RU2498337C1 - Apparatus for selecting clutter reflections from optically unobservable objects ("angels") in area of "local" objects - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: prototype having a series-connected intermediate frequency amplifier also includes a matched filter, a "local" object elimination filter, an amplitude detector, a non-coherent storage and an echo signal detector, as well as a plan view display, a first valve and an "angel" selector, consisting of a second and a third valve, a fast Fourier transform device, a Doppler frequency rough estimating device, an elimination filter tuning frequency generating device, a Doppler frequency filter, an elimination filter number determining device, a Doppler frequency determining device and a threshold device with corresponding connections.

EFFECT: protecting a radar station in the area of local objects from echo signals of angels of an arbitrary amplitude, high probability of detecting stealth and small targets.

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Description

The invention relates to radar and can be used in radar stations.

It is known that during the operation of a radar station, in addition to useful echo signals, various kinds of interference arrive at the input of the receiving path [1, 2]. In particular, interference associated with reflections of probe pulses in the surface layer of the atmosphere from rain, fog, and also from optically unobservable objects, for which the collective name “angels” is accepted, is very common.

The main reason for the appearance of “angels” is considered to be special meteorological conditions that contribute to the occurrence of local inhomogeneities in the lower layers of the troposphere, mainly up to an altitude of 2.5-3 km [3].

Reflections from the "angels" are mostly discrete. Moreover, their highest density (up to 1.5 km ^-2 ) is observed up to a range of 40-80 km in the summer months in areas of the country with a hot and temperate climate. The maximum range for the appearance of interfering reflections can reach 200–250 km [3, 4].

The main difficulty in protecting against this type of interference is their discreteness, which makes them look like a target, and the wide range of possible Doppler frequencies of "angels", especially in the decimeter and centimeter wavelength ranges.

So, the use of a notch filter to protect against "angels" will be ineffective. This is explained by the narrow width of the notch filter rejection zone compared to the wide range of variation of the possible Doppler frequencies of the "angels". Increasing the width of the notch filter notch zone while maintaining the average pulse repetition rate will lead to severe distortions in the speed characteristics of the notch filter and, as a result, to unacceptably large losses in target detection. An increase in the pulse repetition rate is also undesirable, since it is selected based on the required instrumental target detection range, and its increase will lead to ambiguity in measuring the range.

Known "Device for the selection of interfering reflections from optically unobservable objects (" angels ")" [5], which carries out the selection of "angels" and targets. The principle of operation of this device is based on the difference in radial velocities (Doppler frequencies) of targets and "angels". This difference allows the selection of "angels" using a set of notch filters with subsequent evaluation of the suppression coefficients at its output. Moreover, having the zeros of the speed characteristics of the notch filters in the range of the assumed Doppler frequencies of the echoes of the "angels", it is inevitable that at least one notch filter will receive the coefficient of suppression of the echo of the angel, significantly exceeding the suppression coefficient of the echo of the target. Thus, the magnitude of the suppression coefficient is the selection of echoes of "angels" and targets.

At relatively short distances (50-80 km), the echo signals of "local" objects (reflections from mountains, forests, underlying surfaces) additionally arrive at the input of the receiving path of the radar station [1, 4]. Protection against echoes of "local" objects is traditionally carried out using a broadband notch filter tuned to the Doppler frequency zero. To eliminate the zones of "blind" speeds in the speed response of a broadband notch filter, sounding is performed with wobble of the pulse repetition period [1, 4]. A variable pulse repetition period leads to phase distortion, which is introduced by a notch filter into the structure of the echo signals of the angel and the target. This leads to the fact that the use of the device for the selection of "angels", included in the output of the broadband notch filter, does not allow reliable identification of the distorted signal. Thus, the specified device [5] is not able to provide protection for the radar station from the "angels" in the area of "local" objects.

There is also known a device for detecting targets against a background of "angels" [1, 2] by reducing the gain of a radar receiver in the field of view affected by "angels" [2]. With this method of protection, the echoes of "angels", due to their low power, are under the threshold of detection and do not create false marks (false targets) on the circular view indicator of the radar station. This device will be selected as the prototype device as the closest to the proposed technical essence.

The prototype device contains (Fig. 1) a series-connected amplifier of an intermediate frequency 1, a matched filter 2, a notch filter for "local" objects 3, an amplitude detector 4, an incoherent drive 5, an echo signal detection device 6 and a circular viewing indicator 7, as well as a shaper functions of temporary automatic gain control 8, the output connected to the input of the gain control of the intermediate frequency amplifier 1.

In each clock cycle at the moment of the probe signal emission, the generator of the function of temporary automatic gain control 8 is started with a clock pulse, which creates an output signal that grows in time and is proportional to the time squared [2, p. 158]. Moreover, in the field of view affected by the "angels", the gain of the intermediate frequency amplifier 1 is set so that the bulk of the reflections from the "angels" is below the detection threshold.

In most cases, the effective scattering surface of the "angel" is much smaller than the effective scattering surface of the target. However, in some cases [4, Fig. 3.12], the effective scattering surface of the “angel” can be significantly larger than the effective scattering surface of the target. Therefore, it is possible that the “angel” echo of a sufficiently large amplitude exceeds the detection threshold and is perceived as a target echo. Those. the prototype device provides protection of the radar station only from echo signals of the "angels" of the threshold level and is not able to provide protection from echo signals of the "angels" of greater amplitude. Another disadvantage of this device is the omission (non-detection) of small and inconspicuous targets with an effective dispersion surface comparable to the effective dispersion surface of "angels", such as Stele technology aircraft, small ballistic missile warheads, hypersonic cruise missiles.

The technical result of the claimed device is to provide protection for the radar station in the area of "local" objects from echo signals of "angels" of arbitrary amplitude, as well as to increase the likelihood of detecting stealth and small targets.

This result is achieved by the fact that the first valve and selector are added to the prototype device containing an intermediate frequency amplifier connected in series, a matched filter, a notch filter for "local" objects, an amplitude detector, an incoherent drive and an echo detection device, as well as an all-round indicator "angels", consisting of a second valve, a third valve, devices of fast Fourier transform, rough determination of the Doppler frequency, formation of frequencies of notch settings Filtering, Doppler filter number identification devices notch filter, and determining the Doppler frequency threshold device, with corresponding connections.

Figure 2 shows the structural diagram of the inventive device, where indicated:

1 - intermediate frequency amplifier;

2 - matched filter;

3 - notch filter for "local" objects;

4 - amplitude detector;

5 - incoherent drive;

6 - device for detecting echo signals;

7 - indicator circular view;

9, 10, 11 - the first, second and third valves;

12 - fast Fourier transform device;

13 - device rough determination of the Doppler frequency;

14 - a device for forming frequencies of notch filter settings (PCF);

15 - Doppler filter (DF);

16 - device for determining the number of the notch filter;

17 - device for determining the Doppler frequency;

18 is a threshold device.

As can be seen from figure 2, the inventive device includes a detection channel, consisting of a series-connected amplifier of an intermediate frequency 1, a matched filter 2, a notch filter for "local" objects 3, an amplitude detector 4, an incoherent drive 5, an echo signal detection device 6, valve 9 and an all-round viewing indicator 7, and an “angels” selector, consisting of valve 10, valve 11, fast Fourier transform devices 12, rough determination of Doppler frequency 13, formation of notch filter settings frequencies ditch 14, Doppler filter 15, devices for determining the number of the notch filter 16, determining the frequency of the Doppler 17 and the threshold device 18.

The input of the intermediate frequency amplifier 1 is connected in series with the inputs of a matched filter 2, a notch filter for “local” objects 3, an amplitude detector 4, an incoherent drive 5, an echo signal detection device 6, and also with the first input of the first valve 9, the output of which is connected to the indicator input all-round visibility 7.

The input 1 of the valve 10 is connected to the output of the matched filter 2, and the input 2 is the output of the echo detection device 6. The output of the valve 10 is connected to the input 1 of the Doppler filter 15. The input 1 of the valve 11 is connected to the output of the notch filter in “local” objects 3, and input 2 by the output of the echo detection device 6. The output of the valve 11 is connected to the input of the fast Fourier transform device 12. The output of the fast Fourier transform device 12 through the coarse frequency determination device Doppler 13 is connected to the input of the hour forming device from the settings of the notch filters 14 and the input 2 of the Doppler filter 15, which is connected through its output through the device for determining the number of the notch filter 16 to the input 1 of the device for determining the frequency of the Doppler 17. The inputs of 2 devices for determining the number of the notch filter 16 and to determine the frequency of the Doppler 17 are connected to the output of the formation device the frequency settings of the notch filters 14. The device for determining the frequency of the Doppler 17 is connected by its output through the threshold device 18 with the input 2 of the valve 9. The threshold device 18 forms fixed threshold F _max .

The device for determining the number of the notch filter 16 consists (Fig. 3) of N processing channels (each of which includes a second-order notch filter (RF), an amplitude detector (HELL) and an incoherent storage device (NN)) and a channel selection device with minimum signal level (UTMIN).

Notch filters inputs 1 are connected to the output of the Doppler filter 15 (figure 2). The inputs 2 of the notch filters are connected to the output of the device for forming the frequencies of the settings of the notch filters 14 (Fig.2). The outputs of the notch filters through an amplitude detector and an incoherent drive are connected to the inputs of the channel selection device with a minimum signal level, the output connected to input 1 of the Doppler frequency determining device 17 (Fig. 2).

The principle of operation of the claimed device is as follows. The received signal is first fed to the input of the intermediate frequency amplifier 1, where it is amplified. Next, the signal is fed to the input of the matched filter 2, where it is matched by filtering, which increases the signal-to-noise ratio. From the output of the matched filter 2, the signal is fed to the notch filter according to "local" objects 3, the task of which is to reject the echoes of "local" objects. The signal from the output of the notch filter for "local" objects 3 is sequentially fed to an amplitude detector 4 (where it is detected), an incoherent drive 5 (where it is incoherently accumulated in order to further increase the signal-to-noise ratio), an echo signal detection device 6, which detects targets (or "angels") against a background of noise, and then to the first input of the first valve 9. When an echo is detected, the procedure for its identification starts, allowing you to decide type of echo ("angel" or target). The identification procedure is carried out in the "angels" selector, the principle of which is based on the difference between the radial velocities (Doppler frequencies) of the targets and the "angels".

Thus, the “angels” selector is turned on when a target or “angel” is detected, i.e. when applying a signal to the inputs of 2 valves 10 and 11 from the output of the device for detecting echo signals 6.

In this case, first, the signal from the output of the notch filter for “local” objects 3 through the valve 11 is fed sequentially to the fast Fourier transform device 12, where the inter-period spectrum of the analyzed signal S (f) is calculated, and the device for rough determination of the Doppler frequency 13, in which the frequency f is selected ₀ , corresponding to the largest value of S (f ₀ ) in the inter-period spectrum of S (f). The selected frequency f _{0 is} used to configure the Doppler filter 15 and to generate the frequencies of the notch filters in the device for generating the frequencies of the notch filters 14. The generated tuning frequencies are used in the device for determining the number of the notch filter 16 to form the notch zones in the notch filters and in the device for determining the Doppler frequency 17, to determine the Doppler frequency by filter number m.

After that, the signal from the output of the matched filter 2 through the valve 10 is fed to the input 1 of the Doppler filter 15, tuned to a frequency f ₀ . The Doppler filter 15 carries out coherent accumulation of pulses following the wobble period and increases the signal-to-noise ratio, which improves the efficiency of the selection of echo signals of the “angels” of the threshold level. The accumulated signal from the output of the Doppler filter 15 is fed to the input 1 of the device for determining the number of the notch filter 16.

It should be noted that the fast Fourier transform device 12 forms the signal spectrum only in a limited frequency range (from 0 to F _p , where F _p is the average pulse repetition rate), which is significantly less than the range of possible Doppler frequencies of the "angels". This will lead to the fact that the frequency f ₀ will not always correspond to the true Doppler frequency of the "angel" echo. Therefore, to eliminate inaccuracies in determining the Doppler frequency of the analyzed signal in the device for determining the number of the notch filter 16, not one channel with a notch filter having a notch zone at a frequency f _{0 is used} , but several. In each processing channel of the device for determining the number of the notch filter 16, a second-order notch filter with two “zeros” in the amplitude-frequency characteristic is used: one at a frequency of 0 Hz, the second at a frequency f _нj . The frequencies f _{nj are} determined by the device forming the frequencies of the settings of the notch filters 14:

f _nj = f ₀ ± j · F _p / L, where

j is an integer

L is the order of wobble.

The number of filters N is chosen so that the values do not go beyond the range of possible Doppler frequencies of the "angels".

At the output of the notch filters in each processing channel, by detecting and accumulating L pulses, the signal level is estimated and the channel number with the minimum signal level, m, is determined in the channel selection device with the minimum signal level (Fig. 3).

The received number m in the Doppler frequency determining device 17 determines the frequency of the notch filter, which provides the greatest suppression of the input signal | f _nm |, which in the threshold device 18 is compared with the threshold value:

F _max = 2Vr _max / λ, where

λ is the wavelength

Vr _max ~ 120 km / h - the maximum possible speed of the "angels", determined by the wind speed.

If the condition | f _nm |> F _max is satisfied, then the analyzed echo is identified as the echo of the target, otherwise - as the echo of the "angel".

Decision made (“angel” or target) from the output of the threshold device

18 enters the input 2 of valve 9. If the echo is identified as an "angel", then it is blanked in valve 9 and does not go to the circular viewing indicator 7. If the echo is identified as a target, then it passes through valve 9 to the circular viewing indicator 7.

Unlike the prototype device, the claimed device protects the radar station from echo signals of the "angels" of not only a threshold level. So, at sufficiently high powers of the “angels” echo signals in the prototype device, they will exceed the detection threshold and cause an increase in the probability of false alarms. And in the inventive device, an increase in the power of the "angels" echo signals will lead to a more accurate measurement of | f _нm | and, therefore, to increase the likelihood of the correct selection of "angels" and goals. The blanking of the identified “angel” echoes does not increase the likelihood of false alarms.

If the selector "angels" makes a decision that the analyzed signal is an echo signal of the target, then this echo signal is sent to the circular viewing indicator 7 without any changes. Those. The claimed device does not introduce additional losses in the detection of targets. Therefore, the detection characteristics of subtle and small targets when using the inventive device will be better than when using a prototype device, because the principle of operation of the prototype device is based on a decrease in the gain of the intermediate frequency amplifier in the "angels" zone, which leads to losses in the detection of echo signals of "weak" targets.

Thus, the introduction into the device containing an intermediate frequency amplifier 1, a matched filter 2, a notch filter for "local" objects 3, an amplitude detector 4, an incoherent drive 5, an echo detection device 6 and a circular viewing indicator 7, of the first valve 9 into the detection channel targets and selector "angels", consisting of a second valve 10, a third valve 11, fast Fourier transform devices 12, rough determination of the frequency of the Doppler 13, the formation of the frequency settings of the notch filters 14, Doppler filter pa 15, determine the number of notch filter 16, Doppler frequency determination unit 17 and the threshold 18 in the allowed area of "local" objects to provide protection from radar echoes "angel" with arbitrary amplitude and increase the probability of detection of subtle and small targets.

Literature:

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

2. Ibid., Vol. 3, M .: Soviet Radio, 1979, p. 158, 161.179.

3. Report on the research "Aquamarine-G". Under the direction of I.E. Lurie. - Ministry of Radio Industry of the USSR, 1984.

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

5. Patent for invention No. 2308736.

6. Cook Ch., Bernfeld M. Radar signals, M .: Soviet radio, 1971, p.13.

Claims (1)

A device for the selection of interfering reflections from optically unobservable objects ("angels") in the zone of "local" objects, consisting of a detection channel including a series-connected intermediate frequency amplifier, a matched filter, a notch filter for "local" objects, an amplitude detector, an incoherent drive and a device detection of echo signals, as well as a circular viewing indicator, characterized in that the first valve is introduced into the detection channel, the first input of which is connected to the output of the echo detection device taps, and the output is with the input of the all-round indicator, and the “angels” selector, which includes the second and third valves, a fast Fourier transform device, a coarse Doppler frequency detection device, a frequency forming device for notch filters, a Doppler filter, a notch filter number determining device, a Doppler frequency determining device and a threshold device, wherein the first input of the second valve is connected to the output of the matched filter, the first input of the third valve is connected to the output of the notch about the filter according to "local" subjects, the second inputs of the second and third valves are connected to the output of the echo detection device, the output of the second valve is connected to the first input of the Doppler filter, and the output of the third valve is connected to the input of the fast Fourier transform device, the output of which is through the coarse frequency detection device The Doppler filter is connected to the device for forming the frequencies of the notch filters and the second input of the Doppler filter, the output of the Doppler filter through the first input of the device for determining the number a notch filter is connected to the first input of the Doppler frequency determination device, the output of the notch filter settings frequency forming device is connected to the second inputs of the notch filter number determination device and the Doppler frequency determination device, the output of which is connected through the threshold device to the second input of the first valve.

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