Radar signal interference suppression method and system based on microwave photon technology

Abstract

The invention discloses a radar signal interference suppression method and system based on a microwave photon technology. By utilizing the inherent advantages of ultra-large bandwidth, low electromagnetic interference and high-speed parallel processing of a microwave photon technology and combining with the time-frequency flexible regulation and control characteristic of linear canonical transformation, a radar echo signal carrying frequency spectrum dispersion interference or intermittent sampling forwarding interference and a programmable reference signal are respectively modulated to two paths of optical carriers of the same light source; a dynamic adjustable transformation kernel function is constructed through a programmable reference signal, product operation of a simulation domain kernel function and a to-be-transformed signal is achieved through optical frequency mixing and balance detection, linear regular transformation operation is directly completed in a simulation domain, accurate rotation and projection are conducted on a time-frequency plane, accurate separation of a target signal and an interference signal is achieved, and the time-frequency conversion efficiency is improved. The processing complexity is obviously reduced, the real-time performance is improved, and meanwhile, the robustness of interference suppression and the broadband adaptation capability are ensured.

Description

Technical Field

[0001] This invention relates to the field of radar anti-jamming technology, and in particular to a radar signal interference suppression method and system based on microwave photonics technology. Background Technology

[0002] Modern radar systems are rapidly evolving towards broadband, coherent, and digital technologies, placing increasingly higher demands on the accuracy and real-time performance of target detection. Simultaneously, active jamming techniques based on Digital Radio Frequency Memory (DRFM) technology are constantly being upgraded. Among these, precision copy-and-forward jamming, represented by spectrum dispersion jamming and intermittent sampling-and-forward jamming, has become a typical high-efficiency coherent jamming style that restricts radar combat effectiveness.

[0003] Spectrum dispersion jamming is a typical form of active jamming based on DRFM technology. Its core principle involves intermittently sampling and slicing the linear frequency modulated (LFM) signal transmitted by the radar, precisely modulating the modulation frequency of each signal segment to extend the jamming signal spectrum to the full bandwidth of the radar receiver, forming a strong time-frequency domain coupling with the target echo. This type of jamming achieves its effectiveness through the following mechanisms: after the jamming signal is matched and filtered by the radar, its energy is dispersed throughout the entire time-frequency plane of the signal, directly overwhelming the target echo signal; sliced ​​modulation gives the jamming multi-frequency coverage capability, allowing for dynamic adjustment of jamming parameters for radar systems with different bandwidths, resulting in extremely high adaptability; compared to traditional suppression jamming, spectrum dispersion jamming does not require continuous high-power signal transmission, achieving high-efficiency jamming with low power consumption thanks to the precise replication characteristics of DRFM.

[0004] The harm of spectrum dispersion interference to radar systems is mainly manifested in the following ways: it leads to a significant decrease in the probability of target signal detection, and it damages the radar's ability to separate signals in the time and frequency domains. Especially in environments with high interference-to-signal ratios, traditional signal processing algorithms are unable to achieve interference-to-signal decoupling.

[0005] Intermittent sampling and forwarding jamming is another novel intra-pulse modulation coherent jamming technique based on DRFM. Its core lies in its "time-division multiplexing" operation mode, which combines the advantages of real-time sampling and forwarding. Its jamming mechanism can be summarized as follows: periodically and intermittently sampling the radar pulse signal, accurately replicating it through DRFM, and then modulating and forwarding it to the radar receiver by adjusting parameters such as time delay and frequency shift. The jamming signal maintains high coherence with the radar's transmitted signal, forming a dense group of false targets after matched filtering. This combination achieves both energy coverage suppression jamming and deceptive jamming by misleading false targets. By adjusting parameters such as sampling period and forwarding gain, diverse jamming patterns such as leading false targets and synchronous false targets can be flexibly generated, adapting to complex application scenarios such as distributed coherent radar and synthetic aperture radar.

[0006] The prominent harms of this type of interference include: disrupting the coherent parameter estimation process of distributed coherent radar, causing the system to be unable to achieve fully coherent synthetic gain; dense groups of false targets overload the radar data processing system, significantly reducing the probability of identifying real targets, and traditional inter-pulse waveform agility techniques are difficult to effectively counter.

[0007] Current suppression techniques for the above two types of interference mainly focus on electronic domain signal processing, and there are the following key technical bottlenecks:

[0008] The shortcomings of intermittent sampling and forwarding interference suppression: the waveform design method at the transmitter needs to rely on prior information of interference parameters and optimize orthogonal coding through heuristic search, which is highly complex and has poor engineering feasibility; the time-frequency domain filtering at the receiver (such as STFT and wavelet transform) fails under low interference-to-noise ratio (JNR) conditions, and the two-dimensional time-frequency conversion leads to excessive storage burden, exceeding the real-time processing capability; the interference reconstruction and cancellation method depends on accurate interference parameter estimation, and algorithms such as sliding truncation matched filtering have problems such as high two-dimensional search complexity and weak noise resistance.

[0009] The shortcomings of spectrum dispersion interference suppression: Traditional time-frequency domain decoupling methods require repeated iterative calculations, resulting in low processing efficiency and difficulty in adapting to the high-speed signal processing requirements of broadband radar; Compressed sensing algorithms are highly dependent on the interference base dictionary, and when the interference parameters change dynamically, the dictionary adaptability decreases, leading to a deterioration in the suppression effect.

[0010] Existing electronic domain suppression methods are limited by the bandwidth bottlenecks and electromagnetic compatibility issues of semiconductor devices, making it difficult to simultaneously address ultra-wideband, high-dynamic spectral dispersion and intermittent sampling-forwarding combined interference, thus limiting their applicability in complex electromagnetic countermeasure scenarios. Summary of the Invention

[0011] This invention provides a radar signal interference suppression method and system based on microwave photonics technology, which solves the technical problems of existing electronic domain interference suppression methods, such as high computational complexity, insufficient real-time performance, weak broadband adaptability, reliance on prior information, and difficulty in dealing with complex interference.

[0012] This invention provides a radar signal interference suppression method based on microwave photonics technology, comprising:

[0013] The first electro-optic modulator receives the first optical carrier and the radar echo signal carrying interference, respectively, so as to realize the modulation of the first optical carrier by the radar echo signal, and input the modulated optical signal into the optical mixer.

[0014] The second optical carrier and the reference signal are received by the second electro-optic modulator, and the reference signal modulates the second optical carrier. The modulated optical signal is then input into the optical mixer.

[0015] The optical signal is output from the optical mixer to the photodetector to achieve optical mixing and photoelectric conversion.

[0016] The photodetector outputs an electrical signal to a spectrum analyzer to obtain the target signal after interference suppression; specifically, interference-signal separation is achieved by adjusting the starting frequency and frequency modulation slope of the reference signal to obtain the target signal.

[0017] Specifically, the step of achieving interference-signal separation by adjusting the starting frequency and frequency modulation slope of the reference signal to obtain the target signal includes:

[0018] To address spectral dispersion interference, the frequency modulation slope of the reference signal is adjusted to match the optimal fractional Fourier transform order of the target signal. In this case, the time-frequency planes of the target signal and the interference signal rotate. Under the optimal order transformation of the signal, the target signal's energy is focused in the transform domain, while the multiple sub-pulses of the interference signal are dispersed due to the frequency modulation mismatch. The focused target signal energy is significantly higher than the dispersed interference signal energy, allowing the target signal to be displayed and achieving interference-signal separation.

[0019] Specifically, the step of achieving interference-signal separation by adjusting the starting frequency and frequency modulation slope of the reference signal to obtain the target signal includes:

[0020] To address intermittent sampling and forwarding interference, a gate function is multiplied on the reference signal kernel function to achieve the superposition of the kernel function and the gate function. The gate function avoids the discontinuous time domain interval of the interference signal by setting the interval between 0 and 1, and the energy of the interference signal is completely eliminated. The kernel function causes the time-frequency plane to rotate, so that the energy of the target signal is focused and superimposed, and the target signal can be displayed, thus achieving interference-signal separation.

[0021] Specifically, it also includes:

[0022] The interference time-frequency relationship is obtained from the radar echo signal carrying interference using the short-time Fourier algorithm;

[0023] The interference type can be determined by the time-frequency relationship of the interference, which is either spectral dispersion interference or intermittent sampling and forwarding interference.

[0024] Specifically, determining whether the interference type is spectrum dispersion interference or intermittent sampling forwarding interference based on the interference time-frequency relationship includes:

[0025] If the time-frequency plane presents a continuously distributed linear frequency modulation sub-signal splicing structure, and the slope of each sub-signal is an integer multiple of the slope of the transmitted signal, then the interference type is determined to be spectral dispersion interference.

[0026] If the time-frequency plane shows a segmented discrete distribution of time-frequency peaks over time, with each peak having an equal duration and being a linear frequency modulated signal with the same slope as the transmitted signal, then the interference type is determined to be intermittent sampling and forwarding interference.

[0027] Specifically, after obtaining the target signal, the process further includes:

[0028] Divide the frequency value corresponding to the peak position on the spectrum of the target signal by the slope of the transmitted signal to obtain the time delay between the transmitted and received signals.

[0029] Multiplying the time delay by half the speed of light yields the target's distance. Combining this with the beam direction of the radar's transmitted signal, the target's exact location is obtained.

[0030] This invention also provides a radar signal interference suppression system based on microwave photonics technology, comprising: a light source module, an optical power divider, a first electro-optic modulator, a second electro-optic modulator, an optical signal generator, an optical mixer, a photodetector, and a spectrum analyzer; the optical output terminal of the light source module is optically connected to the optical input terminal of the optical power divider, the first optical output terminal of the optical power divider is optically connected to the first optical input terminal of the first electro-optic modulator, and the second optical output terminal of the optical power divider is optically connected to the first optical input terminal of the second electro-optic modulator; the second optical input terminal of the first electro-optic modulator... Used to receive radar echo signals; the second optical input terminal of the second electro-optic modulator is connected to the optical output terminal of the optical signal generator; the optical output terminals of the first and second electro-optic modulators are respectively connected to the optical input terminal of the optical mixer, the optical output terminal of the optical mixer is connected to the optical input terminal of the photodetector, and the optical output terminal of the photodetector is connected to the optical input terminal of the spectrum analyzer; interference-signal separation is achieved by adjusting the starting frequency and frequency modulation slope of the reference signal through the optical signal generator to obtain the target signal.

[0031] Specifically, it also includes:

[0032] The interference type determination module is used to obtain the interference time-frequency relationship from the radar echo signal carrying interference using a short-time Fourier algorithm, determine the interference type as spectral dispersion interference or intermittent sampling forwarding interference based on the interference time-frequency relationship, and send the determined interference type to the optical signal generator to suppress different types of interference signals.

[0033] Specifically, it also includes:

[0034] The time delay calculation module is used to divide the frequency value corresponding to the peak position on the spectrum of the target signal by the slope of the transmitted signal to obtain the time delay between the transmitted signal and the received signal.

[0035] The target positioning module is used to multiply the time delay by half the speed of light to obtain the distance to the target, and combine it with the beam direction of the radar transmitted signal to obtain the specific location of the target.

[0036] Specifically, it also includes: a low-noise amplifier; the electrical output terminal of the photodetector is communicatively connected to the electrical input terminal of the low-noise amplifier, and the electrical output terminal of the low-noise amplifier is communicatively connected to the electrical input terminal of the spectrum analyzer.

[0037] One or more technical solutions provided in this invention have at least the following technical effects or advantages:

[0038] Leveraging the inherent advantages of microwave photonics technology—ultra-wide bandwidth, low electromagnetic interference, and high-speed parallel processing—and combining the flexible time-frequency control characteristics of linear canonical transform (LCT), radar echo signals carrying spectral dispersion interference or intermittent sampling and forwarding interference are modulated onto two optical carriers of the same light source along with a programmable reference signal. A dynamically adjustable transform kernel function is constructed using the programmable reference signal. Optical mixing and balanced detection are used to perform the product operation between the analog domain kernel function and the signal to be transformed. The linear canonical transform operation is directly performed in the analog domain to accurately rotate and project the time-frequency plane, achieving precise separation of the target signal and the interference signal. This significantly reduces processing complexity, improves real-time performance, and ensures robustness in interference suppression and broadband adaptability. Attached Figure Description

[0039] Figure 1 A schematic diagram of a radar signal interference suppression method based on microwave photonics technology provided in an embodiment of the present invention;

[0040] Figure 2 A structural diagram of a radar signal interference suppression system based on microwave photonics technology provided in an embodiment of the present invention;

[0041] Figure 3 This is a comparison chart of experimental results for suppressing spectral dispersion interference.

[0042] Figure 4 A comparison chart showing the suppression effects of three different types of intermittent sampling forwarding interference. Detailed Implementation

[0043] This invention provides a radar signal interference suppression method and system based on microwave photonics technology, which solves the technical problems of existing electronic domain interference suppression methods, such as high computational complexity, insufficient real-time performance, weak broadband adaptability, reliance on prior information, and difficulty in dealing with complex interference.

[0044] The technical solutions in the embodiments of the present invention are intended to solve the above-mentioned technical problems, and the overall approach is as follows:

[0045] After the radar's transmitted signal is intercepted by the jammer, it is precisely modulated and forwarded, generating spectral dispersion or intermittent sampling and forwarding interference that overlaps with the target echo signal. After the radar receives the jammed echo signal, the signal is directly modulated onto the light by an electro-optic modulator. In the optical domain, the kernel function and the echo signal are mixed in the optical domain and then photoelectric conversion is performed to achieve linear canonical transformation. By adjusting the kernel function, different linear canonical transformations are achieved, thereby rotating and intercepting the time-frequency plane of the jammed echo signal, completing the dispersion or elimination of interference energy. The output signal after interference suppression can be directly used for target detection and connected to the radar intelligence system.

[0046] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0047] like Figure 1 As shown, the radar signal interference suppression method based on microwave photonics technology provided in this embodiment of the invention includes:

[0048] The first electro-optic modulator receives the first optical carrier and the radar echo signal carrying interference, respectively, so as to realize the modulation of the first optical carrier by the radar echo signal, and input the modulated optical signal into the optical mixer.

[0049] The second electro-optic modulator receives the second optical carrier and the reference signal respectively, realizes the modulation of the second optical carrier by the reference signal, and inputs the modulated optical signal into the optical mixer;

[0050] The optical signal is output to the balanced photodetector via an optical mixer to achieve... Optical mixing and photoelectric conversion;

[0051] The target signal after interference suppression is obtained by sending the output electrical signal of the balanced photodetector to a spectrum analyzer. Specifically, interference-signal separation is achieved by adjusting the starting frequency and modulation slope of the reference signal to obtain the target signal. In this embodiment, the reference signal can be generated and parameters adjusted by receiving external control commands through a programmable interface.

[0052] Specifically, interference-signal separation is achieved by adjusting the starting frequency and frequency modulation slope of the reference signal to obtain the target signal, including:

[0053] To address spectral dispersion interference, the frequency modulation slope of the reference signal is adjusted to match the optimal fractional Fourier transform order of the target signal. In this case, the time-frequency planes of the target signal and the interference signal rotate. Because the slopes of the target signal and the interference signal are different, under the optimal order transformation of the signal, the target signal's energy is focused in the transform domain, while the multiple sub-pulses of the interference signal are dispersed due to the frequency modulation mismatch. The focused target signal energy is significantly higher than the dispersed interference signal energy, allowing the target signal to be displayed and achieving interference-signal separation.

[0054] To address intermittent sampling and forwarding interference, a gate function is multiplied onto the reference signal kernel function to achieve the superposition of the kernel function and the gate function. The gate function avoids the discontinuous time domain intervals of the interference signal by setting intervals of 0 and 1, and the energy of the interference signal is completely eliminated. The kernel function rotates the time-frequency plane, which focuses the energy of the target signal and superimposes it, allowing the target signal to be displayed, thus achieving interference-signal separation.

[0055] The radar signal interference suppression method based on microwave photonics technology provided in the embodiments of the present invention is further described, and also includes:

[0056] The time-frequency relationship of interference is obtained from the radar echo signal carrying interference using the short-time Fourier algorithm.

[0057] The type of interference can be determined by the time-frequency relationship between the interference and the spectrum dispersion interference or intermittent sampling and forwarding interference.

[0058] Specifically, the type of interference can be determined by the time-frequency relationship between the interference, including whether it is spectrum dispersion interference or intermittent sampling and forwarding interference.

[0059] If the time-frequency plane presents a continuously distributed linear frequency modulation sub-signal splicing structure, and the slope of each sub-signal is an integer multiple of the slope of the transmitted signal, then the interference type is determined to be spectral dispersion interference.

[0060] If the time-frequency plane shows a segmented discrete distribution of time-frequency peaks over time, with each peak having an equal duration and being a linear frequency modulated signal with the same slope as the transmitted signal, then the interference type is determined to be intermittent sampling and forwarding interference.

[0061] To obtain the target's exact location, after receiving the target signal, the following steps are also included:

[0062] Divide the frequency value corresponding to the peak position on the spectrum of the target signal by the slope of the transmitted signal to obtain the time delay between the transmitted and received signals.

[0063] Multiply the time delay by half the speed of light to get the distance to the target. Combine this with the beam direction of the radar signal to get the target's exact location.

[0064] like Figure 2As shown, the radar signal interference suppression system based on microwave photonics technology provided in this embodiment of the invention includes: a light source module, an optical power divider, a first electro-optic modulator, a second electro-optic modulator, an optical signal generator, an optical mixer, a photodetector, and a spectrum analyzer; the optical output terminal of the light source module is connected to the optical input terminal of the optical power divider, splitting a single optical carrier into two equal-power optical signals; the first optical output terminal of the optical power divider is connected to the first optical input terminal of the first electro-optic modulator, and the second optical output terminal of the optical power divider is connected to the first optical input terminal of the second electro-optic modulator; the second optical input terminal of the first electro-optic modulator is used for... The system receives radar echo signals; the second optical input of the second electro-optic modulator is connected to the optical output of the optical signal generator to achieve modulation of the second optical carrier by the reference signal; the optical outputs of the first and second electro-optic modulators are respectively connected to the optical input of the optical mixer, and the optical output of the optical mixer is connected to the optical input of the photodetector to achieve 90° optical mixing and photoelectric conversion; the optical output of the photodetector is connected to the optical input of the spectrum analyzer; and interference-signal separation is achieved by adjusting the starting frequency and modulation slope of the reference signal through the optical signal generator to obtain the target signal.

[0065] The radar signal interference suppression system based on microwave photonics technology provided in the embodiments of the present invention further includes:

[0066] The interference type determination module is used to obtain the interference time-frequency relationship from the radar echo signal carrying interference using the short-time Fourier algorithm. Based on the interference time-frequency relationship, it determines whether the interference type is spectral dispersion interference or intermittent sampling forwarding interference, and sends the determined interference type to the optical signal generator to suppress different types of interference signals.

[0067] Specifically, the interference type determination module can be added as an independent functional module to the radar or the first electro-optic modulator. In this embodiment of the invention, the specific placement of the interference type determination module is not specifically limited.

[0068] To obtain the specific location of the target, it also includes:

[0069] The time delay calculation module is used to divide the frequency value corresponding to the peak position on the spectrum of the target signal by the slope of the transmitted signal to obtain the time delay between the transmitted and received signals.

[0070] The target localization module is used to multiply the time delay by half the speed of light to obtain the distance to the target, and combine this with the beam direction of the radar signal to obtain the target's specific location.

[0071] Specifically, the time delay calculation module and the target positioning module can be added to the spectrum analyzer as independent functional modules or deployed independently externally. In this embodiment of the invention, no specific limitation is made on the specific deployment location of the time delay calculation module and the target positioning module.

[0072] Further description of the radar signal interference suppression system based on microwave photonics technology provided in the embodiments of the present invention includes: a low-noise amplifier; the electrical output terminal of the photodetector is communicatively connected to the electrical input terminal of the low-noise amplifier, and the electrical output terminal of the low-noise amplifier is communicatively connected to the electrical input terminal of the spectrum analyzer.

[0073] In this embodiment, the light source module is a laser, and the photodetector is a balanced photodetector.

[0074] Figure 3 The figures show a comparison of experimental results for suppressing spectral dispersion interference. (a) shows the time-domain waveform of the interfered echo; (b) shows the time-frequency analysis of the interfered echo, where the interference energy is greater than the target echo energy, and the time-frequency relationship between the interference and the target is coupled; (c) shows the result of traditional matched filtering, where the target is submerged in the pulse compression result of the interference because the interference energy is much greater than the echo energy, making it difficult for radar to detect; (d) and (e) show the output results of the method of this invention under different interference-to-signal ratios (SNRs). As the SNR increases, the target energy decreases. For spectral dispersion interference, the SNR is 23 dB when the SNR is 10 dB after interference suppression, and 3 dB when the SNR is 32 dB after interference suppression; (f) shows the time-frequency relationship after linear canonical transformation using the method of this invention, rotated by a certain angle. It can be seen that the target energy can be focused on the frequency domain projection, while the interference energy is dispersed in the frequency domain projection, thus the target can be displayed.

[0075] Figure 4The diagrams compare the suppression effects of three different types of intermittent sampling forwarding interference. (a), (b), and (c) show the time-frequency relationships of intermittent sampling direct forwarding interference, intermittent sampling cyclic forwarding interference, and intermittent sampling repeated forwarding interference, respectively. The time-frequency curves of the intermittent sampling direct forwarding interference signal are distributed on a single straight line. Due to the three repeated forwarding times, the time-frequency curves of the intermittent sampling direct forwarding interference signal are distributed on three straight lines. Due to the influence of the slice length, the time-frequency curves of the intermittent sampling direct forwarding interference signal are distributed on five straight lines. Furthermore, due to the different forwarding times, the time-frequency curves appear as five straight lines of different lengths, exhibiting discontinuity in the time domain due to the forwarding mechanism. (d), (e), and (f) show the suppression effects of the three types of interference. The result of pulse compression of the interference echo is shown in the example of intermittent sampling and repeated relay interference. After pulse compression, the interference signal is lags behind the real target by five gradually weakening peaks. However, because the interference signal strength is significantly greater than the echo signal, even the minimum amplitude of the interference signal will be significantly greater than the signal amplitude, making it impossible to determine the real target position. (g) is the result of linear canonical transformation of the intermittent sampling and repeated relay interference signal. The interference signal and the target signal can be distinguished, but the amplitude value of the interference signal projection is still significantly greater than the target signal. For subsequent target detection by the radar system, the amplitude of the interference signal will increase the threshold value of target detection, and the real target cannot be detected. Compared to traditional matched filtering, this method is equally effective against this type of interference. The same applies to intermittent sampling repetition and cyclic forwarding interference. (h) and (i) are gate functions designed for intermittent sampling cyclic forwarding and intermittent sampling repetition forwarding interference types. The green box diagram is the expression of the gate function in the time domain. The time domain interval where the interference is located can be obtained from the time-frequency relationship diagrams (a), (b) and (c) obtained from short-time Fourier analysis. Based on this, the gate function is designed with a value of 0 for the interval where the interference is located and a value of 1 for the rest.The gate function for the time domain interval where the interference is located is set to a low level, while the gate function for the time domain interval where the signal without interference is located is set to a high level. Different gate functions need to be designed for different types of interference to avoid the time domain interval where the interference is located. The gate function for intermittent sampling and direct forwarding interference is similar to that for intermittent sampling and cyclic forwarding due to its sampling and forwarding characteristics, so it is not shown here. (j) shows the time-frequency relationship of the signal after the fractional Fourier transform of the intermittent sampling and direct forwarding interference. It can be seen that the target energy projection is continuous in the time domain, while the interference energy is discontinuous due to the principle of sampling and forwarding. (k) and (j) show the time-frequency relationship of the linear canonical transform kernel function with the gate function applied. Applying a gate function to the kernel function of the linear canonical transform avoids the time domain where the interference signal exists, which is equivalent to performing time-domain filtering on the echo signal. For pulse compression, this time-domain filtering will not be pulse-compressed due to the discontinuity of the signal. However, for the proposed linear canonical transform process, the echo signal can be compressed. The presence or absence of a target is determined by projecting the signal onto the linear regularized domain. For discontinuous signals with a gate function applied, only the energy value after projection is lost, without affecting the display of the target result. (m) and (n) are the time-frequency relationships after applying kernel function transformation with added gate function to intermittent sampling cyclic forwarding interference and intermittent sampling repeated forwarding interference, respectively. It can be seen that the interference energy is completely eliminated, and the target energy is partially retained. The kernel function will bring a certain energy loss, but the interference energy is completely eliminated. Therefore, the target signal echo will not be submerged by the interference signal or affected by its amplitude. Therefore, for signal detection, this is a relatively weak effect. Experimental results show that this loss will not affect the detection of most targets. (o) is the effect of linear regularized transformation after adding gate function transformation kernel to combat intermittent sampling direct forwarding interference. With an interference-to-signal ratio of 30dB, the echo signal has a signal-to-noise ratio of 28dB after transformation.

[0076] The radar transmits the LFM signal as follows:

[0077]

[0078] in, The amplitude of the transmitted signal, For signal pulse width, For carrier frequency, For frequency modulation slope ( (for signal bandwidth) This is a rectangular window function. Spectral dispersion interference (SMI) is a composite interference generated based on DRFM technology. It involves intermittently sampling and slicing the radar linear frequency modulated (LFM) signal, modulating it at the frequency, and then delaying and splicing the resulting segments. Its core characteristic is that the interference spectrum covers the entire radar receiving bandwidth and is strongly time-frequency coupled with the target echo. SMI is composed of N delayed sub-LFM signals spliced ​​together. The model of a single sub-signal is as follows:

[0079]

[0080] in, To determine the interference amplitude, the sub-signal frequency modulation slope is N times that of the original signal, and the time width is 1 / N of the original signal, ensuring that the interference bandwidth matches the radar signal bandwidth.

[0081] The overall interference signal model is as follows:

[0082]

[0083] n is an integer representing the nth jamming segment. After being matched and filtered by the radar, the jamming forms a dense comb-shaped group of false targets, which has both deception and suppression effects. The target echo is overwhelmed by the jamming energy.

[0084] Intermittent sampling and forwarding jamming is generated by periodically sampling radar signals through DRFM, modulating and forwarding them in real time. It is divided into three types: direct forwarding, repeated forwarding, and cyclic forwarding. Its core feature is that the jamming is highly coherent with the radar signal, forming false targets that are either lagging behind or leading the signal.

[0085] Intermittent sampling and direct forwarding interference involves a single forwarding immediately after sampling. The model is as follows:

[0086]

[0087] in, For the sampling repetition period, M represents the sampling pulse width, and M represents the number of samplings.

[0088] Intermittent sampling and repeated forwarding interference occurs when a single sample is followed by multiple forwardings. The model is as follows:

[0089]

[0090] Where K is the number of forwards in a single sampling, forming multiple equal-amplitude false targets.

[0091] Intermittent sampling and cyclic forwarding interference involves forwarding the previously sampled signal in sequence with a frequency shift after sampling. The model is as follows:

[0092]

[0093] Where R is the number of loop forwardings, forming a pseudo-target group with gradually changing amplitude after pulse compression.

[0094] This invention achieves time-frequency separation in the LCT domain using microwave photonics technology. The core of this invention lies in replicating the function of the LCT kernel function using optical domain simulation calculations, and combining the differences in LCT domain characteristics between the target and the interference to achieve interference energy dispersion and target energy focusing.

[0095] The system operates using the equivalent LCT kernel function of a dual-path optical modulation-optical mixing architecture. The specific process is as follows:

[0096] Single-frequency laser output optical carrier , The amplitude of the optical carrier wave. The center frequency of the optical carrier is split into two equal-power signals by an optical power divider.

[0097] Assume the target echo is the LFM signal reflected from the point target:

[0098]

[0099] The amplitude of the echo signal, in the upper branch, is a mixed signal of the target echo and interference. The optical carrier is loaded by the first electro-optic modulator, and the output is:

[0100]

[0101] in, This represents the modulation index of the first electro-optic modulator. In the lower branch, the optical signal generator outputs a programmable LFM signal. The light is loaded onto the optical carrier via a second electro-optic modulator, and the output is:

[0102]

[0103] in, This is the modulation index of the second electro-optic modulator. The two optical signals are combined via an optical coupler. Optical mixer interference, output beat frequency component

[0104]

[0105] The balanced photodetector suppresses optical carrier and common-mode noise, outputs a current signal, which is amplified by a low-noise amplifier and then input to a spectrum analyzer.

[0106] The definition of linear canonical transform is:

[0107]

[0108] in:

[0109]

[0110] Where A, B, and D are integers, therefore, formula (11) can also be written as:

[0111]

[0112] By adjusting the frequency modulation slope of the reference signal Starting frequency ,make The equivalent LCT kernel function, and the Fourier transform result of it by a spectrum analyzer, is the LCT result of the mixed signal:

[0113]

[0114] At this time, the target signal The spectrum of the output after the linear canonical transform is:

[0115]

[0116] As can be seen from the spectrum, It is a constant. This is a phase term and does not affect the peak position; it is the target echo. In the LCT domain, the energy is concentrated and focused as a single peak of the sinc function. After coordinate transformation in the spectrum output by the spectrum analyzer and combined with the beam direction of the radar transmitted signal, the target's position information can be obtained.

[0117] SMSP interference Because the frequency modulation slope does not match the LCT parameters, the spectrum output after its linear canonical transformation is:

[0118]

[0119] Substitute LCT parameters Simplify the phase term (C=0, phase term is 1), and the sub-signal frequency modulation slope is The LCT parameters do not match the target parameters, therefore the LCT result of the sub-signal is a broadened rectangular function. The final spectrum after the linear canonical transform of the spectral dispersion interference is:

[0120]

[0121] As a broadened rectangular function, the LCT result of the interference signal is diffusely distributed, with energy dispersed in the frequency domain. The energy focused by a single peak of the target is higher than the energy dispersed by the interference, allowing the target to be displayed amidst the interference.

[0122] Adjust the matching target signal LCT parameters through reference signal parameters, and combine the LCT domain offset characteristics of ISRJ: The LCT peak of the target echo focuses on position; Due to the forwarding delay of ISRJ , its linear canonical transform result is:

[0123]

[0124] Its LCT peak shifts to , and multiple forwarding modes result in multiple offset peaks; For the offset rules of intermittent sampling direct / repeat / cyclic forwarding interference, further superimpose a gate function on the reference signal to avoid the time domain interval of interference sampling-forwarding. The form of the gate function is:

[0125]

[0126] where [t1, t2] is the "passband time domain interval" of the gate function, which needs to accurately match the continuous time domain range of the target signal (determined by the pulse width of the radar transmitted signal and the target distance); Outside the interval (t < t1 or t > t2) is the intermittent interval of the interference signal, and the value of the gate function is 0 to achieve interference energy elimination. The time domain interval of the gate function needs to be dynamically adjusted according to the sampling period and forwarding delay of the interference (programmable configuration through an optical signal generator); This process is equivalent to time domain filtering, which can completely eliminate interference energy. Only part of the energy of the target signal is lost, and it does not affect normal target detection. After applying the gate function, the spectrum result of the output after the linear canonical transform of the interfered echo is:

[0127]

[0128] where N is the number of intervals where the target exists and the interference does not exist. The target appears in the form of a superposition of multiple intermittent peaks, and the peak points are , [[ID=3三十三]] The phase term is a quadratic function of u, which does not affect the amplitude focusing characteristic and only changes the phase distribution. The spectrum of the echo signal after interference suppression output by the spectrum analyzer can obtain the position information of the target after coordinate transformation and in combination with the beam pointing of the radar transmitted signal.

[0129] In summary, the embodiments of the present invention provide a method and system for suppressing radar precise replication and forwarding interference based on microwave photon technology, which is applicable to complex electromagnetic confrontation scenarios such as broadband coherent radars and distributed coherent radars.

[0130] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0131] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0132] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0133] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0134] Any aspects of this invention not described in detail in the embodiments are well-known techniques to those skilled in the art. Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this invention and not to limit it. Although this invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this invention without departing from the spirit and scope of this invention, and all such modifications and substitutions should be covered within the scope of the claims of this invention.

Claims

1. A radar signal interference suppression method based on microwave photonics technology, characterized in that, include: The first electro-optic modulator receives the first optical carrier and the radar echo signal carrying interference, respectively, so as to realize the modulation of the first optical carrier by the radar echo signal, and input the modulated optical signal into the optical mixer. The second optical carrier and the reference signal are received by the second electro-optic modulator, and the reference signal modulates the second optical carrier. The modulated optical signal is then input into the optical mixer. The optical signal is output from the optical mixer to the photodetector to achieve optical mixing and photoelectric conversion. The photodetector outputs an electrical signal to a spectrum analyzer to obtain the target signal after interference suppression; specifically, interference-signal separation is achieved by adjusting the starting frequency and frequency modulation slope of the reference signal to obtain the target signal.

2. The radar signal interference suppression method based on microwave photonics technology as described in claim 1, characterized in that, The process of achieving interference-signal separation by adjusting the starting frequency and frequency modulation slope of the reference signal to obtain the target signal includes: To address spectral dispersion interference, the frequency modulation slope of the reference signal is adjusted to match the optimal fractional Fourier transform order of the target signal. In this case, the time-frequency planes of the target signal and the interference signal rotate. Under the optimal order transformation of the signal, the target signal's energy is focused in the transform domain, while the multiple sub-pulses of the interference signal are dispersed due to the frequency modulation mismatch. The focused target signal energy is significantly higher than the dispersed interference signal energy, allowing the target signal to be displayed and achieving interference-signal separation.

3. The radar signal interference suppression method based on microwave photonics technology as described in claim 1, characterized in that, The process of achieving interference-signal separation by adjusting the starting frequency and frequency modulation slope of the reference signal to obtain the target signal includes: To address intermittent sampling and forwarding interference, a gate function is multiplied on the reference signal kernel function to achieve the superposition of the kernel function and the gate function. The gate function avoids the discontinuous time domain interval of the interference signal by setting the interval between 0 and 1, and the energy of the interference signal is completely eliminated. The kernel function causes the time-frequency plane to rotate, so that the energy of the target signal is focused and superimposed, and the target signal can be displayed, thus achieving interference-signal separation.

4. The radar signal interference suppression method based on microwave photonics technology as described in claim 2 or 3, characterized in that, Also includes: The interference time-frequency relationship is obtained from the radar echo signal carrying interference using the short-time Fourier algorithm; The interference type can be determined by the time-frequency relationship of the interference, which is either spectral dispersion interference or intermittent sampling and forwarding interference.

5. The radar signal interference suppression method based on microwave photonics technology as described in claim 4, characterized in that, The step of determining whether the interference type is spectrum dispersion interference or intermittent sampling forwarding interference based on the interference time-frequency relationship includes: If the time-frequency plane presents a continuously distributed linear frequency modulation sub-signal splicing structure, and the slope of each sub-signal is an integer multiple of the slope of the transmitted signal, then the interference type is determined to be spectral dispersion interference. If the time-frequency plane shows a segmented discrete distribution of time-frequency peaks over time, with each peak having an equal duration and being a linear frequency modulated signal with the same slope as the transmitted signal, then the interference type is determined to be intermittent sampling and forwarding interference.

6. The radar signal interference suppression method based on microwave photonics technology as described in claim 1, characterized in that, After obtaining the target signal, the process further includes: Divide the frequency value corresponding to the peak position on the spectrum of the target signal by the slope of the transmitted signal to obtain the time delay between the transmitted and received signals. Multiplying the time delay by half the speed of light yields the target's distance. Combining this with the beam direction of the radar's transmitted signal, the target's exact location is obtained.

7. A radar signal interference suppression system based on microwave photonics technology, characterized in that, include: The system comprises a light source module, an optical power divider, a first electro-optic modulator, a second electro-optic modulator, an optical signal generator, an optical mixer, a photodetector, and a spectrum analyzer. The optical output terminal of the light source module is connected to the optical input terminal of the optical power divider. The first optical output terminal of the optical power divider is connected to the first optical input terminal of the first electro-optic modulator, and the second optical output terminal of the optical power divider is connected to the first optical input terminal of the second electro-optic modulator. The second optical input terminal of the first electro-optic modulator is used to receive radar echo signals. The second optical input terminal of the second electro-optic modulator is connected to the optical output terminal of the optical signal generator. The optical output terminals of the first and second electro-optic modulators are respectively connected to the optical input terminal of the optical mixer. The optical output terminal of the optical mixer is connected to the optical input terminal of the photodetector, and the optical output terminal of the photodetector is connected to the optical input terminal of the spectrum analyzer. Interference-signal separation is achieved by adjusting the starting frequency and modulation slope of the reference signal through the optical signal generator to obtain the target signal.

8. The radar signal interference suppression system based on microwave photonics technology as described in claim 7, characterized in that, Also includes: The interference type determination module is used to obtain the interference time-frequency relationship from the radar echo signal carrying interference using a short-time Fourier algorithm, determine the interference type as spectral dispersion interference or intermittent sampling forwarding interference based on the interference time-frequency relationship, and send the determined interference type to the optical signal generator to suppress different types of interference signals.

9. The radar signal interference suppression system based on microwave photonics technology as described in claim 7, characterized in that, Also includes: The time delay calculation module is used to divide the frequency value corresponding to the peak position on the spectrum of the target signal by the slope of the transmitted signal to obtain the time delay between the transmitted signal and the received signal. The target positioning module is used to multiply the time delay by half the speed of light to obtain the distance to the target, and combine it with the beam direction of the radar transmitted signal to obtain the specific location of the target.

10. The radar signal interference suppression system based on microwave photonics technology as described in claim 7, characterized in that, Also includes: Low-noise amplifier; The electrical output terminal of the photodetector is communicatively connected to the electrical input terminal of the low-noise amplifier, and the electrical output terminal of the low-noise amplifier is communicatively connected to the electrical input terminal of the spectrum analyzer.

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