Scattered wave interference method based on position modulation and gain modulation

Abstract

The present invention discloses a scattered wave interference method based on position modulation and gain modulation, and the implementation steps are: phase modulating the time domain signal of the radar intercepted by the jammer, position modulating the phase modulated signal, gain modulating the position modulated signal, and forwarding the gain modulated signal to the jammer irradiation area to form scattered wave interference. The present invention can be used for the scattered wave interference of SAR, adopts the range modulation coefficient and the azimuth modulation coefficient to respectively perform position modulation on the scattered wave interference signal, and then uses the gain modulation coefficient to perform gain modulation on the scattered wave interference signal, which not only realizes the coverage of the interference image to the target area, but also makes the brightness of the interference image close to the ambient brightness, which increases the difficulty of SAR identifying the scattered wave interference from the imaging result.

Description

Technical Field

[0001] The present invention belongs to the field of signal processing technology, and further relates to a scattered wave interference method based on position modulation and gain modulation in the field of radar signal processing technology. The present invention can be used to interfere with synthetic aperture radar SAR (Synthetic Aperture Radar), and by jointly modulating the position and gain of the scattered wave interference signal, an interference image with variable brightness is generated at a specific position in the SAR imaging area. Background Art

[0002] Scattered wave interference is a type of deception interference. It refers to the jammer receiving the signal transmitted by the radar, modulating the signal and projecting it to an area with false ground object information, and then scattering it from the ground object. The scattered wave interference signal is mixed with the original echo signal of the radar and received by the radar, thereby destroying the radar's recognition of the target. Scattered wave interference is usually used to interfere with SAR. The existing scattered wave interference technology analyzes the interference effect of scattered wave interference in the range and azimuth directions of SAR, and also discusses the position offset of the interference image and the problem of image defocus. However, the position of the interference image generated is fixed, that is, the interference image generated by the existing scattered wave interference technology appears in the SAR imaging result at the same time as the target area. The interference image cannot cover the target area, resulting in SAR still being able to identify the target area.

[0003] Harbin Engineering University has disclosed a method for generating deceptive interference signals based on image inversion technology in its patent document "Synthetic Aperture Radar (SAR) Scene Deception Interference Method Based on Image Inversion" (Application Number: CN 202210177716.3; Application Publication Number: CN 114609598A). The generated deceptive interference signal contains the scattering information of the original image, similar to the scattered wave interference signal carrying the scattering information of the ground object after being scattered by the ground object in the area illuminated by the jammer. This method uses the CS inversion algorithm for the template of the SAR interference image, and inverts the SAR interference image template to generate a deceptive interference signal. The false interference image generated by the deceptive interference signal is consistent with the contour of the real target image, and the focusing effect of the interference image is good. However, the method still has the disadvantage that the SAR deceptive interference signal is generated only according to the image inversion algorithm, while the modulation of the interference signal is ignored, resulting in the position of the interference image generated by the deceptive interference signal in the SAR imaging result cannot be changed, that is, the interference image and the target area to be protected appear in the SAR imaging result at the same time, the interference image cannot accurately cover the target area, and the SAR can still identify the target area.

[0004] Xidian University disclosed a method for SAR scattering wave interference in its patent application "Improved SAR scattering wave interference method based on floating platform" (application number: CN 201310653909.2; application publication number: CN 103616670A). This method performs phase modulation and gain modulation on the intercepted radar signal according to the process difference between the scattering wave interference signal and the radar echo signal to form an interference signal, which is then irradiated to the target area through a jammer, and superimposed with the target echo after being scattered by the target, thereby achieving scattering wave interference. However, the method still has the disadvantage that it only expands the distance range of the interference image, while ignoring the control of the interference image position, resulting in the inability to flexibly change the position of the interference image according to demand, so that the interference image cannot cover the target area. Summary of the invention

[0005] The purpose of the present invention is to provide a scattered wave interference method based on position modulation and gain modulation in view of the shortcomings of the above-mentioned prior art, so as to solve the problem that the existing scattered wave interference technology cannot produce an interference image at the position of the target area, and the brightness of the interference image is much greater than the brightness of the environment where the target is located in the SAR imaging result.

[0006] The idea of ​​realizing the purpose of the present invention is as follows: the present invention adopts the range modulation coefficient and the azimuth modulation coefficient to respectively modulate the position of the scattered wave interference signal, thereby overcoming the deficiency that the interference image generated by the prior art cannot cover the target area. The range position and azimuth position of the interference image generated after the position modulation can be the same as the position of the target area, so that the interference image appears at the position of the target area to be protected in the SAR imaging result, thereby solving the coverage of the target area, so that the SAR can only identify the interference image in the target area, thereby protecting the target area. The present invention uses the gain modulation coefficient to gain modulate the scattered wave interference signal, so that the brightness of the interference image of the generated scattered wave interference signal in the SAR imaging result is controllable, that is, the brightness of the interference image is controlled by the gain coefficient according to the background environment of the target area, thereby overcoming the defect that the brightness of the interference image generated by the prior art is much higher than the ambient brightness and is therefore easily recognized by the radar side, and the brightness of the interference image generated after the gain modulation is close to the ambient brightness, thereby improving the realism of the interference image.

[0007] The specific steps of the present invention include the following:

[0008] Step 1, the jammer intercepts the radar time domain signal:

[0009] Use the jammer to conduct real-time reconnaissance and reception of the radar time domain signals irradiating the protected area, and intercept the radar time domain signals;

[0010] Step 2: Phase modulate the intercepted radar time domain signal according to the following formula:

[0011]

[0012] Among them, s J1 (t r ,t a ) represents the phase modulated signal, s(t r ,t a ) represents the distance to fast time t r is the row vector, the azimuth slow time t a is the radar time domain signal matrix composed of column vectors, * represents the convolution operation, δ(·) represents the impulse function, R P (t a ) represents the instantaneous slant distance of the center point of the target area detected by the jammer, R I (t a ) represents the instantaneous slant range of the center point of the jammer illumination area detected by the jammer, exp(·) represents the exponential operation with the natural constant e as the base, j represents the symbol of the imaginary unit, π represents the circumference of a circle, and λ represents the wavelength of the radar transmission signal;

[0013] Step 3: Perform position modulation on the phase modulated signal according to the following formula:

[0014]

[0015] Among them, s J2 (t r ,t a ) represents the position modulated signal, s J1 (t r ,t a ) represents the phase modulated signal, M1 represents the distance position modulation coefficient, and M2 represents the azimuth position modulation coefficient;

[0016] Step 4: Perform gain modulation on the position modulated signal according to the following formula:

[0017] s J3 (t r ,t a )=s J2 (t r ,t a )·G F

[0018] Among them, s J3 (t r ,t a ) represents the gain modulated signal, G F represents the gain modulation coefficient;

[0019] Step 5, forward the gain modulated signal to the jammer illumination area to form scattered wave interference.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] First, the present invention adopts the range modulation coefficient and the azimuth modulation coefficient to respectively perform position modulation on the scattered wave interference signal, thereby overcoming the deficiency that the interference image generated by the prior art cannot cover the target area. The present invention not only reduces the distortion of the interference scene generated by the traditional scattered wave interference signal in the range and azimuth directions, but also realizes the effective coverage of the interference image to the real scene.

[0022] Second, the present invention utilizes a gain modulation coefficient to perform gain modulation on the scattered wave interference signal, thereby overcoming the defect that the brightness of the interference image generated by the prior art is much higher than the ambient brightness and is therefore very easy to be identified by the radar. The scattered wave interference method of the present invention can obtain a more realistic interference scene image, which not only increases the difficulty of SAR identifying the interference image formed by the scattered wave interference from the entire imaging result, but also reduces the demand for interference power of the jammer. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a flow chart of the present invention;

[0024] Figure 2 A schematic diagram of a scene for performing scattered wave interference in the present invention;

[0025] Figure 3 This is a simulation diagram of the present invention performing scattered wave interference on a point target;

[0026] Figure 4 This is a simulation diagram of the scattered wave interference on the SAR imaging scene according to the present invention. DETAILED DESCRIPTION

[0027] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0028] Reference Figure 1 , the implementation steps of the embodiments of the present invention are further described in detail.

[0029] Step 1: The jammer intercepts the radar time domain signal.

[0030] The jammer is used to conduct real-time reconnaissance and reception of radar time domain signals irradiating the protected area, and the radar time domain signals are intercepted.

[0031] Step 2: Phase modulate the radar time domain signal.

[0032] See also Figure 2 , further describes the scenario of the phase modulation process of radar time domain signal. Figure 2 The S in the equation represents the airborne SAR. The flight path of the platform on which the SAR is located is an ideal straight line and flies at a constant speed v. a =0, and the projection position of the platform on the ground at this time is taken as the origin of the coordinate system. The x-axis is parallel to the platform track and the velocity direction of the platform is taken as the positive direction. The z-axis is perpendicular to the ground and the upward direction is the positive direction. The y-axis is determined by the right-hand rule. Figure 2 J in the figure represents the jammer, P represents the center point of the target area, I represents the center point of the jammer irradiation area, and F represents the center point of the false image. Figure 2 The β in represents the downward viewing angle of the radar beam.

[0033] The jammer detects the instantaneous slant range of the center point of the target area The instantaneous slant range of the center point of the jammer's illumination area is Among them, |·| means taking the absolute value, The slant range vector from the radar to the center point of the target area, Represents the slant range vector from the center of the target area to the radar, represents the slant range vector from the radar to the jammer, Represents the slant range vector from the jammer to the center of the jammer's illumination area, Represents the slant range vector from the center point of the jammer's illumination area to the radar.

[0034] According to the following formula, the intercepted radar time domain signal is phase modulated:

[0035]

[0036] Among them, s J1 (t r ,t a ) represents the signal data after phase modulation, s(t r ,t a ) represents the distance to fast time t r is the row vector, the azimuth slow time t a is a radar time domain signal matrix composed of column vectors, * represents the convolution operation, δ(·) represents the impulse function, exp(·) represents the exponential operation with the natural constant e as the base, j represents the imaginary unit symbol, π represents the circumference of the circle, and λ represents the wavelength of the radar transmission signal. The interference image generated by the phase modulated scattered wave interference signal has a smaller image defocusing degree in the range direction than that before modulation, thereby ensuring the realism of the interference image in the range direction.

[0037] Step 3: Perform position modulation on the phase modulated signal.

[0038] In the SAR imaging results, the interference image generated by the phase-modulated scattered wave interference signal appears at the same time as the target area to be protected, that is, the interference image cannot cover the area to be protected. The interference image obtained by position modulation of the phase-modulated interference signal can accurately image the target area.

[0039] According to the following formula, the phase modulated signal is position modulated:

[0040]

[0041] Among them, s J2 (t r ,t a ) represents the signal data after position modulation, s J1 (t r ,t a ) represents the signal data after phase modulation, M1 represents the range position modulation coefficient, M2 represents the azimuth position modulation coefficient, and the modulation coefficients M1 and M2 independently control the range and azimuth positions of the false image, respectively, so that the scattered wave interference signal after position modulation is imaged at the position of the target area, thereby ensuring that the interference image can cover the target area to be protected.

[0042] The distance position modulation coefficient M1 is obtained by the following formula:

[0043] M1=tanβ·(y F -y F ')

[0044] Where tan represents the tangent operation, β represents the radar beam angle detected by the jammer, and y F Indicates the distance position of the interference image before adjustment, y F 'Indicates the distance position of the interference image after adjustment.

[0045] The azimuth position modulation coefficient M2 is obtained by the following formula:

[0046] M2=k·(x F -x F ')

[0047] Wherein, k represents a constant coefficient corresponding to the SAR imaging algorithm, and in the embodiment of the present invention, the value is -5;

[0048] x F Indicates the azimuth position of the interference image before adjustment, x F 'Indicates the azimuth position of the interference image after adjustment.

[0049] Step 4: Perform gain modulation on the position modulated signal.

[0050] The image brightness of the interference image generated by the position-modulated scattered wave interference signal is significantly different from the surrounding environment, which makes it easy for the radar to identify the interfered area. The interference signal after position modulation is gain modulated, and the brightness of the interference image obtained can be consistent with the brightness of the environment in which it is located.

[0051] According to the following formula, the position modulated signal is gain modulated:

[0052] s J3 (t r ,t a )=s J2 (t r ,t a )·G F

[0053] Among them, s J3 (t r ,t a ) represents the signal data after gain modulation, s J2 (t r ,t a ) represents the signal data after position modulation, G F represents the gain modulation coefficient. The change of this coefficient value can control the brightness of the interference image in the SAR imaging result. According to the G calculated in this step F It can ensure that the brightness of the interference image is consistent with the brightness of the environment where the real target is located.

[0054] The gain modulation coefficient G F It is obtained from the following formula:

[0055]

[0056] Among them, ρ P represents the power density of the radar signal detected by the jammer at the center of the target area, σ P represents the scattering coefficient at the center of the target area detected by the jammer, σ I It represents the scattering coefficient at the center of the jammer's illumination area detected by the jammer, P J Indicates the jammer transmission power, G J represents the jammer transmitting antenna gain, R JI Indicates the distance between the jammer and the center of the jammer's illumination area, R IS Indicates the distance between the center of the jammer's illumination area and the SAR, R SP Indicates the distance between the SAR and the center of the target area.

[0057] Step 5, forward the gain modulated signal to the jammer illumination area to form scattered wave interference.

[0058] The interference signal s obtained after gain modulation J3 (t r ,t a ) is forwarded to the jammer's illuminated area, and the SAR simultaneously receives the ground object scattered echo in the illuminated area and the echo signal in the target area, so that the real scene radar echo signal and the jamming signal are superimposed, thereby realizing the scattered wave interference to the airborne SAR. At the same time, the interference image generated by the modulated scattered wave interference signal is not only highly realistic, but also can cover the target area to be protected, and the brightness of the interference image is close to the brightness of the environment to which the target area belongs, making it difficult for the airborne SAR to identify the target area, greatly improving the interference efficiency of the scattered wave interference to the airborne SAR.

[0059] The effect of the present invention is further described below in conjunction with simulation experiments:

[0060] 1. Simulation experiment conditions:

[0061] The hardware platform of the simulation experiment of the present invention is: the processor is Intel i5 7200U CPU, the main frequency is 2.5GHz, and the memory is 4GB.

[0062] The software platforms for the simulation experiment of the present invention are: Windows 10 operating system and MATLAB R2021b.

[0063] The SAR system working mode used in this simulation is positive side view, the initial coordinates of the radar platform are (0,0,5000)m, the wavelength of the transmitted signal λ=0.3m, the pulse width is 5μs, the angle of view under the beam β=45°, and the flight speed v=100m / s. The range resolution of the SAR imaging algorithm is 5m, and the azimuth resolution is 2m. The coordinates of the jammer J are set to (10,10000,0)m, and the coordinates of the center point I of the jammer irradiation area are (20,9800,0)m. The gain of the jammer receiving antenna is 10dB, and the gain of the transmitting antenna is 10dB. In this simulation, the number of sampling points in the range is selected as 1024, and the number of sampling points in the azimuth is selected as 512. At the same time, the coordinates of the center point P of the target area are set to (0,10000,0)m.

[0064] 2. Simulation content and results analysis:

[0065] There are two simulation experiments of the present invention.

[0066] The simulation experiment 1 of the present invention adopts the method of the present invention and an existing technology to interfere with the scattered waves of the point target P(0,10000,0)m set in the simulation conditions, and obtains the SAR imaging effect diagram containing the false point target F as shown in the figure Figure 3 shown.

[0067] The simulation experiment 2 of the present invention adopts the method of the present invention and an existing technology to interfere the SAR imaging scene with scattered waves, and obtains the SAR imaging effect diagram including the interference image as shown in FIG. Figure 4 shown.

[0068] The prior art used in the two simulation experiments of the present invention refers to:

[0069] Xidian University proposed a method for jamming SAR scattered waves in its patent application “An improved SAR scattered wave jamming method based on a floating platform” (application number: CN 201310653909.2; application publication number: CN 103616670A).

[0070] Combine the following Figure 3 and Figure 4 The simulation diagram of the present invention is further described.

[0071] exist Figure 3 The horizontal coordinate represents the distance position in meters, and the vertical coordinate represents the azimuth position in meters. Figure 3 (a) is the imaging result after the scattered wave interference of the point target P using the existing technology. Figure 3 (b) is the imaging result after the scattered wave interference of the point target P using the method of the present invention.

[0072] Depend on Figure 3 (a) It can be seen that the distance and azimuth position differences between the false point target F (9825.67, 22.47) generated by the prior art and the real point target P (10004.8, -0.13) are 179.13m and 22.6m respectively, both of which are greater than the resolution of the SAR imaging algorithm. This is mainly because this method only performs phase modulation on the scattered wave interference signal without position modulation, which makes it impossible for the false point target to be imaged at the real point target position.

[0073] Depend on Figure 3 (b) It can be seen that the range error between the false point target F (10002.3, -0.13) generated by the scattered wave interference technology of the present invention and the real point target P (10004.8, -0.13) is 2.5m, which is less than the range resolution of the SAR imaging algorithm, and the azimuth error is 0.0001m, which is less than the azimuth resolution of the SAR imaging algorithm. Therefore, the false point target F completely covers the point target P in the SAR imaging result map.

[0074] Depend on Figure 3 (a) and Figure 3From the comparison of (b), it can be seen that the position difference between the false point target F and the real target P generated by the scattered wave interference method of the present invention is smaller than that of the scattered wave interference method of the prior art, which means that the scattered wave interference generated by the method of the present invention can be imaged at the position of the point target P, thereby protecting the real target P, proving that the scattered wave interference method of the present invention is superior to the scattered wave interference method of the prior art in terms of interference performance.

[0075] exist Figure 4 The horizontal coordinate represents the distance position in meters, and the vertical coordinate represents the azimuth position in meters. Figure 4 (a) is the SAR imaging result before interference. Figure 4 (b) is an interference image carrying ground object scattering information after scattered wave interference using existing technology. Figure 4 (c) is an interference image carrying ground object scattering information after scattered wave interference using the method of the present invention. Figure 4 (d) is the imaging result after the scattered wave interference is performed on the target area to be protected using the method of the present invention.

[0076] Depend on Figure 4 (a) It can be seen that the imaging range of SAR in range is [9600m, 10300m], and the imaging range in azimuth is [-350m, 350m]. The coordinates of the center point P of the target area to be protected are (230, 10050), and the coordinates of the center point I of the jammer irradiation area are (85, 9820). The areas of the target area to be protected and the jammer irradiation area are equal.

[0077] Depend on Figure 4 (b) It can be seen that the coordinates of the center point of the interference image generated by the prior art are (0,9480), and the distance between the interference image and the area to be protected is too large, so the interference image cannot be imaged at the position of the area to be protected.

[0078] Depend on Figure 4 (c) It can be seen that the coordinates of the center point of the interference image generated by the scattered wave interference technology of the present invention are (230, 10050), and the false image can be accurately imaged at the position of the target area.

[0079] Depend on Figure 4 (d) It can be seen that the interference image generated by the scattered wave interference technology of the present invention can accurately cover the target area, and the brightness of the interference image is similar to the brightness of the environment where the target area is located. At this time, the interference scene is superimposed on the real scene, so that the target characteristics of the real scene are weakened by the interference image, and the brightness of the interference image is slightly higher than the brightness of the real target area, so the target area will be displayed as an interference image when SAR is imaging.

[0080] The above simulation results show that after the scattered wave interference signal is position modulated and gain modulated by the method of the present invention, the interference image generated by the scattered wave interference signal in the SAR imaging result is highly realistic, covers the target area to be protected, and the brightness of the interference image is similar to the brightness of the environment where the target area is located, which increases the difficulty of SAR to identify the target area, thereby improving the interference efficiency of the scattered wave interference.

Claims

1. A scattered wave interference method based on position modulation and gain modulation, characterized in that: Position modulation and gain modulation are respectively performed on the radar time domain signal intercepted by the jammer, and the gain-modulated signal is forwarded to the jammer illumination area to form scattered wave interference; the steps of the jamming method include the following: Step 1, the jammer intercepts the radar time domain signal: Use the jammer to conduct real-time reconnaissance and reception of the radar time domain signals irradiating the protected area, and intercept the radar time domain signals; Step 2: Phase modulate the intercepted radar time domain signal according to the following formula: Among them, s J1 (t r ,t a ) represents the phase modulated signal, s(t r ,t a ) represents the distance to fast time t r is the row vector, the azimuth slow time t a is the radar time domain signal matrix composed of column vectors, * represents the convolution operation, δ(·) represents the impulse function, R P (t a ) represents the instantaneous slant distance of the center point of the target area detected by the jammer, R I (t a ) represents the instantaneous slant range of the center point of the jammer illumination area detected by the jammer, exp(·) represents the exponential operation with the natural constant e as the base, j represents the symbol of the imaginary unit, π represents the circumference of a circle, and λ represents the wavelength of the radar transmission signal; Step 3: Perform position modulation on the phase modulated signal according to the following formula: Among them, s J2 (t r ,t a ) represents the position modulated signal, s J1 (t r ,t a ) represents the phase modulated signal, M1 represents the distance position modulation coefficient, and M2 represents the azimuth position modulation coefficient; Step 4: Perform gain modulation on the position modulated signal according to the following formula: s J3 (t r ,t a )=s J2 (t r ,t a )·G F Among them, s J3 (t r ,t a ) represents the gain modulated signal, G F represents the gain modulation coefficient; Step 5, forward the gain modulated signal to the jammer illumination area to form scattered wave interference.

2. The scattered wave interference method based on position modulation and gain modulation according to claim 1 is characterized in that: The distance position modulation coefficient M1 described in step 3 is obtained by the following formula: M1=tanβ·(y F -y F ') Where tan represents the tangent operation, β represents the radar beam angle detected by the jammer, and y F represents the distance position of the interference image before range modulation, y F ' represents the distance position of the interference image after range modulation.

3. The scattered wave interference method based on position modulation and gain modulation according to claim 1 is characterized in that: The azimuth position modulation coefficient M2 described in step 3 is obtained by the following formula: M2=k·(x F -x F ') Where k represents the constant coefficient corresponding to the SAR imaging algorithm, and its value is -5; x F represents the azimuth position of the interference image before azimuth modulation, x F ' represents the azimuth position of the interference image after azimuth modulation.

4. The scattered wave interference method based on position modulation and gain modulation according to claim 1, characterized in that: The gain modulation coefficient G in step 4 F It is obtained from the following formula: Among them, ρ P represents the power density of the radar signal detected by the jammer at the center of the target area, σ P represents the scattering coefficient at the center of the target area detected by the jammer, σ I It represents the scattering coefficient at the center of the jammer's illumination area detected by the jammer, P J Indicates the jammer transmission power, G J represents the jammer transmitting antenna gain, R JI Indicates the distance between the jammer and the center of the jammer's illumination area, R IS Indicates the distance between the center of the jammer's illumination area and the SAR, R SP Indicates the distance between the SAR and the center of the target area.

Images