Precise deception jamming signal photonics generation method for synthetic aperture radar

Abstract

The invention discloses a precise deception jamming signal photonics generation method for a synthetic aperture radar (SAR), and relates to the field of optical communication, microwave technology and electronic countermeasure. According to the method, a laser device LD, a dual-polarization quadrature phase shift keying modulator DP-QPSK, a bridge, an arbitrary waveform generator AWG, an optical band pass filter OBPF, an erbium-doped fiber amplifier EDFA, a polarization controller PC, a polarizer Pol and a photoelectric detector PD are included. According to the invention, high-fidelity false target deception can be realized by using only one DP-QPSK modulator, a template signal generation method directly used for a microwave photon frequency conversion system is designed, complex signal processing is not needed, SAR deception jamming signals can be generated through one photon mixing, the signal processing complexity is reduced, and the signal processing efficiency is improved. The method is simple in structure, good in real-time performance and high in parameter reconfigurable capability, a false target image is highly similar to a real target, effective cheating can be achieved, the method conforms to the future development trend of an electronic countermeasure system, and the method has application value in the fields of future radar electronic warfare and the like.

Description

Technical Field

[0001] The present invention relates to the fields of optical communication technology, microwave technology and radar countermeasure technology, and mainly relates to realizing SAR interference signal generation by utilizing photonics technology. Background Art

[0002] As an active detection method, synthetic aperture radar (SAR) offers the advantages of strong penetration, high-resolution imaging, and all-day and all-weather operation. It significantly outperforms traditional radar in acquiring target information and sensing multi-dimensional parameters. Currently, SAR is widely used in areas such as regional monitoring, geological mapping, and remote sensing imaging. To prevent malicious detection and protect the information security of critical targets, research on electronic jamming technologies targeting SAR has become a hot topic.

[0003] Current research on SAR jamming techniques is categorized by their effectiveness into suppression jamming and deception jamming. Suppression jamming typically involves transmitting high-power incoherent or partially coherent noise signals to disrupt SAR echo acquisition, preventing proper imaging. While suppression jamming is easy to implement, it requires the noise power to be significantly greater than the SAR signal echo power to achieve effective interference. Deception jamming, by simulating the coherent properties of SAR echoes, can effectively deceive SAR imaging systems at lower transmission power, obfuscating SAR information acquisition. This highly concealed approach has become a research hotspot in the field of SAR jamming.

[0004] A common electronic-based approach to SAR deception jamming relies on digital radio frequency memory (DRFM), which samples, stores, modulates, and retransmits received SAR signals. Numerous digital signal processing algorithms have been proposed to improve the fidelity of decoy targets. However, because ADCs cannot simultaneously achieve high-speed and high-fidelity sampling, these algorithms can only process narrow-bandwidth SAR signals, leaving them with limited processing capabilities for wide-bandwidth, high-resolution SAR signals.

[0005] Photonic signal processing offers the technical advantages of a wide frequency range, large instantaneous bandwidth, immunity to electromagnetic interference, and low loss. It can effectively overcome the limitations of DRFM-based SAR deception jamming systems in terms of operating frequency range, instantaneous bandwidth, and processing speed. In recent years, microwave photon-based radar jamming systems have been widely researched, with implementations of intermittent sampling jamming (ISRJ), comb spectrum modulation jamming (CSMJ), cosine phase modulation jamming, sawtooth frequency shift jamming, and multi-pattern composite jamming. However, these jamming methods can only produce point targets or multiple point targets in SAR imaging results and cannot simulate real-world target imaging. Point targets are easily identified and eliminated, and the high jamming power required can easily reveal the jammer's location, making it difficult to achieve high-fidelity deceptive jamming. Summary of the Invention

[0006] To address the problems presented in the prior art, the present invention proposes a photonics method for generating precise deceptive jamming signals for synthetic aperture radar (SAR). This method utilizes a single dual-polarization quadrature phase-shift keying (DP-QPSK) modulator to precisely generate SAR deceptive jamming signals. A unique template signal generation method is designed. The amplitude envelope and frequency components of the template signal are determined by the backscatter coefficient of the target template and the desired position of the decoy target. By controlling the angle between the principal axes of the polarization controller (PC) and the polarizer (Pol), a precise deceptive jamming signal for the SAR is generated through photoelectric conversion.

[0007] The present invention employs a technical solution to solve the technical problem. The device comprises a laser (LD), a dual-polarization quadrature phase-shift keying (DP-QPSK) modulator, a 90° bridge, an arbitrary waveform generator (AWG), an optical bandpass filter (OBPF), an erbium-doped fiber amplifier (EDFA), a polarization controller (PC), a polarizer (Pol), and a photodetector (PD). The DP-QPSK modulator internally comprises an optical beam splitter, two parallel Mach-Zehnder modulators (DP-MZM1 and DP-MZM2) connected in parallel, a 90° polarization rotator (PR), and a polarization beam combiner (PBC). The LD output is connected to the DP-QPSK input. The SAR signal received by the antenna is split into two paths and applied to the two RF input ports of the DP-QPSK upstream channel (DP-MZM1), achieving suppressed carrier double-sideband modulation of the SAR signal in the X polarization state of the optical carrier. Aiming at the needs of SAR imaging deception, a template signal amplitude, frequency and phase control method is proposed according to the characteristics of microwave photonic link. By adjusting the size and amplitude of each frequency component in the template signal and the phase relationship between different pulses, the false target image can be accurately positioned and the realism of the false target image can be improved. The frequency component value is determined by the distance position of the desired false target imaging, the amplitude envelope of the template signal is determined by the backscattering coefficient of the target template, and the phase relationship between different pulses is determined by the azimuth position of the desired false target imaging. The template signal is generated by AWG and divided into two phase-orthogonal signals through a 90° bridge. They are loaded on the two RF input ports of the lower DP-MZM2 respectively, and then 90° polarization rotation is performed through PR. Suppressed carrier single-sideband modulation of the template signal is implemented on the carrier's Y polarization state. The output of DP-MZM2 and the output of DP-MZM1 are input to PBC to form a polarization-multiplexed optical signal. The modulated template signal is essentially the spectrum expansion and shaping of the optical carrier in terms of amplitude, frequency, and phase. The output of DP-QPSK is connected to OBPF and EDFA in sequence to filter out the positive sideband of the SAR signal and perform power amplification. The angle between the PC and Pol main axes is adjusted to convert the polarization-multiplexed optical signal into a single polarization state signal. After input to PD for photoelectric conversion, the amplitude, frequency, and phase information in the template signal can be modulated onto the SAR signal to obtain a precise SAR deception interference signal. This technical solution has the significant advantages of compact structure, adjustable parameters, and strong real-time performance.

[0008] The present invention comprises the following steps when working: (1) An optical carrier is emitted from a light source and input into the DP-QPSK modulator; (2) The SAR signal received by the antenna is input to the RF port of DP-MZM1, and the bias voltage of DP-MZM1 is adjusted, where the two sub-modulators operate at the minimum point and the main modulator operates at the orthogonal point. After modulation, a suppressed carrier double-sideband modulated signal in the X polarization state is output; (3) According to the backscatter coefficient of the target template and the position of the false target image expected to be generated in the final imaging result, the frequency components, envelope amplitude and phase relationship between pulses required by the template signal are obtained, and the corresponding template signal is generated; (4) The template signal is divided into two signals with orthogonal phases through a 90° bridge and input to the two RF ports of DP-MZM2. The bias voltage of DP-MZM2 is adjusted to be the same as that of DP-MZM1, and the output is modulated. The suppressed carrier single-sideband modulated signal in the Y polarization state is combined with the added output signal through PBC to form a polarization-multiplexed optical signal. (5) The DP-QPSK output signal is filtered out by the OBPF to remove the positive first-order sideband of the SAR signal and then amplified by the EDFA; (6) The signal amplified by the EDFA is injected into the PC, and the PC is adjusted so that the angle between it and the main axis of the Pol is 45°. The polarization-multiplexed optical signal is converted into a single polarization state. The optical signal output by the Pol is input into the PD for photoelectric conversion to obtain the precise deceptive interference signal of the SAR.

[0009] The substantial features and significant advances of the present invention include: the proposed SAR microwave photon precise deceptive jamming forwarding structure can generate false targets that are highly similar to real targets at relatively low forwarding power, providing an effective means for countering large-bandwidth, high-resolution SAR systems; eliminating the need for digital radio frequency memory (DRFM), significantly improving the operating frequency band, instantaneous bandwidth, and real-time performance of the SAR deceptive jamming system; a unique intermediate frequency template signal generation method is proposed, enabling precise control of the imaging position and fidelity of false target images. Precise deceptive jamming signals for SAR can be generated through simple microwave photon mixing, reducing the difficulty of signal processing in actual use. The resulting false target images achieve a structural similarity of over 85% with the real target; for SAR signals of different frequencies and bandwidths, corresponding deceptive jamming signals can be generated by simply controlling the intervals between the frequency components in the template signal. This allows for rapid template signal switching and real-time updating, avoids the need for repeated jamming waveform design for different SAR parameters, simplifies the system architecture and implementation process, and is adaptable to a variety of complex electronic countermeasure application scenarios with good scalability. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 The schematic diagram of the optical generation method of deceptive jamming signals for SAR; Figure 2 is the SAR reference image used to generate the template signal; Figure 3Figure 2 shows the waveforms and electrical spectra of the simulated SAR signal and template signal. (ai) is the waveform of the SAR signal with a center frequency of 8 GHz and a bandwidth of 200 MHz, (a-ii) is a local magnified view of the SAR signal waveform, and (a-iii) is the electrical spectrum of the SAR signal. (bi) is the waveform of the designed template signal, (b-ii) is a local magnified view of the template signal waveform, and (b-iii) is the electrical spectrum of the template signal. Figure 4 The 8 GHz interference signal generated, (a) is the waveform of the interference signal, (b) is the electric spectrum of the interference signal, (c) is the local magnification of the interference signal waveform, (d) is the SAR imaging result of the interference signal, and (e) is the grayscale histogram comparison result between the generated false target image and the reference SAR image; Figure 5 Template signal that can generate multiple false target images, (a) waveform of template signal, (b) electrical spectrum of template signal; Figure 6 The interference signal can generate multiple false target images. (a) is the waveform of the interference signal, (b) is the electric spectrum of the interference signal, (c) is the local magnification of the interference signal waveform, and (d) is the SAR imaging result. Figure 7 for Figure 6 Grayscale histogram comparison results of the false target image generated by the interference signal and the reference SAR image. (a), (b), and (c) are the grayscale histogram comparison results of three false target images respectively; Figure 8 The template signal designed for the SAR signal with a center frequency of 16 GHz. (a) is the waveform of the template signal, and (b) is the electrical spectrum of the template signal. Figure 9 The 16 GHz interference signal generated, (a) is the waveform of the interference signal, (b) is the electric spectrum of the interference signal, (c) is a local magnified view of the interference signal waveform, (d) is the SAR imaging result of the interference signal, and (e) is the grayscale histogram comparison result between the generated false target image and the reference SAR image; DETAILED DESCRIPTION

[0011] The following is a detailed description of an embodiment of the present invention in conjunction with the accompanying drawings and mathematical derivations: This embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation method and specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments.

[0012] As attached Figure 1As shown, this example includes a laser LD, a dual-polarization quadrature phase-shift keying modulator DP-QPSK, a 90° bridge, an arbitrary waveform generator AWG, an optical bandpass filter OBPF, an erbium-doped fiber amplifier EDFA, a polarization controller PC, a polarizer Pol, and a photodetector PD.

[0013] use Figure 1 The structure shown in the figure has the following specific steps to generate a precise SAR deception jamming signal:

[0014] Step 1: Use the laser LD to generate a continuous optical signal with a wavelength of λ, which is input into the DP-QPSK modulator as an optical carrier. The optical carrier can be expressed as E in (t) = E c exp(jω c t), where E c and ω c are the amplitude and angular frequency of the optical carrier.

[0015] Step 2: The SAR signal received by the antenna is divided into two paths and input into the two RF ports of DP-MZM1. The mathematical expression of the received SAR signal is: Among them, V s and ω s is the amplitude and carrier frequency of the SAR signal, t r and t a Indicates fast time and slow time, R j (t a ) is the instantaneous slant distance, T p is the pulse width of the SAR signal, T a is the synthetic aperture time, v s is the moving speed of the SAR platform, y j is the moving distance of the SAR platform, c is the speed of light, K r is the frequency modulation slope of the SAR signal. The two sub-modulators of DP-MZM1 operate at the minimum point MITP, and the main modulator operates at the orthogonal point QTP to achieve suppressed carrier double-sideband modulation in the X polarization state. The output signal of DP-MZM1 can be expressed as Where m1 = πV s / 2V π is the modulation index of the SAR signal, V π is the half-wave voltage of the modulator.

[0016] Step 3: According to Figure 2 The SAR reference image shown in (a) generates a template signal. The generated template signal can be expressed as where N r and N a are the number of scattering points that divide the target template in distance and azimuth, σ m,n is the backscattering coefficient of each scattering point of the target template, ω m and ω n are the frequency shifts required for each scattering point in the distance dimension and azimuth dimension, respectively, and are calculated as ω m =4πK r u m / c,ω n =2πK a a n / v s , K a is the frequency modulation in azimuth, u m and a n The expected positions of each scattering point in the range and azimuth dimensions in the imaging result are respectively. The template signal is divided into a group of phase-orthogonal signals through a 90° bridge and input into the two RF ports of DP-MZM2. The three working points of DP-MZM2 are set the same as those of DP-MZM1 to realize suppressed carrier single-sideband modulation in the Y polarization state. The mathematical expression of the output signal of DP-MZM2 is shown as follows: Where β=π / 2V π After that, the output of DP-MZM2 undergoes 90° polarization rotation and is combined with the output of DP-MZM1 through PBC to form a polarization multiplexed optical signal. The output of DP-QPSK is expressed as

[0017] Step 4: Input the output signal of the DP-QPSK modulator into the OBPF for filtering to filter out the positive sideband optical signal of the X polarization state.

[0018] Step 5: Input the filtered optical signal into the EDFA for power amplification.

[0019] Step 6: Input the amplified optical signal into PC and adjust the angle between PC and Pol main axis to maximize the signal amplitude after PD beat frequency. The electrical signal output after PD beat frequency is expressed as

[0020] Step 7: Use an oscilloscope and an electric spectrometer to collect the interference signal waveform and electric spectrum output by the PD respectively, perform SAR imaging processing on the collected waveform data, and test the interference effect.

[0021] Step 8: In order to explore the multi-false target generation capability of the present invention, Figure 2The target template image shown in (a) is copied to generate a corresponding template signal, which replaces the template signal in step 3, and steps 3 to 7 are repeated.

[0022] Step 9: In order to explore the deceptive jamming capability of the present invention on wide-band and large-bandwidth SAR signals, the SAR signal in step 2 is replaced with a center frequency of 16 GHz and a bandwidth of 500 MHz, and the target template is replaced with Figure 2 (b) generates a corresponding template signal for the reference image shown in step 3, replaces the template signal in step 3, and repeats steps 3 to 7.

[0023] Figure 2 It is the SAR reference image used to generate the template signal. Figure 3 (ai), Figure 3 (a-ii) and Figure 3 (a-iii) are the waveform of the SAR signal with a carrier frequency of 8 GHz received by the antenna, the local magnified view of the waveform, and the electric spectrum. They are the input signals of DP-MZM1. Figure 3 (bi), Figure 3 (b-ii), Figure 3 (b-iii) is based on Figure 2 The waveform of the template signal generated by the target template shown in (a), the local magnified view of the waveform, and the electric spectrum are the input signals of DP-MZM2. Figure 4 The following figure shows the waveform and spectrum of the 8GHz SAR jammer generated by PD beating, the resulting image after imaging processing, and the image histogram comparison with the real target image. The comparison results show that the structural similarity (SSIM) between the generated decoy image and the real target image reaches 78.41%. Figure 5 This is to explore the waveform and spectrum of the template signal generated by the multi-false target generation capability of the present invention, which is the input signal of DP-MZM2 in step eight. Figure 6 The waveform, electric spectrum, and imaging result of the interference signal generated after PD beat frequency in step 8 are shown in the following figure. As can be seen from the imaging result, three false target images are generated, and the position of each false target in the image can be set arbitrarily. Figure 7 yes Figure 6 (d) Comparison of the grayscale histograms of the three generated decoy images and the reference image. As can be seen from the comparison results, when the desired decoy imaging position is far away from the jammer position, the quality of the generated decoy image decreases accordingly, but the SSIM of each decoy relative to the real target is greater than 70%. Figure 8This is to explore the waveform and electrical spectrum of the template signal generated by the wide-band and large-bandwidth deception jamming capability of the present invention, which is the input signal of DP-MZM2 in step nine. Figure 9 The waveform and spectrum of the interference signal generated by the PD beat frequency in step 9, the imaging result after imaging processing, and the image histogram comparison result with the real target image are shown. From the comparison results, it can be seen that the SSIM of the generated false target image and the real target image is 85.00%.

[0024] In summary, the present invention realizes a photonic generation method of precise deception jamming signal for synthetic aperture radar. The present invention can realize highly realistic SAR false target deception jamming by using only one DP-QPSK modulator. The present invention also designs a method for generating intermediate frequency template signal that can be directly used in microwave photon frequency conversion system. It does not require complicated sampling, modulation and forwarding processes. It can generate high frequency band and large instantaneous bandwidth SAR deception jamming signal by only one microwave photon mixing, which greatly reduces the signal processing calculation complexity in the implementation process. The method has simple structure, good real-time performance and strong parameter reconfiguration capability. The position of the false target image generated can be flexibly adjusted and is highly similar to the real target image, which has good deception and confusion effect, conforms to the future development trend of electronic countermeasure system and has application value in the fields of future radar electronic warfare.

[0025] In summary, the above-described embodiments are merely examples of the present invention and are not intended to limit the scope of protection of the present invention. It should be noted that those skilled in the art will readily appreciate that various equivalent variations and substitutions can be made based on the disclosure of the present invention. These variations and substitutions, as well as adjustments to the frequency range, can also be made to the optical wavelength, optical power, power of the radio frequency signal, carrier frequency, frequency range, and bandwidth of the broadband signal. These equivalent variations and substitutions, as well as adjustments to the frequency range, are also within the scope of protection of the present invention.

Claims

1. A method for generating precise deceptive jamming signals for synthetic aperture radar using photonics, comprising a laser (LD), a dual-polarization quadrature phase-shift keying (DP-QPSK) modulator, a 90° bridge, an arbitrary waveform generator (AWG), an optical bandpass filter (OBPF), an erbium-doped fiber amplifier (EDFA), a polarization controller (PC), a polarizer (Pol), and a photodetector (PD). The DP-QPSK modulator is internally integrated with an optical beam splitter, two parallel dual-parallel Mach-Zehnder modulators (DP-MZM1 and DP-MZM2), a 90° polarization rotator, and a polarization combiner. The DP-MZM1 and DP-MZM2 in the DP-QPSK modulator are used to modulate the intercepted radar signal and a specially designed template signal, respectively. The modulated polarization-multiplexed optical signal is filtered, amplified, and polarization-controlled before being converted into a radio frequency jamming signal by the photodetector (PD). The method is characterized in that: The specially designed template signal is based on the two-dimensional frequency shift theory. According to the scattering point distribution information of the template target, the distance dimension and azimuth dimension frequency shift required for each scattering point in the template signal are calculated, and the waveform envelope amplitude of the template signal is designed according to the backscattering intensity of the template target. The template signal design method is specially designed for the microwave photon mixing structure. It is an intermediate frequency signal independent of the radar signal and is used to generate a radio frequency interference signal. The radar interference signal is generated by this scheme without the need for complex digital modulation processes such as IQ demodulation, convolution operation, and two-dimensional Fourier transform. Only one microwave photon mixing is required to generate an accurate deceptive interference signal for SAR, which reduces the difficulty of signal processing in actual use. While ensuring the high fidelity of the false target image, the computational complexity of the interference signal generation is effectively reduced. After imaging processing, a false target image with a high similarity to the real target can be generated.

2. The method for generating precise deceptive jamming signals for synthetic aperture radar according to claim 1, characterized in that: For SAR signals of different frequencies and bandwidths, the corresponding deceptive jamming signals can be generated by simply controlling the intervals between the frequency components in the template signal. The template signal can be quickly switched and updated in real time, avoiding the need to repeatedly design jamming waveforms for different SAR parameters.

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