A radar anti-jamming imaging method

Abstract

The application discloses a radar anti-interference imaging method, which is applied to the field of radar anti-interference and aims at the problem that a forward-looking scanning radar is difficult to image in an electronic interference environment. Firstly, a dual-frequency radar echo model is established to represent the mathematical relationship between target scattering and dual-frequency radar echo data. Then, a dual-frequency anti-interference strategy is proposed, and inter-pulse frequency hopping is adopted to resist the suppressive interference of an enemy. Then, an adaptive dual-frequency sampling model is adopted to remove residual strip interference signals in the echo. Finally, according to the weighted least square criterion, the adaptive dual-frequency sampling model is solved in an iterative mode, and super-resolution imaging in an interference environment is realized. Compared with a traditional anti-interference imaging method, the method can effectively resist the suppressive interference signals with a large bandwidth, and realizes robust super-resolution imaging in an interference environment.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of radar anti-jamming, and particularly relates to an anti-jamming super-resolution imaging technology. BACKGROUND

[0002] With the development of electronic jamming technology, the jamming bandwidth gradually increases, and the jamming form gradually becomes flexible and complex, which seriously affects the application scene of the radar. In order to resist the increasingly complex jamming form and enhance the radar detection performance in the jamming environment, researchers have proposed many jamming suppression methods.

[0003] The document "Z.-h. Wang, Z. Zhao and X.-q. Shi, "Median Filter Based FM Interference Suppression for PRC-CW Radar," 2011 International Conference on Multimedia and Signal Processing, Guilin, China, 2011, pp. 315-318." proposes a frequency modulation interference suppression method based on adaptive short-time Fourier transform and median filter. Simulation results show that this method can effectively suppress frequency modulation interference and significantly improve target detection performance, but its interference suppression capability is limited. In the document "S. Dong, Y. Quan, W. Fang and H. Wang, "Anti-intermittent Sampling Jamming Method Based on Frequency Agile Radar and K-means," 2021 CIE International Conference on Radar (Radar), Haikou, Hainan, China, 2021, pp. 1140-1144.", an anti-interference method based on frequency agile radar and K-means clustering is proposed. This method designs radar transmission signals in the form of inter-pulse frequency agility and uses K-means clustering algorithm to suppress interference. Finally, the effectiveness of this method is verified through simulation experiments. In the document "C. Niu, Q. Lin, Y. Ma, M. Duan and H. Zhang, "An intermittent sampling and forwarding interference suppression method based on intra-pulse frequency-time-delay agile waveform," 2023 3rd International Conference on Neural Networks, Information and Communication Engineering (NNICE), Guangzhou, China, 2023, pp. 536-541.", an interference suppression method based on intra-pulse frequency-time-delay agile waveform is proposed. This method has good performance in resisting intermittent sampling and forwarding interference, but it cannot resist suppressive interference signals with large bandwidth. SUMMARY

[0004] To solve the above technical problems, the application provides a radar anti-interference imaging method, which adopts a dual-frequency pulse interval hopping strategy to resist suppressive interference, and adopts an adaptive dual-frequency sampling model to remove residual interference, thereby realizing super-resolution imaging in an interference environment.

[0005] The technical scheme adopted by the application is as follows: a radar anti-interference imaging method, comprising:

[0006] S1, the span between the two carrier frequencies carried by the dual-frequency radar system is far greater than the covered frequency band of the suppressive interference, and the interference range is escaped through dual-frequency hopping;

[0007] S2, a dual-frequency hopping pattern is obtained according to interference detection and a dual-frequency hopping process:

[0008] K=[K1,K2,...,K M ]

[0009] wherein K1=1 indicates that the first pulse is transmitted by the dual-frequency radar, K m ,m=2,...,M-1 indicates that hopping is performed at the mth pulse position, K M =N indicates that detection ends at the Nth pulse position;

[0010] S3, a dual-frequency antenna directional diagram is constructed according to the hopping pattern;

[0011] S4, a dual-frequency radar echo model is constructed based on the dual-frequency antenna directional diagram;

[0012] S5, according to the dual-frequency hopping pattern, the interfered pulse position is obtained, and an adaptive dual-frequency sampling model is established;

[0013] S6, according to the dual-frequency radar echo model and the adaptive dual-frequency sampling model, azimuth echo data based on the adaptive dual-frequency sampling model is obtained;

[0014] S7, according to the weighted least square criterion, the azimuth echo data based on the adaptive dual-frequency sampling model is solved in an iterative manner, and super-resolution imaging in an interference environment is realized.

[0015] The application has the following beneficial effects: the dual-frequency radar echo model is constructed to represent dual-frequency echo characteristics, then the dual-frequency pulse interval hopping strategy is adopted to resist suppressive interference, then an adaptive dual-frequency sampling model is constructed to remove residual strip interference signals in the echo, and finally the solution is performed in an iterative form, which can resist large-bandwidth suppressive interference signals and realize robust super-resolution imaging. The related method is still within the protection scope of the application. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 The application provides a flowchart of the method.

[0017] Figure 2 The dual-frequency antenna pattern in the present application.

[0018] Figure 3 The simulation experiment results in the present application;

[0019] Wherein, Figure 3 (a) is the original scene of the simulation setting, Figure 3 (b) is the suppressed interference echo data, Figure 3 (c) is the obtained echo data under the dual-frequency hopping model, Figure 3 (d) is the super-resolution result of the suppressed interference echo data, Figure 3 (e) is the super-resolution result of the dual-frequency hopping echo data, Figure 3 (f) is the super-resolution result of the method of the present application. DETAILED DESCRIPTION

[0020] The present application adopts simulation experiments to demonstrate the effectiveness of the proposed method, and all the steps and conclusions of the present application are verified on the Matlab2020b simulation platform, and the specific implementation steps are as shown in Figure 1 In order to enable those skilled in the art to understand the content of the present application, the present application is further described below in conjunction with the drawings.

[0021] Step one: Establishing a dual-frequency radar echo model

[0022] The dual-frequency radar system can transmit two different frequency signals at the transmitting end by carrying two dual-channel radars with a large span, and at the receiving end, the signal receiving and processing process of each frequency is independent and synchronous. The working frequency bands of the dual-frequency radar system used in the simulation of the present application are Ku band and Ka band, and the specific system parameters are as shown in Table 1.

[0023] In the present application, the transmitting bandwidth of the dual-frequency radar system is 50MHz, and the carrier frequencies are f0=14GHz and f1=28GHz linear frequency modulation signals, i.e.

[0024]

[0025]

[0026] Wherein, τ represents the distance time, T r represents the time width of the transmitted linear frequency modulation signal, K r is the frequency modulation slope of the linear frequency modulation signal, f0 and f1 are the carrier frequencies, s0(τ) represents the linear frequency modulation signal with the carrier frequency f0, s1(τ) represents the linear frequency modulation signal with the carrier frequency f1, and rect(·) represents the rectangular window function, i.e.

[0027]

[0028] Considering the antenna beam scanning process, the echo data of the target scene of the dual-frequency radar in the azimuth direction can be expressed as a convolution process of the antenna pattern and the target scattering coefficient, that is,

[0029] y = As + e (4)

[0030] where y ∈ C N×1 represents the azimuth echo data vector, s ∈ C N×1 represents the reflection coefficient vector of the target in the azimuth direction, e ∈ C N×1 represents an additive noise vector, N is the number of sampling points in the azimuth direction, that is, the number of pulses, and in the present application, the number of azimuth sampling points N = 500. A ∈ C N×N represents the dual-frequency radar antenna pattern measurement matrix ignoring the influence of beam scanning in and scanning out, and the construction mode is controlled by the hopping pattern obtained from the dual-frequency hopping process. Those skilled in the art should know that C here is a general symbol in mathematics representing the dimension of data.

[0031] Step two: dual-frequency hopping anti-jamming strategy

[0032] Since the suppressive jamming signal is directly related to the radar center frequency, the present application proposes an inter-pulse frequency hopping strategy to counter enemy suppressive jamming. First, the dual-frequency radar system transmits a single carrier frequency signal to detect the target scene, and when the enemy jammer detects the radar signal and interferes, our side adopts a hopping strategy to counter through jamming signal detection. In the present application, the span between the two carrier frequencies carried by the dual-frequency radar system reaches 14 GHz, far exceeding the coverage range of suppressive jamming, so it can effectively escape the interference range.

[0033] Since the suppressive jamming has the characteristic of high power, the present application adopts the energy detection method for jamming signal detection, and the decision expression of the energy detection method is as follows:

[0034]

[0035] where σ1 represents the initial corrected echo and noise power level, σ2 represents the power level of each pulse echo, and k represents the decision threshold, which can be appropriately adjusted according to the actual situation. When k is equal to 2, it means that the power level of the echo is 3 dB higher than the corrected power level, that is, it is considered to be jammed.

[0036] In the dual-frequency radar system, there is a carrier frequency hopping switch to control the switching between the carrier frequencies f0 and f1. When the system decides that there is jamming, frequency hopping is performed to escape the interference range, so the dual-frequency working time sequence can be expressed as

[0037]

[0038] Wherein f represents radar operating frequency, η represents carrier frequency hopping switch, when η = 0, it indicates that the radar works at f0 frequency, and when η = 1, it indicates that the radar works at f1 frequency.

[0039] By dual-frequency cycle hopping, the enemy suppressive jamming signal can be effectively resisted, and a dual-frequency hopping pattern can be obtained according to jamming detection and dual-frequency hopping process:

[0040] K = [K1, K2,..., K M ] (7)

[0041] Wherein K1 = 1 indicates that the dual-frequency radar transmits the first pulse, K m ,m = 2,..., M-1 indicates that hopping is carried out at the mth pulse position, K M =N indicates that detection is ended at the Nth pulse position, so the actual frequency hopping times are M-2 times.

[0042] In the application, M = 8, that is, the frequency hopping times are 6 times, the frequency hopping process adopts random frequency hopping, and the obtained dual-frequency hopping pattern is K = [1, 61, 143, 198, 245, 330, 413, 500].

[0043] Step three: constructing a dual-frequency antenna pattern

[0044] The dual-frequency antenna pattern A is spliced by two antenna patterns with carrier frequencies f0 and f1. Wherein the radar antenna pattern with carrier frequency f0 is defined as

[0045]

[0046] The radar antenna pattern with carrier frequency f1 is defined as

[0047]

[0048] Wherein L0 and L1 respectively represent the sampling point numbers of the antenna patterns with carrier frequencies f0 and f1.

[0049] According to the dual-frequency hopping pattern K obtained in step one, the dual-frequency antenna pattern A can be represented as:

[0050]

[0051] Wherein A0 (K m-1 :K m ,) represents the K m-1 ~K m row data of matrix A0, and A1 (K m :K m+1 ,) represents the K m ~K m+1Row data. The dual-frequency antenna pattern A constructed by formula (10) is substituted into formula (4) to obtain a dual-frequency echo data convolution model.

[0052] In the application, the number of antenna pattern sampling points of the simulation data is respectively L0=189 and L1=95.

[0053] Step four: adaptive dual-frequency sampling model

[0054] The application removes residual strip interference signals in the echo by constructing an adaptive dual-frequency sampling model. m -δ~K m Therefore, according to the disturbed pulse position K m -δ~K m A dual-frequency adaptive sampling matrix G is established, and the sampling matrix is constructed by a unit matrix I, and the specific construction mode is as follows:

[0055]

[0056] Wherein, δ represents the number of disturbed pulses before frequency hopping, and in the application, δ=4, which depends on the sensitivity of interference detection. The function represents that K m -δ to K m Row data. In the application, the data dimension of the constructed sampling matrix G is 476*500.

[0057] Therefore, the azimuth echo data based on the adaptive dual-frequency sampling model can be represented as:

[0058] Gy=GAs+Ge (12)

[0059] Step five: iterative solution

[0060] According to the adaptive dual-frequency sampling model constructed in step four, according to the weighted least square criterion, the azimuth echo data is defined as follows:

[0061]

[0062]

[0063]

[0064] Wherein θ n represents the position parameter of the n th pulse in the azimuth direction, n=1, 2,..., N, represents the target scattering coefficient estimation pointing to the azimuth angle θ n n ​represents a column vector of the dual-frequency antenna pattern A constructed by formula (10) pointing to the azimuth angle n , R represents a correlation matrix, (·) H represents a conjugate transpose, P = diag[p1, p2,..., p N ], wherein diag(·) represents constructing a diagonal matrix. In the present application, the iteration number is 8 times, and the azimuth echo data under the adaptive dual-frequency sampling model is iteratively solved through formula (13), (14) and (15), so that the residual strip interference can be removed, and the super-resolution estimation of the target scene can be obtained

[0065] The method of the present application counteracts the suppressive interference through the dual-frequency inter-pulse hopping strategy, and realizes the robust super-resolution imaging in the interference environment through the construction of the adaptive dual-frequency sampling model.

[0066] In order to prove the effectiveness of the present application, the following simulation experiment verification is carried out on the PC platform of 64-bit Matlab2020b. The dual-frequency radar system parameters used in the simulation are shown in Table 1. In the simulation data processing process, 10dB background noise is added to the echo scene, and the signal-to-interference ratio of the suppressive interference set in the simulation is-20dB.

[0067] Table 1 Dual-frequency radar system parameter table

[0068] System parameters Values carrier frequency f0 14 GHz carrier frequency f1 28 GHz Carrier frequency f0 beamwidth 5° Carrier frequency f1 beamwidth 2.5° Pulse repetition frequency 1000 Hz Bandwidth 50 MHz Scan speed 60° / s Imaging area -15°～15°

[0069] Figure 2 is the dual-frequency antenna pattern in the present application, which presents a spliced shape due to frequency hopping. Figure 3 is the simulation experiment result in the present application. Figure 3 (a) is the original scene set in the simulation, and 8 point targets are set in the scene. Figure 3 (b) is the suppressive interference echo data, and it can be seen that the effective echo data of the scene is completely submerged under the suppressive interference. Figure 3 (c) is the echo data obtained under the dual-frequency hopping model, and the target scene echo data can be observed. However, due to the timeliness problem of interference detection, there is residual strip noise in the echo. Figure 3 (d) is the super-resolution result of the suppressive interference echo data, and the effective estimation of the target scene cannot be obtained. Figure 3 (e) is the super-resolution result of the dual-frequency hopping echo data, and from the figure, the general content of the target scene can be seen. However, due to the existence of residual interference, the resolution performance is poor, and the two point targets at the bottom cannot be effectively resolved. Figure 3(f) The super-resolution result of the method of the present application effectively removes the suppressing interference firstly through the double-frequency hopping mode, and removes the influence of the residual interference through the adaptive double-frequency sampling model, so that the target scene can be effectively distinguished, and the distinguishing performance is greatly improved.

[0070] Those skilled in the art will appreciate that the embodiments described herein are presented for purposes of illustration and understanding of the principles of the present application and should not be interpreted as limiting the scope of the present application to these particular described embodiments. The present application can be modified and varied in various ways and can be used in conjunction with other applications and devices. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

Claims

1. A radar anti-jamming imaging method, characterized in that, include: S1, the two carrier frequencies of the dual-frequency radar system have a span that far exceeds the frequency band of the suppression interference coverage, and escape the interference range by switching between the two frequencies; S2. Employ an inter-pulse frequency switching strategy to counter enemy suppressive interference, and obtain the switching pattern K based on the switching process; S3. Construct the dual-band antenna pattern based on the jump pattern; S4. Construct a dual-frequency radar echo model based on the dual-frequency antenna pattern; S5. Based on the dual-frequency switching pattern, obtain the position of the interfered pulse, and thus establish an adaptive dual-frequency sampling model. S6. Based on the dual-frequency radar echo model and the adaptive dual-frequency sampling model, obtain the azimuth echo data based on the adaptive dual-frequency sampling model. S7. Based on the weighted least squares criterion, the azimuth echo data based on the adaptive dual-frequency sampling model is solved iteratively to achieve super-resolution imaging under interference conditions.

2. The radar anti-jamming imaging method according to claim 1, characterized in that, The dual-frequency radar system operates in the Ku-band and Ka-band frequencies, respectively.

3. The radar anti-jamming imaging method according to claim 1, characterized in that, The implementation process of step S2 is as follows: A1. The dual-frequency radar system transmits one of the carrier frequency signals to detect the target scene, and uses dual-frequency switching to counteract interference by detecting interference signals; A2. Based on interference detection and the dual-frequency hopping process, the dual-frequency hopping pattern is represented as follows: K=[K1,K2,...,K M ] Where K1 = 1 indicates that the dual-frequency radar transmits the first pulse, K m ,m=2,...,M-1 indicates that the transition occurs at the m-th pulse position, K M =N indicates that the detection ended at the Nth pulse position.

4. The radar anti-jamming imaging method according to claim 3, characterized in that, Interference signals are detected using the energy detection method.

5. The radar anti-jamming imaging method according to claim 4, characterized in that, The dual-frequency switching process uses random frequency hopping.

6. The radar anti-jamming imaging method according to claim 4, characterized in that, Step S3 is as follows: S31. Let f0 and f1 be two carrier frequencies. The radiation pattern of a radar antenna with carrier frequency f0 is defined as follows: The radar antenna pattern with carrier frequency f1 is defined as Where L0 and L1 represent the number of sampling points of the antenna pattern at carrier frequencies f0 and f1, respectively; S32. Based on the dual-frequency hopping pattern K, the dual-frequency antenna radiation pattern A is represented as follows: Among them, A0(K) m-1 :K m ,:) represents the K of matrix A0 m-1 ~K m Row data, A1(K) m :K m+1 ,:) represents the K of matrix A1 m ~K m+1 Row data.

7. The radar anti-jamming imaging method according to claim 6, characterized in that, The dual-frequency radar echo model constructed in step S4 is represented as follows: y = As + e Where y represents the azimuth echo data vector, s represents the reflection coefficient vector of the azimuth target, and e represents the additive noise vector.

8. The radar anti-jamming imaging method according to claim 7, characterized in that, Step S5 is as follows: Let K be the location of the interfered pulse obtained from the dual-frequency switching pattern K. m -δ~K m According to the position K of the interfered pulse m -δ~K m Establish a dual-frequency adaptive sampling matrix G: Where δ represents the number of pulses interfered with before the frequency jump, and the function... K represents the removal of the identity matrix I. m -δtoK m Row data.

9. The radar anti-jamming imaging method according to claim 8, characterized in that, The azimuth echo data based on the adaptive dual-frequency sampling model described in step S6 is represented as follows: Gy = GAs + Ge.

10. A radar anti-jamming imaging method according to claim 9, characterized in that, Step S6 specifically involves iteratively solving the azimuth echo data under the adaptive dual-frequency sampling model using the following formula to obtain the super-resolution estimate of the target scene. Where, θ n This represents the position parameter of the nth pulse in the azimuth direction, where n = 1, 2, ..., N. Indicates the azimuth angle θ n Target scattering coefficient estimation at point a(θ) n The symbol θ represents the azimuth angle in pattern A of the dual-band antenna. n , where R represents the column vector, and (·) H To represent the conjugate transpose, P = diag[p1, p2, ..., p N ], diag(·) represents constructing a diagonal matrix.

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