RU1840935C - Radar signal discriminator with intrapulse frequency modulation - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: radar signal discriminator includes an autocorrelator, a control pulse former, an incidental frequency modulation elimination unit, a comparator, a logic threshold unit, a delay line, a first circuit consisting of series-connected first switch, first counter, comparator unit, a second circuit consisting of series-connected second switch, second counter, divider unit. The radar signal discriminator also includes a duration measuring device and a half-gate former, wherein all said components are made and connected to each other in a certain manner.

EFFECT: high accuracy of distinguishing radar signals.

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Description

The invention also relates to pulsed information receivers operating in a wide range of signal modulation parameters and is intended for use in radio intelligence systems (RTR) and passive target designation systems (PSTS) as equipment for distinguishing signals by the type of intrapulse modulation.

At present, devices are known for distinguishing complex radar signals by the type of intrapulse modulation and measuring their parameters of modulating functions.

A device is known that generates a sign of the type of modulation of signals with in-pulse linear frequency modulation (LFM) and binary (0, π) phase shift keying (FM), and also measures the beat frequency of the LFM signals and determines the number of phase overshoots in the code of the FM signals.

A disadvantage of the known device is a narrow range of operating frequencies in the analysis of FM signals, as well as low sensitivity.

Another device also forms a sign of the type of modulation and measures the modulation parameters of the LFM and FM signals. The known device is highly sensitive, however, a narrow range of operating frequencies and a narrow range of the analyzed modulation parameters of complex signals significantly limit its practical use.

Devices by auth. testimonial. No. 1840896 (application No. 2206387 of July 5, 1976) and author. testimonial. No. 1840900 (application No. 2229070 of 12.19.77) perform the same operations as the first and second analogues, are characterized by high sensitivity, a wide range of changes in operating frequencies and modulation parameters of complex signals. These devices exclude the passage of simple radio-pulse signals to their outputs.

The device according to ed. testimonial. No. 1840877 (application for invention No. 2235624 of 04/13/78) makes a distinction between pulsed LFM and FM signals and measures the parameters of their modulating functions. The known device in comparison with the above analogues has a higher reliability of distinguishing chirp signals. An increase in the reliability of discrimination is achieved through the use in the channel of the LFM feature formation of the scheme for eliminating spurious frequency modulation at the fronts of real simple signals.

It should be noted that a common drawback of the considered analogues is their limited functionality, which is expressed in the fact that the known devices distinguish only two types of complex signals - LFM and FM and measure the parameters of their modulating functions.

The device distinguishes between FM, LFM and signals with intrapulse quadratic frequency modulation (EHF), and also measures the parameters of their modulating functions in a wide frequency range. The distinction between chirp and EHF signals is based on the difference in the responses of the autocorrelator to these signals. The device encodes the time intervals between the zero-transitions of the autocorrelator response and determines the current difference between the codes of the previous and subsequent time intervals, which are then summed modulo. Since, when processing LFM signals, the distance between the zero-transitions of the beat voltage is constant, because Since the autocorrelator's response to the chirp signal is a beating with a constant frequency, the total difference code at the output of the device is close to zero. When processing EHF signals, the intervals between zero transitions are different, because the response of the autocorrelator to the EHF signal is a beating with a ramp frequency.

In this case, the total difference code at the output of the device is much greater than zero, which is a sign of the EHF signal.

This device allows to obtain high reliability of the distinction between LFM and EHF signals with a smooth (undistorted) shape of the envelopes. Such a situation occurs when the reconnaissable source is located at a distance not exceeding the range of the radio horizon of the RTR and PSTSU systems.

An extremely important task of the RTR and PSTSU systems is the detection, discrimination and measurement of parameters of radio signals whose radiation sources are at distances significantly exceeding the range of the radio horizon. In this case, the intercepted radio signals are distorted by interference. The distortion of signals is manifested mainly in the distortion of the structure of their envelopes. Distortion of the envelopes of the LFM signals causes distortion of the response shape of the autocorrelator, which leads to the confusion of the LFM and EHF signals.

We illustrate what has been said with an example. Figure 1a shows the beat voltage at the output of the autocorrelator with an undistorted envelope of the LFM signal. In the known device at time instants corresponding to zero-voltage transitions of the beats, standard video signals are generated (Fig. 1b). As a result of summing the differences of the codes of the previous and subsequent time intervals between zero-transitions at the output of the device, we obtain a code whose value is close to zero, and there is no pulse at the output of the "EHF" of the device.

On figa presents a graph of the voltage of the beats at the output of the autocorrelator, obtained as a result of experimental studies of LFM signals with distorted envelopes.

Comparing Figa and Figa, it is seen that the forms of voltage beats are different. Distortion of the voltage of the beats leads to the appearance of new zero transitions and, accordingly, to the violation of the equality of time intervals between zero transitions (Fig.2b).

The output of the known device generates a code of the sum of the differences in time intervals, the value of which is much more than zero. A chirped signal with a distorted envelope will be perceived by this device as a signal with an EHF, i.e. there is a confusion between the LFM and EHF signals. Thus, the known device has a low reliability of distinguishing frequency-modulated signals with a distorted envelope.

One of the important tasks in modern RTR and PSTSU systems is to increase the reliability of distinguishing intercepted radar signals by the type of intrapulse modulation. The solution to this problem will increase the likelihood of correct recognition of the types of radar of the probable enemy and their carriers.

This invention is aimed at increasing the reliability of distinguishing between LFM and EHFM signals with a distorted envelope shape. A positive effect is achieved by introducing new elements and relationships only in that part of the prototype, which is used to process EHF signals. Therefore, in the future, in order to limit the scope of claims and simplify the description of the object of the invention proposed in this application, we consider it expedient to exclude elements and connections from the functional diagram of the prototype that do not create a positive effect and are not functionally related to the proposed device. The prototype diagram is shown in figure 3 of the materials of this application.

The known device comprises an autocorrelator, a circuit consisting of a first delay line, a first key, a second delay line, and a second key, which will be referred to hereinafter as the parasitic FM exclusion block, a control pulse shaper, a comparator in series, a block matches, interval-code converter, write register, subtraction block, accumulating adder, logical threshold block.

The inputs of the autocorrelator and the shaper of the control pulses are connected together and are the input of the device. The autocorrelator output is connected to the input of the parasitic FM exception block, the output of which is connected to the comparator input.

The first output of the control pulse shaper is connected to the second inputs of the parasitic FM exclusion block and the coincidence block, the output of which is connected to the second input of the control pulse shaper, the third output of which is connected to the second input of the write register, the second output of the control pulse shaper is connected to the third input of the write register and second the inputs of the accumulating adder and the interval-code converter, the output of which is connected to the second input of the subtraction unit, the fourth output of the driver x pulses connected to the third input of the accumulating adder, the output of which is connected to its fourth input.

A disadvantage of the known device is the low reliability of distinguishing chirp and EHF signals with a distorted envelope shape.

The aim of the present invention is to increase the reliability of distinguishing chirp and EHF signals with a distorted envelope shape.

This goal is achieved by the fact that in a known device containing an autocorrelator, a driver of control pulses, serially connected elimination block of parasitic FM and a comparator, a logical threshold unit, the inputs of the autocorrelator and driver of control pulses are connected together and are the input of the device, the output of the autocorrelator is connected to the input of the exception unit parasitic FM, the second input of which is connected to the first output of the driver of the control pulses, an additional delay line is introduced, the first a circuit consisting of a series-connected key, counter, a comparison unit, a second circuit consisting of a series-connected key, counter, a division block, a series-connected duration meter and a half-gate former, the output of the comparator is connected to the input of the delay line, the output of which is connected to the inputs connected together keys of the first and second circuit, the output of the counter of the first circuit is connected to the second input of the division unit, the output of the counter of the second circuit is connected to the second input of the comparison unit, the output of which is connected is connected to the third input of the division block, the output of which is connected to the input of the logical threshold block, the first and second outputs of the half-gate driver are respectively connected to the control inputs of the keys of the first and second chains, the second input of the half-gate driver is connected to the input of the duration meter and connected to the first output of the control pulse generator , the second output of which is connected to the reset inputs of the counters of the first and second circuits, duration meter and half-gate former, control output of the former directs pulses is connected to the fourth input of the divider.

The introduction of additional elements and connections into the known device made it possible to obtain a new effect - to increase the reliability of distinguishing between LFM and EHFM signals with a distorted envelope.

Figure 4 shows a functional diagram of the proposed device.

The device contains an autocorrelator 1, keys 2, 3, a driver pulse generator 4, an exception block for parasitic FM 5, counters 6, 7, a duration meter 8, a comparator 9, a comparison unit 10, a division unit 11, a half-gate former 12, a delay line 13, a logical threshold block 14.

The inputs of the autocorrelator 1 and the shaper 4 are connected together and are the input of the device. The output of the autocorrelator 1 is connected to the first input of block 5. The comparator 9 and the delay line 13 are connected in series. The output of block 5 is connected to the input of the comparator 9. The inputs of the first circuit, consisting of a series-connected key 2, counter 6, a comparison unit 10, and a second circuit, consisting of a series-connected key 3, counter 7, division unit 11, are connected together and connected to the line output delays 13. The output of counter 6 is connected to the second input of block 11, the output of counter 7 is connected to the second input of block 10, the output of which is connected to the third input of block 11, the output of which is connected to the input of the logical threshold block 14. The output of meter 8 is connected to input an ode to the half-gate driver 12, the first and second outputs of which are connected to the control inputs of keys 2 and 3, respectively. The second inputs of the shaper 12, block 5 and the input of the meter 8 are connected together and connected to the first output of the shaper 4, the second output of which is connected to the reset inputs of the counters 6, 7 of the meter 8, the shaper 12. The control output of the shaper 4 is connected to the fourth input of the division unit 11.

The output of the device is the output of the "EHF" of the logical threshold block 14.

Consider the operation of the proposed device.

Let the LFM signal be input to the device.

The response of the autocorrelator 1 to the LFM radio signal with a distorted envelope is the beating voltage shown in Fig.2A. The voltage of the beats from the output of the autocorrelator 1 is supplied to block 5, which is opened by the pulse of the shaper 4, for a time corresponding to the duration of the envelope τ of the input signal. Block 5 excludes from the processing spurious frequency modulation at the signal fronts. The voltage of the beats from the output of block 5 is supplied to the comparator 9, which generates short video pulses at time instants corresponding to zero-transitions of the voltage of the beats (Fig.2b).

The pulses of the comparator 9 are received on the delay line 13, where they are delayed for the duration of the maximum duration of the input signal. From the first output of the shaper 4, a video pulse of duration τ is supplied to the first input of the meter 8 and to the second input of the shaper 12.

The driver 8 generates a binary code for the duration of the input signal. This code is fed to the first input of the shaper 12, which generates two half-gates of duration τ / 2, arranged in series in time.

The temporary position of the leading edge of the first half-gate corresponds to the falling edge of the input signal. The first and second half-gates coming from the first and second outputs of the shaper 12 open the keys 2 and 3. In this case, the video pulses from the output of the delay line 13 go to the inputs of the counters 6, 7. At the outputs of the counters 6, 7 there are a binary number of pulses respectively for the first and the second half of the signal duration. When processing LFM signals with a distorted envelope of the number of zero-transitions of the beat voltage during the first N _{1, LFM} and second N _{2, LFM are} approximately equal, i.e. N _{1, LFM} ≈ N _{2, LFM} .

The code number N _{1, LFM} from the output of counter 6 is fed to the first input of the comparison unit 10 and to the second input of the division unit 11. Code N _{2, LFM} from the output of the counter 7 is fed to the first input of block 11 and to the second input of the comparison unit 10.

In block 10, the codes N _{1, LFM} and N _{2, LFM} are compared. At the same time, a sign of a larger code is issued to block 11 from the output of block 10. In block 11, at the command of the shaper 4 (control output) received at the fourth input of block 11, the code of the larger number is divided by the code of the smaller number of zero transitions. As a result of division at the output of block 11, we have code N _{3, LFM} , the numerical value of which is close to unit N _{3, LFM} ≈1. The response threshold of block 14 is selected so that for 1 <N _{3, LFM} <2, the logical threshold block 14 does not work and there is no information at the output of the "EHF" of the device, i.e. increases the reliability of distinguishing signals. After the measurement process from the second output of the shaper 4, the reset pulses are fed to the reset inputs of the counters 6 and 7, the meter 8 and the shaper 12 and prepare these elements for processing the next signal.

Consider the features of the proposed device when processing EHF signals. In this case, the processing algorithm is similar to the LFM signal processing algorithm discussed above.

The response of the autocorrelator 1 to the EHF signal with an undistorted envelope is, as noted, a previously low-frequency beating voltage with a linearly varying frequency. In the counters 6 and 7, codes are recorded corresponding to the number of zero-transitions of the beat voltage during the first (N _{1, EHF} ) and second (N _{2, EHF} ) half- _gates . Moreover, the ratio of numbers

намного больше единицы. $${\mathrm{<figure-callout\; id="3"\; label="N"\; filenames="00000005.png"\; state="\{\{state\}\}">N</figure-callout>}}_{3\text{EHF}}=\frac{N_{\mathrm{one,}\text{<figure-callout id="2" label="EHF N" filenames="00000005.png" state="{{state}}">EHF </figure-callout>}}}{N_{}}>>\mathrm{one}$$

much more than one.

Therefore, at the output of block 11, as a result of dividing the codes N _{1, EHF} by N _{2, EHF,} we will have code N _{3, EHF} , the numerical value of which is more than two. The number N _{3, EHF} exceeds the threshold of block 14.

At the output of the EHF device, an impulse of a sign of receiving an EHF signal is generated.

With a distorted envelope of the EHF signal (as in the case of an LFM signal with a distorted envelope), zero-transition splitting occurs. However, the number N _{3, EHF} remains almost the same as in the undistorted shape of the envelope of the EHF signal.

In the proposed device, all the elements are made according to well-known standard schemes of modern digital technology.

Thus, the proposed device allows to obtain a new effect - to increase the reliability of distinguishing between LFM and EHF signals with a distorted envelope shape.

This allows us to improve the quality of solving problems of signal selection and identification in RTR and PSTSU systems, increase the likelihood of correct recognition of radar types and their carriers, and also increase the efficiency of electronic suppression of a probable enemy’s radar by radio countermeasures systems.

Claims (2)

1. The discriminator of radar signals with intrapulse frequency modulation, containing an autocorrelator, a driver of the control pulses, a serially connected elimination block of parasitic frequency modulation and a comparator, as well as a logical threshold unit, the inputs of the autocorrelator and the driver of control pulses are connected together and are the input of the discriminator, the output of the autocorrelator is connected to the signal input of the block stray frequency modulation, the control input of which is connected to the first output a control pulse generator, characterized in that, in order to increase the reliability of distinguishing between linear frequency modulation (LFM) and quadratic frequency modulation (EHF) of signals with a distorted envelope, a delay line is additionally introduced, the first circuit consisting of the first key, the first counter connected in series, comparison unit, the second chain consists of a second key, a second counter, a second division unit, a duration meter and a half-gate former sequentially connected, while the output of the comparator is connected to the input of the delay line, the output of which is connected to the key inputs of the first and second circuits connected together, the output of the first counter is connected to the second input of the division unit, the output of the second counter is connected to the second input of the comparison unit, the output of which is connected to the control input of the division unit, the output of the division block is connected to the input of the logical threshold block, the first and second outputs of the half-gate former are connected to the control inputs of the first and second keys, respectively, the second input of the former of oustrobes is connected to the input of the duration meter and the first output of the control pulse shaper, the second output of which is connected to the reset inputs of the first and second counter, the duration meter and the half-gate shaper, the control output of the control pulse shaper is connected to the control input of the division unit. 2. The discriminator of radar signals with in-pulse frequency modulation according to claim 1, characterized in that the block excluding spurious frequency modulation is made in the form of series-connected first delay line, first key, second delay line and second key, and the input of the first delay line is a signal input block excluding spurious frequency modulation, the output of the second key is the output of the block, and the control inputs of the keys are the control input of the block.

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