Method and system for realizing controllable SAR interference in two-dimensional sine frequency modulation region

Abstract

The invention discloses a two-dimensional sine frequency modulation region controllable SAR interference implementation method and system, and belongs to the technical field of radar interference. The method comprises the following steps: performing down-conversion processing on a received radar signal; inputting the obtained intermediate-frequency signal into an FPGA (Field Programmable Gate Array), and carrying out the following processing: carrying out ADC (Analog to Digital Converter) sampling on the intermediate-frequency signal to obtain a plurality of paths of digital signals; calculating based on the multi-path digital signals and preset interference parameters, and generating distance direction and azimuth direction interference by using a DDS IP core so as to generate a two-dimensional sine frequency modulation forwarding interference signal; converting the two-dimensional sine frequency modulation forwarding interference signal into an analog signal; and after up-conversion processing is carried out on the analog signal, the analog signal is sent out through a transmitting antenna, so that a two-dimensional interference signal is formed when an SAR receives echoes to carry out coherent accumulation. According to the method, by adjusting the preset interference parameters, accurate control over the interference range in the azimuth direction and the distance direction is achieved, and the problem of controlling the interference intensity within the determined interference range is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of radar jamming, and in particular relates to a method for realizing two-dimensional sinusoidal frequency modulation area controllable SAR (Synthetic Aperture Radar) jamming. Background Art

[0002] Synthetic aperture radar has the characteristics of high resolution, strong perspective, excellent anti-interference ability and all-weather operation, and is widely used in earth observation, military monitoring and intelligence collection. Synthetic aperture radar occupies an increasingly important position in the field of electronic countermeasures. How to interfere with synthetic aperture radar and protect one's own targets has become an important issue in the modern military field.

[0003] Interference to SAR can be classified from different perspectives. According to the different sources of interference signal energy, interference can be divided into two categories: active interference and passive interference. The modulation methods of active interference are diverse, the interference styles are complex and variable, and they are quite active. They are the mainstream direction of current interference development. According to the role of interference, active interference can be divided into deception interference and suppression interference. Deception interference is to hide the truth and show the false, so that the radar party can "discover" false target information, while suppression interference is to cover up important target information. According to the coherence of the interference signal and the radar signal, active interference can be divided into coherent interference, partially coherent interference and incoherent interference. Among them, coherent interference has high interference energy utilization, but it has high requirements for the reconnaissance of radar signals and the processing level of interference signals. Incoherent interference generally only requires the carrier frequency and bandwidth information of the radar, and has low requirements for the processing of reconnaissance and interference signals. The energy utilization rate and the requirements for the processing of reconnaissance and interference signals of partially coherent interference are between the first two.

[0004] At present, forwarding interference is one of the most commonly used interference methods in the field of interference. Pulse-by-pulse forwarding forms a point target for SAR. To achieve large-area coverage, the signal must be modulated. One-dimensional cosine phase modulation forwarding interference can form a linear false target string; two-dimensional cosine phase modulation interference forwards the SAR signal with modulated cosine phase, so that the SAR echo is extended in pairs in the frequency domain of the range and the Doppler domain of the azimuth. The linear frequency modulation signal can form an equally spaced target after pulse compression processing, realizing the interference of multiple false targets on SAR. By flexibly setting the interference modulation parameters, various interference effects such as compact surface false targets and grid-shaped false target strings can be formed to achieve the purpose of covering distributed important targets; two-dimensional expansion interference based on effective suppression area of ​​two-dimensional cosine phase modulation, that is, on the basis of two-dimensional cosine phase modulation interference, intermittent sampling in the azimuth direction is performed to expand the interference range in the azimuth direction, and frequency shifting in the range direction can effectively expand the interference range in the range direction; interference method based on two-dimensional cosine phase modulation secondary modulation, that is, taking a two-dimensional cosine phase modulation as the generated sample, the sample is subjected to a second one-dimensional or two-dimensional cosine phase modulation. The size of the false target generated by this method can be set as needed, and can present different interference effects as suppression interference.

[0005] However, the existing two-dimensional cosine phase modulation interference and the two-dimensional extended interference with effective suppression area based on two-dimensional cosine phase modulation are both difficult to control the interference intensity within a certain interference range; the interference method based on two-dimensional cosine phase modulation secondary modulation, the generated interference range can be set according to needs, but the secondary modulation based on two-dimensional interference increases the complexity of interference implementation, which is not conducive to engineering implementation. Summary of the invention

[0006] In order to solve the above problems existing in the prior art, the present invention provides a method and system for realizing two-dimensional sinusoidal frequency modulation regional controllable SAR interference. The technical problem to be solved by the present invention is achieved through the following technical solutions: In a first aspect, the present invention proposes a method for implementing two-dimensional sinusoidal frequency modulation regional controllable SAR interference, comprising: Step 1: Down-convert the received radar signal to obtain an intermediate frequency signal; Step 2: Input the intermediate frequency signal into the FPGA (Field Programmable Gate Array) and perform the following processing: Perform ADC sampling on the intermediate frequency signal to obtain multiple digital signals; Based on multi-channel digital signals and preset interference parameters, calculations are performed and DDS (Direct Digital Synthesizer) IP (Intellectual Property) core is used to generate range and azimuth interference, thereby generating a two-dimensional sinusoidal frequency modulation forwarding interference signal; Converting a two-dimensional sinusoidal frequency modulated repeater interference signal into an analog signal; Step 3: After the analog signal is up-converted, it is sent out through the transmitting antenna so that the SAR receives the echo and forms a two-dimensional interference signal during coherent accumulation.

[0007] In the second aspect, the present invention proposes a two-dimensional sinusoidal frequency modulation regional controllable SAR interference realization system, which is used to implement the method proposed in the first aspect of the present invention. The system includes a receiving antenna, a microwave board, an ADC signal acquisition module, an FPGA digital signal processing board, a host computer, a DAC digital-to-analog conversion module and a transmitting antenna; wherein, The receiving antenna is used to receive radar signals; The microwave board is used to down-convert the received radar signal to obtain an intermediate frequency signal; The ADC signal acquisition module is used to perform ADC sampling on the intermediate frequency signal to obtain multiple digital signals; The FPGA digital signal processing board is used to perform calculations based on multi-channel digital signals and preset interference parameters, and use the DDS IP core to generate range and azimuth interference, thereby generating a two-dimensional sinusoidal frequency modulation forwarding interference signal; The host computer is used to provide preset interference parameters to the FPGA digital signal processing board; The DAC digital-to-analog conversion module is used to convert the two-dimensional sinusoidal frequency modulation forwarding interference signal into an analog signal; Microwave boards are also used to up-convert analog signals; The transmitting antenna is used to transmit the signal after frequency conversion processing so that the SAR can form a two-dimensional interference signal when receiving the echo for coherent accumulation.

[0008] Beneficial effects of the present invention: The invention provides a method for realizing two-dimensional sinusoidal frequency modulation regional controllable SAR interference. First, the received radar signal is down-converted; then the intermediate frequency signal obtained is input into the FPGA for the following processing: ADC sampling is performed on the intermediate frequency signal to obtain a multi-channel digital signal; calculation is performed based on the multi-channel digital signal and the preset interference parameters, and the DDSIP core is used to generate the interference in the range and azimuth directions, thereby generating a two-dimensional sinusoidal frequency modulation forwarding interference signal; the two-dimensional sinusoidal frequency modulation forwarding interference signal is converted into an analog signal; finally, after the analog signal is up-converted, it is sent out through the transmitting antenna so that the SAR receives the echo and forms a two-dimensional interference signal when the echo is coherently accumulated. The method can realize accurate control of the interference range in the azimuth and range directions by adjusting the interference parameters input into the FPGA, and effectively solves the problem of controlling the interference intensity within the determined interference range, thereby realizing two-dimensional sinusoidal frequency modulation regional controllable SAR interference. In addition, the method uses a multi-channel parallel DDS IP core in the FPGA to generate interference signals, solves the problem that the existing multi-channel parallel signal generation module generates a small amount of data, has high flexibility, improves the performance and operability of the system, and is conducive to engineering implementation.

[0009] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a flow chart of a method for implementing two-dimensional sinusoidal frequency modulation regional controllable SAR interference provided by an embodiment of the present invention; Figure 2 It is a flow chart of another method for implementing two-dimensional sinusoidal frequency modulation regional controllable SAR interference provided by an embodiment of the present invention; Figure 3 It is a schematic diagram of a flow chart of generating a two-dimensional sinusoidal frequency modulation forwarding interference signal in an FPGA provided by an embodiment of the present invention; Figure 4 It is a schematic diagram of the operating principle of an 8-channel parallel DDS IP core generating an interference signal provided by an embodiment of the present invention; Figure 5 Schematic diagram of the output effect of an 8-channel parallel DDS IP core provided by an embodiment of the present invention; Figure 6 This is an actual test diagram of the BLOCKRAM resource occupancy of the 8-channel parallel DDS IP core provided by the embodiment of the present invention; Figure 7 It is a structural block diagram of a two-dimensional sinusoidal frequency modulation regional controllable SAR interference implementation system provided by an embodiment of the present invention; Figure 8 It is a hardware design diagram of a two-dimensional sinusoidal frequency modulation regional controllable SAR interference implementation system provided by an embodiment of the present invention; Fig. 9 This is the MATLAB frequency domain diagram of the DAC output data when the range interference modulation coefficient is 4 in the simulation experiment; Fig.10 This is the MATLAB frequency domain diagram of the DAC output data when the range interference modulation coefficient is 100 in the simulation experiment; Fig.11 It is the imaging result of the original data of spaceborne SAR in the simulation experiment; Fig.12 It is the imaging result after implementing two-dimensional sinusoidal frequency modulation regional controllable interference when the range interference modulation coefficient is 100, the range interference range is 1km, the azimuth interference modulation coefficient is 100, and the azimuth interference range is 1km in the simulation experiment; Fig.13 It is the imaging result after implementing two-dimensional sinusoidal frequency modulation regional controllable interference when the range interference modulation coefficient is 4, the range interference range is 1km, the azimuth interference modulation coefficient is 2, and the azimuth interference range is 1km in the simulation experiment; Fig.14 It is the imaging result after implementing two-dimensional sinusoidal frequency modulation regional controllable interference when the range interference modulation coefficient is 100, the range interference range is 5km, the azimuth interference modulation coefficient is 100, and the azimuth interference range is 10km in the simulation experiment; Fig.15 This is the imaging result after implementing two-dimensional sinusoidal frequency modulation regional controllable interference in the simulation experiment when the range interference modulation coefficient is 4, the range interference range is 5km, the azimuth interference modulation coefficient is 2, and the azimuth interference range is 10km. DETAILED DESCRIPTION

[0011] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0012] The first aspect of the present invention provides a method for implementing two-dimensional sinusoidal frequency modulation regional controllable SAR interference. Figure 1 and Figure 2 , Figure 1 is a flow chart of a method for implementing two-dimensional sinusoidal frequency modulation regional controllable SAR interference provided by an embodiment of the present invention. Figure 2 1 is a flow chart of another two-dimensional sinusoidal frequency modulation regional controllable SAR interference implementation method provided by an embodiment of the present invention. The two-dimensional sinusoidal frequency modulation regional controllable SAR interference implementation method provided by the present invention mainly includes the following steps: Step 1: Down-convert the received radar signal to obtain an intermediate frequency signal.

[0013] In this embodiment, after the radar signal is received by the receiving antenna, the radar signal may be down-converted by the microwave board to obtain a radar intermediate frequency signal.

[0014] Step 2: Input the intermediate frequency signal into the FPGA and perform the following processing: 21) Perform ADC sampling on the intermediate frequency signal to obtain multiple digital signals.

[0015] Optionally, as an implementation manner, the multi-channel digital signals obtained by ADC sampling in this embodiment can be 8 channels of 12-bit digital signals, that is, 8 channels of real parts of radar intermediate frequency signals.

[0016] 22) Based on the multi-channel digital signals and the preset interference parameters, the DDS IP core is used to generate the interference in the range and azimuth directions, thereby generating a two-dimensional sinusoidal frequency modulation forwarding interference signal.

[0017] 22a) Detect multiple digital signals and obtain effective radar pulse signals.

[0018] It is understandable that after the FPGA, the multi-channel digital signals need to be detected and processed first to obtain the signal's carrier frequency, pulse width, bandwidth and other information. At the same time, through envelope detection, the radar pulse effective signal can also be obtained. Furthermore, the radar range modulation frequency can be obtained by dividing the bandwidth by the pulse width. , using the speed of light Dividing by the carrier frequency can also give the carrier wavelength This information is then used to perform calculations to generate interference signals in range and azimuth.

[0019] 22b) Based on the radar pulse effective signal and the preset range interference parameters, the DDS IP core is used to generate the range interference signal.

[0020] Specifically, in FPGA, the rising edge and falling edge of the effective signal of the radar pulse are extracted. When the rising edge is triggered, the distance fast time counting starts, and when the falling edge is triggered, it ends, that is, the distance fast time records the number of sampling points in the pulse. The intermediate frequency range interference signal is expressed as: ; in, is the distance sinusoidal modulation frequency, is the range interference modulation coefficient, is the amplitude coefficient, is the frequency modulation of the interference signal. According to the Carson formula, the effective bandwidth of the distance interference is: .

[0021] Obviously, as the interference modulation factor increases, the effective interference bandwidth also increases. times, the number of false targets is According to the frequency shift principle, the distance between adjacent false targets is for: ; in, is the speed of light, is the radar range modulation frequency, so the range interference range is: .

[0022] Optionally, since the ADC sampling signal in this embodiment is 8-channel 12-bit digital signal, that is, 8-channel radar intermediate frequency signal real part, the range interference signal to be generated is also 8-channel real signal. In this embodiment, a multi-channel parallel DDS IP core is used to generate the range interference signal, and the number of channels is set to 8, which can be understood as an 8-channel parallel DDS IP core signal generation module.

[0023] For details, see Figure 3 , Figure 3 It is a schematic diagram of a process of generating a two-dimensional sinusoidal frequency modulation forwarding interference signal in an FPGA provided by an embodiment of the present invention, wherein the specific method of generating the range interference signal is shown in the following steps S101-S103.

[0024] S101, according to the preset distance to the interference range and the range interference modulation coefficient , use the FPGA internal divider Divider IP core and multiplier IP core to calculate the distance to the adjacent false target interval and the range modulation frequency , the calculation formula is: ; Among them, the preset parameters can be configured by the host computer to the FPGA and can be adjusted according to actual needs.

[0025] S102, modulate frequency according to distance and the range interference modulation coefficient , calculate the range frequency control word.

[0026] As can be seen from the previous text, the expression of the intermediate frequency range interference signal is: ; Then the phase function of the intermediate frequency range interference signal can be obtained as: ; By differentiating the phase function, the frequency function can be obtained as: .

[0027] It is understandable that if 8-way intermediate frequency range interference real signals are obtained through the 8-channel parallel DDS IP core signal generation module, the intermediate frequency range interference signal frequency control word must be obtained. The frequency of the output signal of the 8-channel parallel DDS IP core signal generation module is expected to be: ; DDS IP Core Frequency Control Word With output frequency The relationship is: ; in, Input control word width for DDS IP core. It is the working clock of DDS IP core. is the output signal frequency.

[0028] Then the intermediate frequency range interference signal frequency control word can be designed as: ; in, It is the frequency control word width of the DDS IP core in the 8-channel parallel DDS IP core signal generation module.

[0029] Furthermore, to calculate in FPGA First, you need to instantiate a single DDS IP core to generate Cosine signal, the expected single DDS IP core output cosine signal frequency is Similarly, based on the relationship between the DDS IP core frequency control word and the output frequency, the frequency control word of a single DDS IP core is designed: ; That is, the distance frequency control word of a single DDS IP core is: ; in Input control word width for a single DDS IP core. It is the working clock of DDS IP core. is the frequency of the distance output signal. After getting a single DDS IP core, you can get Cosine signal.

[0030] Get the cosine signal Then, use the Multiplier IP core three times to achieve Multiply by the range modulation frequency , then multiplied by the range modulation coefficient , and finally multiply by , the frequency control word of the intermediate frequency range interference signal can be obtained .

[0031] S103, inputting the range frequency control word into the multi-channel parallel DDS IP core to generate multi-channel parallel range interference signals.

[0032] Specifically, according to the relationship between the frequency control word and the phase control word of the DDS IP core and the principle of the DDS IP core generating signals, a multi-channel parallel DDS IP core is designed in this embodiment to generate interference signals, which is expressed as: ; In the formula, Indicates channel The azimuth interference signal generated, Indicates the channel number; Indicates the total number of channels.

[0033] Optional, take 8 channels as an example, see Figure 4 , Figure 4 Schematic diagram of the operation principle of the 8-channel parallel DDS IP core provided by the embodiment of the present invention. The frequency control words of the 8 instantiated DDS IP cores are the same; the phase control word uses a differential input method that increases step by step, that is, the phase control word is composed of Increment to , the phase control word step is The multi-channel parallel signal generation module outputs 8 real signals, namely 8 cosine signals: .

[0034] Furthermore, Figure 5 The output effect diagram of the 8-channel parallel DDS IP core is shown; assuming that the frequency of the input signal generated by the 8-channel parallel DDS IP core is , output 8 real signals, The serial arrangement outputs a frequency of The cosine signal.

[0035] In the existing multi-channel parallel signal generation module, the DDS IP core is instantiated once to generate one signal, and then the one signal is converted into multiple signals through the channel conversion module. Although the DDS IP core is only used once, a large amount of RAM storage and reading operations are required in the channel conversion module. Converting one signal into eight signals requires instantiation of 16 RAM IP cores. The more signal conversion channels, the more RAM IP cores need to be instantiated, resulting in an increase in the BLOCKRAM resource occupancy rate in the FPGA. In addition, the RAM storage depth is limited, so the amount of data generated by the channel conversion method for multiple parallel signals is also limited by the RAM storage depth.

[0036] The present invention is designed as Figure 4 The 8-channel parallel DDS IP core shown generates interference signals, and does not use data storage and reading IP cores such as RAM. There is no limit on the amount of data generated, and the occupancy rate of BLOCKRAM is low. Figure 6 The actual test diagram of the BLOCKRAM resource usage of the 8-channel parallel DDS IP core is shown; the module instantiation of the 8-channel parallel DDS IP core generating the signal is named Distance_SIGNAL, and the BLOCKRAM resource usage is 16 RAMs, while the BLOCKRAM resource usage of each DDS IP core is only 2 RAMs. For radar signals with large pulse widths and a large number of ADC sampling points, the 8-channel parallel DDS IP core shows a lower resource usage rate, better applicability and flexibility.

[0037] 22c) Based on the radar pulse effective signal and the preset azimuth interference parameters, the DDS IP core is used to generate an azimuth interference signal.

[0038] In FPGA, the rising edge of the pulse valid enable signal is extracted, and the azimuth slow time counting starts when the rising edge arrives, that is, the azimuth slow time records the number of pulses. The expression of the intermediate frequency azimuth interference signal is: ; In the formula, is the azimuth sinusoidal frequency, is the azimuth modulation coefficient. According to the Casson formula, the effective bandwidth of azimuth interference is: ; Forwarding interference signal spectrum times, the number of false targets formed is According to the frequency shift principle, the interval between adjacent false targets in azimuth is for: ; in, represents the carrier wavelength, represents the center slope distance, represents the flight speed of the SAR platform, so the interference range in azimuth is: .

[0039] Similarly, since the ADC sampling signal is 8-channel 12-bit digital signals, the azimuth interference signal only needs to generate 8-channel real signals.

[0040] Please continue to see Figure 3 , the specific method of generating the azimuth interference signal refers to the following steps S201-S203.

[0041] S201, according to the preset azimuth interference range and azimuth interference modulation coefficient , use the FPGA internal divider IP core and multiplier IP core to calculate the azimuth interval between adjacent false targets and azimuth modulation frequency , the calculation formula is as follows: ; In the formula, Indicates the flight speed of the SAR platform; Indicates the carrier wavelength; Indicates the center slant distance. These parameters can be configured from the host computer to the FPGA and can be adjusted according to actual conditions.

[0042] S202, modulate frequency according to azimuth , SAR platform flight speed and center slope distance Calculate the azimuth frequency control word.

[0043] As can be seen from the previous text, the expression of the intermediate frequency azimuth interference signal is: ; Then the phase function of the intermediate frequency azimuth interference signal can be obtained as: ; By differentiating the phase function, the frequency function can be obtained as: ; In the formula, is the radar signal pulse width, is the radar signal pulse repetition period, the distance to fast time Record the number of sampling points in the pulse, azimuth slow time Record the number of pulses. Count from 0 to , Each count is increased by 1, and the count relationship is mapped to the timing of the interference signal. The number of digital signal points generating distance interference is At this time, only one interference digital signal is generated in the azimuth direction.

[0044] Using the rising edge trigger of the radar pulse valid signal as the valid condition of the DDS IP core control word input, the generated 1-way azimuth interference signal is copied into 8-way parallel signals, which can meet the timing and number requirements of the azimuth interference signal.

[0045] Specifically, a single DDS IP core is instantiated to generate a 1-way intermediate frequency azimuth interference signal, and the expected output signal frequency is: ; The relationship between the DDS IP core frequency control word and the output frequency is: ; in, Input control word width for DDS IP core. It is the working clock of DDS IP core. is the output signal frequency.

[0046] Then the frequency control word of the intermediate frequency azimuth interference signal can be designed as: ; in, This is the frequency control word width of a single DDS IP core.

[0047] Furthermore, to calculate in FPGA First, you need to instantiate a single DDS IP core to generate Cosine signal, the expected single DDS IP core output cosine signal frequency is Similarly, based on the relationship between the DDS IP core frequency control word and the output frequency, the frequency control word of a single DDS IP core is designed: ; That is, the azimuth frequency control word of a single DDS IP core is: ; in, Input control word width for a single DDS IP core. It is the working clock of DDS IP core. is the azimuth output signal frequency. After getting a single DDS IP core, you can get Cosine signal.

[0048] Get the cosine signal Then, use the Multiplier IP core three times to achieve Multiply by the range modulation frequency , then multiplied by the range modulation coefficient , and finally multiply by , the frequency control word of the intermediate frequency azimuth interference signal can be obtained .

[0049] S203, inputting the azimuth frequency control word into a single DDS IP core, generating one azimuth interference signal, and duplicating it into multiple parallel signals to obtain multiple parallel azimuth interference signals.

[0050] Specifically, the azimuth frequency control word is used as the frequency control word of a single DDS, and the rising edge trigger of the radar pulse valid signal is used as the valid condition of the DDS IP core control word input, so as to generate one azimuth interference signal and copy it into 8 parallel signals to obtain 8 parallel azimuth interference signals.

[0051] 22d) Multiplying the distance interference signal, the azimuth interference signal and the multi-channel digital signal to generate a two-dimensional sinusoidal frequency modulation forwarding interference signal.

[0052] Specifically, according to the generation process of the range interference signal in S101-S103 and the azimuth interference signal in S201-S203, the two exist independently and do not affect each other. Suppose the radar signal sampled by the ADC is , then the two-dimensional sinusoidal FM forwarding interference signal is: ; Finally, the 8-way ADC samples the signal 8-way distance interference signal 8-way azimuth interference signals to generate interference signals.

[0053] Since the interference pattern implemented in this embodiment is two-dimensional coherent interference, the interference signal can obtain a processing gain equivalent to that of the transmission signal, so the interference power required is smaller than that of the traditional FPGA-based suppression interference.

[0054] 23) Convert the two-dimensional sinusoidal frequency modulated repeater interference signal into an analog signal.

[0055] Specifically, the generated two-dimensional sinusoidal frequency modulation forwarding interference signal is converted into an analog signal output through an 8-channel DAC.

[0056] Step 3: After up-conversion processing, the analog signal is sent out through the transmitting antenna so that a two-dimensional interference signal is formed when the SAR receives the echo and performs coherent accumulation.

[0057] Specifically, the analog signal can be up-converted by using a microwave board and then transmitted through a transmitting antenna, so that a two-dimensional interference signal can be formed when the SAR receives the echo and performs coherent accumulation.

[0058] The invention provides a method for realizing two-dimensional sinusoidal frequency modulation regional controllable SAR interference. First, the received radar signal is down-converted; then the intermediate frequency signal obtained is input into the FPGA for the following processing: ADC sampling is performed on the intermediate frequency signal to obtain a multi-channel digital signal; calculation is performed based on the multi-channel digital signal and the preset interference parameters, and the DDSIP core is used to generate the interference in the range and azimuth directions, thereby generating a two-dimensional sinusoidal frequency modulation forwarding interference signal; the two-dimensional sinusoidal frequency modulation forwarding interference signal is converted into an analog signal; finally, after the analog signal is up-converted, it is sent out through the transmitting antenna so that the SAR receives the echo and forms a two-dimensional interference signal when the echo is coherently accumulated. The method can realize accurate control of the interference range in the azimuth and range directions by adjusting the interference parameters input into the FPGA, and effectively solves the problem of controlling the interference intensity within the determined interference range, thereby realizing two-dimensional sinusoidal frequency modulation regional controllable SAR interference. In addition, the method uses a multi-channel parallel DDS IP core in the FPGA to generate interference signals, solves the problem that the existing multi-channel parallel signal generation module generates a small amount of data, has high flexibility, improves the performance and operability of the system, and is conducive to engineering implementation.

[0059] Based on the same inventive concept, the second aspect of the present invention provides a two-dimensional sinusoidal frequency modulation regional controllable SAR interference implementation system. Figure 7 , Figure 7 This is a structural block diagram of a two-dimensional sinusoidal frequency modulation regional controllable SAR interference implementation system provided by an embodiment of the present invention. The system includes: a receiving antenna, a microwave board, an ADC signal acquisition module, an FPGA digital signal processing board, a host computer, a DAC digital-to-analog conversion module and a transmitting antenna; wherein, The receiving antenna is used to receive radar signals; The microwave board is used to down-convert the received radar signal to obtain an intermediate frequency signal; The ADC signal acquisition module is used to perform ADC sampling on the intermediate frequency signal to obtain multiple digital signals; The FPGA digital signal processing board is used to perform calculations based on multi-channel digital signals and preset interference parameters, and use the DDS IP core to generate range and azimuth interference, thereby generating a two-dimensional sinusoidal frequency modulation forwarding interference signal; The host computer is used to provide preset interference parameters to the FPGA digital signal processing board; The DAC digital-to-analog conversion module is used to convert the two-dimensional sinusoidal frequency modulation forwarding interference signal into an analog signal; Microwave boards are also used to up-convert analog signals; The transmitting antenna is used to transmit the signal after frequency conversion processing so that the SAR can form a two-dimensional interference signal when receiving the echo for coherent accumulation.

[0060] Optionally, as an implementation, Figure 8 This is a hardware design diagram of a two-dimensional sinusoidal frequency modulation regional controllable SAR interference implementation system provided by an embodiment of the present invention. In this embodiment, the ADC signal acquisition module can be implemented by ADC12DJ3200, the FPGA digital signal processing board can be implemented by XCU13P-2FHGB2104I, and the DAC digital-to-analog conversion module can be implemented by AD9164.

[0061] It can be understood that the system provided in this embodiment also includes a high-speed interface module and a power module, wherein the high-speed interface module is used to realize data transmission between modules, and the power module is used to supply power to the entire system.

[0062] The system provided in this embodiment can be used to implement the method proposed in the first aspect above. Since it is basically similar to the method embodiment, the description is relatively simple. For the relevant parts, please refer to the partial description of the method embodiment. Therefore, the system also has the same or similar beneficial effects as the above method.

[0063] The beneficial effects of the present invention are verified and explained below through simulation experiments.

[0064] 1. Experimental conditions This experiment focuses on the interference technology of SAR. The DDR (MT40A512M16L) module is used to store and read the output signal of DAC. Data analysis is performed in MATLAB to verify the correctness of the intermediate frequency interference signal generated by the FPGA signal processing board. Finally, the data after two-dimensional sinusoidal frequency modulation regional controllable interference is imaged on the space-borne SAR to verify the correctness and engineering practicality of the invention.

[0065] The experimental parameters are: spaceborne SAR carrier frequency , IF carrier frequency , Pulse Width ,bandwidth , Initial center slope distance , SAR platform flight speed .

[0066] 2. Experimental content and results analysis See also Figure 9-10 , Fig. 9 This is the MATLAB frequency domain diagram of the DAC output data when the range interference modulation coefficient is 4 in the simulation experiment; , forwarding interference signal spectrum Theoretically, the number of false targets generated is As you can see, Fig. 9 There are 11 frequency components in it, which is consistent with the number of frequency components generated theoretically.

[0067] Fig.10 This is the MATLAB frequency domain diagram of the DAC output data when the range interference modulation coefficient is 100 in the simulation experiment; , forwarding interference signal spectrum Theoretically, the number of false targets generated is ,observe Fig.11 The number of frequency components is large and densely distributed, which is basically consistent with the theoretical expectation of the number of frequency components.

[0068] See also Fig.11 , Fig.11 This is the imaging result of the original data of the spaceborne SAR in the simulation experiment. The data after the spaceborne SAR is subjected to two-dimensional sinusoidal frequency modulation regional controllable interference is imaged. The results are as follows Figure 12-15 As shown, Fig.12 It is the imaging result after implementing two-dimensional sinusoidal frequency modulation regional controllable interference when the range interference modulation coefficient is 100, the range interference range is 1km, the azimuth interference modulation coefficient is 100, and the azimuth interference range is 1km in the simulation experiment; Fig.13 It is the imaging result after implementing two-dimensional sinusoidal frequency modulation regional controllable interference when the range interference modulation coefficient is 4, the range interference range is 1km, the azimuth interference modulation coefficient is 2, and the azimuth interference range is 1km in the simulation experiment; Fig.14 It is the imaging result after implementing two-dimensional sinusoidal frequency modulation regional controllable interference when the range interference modulation coefficient is 100, the range interference range is 5km, the azimuth interference modulation coefficient is 100, and the azimuth interference range is 10km in the simulation experiment; Fig.15 This is the imaging result after implementing two-dimensional sinusoidal frequency modulation regional controllable interference in the simulation experiment when the range interference modulation coefficient is 4, the range interference range is 5km, the azimuth interference modulation coefficient is 2, and the azimuth interference range is 10km.

[0069] The interference ranges in the range and azimuth directions controlled by this experiment are and ,according to Fig.14 and Fig.15 The imaging results show that the present invention achieves accurate control of the interference range. In this experiment, the interference modulation coefficient is controlled to be the same as the interference range. and According to the imaging results, the present invention not only realizes accurate control of the interference range, but also realizes accurate control of the interference intensity within the determined interference range.

[0070] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A two-dimensional sinusoidal frequency modulation regional controllable SAR interference implementation method, characterized in that: include: Step 1: Down-convert the received radar signal to obtain an intermediate frequency signal; Step 2: Input the intermediate frequency signal into the FPGA and perform the following processing: Performing ADC sampling on the intermediate frequency signal to obtain multiple digital signals; Calculation is performed based on the multi-channel digital signals and preset interference parameters, and the DDS IP core is used to generate interference in the range and azimuth directions, thereby generating a two-dimensional sinusoidal frequency modulation forwarding interference signal; Converting the two-dimensional sinusoidal frequency modulation forwarding interference signal into an analog signal; Step 3: After up-conversion processing is performed on the analog signal, it is sent out through a transmitting antenna so that a two-dimensional interference signal is formed when the SAR receives the echo and performs coherent accumulation.

2. A two-dimensional sinusoidal frequency modulation regional controllable SAR interference implementation method according to claim 1, characterized in that: In step 2, calculation is performed based on the multi-channel digital signals and preset interference parameters, and the DDS IP core is used to generate interference in the range and azimuth directions, thereby generating a two-dimensional sinusoidal frequency modulation forwarding interference signal, including: Conducting reconnaissance on the multiple digital signals to obtain effective radar pulse signals; Based on the radar pulse effective signal and the preset range interference parameters, a range interference signal is generated using the DDS IP core; Based on the radar pulse effective signal and the preset azimuth interference parameters, the DDS IP core is used to generate an azimuth interference signal; The distance interference signal, the azimuth interference signal and the multi-channel digital signal are multiplied to generate a two-dimensional sinusoidal frequency modulation forwarding interference signal.

3. A two-dimensional sinusoidal frequency modulation regional controllable SAR interference implementation method according to claim 2, characterized in that: Based on the radar pulse effective signal and the preset range interference parameters, the DDS IP core is used to generate a range interference signal, including: According to the preset range interference range and range interference modulation coefficient, the FPGA internal divider IP core and multiplier IP core are used to calculate the interval between adjacent false targets and the range modulation frequency. Calculating a range frequency control word according to the range modulation frequency and the range interference modulation coefficient; The range frequency control word is input into a multi-channel parallel DDS IP core to generate a multi-channel parallel range interference signal.

4. A two-dimensional sinusoidal frequency modulation regional controllable SAR interference implementation method according to claim 3, characterized in that: The calculation formulas for the interval between adjacent false targets in the range direction and the modulation frequency in the range direction are: ； In the formula, Indicates the distance to adjacent false targets; Indicates the interference range in distance direction; represents the interference modulation coefficient in the range direction; represents the range modulation frequency; represents the range modulation frequency, which is obtained by dividing the bandwidth of the effective radar pulse signal by the pulse width; Represents the speed of light.

5. A two-dimensional sinusoidal frequency modulation regional controllable SAR interference implementation method according to claim 4, characterized in that: The calculation formula of the distance frequency control word is: ； In the formula, Indicates the range frequency control word; Indicates distance to fast time; Indicates the distance frequency control word width of the multi-channel parallel DDS IP core; Indicates the working clock of the DDS IP core.

6. A two-dimensional sinusoidal frequency modulation regional controllable SAR interference implementation method according to claim 5, characterized in that: The multi-path parallel range interference signal is expressed as: ； In the formula, Indicates channel The distance interference signal generated is Indicates the channel number; Indicates the total number of channels.

7. A two-dimensional sinusoidal frequency modulation regional controllable SAR interference implementation method according to claim 2, characterized in that: Based on the radar pulse effective signal and the preset azimuth interference parameters, the DDS IP core is used to generate an azimuth interference signal, including: According to the preset azimuth interference range and azimuth interference modulation coefficient, the azimuth modulation frequency of the interval between adjacent false targets in azimuth is calculated using the internal FPGA divider IP core and multiplier IP core. Calculate the azimuth frequency control word according to the azimuth modulation frequency, the flight speed of the SAR platform and the center slant range; The azimuth frequency control word is input into a single DDS IP core to generate one azimuth interference signal, and the one azimuth interference signal is copied into multiple parallel signals to obtain multiple parallel azimuth interference signals.

8. A two-dimensional sinusoidal frequency modulation regional controllable SAR interference implementation method according to claim 7, characterized in that: The calculation formula of the adjacent false target interval in the azimuth direction and the modulation frequency in the azimuth direction is: ； In the formula, Indicates the interval between adjacent false targets in azimuth; Indicates the interference range in azimuth; Indicates the interference modulation coefficient in azimuth; Indicates the azimuth modulation frequency; Indicates the flight speed of the SAR platform; Indicates the carrier wavelength; Indicates the center slope distance.

9. A two-dimensional sinusoidal frequency modulation regional controllable SAR interference implementation method according to claim 8, characterized in that: The calculation formula of the azimuth frequency control word is: ； In the formula, Indicates the azimuth frequency control word; Indicates azimuth slow time; Indicates the azimuth frequency control word width of the DDS IP core; Indicates the working clock of the DDS IP core.

10. A two-dimensional sinusoidal frequency modulation regional controllable SAR interference implementation system, used to implement the method described in any one of claims 1 to 9, characterized in that: The system includes a receiving antenna, a microwave board, an ADC signal acquisition module, an FPGA digital signal processing board, a host computer, a DAC digital-to-analog conversion module and a transmitting antenna; The receiving antenna is used to receive radar signals; The microwave board is used to perform down-conversion processing on the received radar signal to obtain an intermediate frequency signal; The ADC signal acquisition module is used to perform ADC sampling on the intermediate frequency signal to obtain multiple digital signals; The FPGA digital signal processing board is used to perform calculations based on the multi-channel digital signals and preset interference parameters, and use the DDS IP core to generate interference in the range and azimuth directions, thereby generating a two-dimensional sinusoidal frequency modulation forwarding interference signal; The host computer is used to provide preset interference parameters to the FPGA digital signal processing board; The DAC digital-to-analog conversion module is used to convert the two-dimensional sinusoidal frequency modulation forwarding interference signal into an analog signal; The microwave board is also used to perform up-conversion processing on the analog signal; The transmitting antenna is used to transmit the signal after the frequency conversion processing, so that the SAR receives the echo and performs coherent accumulation to form a two-dimensional interference signal.

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