar station and compared with the threshold detection. From the first output of the signal detector 1, binary information ("0" or "1") is supplied to the first input of the logical element "And" 2 and is recorded in the random access memory 8. From the second output of the signal detector 1, the amplitude information (after inter-period processing) is transmitted to ranking device input 11.

Random access memory 8 is designed to store azimuthal-range information about the detected objects from a previous review.

From the output of random access memory 8, the signal is fed to the input of the strobe expansion device in range 5, the task of which is to form an extended-range inter-review strobe around each detected signal.

The size of the gate in range is determined by the double value of the maximum possible displacement along the range of the mark from passive interference in one review. Given that the expanded interobzor strobe should be formed around the signal mark, then reading from the random access memory 8 should be carried out with a lead that corresponds to the size of the interobzor strobe in range.

The generated extended interobzor gate from the output of the strobe expansion device in range 5 is fed to the second input of the logic element "AND" 2, in which the interobzor identification of signals takes place.

To provide mapping of interference that rapidly changes its location in space, for example, such as the leading “edges” of dipole interference, a range-wide strobe extension device 3 is provided for expanding the range strobe around each signal passing through the AND gate 2 and line delays 9. The dimensions of this strobe are selected from the condition that it matches the maximum movement of the jammer in any direction during the review period. Thus, at the output of the strobe extension device over a range of 3, an inter-survey strobe is formed that provides mapping of passive interference not only at the places where it coincides in two surveys, but also taking into account its possible movement in any direction with the speed of the jammer. The formed interobzor gate is fed to the first input of the logical element "AND" 4.

Since not only passive interference, but also single low-speed targets can be mapped at the output of the AND gate 2, the device has an energy criterion that excludes the formation of a mapping signal from them.

The azimuthal directions in which a dipole interference signal is present are characterized by a large number of spatial elements affected by the interference. Unlike interference, low-speed targets are found only in a few spatial elements. Therefore, it is possible to implement energy differences between goals and interference. To do this, using the target counter 6 and the threshold device 7 in each repetition period, the number of quanta affected by the interference is determined, which is then compared with the selected threshold. If the number of such quanta is greater than the threshold, then a decision is made on the presence of passive interference in a given repetition period (in a given azimuthal direction). At the same time, from the output of the threshold device 7, a signal of a logical unit is supplied to the second input of the logical element "AND" 4, allowing the passage of the mapping signal to the output of the device. If the selected threshold does not exceed the passage of the mapping signal to the output of the device is prohibited.

The intra-period energy criterion makes it possible to distinguish the echo signal of passive interference from the echo signal of targets, however, as mentioned earlier, when using LFM signals, the mapping signal will also be generated for two (or more) closely spaced targets.

This disadvantage in the invention is eliminated by using the adaptive detection threshold generation circuit. To do this, in ranking device 11 in a “sliding” range window, a series of ordinal statistics X is formed, followed by selecting an element with serial number κ and multiplying it by a factor α in multiplier 12. The size of the “sliding” window N, the constants κ and α are selected using mathematical modeling. To compensate for the delay that occurs in the ranking device, a delay line 9 of N / 2 quanta is used, where N is the size of the "sliding" window in the ranking device 11.

The generated adaptive threshold in the threshold device 13 is compared with the detection threshold, which is a constant value. Figure 2-4 presents test situations showing the ratio of the adaptive threshold and the detection threshold in various interference and target environments.

As can be seen from figure 2 and 3, in the field of passive interference due to its length in range, the adaptive threshold exceeds the detection threshold. From the output of the threshold device 13 to the second input of the logical element "AND" 10 is fed a signal of a logical unit, allowing the passage of signals to the target counter 6.

In turn, in the field of targets and satellite signals (FIGS. 2, 4), due to the presence of a “noise” well, the adaptive threshold does not exceed the detection threshold. It is forbidden to transmit signals to the target counter 6, which leads to the failure of the energy criterion for the signals of the targets and satellite signals.

In this case, according to the passive interference signal, the energy criterion is satisfied, but not according to target signals and satellite signals, i.e., unlike the prototype device, the formation of a mapping signal in the inventive device does not occur in the presence of two (or) more closely located targets will be.

Thus, the introduction into the device containing the signal detector, two logical elements "And", two devices for expanding the strobe in range, the target counter and threshold device, the third logical element "And", the delay line, random access memory, ranking device, multiplier and the second threshold device eliminated the formation of a false mapping signal for two (or more) closely spaced targets, while maintaining the same quality of mapping passive interference.

Literature

1. Reference radar. Ed. Skolnik M., vol. 1, M .: Soviet Radio, 1976, p. 256-263;

2. Bakulev P.A. Methods and devices for the selection of moving targets, M .: Radio and communication, 1986;

3. French patent No. 2241077, IPC G01S 9/42, 1975;

4. US patent No. 4068231, IPC G01S 9/02, 1978;

5. RF patent No. 2040802, IPC G01S 13/89, G01S 7/36, 1985;

6. Lezin Yu.S. Introduction to the theory and technique of radio systems. Textbook for higher education. - M.: Radio and Communications, 1986.

Claims (1)

Inter-passive jamming mapping device containing a signal detector, the first output connected to the first input of the first logical element "I", the second input of which is connected to the output of the second gate expansion device, the first range expansion gate connected to the first input of the second logic element " And ", the second input of which through the first threshold device is connected to the output of the target counter, the output of the second logical element" AND "is the output of the entire device, characterized in that random access memory is inserted into it, connected to the input of the second strobe expansion device by distance, and input to the first output of the signal detector, the second output of which is connected in series through the ranking device, the multiplier, and the second threshold device with the second input of the third logical element "And", the first input of which, as well as the input of the first device to expand the gate in range through the delay line is connected to the output of the first logical element "And", and the output d - to the input of counter goals.

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