CN109471080B - High-speed platform radar echo signal simulation system based on simulink - Google Patents

Abstract

The invention discloses a high-speed platform radar echo signal simulation system based on simulink, which mainly solves the problems of low simulation accuracy and echo efficiency in the prior art. The scheme is: design different functional modules in simulink, among which the PRT synchronization module generates pulse trigger signals to control timing synchronization; the radar pulse transmission module simulates the transmission of radar pulse baseband signals; the radar track import module outputs the real-time position and motion information of the radar; the beam center The calculation module calculates and outputs real-time beam center coordinates; the sub-scene interception module intercepts the imaging sub-scene according to the beam center; the antenna pattern module calculates and updates the antenna gain of each point in the sub-scene; the system function calculation module calculates and updates the echo system in real time Function; the echo generation module convolutes to generate the original echo signal. The invention improves the echo simulation efficiency and precision, and is used for simulating radar echo signals under different radar working modes, environments and target scenes.

Description

High-speed platform radar echo signal simulation system based on simulink

technical field

The invention belongs to the technical field of radar, in particular to a radar echo signal simulation system, which can be used for radar system design, verification and evaluation of SAR system performance.

Background technique

Synthetic Aperture Radar (SAR) is a modern high-resolution microwave imaging radar that has been widely used in various fields. Performance verification and evaluation play an extremely important role. However, the SAR system is very complex, and it will face various known, complex or even unknown, extreme situations and external conditions in practical applications. Design, modify, optimize and improve the algorithm. If such a huge amount of echo data is obtained only by mounting the SAR to an actual flight device, such as an aircraft or a satellite for actual measurement, cost and safety are big problems, and errors are prone to occur. The emergence and development of SAR echo simulation technology has brought great convenience to the research and development of SAR systems.

The application of echo simulation technology has greatly reduced the R&D cost of the SAR system. During the R&D process of SAR, each module can be tested and debugged at any time without waiting for the mounting test after the whole machine is completed. , Radar echoes of various scenarios can be obtained through echo simulation technology, which can greatly improve the reliability of SAR.

At present, many achievements have been made in SAR echo simulation at home and abroad, including pure theoretical model, semi-physical simulation system, computer software simulation, and pure hardware platform to realize FPGA and DPS. However, there are deficiencies in different models and systems, or the amount of calculation is too large, especially for large scenes, or the hardware system is too large, and the echo simulation support for natural scenes is poor.

In 1978, V.H.Kaupp and J.C.Holtaman of the University of Kansas developed a Ku radar simulator called RIS, which is based on the point scattering model and can simulate many different types of scenarios, but due to the backscattering coefficient Data are limited and not widely available.

In 2004, Mori et al. proposed a multi-working-mode SAR echo simulator based on time-domain algorithms, which can simulate the original echo signals in various non-ideal situations, but the calculation amount is relatively large when the scene is too large. big.

In 2006, Yu Mingcheng of Tsinghua University and others proposed a method for simulating the original echo signal of SAR based on the inverse wave number domain algorithm. This method obtains the backscattering coefficient of the scene by processing the optical image, and then inverts it through the wave number domain algorithm to obtain Although the simulation efficiency of this method is high, the simulation accuracy is low in non-ideal conditions such as platform jitter and motion track offset.

In 2010, the American company Mistral developed a new SAR echo simulator RTS-RF. The system has various functions and convenient human-computer interaction, but the hardware system is too large, and the echo simulation support for natural scenes is poor.

Contents of the invention

The purpose of the present invention is to address the deficiencies in the above-mentioned radar echo simulation technology, and propose a high-speed platform radar echo signal simulation system based on simulink, so as to simulate radar echoes in different radar operating modes, different external environments, and different target scenarios. Wave signal, and under the premise of ensuring the accuracy, get rid of the huge hardware system, reduce the amount of calculation, and improve the efficiency of echo simulation.

In order to achieve the above object, the technical solution of the present invention is to generate different modules by simulink, and it is characterized in that, the generated modules include:

The PRT synchronization module is used to complete the synchronization pulse generation and output to each module to synchronize the clock of the whole system;

The radar pulse signal transmission module is used to receive the PRT synchronous pulse input, generate the radar pulse transmission signal, and output the radar pulse transmission signal to the echo generation module;

The radar trajectory import module is used to read the radar trajectory file information under the control of the PRT synchronous pulse, and output the read radar trajectory information to the beam center calculation module, sub-scene interception module, antenna pattern calculation module and system respectively function computing module;

The beam center calculation module is used to update the pixel coordinate information of the beam center in the scene map according to the input radar and the current mode flag under the control of the PRT synchronization pulse, and output the beam center coordinate information to the sub-scene interception respectively module, antenna pattern calculation module and system function calculation module;

The sub-scene interception module is used to intercept the imaging sub-scene from the imported large scene according to the different beam irradiation modes of different radar modes and the input beam center coordinates and radar track information under the control of the PRT synchronous pulse, and convert the sub-scene The data of the sub-scenes are respectively output to the antenna pattern calculation module and the system function calculation module;

The antenna pattern calculation module is used to, under the control of the PRT synchronization pulse, according to the input radar trajectory information, beam center coordinate information, sub-scene size, receiving beam offset angle, range and azimuth resolution, antenna beam width, Calculate the antenna gain of each point in the sub-scene, and output the result to the system function calculation module;

The system function calculation module is used to calculate the echo by using the concentric circle algorithm under the control of the PRT synchronous pulse, according to the input radar position, beam center coordinates, sub-scene data, antenna pattern, and initial range gate information of the echo system function, and output the system function to the echo generation module;

The echo generation module is used to convolve the radar pulse transmission signal with the system function, and generate the original echo signal under the control of the PRT synchronous pulse, and output the result to the delay and range gate gating module;

The delay and range gate gating module is used to make the echo data output in a "stream" mode under the control of the PRT synchronous pulse, so as to better simulate the radar echo signal flow.

The present invention has the following advantages:

1. Since the present invention is based on simulink for modular and hierarchical design, the system construction is relatively simple, and the function is huge, and it can be conveniently and flexibly simulated according to the input SAR mode identifier, the imported radar trajectory information file and the target scene. Radar echo signals under different radar working modes, different external environments, and different target scenarios;

2. Since the present invention uses the concentric circle algorithm to calculate the system function of the echo, it can get rid of the huge hardware system, reduce the calculation amount, and have higher echo simulation efficiency under the premise of ensuring accuracy.

Description of drawings

Figure 1 is a block diagram of the radar echo signal simulation system;

Fig. 2 is a flow chart of generating radar echo signal simulation system in simulink;

Fig. 3 is the flow chart of using the system of the present invention to simulate the radar echo signal;

Fig. 4 is a schematic diagram of point target imaging using imaging algorithm under front and side view;

Fig. 5 is a geometric model of the echo system function generated by the system function calculation module using the concentric circle algorithm in the present invention.

Detailed ways

The present invention is described in further detail below with reference to accompanying drawing:

At present, many achievements have been made in SAR echo simulation at home and abroad, including pure theoretical model, semi-physical simulation system, computer software simulation, and pure hardware platform to realize FPGA and DPS. The invention utilizes simulink to carry out modular design on the radar echo signal simulation system.

As a visual simulation tool in MATLAB, simulink provides an integrated environment for dynamic system modeling, simulation and comprehensive analysis. It does not need to write lengthy programs and can construct complex systems through simple and intuitive interface operations. It is widely used in control Complex simulation and design of theoretical and digital signal processing.

The present invention uses simulink to carry out the flow chart of system construction as shown in Figure 2. First, define the basic parameters required by the seeker system through the M script, then build the model of each module in simulink, set the input and output ports, realize the functions of each module, and then call the S function to encapsulate each module and generate parameters Set up the interface, and finally connect the corresponding input and output ports of each module to generate a radar echo signal simulation system, as shown in Figure 1.

With reference to Fig. 1, the radar echo signal simulation system that the present invention utilizes simulink to generate, comprises PRT synchronous module 1, radar pulse signal transmission module 2, radar trajectory import module 3, beam center calculation module 4, sub-scene interception module 5, antenna direction Figure calculation module 6, system function calculation module 7, echo generation module 8 and time delay and range gate gating module 9, wherein:

PRT synchronization module 1 is used to complete the synchronization pulse generation and output to each module to synchronize the clock of the whole system;

The radar pulse signal transmission module 2 is used to receive the PRT synchronous pulse input, generate the radar pulse transmission signal, and output the radar pulse transmission signal to the echo generation module 8;

The radar trajectory import module 3 is used to read the radar trajectory file information under the control of the PRT synchronous pulse, and output the read radar trajectory information to the beam center calculation module 4, sub-scene interception module 5, and antenna pattern calculation Module 6 and system function calculation module 7;

The beam center calculation module 4 is used to update the pixel coordinate information of the beam center in the scene graph according to the input radar and the current mode flag under the control of the PRT synchronization pulse, and output the beam center coordinate information to the sub-scene interception Module 5, antenna pattern calculation module 6 and system function calculation module 7;

The sub-scene interception module 5 is used to intercept the imaging sub-scene from the imported large scene according to the different beam irradiation modes of different modes of the radar and the input beam center coordinates and radar track information under the control of the PRT synchronous pulse. The data of the sub-scene is output to the antenna pattern calculation module 6 and the system function calculation module 7;

The antenna pattern calculation module 6 is used to, under the control of the PRT synchronous pulse, according to the input radar trajectory information, beam center coordinate information, sub-scene size, receiving beam offset angle, range and azimuth resolution, antenna beam width , calculate the antenna gain of each point in the sub-scene, and output the result to the system function calculation module 7;

The system function calculation module 7 is used to calculate the echo by using the concentric circle algorithm according to the input radar position, beam center coordinates, sub-scene data, antenna pattern, and initial range gate information of the echo under the control of the PRT synchronous pulse. The system function of the wave, and output the system function to the echo generating module 8;

The echo generation module 8 is used to convolve the radar pulse transmission signal with the system function, and under the control of the PRT synchronous pulse, generate the original echo signal, and output the result to the delay and range gate gating module 9;

The delay and range gate gating module 9 is used to output the echo data in a "stream" mode under the control of the PRT synchronous pulse, thereby better simulating the radar echo signal flow.

Referring to Fig. 3, the process of using the system of the present invention to simulate the radar echo signal is as follows:

Process 1, PRT synchronization module 1 reads the radar operating frequency, sampling frequency, transmit signal pulse width, transmit signal bandwidth, pulse repetition time and the number of transmit pulses in various modes from the simulation interface, and outputs the PRT synchronization signal PRTTrigger to each module, and output the identifier FrameTrigger of the radar working mode to the beam center calculation module.

Process 2, the radar pulse signal transmitting module 2 receives the PRT synchronous pulse input, detects the rising edge, generates the baseband linear frequency modulation signal LFM when the rising edge comes, and outputs N _a LFM pulse signals to the echo generation module according to the pulse repetition period PRT 8;

Described generation baseband chirp signal LFM expression is as follows:

t为快时间，t_m为慢时间，T_p为LFM信号脉宽，f_c为载波频率，k_r为线性调频率；in,

t is the fast time, t _m is the slow time, T _p is the pulse width of the LFM signal, f _c is the carrier frequency, and k _r is the linear modulation frequency;

Process 3, the radar trajectory import module 3 receives the PRT synchronous pulse input trigger, detects the rising edge, and when the rising edge comes, reads the trajectory file information, updates the radar position, velocity, acceleration, incident angle, velocity vector and beam projection folder on the ground Angle and radar position information with errors, and output the results to beam center calculation module 4, sub-scene interception module 5, antenna pattern calculation module 6 and system function calculation module 7.

Process 4, the beam center calculation module 4 receives the PRT synchronous pulse input trigger, detects the rising edge, when the rising edge comes, input the radar position, speed, target position coordinates, current mode flag, and calculate the pixel of the beam center in the scene map Point coordinate information, and output the result to sub-scene interception module 5, antenna pattern calculation module 6 and system function calculation module 7.

Process 5, the sub-scene interception module 5 inputs beam center coordinates and radar position coordinates according to different beam irradiation modes of different radar modes, and is triggered synchronously by the PRT to intercept the imaging sub-scene from the imported large scene, and then output the data To the antenna pattern calculation module 6 and the system function calculation module 7.

Process 6, the antenna pattern calculation module 6 inputs radar position information, pixel coordinate information of the beam center in the large scene, sub-scene size, receiving beam offset angle, range and azimuth resolution, antenna beam width, and receives The PRT synchronization pulse input triggers, detects the rising edge, and when the rising edge comes, calculates the antenna gain of each point in the sub-scene, and outputs the result to the system function calculation module 7 .

There are two modes for calculating the antenna gain of each point in the sub-scene:

The first is to calculate in the SAR imaging mode using the direction diagram of a single antenna and the offset angle of the receiving antenna is 0, that is, to obtain the beam center according to the input radar position information and the coordinates of the beam center at the pixel point in the center of the scene The azimuth angle α _c and elevation angle β _c , the azimuth angle α _RT and elevation angle β _RT of the target relative to the radar; then calculate the antenna gain rcs ₁ after modulation of the transmitting antenna pattern:

rcs ₁ ＝abs((sinc(α _RT -α _c ))*(sinc(β _RT -β _c ))) <2>

Among them, abs is the absolute value function, * means multiplication,

The second is to use four single antennas in monopulse mode, and set the corresponding receiving offset angles to form a four-antenna pattern for calculation, that is, according to the input radar position information, the center of the beam at the pixel point of the center of the scene The coordinates and sub-beams are relative to the beam's azimuth deviation angle ±Δα, and the pitch deviation angle ±Δβ, to obtain the azimuth angle α _c and elevation angle β _c of the beam center, and the azimuth angle α _RT and elevation angle β _RT of the target relative to the radar; and then respectively Calculate the antenna gains rcs ₂₁ , rcs ₂₂ , rcs ₂₃ , rcs ₂₄ modulated by the transmitting antenna pattern with different offsets:

rcs ₂₁ ＝abs((sinc(α _RT +Δα-α _c ))*(sinc(β _RT +Δβ-β _c ))) <3>

rcs ₂₂ ＝abs((sinc(α _RT +Δα-α _c ))*(sinc(β _RT -Δβ-β _c ))) <4>

rcs ₂₃ ＝abs((sinc(α _RT -Δα-α _c ))*(sinc(β _RT +Δβ-β _c ))) <5>

rcs ₂₄ ＝abs((sinc(α _RT -Δα-α _c ))*(sinc(β _RT -Δβ-β _c ))) <6>

The total antenna gain rcs ₂ is:

rcs ₂ = rcs ₂₁ * rcs ₂₂ * rcs ₂₃ * rcs ₂₄ <7>

Among them, rcs ₂₁ is the antenna gain with the relative sub-beam azimuth deviation angle of Δα and the pitch deviation angle of Δβ, and rcs ₂₂ is the antenna gain with the sub-beam relative and beam azimuth deviation angle of Δα and the pitch deviation angle of -Δβ , rcs ₂₃ is the antenna gain with the sub-beam relative and beam azimuth deviation angle being -Δα, and the pitch deviation angle is Δβ, and rcs ₂₄ is the antenna whose sub-beam relative and beam azimuth deviation angle is -Δα, and the pitch deviation angle is -Δβ gain.

Process 7, the system function calculation module 7 inputs the position of the radar, the coordinates of the center of the beam, the sub-scene data, the antenna pattern, and the initial range gate information of the echo, and receives the PRT synchronization pulse input trigger to detect the rising edge, when the rising edge comes When , use the concentric circle algorithm to calculate the system function of the echo, and output the result to the echo generation module 8;

The principle of the concentric circle algorithm is as follows:

Without considering the bending of the wave front, taking the front side view as an example, the distribution of the echo of the point target on the two-dimensional plane is a rectangular array as shown in the first picture of Figure 4. After the range pulse compression, it will become The result of the second image, this is the curvature created by the radar motion. After correcting the bending, the energy distribution of the target at this point will be in the same distance unit, as shown in the third picture in 4. At this time, the azimuth imaging of the target can be performed along the azimuth direction, and the imaging result of the target at this point can be obtained , as shown in the last figure of 4.

It can be seen that different point targets will be distributed in different distance units due to the different distances from the radar platform. This is because the distances from different target points to the radar platform are different, resulting in different delay times. The distance sampling frequency f _s samples the distance delay of the target point, the sampling unit interval is c/2f _s , c is the speed of light, and the echo distribution of each target point is distributed according to the integer multiple of the sampling unit interval; at different azimuth moments For target points in the scene with the same radar range, their integer multiples of sampling units are the same. Therefore, their complex echoes will be accumulated in the same distance unit. It is not difficult to imagine that at a certain azimuth moment, distributed in Point targets on the same concentric circle with the radar platform as the origin have the same distance to the radar, so their energy should be accumulated and distributed in the same distance unit.

Therefore, in order to quickly obtain the echo system function to meet the requirements of real-time echo signal generation, and at the same time maintain the calculation accuracy of the echo signal, considering that the points with the same length from the radar are located on the same distance unit, firstly, the The points are accumulated along the concentric circle with the radar as the center to obtain the one-dimensional range image of the radar, and then the echo system function is quickly realized in the frequency domain by using FFT, so that multiple points can be processed at the same time, reducing the amount of calculation.

According to the above ideas, the specific method of calculating the echo system function is as follows:

At each azimuth moment, the distance R(k) from all point targets in the scene to the radar must be calculated first, and the distance is compared with the distance sampling unit to obtain the distribution of points on all concentric circles, namely

In formula <8>, _nk represents the position of the distance unit, that is, on which concentric circle the point is distributed on, δ _r is the size of the distance unit, and

As shown in Figure 5, after obtaining the distribution of concentric circles, there are P point targets on a certain concentric circle within the beam irradiation range. According to formula <9>, it can be known that these P scattering points should be distributed at the same distance In the unit, they can uniformly generate the echo signal, and since the azimuth and phase information of the echo signal is more sensitive than the range envelope information, it is necessary to ensure the integrity of the azimuth phase information, that is, the formula <9> Carry out approximate distance calculation, so the azimuth phase signal s(mT; R _B ) of each point needs to be calculated independently:

Among them, σ is the gray value of the point target, mT is the discrete form of t _m , R _B is the shortest distance from the radar to the target, λ is the working wavelength of the radar, and R(mT; R) is the distance from the radar to the scattering point at mT , exp represents the exponential function.

Afterwards, sum the formula <10> to obtain the azimuth phase signal s ₂ of the point target on the same concentric circle:

Among them, σ _i is the gray value of the i-th point target on the same concentric circle.

Sum the formula <11> to get all the distance unit data s ₃ at the whole time:

In formula <12>, δ is the shock response function, k represents the number of distance units that fall within, and P _n represents the number of point targets within the nth distance unit. The number of ground scattering points in different distance units is different, and the difficulty of the accumulation process is also different. Carry out Fourier transform FFT to equation <12> and change it to the frequency domain multiplied by the FM item in the distance direction, and then use the inverse Fourier transform IFFT to transform back to the time domain to obtain the echo system function s ₄ (k , mT; R _B ):

where f _r represents the range frequency.

Process 8, the echo generation module 8 inputs the system function and the baseband linear frequency modulation signal LFM, performs convolution operation, generates the original echo signal, and receives the PRT synchronous pulse input trigger, detects the rising edge, and outputs the result when the rising edge comes To delay and range gate gating module 9.

In process 9, the delay and range gate gating module 9 outputs the input original echo signal in the form of "stream" under the control of the PRT synchronous pulse.

In summary, the high-speed platform radar echo signal simulation system based on simulink proposed in this paper has a modular and hierarchical design, which can conveniently and flexibly simulate radar echoes under different radar working modes, different external environments, and different target scenarios Signals help researchers get rid of the limitations of radar equipment conditions, and do not need to rely on expensive radar equipment to obtain relevant radar echo data, which is more efficient and convenient than traditional measured data methods.

The above disclosure is only a preferred embodiment of the present invention, which obviously cannot limit the scope of rights of the present invention. Therefore, equivalent changes made according to the claims of the present invention still fall within the scope of the present invention.

Claims (4)

1. High-speed platform radar return signal analog system based on simulink generates different modules through simulink, its characterized in that, the module that generates includes:

the PRT synchronization module (1) is used for finishing the generation of synchronization pulses, outputting the synchronization pulses to each module and synchronizing the clock of the whole system;

the radar pulse signal transmitting module (2) is used for receiving PRT synchronous pulse input, generating a radar pulse transmitting signal and outputting the radar pulse transmitting signal to the echo generating module (8);

the radar track importing module (3) is used for reading radar track file information under the control of PRT synchronous pulse, and respectively outputting the read radar track information to the beam center computing module (4), the sub-scene intercepting module (5), the antenna directional diagram computing module (6) and the system function computing module (7);

the beam center calculating module (4) is used for updating pixel point coordinate information of a beam center in a scene graph according to the input radar and the current mode marking bit under the control of a PRT synchronous pulse, and outputting the beam center coordinate information to the sub-scene intercepting module (5), the antenna directional diagram calculating module (6) and the system function calculating module (7);

the sub-scene intercepting module (5) is used for intercepting an imaged sub-scene from a guided large scene according to different beam irradiation modes of different modes of the radar, input beam center coordinates and radar track information under the control of the PRT synchronous pulse, and outputting data of the sub-scene to the antenna directional diagram calculating module (6) and the system function calculating module (7);

an antenna directional pattern calculation module (6) for calculating the antenna gain of each point in the sub-scene according to the input radar track information, the beam center coordinate information, the sub-scene size, the receiving beam bias angle, the distance direction and azimuth direction resolution and the antenna beam width under the control of the PRT synchronous pulse, and outputting the result to a system function calculation module (7);

the system function calculation module (7) is used for calculating a system function of an echo by utilizing a concentric circle algorithm according to an input radar position, a beam center coordinate, sub-scene data, an antenna directional diagram and initial range gate information of the echo under the control of a PRT synchronous pulse, and outputting the system function to the echo generation module (8);

the echo generating module (8) is used for convolving the radar pulse transmitting signal with a system function, generating an original echo signal under the control of a PRT synchronous pulse, and outputting a result to the delay and range gate gating module (9);

and the time delay and range gate gating module (9) is used for outputting echo data in a 'streaming' mode under the control of the PRT synchronous pulse, so that the radar echo signal stream is better simulated.

2. The system of claim 1, wherein different modules are generated by simulink, which is implemented as follows:

defining basic parameters required by a seeker system through an M script, constructing a model of each module in a simulink, and setting input and output ports to realize the functions of each module;

calling an S function to package each module and generating a parameter setting interface;

and connecting corresponding input and output ports in each module.

3. The system according to claim 1, characterized in that the antenna pattern calculation module (6) calculates the antenna gain for each point in the sub-scene, which is implemented as follows:

firstly, according to the input radar position information, the beam center coordinate information, the receiving beam offset angle and the antenna beam width, the azimuth angle alpha of the beam center is obtained _c And a pitch angle β _c Azimuth angle alpha of target relative to radar _RT And a pitch angle β _RT ；

And then calculating the antenna gain rcs after the directional diagram modulation of the transmitting antenna:

rcs＝abs((sinc(α _RT -α _c ))*(sinc(β _RT -β _c )))， <1>

wherein abs is a function of absolute value, which means multiplication,

4. the system according to claim 1, characterized in that the system function calculation module (7) calculates the system function of the echo using a concentric circle algorithm, which is implemented as follows:

calculating the distances R (k) from all point targets to the radar in the scene, and comparing the distances with a distance sampling unit to obtain the distribution condition of points of all concentric circles, namely obtaining P point targets on a certain concentric circle in total in the beam irradiation range;

distributing the P scattering points in the same range unit, and calculating azimuth phase signal s of each point ₁ (mT；R _B ):

Wherein σ is the gray value of the point target; mT is the slow time t _m Of discrete form of (A), R _B Is the closest distance of the radar to the scattering point, λ is the radar operating wavelength, R (mT; R) _B ) Is the distance of the radar to the scattering point at time mT;

by adding point targets on the same concentric circle, i.e. pair<2>Summing to obtain a distance sheetData s of elements containing azimuth phase ₂ ：

In pair type<3>Summing to obtain all the distance unit data s at the whole moment ₃ ：

Wherein, δ is an impact response function, and k is within a few distance units;

in pair type<4>Fourier transform FFT is carried out, the FFT is converted into a frequency domain multiplied by a frequency modulation item in the distance direction, and then inverse Fourier transform IFFT is utilized to convert the frequency domain back into a time domain, so that a system function s of an echo can be obtained ₄ (k,mT；R _B )：

Wherein k is _r Indicating the range chirp, f _r Indicating the range-wise frequency.

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