Multi-pattern interference signal optical generation method for synthetic aperture radar

Abstract

The invention discloses a multi-pattern interference signal optical generation method for a synthetic aperture radar, and relates to the technical field of optical communication, the technical field of microwaves and the technical field of electronic countermeasures. The method is shown in a figure 1 in the specification, and comprises a laser LD, a dual-parallel Mach-Zehnder modulator DP-MZM and a photoelectric detector PD. Carrier suppression double-sideband modulation of intercepted radar signals is realized through the MZM2 of the lower arm of the DP-MZM, different phase modulation is performed on each echo through the main modulator, azimuth cosine phase modulation is realized, and two-dimensional cosine phase modulation interference signals can be generated after the radar signals and MZM1 modulated cosine signals of the upper arm of the DP-MZM pass through the photoelectric detector. The device is simple in structure and good in interference real-time performance, overcomes the electronic bottleneck, can generate radar interference signals with wide frequency bands and large instantaneous bandwidth, realizes deception and suppression interference, and adapts to the requirements and development trend of radar electronic warfare.

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 the generation of radar interference signals by using photonics technology. Background Art

[0002] Synthetic Aperture Radar (SAR) is an all-weather and all-day high-resolution imaging radar. Compared with traditional detection radars, SAR has obvious advantages in the ability to obtain multi-dimensional information of targets and is widely used in terrain mapping, environmental detection, and military reconnaissance fields. In recent years, with the gradual maturity of SAR imaging technology, a new trend of "reconnaissance and strike integration" has emerged in its military applications. The target surveillance and strike system based on SAR poses a great threat to the security of our important facilities. The radar interference technology against SAR has become a research hotspot in the field of electronic warfare in various countries.

[0003] The interference methods against SAR are divided into suppression interference and deception interference. Suppression interference generally uses noise to perform convolution or multiplication processing on radar signals to achieve a suppression effect within a certain range and protect the targets in this area. Deception interference mainly generates multiple false targets extremely similar to real targets in the area where the enemy radar images by modulating the radar signals through frequency shift, intermittent sampling, and cosine phase modulation, making it impossible to identify the real targets.

[0004] In the traditional electrical domain, Digital Radio Frequency Memory (DRFM) is a key device for generating coherent interference signals. Limited by the electronic bottleneck, the operating frequency of commercial DRFM is limited to several GHz, and the instantaneous bandwidth is limited to 1 - 2 GHz. Although the DRFM based on channelization can increase the operating frequency and instantaneous bandwidth, the channelization system is always limited by high complexity. In addition, the effective number of bits of high-speed analog-to-digital converters is small, which will increase the quantization noise of radar interference signals and reduce the signal-to-noise ratio of radar interference signals.

[0005] Microwave photon technology has the advantages of a large operating frequency range, broadband processing ability, electromagnetic interference resistance, and low loss, etc., which can overcome the electronic bottleneck of traditional radar interference and improve the interference effect. And the microwave photon broadband radar signal processing technology can generate radar interference signals in real time, which is an effective solution to overcome the inherent electronic bottleneck.

[0006] Common microwave photon interference signal generation schemes mainly include generating intermittent sampling interference signals by using square wave signals to control the intermittent suppression of optical carriers, generating frequency shift interference signals by mixing sawtooth wave signals with radar signals, and generating cosine phase modulation interference signals by modulating radar signals with cosine signals, and derived interference schemes that combine two or more methods, which can generate multiple indistinguishable false targets. However, the above interference schemes can only interfere with the target range direction. In the imaging results of the enemy radar, there is only a string of false targets in the range dimension, which is difficult to effectively interfere with the enemy radar. In addition, since the size of the generated false target is fixed at the SAR physical resolution size and cannot simulate object targets of different sizes, it is easier to be identified by the enemy radar as deceptive interference. Summary of the Invention

[0007] To solve the problems existing in the background technology, the present invention proposes an optical generation method for diverse interference signals for synthetic aperture radar. This method uses a dual-parallel Mach-Zehnder modulator (DP-MZM) to generate two-dimensional deceptive or suppression interference signals. By changing the frequencies and powers of the cosine signal input to MZM1 and the cosine stepped wave signal of the main modulator bias, the positions, sizes, and coverage ranges of the false targets after imaging processing can be adjusted, and the effects of deceptive interference or suppression interference can be generated according to actual requirements.

[0008] The technical solution adopted by the present invention is as follows: The device includes a laser diode (LD), a dual-parallel Mach-Zehnder modulator (DP-MZM), and a photodetector (PD). The intercepted radar signal is subjected to suppressed-carrier double-sideband modulation through MZM2, and then the cosine stepped wave signal is injected into the main modulator bias port. The intercepted radar signal is phase-modulated by adjusting the main modulator bias to achieve azimuth cosine phase modulation; the cosine signal is injected into the radio frequency port of MZM1 to achieve double-sideband modulation. The upper and lower optical signals are combined and input to the PD, and a two-dimensional cosine phase modulation interference signal for the SAR radar can be generated through PD beat frequency.

[0009] The present invention includes the following steps during operation: (1) An optical carrier with a wavelength of λ emitted from the light source is input into the DP-MZM; (2) The cosine signal is input into the radio frequency port of MZM1, and the bias of MZM1 is set to the quadrature point to output a double-sideband modulation signal; (3) The intercepted SAR radar signal is input into the radio frequency port of MZM2, and the bias of MZM2 is set to the minimum point to output a suppressed-carrier double-sideband modulation signal; (4) Set the cosine stepped-wave voltage to vary between the maximum and minimum operating points of the main modulator. The duration of each stepped voltage is in the millisecond range and is consistent with the pulse repetition interval of the intercepted radar signal. Then, inject the cosine stepped-wave signal into the bias port of the main modulator to perform slow-time cosine phase modulation on the intercepted radar signal. (5) After combining the signals of the upper and lower arms of the DP-MZM and inputting them into the PD, a two-dimensional cosine phase modulation interference signal for the SAR radar can be obtained after photoelectric detection.

[0010] The present invention proposes an optical generation method for diverse interference signals against synthetic aperture radar, which uses a DP-MZM modulator to respectively implement double-sideband modulation of cosine signals and suppressed-carrier double-sideband modulation of intercepted radar signals. Phase modulation is performed on the intercepted radar signal by adjusting the bias voltage of the main modulator to achieve slow-time cosine phase modulation. After combining the upper and lower optical signals and performing beat frequency through the PD, a two-dimensional cosine phase modulation interference signal can be obtained. By changing the frequency and power of the cosine signal input to MZM1, the position and coverage range of the false target in the range direction after imaging processing can be adjusted; in the azimuth direction, by adjusting the amplitude of the cosine stepped-wave signal and the duration of the stepped voltage input to the main modulator, the position and coverage range of the false target in the azimuth direction after imaging processing can be changed, and the effects of deception interference or suppression interference can be generated according to actual needs.

[0011] The structure of the present invention is simple, only using one integrated modulator, which avoids the phase noise introduced by optical path separation, thus ensuring the stability of the system. The present invention can adjust the position, size and coverage range of the false target after imaging processing, can flexibly select the interference pattern according to actual needs, can quickly respond to non-cooperative radar signals, and has application value in electronic warfare systems. Description of the Drawings

[0012] Figure 1 It is the schematic diagram of the optical generation method for diverse interference signals against synthetic aperture radar. Figure 2 It is the waveform diagram of the signal input to the RF port of MZM1. (a) Single-tone cosine signal with a frequency of 13.3 MHz, (b) Dual-tone cosine signals with frequencies of 0.93 MHz and 20 MHz. Figure 3 It is the output spectrum diagram of the upper arm of the DP-MZM. (a) is the output spectrum diagram of the upper arm of the DP-MZM when inputting Figure 2 (a) signal, (b) is the output spectrum diagram of the upper arm of the DP-MZM when inputting Figure 2 (b) signal Figure 4Cosine stepped wave signal waveform diagram for the input main modulator bias port, (a) single-tone cosine stepped wave signal with a frequency of 19.12 Hz, (b) dual-tone cosine stepped wave signal with frequencies of 1.34 Hz and 28.68 Hz. Figure 5 Output optical spectrum diagram of the lower arm of the DP-MZM, (a) for the input Figure 4 (a) Output optical spectrum diagram of the lower arm of the DP-MZM when the signal is input, (b) for the input Figure 4 (b) Output optical spectrum diagram of the lower arm of the DP-MZM when the signal is input. Figure 6 Output optical spectrum diagram of the DP-MZM, (a) for the input Figure 2 (a) and Figure 4 (a) Output optical spectrum diagram of the DP-MZM when the signal is input, (b) for the input Figure 2 (b) and Figure 4 (b) Output optical spectrum diagram of the DP-MZM when the signal is input Figure 7 Electrical spectrum diagram after PD beat frequency, (a) for Figure 6 (a) Electrical spectrum diagram after PD beat frequency, (b) for Figure 6 (b) Electrical spectrum diagram after PD beat frequency. Figure 8 Generated radar interference signal pulse, (a) waveform of the generated interference signal in fast time and slow time, (b) change trend of the generated interference signal in slow time. Figure 9 Imaging result diagram modulated by a single-tone signal, two-dimensional false target intervals are (a) 15 m, (b) 10 m, (c) 0.7 m. Figure 10 Imaging result diagram modulated by a dual-tone signal, two-dimensional false target intervals are (a) 15 m, (b) 4 m. Figure 11 Imaging result diagram modulated by a dual-tone signal, two-dimensional false target interval is 15 m, input powers of MZM1 and the main modulator are respectively (a) 1.2 and 1.2 times the original, (b) 1 and 1.5 times the original. Specific implementation manner

[0013] The following will describe the embodiments of the present invention in detail with reference to the accompanying drawings: These embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation manners and specific operation procedures are given, but the protection scope of the present invention is not limited to the following embodiments.

[0014] Figure 1Schematic diagram of an optical generation method for diverse interference signals against synthetic aperture radar, including a laser diode LD, a dual-parallel Mach-Zehnder modulator DP-MZM, and a photodetector PD. The dual-parallel Mach-Zehnder modulator DP-MZM integrates two Mach-Zehnder modulators MZM and a main modulator. Among them, the sub-modulators MZM1 and MZM2 are embedded in the upper and lower arms of the main modulator. In addition, there is a modulation electrode on one of the arms of the main modulator, which can load a DC bias voltage to introduce an adjustable phase shift to the optical signal on this arm. The optical carrier output by the laser diode LD enters the DP-MZM and is divided into two paths. The upper-path optical carrier is modulated by a cosine signal through MZM1 to generate multi-order optical sidebands. The lower-path optical carrier is subjected to suppressed-carrier double-sideband modulation by the intercepted radar signal through MZM2, and then the cosine stepped-wave signal is injected into the bias port of the main modulator to perform slow-time cosine phase modulation on the radar signal. The upper and lower path signals are coupled and then input into the photodetector PD to obtain the required radar interference signal.

[0015] In this example, the specific implementation steps of the method are as follows: Step 1: The laser diode LD generates a continuous optical wave with a working wavelength of 1550 nm and a power of 15 dBm. This continuous optical wave is input into the DP-MZM modulator as an optical carrier. Step 2: A cosine signal as shown in Figure 2 (a) with a power of 20 dBm is input into the RF port of MZM1 and operates at the quadrature point QTP. Step 3: The SAR radar signal is a set of linear frequency modulation LFM signals with a carrier frequency of 5 GHz, a bandwidth of 200 MHz, a range modulation frequency of 2×10 14 , and the Doppler bandwidth of this set of LFM signals is 295 Hz, the azimuth modulation frequency is 478, and the slant range of the scene center is 8 km. The intercepted radar signal is input into the RF port of MZM2, and MZM2 operates at the minimum point to achieve suppressed-carrier double-sideband modulation. A cosine stepped-wave signal as shown in Figure 4 (a) is input into the main modulator to modulate different phases for each radar signal. Step 4: The optical signal output by the DP-MZM is input into the PD, and a spectrum analyzer is used to observe and analyze the spectrum information of the signal output by the photodetector PD. Step 5: An oscilloscope is used to collect the waveform of the interference signal output by the PD, and the collected data is subjected to SAR imaging processing to test the interference effect. Step 6: The RF input of MZM1 is changed to a dual-tone cosine signal with frequencies of 0.93 MHz and 20 MHz as shown in Figure 2 (b), and the bias voltage input to the main modulator is changed to as shown in Figure 4(b) Dual-tone cosine stepped wave signals with frequencies of 1.34 Hz and 28.68 Hz, and repeat Steps 4 and 5. Step 7: To explore the tuning ability of the false target coverage range, adjust the input signal powers of MZM1 and the main modulator, and repeat Steps 4 and 5.

[0016] Figure 2 (a) and (b) are a single-tone cosine signal with a frequency of 13.3 MHz and dual-tone cosine signals with frequencies of 0.93 MHz and 20 MHz, respectively. Figure 3 (a) and (b) are the input Figure 2 (a) signal and Figure 2 (b) signal output spectrograms of the upper arm of the DP-MZM. Figure 4 (a) and (b) are a single-tone cosine stepped wave signal with a frequency of 19.12 Hz and dual-tone cosine stepped wave signals with frequencies of 1.34 Hz and 28.68 Hz, respectively. Figure 5 (a) and (b) are the input Figure 4 (a) signal and Figure 4 (b) signal output spectrograms of the lower arm of the DP-MZM. Figure 6 (a) and (b) are the output spectrograms of the DP-MZM when single-tone and dual-tone signals are input to both MZM1 and the main modulator, respectively. Figure 7 (a) and (b) are respectively Figure 6 (a) and Figure 6 (b) electrical spectrograms after PD beat frequency. Figure 8 (a) is the waveform of the generated interference signal in fast time and slow time, Figure 8 (b) is the change trend of the generated interference signal in slow time. Figure 9 (a), (b), and (c) are respectively the imaging result diagrams of the interference signals generated when a single-tone cosine signal with a frequency of 20 MHz, 13.3 MHz, and 0.93 MHz is input to the RF port of MZM1, and a single-tone cosine stepped wave signal with a frequency of 28.68 Hz, 19.12 Hz, and 1.34 Hz is input to the bias port of the main modulator. Figure 10 (a) and (b) are respectively the imaging result diagrams of the interference signals generated when different-frequency dual-tone cosine signals and different-frequency dual-tone cosine stepped wave signals are input to the RF port of MZM1 and the bias port of the main modulator. Figure 11 (a) and (b) are respectively the imaging result diagrams of the interference signals generated when different-power dual-tone cosine signals and dual-tone cosine stepped wave signals are input to the RF port of MZM1 and the bias port of the main modulator.

[0017] In summary, the present invention realizes an optical generation method for diverse interference signals for synthetic aperture radar. This method uses a dual-parallel Mach-Zehnder modulator (DP-MZM) to achieve two-dimensional deception and suppression interference. The structure of the present invention is simple, has good real-time performance, and the generated interference signals have a high frequency band, a large instantaneous bandwidth, and strong tunability. It can not only generate two-dimensional false targets with adjustable sizes, but also form a suppression effect within a certain range, meeting the current radar electronic warfare requirements and development trends.

[0018] In conclusion, the above-described embodiments are only examples of the present invention and are not only used to limit the protection scope of the present invention. It should be noted that for those of ordinary skill in the art, several equivalent deformations and substitutions can be made on the basis of the content disclosed in the present invention. The optical wavelength, optical power, power of the radio frequency electrical signal, carrier frequency, frequency range of the broadband signal, and bandwidth of the broadband signal can all be changed. These equivalent deformations, substitutions, and adjustments of the frequency range should also be regarded as the protection scope of the present invention.

Claims

1. An optical generation method for diverse interference signals against synthetic aperture radar, comprising a laser diode LD, a dual-parallel Mach-Zehnder modulator DP-MZM, and a photodetector PD. The DP-MZM is internally integrated with a Y-type splitter, two parallel Mach-Zehnder modulators MZM1 and MZM2, and a main modulator, and is characterized in that The continuous optical carrier output by the LD is injected into the DP-MZM. The intercepted radar signal is input into the RF port of MZM2. The bias voltage is adjusted to the minimum point to achieve suppression of the carrier double-sideband modulation. Then, the cosine stepped-wave signal is injected into the bias port of the main modulator to modulate different phases of the radar signal in different periods, realizing slow-time cosine phase modulation of the radar signal. The cosine signal is input into the RF port of MZM1, and MZM1 operates at the quadrature point to achieve double-sideband modulation. After the upper and lower optical signals are combined, the two-dimensional cosine phase modulation interference signal can be obtained through PD beat frequency. By changing the frequencies and powers of the bias signals input to MZM1 and the main modulator, the position, size, and coverage range of the false target after imaging processing can be adjusted, and the effects of deception interference or suppression interference can be generated according to actual requirements.

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