SAR cosine phase modulation deception jamming method based on electromagnetic metasurface technology

Abstract

The invention discloses an SAR (Synthetic Aperture Radar) cosine phase modulation deception jamming method based on an electromagnetic metasurface technology, and relates to the technical field of signal processing. An II-shaped metal branch structure is adopted, and the length of a top metal branch is ingeniously set to be greater than that of a bottom, so that the control capability of a metasurface unit on electromagnetic waves is enhanced, and the deception jamming effect is improved. The phase, the amplitude and the polarization state of the electromagnetic waves are comprehensively regulated and controlled, so that the metasurface can adapt to the electromagnetic waves with different frequencies and different polarization directions; meanwhile, gaps are formed in the metal branch structures, variable capacitance diodes are arranged, and continuous change regulation and control on the phase of incident electromagnetic waves are achieved; therefore, the electromagnetic metasurface can perform continuous change regulation and control on phases of electromagnetic waves with different frequencies and different polarization directions, the uncertainty of the electromagnetic metasurface in modulation is screened out, continuous phase regulation and control can be realized, and the interference effect on an SAR radar is improved.

Description

Technical Field

[0001] The present invention relates to the field of signal processing technology, and in particular to a SAR cosine phase modulation deception jamming method, device, equipment and medium based on electromagnetic metasurface technology. Background Art

[0002] The Synthetic Aperture Radar (SAR) system has the capability of all-weather, long-range, high-resolution imaging, posing a serious threat to the military deployment, combat status, and wartime survival of important targets. Therefore, exploring effective interference countermeasures against the SAR system has become a key research direction for anti-space / air-based reconnaissance.

[0003] Traditional SAR jamming methods can be divided into active jamming and passive jamming. Active jamming uses an active jammer to transmit jamming signals to the SAR system. This method generally requires high-power jammers and sensors, which is costly and has the risk of exposing the target area. Passive jamming does not actively transmit signals, but generates false echoes through passive devices. However, passive jamming lacks flexibility, that is, once the passive jammer is processed, it is difficult to change its technical parameters in real time according to changes in the environment, and it is difficult to finely modulate the radar echo.

[0004] The emergence and development of electromagnetic metasurface technology provides a good opportunity to solve the problems of active interference and passive interference; metasurface technology can be used to achieve precise control of important parameters such as radar echo delay, polarization, phase, frequency, amplitude, etc. without actively transmitting signals; the current electromagnetic metasurfaces are usually optical metasurfaces, which use subwavelength microstructures to control the polarization, phase, amplitude, frequency and other characteristics of electromagnetic waves, and have wide applications in plane lenses, holographic optics, ultra-high resolution imaging and other fields; but optical metasurfaces are easily affected by uncertain factors in the environment. When modulating the phase, amplitude and polarization state of the incident electromagnetic wave, the modulation uncertainty is usually high, which makes it difficult to achieve continuous modulation when modulating the electromagnetic wave, so that the interference effect on SAR radar is poor. Summary of the invention

[0005] The embodiment of the present invention provides a SAR cosine phase modulation deception jamming method based on electromagnetic metasurface technology, which can solve the problem in the prior art that the current methods usually have high modulation uncertainty, making it difficult to achieve continuous modulation when modulating electromagnetic waves, resulting in poor interference effect on SAR radar.

[0006] The embodiment of the present invention provides a SAR cosine phase modulation deception jamming method based on electromagnetic metasurface technology, comprising the following steps:

[0007] Designing a phase-controlled metasurface and installing it on the surface of the protection target; the phase-controlled metasurface is composed of a plurality of metasurface units arranged in an array;

[0008] The metasurface unit is a II-shaped metal branch structure, and the length of the metal branch at the top of the metal branch structure is longer than the length of the metal branch at the bottom, which is used to control the phase, amplitude and polarization state of the electromagnetic wave incident on the metasurface unit;

[0009] The two vertical metal branches of the metal branch structure are both provided with gaps, and a varactor is provided at the gap of one of the metal branches; by changing the voltage applied to the top metal branch and the bottom metal branch of the metal branch structure, the voltage on both sides of the varactor is changed, and the equivalent capacitance of the varactor is adjusted in real time, so that the phase of the electromagnetic wave incident on the metasurface unit is adjusted to be continuously changed;

[0010] The phase-controlled metasurface receives the transmission signal of the SAR radar, performs cosine phase modulation on the transmission signal and reflects it, and deceives and interferes with the SAR radar through the reflected signal.

[0011] Preferably, performing cosine phase modulation on the transmission signal comprises:

[0012] When the transmission signal of the SAR radar is incident on the phase-controlled metasurface, the voltage on both sides of the varactor diode is changed by changing the voltage applied to the top metal branch and the bottom metal branch of the metal branch structure, so as to adjust the equivalent capacitance of the varactor diode in real time, and perform slow-time cosine phase modulation on the phase of the electromagnetic wave signal incident on the phase-controlled metasurface to obtain a cosine phase modulated signal.

[0013] The cosine phase modulation signal is:

[0014] p(t m )=exp[jβcos(2πf m t m )];

[0015] Where: p(t m ) represents the cosine phase modulation signal; β represents the modulation index of the cosine phase modulation signal; f m represents the modulation frequency of the cosine phase modulation signal; t m Indicates slow time.

[0016] Preferably, the forming of the reflection signal comprises:

[0017] The phase-controlled metasurface on the stationary target receives the transmission signal of the SAR radar and performs slow-time cosine phase modulation on the transmission signal to obtain a cosine phase modulated signal;

[0018] The spectrum of the cosine phase modulated signal in the frequency domain is extracted, and the spectrum of the cosine phase modulated signal is bidirectionally and multiple times shifted in the azimuth direction of the protected target. The spectrum of the cosine phase modulated signal is replaced with multiple copied different spectra in sequence to form multiple harmonic components of the cosine phase modulated signal, and the multiple harmonic components are synthesized into a cosine phase interference signal, which is a reflected signal.

[0019] Preferably, the cosine phase interference signal is:

[0020]

[0021] Among them: J n (β) represents the first-kind n-th-order Bessel function; f m represents the modulation frequency of the cosine phase modulated signal; f a +nf m Indicates the spectrum offset of the cosine phase interference signal.

[0022] Preferably, the deceptive interference to the SAR radar includes:

[0023] The SAR radar receives the cosine phase interference signal and performs range matching filtering, range migration correction and clutter suppression on the interference signal, forming a two-way false target string along the azimuth of the protected target in the interference image, thereby achieving deceptive interference to the SAR radar;

[0024] The offset of the nth false target in the azimuth dimension is:

[0025]

[0026] Where: f m represents the modulation frequency of the cosine phase modulation signal; γ represents the Doppler modulation frequency.

[0027] The embodiment of the present invention also provides a SAR cosine phase modulation deception jamming device based on electromagnetic metasurface technology, including:

[0028] A design module, used for designing a phase-controlled metasurface and installing it on a protected target surface; the phase-controlled metasurface is composed of a plurality of metasurface units arranged in an array;

[0029] The metasurface unit is a II-shaped metal branch structure, and the length of the metal branch at the top of the metal branch structure is longer than the length of the metal branch at the bottom, which is used to control the phase, amplitude and polarization state of the electromagnetic wave incident on the metasurface unit;

[0030] The two vertical metal branches of the metal branch structure are both provided with gaps, and a varactor is provided at the gap of one of the metal branches; by changing the voltage applied to the top metal branch and the bottom metal branch of the metal branch structure, the voltage on both sides of the varactor is changed, and the equivalent capacitance of the varactor is adjusted in real time, so that the phase of the electromagnetic wave incident on the metasurface unit is adjusted to be continuously changed;

[0031] SAR radar jammer module, the phase-controlled metasurface receives the transmission signal of the SAR radar, performs cosine phase modulation on the transmission signal and reflects it, and deceives and jams the SAR radar through the reflected signal.

[0032] An embodiment of the present invention further provides an electronic device, including a memory and a processor;

[0033] The memory is used to store computer programs;

[0034] The processor is used to implement the steps of the SAR cosine phase modulation deception interference method based on electromagnetic metasurface technology as described above when executing the computer program stored in the memory.

[0035] An embodiment of the present invention further provides a computer-readable storage medium for storing a computer program, which, when executed by a processor, implements the steps of the SAR cosine phase modulation deception interference method based on electromagnetic metasurface technology as described above.

[0036] The embodiment of the present invention provides a SAR cosine phase modulation deception jamming method based on electromagnetic metasurface technology. Compared with the prior art, the method has the following beneficial effects:

[0037] The present invention adopts a II-shaped metal branch structure and cleverly sets the length of the top metal branch to be longer than the bottom. This design not only enhances the ability of the metasurface unit to control electromagnetic waves, but also realizes comprehensive regulation of the phase, amplitude and polarization state of the electromagnetic waves, so that the metasurface can adapt to electromagnetic waves of different frequencies and polarization directions. At the same time, gaps are opened on the metal branch structure and varactor diodes are set to achieve continuous change regulation of the phase of the incident electromagnetic wave. Therefore, the electromagnetic metasurface can continuously change the phase of electromagnetic waves of different frequencies and polarization directions, eliminates the uncertainty of the electromagnetic metasurface in modulation, and can achieve continuous phase regulation, thereby improving the interference effect on SAR radar.

[0038] Moreover, the phase-controlled metasurface can not only receive the transmission signal of the SAR radar, but also perform cosine phase modulation and reflection on the transmission signal. Such reflected signal is significantly different from the original signal, thus being able to cause deceptive interference to the SAR radar. It has the characteristics of strong concealment and good interference effect, and can effectively protect the target from detection and identification by the SAR radar. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A schematic diagram of the overall process of the SAR cosine phase modulation deception jamming method based on electromagnetic metasurface technology provided by an embodiment of the present invention;

[0040] Figure 2 A schematic diagram of an interference model of a SAR cosine phase modulation deception interference method based on electromagnetic metasurface technology provided in an embodiment of the present invention;

[0041] Figure 3 A schematic diagram of the electromagnetic metasurface design of the SAR cosine phase modulation deception jamming method based on the electromagnetic metasurface technology provided in an embodiment of the present invention; (a) is a schematic diagram of the formed metasurface array, and (b) is a schematic diagram of the metasurface array test;

[0042] Figure 4 A schematic diagram of the original SAR imaging result without interference using the SAR cosine phase modulation deception jamming method based on the electromagnetic metasurface technology provided by an embodiment of the present invention;

[0043] Figure 5 A schematic diagram of modulation phase distribution of a SAR cosine phase modulation deception jamming method based on electromagnetic metasurface technology provided in an embodiment of the present invention;

[0044] Figure 6 A schematic diagram of interference imaging results of a SAR cosine phase modulation deception interference method based on electromagnetic metasurface technology provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0045] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0046] See also Figure 1 The embodiment of the present invention provides a SAR cosine phase modulation deception jamming method based on electromagnetic metasurface technology, comprising the following steps:

[0047] Step 1: Construction of SAR imaging interference model based on electromagnetic metasurface.

[0048] Step 2: Design of electromagnetic metasurface.

[0049] Step 3: Establishment and generation of cosine phase modulation signal model based on electromagnetic metasurface.

[0050] Step 4: SAR imaging processing and imaging interference effect analysis.

[0051] The construction of the SAR imaging interference model in step 1 is as follows:

[0052] SAR imaging interference model based on electromagnetic metasurface Figure 2 As shown in the figure, a two-dimensional rectangular coordinate system XOR is established on the SAR data acquisition plane. The SAR system moves from the origin O along the X-axis at a constant speed V, and the distance direction perpendicular to the flight trajectory to the center of the observation scene is recorded as the R axis. The hypersurface is placed on the surface p of the protected target in the observation scene. t (x0, R0), where (x0, R0) represents the target position; the instantaneous slant range between the SAR system and the protected target can be expressed as:

[0053]

[0054] Where: tm represents the azimuth slow time; R B =minR(t m ).

[0055] Assume that the LFM signal transmitted by the SAR system is expressed as:

[0056]

[0057] in: Indicates distance to fast time; T r represents the pulse width; rect(·) represents the rectangular function; f0 represents the center frequency of the transmitted signal; μ represents the modulation frequency of the transmitted LFM signal.

[0058] The metasurface on the target surface intercepts the signal transmitted by the radar and performs interference modulation on it. Since the metasurface itself does not actively radiate high-power signals to the outside world, it avoids the shortcomings of traditional active interference methods, which are high cost and easy to expose the target area. Under the control of external bias voltage, the time metasurface can realize real-time modulation of the phase and amplitude information of the transmitted signal, and forward the modulated signal to the SAR imaging system. The SAR system performs detection and demodulation on the received interference echo signal, and its complex baseband interference signal can be expressed as:

[0059]

[0060] Where: p(t m ) represents a modulation signal generated based on the metasurface; represents the unmodulated echo signal, and the expression is:

[0061]

[0062] Where: A represents the complex reflection coefficient of the target; T a represents the synthetic aperture time; λ and c represent the wavelength and the speed of light, respectively.

[0063] Since the phase or amplitude information in the SAR echo signal is destroyed by the modulation signal, false targets or defocused images appear in the SAR image after imaging processing, effectively realizing SAR imaging interference.

[0064] The design of the electromagnetic metasurface in step 2 is specifically as follows:

[0065] First, a gap metal branch structure is designed, and a lumped element, a varactor diode, is added between the metal gaps. The voltage on both sides of the varactor diode is adjusted to change the equivalent capacitance, so that the phase of the incident electromagnetic wave can be continuously changed. The designed electromagnetic metasurface unit structure and array structure are shown in Figure 2. Figure 3 As shown, the array structure layout is achieved by performing a two-dimensional periodic translation of the unit structure, thereby realizing a complete two-dimensional electromagnetic metasurface array structure.

[0066] The establishment and generation of the cosine phase modulation signal model in step 3 is as follows:

[0067] The cosine phase modulated signal is expressed as:

[0068] p(t m )=exp[jβcos(2πf m t m )];

[0069] Where: β represents the modulation index; f m Indicates the modulation frequency.

[0070] p(t m ) is expressed in the frequency domain as:

[0071]

[0072] Therefore, the interference signal can be expressed in the frequency domain as:

[0073]

[0074] It can be seen from the above formula that the spectrum of the interference signal is obtained by shifting the spectrum of the signal 2β+3 times, and the shift amounts are nf m ,n=-2,-1,0,1,2, thus forming 2β+3 false targets around the real target. When n=0, a false target with the same position as the real target is generated. At the same time, the amplitude of each harmonic component is affected by J n (β) modulation.

[0075] The SAR imaging processing and imaging interference effect analysis in step 4 are as follows:

[0076] The SAR interference signal is processed by range-Doppler SAR imaging. The interference signal after range matched filtering and range migration correction can be expressed as:

[0077]

[0078] Among them: B r Indicates the transmit signal bandwidth.

[0079] The above interference signal is processed by azimuth matched filtering to obtain the final interference SAR image, and its formula is:

[0080]

[0081] in:

[0082] Among them: B a represents the signal Doppler bandwidth; γ represents the Doppler modulation frequency.

[0083] It can be seen that 2β+3 false targets are generated in the jamming SAR image, and the offset of the nth false target in the azimuth dimension is:

[0084]

[0085] The specific tests are:

[0086] A reference target RT and three protected targets PT1-3 are set in the center of the imaging scene; the unmodulated radar echo is processed by range-Doppler SAR imaging to obtain the unmodulated original SAR imaging result, such as Figure 4 As shown, it can be observed that four targets with high focus quality can be seen in the SAR image.

[0087] The electromagnetic metasurface designed by the present invention is used to perform cosine phase modulation on the echo signal of the protected target, and the modulation index is set to β=1 and the modulation frequency is f m =10Hz, the cosine modulation phase is as follows Figure 5 As shown; after range-Doppler imaging processing, the interference imaging result is obtained, as shown Figure 6 As shown, it can be seen that after the cosine phase modulation processing based on the electromagnetic metasurface technology, the protected target PTi, (i = 1, 2, 3) can generate 5 false targets, and the azimuth offset of each false target is proportional to the modulation frequency, thereby achieving the purpose of deception.

[0088] The present invention utilizes electromagnetic metasurface technology to perform real-time phase modulation on radar signals through an external control system to generate SAR cosine phase-modulated interference signals; by performing imaging processing on the SAR interference signals, theoretical analysis and experimental results show that the present invention can generate multiple false targets along the azimuth direction whose azimuth positions are flexibly controllable and whose topological structures are similar to those of the protected targets, has a highly flexible, high-fidelity, low-cost interference imaging effect, and has strong practical application value.

[0089] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A SAR cosine phase modulation deception jamming method based on electromagnetic metasurface technology, characterized in that: The following steps are involved: Designing a phase-controlled metasurface and installing it on the surface of the protection target; the phase-controlled metasurface is composed of a plurality of metasurface units arranged in an array; The metasurface unit is a II-shaped metal branch structure, and the length of the metal branch at the top of the metal branch structure is longer than the length of the metal branch at the bottom, which is used to control the phase, amplitude and polarization state of the electromagnetic wave incident on the metasurface unit; The two vertical metal branches of the metal branch structure are both provided with gaps, and a varactor is provided at the gap of one of the metal branches; by changing the voltage applied to the top metal branch and the bottom metal branch of the metal branch structure, the voltage on both sides of the varactor is changed, and the equivalent capacitance of the varactor is adjusted in real time, so that the phase of the electromagnetic wave incident on the metasurface unit is adjusted to be continuously changed; The phase-controlled metasurface receives the transmission signal of the SAR radar, performs cosine phase modulation on the transmission signal and reflects it, and deceives and interferes with the SAR radar through the reflected signal.

2. The SAR cosine phase modulation deception jamming method based on electromagnetic metasurface technology according to claim 1 is characterized in that: The method of performing cosine phase modulation on the transmission signal comprises: When the transmission signal of the SAR radar is incident on the phase-controlled metasurface, the voltage on both sides of the varactor diode is changed by changing the voltage applied to the top metal branch and the bottom metal branch of the metal branch structure, so as to adjust the equivalent capacitance of the varactor diode in real time, and perform slow-time cosine phase modulation on the phase of the electromagnetic wave signal incident on the phase-controlled metasurface to obtain a cosine phase modulated signal. The cosine phase modulation signal is: p(t m )=exp[jβcos(2πf m t m )]; Where: p(t m ) represents the cosine phase modulation signal; β represents the modulation index of the cosine phase modulation signal; f m represents the modulation frequency of the cosine phase modulation signal; t m Indicates slow time.

3. The SAR cosine phase modulation deception jamming method based on electromagnetic metasurface technology according to claim 1 is characterized in that: The forming of the reflection signal comprises: The phase-controlled metasurface on the stationary target receives the transmission signal of the SAR radar and performs slow-time cosine phase modulation on the transmission signal to obtain a cosine phase modulated signal; The spectrum of the cosine phase modulated signal in the frequency domain is extracted, and the spectrum of the cosine phase modulated signal is bidirectionally and multiple times shifted in the azimuth direction of the protected target. The spectrum of the cosine phase modulated signal is replaced with multiple copied different spectra in sequence to form multiple harmonic components of the cosine phase modulated signal, and the multiple harmonic components are synthesized into a cosine phase interference signal, which is a reflected signal.

4. The SAR cosine phase modulation deception jamming method based on electromagnetic metasurface technology according to claim 3 is characterized in that: The cosine phase interference signal is: Among them: J n (β) represents the first-kind n-th-order Bessel function; f m represents the modulation frequency of the cosine phase modulated signal; f a +nf m Indicates the spectrum offset of the cosine phase interference signal.

5. The SAR cosine phase modulation deception jamming method based on electromagnetic metasurface technology according to claim 4 is characterized in that: The deceptive interference to the SAR radar includes: The SAR radar receives the cosine phase interference signal and performs range matching filtering, range migration correction and clutter suppression on the interference signal, forming a two-way false target string along the azimuth of the protected target in the interference image, thereby achieving deceptive interference to the SAR radar; The offset of the nth false target in the azimuth dimension is: Where: f m represents the modulation frequency of the cosine phase modulation signal; γ represents the Doppler modulation frequency.

6. SAR cosine phase modulation deception jammer based on electromagnetic metasurface technology, characterized in that: include: A design module, used to design a phase-controlled metasurface and install it on the target surface; The phase control metasurface is composed of a plurality of metasurface units arranged in an array; The metasurface unit is a II-shaped metal branch structure, and the length of the metal branch at the top of the metal branch structure is longer than the length of the metal branch at the bottom, which is used to control the phase, amplitude and polarization state of the electromagnetic wave incident on the metasurface unit; The two vertical metal branches of the metal branch structure are both provided with gaps, and a varactor is provided at the gap of one of the metal branches; by changing the voltage applied to the top metal branch and the bottom metal branch of the metal branch structure, the voltage on both sides of the varactor is changed, and the equivalent capacitance of the varactor is adjusted in real time, so that the phase of the electromagnetic wave incident on the metasurface unit is adjusted to be continuously changed; SAR radar jammer module, the phase-controlled metasurface receives the transmission signal of the SAR radar, performs cosine phase modulation on the transmission signal and reflects it, and deceives and jams the SAR radar through the reflected signal.

7. An electronic device, characterized in that: including memory and processor; The memory is used to store computer programs; The processor is used to implement the steps of the SAR cosine phase modulation deception interference method based on electromagnetic metasurface technology as described in any one of claims 1 to 5 when executing the computer program stored in the memory.

8. A computer-readable storage medium, characterized in that: Used to store a computer program, which, when executed by a processor, implements the steps of the SAR cosine phase modulation deception interference method based on electromagnetic metasurface technology as described in any one of claims 1 to 5.

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