RU2808450C1 - V-frequency modulation signal filter - Google Patents

Abstract

FIELD: radar.

SUBSTANCE: methods and techniques for processing radar signals used to construct radar signal processing devices. The V-frequency modulation signal filter further comprises a third compression filter, a second adder, a second subtraction block, a third and fourth bottom limiter, and a second and third intersection block.

EFFECT: reducing the number and level of side peaks of the autocorrelation function and the relative level of noise and interference at the filter output.

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Description

The invention relates to the field of radar, in particular, to methods and techniques for processing radar signals and can be used to build radar signal processing devices.

Matched filters for signals with frequency modulation are known, for example, a matched filter for a signal with V-shaped frequency modulation (FM) [Ch. Cook, M. Bernfeld. Radar signals. Per. from English, ed. V.S. Kelzon. - M.: Sov. radio, 1971. - 568 p., ill., fig. 4.17, p. 115 - Block diagram of a matched filter for a V-shaped FM signal].

The disadvantages of the known analogue filter include the high level of side lobes of the autocorrelation function (ACF) and insufficient noise immunity under conditions of noise and interference.

Of the known devices, the closest in technical essence and achieved result to the claimed one (prototype) is a signal filter with a V-shaped FM [Pat. 2767317 Russian Federation, MPK N04V 1/12, N04V 1/707. Signal filter with V-shaped frequency modulation / E.V. Kravtsov, R.I. Ryumshin, M.O. Likhomanov, O.N. Dudarikov, B.M. Yatsenko; applicant and patent holder VUNTS Air Force "VVA". - No. 2021112631 application. 04/29/2021; publ. 03/17/2022].

The known prototype filter contains a signal separation block, the input of which is the input of the filter, the first output of the division block is connected to the input of the first compression filter, the second output of the division block is simultaneously connected through the second compression filter to the second input of the first adder and to the input of the subtracted first subtraction block, the output the first compression filter is simultaneously connected to the first input of the first adder, the output of which is connected through the first limiter from below to the first input of the first intersection block, and with the input of the reduced first subtraction block, the output of which is connected through the second limiter from below to the second input of the first intersection block, while the pulse the response of the first compression filter is consistent with the entire signal, one half of the impulse response of the second compression filter is antiphase to the corresponding half of the impulse response of the first compression filter, and the second half is in phase with the second half of the impulse response of the first compression filter. The output of the known filter is the output of the first intersection block.

The purpose of the elements and operation of the prototype filter, as an integral part of the proposed device, will be described below when explaining the proposed device.

The prototype filter, in comparison with the analogue filter, provides a significant reduction in the level of ACF side lobes and an increase in noise immunity under conditions of noise and interference.

However, the disadvantages of the known prototype filter include the relatively high level of ACF side lobes, especially in the area immediately adjacent to the main lobe. The relative level of these lobes reaches at least 20% of the main one, which leads to masking of weak useful signals.

In addition, under conditions of strong interference, the noise immunity of the prototype filter turns out to be insufficient.

The problem to be solved by the claimed invention is to organize a signal processing structure with V-shaped FM, ensuring orthogonalization of the side peaks of the ACF, especially in the area adjacent to the main lobe, peaks of the VCF, as well as noise and interference in the processing channels and their mutual partial or complete compensation, and leading to increased noise immunity.

The technical result of the invention is to reduce the number and level of side ACF peaks and the relative level of noise and interference at the filter output.

The technical result is achieved by the fact that in the known V-shaped FM signal filter containing a signal separation block, the input of which is the input of the filter, the first output of the division block is connected to the input of the first compression filter, the second output of the separation block is simultaneously connected through the second compression filter to the second the input of the first adder and the input of the subtracted first subtraction block, the output of the first compression filter is simultaneously connected to the first input of the first adder, the output of which is connected through the first limiter from below to the first input of the first intersection block, and the input of the reduced first subtraction block, the output of which is connected through the second limiter from below to the second input of the first intersection block, while the impulse response of the first compression filter is consistent with the entire signal, and one half of the impulse response of the second compression filter is antiphase to the corresponding half of the impulse response of the first compression filter, and the second half is in phase with the second half of the impulse response of the first compression filter, the third is introduced a compression filter connected by the input to the third output of the signal separation block, and the output simultaneously with the second input of the second adder, the output of which is connected through the third limiter from below to the first input of the second intersection block, and the input of the subtracted second subtraction block, the output of which is connected through the fourth limiter from below to the second input of the second intersection block, the output of which is connected to the second input of the third intersection block, the first input of which is connected to the output of the first intersection block, and the first input of the second adder and the input of the reduced second subtraction block are simultaneously connected to the output of the first compression filter, while the impulse response of the third The compression filter is inverse to the signal in terms of the law of frequency change and the output of the third intersection block is the output of the filter.

The essence of the claimed invention is to add to those used in the known filter frequency symmetry of a signal with V-shaped FM in the first compression filter and phase asymmetry in the second compression filter, followed by sum-difference processing, providing orthogonalization of the side lobes of the ACF, VCF, noise and interference at the inputs the first intersection block, using the inversion of the form of the law of frequency change in the third compression filter, followed by similar processing, ensuring the orthogonalization of the specified mixture at the inputs of the second intersection block, which is random in nature relative to the mixture at the inputs of the first intersection block.

Due to the use of various physical factors, the decorrelation of compensated signal elements, noise and interference at the inputs of the third intersection block increases. This increases the degree of suppression of these elements at the filter output. Based on this, it is possible to provide the claimed advantages in signal processing.

The present invention is illustrated by figures of graphic material. In fig. 1 shows a block diagram of the proposed filter. In fig. 2-5 show voltage diagrams obtained as a result of modeling at various points of the circuit and for various cases, illustrating the process and results of signal processing.

In fig. 1 shows: 1 - signal separation block; 2, 3, 4 - first, second and third compression filters; 5, 6 - first and second adders; 7, 8 - first and second subtraction blocks; 9, 10, 11, 12 - first, second, third and fourth limiters from the bottom at the zero level; 13, 14, 15 - first, second, third intersection blocks.

The essence, operability and effectiveness of the proposed filter are explained by simulation of the operation of the structural circuit, which was carried out at a frequency ƒ ₀ equal to 8 MHz, with a sampling frequency of 96 MHz.

A pulse with a V-shaped FM within the duration τ _can be represented as the sum of two linearly frequency-modulated pulses in the form [Ch. Cook, M. Bernfeld. Radar signals. Per. from English, ed. V.S. Kelzon. - M.: Sov. radio, 1971. - 568 p., ill.]

In equality (1) the terms correspond to the expressions

where A is the signal amplitude, μ=ƒ/τ _and is the rate of frequency change. The ACF for such a signal consists of four parts: two autocorrelation terms corresponding and two mutual correlation terms corresponding to two cross products

The total ACF expressed in terms of these terms has the form

The main contribution to this function is made by autocorrelation terms related by the relation Where

The sum of the main terms quickly falls to the level of the pedestal, determined by the intercorrelation terms, the relative value of which determines the level of the side lobes and is [Ch. Cook, M. Bernfeld. Radar signals. Per. from English, ed. V.S. Kelzon. - M.: Sov. radio, 1971. - 568 p., ill.]:

As shown below, the pedestal exists over the entire interval equal to twice the pulse duration, and the processing task is to almost completely compensate for it in combination with attenuation of noise and interference.

The time and frequency parameters of the V-shaped FM radio pulse, synthesized in accordance with (1)-(3), are accepted as follows: pulse duration τ _and ≈5.2 μs; spectrum width at the level of 0.1 - Δƒ≈10.8 MHz; signal base - B≈56.

The signal and impulse characteristics of the compression filters obtained for the study are shown in Fig. 2, where indicated: 16 - input pulse with Λ-shaped FM; 17 - impulse response of the first compression filter, consistent with the entire signal; 18 - impulse response of the second compression filter, half of which is antiphase to the corresponding half of the impulse response (IR) of the first filter, and the second half is in phase with the second half of the IR of the first filter, 19 - impulse response of the third compression filter, which is mirror according to the law of frequency change to the input radio pulse and has the form :V

The impulse response of the first compression filter (diagram 17) is described by expressions (1)-(3) taking into account the specularity of the time function displaying the signal (diagram 17).

The impulse response of the second compression filter (diagram 18) can also be obtained based on (1)-(3), if in expression (3) we introduce an initial phase shift equal to l. IM is synthesized in the form of two halves mutually symmetrical in frequency and opposite in phase.

The impulse response of the third compression filter (diagram 19) is obtained based on (1)-(3), if in expressions (2) and (3) the signs in the exponential factors are changed to the opposite. Then the IM acquires an “inverted” FM of the form “V” in comparison with the signal.

It should be noted that the choice of the type of FM input signal to V-shaped or “inverted” - L, as in the case under consideration, does not affect the explanation of the principle and the simulation results. In each case, the impulse responses of the compression filters are set accordingly. The name of the proposed device uses established terminology: “V-shaped FM signal filter.”

The process of processing the input signal in the circuit of Fig. 1 is illustrated by diagrams at characteristic points of the diagram shown in Fig. 3.

Signal with Λ-shaped FM (diagram 16 of Fig. 2) arrives at the input of signal separation block 1 (Fig. 1). The splitter, acting as a power divider, supplies three identical signals to the first, second and third compression filters.

Since the IR of the first compression filter is matched to the signal this signal is compressed and ACF takes place at the output of block 2 with a maximum at the end of the input signal (Fig. 3, diagram 20) and side lobes in the form of a pedestal for 2τ _and .

At the same time, due to the indicated mismatch of the IR of the second compression filter 3 relative to the signal, a CCF occurs at the output of this filter with a zero value at the end of the input signal (Fig. 3, diagram 21) and a uniform level approximately equal to the ACF pedestal for 2τ _and . The phases of the side peaks of the ACF and the peaks of the VCF differ. To the left of the main ACF peak they are antiphase, and to the right they are in phase. The scale adopted during modeling does not allow this to be detected on the diagrams.

Next is the ACF signal arrives at the first input of the first adder 5, and the VKF signal - to the second input of adder 5. The first adder coherently sums the instantaneous values of ACF and VCF, and its output will be a coherent sum (Fig. 3, diagram 22). In this case, due to the antiphase of the side lobes of the ACF and the VCF to the left of the ACF maximum, they are mutually compensated. At the same time, due to the in-phase to the right of the ACF maximum, they double.

The signal from the output of block 5 is limited from below in the first limiter from below at the zero level 9, which “thin out” the ACF side lobes, VCF emissions, noise and interference (if any), excluding negative values. Plot 23 represents the output signal of block 9.

Signal also arrives at the input of the reduced first subtraction block 7, and the signal - to the input of subtracted block 7. At the output of the first subtraction block there will be a coherent difference of the received signals in the form: (Fig. 3, diagram 24). A picture is observed that is opposite to the output signal of adder 5. The side lobes of the ACF turn out to be compensated to the right of the maximum and doubled to the left.

From the output of block 7, the signal is limited from below in the second limiter from below at zero level 10. Limiter 10, like 9, “thin out” the side lobes of the ACF, emissions of the VCF, noise and interference, excluding their negative values. The signal at the output of block 10 is represented by diagram 25.

Further signals from the output of the first and second limiters from below they simultaneously arrive at the first and second inputs of the first intersection block 13, where they undergo an intersection operation, the properties and structural implementation of which are given, for example, in Gordienko V.I., Dubrovsky S.E., Ryumshin R.I. ., Fenev D.V. Universal multifunctional structural element of information processing systems // Radioelectronics. Izv. Universities, No. 3. - 1998. - P. 13-17, fig. 1. In relation to the indicated signals, the operation has the form

From (6) it follows that the intersection procedure ensures the choice of the smaller absolute value of two compared values (signals) with a sign equal to the product of the signs of these values. The use of this operation makes it possible to eliminate or minimize the side peaks of the ACF and VCF, as well as to significantly reduce the level of noise and interference.

This is indicated by the signal from the output of the intersection block 13, shown in FIG. 3 with diagram 26. Essentially, this signal is the output signal of the prototype filter.

As follows from diagram 26, the side lobes of the ACF and VCF are compensated for almost the entire duration. However, there are uncompensated “residues” in the area immediately adjacent to the main lobe (diagram 26). As modeling shows, the relative level of these side lobes is quite large and amounts to at least 20% of the main one, which can lead to masking of weak useful signals located in the area adjacent to the main lobe of a more powerful useful signal.

The reduction in the level of the near side lobes is realized by the elements introduced in the inventive device, which actually form the second processing channel, as part of the third compression filter 4 connected to the third output of the signal separation unit 1, the second adder 6, the second subtraction unit 8, the third 11 and fourth 12 limiters from below and the second block of intersection 14, and the connections that unite these elements with each other and with other blocks of the circuit.

The operation of this channel is illustrated by diagrams 27-32 shown in Fig. 3.

Plot 27 represents the output signal of the third compression filter 4 The type of this signal is determined by the impulse response of block 4, which, as stated earlier, is mirror-image according to the law of frequency change to the input radio pulse (diagram 19, Fig. 2). Signal 27 is a specific form of VCF, where the main lobe in the center of the signal is eliminated, and two side lobes of the VCF are located at the edges. The entire ACF has exactly half the duration of the ACF, symmetrical relative to the center. The exclusion of the main lobe in the center of the VCF is of fundamental importance, just as in the VCF at the output of the second compression filter (diagram 21).

This allows you to apply all the processing procedures used previously in the first channel, but with a different VCF.

VKF signal from the output of block 4 goes to the second input of the second adder 6. At the same time, the ACF signal arrives at the first input of this adder (plot 20) from the output of the first compression filter 2.

The second adder 6 coherently sums the instantaneous values of the ACF and VCF and its output will be a coherent sum of the latter:

At the same time, the ACF signal arrives at the input of the reduced second subtraction block 8, and the VCF signal - to the input of the subtracted block 8. At the output of the second subtraction block there will be a coherent difference of the received signals in the form:

This ensures time and phase orthogonalization of the side lobes of the coherent sum (plot 28) and coherent difference (plot 30) with the main lobe of the ACF preserved in both cases.

To compensate for the ACF side lobes, the signal from the output of block 6 is limited from below in the third limiter from below at zero level 11. Type of signal at the output of block 11 it is represented by diagram 29.

At the same time, the signal from the output of block 8 is limited from below in the fourth limiter from below at zero level 12. Type of signal at the output of block 12 it is represented by diagram 31.

Limiters 11 and 12, as in the first channel, partially “thin out” the side lobes of the ACF, emissions of the ACF, noise and interference, eliminating their negative values and maintaining temporal orthogonalization.

Further signals from the output of the third and fourth limiters from below, they simultaneously arrive at the first and second inputs of the second intersection block 14, where they undergo intersection operations in the form

Signal at the output of the second intersection block 14 represented by diagram 32 (Fig. 3). It is the output signal of the second processing channel.

As follows from diagram 32, the main lobe of the ACF is preserved, the side lobes are significantly thinned out, are located throughout the entire duration interval of the ACF and have a low level and, most importantly, a low level is characteristic of the area adjacent to the main lobe.

This signal is supplied to the second input of the third intersection block 15, the first input of which receives a signal from the output of the first intersection block 13 (diagram 26).

The third intersection block 15 implements the intersection operation over the received signals (diagram 26 and diagram 32) in the form

The result of this operation is the output of the third intersection block represented by diagram 33 and being the output signal of the proposed circuit.

Comparison of this signal with the output signal of the prototype (diagram 26) allows us to record the advantages of the proposed circuit in terms of the side lobes of the ACF.

For a more clear comparison, the output signals of the known and proposed circuits are presented in a normalized (relative to the main lobe) form and on a larger scale in Fig. 4, where diagram 34 corresponds to the output signal of a known filter, and diagram 35 corresponds to the output signal of the inventive filter.

As follows from the compared diagrams, at the qualitative level of assessment, the gain in ACF side lobes for the proposed filter is obvious, both in the number of petals and in their level.

A quantitative estimate of the gain in the level of ACF side lobes is found in the form of the ratio of the normalized average levels of side lobes for the prototype filter and the proposed filter side lobe dispersion ratios _Dpr and _D3 , respectively; ratios of maximum values - respectively U _{m pr} and U _{m 3} :

A quantitative assessment of work in noise was found by averaging over multiple implementations in the form of a ratio of normalized average levels of noise emissions for a prototype filter and the proposed filter as well as the ratio of the variances of noise emissions D _{sh pr} and D _{sh 3} , respectively:

Comparative results of quantitative assessment of performance in noise indicate no less than a one and a half reduction in both the average level and noise dispersion in the proposed filter relative to the prototype. Since the noise normalized to the useful signal was compared, the gain in terms of dispersion is essentially a gain in the signal-to-noise ratio of the proposed filter compared to the prototype. This gain is due to noise compensation in the inventive filter.

To evaluate interference compensation, the proposed filter generates an input signal as the sum of the useful signal noise n(t), distributed according to the normal law with zero average value and standard deviation (RMS) σ _w = 1 V and a set of arbitrary standard noise operating at the frequency of the useful signal: Moreover, the interference does not interfere with the useful signal and is separate in duration.

The type of input signal is illustrated by diagram 36 in Fig. 5, where the useful signal is hidden in noise (U _c / σ _w = 1), and interference is indicated by Roman numerals.

The following were used as interference: I - broadband pulse interference in the form of a phase-code-manipulated pulse (PCM) with arbitrary manipulation of the initial phases of partial pulses in the form {0, 0, π, π, 0, π) and a spectrum width of approximately 3 MHz; II - powerful noise interference, “covering” the spectrum of the useful signal; III - interference in the form of a short radio pulse, approximately the same in duration as the compressed useful signal; IV - interference in the form of a long radio pulse.

The amplitudes of all interference, as seen in Fig. 5, significantly exceed the useful signal U _{p i max} >>U _c . The durations of interference I, II and III approximately coincide with the duration of the useful signal. In terms of exposure time, the interference is slightly spaced apart so that, “stretching” in the compression filters, they overlap each other, forming some kind of “integral” interference. This makes it possible to obtain an approximate generalized estimate of the noise immunity of the compared filters, generally representing a rather complex version of the impact.

The same noise was used in the simulation as in the prototype study. The scale adopted for modeling does not allow us to display the “fine” structure of interference signals.

The process of processing the input mixture of useful signal, noise and interference is similar to the previously discussed in detail processing of the useful signal (Fig. 3, 4). Therefore, in FIG. Figure 5 shows only the results of processing in the form of diagrams of output voltages 37 and 38, given for the possibility of comparison to a single amplitude scale by normalizing to the amplitude of the useful signal. That is, the useful signal at the outputs of the circuits has a unit amplitude, and the interference is the ratio of interference/signal, noise/signal at the outputs of the compared circuits.

Diagram 37 in Fig. 5 represents the output signal of the prototype filter, and diagram 38 represents the output signal of the inventive filter. Comparing the diagrams of output signals at a qualitative level allows us to conclude that the proposed filter has improved noise immunity under conditions of exposure to “integral” noise. The noise at the output of the proposed filter is smaller in amplitude and more sparse in time.

A quantitative assessment of noise immunity was found in the form of the ratio of the average levels of the normalized integral noise at the output for the prototype filter and the proposed filter as well as the ratio of interference dispersions D _{p pr} and D _{p 3} , respectively:

There is a twofold gain in noise immunity of the proposed filter relative to the known one.

All quantitative estimates were found for noise and interference normalized to the useful signal, so the comparisons seem quite correct, and the relative nature of the comparison and the generalized representation of interference in the form of “integral interference” allow us to consider the obtained noise immunity estimates as general enough to make a conclusion about the effectiveness of the proposed filter.

Thus, the implementation of the proposed signal filter with V-shaped FM in comparison with the known filter provides:

reduction in the number and relative level of ACF side peaks by at least two times;

reduction of the average noise level and dispersion by at least one and a half times;

double gain in noise immunity under the influence of “integral” interference.

The possibilities for technical implementation of the elements of the proposed filter do not cause difficulties.

Signal separation block 1 can be made in the form of a simple three-terminal network of four nodes and three branches, for example, based on the structure given in Zinoviev A.L., Filippov L.I. Introduction to the theory of signals and circuits. - M.: Higher School, 1975. - 263 p. ill., p. 138, fig. 3.3, a.

Compression filters can be implemented in the form of widespread devices on surface acoustic waves (SAW), for example, as matched signal filters with linear frequency modulation on SAW, described in Yu.T. Davydov, Yu.S. Danich, A.P. Zhukovsky. etc. Radio receivers. Ed. Professor A.P. Zhukovsky M.: Higher School, 1989. - 342 pp., ill., p. 250, fig. 12.22, 12.23; or as surfactant convolvers (see ibid., p. 251, Fig. 12.26).

Adders and subtraction blocks can be made according to the usual amplifier circuit with two inputs or with direct and inverse inputs of the type described in A.G. Alekseenko. Application of precision analog integrated circuits. - M.: Radio and Communications, 1981. - 354 p., ill., p. 77, fig. 3.2.

Limiters from below at the zero level can be made according to a simple diode detector circuit [Golubkov A.P., Dalmatov A.D., Lukoshkin A.P. and others. Design of radar receiving devices. Ed. M.A. Sokolova. - M.: Higher School, 1984. - 335 pp., p. 140, fig. 5.12].

Intersection blocks can be implemented on the basis of adders, subtracting devices and module calculation devices ([Gordienko V.I., Dubrovsky S.E., Ryumshin R.I., Fenev D.V. Universal multifunctional structural element of information processing systems // Radioelectronics Izv. Universities, No. 3. - 1998. - P. 13-17, p. 14, Fig. 1] [Alekseenko A.G. Application of precision analog integrated circuits. - M.: Radio and Communications, 1981. - 354 pp., p. 77, Fig. 2, 3]; [Borovsky V.P., Kostenko V.I., Mikhailenko V.M., etc. Handbook of circuit design for the radio amateur. Edited by A.P. Bobrovsky . - K.: Tekhnika, 1989. - 456 pp., ill.„ p. 211, Fig. 12.4]).

An analysis of known technical solutions in the field of radar shows that the claimed invention, thanks to the essential features in the composition of the introduced elements and connections, determined the way to achieve the technical result, which consists in reducing the number and reducing the level of side peaks of the ACF, reducing the relative level of noise and interference at the filter output, does not follow clearly from the prior art for a specialist in the given subject area and meets the requirement of “inventive step”.

The applicant has not discovered an analogue characterized by features identical to all the essential features of the claimed invention. The definition of a prototype as the closest analogue in terms of a set of characteristics has made it possible to identify distinctive features in the claimed object that are significant in relation to the technical result, which allows us to consider the claimed invention as satisfying the criterion of “inventive novelty”.

The proposed technical solution is industrially applicable, since standard radio engineering elements and devices used in radar and communications technology can be used for its implementation.

Claims (1)

A signal filter with V-shaped frequency modulation, containing a signal separation unit, the input of which is the filter input, the first output of the separation unit is connected to the input of the first compression filter, the second output of the separation unit is simultaneously connected through the second compression filter to the second input of the first adder and the input of the first subtractor subtraction block, the output of the first compression filter is simultaneously connected to the first input of the first adder, the output of which is connected through the first limiter from below to the first input of the first intersection block, and the input of the reduced first subtraction block, the output of which is connected through the second limiter from below to the second input of the first intersection block, wherein the impulse response of the first compression filter is consistent with the entire signal, and one half of the impulse response of the second compression filter is antiphase to the corresponding half of the impulse response of the first compression filter, and the second half is in phase with the second half of the impulse response of the first compression filter, characterized in that a third compression filter is introduced, connected by the input to the third output of the signal separation block, and the output simultaneously with the second input of the second adder, the output of which is connected through the third limiter from below to the first input of the second intersection block, and the input of the subtracted second subtraction block, the output of which is connected through the fourth limiter from below to the second input of the second an intersection block, the output of which is connected to the second input of the third intersection block, the first input of which is connected to the output of the first intersection block, and the first input of the second adder and the input of the reduced second subtraction block are simultaneously connected to the output of the first compression filter, while the impulse response of the third compression filter is inverse signal according to the law of frequency change and the output of the third intersection block is the filter output.