Coherent suppressing interference signal generation method based on optical time stretching

Abstract

The invention discloses a coherent suppression interference signal generation method based on optical time stretching. The method relates to the technical field of optical communication, the technical field of microwaves and the technical field of electronic countermeasures. The method comprises a mode-locked laser MLL, a dual-drive Mach-Zehnder modulator DDMZM, an arbitrary waveform generator AWG, a vector signal generator VSG, an erbium-doped fiber amplifier EDFA, a dispersion compensation fiber DCF and a photoelectric detector PD. An MLL and a DDMZM are adopted to copy a radar signal and a phase step signal in a frequency domain, controllable delay inequality is applied to the copied signal by utilizing the time stretching capability of a DCF, a coherent suppression interference signal is generated through PD beat frequency, coherent suppression interference can be carried out on a synthetic aperture radar (SAR), an inverse synthetic aperture radar (ISAR), a pulse Doppler radar and a continuous wave radar, and the method has the advantages of being simple in structure, convenient to operate and high in practicability. The requirements for transmitting power and parameter reconnaissance are reduced, the limitation of frequency bands and bandwidths of a traditional electronic interference system is overcome, and the future development trend of an electronic countermeasure system is met.

Description

Technical Field

[0001] This invention relates to the fields of optical communication technology, microwave technology, and radar countermeasures technology, and mainly to the generation of radar coherent suppression jamming signals using photonics technology. Background Technology

[0002] Radar, as an active electromagnetic detection system, detects targets by receiving radiated electromagnetic echo signals. It includes synthetic aperture radar (SAR) and inverse synthetic aperture radar (ISAR) used for imaging detection, as well as pulse-Doppler and continuous-wave radars for range and velocity detection. The use of radar systems for surveillance and strikes against important military facilities demonstrates a trend towards integrated reconnaissance and strike capabilities, posing a serious challenge to the security of key targets. Therefore, radar jamming and countermeasures technologies have become an important research direction in the field of electronic warfare.

[0003] Jamming techniques targeting various radar systems are mainly divided into two categories: deception jamming and suppression jamming. Deception jamming simulates the coherent characteristics of radar echoes to create false targets in the radar imaging area. However, it requires precise detection of radar signal parameters, design of different deception templates according to actual needs, large data processing volume, and complex system implementation. Suppression jamming can be divided into coherent suppression jamming and non-coherent suppression jamming. Compared to non-coherent suppression jamming, coherent suppression jamming signals can form coherent superposition in the radar receiver, obtaining pulse compression processing gain. It can achieve good suppression effect at lower transmit power, improving the stealth of the jamming system.

[0004] Traditional electronic jamming often uses the mature Digital Radio Frequency Storage (DRFM) technology to achieve radar coherent jamming. However, due to electronic bottlenecks, the operating frequency and instantaneous bandwidth of the DRFM system are limited, making it unable to handle radar signals with large instantaneous bandwidth. Furthermore, multi-stage frequency conversion is required for high-frequency radar signals, which results in large inherent system delays and poor real-time jamming performance.

[0005] Microwave photonics technology boasts advantages such as wide frequency band, large bandwidth, resistance to electromagnetic interference, and low loss, effectively overcoming the limitations of traditional electronic radar jamming systems in terms of operating frequency range, instantaneous bandwidth, and processing speed. Common microwave photonic radar jamming generation schemes mainly include intermittent sampling jamming (ISRJ), comb spectrum modulation jamming (CSMJ), cosine phase modulation jamming, sawtooth wave frequency shifting jamming, and multi-style composite jamming. However, these jamming methods require accurate reconnaissance parameters to ensure jamming effectiveness, heavily rely on the performance of the reconnaissance system, and can only generate single or multiple point targets, resulting in a limited jamming range. Summary of the Invention

[0006] To address the problems existing in the background technology, this invention proposes a method for generating coherent suppression interference signals based on optical time stretching. This method uses a mode-locked laser (MLL) and a dual-drive Mach-Zehnder modulator (DDMZM) to repeatedly copy the intercepted radar signal and the generated phase step signal. After amplification by an erbium-doped fiber amplifier (EDFA), the signal is injected into a dispersion-compensating fiber (DCF). The time stretching capability of the DCF introduces different time delays into the copied radar signals at different comb frequencies. By passing the signal through a photodetector (PD) for beat frequency analysis, a continuously delayed coherent suppression interference signal can be obtained.

[0007] The technical solution adopted by this invention to solve its technical problem is as follows: The solution includes a mode-locked laser (MLL), a dual-drive Mach-Zehnder modulator (DDMZM), an arbitrary waveform generator (AWG), a vector signal generator (VSG), an erbium-doped fiber amplifier (EDFA), a dispersion-compensating fiber (DCF), and a photodetector (PD). A fixed-repetition-rate optical comb output from the MLL is injected into the DDMZM. ​​The VSG and AWG output radar signals and phase step signals, respectively, and are input to the RF ports of the DDMZM. ​​The bias voltage is controlled to make the DDMZM operate at the minimum point MITP (mitted-particle modulation) to achieve suppressed-carrier double-sideband modulation. The radar signal and phase step signal are replicated at each comb tooth frequency. The DDMZM output signal is amplified by the EDFA and then injected into the DCF. The time-stretching capability of the DCF introduces different time delays into the radar signals replicated at different comb tooth frequencies. These delays are then beat-frequency with the phase step signal by the PD to obtain a coherent suppression interference signal with a continuous time delay.

[0008] The present invention includes the following steps in operation: (1) Use MLL to generate an optical frequency comb with a wavelength range of Δλ and inject it into DDMZM; (2) Based on the azimuth suppression interference range, the required frequency components and the phase relationship between pulses are obtained, and the corresponding phase step signal is generated. (3) The radar signal and the phase step signal are injected into the two radio frequency ports of the DDMZM respectively. The DDMZM operates at the minimum point MITP and performs suppressed carrier double-sideband modulation to replicate the radar signal and the phase step signal. (4) The DDMZM output signal is amplified by EDFA and then injected into DCF, introducing different time delays to the radar signal at different comb frequencies; (5) Input the optical signal output by DCF into PD for photoelectric conversion to obtain a coherent suppression interference signal.

[0009] The essential features and significant advancements of this invention are as follows: This invention proposes a coherent suppression jamming signal generation method based on optical time stretching. It employs MLL and DDMZM structures to repeatedly replicate radar signals and phase step signals at different frequencies. Then, DCF is used to introduce different time delays into optical signals of different wavelengths, thereby applying a controllable time delay difference to each replicated signal. The radar signal and phase step signal are beat-frequencyd by PD, modulating different phases of the radar signal within different periods, thus generating a coherent suppression jamming signal with a continuous time delay structure. This invention reduces the requirements for transmission power and parameter reconnaissance in jamming systems, achieving coherent suppression jamming that is difficult to achieve with traditional electronic domain jamming techniques. Utilizing the advantages of microwave photonic signal processing—wideband, large bandwidth, and low loss—it achieves coherent suppression jamming against wideband, large time-width, and large bandwidth radar systems. This effectively reduces the difficulty of signal processing in practical applications, overcomes the frequency band and bandwidth limitations of traditional electronic jamming systems, aligns with the future development trend of electronic countermeasures systems, and is particularly suitable for key scenarios such as high-resolution imaging radar suppression and electronic warfare countermeasures. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of a coherent suppression interference signal generation method based on optical time stretching. Figure 2 The optical frequency comb has a frequency range of 2.5THz and a repetition rate of 500MHz for the MLL output. (a) is the spectrum of the optical frequency comb, and (b) is a magnified view of a portion of the spectrum of the optical frequency comb. Figure 3 The radar signal has a center frequency of 9.1 GHz and a bandwidth of 200 MHz. (a) is the signal waveform diagram, and (b) is the signal spectrum diagram. Figure 4 (a), (b) and (c) are waveform diagrams of the generated phase ladder signal, which control the 1kHz Doppler frequency shift, 10m and 20m azimuth suppression interference range, respectively; Figure 5 The output signal of the DDMZM is shown in (a) and (b) is a magnified view of the output signal spectrum. Figure 6 The results of this invention's interference with pulse Doppler radar are shown, where the DCF dispersion is 4000 ps / nm. (a), (b), and (c) are respectively... Figure 3 and Figure 4 (a) Waveform, electrical spectrum and range Doppler detection results of the suppressed interference signal obtained as the input signal; Figure 7 The image interference results of SAR in this invention are shown, where the DCF dispersion is 4000 ps / nm, and (a1), (a-ii), and (a-iii) are respectively Figure 3 and Figure 4 (b) Waveform, electrical spectrum, and radar imaging results of the coherent suppression interference signal obtained as the input signal, where (bi), (b-ii), and (b-iii) are respectively Figure 3 and Figure 4 (c) Waveform, electrical spectrum and radar imaging results of the coherent suppression interference signal obtained as an input signal; Figure 8 The image interference results of SAR in this invention are shown, where the DCF dispersion is 2000 ps / nm, and (a1), (a-ii), and (a-iii) are respectively Figure 3 and Figure 4 (b) Waveform, electrical spectrum, and radar imaging results of the coherent suppression interference signal obtained as the input signal, where (bi), (b-ii), and (b-iii) are respectively Figure 3 and Figure 4 (c) Waveform, electrical spectrum and radar imaging results of the coherent suppression interference signal obtained as an input signal; Detailed Implementation

[0011] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings and mathematical derivations: These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation procedures, but the protection scope of the present invention is not limited to the following embodiments.

[0012] As attached Figure 1 As shown, this example includes a mode-locked laser (MLL), a dual-drive Mach-Zehnder modulator (DDMZM), an arbitrary waveform generator (AWG), a vector signal generator (VSG), an erbium-doped fiber amplifier (EDFA), a dispersion-compensating fiber (DCF), and a photodetector (PD).

[0013] use Figure 1 The specific implementation steps for generating radar coherent suppression jamming signals using the structure shown are as follows:

[0014] Step 1: Use a mode-locked laser (MLL) to generate a repetition rate of ω. r The optical frequency comb signal is input as an optical carrier to the DDMZM. ​​The optical carrier can be represented as...

[0015] Step 2: The radar signal received by the antenna and the designed phase step signal are injected into the two RF ports of the DDMZM respectively. The mathematical expression for the received radar signal is: Where V s and ω s For the amplitude and carrier frequency of the radar signal, tr and t a R represents fast time and slow time. j (t a T represents the instantaneous slant distance. p T is the pulse width of the radar signal. a For the time to synthesize the aperture, v s Let y be the relative speed. j Let c be the relative distance traveled, and K be the speed of light. r This represents the frequency modulation slope of the radar signal.

[0016] Step 3: The phase ladder signal can be represented as Where V j and ω p The amplitude of the phase step signal and the Doppler frequency shift introduced in the azimuth direction are calculated as ω. p =2πK a a p / v s K a For the azimuth frequency modulation, a p Let P be the desired position of each interference point in the azimuth dimension of the imaging region, and P be the number of interference points in the azimuth direction. By controlling the DDMZM to operate at the minimum point MITP, carrier-suppressed double-sideband modulation is achieved. The DDMZM output signal can be expressed as... Where m1 = πV s / 2V π and m2=πV j / 2V π V represents the modulation index of the radar signal and the phase step signal, respectively. π This is the half-wave voltage of the modulator.

[0017] Step 4: The DDMZM output signal is amplified by the EDFA and then injected into the DCF. The DCF introduces a continuous time delay into the replicated radar signal. The DCF output signal can be expressed as... Where N represents the number of comb teeth, θ0, θ1+2nθ2ω r The fixed phase and continuous time delay introduced by DCF are respectively the group velocity dispersion coefficient θ2=Dλ 2 / 2πc, the dispersion coefficient D represents the amount of dispersion per unit length of optical fiber.

[0018] Step 5: Inject the optical signal output from the DCF into the PD for frequency beat detection. The output electrical signal after frequency beat detection is represented as follows: in To achieve the responsivity of the PD, a continuous time delay is introduced into the replicated radar signal using DCF, and the resulting coherent suppression interference signal with the introduced continuous time delay is obtained by PD beat frequency.

[0019] Step 6: Use an oscilloscope and an electromagnetic spectrum analyzer to acquire the waveform and electromagnetic spectrum of the interference signal output by the PD, respectively. Perform radar imaging processing on the acquired waveform data to test the interference effect.

[0020] Step 7: To explore the flexible tuning capability of this invention, the phase step signal was set to... Figure 4 (a), (b) and (c), the DCF dispersion is set to 4000 ps / nm and 2000 ps / nm respectively, and steps three to six are repeated.

[0021] Figure 2 It is an optical frequency comb with an output frequency range of 2.5THz and a repetition rate of 500MHz for MLL. Figure 3 It is a radar signal with a center frequency of 9.1 GHz and a bandwidth of 200 MHz. Figure 4 (a), (b) and (c) are waveform diagrams of the generated phase ladder signal, which control the 1kHz Doppler frequency shift, 10m and 20m azimuth suppression interference range, respectively. Figure 5 This is the spectrum of the output optical signal after DDMZM undergoes suppressed carrier double-sideband modulation. Figure 6 The results of this invention's interference with pulse Doppler radar are shown, where the DCF dispersion is 4000 ps / nm. (a), (b), and (c) are respectively... Figure 3 and Figure 4 (a) Waveform, electrical spectrum and range Doppler detection results of the suppressed interference signal obtained as input signal. Figure 7 and Figure 8 To verify the interference performance of this invention against SAR, the waveform diagram, electrical spectrum diagram, and radar imaging results of the interference signal were observed by changing the DCF dispersion and phase modulation step signal. Figure 7 The image interference results of SAR in this invention are shown, where the DCF dispersion is 4000 ps / nm, and (a1), (a-ii), and (a-iii) are respectively Figure 3 and Figure 4 (b) Waveform, electrical spectrum, and radar imaging results of the coherent suppression interference signal obtained as the input signal, where (bi), (b-ii), and (b-iii) are respectively Figure 3and Figure 4 (c) Waveform, electrical spectrum and radar imaging results of the coherent suppression interference signal obtained as input signal. Figure 8 The image interference results of SAR in this invention are shown, where the DCF dispersion is 2000 ps / nm, and (a1), (a-ii), and (a-iii) are respectively Figure 3 and Figure 4 (b) Waveform, electrical spectrum, and radar imaging results of the coherent suppression interference signal obtained as the input signal, where (bi), (b-ii), and (b-iii) are respectively Figure 3 and Figure 4 (c) Waveform, electrical spectrum and radar imaging results of the coherent suppression interference signal obtained as input signal.

[0022] In summary, this invention provides a method for generating coherent suppression interference signals based on optical time stretching, as shown in the accompanying drawings. Figure 1 As shown, the system includes a mode-locked laser (MLL), a dual-drive Mach-Zehnder modulator (DDMZM), an arbitrary waveform generator (AWG), a vector signal generator (VSG), an erbium-doped fiber amplifier (EDFA), a dispersion-compensating fiber (DCF), and a photodetector (PD). This invention uses the DCF to introduce continuous interference delay into the radar signal, achieving a coherent suppression method that is difficult to achieve with traditional electronic domain jamming techniques. This reduces the system's transmit power and parameter reconnaissance requirements, aligns with the future development trend of electronic countermeasures systems, and has application value in the future field of radar electronic warfare.

[0023] 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 can make several equivalent modifications and substitutions based on the content disclosed in the present invention, such as changing the optical wavelength, optical power, radio frequency signal power, carrier frequency, frequency range of the broadband signal, and bandwidth of the broadband signal. These equivalent modifications and substitutions, as well as adjustments to the frequency range, should also be considered within the scope of protection of the present invention.

Claims

1. A method for generating coherent suppression interference signals based on optical time stretching, comprising a mode-locked laser (MLL), a dual-drive Mach-Zehnder modulator (DDMZM), an arbitrary waveform generator (AWG), a vector signal generator (VSG), an erbium-doped fiber amplifier (EDFA), a dispersion-compensating fiber (DCF), and a photodetector (PD), wherein the two radio frequency ports of the DDMZM are respectively injected with intercepted radar signals and generated phase step signals, characterized in that, The optical frequency comb output from the MLL is injected into the DDMZM. ​​The intercepted radar signal and the generated phase step signal are respectively fed into the two radio frequency ports of the DDMZM. ​​The DDMZM operates at its minimum point. The optical frequency comb replicates the radar signal and the phase step signal multiple times at different comb tooth frequencies. The phase step signal modulates different phases of the radar signal within different periods. The output signal of the DDMZM is amplified by the EDFA and then injected into the DCF. Utilizing the time stretching capability of the DCF, different time delays are introduced into the radar signals at different comb tooth frequencies. The output signal of the DCF is beat-frequencyd by the PD to obtain the coherent suppression jamming signal. This method reduces the requirement for parameter reconnaissance in the jamming system and can achieve coherent jamming of wide-band, large-time-width, and large-bandwidth radar systems. It can effectively reduce the difficulty of signal processing in actual use and improve the power efficiency of jamming suppression.

2. The method for generating coherent suppression interference signals based on optical time stretching according to claim 1, characterized in that, For synthetic aperture radar (SAR), inverse synthetic aperture radar (ISAR), pulse Doppler radar, and continuous wave radar signals with different carrier frequencies, time widths, and bandwidths, the range of the suppression area can be flexibly adjusted simply by adjusting the step amplitude of the phase step signal, the coverage range of the MLL optical frequency comb, and the dispersion of the DCF.

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