RU2782574C1 - Digital signal processing device in pulse-doppler radar with compensation of fm of doppler signals for one period of radiation and reception of a packet of radio pulses - Google Patents

Abstract

FIELD: radar technology.

SUBSTANCE: invention relates to the field of radar and is intended for use in pulse-Doppler radar stations (radars) operating with highly maneuverable targets moving with variable radial velocity. The claimed device contains a digital shaper of quadrature components, a matched filter, a range-time portrait shaper, an element matrix multiplier, a range-frequency portrait shaper, a module calculator and a threshold processing unit, as well as an autofocus signal shaper, an amplitude spectrum calculator, an amplitude spectrum symmetry center calculator, a reference signal matrix shaper.

EFFECT: reduction in the number of periods of radiation and reception of packets of radio pulses in pulse-Doppler radars to compensate for the frequency modulation of Doppler signals of highly maneuverable targets.

1 cl, 2 dwg

Description

The invention relates to the field of radar and is intended for use in pulse-Doppler (ID) radar stations (RLS) operating with highly maneuverable targets moving at variable radial speed. Achievable technical result is to reduce the number of periods of radiation and reception of bursts of radio pulses in the ID radar to compensate for frequency modulation (FM) Doppler signals of highly maneuverable targets.

A radar ID is known, the receiving path of which is made according to the traditional scheme of superheterodyne receivers, the output signals of which are digitally fed to the radar processor, which detects targets and measures their coordinates [1, p. 235-248]. In each range channel, a digital filter performs frequency selection of the clutter-free region and Doppler filtering of the received signals using an efficient Fast Fourier Transform (FFT) algorithm. After the FFT operation, the output signal module of the Doppler selection filters is formed, which is fed to the threshold circuit for comparison with the detection threshold. Next, the Doppler frequency shift and range to the target are estimated.

A device is known that implements the method of digital signal processing (DSP) in ID radar, the block diagram of which is presented in [2].

In this method, with the help of digital formation of quadrature components, the complex envelope of the signals coming from the output of the intermediate frequency amplifier is calculated, its matched filtering is performed, the long-range-time portrait (DWP) and the range-frequency portrait (LFR) of targets are formed, the module of the signal spectra is calculated and its thresholding.

The DWP of a radar target is understood as a two-dimensional matrix formed from discrete samples of echo signals corresponding to different range channels by means of multiple sounding of space. The signal of each DWT column represents echo signal samples obtained in one probing period and corresponding sequentially in time to all range channels. The signal of each line in the DWT (Doppler signal) is the echo signal samples corresponding to one range channel in all periods of the probing signal emission.

The DFS of a radar target is understood as a two-dimensional matrix formed from discrete samples, which are a one-dimensional discrete Fourier transform (DFT) of the Doppler signal samples of each line of the DWT, obtained using the FFT algorithm.

The disadvantage of these analogs lies in the fact that when processing echo signals from highly maneuverable targets moving with variable radial velocities, the potentially achievable signal-to-noise ratio (SNR) and speed resolution of the targets are reduced.

The reason for the deficiencies is as follows.

During the accumulation time required for multiple probing of a highly maneuverable target and receiving echo signals, in the Doppler signal, the samples of which in different repetition periods correspond to the same range element, a spurious FM appears in the DWT due to the action of the Doppler effect with a variable time scale conversion factor [3 ]. This leads to the expansion of the spectrum of the Doppler signal in the DFS and does not allow coherent accumulation of the Doppler signal at one frequency in the DFS. A signal appears at the output of neighboring Doppler filters (FFT filters), the amplitude of which is less than the potentially achievable value at the output of one filter, corresponding to a constant target speed. As a result, the SNR at the DFS output decreases, and the target image on the DFS turns out to be “smeared” over the velocity channels, which significantly reduces the ability to resolve targets in terms of speed.

The closest analogue of the claimed invention in terms of technical essence is a device for digital signal processing in an ID radar with FM Doppler signal compensation operating in the target resolution mode (after target detection and evaluation), described in patent RU 2657462 C1 [4]. Let's take it as a prototype.

The difference between the prototype and other analogues is the compensation of FM Doppler signals, which allows to increase the increase in SNR and speed resolution of highly maneuverable targets moving with variable radial speed.

This result is achieved by the fact that in the well-known prototype device, the input signal is fed to the input of a serially connected digital quadrature generator (DFC), a matched filter (SF), a DWT generator, an element-wise matrix multiplier, a DFS generator and a module calculator, and the second output of the generator The DVP is connected to the autofocus (AF) signal generator, the amplitude spectrum calculator, the amplitude spectrum symmetry center calculator and the reference signal matrix generator connected in series, the output of which is connected to the second input of the element-by-element matrix multiplier, and there is a second input of the FFS generator for receiving target designation in range.

The prototype device, for two periods of radiation and reception of a burst of radio pulses, compensates for the spurious FM of Doppler signals, which increases the SNR and improves the speed resolution of highly maneuverable targets in the ID radar, operating after detecting and evaluating the target parameters in the tracking and target resolution modes.

The operation of the prototype is illustrated by the block diagram shown in Fig. 1. Device DSP ID radar with compensation of spurious FM Doppler signals operates as follows.

In the DSFCS, the input analog signals are converted into digital form and their quadrature components are formed. In the SF, a matched filtering of the complex envelope of echo signals is performed. The samples of the received signals of each probing period enter the DWT shaper and are recorded in a two-dimensional DWT matrix.

Simultaneously with the start of the target resolution mode (after detection and evaluation of the target parameters), target designation in range of a moving highly maneuverable target is sent to the second input of the device. From the DWP shaper, N _E lines are read, symmetrically located relative to the target designation in range, into the AF signal shaper, in which AF signals are formed by forming time-shifted and complex-conjugate Doppler signals.

Further, the AF signals enter the amplitude spectrum calculator, in which the DFT module is calculated. Then the average amplitude spectrum is calculated from the input N _E amplitude spectra of the AF signals.

The signal of the amplitude spectrum enters the calculator of the center of symmetry of the amplitude spectrum, in which the autoconvolution of the incoming signal is calculated and the coordinate corresponding to the maximum of the calculated function is determined.

In the reference signal matrix generator, the FM index of the Doppler signal is calculated and the reference signal matrix is formed to compensate for the spurious FM. Doppler signals with compensated parasitic FM are formed at the output of the multiplier of the element-by-element matrix multiplier. Further, the signal counts are fed to the FFS shaper and the module calculator, the output signals of which are used to confirm the detection, clarify the speed of objects and resolve highly maneuverable targets in terms of speed.

The disadvantage of the prototype is the need for double emission and reception of a burst of radio pulses to compensate for FM Doppler signals, which increases the time to obtain the most important information about the target (increased accuracy in determining the speed of a single target, the resolution of highly maneuverable targets in terms of speed in a group target). The first period of radiation and reception of a burst of radio pulses is performed in the modes of detection and determination of target parameters to determine the range of a target or a group of targets. The second period of radiation and reception of a burst of radio pulses is performed in the modes of tracking and resolving targets to increase the SNR and refine the speed of the target or resolve targets in terms of speed in the selected group.

In the claimed invention, the time to obtain the most important information about the target (increased accuracy in determining the speed of a single highly maneuverable target, the resolution of targets in terms of speed in a group target) is halved, since the compensation of parasitic FM Doppler signals of highly maneuverable targets is achieved during one period of radiation and reception of a burst of radio pulses .

The technical result of the claimed invention is to reduce the number of periods of emission and reception of bursts of radio pulses in the ID radar to compensate for the FM Doppler signals of highly maneuverable targets.

The specified technical result is achieved by the fact that in a known device containing serially connected DSFKS 1, the input of which is the input of the device, SF 2, the shaper of the DVP 3, the element-wise matrix multiplier 4, the shaper of the DFS 5 and the calculator of the module 6, as well as connected in series to the first output signal generator AF 3 signal conditioner AF 7, amplitude spectrum calculator 8, amplitude spectrum symmetry center calculator 9 and reference signal matrix generator 10, the output of which is connected to the second input of the element-wise matrix multiplier 4, a threshold processing unit 11 is introduced, the input of which is connected to the output of the module calculator 6, and the output is the output of the device; the second output of the shaper DVP 3 is connected to the second input of the shaper DFS 5, and the control output of the threshold processing unit 11 is connected to the control input of the shaper DVP 3.

Due to the introduction of a set of essential distinguishing features into the known prototype device, the proposed device provides the technical result of the invention - reducing the number of periods of emission and reception of bursts of radio pulses in the ID radar to compensate for the FM Doppler signals of highly maneuverable targets. The essence of the invention is illustrated by the block diagram shown in Fig. 2, where it is indicated:

1 - CFKS;

2 - SF;

3 - fiberboard shaper;

4 - element-by-element matrix multiplier;

5 - shaper DCP;

6 - module calculator;

7 - AF signal conditioner;

8 - amplitude spectrum calculator;

9 - calculator of the center of symmetry of the amplitude spectrum;

10 - shaper matrix of the reference signal;

11 - block thresholding.

The input of the device is the input of the DSFCS 1, the output of which is connected to the input of the SF 2, the output of which is connected to the input of the shaper DVP 3, the first output of which is connected to the first input of the element-wise multiplier of the matrices 4, the output of which is connected to the first input of the shaper of the DCHP 5; the second output of the shaper DVP 3 is connected to the second input of the shaper DCHP 5, the output of which is connected to the input of the calculator module 6; AF signal conditioner 7 is also connected to the first output of the DWP generator, the output of which is connected to the input of the amplitude spectrum calculator 8, the output of which is connected to the input of the calculator of the center of symmetry of the amplitude spectrum 9, the output of which is connected to the input of the reference signal matrix generator 10, the output of which is connected to the second the input of the element-by-element matrix multiplier 4; the input of the threshold processing unit 11 is connected to the output of the calculator module 6, the first output of the threshold processing unit 11 is the output of the device, and the second control output is connected to the control input of the DVP shaper 3.

The device DSP ID radar with compensation of parasitic FM Doppler signals in the modes of detection and determination of target parameters in one period of radiation and reception of a burst of radio pulses operates as follows.

An analog intermediate frequency signal is fed to the input of the device from the output of the radar receiver. The signal is fed to the input of the DSFCS 1, in which the samples of the quadrature components are digitally formed (the signal is digitized, multiplied by the exponential, filtered in digital low-pass filters, followed by decimation of the output samples) [6].

The samples of the complex envelope (CO) of the signal are fed to the input of the SF 2, in which the echo signals are matched filtered in the time domain using a non-recursive digital filter or in the frequency domain using the “fast” convolution method [6].

Next, the readings of the burst of echo signals of the probing period from the output of the SF 2 are fed to the shaper of the DTP. The readings are recorded in the column of the two-dimensional DWT matrix corresponding to the given sounding period. During the period of accumulation of a burst of echo signals in the shaper 3, a DWP of a single or group target is formed.

Samples of the signals of the shaper DVP 3 are sent to the shaper DCHP 5, which calculates the samples of the DFT of the Doppler signals corresponding to each element of the range. The obtained readings of the DFS are fed into the calculator of modules 6.

In the module calculator 6, the modules of complex readings of the Doppler signal spectra are determined, which, after comparison with the threshold in the threshold processing unit 11, are sent to the output of the device and can be used to detect, estimate the range and roughly estimate the speed of highly maneuverable targets.

After detecting and evaluating the parameters of the target from the control output of the threshold processing unit 11 to the control input of the DVP shaper 3, the target designation of the range of the moving highly maneuverable target is received (i _D is the row number in the two-dimensional DFS matrix with the maximum amplitude corresponding to the target range and N _E is the number of lines of readings by range in the two-dimensional DFS matrix corresponding to the duration estimate by the target range).

After receiving target indications about the range of a highly maneuverable target, N _E lines are read from the DVP shaper 3, symmetrically located relative to the target designation in range i _D , into the AF signal shaper 7, in which N _E autofocus signals are generated (for each range channel) by forming time-shifted and complex-conjugate Doppler signals, multiplying them, inverting the sign of the imaginary component of each received complex reading (to simplify the implementation of the device).

From the output of the shaper 7, the AF signals enter the amplitude spectrum calculator 8, in which their DFTs are calculated using the FFT algorithm and its module. Then, the average amplitude spectrum is calculated from the input N _E amplitude spectra of the AF signals (incoherent accumulation of spectra to increase the SNR) and the mathematical expectation is eliminated from the resulting signal.

From the output of calculator 8, the averaged centered amplitude spectrum of the AF signal enters the calculator of the center of symmetry of the amplitude spectrum 9, in which the autoconvolution of the averaged centered amplitude spectrum is calculated by the “fast” convolution method and the coordinate corresponding to the maximum of the calculated function is determined [6].

The coordinate value obtained in 9 is used in the reference signal matrix generator 10 to calculate the FM index of the Doppler signal and generate the reference signal necessary to compensate for the spurious FM in the input signal. At the output 10, a reference signal matrix is formed, in which each row is equal to the reports of the found reference signal, and the number of rows is equal to N _E - the number of range elements in the probing period, symmetrically located relative to the target designation in range i _D .

In the element-by-element matrix multiplier 4, the matrices coming from the first output of the DWP generator 3 are multiplied upon request from the threshold processing unit 11 and the reference signal matrix generator 10, the result of which is a two-dimensional matrix, each element of which is the product of the corresponding matrix elements. At the output of the multiplier 4, Doppler signals are formed with a compensated parasitic FM due to the accelerated movement of targets.

Next, the received signal samples are sent to the DFS generator 5, in which the DFT samples of the demodulated Doppler signals corresponding to each range element are calculated. The obtained readings of the DFS are sent to the calculator of module 6.

In the module calculator 6, the modules of complex readings of the spectra of Doppler signals are determined, which are fed to the threshold processing unit 11.

After comparing the modules of DFS readings with a threshold in the threshold processing unit 11, the signals are sent to the output of the device and can be used to confirm the detection and range of the target, as well as to refine the speed of a single target or resolve highly maneuverable targets in a group.

Thus, the proposed invention provides a technical result, which consists in compensating for parasitic FM Doppler signals of highly maneuverable targets in one period of radiation and reception of a burst of radio pulses, which increases the SNR and speed resolution in the ID radar in the modes of detection and determination of the parameters of highly maneuverable targets.

Let us consider signal conversion in the DSP device of the ID radar with FM Doppler signals compensation for one period of radiation and reception of a burst of radio pulses with linear frequency modulation (chirp).

The expression for the complex envelope of the Doppler chirp signal corresponding to a given range and formed from an echo signal from a moving single target located at a specified range can be represented as:

where U ₀ - signal amplitude;

- центральная частота ЛЧМ сигнала;

- central frequency of the chirp signal;

- индекс модуляции;

- modulation index;

Δω _d - frequency deviation;

T _c - signal duration;

ϕ ₀ - initial phase (further set equal to zero).

The law of instantaneous frequency change in the interval 0≤t≤T _s :

состоящих из отсчетов КО доплеровских сигналов, в котором формируются N_E дискретных сигналов АФ по одинаковому правилу для всех каналов дальности: _{N _ _} strings of discrete signals

consisting of samples of QoS of Doppler signals, in which N _E discrete AF signals are formed according to the same rule for all range channels:

where T _p =1/F _p - period and frequency of repetition of probing signals;

- сдвинутый во времени на N_сдв << N_кс отсчетов сигнал относительно

- shifted in time by N _shift << N _ks samples signal relative to

- комплексно-сопряженный сигнал

- complex conjugate signal

и

как радиоимпульсы с ЛЧМ:Imagine Signals

and

as radio pulses with chirp:

where

where

where

where

Then the AF signal is:

представляет собой отрезок комплексной гармоники длительностью N_кс - N_сдв ≈ N_кс с частотой - μN_сдвT_п.It follows from the obtained expressions that the AF signal

is a segment of the complex harmonic with a duration N _ks - N _shift ≈ N _ks with a frequency - _{μN shift} T _p .

In the general case, if there are several targets (from two or more), the spectrum of the AF signal becomes symmetrical with respect to the spectral component with a frequency _{μM shift} T _p (not necessarily the maximum) used to estimate the parameter μ. The number of spectral components in the autofocus signal spectrum is 2N _targets - 1.

To form the reference signal necessary to compensate for parasitic FM, it is required to find the modulation index μ, which is uniquely related to the obtained frequency of the center of symmetry of the AF signal spectrum.

Let us determine the indicated relationship in Doppler signals using the example of discrete output DWT signals of length N _ks samples. We believe that with a small artificial signal shift by N _shift << N _ks , all harmonics of the AF signal are closely located relative to the center of symmetry of the spectrum, i.e. narrowband signal.

The frequency of the center of symmetry of the spectrum of the AF signal, coinciding with the central spectral component (not necessarily the maximum), is equal to:

After calculating the FFT of size N _ks , we have in the spectrum the central component k _ts (the center of symmetry of the spectrum), associated with μ as follows:

}

}

To obtain the frequency of the AF signal always with the same (positive) sign in the shaper 4, we will first perform the inversion of the sign of each odd sample of the AF signal before the FFT procedure

при

at

When using non-inverted AF signals in situations that deviate at ±Δƒ, the spectral components will be in the region of zero frequency, which presents additional difficulties when programming with a signed frequency components. Therefore, an inversion of odd samples or a frequency shift of half the sampling frequency is applied.

After performing the FFT, the number of the central spectral component will be in the center of the range from 0 to N _FFT -1:

Then the expressions for ƒ _tss and μ can be represented as:

However, in the spectrum of the AF signal containing several spectral components of different levels (in the general case, subject to the presence of several targets), it is difficult to find the central spectral component ƒ _tss , which is not necessarily the maximum. For this, the calculator of the center of symmetry of the amplitude spectrum 6 uses the autoconvolution procedure (calculation of the autoconvolution of the amplitude spectrum of the inverted AF signal), which makes it possible to find the center of the symmetrical spectrum.

To eliminate the "triangular component" in the autoconvolution signal, due to the presence of a constant component (from the noise envelope) in the amplitude spectrum module, the calculator 9 preliminarily applies the procedure for centering the amplitude spectrum signals. This will increase the accuracy of determining the maximum of the autoconvolution signal in the presence of interference.

After calculating the autoconvolutions, the central spectral components (centers of symmetry of the spectra) will become maximum, regardless of their initial values, and it will be possible to determine them using the maximum determination procedure.

After calculating the linear autoconvolution, the number of the maximum autoconvolution count of the amplitude spectrum of the inverted AF signal will be equal to:

Where

and the experimentally found index of the FM Doppler signal

In the shaper of the reference signal matrix 10 for each range channel N _E DVP 3 a single reference signal is formed:

In the element-by-element multiplier of matrices 4, the samples of each of the N _E rows of the DWT 3 are multiplied by the samples of the reference signal

Under the condition of equality μ*=μ, the FM signals of each channel of the range of the DVP 3 are demodulated, and the DFS shaper 5 receives from the element-by-element matrix multiplier 4 the implementation of complex harmonic signals:

where

In the shaper 5 in each line, using the FFT procedure, the spectrum of incoming information is calculated. In the calculator of the module 6, the amplitude spectrum of the signal of each row of the matrix of the FPD generator 5 is allocated.

Parasitic FM compensation leads to spectrum compression along the velocity axis and a corresponding increase in its maximum value and SNR, which is important for confirming target detection and tracking.

The increase in velocity resolution due to spectrum compression is also an important result, which makes it possible to resolve in velocity targets moving rapidly with close velocities.

Thus, the proposed DSP device allows demodulation of spurious FM Doppler signals in the ID radar in one period of radiation and reception of a burst of radio pulses. This reduces the time to obtain important information about the parameters of detected highly maneuverable targets (without the use of a second emission and receiving a burst of radio pulses): increased SNR to confirm detection and improved radar speed resolution to resolve closely spaced highly maneuverable targets in a group.

The results of experimental studies of the developed device for compensating parasitic FM in one period of radiation and reception of a burst of radio pulses showed its operability and high efficiency of use in ID radars designed to work with nearby targets moving at a variable speed.

Thus, the correct functioning of the developed device and the high efficiency of its use in processing echo signals from airborne rapidly moving targets, which consists in increasing the SNR and increasing the speed resolution to practically possible values for one period of radiation and reception of a burst of radio pulses, have been confirmed.

Sources of information:

1. Dudnik P.I., Ilchuk A.R., Tatarsky B.G. Multifunctional radar systems. Uch. manual for universities / ed. B.G. Tatarsky. - M.: Bustard, 2007. - 283 p.

2. Markovich I.I., Zavtur E.E. Methods for digital processing of signals reflected from highly maneuverable air targets // Bulletin of Aerospace Defense. - Scientific and technical journal of PJSC "NPO" Almaz "named after. acad. A.A. Raspletin. - 2016 - Issue 3 (11). - P.17-23.

3. Markovich I.I. Signal Uncertainty Function for Quasi-Optimal Processing in a Linear Filter with Variable Parameters // Radiotekhnika. - 1989. - No. 6. - P.55-56.

4. Patent 2657462 RF, IPC 2006, G01S 13/53. Device for digital signal processing in a pulse-Doppler radar with compensation for FM Doppler signals / I.I. Markovich. Applicant and patentee - FGAOU VO "Southern Federal University". - 2017122902. Appl. 06/28/2017. Published 06/14/2018. Bull. No. 17.

5. Markovich I.I. Digital signal processing in systems and devices: monograph. - Rostov-on-Don: Publishing House of the Southern Federal University, 2012. - 236 p.

Claims (1)

A device for digital signal processing in a pulse-Doppler radar with FM Doppler signals compensation for one period of radiation and reception of a burst of radio pulses, containing serially connected digital shaper of quadrature components 1, the input of which is the input of the device, a matched filter 2, a long-range-time portrait shaper 3, element-by-element matrix multiplier 4, long-range portrait shaper 5 and module calculator 6, as well as autofocus signal shaper 7, amplitude spectrum calculator 8, amplitude spectrum symmetry center calculator 9 and reference signal matrix shaper 10 connected in series to the first output of the long-range portrait shaper 3 , the output of which is connected to the second input of the element-by-element matrix multiplier 4, characterized in that a threshold processing unit 11 is introduced, the input of which is connected to the output of the calculator module 6, and the output is the output of the device; the second output of the long-range-time portrait shaper 3 is connected to the second input of the long-range-frequency portrait shaper 5, and the control output of the threshold processing unit 11 is connected to the control input of the long-range-time portrait shaper 3.

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