RU2522502C1 - Synthetic aperture radar signal simulator - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: method is realised through communication of a synthetic aperture radar (SAR) and a signal simulator via a radio link, where the signal simulator receives in real time a SAR probing signal, transfers said signal to an intermediate frequency, digitises, delays to the beginning of the simulated scene signal with corresponding radial velocity, rolls up with a pulsed scene characteristic which is offset and pre-calculated for each update cycle, compensates for the effect of the introduced offset of the pulsed scene characteristic with a simulated radar scene image, transfers the obtained signal to carrier frequency and re-emits towards the SAR.

EFFECT: high reliability of simulating a reflected synthetic aperture radar signal.

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Description

The invention relates to radar, in particular to simulators of the reflected signal of a radar station with synthesizing aperture (PCA), operating on land and sea targets, and can be used for semi-field tests of PCA, including for the study of detection and tracking of objects against an extended background surface.

A known PCA target simulator [1], where during the synthesis of the aperture with high accuracy both the Doppler shift and the change in range to a single moving target are simulated, while the change in range during the synthesis of the aperture can be significant compared to the size of the resolution element. The received radar signal through the mixer using the first heterodyne signal is transferred to the video frequency, passes a low-pass (low-pass) filter, digitized and recorded in memory. The recording address changes with the signal sampling cycle. The clock cycle of the signal is formed by dividing the frequency of the first local oscillator N times. The recorded signal is read with a delay corresponding to the simulated target range, the digitized signal is converted to analog form, filtered in the low-pass filter, transferred to the carrier and radiated to the PCA side. A feature of reproducing the target signal is that the frequency of the second local oscillator differs from the frequency of the first local oscillator by the simulated current Doppler frequency of the target signal (radial velocity of the target). In this case, the synthesizer of the second heterodyne frequency is controlled by the controller and provides the calculated frequency change in time. To ensure the coherence of the simulated signal, the synthesizer of the second heterodyne frequency is synchronized with the frequency of the first local oscillator. The reading cycle of the recorded signal is formed by dividing the frequency of the second local oscillator N times. The read address is formed by a read pulse counter. The initial address value corresponds to the delay of the simulated target signal.

The advantage of the device is the possibility of the simulator working with an arbitrary radar signal, which can vary from pulse to pulse, both in modulation and in the repetition period.

The disadvantage of the simulator is that it does not simulate the signal of an extended (in range and Doppler shift) target, the background signal, and the fluctuation of the resolved signals in time.

Known simulator of the scene signal [2], used when checking a radar station (radar) at an intermediate frequency (IF) or on a carrier with a known modulation without turning on the transmitter. The method of simulating a scene signal includes: 1) obtaining the spectra of the radar modulation signal and the impulse characteristics of the scene at different Doppler frequency shifts, 2) multiplying the spectra (convolution of the impulse response of the scene signal and modulating the signal in the frequency domain), 3) transform the results using the inverse Fourier transform convolutions in the time domain, 4) recording the received scene signal at the video frequency, 5) using the digitized quadrature of the temporary signal at the video frequency to obtain the corresponding signal IF with a corresponding Doppler shift, 6) the summation signal at the IF signal with the simulated noise signal in the introduction effects associated with the weather and the like, 7) to transfer the sum signal IF the carrier frequency.

The advantage of the simulator is the ability to simulate a scene signal in a wide range of ranges and Doppler frequencies, taking into account the position and radiation pattern of the antenna.

The disadvantage of the simulator is the formation of a simulated signal not by the actual signal of the transmitter, but by its virtual spectrum and repetition period.

A known device for testing a radar [3] in terrestrial conditions, where the radar antenna with an inertial navigation system (ANN) is stationary. The target is simulated by delaying the signal received by the simulator on a moving platform and the movement of the platform. At the same time, both the range and the Doppler frequency of the target signal change in time. The delayed signal is emitted towards the radar. The processor software-controlled movement of the simulator platform relative to the radar. An optical delay line is used to delay the simulated signal. In the process of processing the simulated target signal in the radar, the current data of the ANN and the GPS satellite navigation system are involved.

The advantage of the device is the high accuracy of simulating a signal of a single target on the aperture synthesis interval.

The disadvantage of the testing device is the inability to simulate a long-range and Doppler frequency target and the background on which it is observed.

A device for simulating a signal of a pulsed Doppler radar when working on an extended target using a complex signal [4], adopted as a prototype. In this case, before work, the initial impulse response of the scene is introduced into the simulator memory in a complex form in the coordinates range - Doppler - angular position of the radar antenna, modulated radar signal digitized at the video frequency (this signal is used to simulate a scene in which all range-resolved elements have zero Doppler frequency), the value of the Doppler frequency (one of eight) for each resolved range element of the scene impulse response (used to simulate the operation of a radar with a simple signal m), the values of the intermediate frequency and heterodyne frequencies, with which the scene signal simulated on the video frequency is transferred to the carrier frequency, the reference frequency, which synchronizes the formation of the intermediate and heterodyne frequencies (ensures the receipt of coherent scene signals and the formation of internal synchronizing signals of the simulator), the current position code radar antennas (used in conjunction with the range code to form the read address of the current value of the impulse response of the scene recorded in the memory), and pulses of the repetition period. Each of the four repetition pulses starts its own range counter, the code of each range counter is the read address of the previously recorded initial impulse response of the scene in the form of amplitudes and Doppler frequencies of the signals of the scene elements. The amplitude of each scene element, read in range in the current repetition period, is quadrature modulated by the corresponding Doppler frequency, the obtained sweeps of the complex signals of the scene elements are added (a simulation of the envelope of the scene signal is provided when the impulse response of the scene is longer than the repetition period) and are sent to two similar filters with a finite impulse response (FIR filters), the outputs of which are quadratures of the simulated scene signal at the video frequency. The impulse response of the first FIR filter corresponds to the real part of the modulated probe signal recorded in the memory, for the second, the imaginary part of the same signal. The quadrature components of the signal from the outputs of the FIR filters (the complex digital signal of the scene at the video frequency) are fed to a single-band modulator (quadrature balanced mixer), the output of which is used to obtain an analog scene signal at an intermediate frequency using the intermediate frequency signal, then the scene signal using the local oscillator signal and the mixer is transferred to the carrier frequency. Additionally, an interference signal is simulated at the radar carrier frequency. Both signals (scene signal and interference) after addition are fed to the tested radar.

This device provides an imitation of the scene signal of a pulsed radar for various types of applications, taking into account the impulse response of the scene specified by the source data, with an ambiguous repetition period and wobble of the probe signal repetition period.

The disadvantages of the device are: 1) incomplete simulation of the scene signal associated with the virtual signal of the transmitter specified by the source data, the scattering of the reflected signal by the Doppler frequency is not simulated when working with a complex signal, the simulation of signal scattering by the Doppler frequency is possible only for point targets at work with a simple signal, 2) to ensure the coherence of the simulated signals, it is necessary to synchronize the simulator with the reference reference frequency and the repetition period from overyaemoy radar 3) simulated reflection signal associated with a significant change in the range and doppler frequency of the scene elements aperture during synthesis, is not provided.

The aim of the invention is to increase the reliability of the simulation of the reflected signal of the SAR.

The goal is realized through the communication of the SAR and the signal simulator through a radio channel, in which the signal simulator real-time receives the SAR signal, transfers it to an intermediate frequency, digitizes, delays the scene at the beginning of the simulated signal with the corresponding radial speed, rolls it up with the offset, previously calculated for each update step by the scene impulse response, compensates for the effect of the entered scene impulse response bias on the simulated radar image prices, transfers the received signal to the carrier frequency and re-emits in the direction of X-ray diffraction.

To achieve this goal, a scene simulator [4] containing a first random access memory (RAM), a first and second filter with a finite impulse response, a first digital-to-analog converter and a third band-pass filter connected in series, a second digital-to-analog converter and a fourth band-pass filter, a single-band modulator , hereinafter referred to as the quadrature modulator, the second RAM, the output of which is connected to the second inputs of the first and second filters with a finite impulse response controlled by a local oscillator, a synchronizer, hereinafter referred to as a crystal oscillator, a first range pulse counter, the output of which is connected to the third input of the first RAM, a frequency synthesizer, a processor, the second input-output of which is connected to the inputs / outputs of the frequency synthesizer, the first pulse counter range controlled by the local oscillator and the second RAM, the output of the controlled local oscillator is connected to the third input of the quadrature modulator, the first input-output of the processor is an interface connection of a torus with SAR, through which initial data on the effective area of the scene elements and their coordinates, which are used by the processor to calculate the current value of the complex impulse response of the scene, are input, differs in that a series-connected antenna, antenna switch, directional coupler, quadrature mixer, first bandpass filter, the first analog-to-digital converter (ADC), the output of which is connected to the first input of the first RAM, the second band-pass filter connected through the second AD with a second input of the first RAM, a second range pulse counter connected to the fourth input of the first RAM, a complex number adder and a complex multiplier connected in series, the first and second outputs of which are connected to the inputs of the first and second digital-to-analog converter, respectively, a direct digital synthesis generator, the output of which connected to the second input of the complex number multiplier, an amplifier, the output of which is connected to the input of the antenna switch, a detector and the output device of which is connected to the input of the processor, the output of the crystal oscillator through the frequency synthesizer is connected to the input of the first counter of range pulses, the second output of the frequency synthesizer is connected to the inputs of the second counter of range pulses and the direct digital synthesis generator, the second output of the directional coupler is connected to the detector input, the second output of the quadrature mixer is connected to the input of the second bandpass filter, the output of the controlled local oscillator is connected to the second input of the quadrature mixer, you One third bandpass filter is connected to the first input of the quadrature modulator, the fourth bandpass filter is connected to the second input of the quadrature modulator, the first output of the first RAM through the first filter with finite impulse response is connected to the first input of the complex number adder, the second output of the first RAM through the second filter with the final impulse response is connected to the second input of the adder complex numbers, the second input-output of the processor is connected to the inputs and outputs of the second counter and a direct digital synthesis generator, the output of the quadrature modulator is connected to the input of the amplifier.

The invention is illustrated by a further description and drawings of a radar signal simulator.

Figure 1 shows the structure of a radar simulator.

Figure 2 shows a filter with a finite impulse response.

In figure 1, the following notation:

1 - antenna simulator (A);

2 - antenna switch (AP);

3 - directional coupler (BUT);

4 - detector (D);

5 - quadrature mixer (KS);

6 - band-pass filter (PF1);

7 - the first analog-to-digital Converter (ADC1);

8 - second band-pass filter (PF2);

9 - the second analog-to-digital converter (ADC2);

10 - the first random access memory (RAM1);

11 - the first filter with a finite impulse response (FCI1);

12 - adder of complex numbers (KSum);

13 - the second filter with a finite impulse response (FKIKH2);

14 - the multiplier of complex numbers (KUm);

15 - the first digital-to-analog converter (DAC1);

16 - the second digital-to-analog converter (DAC2);

17 - threshold device (PU);

18 - controlled local oscillator (UG);

19 - crystal oscillator (KB);

20 - the first counter of range pulses (LED1);

21 - second counter of range pulses (LED2);

22 - second random access memory (RAM2);

23 - third band-pass filter (PF3);

24 - fourth band-pass filter (PF4);

25 - processor (PRC);

26 - frequency synthesizer (MF);

27 - direct digital synthesis generator (GPCS);

28 - quadrature modulator (KM);

29 - amplifier (CSS).

In figure 2, the following notation:

30-k - delay device equal to half the resolution of the radar signal in time (Uzk);

31-k - multiplier (Umk);

32-k - adder (Sum).

In figure 1, the antenna 1, the antenna switch 2, the directional coupler 3, the quadrature mixer 5, the first bandpass filter 6, the first analog-to-digital converter (ADC) 7, the first random access memory (RAM) 10, the first filter with a finite pulse are connected in series characteristic 11, the complex number adder 12, the complex number multiplier 14, the first digital-to-analog converter 15, the third bandpass filter 23, the quadrature modulator 28, the amplifier 29, the second output of the quadrature mixer 5 through a series connection The second bandpass filter 8 and the second ADC 9 are connected to the second input of the first RAM 10, the second output of the directional coupler 3 is connected through the series-connected detector 4 and the threshold device 17 to the input of the processor 25, the second RAM 22 is connected to the second inputs of the first and second filters with the final pulse characteristics 11 and 13, respectively, the second output of the first RAM 10 through a second filter with a finite pulse characteristic 13 is connected to the second input of the adder complex numbers 12, the second output of the multiplier complex l 14 through a series-connected second digital-to-analog converter 16 and a fourth band-pass filter 24 connected to the second input of the quadrature modulator 28, the first input-output of the processor 25 is an interface connection of the simulator with an external operator, the second input-output of the processor 25 is connected to the input-outputs of the controlled local oscillator 18 , a frequency synthesizer 26, a first 20 and a second 21 range pulse counters, a second RAM 22 and a direct digital synthesis generator 27, the output of the amplifier 29 is connected to the input of the antenna switch 2, the output the oscillator generator 19 through series-connected frequency synthesizer 26 and the first range pulse counter 20 is connected to the third input of the first RAM 10, the second output of the frequency synthesizer 26 through the second range pulse counter 21 is connected to the fourth input of the first RAM 10, the input of the direct digital synthesis generator 27 is connected to the second output of the frequency synthesizer 26, the output of the controlled local oscillator 18 is connected to the second input of the quadrature mixer 5 and to the third input of the quadrature modulator 24, the output of the direct digital si thesis 27 is connected to the second input of the multiplier 14 complex numbers.

соединены с соответствующими входами 2-k фильтра с конечной импульсной характеристикой 11, выход умножителя 31-1 через последовательно соединенные сумматоры 32-k для $$k=\overline{\mathrm{1,}K}$$

соединен с выходом фильтра с конечной импульсной характеристикой 11, вторые входы сумматоров 32-k соединены с выходами умножителей 31-(k+1).In Fig.2, the first filter input with a finite impulse response 11 is connected to the input of series-connected K delay devices 30-1 to 30-K, the inputs of all delay devices 30-k are connected to the corresponding first inputs of the multipliers 31-k, the output of the delay device 30 -K is connected to the first input of the multiplier 31- (K + 1), the second inputs of the multipliers 31-k for $$k=\overline{\mathrm{one,}K+\mathrm{one}}$$

connected to the corresponding inputs of the 2-k filter with a finite impulse response 11, the output of the multiplier 31-1 through series-connected adders 32-k for $$k=\overline{\mathrm{one,}K}$$

connected to the output of the filter with a finite impulse response 11, the second inputs of the adders 32-k are connected to the outputs of the multipliers 31- (k + 1).

A controlled local oscillator 18 can be built on the basis of a frequency synthesizer with a phase locked loop [5, Fig.3.3a, p.66].

As the quadrature mixer 5 and the quadrature modulator 28, microcircuits NMS522 and HMC924LC5 of Hittite Microwave Corp. can be used, respectively.

As a frequency synthesizer 26 and a direct digital synthesis generator 27, a direct digital synthesis generator based on a DD9959 chip from Analog Device can be used.

The first 11 and second 13 filters with a finite impulse response, together with an adder 12 and a complex number multiplier 14, can be implemented on a Virtex6 XC6VLX130T programmable logic integrated circuit.

The remaining elements are widely used in radar and do not require explanation for implementation.

The algorithm of the simulator includes preparation for work and combat work. Preparation for work begins with the input to the first input-output of the processor 25 of the initial data from the operator about the SAR, its carrier and scene:

- PCA signal bandwidth Δf _C ;

- carrier frequency SAR f _N ;

- beam width (BOTTOM) in azimuth Δθ and elevation Δβ;

- angular coordinates of the axis of sight of the PCA (θ, β) relative to the axes of the carrier of the PCA;

- azimuthal resolution of the SAR δ _AZ ;

- vector of the PCA carrier velocity path (V _TX , V _TY , V _TZ ) in the correction area (uniform straight flight is assumed);

- the initial coordinates of the path of the PCA carrier (X _TO , Y _TO , Z _TO );

, $$Y_{i0}^{Ц}$$

, $$Z_{i0}^{Ц}$$

);- the initial coordinates of the i-th point targets ( $$X_{i0}^{\mathrm{Ts}}$$

, $$Y_{i0}^{\mathrm{Ts}}$$

, $$Z_{i0}^{\mathrm{Ts}}$$

);

, $$V_{iY}^{Ц}$$

, $$V_{iY}^{Ц}$$

);is the velocity vector of the i-th point targets ( $$V_{iX}^{\mathrm{Ts}}$$

, $$V_{iY}^{\mathrm{Ts}}$$

, $$V_{iY}^{\mathrm{Ts}}$$

);

- coordinates of the i-th background points (X _i , Y _i , Z _i );

и фона $${\sigma }_i^{Ф}$$

(элементов сцены размером δ_X*δ_Y, где δ_X=δ_Y=0,5δ_АЗ),- effective scattering areas (EPR) of i-th targets $${\sigma }_i^{\mathrm{Ts}}$$

and background $${\sigma }_i^F$$

(scene elements of size δ _X * δ _Y , where δ _X = δ _Y = 0.5δ _AZ ),

- the size of the simulated radar image scene frame by horizontal distance 2ΔG _{radar data;}

- the number of consecutive independent scene frames (synthesis intervals) M _C.

Based on the source data, the processor 25 performs calculations including the determination of:

- the width of the Doppler spectrum of the signal ΔF _D ;

- the update period of the impulse response of the scene T <1 / 2ΔF _D ;

, соответственно частоту выборки $$F_{СЧ1}=\frac{1}{{\Delta }_{T1}}$$

;- step of sampling the SAR signal in time $${\Delta }_{T\mathrm{one}}<\frac{\mathrm{one}}{2\Delta f_C}$$

, respectively, the sampling rate $$F_{\mathrm{FROM}H\mathrm{one}}=\frac{\mathrm{one}}{{\Delta }_{T\mathrm{one}}}$$

;

- coordinates of the anchor point (X ₀ , Y ₀ , Z ₀ ) of the frame of the radar image (RLI) of the scene (the point of intersection of the surface with the bottom axis (θ, β) at the beginning of the correction interval);

- the duration of the synthesis interval T _synth (θ, β, δ _AZ );

- the transit time of the correction section T _KOR = M _C T _SINT (θ, β, δ _AZ );

- coordinates of the PCA carrier (X _T (p), Y _T (p), Z _T (p)) at time points rT≤T _COR ;

- trajectory range to the anchor point R ₀ (p) at time points rT;

- a partition of the implementation of R ₀ (p) into M consecutive adjacent sections R0 (p) = R0 (n, m), providing a piecewise approximation of each m-th section of R ₀ (n, m) by a polynomial of the second degree, while:

$$p={\displaystyle \sum _0^m{N}_m+n}$$

N _m - the number of intervals of duration T on the m-th section of the trajectory;

- индекс текущего участка траектории; $$m=\overline{0M-\mathrm{one}}$$

- index of the current section of the trajectory;

- на каждом m-ном участке траектории; $$n=\overline{0N_m\mathrm{one}}$$

- on each m-th section of the trajectory;

$$R_0^{\mathrm{BUT}PR}\left(n,m\right)=R_{00}^m+V_{R0}^{m}nT+\frac{a_0^m{\left(nT\right)}^2}{2}$$

$$|\; |\; |R_0\left(n,m\right)-R_0^{\mathrm{BUT}PR}\left(n,m\right)|\; |\; |\le \delta \lambda$$

- аппроксимация R₀(n, m) полиномом второй степени; $$R_0^{\mathrm{BUT}PR}\left(n,m\right)$$

- approximation of R ₀ (n, m) by a polynomial of the second degree;

и $$a_0^m$$

- коэффициенты аппроксимации R₀(n, m); $$R_{00}^m$$

and $$a_0^m$$

- approximation coefficients R ₀ (n, m);

δ <0.0625 - coefficient determining the permissible error of imitation of the phase of the signal reflected by the reference point;

λ is the wavelength of the probe signal of the SAR;

, $$Y_i^{Ц}\left(n,m\right)$$

, $$Z_i^{Ц}\left(n,m\right)$$

);- target coordinates ( $$X_i^{\mathrm{Ts}}\left(n,m\right)$$

, $$Y_i^{\mathrm{Ts}}\left(n,m\right)$$

, $$Z_i^{\mathrm{Ts}}\left(n,m\right)$$

);

, $$R_i^{Ц}\left(n,m\right)$$

;- trajectory range from SAR to scene elements $$R_i^F\left(n,m\right)$$

, $$R_i^{\mathrm{Ts}}\left(n,m\right)$$

;

- the local oscillator frequency f _G = f _H -f _PR , with which the received PCA signal is shifted in the simulator to an intermediate frequency f _PR = Δf _C / 2;

- the amplitude of the signal reflected by the scene element on the m-th section of the trajectory:

$$A_i\left(n,m\right)=A_i\left(w\right)=\frac{{\sigma }_i^{\mathrm{Ts}}}{R_i^2\left(n,m\right)}{Q}_{iw}\exp \left(j{F}_{iw}\right)$$

$$w=\left]\frac{pT}{T_{\mathrm{from}\mathrm{and}nt}}\right[=\left]\frac{\left({\displaystyle \sum {}_0^m{N}_m+n}\right)T}{T_{\mathrm{from}\mathrm{and}nt}}\right[$$

where Q _iw and Ф _iw are the laws of fluctuation of the amplitude and phase in the i-th element of the scene on the w-th synthesis interval;

- coefficients of approximation of the change in the Doppler frequency of the signal f _Д0 (t, m), reflected by the anchor point on each m-th section of the trajectory

$$f_{D0}\left(t,m\right)=\frac{2f_n{V}_0\left(t\right)}{c}=\frac{2f_n\left(V_{R0}^m+a_0^m(t-T{\displaystyle \sum {}_0^m{N}_m}\right)}{c}=f_{00}^m+k_{f\mathrm{one}}^m\left(t-T{\displaystyle \sum {}_0^m{N}_m}\right)$$

where c is the speed of light;

и $$k_{f1}^m$$

- коэффициенты аппроксимации изменения доплеровской частоты сигнала, отраженного точкой привязки на m-том участке траектории; $$f_{00}^m$$

and $$k_{f\mathrm{one}}^m$$

- coefficients of approximation of the change in the Doppler frequency of the signal reflected by the anchor point on the m-th section of the trajectory;

- the law of change in the sampling frequency of the signal delayed by the simulator on each m-th section of the trajectory:

$$F_{\mathrm{FROM}H2}\left(t,m\right)=F_{\mathrm{FROM}H\mathrm{one}}\left(\mathrm{one}+\frac{2\left(V_{R0}^m+a_0^m(t-{\displaystyle \sum {}_0^m{N}_m}\right)}{\mathrm{from}}\right)=F_{\mathrm{twenty}}^m+k_{f2}^m\left(t-T{\displaystyle \sum {}_0^m{N}_m}\right)$$

- ahead of the beginning of the simulated scene signal from the anchor point

$${\tau }_H=\frac{2\Delta G_{RL\mathrm{AND}}}{c\cdot \cos \beta }$$

- approximation of the impulse response of the scene in time t (n, m):

B (n, m, q) = B (n, m, k + <q ₀ ) = expjφ ₀ (n, m) B (n, m, k + q ₀ ) exp [-jφ ₀ (n, m)] = expjφ ₀ (n, m) G (n, m, k + q ₀ ),

и φ₀(m, n) для импульса РСА, излученного в момент t(n, m); φ₀(n, m) - фаза сигнала, отраженного от точки привязки (i=0), в момент t(n, m);where G (n, m, k) is the impulse response of the scene, shifted by distance by $$q_0\left(\frac{c{\Delta }_{T\mathrm{one}}}{2}\right)$$

and φ ₀ (m, n) for the SAR pulse emitted at time t (n, m); φ ₀ (n, m) is the phase of the signal reflected from the anchor point (i = 0) at the moment t (n, m);

q is the range index;

- индекс дальности РСА до ближней точки кадра сцены; $$q_0=\left]\left(\frac{2R_0\left(n,m\right)}{c{\Delta }_{T\mathrm{one}}}-\frac{{\tau }_N}{{\Delta }_{T\mathrm{one}}}\right)\right[$$

- index of the range of the SAR to the near point of the scene frame;

][ - the integer part of number;

k = qq ₀ is the difference in the range indices from the SAR to the scene element and the near point of the scene frame;

$$G\left(n,m,k\right)=\{\begin{array}{c}{\displaystyle \sum _i{d}_{ki}(n,m)A_i(n,m)\exp j[{\varphi }_i(n,m0-{\varphi }_0(n,m)],k=q_i-q_0=k_i(n,m);}\\ \begin{array}{c}{\displaystyle \sum _i(\mathrm{one}-d_{ki}(n,m))A_i(n,m)\exp j[{\varphi }_i(n,m)-{\varphi }_0(n,m)],k=k_i(n,m)+\mathrm{one};}\\ 0\mathrm{about}\mathrm{from}t\mathrm{but}lbnse\mathrm{from}l\mathrm{at}h\mathrm{but}\mathrm{and};\end{array}\end{array}$$

- индекс дальности РСА до i-того элемента сцены;Where $$q_i=\left]\frac{2R_i(n,m)}{c{\Delta }_{T\mathrm{one}}}\right[$$

- index of the range of the SAR to the i-th element of the scene;

- разница индексов дальности РСА до i-того элемента сцены и ближней точки кадра сцены в момент t(n, m); $$k_i(n,m)=\left]\frac{2{\tilde{R}}_i(n,m)}{c{\Delta }_{T\mathrm{one}}}\right[$$

- the difference between the SAR range indices to the ith element of the scene and the near point of the scene frame at time t (n, m);

- разница дальностей от РСА до i-того элемента сцены и ближней точки кадра сцены в момент t(n, m); $${\tilde{R}}_{i0}(n,m)=R_i(n,m)-R_0(n,m)+\frac{c{\tau }_H}{2}$$

- the difference between the ranges from the SAR to the ith element of the scene and the near point of the scene frame at time t (n, m);

- амплитудный весовой коэффициент, значение которого учитывает близость i-того элемента сцены к k_i узлу сетки дальности в момент t(n, m); $$d_{ki}(n,m)=\frac{{\tilde{R}}_{i0}(n,m)}{c{\Delta }_{T\mathrm{one}}/2}-k_i(n,m)$$

- amplitude weighting coefficient, the value of which takes into account the proximity of the ith element of the scene to the k _i node of the range grid at time t (n, m);

φ _i (n, m) = 2πf _n k _i (n, m) Δ _T1 is the phase of the signal reflected from the ith element of the scene received from the probing SAR signal at time t (n, m).

The weighted summation of the amplitudes of the scene signals A _i (n, m) in the expression G (n, m, k) provides during combat operation a smooth change in the position of the simulated scene signals in range between the nodes of the range grid [6, p.11-13], respectively, when Reception of the simulated signal in the SAR provides a reduction in the side lobes of the scene signals associated with the discreteness of the simulation of the delay of the scene signals in time.

, $$k_{f1}^0$$

) в генератор прямого цифрового синтеза 27, частоту гетеродина f_Г в управляемый гетеродин 18, значение частоты F_СЧ1 и параметры ( $$F_{20}^0$$

, $$k_{f2}^0$$

) в синтезатор частоты 26, в первый счетчик дальности нулевой код, во второй счетчик дальности код, соответствующий начальной задержке имитируемого сигнала сцены $$q_0=\left]\left(\frac{2R_0(n,m)}{c{\Delta }_{T1}}-\frac{{\tau }_H}{{\Delta }_{T1}}\right)\right[$$

- исходное состояние в синтезатор частот 26 и генератор прямого цифрового синтеза 27. Далее имитатор находится в ожидании боевой работы.According to the calculation results, the processor 25 through the second input-output enters the values of the offset impulse response of the scene G (n, m, k) into the second RAM 22, frequency parameters ( $$f_{00}^0$$

, $$k_{f\mathrm{one}}^0$$

) to the direct digital synthesis generator 27, the local oscillator frequency f _G to the controlled local oscillator 18, the frequency value F _SCH1 and the parameters ( $$F_{\mathrm{twenty}}^0$$

, $${\mathrm{<figure-callout\; id="2"\; label="k\; f"\; filenames="00000055.png"\; state="\{\{state\}\}">k\; </figure-callout>}}_f^2$$

) in the frequency synthesizer 26, in the first range counter the zero code, in the second range counter the code corresponding to the initial delay of the simulated scene signal $$q_0=\left]\left(\frac{2R_0(n,m)}{c{\Delta }_{T\mathrm{one}}}-\frac{{\tau }_H}{{\Delta }_{T\mathrm{one}}}\right)\right[$$

- the initial state in the frequency synthesizer 26 and the direct digital synthesis generator 27. Next, the simulator is waiting for combat work.

.With the beginning of the radiation of the SAR antenna of the simulator through the radio link, sensing signals are received, which through the antenna switch 2 and detector 4 are supplied to the threshold device 17. When the signal of detector 4 is first exceeded, the processor 25 removes the initial state from the frequency synthesizer 26, counters 21, 22, and puts the simulator in combat mode. In this case, the frequency synthesizer 26 starts the generation of frequencies F _MF1 and F _MF2 at the first and second outputs, respectively, similarly, the direct digital synthesis generator 27 generates digital samples of quadrature signals H _C (l, m) = cosφ _D0 (l, m) and H _S ( l, m) = sinφ _D0 (l, m), where φ _D0 (l = 0, m) = φ ₀ (n = 0, m), at the Doppler frequency $$f_{D0}(l,m)=f_{00}^m+k_{f\mathrm{one}}^m{\Delta }_{T2}l$$

.

The signal sampling index l suggests that

$$n=\left]\frac{l}{L}\right[$$

LΔ _T2 = T, f _D0 (l, m) << F _SCH2 = 1 / Δ _T2 , which ensures that the phase change of the reflected signal from the scene elements _takes into account the duration of the SAR signal.

, $$k_{f2}^m$$

) и ( $$f_{00}^m$$

, $$k_{f1}^m$$

) соответственно, исключая скачок фазы φ_СЧ2(t, m) и φ_Д0(t, m) при смене m.The processor 25 with a clock T through the second input-output provides to the RAM 22 the current address (n, m) for reading the impulse response of the scene G (n, m, k) recorded in the second RAM 22, while the initial address code is zero. At the beginning of each mth section of the trajectory, the processor 25 switches the settings of the frequency synthesizer 26 and the direct digital synthesis generator 27, in accordance with the previously calculated values ( $$F_{\mathrm{twenty}}^m$$

, $$k_{f2}^m$$

) and ( $$f_{00}^m$$

, $$k_{f\mathrm{one}}^m$$

), respectively, excluding the phase jump φ _СЧ2 (t, m) and φ _Д0 (t, m) when changing m.

, приходящую с второго выхода синтезатора частоты 26 на вход второго счетчика дальности 21. За счет разности тактов записи и считывания задержка считываемого сигнала РСА относительно зондирующего непрерывно изменяется во времениThe received PCA signal U (t) from the first output of the directional coupler 3 is fed to the quadrature mixer 5, the second input of which receives the signal of the controlled local oscillator 18 at a frequency f _G. The first quadrature output signal U _{C of the} quadrature mixer 5 through a series-connected first band-pass filter 6 and the first analog-to-digital converter (ADC) 7 is fed to the first input of the first RAM 10. The second quadrature signal U _S from the output of the quadrature mixer 5 through a similar second band-pass filter 8 and a second ADC 9 is fed to the second input of the first RAM 10. Address quadrature signal recording on the first and second inputs of the first RAM 10 is formed the first distance counter pulses 20, which comes to the input frequency F _SCH1, formed on the first output of frequency synthesizer 26. Reading the recorded signal from the first RAM 10 is made at the address generated by the second counter 21 and starts range ahead signal from the anchor point on the scene τ _H defined source q _0, introduced in the second range pulse counter 21 processor 25. The current radial speed of the SAR relative to the conditional reference point V ₀ (t) determines the frequency of reading the signal from RAM 10 on the m-th section of the trajectory $$F_{\mathrm{FROM}H2}(t,m)=F_{\mathrm{twenty}}^m+k_{f2}^m(t-T{\displaystyle \sum {}_0^m}{N}_m)$$

coming from the second output of the frequency synthesizer 26 to the input of the second range counter 21. Due to the difference of the write and read clocks, the delay of the read PCA signal relative to the probing one continuously changes over time

$$\tau (t)=\frac{2R_{00}}{c}0{\tau }_N+\frac{2{\displaystyle {\int }_0^t{V}_0(t\text{'}\text{'})dt\text{'}\text{'}}}{c}$$

The delayed quadrature signal from the first and second outputs of the first RAM 10 is fed to a digital reflected signal generating circuit in accordance with the offset impulse response of the scene G (n, m, k) coming from the second RAM 22 and updated through each period T. The reflected signal generating circuit consists of identical filters 11 and 13 with a finite impulse response and an adder of complex numbers 12. Quadrature components S _C (n, q) and S _S (n, q) of the simulated reflected signal S (n, q), index m is omitted, from the outputs adder complex GOVERNMENTAL numbers 12 received at the first input of the multiplier 14 complex numbers, to the second input of which the quadrature signal generator 27 of direct digital synthesis with the Doppler frequency f _A0 anchor point (l, m). As a result, at the output of the complex number multiplier 14, a generated reflected signal of the scene shifted by the frequency f _D0 (l, m) is obtained, i.e. convolution of the impulse response B (n, m, q) with the received PCA signal U (n, m, q):

$$S(l,m,q)=B(l,m,q)\oplus U(l,m,q)=P_l\{P_{q_0}[U(n,m,q)]\oplus G(n,m,q)\}\exp j{\varphi }_0(l,m)$$

,Where $${\varphi }_0(l,m)={\varphi }_0(-\mathrm{one,}m)+2\pi [f_{00}^{m}l{\Delta }_{T\mathrm{one}}+0.5k_{f\mathrm{one}}^m{(l{\Delta }_{T\mathrm{one}})}^2]$$

,

- оператор задержки сигнала U(n, m, q) на q₀Δ_T1; $$P_{q_0}[U(n,m,q)$$

- signal delay operator U (n, m, q) by q ₀ Δ _T1 ;

P _l is the operator of the transformation of the function {} of discrete time n to discrete time l;

⊕ - convolution operator;

φ ₀ (-1, m) is the initial phase value of the Doppler signal simulated by the direct digital synthesis generator 27, which is equal to the phase of the Doppler signal at the time preceding the change of m-1 to m.

The quadrature signal from the output of the complex number multiplier 14 is converted into analog form using digital-to-analog converters 15 and 16 and then smoothed by similar band-pass filters 23 and 24. The output of the band-pass filters 23 and 24 at an intermediate frequency is fed to the first and second inputs of the quadrature modulator 28, where using a heterodyne signal supplied to its third input, it is transferred to the carrier frequency. The output signal of the quadrature modulator 28 through the amplifier 29 and the antenna switch 2 enters the antenna 1 and is radiated towards the PCA. The output signal from the antenna 1 is a scene signal simulated at a carrier frequency.

A filter with a finite impulse response 11 and a similar filter 13 are shown in FIG. Serial-delay devices 30-k create a delay multiple of Δ _T1 (half the resolution of the PCA signal in time). The number of delay elements K corresponds to the length of the impulse response of the scene. Complex multiplication and addition at the nodes 31-k and 32-k of filters with a finite impulse response of 11 and 13 is performed with a sampling cycle T _MF2 = 1- / F _MF2 . In this case, the signal at the output of the adder of complex numbers 12 on each m-th section of the trajectory is equal to:

$$\begin{array}{l}S(n,q)=S_C(n,q)+j{S}_S(n,q)={\displaystyle \sum {}_{k=\mathrm{one}}^{K}U(n,q-k)G(n,k)={\displaystyle \sum {}_{k=\mathrm{one}}^K{U}_C(n,q-k)G(n,k)+}}\\ j{\displaystyle \sum {}_{k=\mathrm{one}}^K{U}_S(n,q-k)G(n,k)=S_{\mathrm{one}}(n,q)+j{S}_2(n,q)}=[S_{\mathrm{one}C}(n,q)-S_{2S}(n,q)+j[S_{\mathrm{one}S}(n,q)+S_{2C}(n,q)];\end{array}$$

where U _C (n, k) and U _S (n, k) are the quadrature components of the PCA signal received by the simulator at the outputs of the first RAM 10;

S _C (n, q) and S _S (n, q) are quadrature signals of the simulated signal at the first and second outputs of the adder of complex numbers 12;

S ₁ (n, q) and S ₂ (n, q) are complex signals at the outputs of the first 11 and second 15 filters with a finite impulse response;

S _iC (n, q) and S _iS (n, q) are the quadrature components of the ith filter with a finite impulse response.

The technical advantage of the proposed simulator of the scene signal over the prototype is the ability to reliably simulate the SAR signal from a three-dimensional scene without limiting the type of modulation of the probe signal, which allows testing the SAR operation both on ground moving and non-moving targets, the range to which during the synthesis can significantly vary compared to the size of the range resolution element. The simulator provides a smooth, time-varying change in the range and phase of the simulated signals from all elements of the scene, without requiring a PCA connection with the simulator of the radio frequency cable.

Using the information presented in the application materials, the radar signal simulator can be made according to the existing technology well-known in the radio industry on the basis of well-known components and used in radar tests on bench tests.

Literature

1. US patent 4450447 from 05.22.84 "Synthetic aperture radar target simulator".

2. US patent 6075480 from 13.07.00 "Down range return simulator".

3. US patent 7365677 from 04.29.08 "Compact radar test range".

4. US patent 6150976 from 11.21.00 "Synthesis of overlapping chirp waveforms".

5. Ryzhkov A.V., Popov V.N. "Frequency synthesizers in radio communication technology." - M .: Radio and communications, 1991.

6. Ostrovityanov R.V., Basalov F.A. "Statistical theory of radar extended targets." - M.: Radio and Communications, 1982.

Claims (1)

The aperture synthesizer radar signal simulator (PCA) signal device comprises a first random access memory (RAM), a first and second filter with a finite impulse response, a first digital-to-analog converter and a third band-pass filter connected in series, a second digital-to-analog converter and a fourth band-pass filter, quadrature a modulator, a second RAM, the output of which is connected to the second inputs of the first and second filters with a finite pulse nature a source, a frequency oscillator, a first counter of range pulses, the output of which is connected to the third input of the first RAM, a frequency synthesizer, a processor, a second input-output of which is connected to the inputs / outputs of a frequency synthesizer, a first range pulse counter, a controlled local oscillator and a second RAM , the output of the controlled local oscillator is connected to the third input of the quadrature modulator, the first input-output of the processor is the interface connection of the simulator with the PCA, through which the initial data on the effective the area of the scene elements and their coordinates, which are used by the processor to calculate the current value of the complex impulse response of the scene, differs in that a series-connected antenna, an antenna switch, a directional coupler, a quadrature mixer, a first band-pass filter, a first analog-to-digital converter (ADC) are introduced, the output of which is connected to the first input of the first RAM, the second bandpass filter connected through the second ADC to the second input of the first RAM, the second range pulse counter, soy shared with the fourth input of the first RAM, the complex numbers adder and the complex numbers multiplier connected in series, the first and second outputs of which are connected to the inputs of the first and second digital-to-analog converters, respectively, the direct digital synthesis generator, the output of which is connected to the second input of the complex numbers multiplier, amplifier, output which is connected to the input of the antenna switch, the detector and a threshold device connected in series, the output of which is connected to the processor input, crystal oscillator through a frequency synthesizer is connected to the input of the first range pulse counter, the second output of the frequency synthesizer is connected to the inputs of the second range pulse counter and direct digital synthesis generator, the second output of the directional coupler is connected to the detector input, the second output of the quadrature mixer is connected to the input of the second bandpass filter, the output of the controlled local oscillator is connected to the second input of the quadrature mixer, the output of the third bandpass filter is connected to the first input of the quadrature of the first modulator, the output of the fourth bandpass filter is connected to the second input of the quadrature modulator, the first output of the first RAM through the first filter with a finite impulse response is connected to the first input of the complex number adder, the second output of the first RAM through a second filter with a finite impulse response is connected to the second input of the complex adder numbers, the second input-output of the processor is connected to the inputs and outputs of the second counter of range pulses and the direct digital synthesis generator, the output of the quadrature module the torus is connected to the amplifier input, additional data on the tested SAR is entered at the first input-output of the processor, including data on the signal band, carrier frequency, beam width (BPS), angular coordinates of the BHA axis, azimuth resolution, SAR carrier data, including initial coordinates of the trajectory and coordinates of the velocity vector in the synthesis section, data on targets, including their initial coordinates and coordinates of the velocity vector in the synthesis interval, coordinates of the background points, the number of independent sequentially generated scenes of signal of the scene, the processor on the basis of information received from the operator calculates the duration of the synthesis interval and the interval of simulation of the scene signal, the update period of the offset impulse response of the scene, the sampling frequency of the PCA signal in time, the local oscillator frequency, the path distance of the PCA to the scene elements, the amplitude of the signal reflected by the elements scenes at each synthesis interval, the coordinates of the anchor point of the frame of the simulated signal, the law of change in the sampling frequency of the delayed signal, the law of change in Doppler the frequency of the signal reflected by the anchor point, the advance of the beginning of the simulated scene signal from the anchor point, the shifted impulse response of the scene, according to the calculation results, enters the values of the offset impulse response into the second RAM, the parameters of the Doppler frequency of the signal from the anchor point into the direct digital synthesis generator, the parameters of the generated frequencies in the frequency synthesizer, the initial state codes of the first and second range counters, determines the beginning and end of the signal simulation interval, turns on the combat mode on the interval of the signal simulation, forms the update cycle of the impulse response of the scene and the address of its reading from the second RAM.

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