A Dual-Band Pulse Compression Coding Frequency Agile Anti-Jamming Method and System

Abstract

The present invention discloses a dual-band pulse compression coding frequency agility anti-interference method and system, relating to the field of radar anti-interference. The method comprises the following steps: Step 1: transmitting a mixed coded signal of the X-band and Ku-band under the triggering of a synchronization signal; Step 2: receiving an echo signal of the mixed coded signal and down-converting the echo signal to an intermediate frequency to obtain an intermediate frequency echo signal; Step 3: sequentially performing pulse compression and signal accumulation processing on the intermediate frequency echo signal to obtain a target signal. The present invention detects targets by transmitting a mixed coded signal of the X-band and Ku-band. When the signal of one frequency band is suppressed by noise interference, the signal of the other frequency band can still operate normally, thereby improving the anti-interference capability of the radar system.

Description

Technical Field

[0001] The present invention relates to the field of radar anti-interference, and in particular to a dual-band pulse compression coding frequency agile anti-interference method and system. Background Art

[0002] Currently, radar jamming methods include noise suppression jamming, drag jamming, and Doppler noise jamming. Noise suppression jamming generates a noise-modulated signal with a bandwidth greater than the radar signal bandwidth within the radar's operating frequency band, blocking or degrading radar echo reception and preventing the radar from properly extracting the echo signal. Drag jamming involves continuously delaying or shifting the center frequency of the deceptive target pulse after the radar locks onto it, gradually shifting the range and velocity gates away from the true target. As the delay / frequency offset of the deceptive signal gradually increases, the interference-to-signal ratio (JSR) of the received signal approaches infinity, causing the radar to completely track the deceptive target. Once the jamming pulse drags the range tracking gate away from the true target to a predetermined position, the jammer is immediately disabled, and the radar loses the target.

[0003] These interference methods pose a severe challenge to the radar's target detection and tracking capabilities. Conventional anti-interference methods include antenna anti-interference (such as sidelobe cancellation technology and beamforming), transmitter anti-interference (such as frequency hopping and transmission waveform coding), receiver anti-interference (such as receiver anti-saturation method) and signal processing anti-interference (such as signal selection method, accumulation method, intra-pulse agile frequency switching and inter-pulse agile frequency switching). However, the interference technologies corresponding to these anti-interference methods are already very mature. By utilizing the characteristics of conventional anti-interference methods or implementing technologies to transmit targeted interference signals, conventional anti-interference methods are difficult to distinguish and it is difficult to counteract their interference signals. Summary of the Invention

[0004] The purpose of the present invention is to solve the problem that conventional anti-interference methods are difficult to counteract interference signals and to improve the anti-interference capability of radar.

[0005] To achieve the above object, the present invention provides a dual-band pulse compression coding frequency agility anti-interference method, the method comprising the following steps:

[0006] Step 1: Triggered by the synchronization signal, a mixed coded signal of X-band and Ku-band is transmitted;

[0007] Step 2: receiving an echo signal of the mixed coded signal, and down-converting the echo signal to an intermediate frequency to obtain an intermediate frequency echo signal;

[0008] Step 3: Perform pulse compression and signal accumulation processing on the intermediate frequency echo signal in sequence to obtain the target signal.

[0009] The present invention improves the anti-interference capability of the radar through the following three aspects:

[0010] First, the hybrid coded signal contains both X-band and Ku-band signals. The X-band signal has a frequency range of 8–12 GHz, and the Ku-band signal has a frequency range of 12–18 GHz. To achieve effective noise suppression jamming, the jammer must simultaneously cover both frequency bands (for a total bandwidth of 10 GHz). However, the instantaneous bandwidth of a conventional jammer typically does not exceed 2 GHz, so it can only cover one frequency band within the hybrid coded signal. In this invention, when the receiving channel of a certain frequency band is suppressed by interference noise, its limiter saturates. Once saturation is detected, the radar system automatically determines that the frequency band is interfered with and discards the data in that frequency band, using information collected from another frequency band instead to avoid interference.

[0011] Second, the present invention implements pulse compression and signal accumulation processing on the intermediate frequency echo signal. Pulse compression processing converts long pulse signals into short pulse signals through matched filtering, which not only improves the range resolution of the radar system, but also enhances the target echo intensity, and can effectively suppress the influence of interference signals. Pulse compression requires that the echo signal maintain strict synchronization in the time domain. Signal accumulation processing performs coherent superposition on the intermediate frequency echo signals of multiple cycles. Since the real echo signal has a stable phase relationship and periodic characteristics, the X-band echo signal and the Ku-band echo signal can completely overlap with their respective corresponding standard pulses at the same time, achieving signal accumulation. The essence of drag jamming is digital frequency storage jamming. The jammer first receives the analog signal transmitted by the radar, analyzes it and converts it into a digital signal, and then delays these digital signals and converts them back into analog signals and transmits them as interference signals. Among them, when the jammer delays the pulse signals of different frequency bands, due to the differences in circuit characteristics, the delay degrees of different frequency points are different, resulting in the interference signal being unable to simultaneously meet the time domain synchronization conditions required for pulse compression and the phase coherence conditions required for signal accumulation, and thus unable to achieve effective pulse compression and signal accumulation, which causes the interference signal to be eliminated from the target signal.

[0012] Third, the present invention downconverts the echo signals to the same intermediate frequency (IF), facilitating subsequent signal processing using the same hardware, thus reducing the complexity of the radar system. Downconverting the echo signals to the IF for signal accumulation enhances signal strength after superposition, as the true target echo signals have phase consistency in the X-band and Ku-band. However, the phases of interfering signals are typically random, and therefore, during signal accumulation, they may cancel each other out, resulting in a weakened signal after superposition.

[0013] Therefore, in order to interfere with the radar signal of the present invention, the following conditions must be met:

[0014] 1. Within one radar sub-pulse period (1μs), the frequency, pulse width, repetition rate and other information of the X-band pulse signal and the Ku-band pulse signal can be simultaneously analyzed;

[0015] 2. Obtain the synchronous trigger time of the echo signal pulse compression of the two bands. In actual application, this trigger time is an internal secret.

[0016] Furthermore, in step 1, the mixed coded signal includes a plurality of mixed pulses;

[0017] The mixed pulse is generated by X-band sub-pulses and Ku-band sub-pulses through intra-pulse frequency coding.

[0018] Intrapulse frequency coding (IPFC) involves encoding the signal's frequency within a single pulse cycle. Because the spectrum of an intrapulse frequency-coded signal has multiple peaks, and the positions and amplitudes of these peaks can be flexibly adjusted, it is difficult for a jammer to accurately simulate a jamming signal that is identical to the radar signal, thereby improving the radar's anti-interference capability.

[0019] Furthermore, the encoding method of the intra-pulse frequency encoding includes:

[0020] Step 101: performing linear frequency modulation on any X-band sub-pulse and Ku-band sub-pulse to be transmitted, and randomly determining the transmission carrier frequency;

[0021] Step 102: Arrange the modulated X-band sub-pulse and Ku-band sub-pulse in the time domain to form the mixed pulse.

[0022] Among them, the present invention adopts the mixed encoding method of X-band sub-pulses and Ku-band sub-pulses to make the radar signal more complex and diverse in the spectrum, further improving the radar's anti-interference capability.

[0023] Furthermore, the X-band sub-pulse includes a first sub-pulse and a second sub-pulse, and the Ku-band sub-pulse includes a third sub-pulse and a fourth sub-pulse.

[0024] Among them, for different mixed pulses, the carrier frequencies of the sub-pulses inside them are randomly determined, which means that each mixed pulse has unique frequency domain characteristics, which greatly increases the complexity of the mixed coded signal and increases the difficulty of interference.

[0025] Furthermore, in the mixed pulse, the X-band sub-pulses and the Ku-band sub-pulses are arranged in the following order: the first sub-pulse, the third sub-pulse, the second sub-pulse and the fourth sub-pulse. By increasing the number of sub-pulses of different frequencies, the mixed pulse has more arrangement methods.

[0026] Furthermore, the encoding method of the intra-pulse frequency encoding further includes: inserting a guard pulse into the mixed pulse;

[0027] The inserting of a guard pulse into the mixed pulse comprises:

[0028] An X-band cover pulse is inserted at the timing position corresponding to the Ku-band sub-pulse, and a Ku-band cover pulse is inserted at the timing position corresponding to the X-band sub-pulse.

[0029] Among them, the present invention further increases the difficulty for the jammer to obtain the real operating frequency of the radar by inserting a cover pulse with a false frequency point; by interweaving the cover pulse and the real sub-pulse in the time domain and frequency domain, the frequency information of the jamming system is misled, greatly increasing the probability of not being intercepted.

[0030] Furthermore, both the X-band sub-pulses and the Ku-band sub-pulses are frequency-modulated waves.

[0031] Furthermore, the frequencies of the first sub-pulse, the second sub-pulse, the third sub-pulse and the fourth sub-pulse are mutually coherent;

[0032] In step 3, the frequency of the synchronous trigger pulse for pulse compression and signal accumulation is coherent with the frequencies of the X-band sub-pulse and the Ku-band sub-pulse, and the frequencies of the X-band sub-pulse and the Ku-band sub-pulse are respectively integer multiples of the frequency of the synchronous trigger pulse.

[0033] The frequencies of the four sub-pulses are mutually coherent and coherent with the frequency of the synchronous trigger pulse, and they are integer multiples of the synchronous trigger pulse. Only when these conditions are met can the intermediate frequency echo signal achieve effective pulse compression and signal accumulation. Therefore, to effectively interfere with this method, the jammer must also know the multiple of the sub-pulse frequency and the synchronous trigger pulse frequency. This multiple is randomly selected by the radar system, reducing the risk of being cracked.

[0034] The present invention also provides a dual-band pulse compression coding frequency agile anti-interference system, the system comprising:

[0035] A signal transmitting unit, configured to transmit a mixed coded signal of X-band and Ku-band under the triggering of a synchronization signal;

[0036] a signal receiving unit, configured to receive an echo signal of the mixed coded signal and down-convert the echo signal to an intermediate frequency to obtain an intermediate frequency echo signal;

[0037] The signal accumulation unit is used to perform pulse compression and signal accumulation processing on the intermediate frequency echo signal in sequence to obtain a target signal.

[0038] One or more technical solutions provided by the present invention have at least the following technical effects or advantages:

[0039] 1. The present invention detects targets by transmitting mixed coded signals of X-band and Ku-band. When the signal of one frequency band is suppressed by noise interference, the signal of the other frequency band can still work normally, thereby improving the anti-interference ability of the radar system.

[0040] 2. This invention combines dual-band frequency agility with intra-pulse frequency coding to achieve dual anti-interference capabilities for radar signals in both the frequency and time domains. In the frequency domain, dual-band frequency agility enables rapid switching of radar signals between the X-band and Ku-band, reducing the likelihood of jammers capturing and tracking radar signals. In the time domain, intra-pulse frequency coding finely encodes the frequency characteristics within the mixed pulse, increasing the complexity and randomness of the radar signal and enhancing the radar's anti-interference capabilities.

[0041] 3. The solution of the present invention can be implemented on a single radar. Compared with the conventional multi-radar collaborative detection, the same synchronous clock signal is used for internal synchronization, without the need for external equipment such as Beidou satellites and GPS. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of the present invention, and do not constitute a limitation of the embodiments of the present invention;

[0043] Figure 1 This is a flow chart of a dual-band pulse compression coding frequency agility anti-interference method in embodiment 1 of the present invention;

[0044] Figure 2 1 is a schematic diagram showing the principle of the down-conversion process in the first embodiment of the present invention;

[0045] Figure 3 Schematic diagram of the intra-pulse frequency encoding method of the X-band pulse signal and the Ku-band pulse signal in the first embodiment of the present invention;

[0046] Figure 4 Schematic diagram of inserting a shield pulse into the mixed pulse sequence in the first embodiment of the present invention;

[0047] Figure 5 This is a schematic diagram of the composition of a dual-band pulse compression coding frequency agile anti-interference system in Example 1 of the present invention. DETAILED DESCRIPTION

[0048] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present invention and the features therein can be combined with each other without conflict.

[0049] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0050] Example 1

[0051] Please refer to Figure 1 The first embodiment of the present invention provides a dual-band pulse compression coding frequency agility anti-interference method, the method comprising the following steps:

[0052] Step 1: Triggered by the synchronization signal, a mixed coded signal of X-band and Ku-band is transmitted;

[0053] Step 2: receiving an echo signal of the mixed coded signal, and down-converting the echo signal to an intermediate frequency to obtain an intermediate frequency echo signal;

[0054] Step 3: Perform pulse compression and signal accumulation processing on the intermediate frequency echo signal in sequence to obtain the target signal.

[0055] Among them, the frequency source used in the anti-interference method of this embodiment is the frequency source involved in the prior art CN213240505U, which can achieve good phase consistency after broadband frequency hopping. In the hybrid coded signal, the X-band signal and the Ku-band signal are transmitted through the X-band phased array active antenna and the Ku-band phased array active antenna respectively. The down-conversion process can be specifically referred to Figure 2 First, the calibration signal is input through the calibration input. After being controlled by the calibration switch, the signal amplitude is limited by the limiter. Then, the signal flow is controlled by the RF switch and enters the low-noise amplifier for low-noise amplification. Then, the signal strength is finely adjusted by the digitally controlled attenuator. The image signal generated by the mixing is filtered out by the image filter. Then, it enters the intermediate frequency processing stage, including intermediate frequency amplification, filtering and switch control. After that, it is mixed with the local oscillator signal through a two-stage mixer (LO2 and LO1), and the RF signal is gradually down-converted to the intermediate frequency. During this period, the unnecessary frequency components are filtered out by the 50M filter, and the signal strength is increased by the amplifier. Finally, the signal amplitude is adjusted again by the digitally controlled attenuator, and the input of the RF signal is controlled by the RF switch. Finally, a 210MHz intermediate frequency signal is output, completing the entire down-conversion process.

[0056] Wherein, in step 1, the mixed coded signal includes a plurality of mixed pulses;

[0057] The mixed pulse is generated by X-band sub-pulses and Ku-band sub-pulses through intra-pulse frequency coding.

[0058] The encoding method of the intra-pulse frequency encoding includes:

[0059] Step 101: performing linear frequency modulation on any X-band sub-pulse and Ku-band sub-pulse to be transmitted, and randomly determining the transmission carrier frequency;

[0060] Step 102: Arrange the modulated X-band sub-pulse and Ku-band sub-pulse in the time domain to form the mixed pulse.

[0061] The X-band sub-pulse includes a first sub-pulse and a second sub-pulse, and the Ku-band sub-pulse includes a third sub-pulse and a fourth sub-pulse.

[0062] Among them, in the mixed pulse, the X-band sub-pulses and the Ku-band sub-pulses are arranged in the following order: the first sub-pulse, the third sub-pulse, the second sub-pulse and the fourth sub-pulse.

[0063] For example, see Figure 3 , this embodiment provides a diagram of the frequency coding of the X-band sub-pulse and the Ku-band sub-pulse, the duration of each sub-pulse is T sub , bandwidth is B sub The waveform is linear frequency modulation. For any X-band sub-pulse, its carrier frequency is randomly determined within the X-band. Similarly, for any Ku-band sub-pulse, its carrier frequency is randomly determined within the Ku-band. This ensures that the carrier frequency of each sub-pulse within the mixed pulse is different, and the carrier frequency distribution of the sub-pulses in different mixed pulses is also different. Finally, the X-band and Ku-band sub-pulses are arranged in the time domain in the order of the first sub-pulse, the third sub-pulse, the second sub-pulse, and the fourth sub-pulse.

[0064] In signal processing, the intermediate frequency echo signal is sorted through a narrowband filter bank to obtain sub-pulse signals corresponding to different frequency codes. The sub-pulse signals undergo analog-to-digital conversion (A / D) sampling to convert them from analog to digital, and then undergo segmented pulse compression. A system-provided synchronization trigger pulse is then used to adjust the timing of all sub-pulse data signals to ensure their temporal alignment. Finally, the adjusted sub-pulse data is spliced together to form a complete radar echo signal dataset. After pulse compression, signal accumulation processing is performed.

[0065] In this embodiment, when the radar system is normally powered on, frequency calibration and phase alignment operations must be performed.

[0066] The intra-pulse frequency coding method further includes: inserting a guard pulse into the mixed pulse;

[0067] The inserting of a guard pulse into the mixed pulse comprises:

[0068] An X-band cover pulse is inserted at the timing position corresponding to the Ku-band sub-pulse, and a Ku-band cover pulse is inserted at the timing position corresponding to the X-band sub-pulse.

[0069] Please refer to Figure 4 , Figure 4 A method for inserting a cover pulse is provided. In some preferred embodiments, in order to further mislead the jamming system, two Ku-band cover pulses can be inserted at the timing positions corresponding to the X-band sub-pulses using the two transmission channels of the third sub-pulse signal and the fourth sub-pulse signal. Similarly, two X-band cover pulses can also be inserted at the timing positions corresponding to the Ku-band sub-pulses.

[0070] The transmission carrier frequency of the X-band cover pulse is different from that of the X-band sub-pulse, and the transmission carrier frequency of the Ku-band cover pulse is different from that of the Ku-band sub-pulse. In some preferred embodiments, different carrier frequencies are used between the cover pulses in the same band.

[0071] Wherein, the X-band pulse signal and the Ku-band pulse signal are both frequency modulated waves.

[0072] wherein the frequencies of the first sub-pulse, the second sub-pulse, the third sub-pulse and the fourth sub-pulse are mutually coherent;

[0073] In step 3, the frequency of the synchronization trigger pulse for pulse compression and signal accumulation is coherent with the frequencies of the X-band sub-pulse and the Ku-band sub-pulse, and the frequencies of the X-band sub-pulse and the Ku-band sub-pulse are integer multiples of the frequency of the synchronization trigger pulse. For example, the frequencies of the first sub-pulse, the second sub-pulse, the third sub-pulse, and the fourth sub-pulse are 1, 2, 3, and 4 times the frequency of the synchronization trigger pulse, respectively.

[0074] Example 2

[0075] Please refer to Figure 5 A second embodiment of the present invention provides a dual-band pulse compression coding frequency agile anti-interference system, the system comprising:

[0076] A signal transmitting unit, configured to transmit a mixed coded signal of X-band and Ku-band under the triggering of a synchronization signal;

[0077] a signal receiving unit, configured to receive an echo signal of the mixed coded signal and down-convert the echo signal to an intermediate frequency to obtain an intermediate frequency echo signal;

[0078] The signal accumulation unit is used to perform pulse compression and signal accumulation processing on the intermediate frequency echo signal in sequence to obtain a target signal.

[0079] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0080] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A dual-band pulse compression coding frequency agility anti-interference method, characterized in that: The method comprises the following steps: Step 1: Triggered by the synchronization signal, a mixed coded signal of X-band and Ku-band is transmitted; Step 2: receiving an echo signal of the mixed coded signal, and down-converting the echo signal to an intermediate frequency to obtain an intermediate frequency echo signal; Step 3: performing pulse compression and signal accumulation processing on the intermediate frequency echo signal in sequence to obtain a target signal; In step 1, the mixed coded signal includes a plurality of mixed pulses; Wherein, the mixed pulse is generated by X-band sub-pulses and Ku-band sub-pulses through intra-pulse frequency coding; The encoding method of the intra-pulse frequency encoding includes: Step 101: performing linear frequency modulation on any X-band sub-pulse and Ku-band sub-pulse to be transmitted, and randomly determining the transmission carrier frequency; Step 102: Arranging the modulated X-band sub-pulse and Ku-band sub-pulse in the time domain to form the mixed pulse; The X-band sub-pulse includes a first sub-pulse and a second sub-pulse, and the Ku-band sub-pulse includes a third sub-pulse and a fourth sub-pulse; In the mixed pulse, the X-band sub-pulses and the Ku-band sub-pulses are arranged in the following order: the first sub-pulse, the third sub-pulse, the second sub-pulse and the fourth sub-pulse.

2. The dual-band pulse compression coding frequency agility anti-interference method according to claim 1, characterized in that: The encoding method of the intra-pulse frequency encoding further includes: inserting a guard pulse into the mixed pulse; The inserting of a guard pulse into the mixed pulse comprises: An X-band cover pulse is inserted at the timing position corresponding to the Ku-band sub-pulse, and a Ku-band cover pulse is inserted at the timing position corresponding to the X-band sub-pulse.

3. The dual-band pulse compression coding frequency agility anti-interference method according to claim 2, characterized in that: The transmission carrier frequency of the X-band cover pulse is different from that of the X-band sub-pulse, and the transmission carrier frequency of the Ku-band cover pulse is different from that of the Ku-band sub-pulse.

4. The dual-band pulse compression coding frequency agility anti-interference method according to claim 1, characterized in that: Both X-band sub-pulses and Ku-band sub-pulses are frequency-modulated waves.

5. The dual-band pulse compression coding frequency agility anti-interference method according to claim 1, characterized in that: The frequencies of the first sub-pulse, the second sub-pulse, the third sub-pulse and the fourth sub-pulse are mutually coherent; In step 3, the frequency of the synchronous trigger pulse for pulse compression and signal accumulation is coherent with the frequencies of the X-band sub-pulse and the Ku-band sub-pulse, and the frequencies of the X-band sub-pulse and the Ku-band sub-pulse are respectively integer multiples of the frequency of the synchronous trigger pulse.

6. A dual-band pulse compression coding frequency agility anti-interference system, characterized in that: The system comprises: A signal transmitting unit, configured to transmit a mixed coded signal of X-band and Ku-band under the triggering of a synchronization signal; a signal receiving unit, configured to receive an echo signal of the mixed coded signal and down-convert the echo signal to an intermediate frequency to obtain an intermediate frequency echo signal; a signal accumulation unit, configured to sequentially perform pulse compression and signal accumulation processing on the intermediate frequency echo signal to obtain a target signal; The mixed coded signal includes a plurality of mixed pulses; Wherein, the mixed pulse is generated by X-band sub-pulses and Ku-band sub-pulses through intra-pulse frequency coding; The encoding method of the intra-pulse frequency encoding includes: Step 101: performing linear frequency modulation on any X-band sub-pulse and Ku-band sub-pulse to be transmitted, and randomly determining the transmission carrier frequency; Step 102: Arranging the modulated X-band sub-pulse and Ku-band sub-pulse in the time domain to form the mixed pulse; The X-band sub-pulse includes a first sub-pulse and a second sub-pulse, and the Ku-band sub-pulse includes a third sub-pulse and a fourth sub-pulse; In the mixed pulse, the X-band sub-pulses and the Ku-band sub-pulses are arranged in the following order: the first sub-pulse, the third sub-pulse, the second sub-pulse and the fourth sub-pulse.

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