A method for anti-interference of FM fuze based on adaptive weighting of harmonic envelope

Abstract

The present invention relates to an anti-interference method for frequency modulation fuses based on adaptive weighting of harmonic envelopes, and belongs to the field of information countermeasure technology. The present invention obtains the coefficients of each harmonic containing target information by performing fast Fourier transform on the difference frequency signal of the frequency modulation fuse, and determines the corresponding harmonic position according to the predetermined explosion height. By adaptive weighted processing between two adjacent harmonics combined with threshold judgment, the logical characteristics in the missile-target intersection process are utilized to identify the real target signal and realize precise control of the explosion point. The present invention obtains the intersection information from far to near contained in the real target echo signal by jointly extracting the harmonic envelope corresponding to the predetermined explosion height and the adjacent high-order harmonic envelope, and can suppress interference signals that do not meet this logical characteristic; by multiplying the two harmonic envelopes, the relative correlation sidelobe level is reduced, the clutter interference is suppressed, and the target detection accuracy is improved.

Description

Technical Field

[0001] The invention relates to a frequency modulation fuze anti-interference method based on harmonic envelope adaptive weighting, belonging to the technical field of information countermeasures. Background Art

[0002] Frequency-modulation (FM) fuzes use the frequency difference between the transmitted and echoed signals to determine distance. Due to their simple algorithm and easy hardware implementation, they offer higher ranging accuracy and more reliable performance than continuous-wave Doppler fuzes. Currently, radio fuzes are widely deployed in various countries, with FM fuzes being the dominant type in recent years. Based on the development of fuzes in various countries, FM fuzes remain a major focus of research and development.

[0003] The frequency modulation fuze transmits a constant amplitude continuous wave signal with frequency change controlled by the modulation signal to the target. The frequency of the transmitted signal is a function of time. By measuring the main frequency components of the intermediate frequency signal obtained by mixing the target echo with the reference signal, the time delay of the relative path to the target is determined, and then the relative distance to the target can be obtained, thereby deciding whether to output the start signal.

[0004] Generally speaking, the detection range of conventional ammunition radio fuzes is relatively short. Ideally, the impact point is controlled by determining the envelope threshold of a single harmonic corresponding to the predetermined burst height in the difference frequency signal. However, in the complex electromagnetic environment of the battlefield, various active electronic devices can cause severe interference to FM fuzes. Taking a typical swept-frequency jammer as an example, the jammer's sweep bandwidth generally covers the fuze's operating frequency band. When the jamming signal frequency falls within the fuze's signal receiving bandwidth, the difference frequency spectrum of the swept jamming signal can completely cover the fuze's true target signal spectrum, affecting the amplitude distribution of each harmonic in the intermediate frequency signal. Furthermore, the jamming signal's energy is generally higher than that of the true target echo signal, which suppresses the spectrum of the true target echo's difference frequency signal, generating a large number of abnormal false peaks. This affects the effectiveness of the traditional FM fuze's burst height determination based on extracted harmonic envelope characteristics, leading to premature detonation or misfire.

[0005] Traditional FM fuze beat frequency signal processing methods rely solely on a simple threshold decision based on a single harmonic envelope corresponding to a predetermined burst height. This poses the risk of performance degradation or even failure in the complex electromagnetic environment of the battlefield. Driven by demand and technology, the countermeasures characteristics of FM fuzes have evolved and are evolving at an accelerating pace. The development of FM fuze jamming technology has necessitated a significant improvement in FM fuze anti-jamming capabilities, which is crucial to ensuring the proper functioning of FM fuzes and maximizing the destructive effectiveness of ammunition. Summary of the Invention

[0006] The purpose of the present invention is to provide an anti-interference method for FM fuze based on harmonic envelope adaptive weighting. By performing fast Fourier transform on the difference frequency signal of the FM fuze, the coefficients of each harmonic containing target information are obtained, and the corresponding harmonic position is determined according to the predetermined explosion height. By adaptive weighting processing between two adjacent harmonics combined with threshold judgment, the logical characteristics of the missile-target rendezvous process are utilized to reduce the level of related side lobes, identify the real target signal, realize precise control of the explosion point, and solve the problem of insufficient anti-interference ability of the FM fuze.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] The present invention discloses a method for anti-interference of a frequency modulation fuze based on harmonic envelope adaptive weighting, comprising the following steps:

[0009] Step 1: Perform fast Fourier transform processing on the FM fuze beat frequency signal according to the data length of an integer multiple of the modulation period to obtain each harmonic containing the target distance information. The specific steps include the following:

[0010] Step 1.1 Fourier transform of the FM fuse beat frequency signal:

[0011] FM fuze transmission signal x t (t) is shown in formula (1):

[0012]

[0013] Among them, f0 is the initial frequency of the FM fuze transmission signal, t is the corresponding time of the current signal, T m is the modulation period, β is the frequency modulation slope, rect(·) is the rectangular window function, n=1,2,3..., is the relative period number;

[0014] True target echo signal x r (t) is shown in formula (2):

[0015]

[0016] Where τ is the relative path delay between the missile and the target;

[0017] Furthermore, ignoring the influence of irregular areas, the difference frequency signal x of the FM fuse Δf (t) is shown in formula (3):

[0018]

[0019] Furthermore, the FM fuse difference frequency signal x Δf (t) is Fourier transformed, as shown in formula (4):

[0020]

[0021] Among them, X(kf m ) is the frequency modulation fuse difference frequency signal x Δf Fourier transform result of (t), k = 1, 2, ..., N is the corresponding harmonic number, N is the signal length;

[0022] Step 1.2 Extract the modulus of the Fourier transform result:

[0023] FM fuse difference frequency signal x Δf The Fourier transform result X(kf m ) is in complex form, extract the Fourier transform result X(kf m ) modulus value |X(kf m )|, as shown in formula (5):

[0024]

[0025] Among them, Re[X(kf m )] is the Fourier transform result X(kf m ), Im[X(kf m )] is the Fourier transform result X(kf m )

[0026] Step 1.3 Extract the harmonic envelopes of different periods:

[0027] Repeat steps 1.1 and 1.2 for the frequency modulation fuze difference frequency signal data of each period during the missile-target rendezvous process. The modulus value of each harmonic in different periods is the harmonic envelope, as shown in formula (6):

[0028]

[0029] Step 2: Determine the corresponding FM fuse beat frequency signal according to the predetermined explosion height, extract the corresponding harmonics and adjacent higher harmonics in step 1, and extract the two harmonic envelopes through low-pass filtering. This specifically includes the following sub-steps:

[0030] Step 2.1 Extract the harmonic envelope corresponding to the predetermined explosion height and its adjacent higher harmonic envelopes:

[0031] According to the actual process of the missile-target intersection from far to near and the difference frequency of the FM fuze difference frequency signal corresponding to the predetermined explosion height, the corresponding harmonic envelope in step 1 and its adjacent high-order harmonic envelope are extracted at the same time. According to formula (6), the relationship between the predetermined explosion height and the harmonic order k of the harmonic envelope peak in the FM fuze difference frequency signal is shown in formula (7):

[0032]

[0033] Where R is the predetermined explosion height, c is the propagation speed of electromagnetic waves in free space;

[0034] Step 2.2: Low-pass filtering of two harmonic envelopes:

[0035] Perform low-pass filtering on the harmonic envelope corresponding to the predetermined explosion height extracted in step 2.1 and its adjacent higher-order harmonic envelopes to reduce the impact of abnormal peaks caused by background noise;

[0036] Step 3: Adaptively weight the two harmonic envelopes extracted in step 2, specifically including the following sub-steps:

[0037] Step 3.1 Determine the optimal delay time:

[0038] Delay the adjacent high-order harmonic envelopes, the optimal delay time τ d As shown in formula (8)

[0039]

[0040] Among them, V r is the relative velocity between the missile and the target, and B is the modulation bandwidth of the transmitting signal;

[0041] Step 3.2 Adaptive weighting processing:

[0042] After delaying the adjacent high-order harmonic envelope, the envelope is multiplied with the harmonic envelope corresponding to the predetermined explosion height as an adaptive weight;

[0043] The two harmonic envelopes contain the logical characteristics of the intersection process of the missile and the target from far to near;

[0044] Step 4: Amplitude threshold judgment:

[0045] The result of adaptive weighted processing is subjected to threshold judgment. If the minimum threshold requirement is met, it is judged as a target signal and the detonation information is output to the next level; if the minimum threshold requirement is not met, it is judged as no target and waits for the next frame of data judgment.

[0046] Beneficial effects:

[0047] 1. The present invention provides an anti-interference method for FM fuzes based on adaptive weighting of harmonic envelopes. By jointly extracting the harmonic envelope corresponding to a predetermined explosion height and the adjacent higher-order harmonic envelopes, the method obtains the far-to-near intersection information contained in the real target echo signal, thereby suppressing interference signals that do not meet this logical characteristic.

[0048] 2. The present invention provides an anti-interference method for FM fuze based on adaptive weighting of harmonic envelopes, which reduces the relative correlation sidelobe level, suppresses clutter interference, and improves target detection accuracy by multiplying two harmonic envelopes. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 This is an overall flow chart of a frequency modulation fuze anti-interference method based on harmonic envelope adaptive weighting of the present invention;

[0050] Figure 2 This is a flow chart of harmonic envelope adaptive weighting processing of a frequency modulation fuze anti-interference method based on harmonic envelope adaptive weighting of the present invention;

[0051] Figure 3 Schematic diagram of 6th harmonic envelope and 7th harmonic envelope information;

[0052] Figure 4 Schematic diagram of the low-pass filtering results of the 6th harmonic envelope and the 7th harmonic envelope;

[0053] Figure 5 This is a schematic diagram comparing the results of single-channel harmonic envelope processing and dual-channel harmonic envelope weighted processing. DETAILED DESCRIPTION

[0054] In order to better illustrate the purpose and advantages of the present invention, the invention is further described below with reference to the accompanying drawings and examples.

[0055] Example 1:

[0056] In this embodiment, the predetermined explosion height is 9m, the transmission signal is a sawtooth frequency modulated continuous wave signal, the modulation period is 100KHz, and the modulation bandwidth is 100MHz. First, a fast Fourier transform of one cycle length is performed on the input FM fuse difference frequency signal to obtain the global Fourier spectrum of the FM fuse difference frequency signal. The harmonic envelope corresponding to the predetermined explosion height and the adjacent high-order harmonic envelope are extracted. The high-order harmonic envelope is delayed and multiplied with the harmonic envelope corresponding to the predetermined explosion height before output. Finally, the signal is compared with the preset threshold. If it exceeds the minimum threshold requirement, it is determined to be a target signal and a start signal is output to the next level. Figure 1 As shown, the specific steps include:

[0057] Step 1: Perform fast Fourier transform processing on the FM fuze beat frequency signal according to the data length of an integer multiple of the modulation period to obtain each harmonic containing the target distance information. The specific steps include the following:

[0058] Step 1.1 Fourier transform of the FM fuse beat frequency signal:

[0059] FM fuze transmission signal x t (t) is shown in formula (1):

[0060]

[0061] Among them, f0 is the initial frequency of the FM fuze transmission signal, t is the corresponding time of the current signal, Tm is the modulation period, β is the frequency modulation slope, rect(·) is the rectangular window function, n=1,2,3..., is the relative period number;

[0062] True target echo signal x r (t) is shown in formula (2):

[0063]

[0064] Where τ is the relative path delay between the missile and the target;

[0065] Furthermore, ignoring the influence of irregular areas, the difference frequency signal x of the FM fuse Δf (t) is shown in formula (3):

[0066]

[0067] Furthermore, the FM fuse difference frequency signal x Δf (t) is Fourier transformed, as shown in formula (4):

[0068]

[0069] Among them, X(kf m ) is the frequency modulation fuse difference frequency signal x Δf Fourier transform result of (t), k = 1, 2, ..., N is the corresponding harmonic number, N is the signal length;

[0070] Step 1.2 Extract the modulus of the Fourier transform result:

[0071] FM fuse difference frequency signal x Δf (t) Perform Fourier transform on the result X(kf m ) is in complex form, extract the Fourier transform result X(kf m ) modulus value |X(kf m )|, as shown in formula (5):

[0072]

[0073] Among them, Re[X(kf m )] is the Fourier transform result X(kf m ), Im[X(kf m )] Fourier transform result X(kf m )

[0074] Step 1.3 Extract the harmonic envelopes of different periods:

[0075] Repeat steps 1.1 and 1.2 for the frequency modulation fuze difference frequency signal data of each period during the missile-target rendezvous process. The modulus value of each harmonic in different periods is the harmonic envelope, as shown in formula (6):

[0076]

[0077] Step 2: Determine the corresponding FM fuse beat frequency signal according to the predetermined explosion height, extract the corresponding harmonics and adjacent higher harmonics in step 1, and extract the two harmonic envelopes through low-pass filtering. This specifically includes the following sub-steps:

[0078] Step 2.1 Extract the harmonic envelope corresponding to the predetermined explosion height and its adjacent higher harmonic envelopes:

[0079] According to the actual process of the missile-target intersection from far to near and the difference frequency of the FM fuze difference frequency signal corresponding to the predetermined explosion height, the corresponding harmonic envelope in step 1 and its adjacent high-order harmonic envelope are extracted at the same time. According to formula (6), the relationship between the predetermined explosion height and the harmonic order k of the harmonic envelope peak in the FM fuze difference frequency signal is shown in formula (7):

[0080]

[0081] Where R is the predetermined explosion height, c is the propagation speed of electromagnetic waves in free space;

[0082] In the embodiment, the predetermined blasting height R is 9m;

[0083] According to formula (7), the harmonic envelope corresponding to the predetermined explosion height is extracted, and the adjacent high-order harmonic envelopes are extracted at the same time;

[0084] Combined with the specific parameters of this embodiment, the 6th harmonic envelope and the adjacent 7th harmonic envelope corresponding to the predetermined explosion height of 9m in the fast Fourier transform result are extracted respectively, as shown in FIG. Figure 3 As shown;

[0085] Step 2.2: Low-pass filtering of two harmonic envelopes:

[0086] Perform low-pass filtering on the 6th harmonic envelope and the 7th harmonic envelope extracted in step 2.1 to reduce the influence of abnormal peaks caused by background noise, such as Figure 4 As shown;

[0087] Step 3: Adaptively weight the two harmonic envelopes extracted in step 2, specifically including the following sub-steps:

[0088] Step 3.1 Determine the optimal delay time:

[0089] Delay the adjacent high-order harmonic envelopes, the optimal delay time τ d As shown in formula (8)

[0090]

[0091] Among them, V r is the relative velocity between the missile and the target, and B is the modulation bandwidth of the transmitting signal;

[0092] In the embodiment, the relative speed V r The transmission speed is 300m / s, and the modulation bandwidth B of the transmitted signal is 100MHz. Then determine the optimal delay time τ d 5ms;

[0093] Step 3.2 Adaptive weighting processing:

[0094] After delaying the adjacent high-order harmonic envelope, the envelope is multiplied with the harmonic envelope corresponding to the predetermined explosion height as an adaptive weight;

[0095] The 7th harmonic envelope is low-pass filtered and delayed by 5ms, and then multiplied with the 6th harmonic envelope by a multiplier and output. The decibel graph of the peak normalized result is as follows Figure 5 As shown in the figure, the relative sidelobe of the output result of the single harmonic envelope is relatively high, at -9.95dB, while the relative sidelobe of the output result of the two-way adaptive weighted harmonic envelope is only -18.72dB. The two-way harmonic adaptive weighted processing method has a stronger clutter suppression capability.

[0096] Step 4: Amplitude threshold judgment:

[0097] Perform threshold judgment on the output result. The specific value of the judgment threshold is related to the performance of the front-end antenna.

[0098] In the embodiment, the decision threshold is set to 0.01V. If the minimum threshold requirement is met, it is determined to be a target signal. If the minimum threshold requirement is not met, it is determined to be no target and waits for the next frame of data to be judged.

[0099] In the embodiment, the peak value of the adaptive weighted harmonic envelope is 0.012V, which meets the minimum threshold requirement and is determined to be a real target corresponding to a blast height of 9m, which is consistent with the actual situation;

[0100] The output results of the two-way adaptive weighted harmonic envelope contain the logical characteristics of the real target's intersection process from far to near, which enhances the anti-interference ability. After the adaptive weighted multiplication processing, the related sidelobes are suppressed, which is conducive to the selection of the minimum threshold. Compared with the traditional single-way harmonic envelope threshold judgment, it has stronger robustness.

[0101] The above specific description further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A frequency modulation fuze anti-interference method based on harmonic envelope adaptive weighting, characterized by: The steps include: Step 1: Perform fast Fourier transform on the FM fuze beat frequency signal according to the data length of integer multiples of the modulation period to obtain each harmonic containing the target distance information; Step 2: Determine the beat frequency of the FM fuse beat frequency signal according to the predetermined explosion height, extract the harmonic of the corresponding order in step 1 and the adjacent higher harmonics, and extract the two harmonic envelopes through low-pass filtering; Step 3: Adaptively weight the two harmonic envelopes extracted in step 2; specifically, the following sub-steps are included: Step 3.1 Determine the optimal delay time: Delay the adjacent high-order harmonic envelopes, the optimal delay time τ d As shown in formula (8) Among them, V r is the relative velocity between the missile and the target, and B is the modulation bandwidth of the transmitting signal; Step 3.2 Adaptive weighting processing: After delaying the adjacent high-order harmonic envelope, the envelope is multiplied with the harmonic envelope corresponding to the predetermined explosion height as an adaptive weight; The two harmonic envelopes contain the logical characteristics of the intersection process of the missile and the target from far to near; Step 4: Amplitude threshold judgment: The result of adaptive weighted processing is subjected to threshold judgment. If the minimum threshold requirement is met, it is judged as a target signal and the detonation information is output to the next level; if the minimum threshold requirement is not met, it is judged as no target and waits for the next frame of data judgment.

2. The method for anti-interference of FM fuze based on harmonic envelope adaptive weighting according to claim 1, characterized in that: Step 1 specifically includes the following sub-steps: Step 1.1 Fourier transform of the FM fuse beat frequency signal: FM fuze transmission signal x t (t) is shown in formula (1): Among them, f0 is the initial frequency of the FM fuze transmission signal, t is the corresponding time of the current signal, T m is the modulation period, β is the frequency modulation slope, rect(·) is the rectangular window function, n=1,2,3..., is the relative period number; True target echo signal x r (t) is shown in formula (2): Where τ is the relative path delay between the missile and the target; Furthermore, ignoring the influence of irregular areas, the difference frequency signal x of the FM fuse Δf (t) is shown in formula (3): Furthermore, the FM fuse difference frequency signal x Δf (t) is Fourier transformed, as shown in formula (4): Among them, X(kf m ) is the frequency modulation fuse difference frequency signal x Δf Fourier transform result of (t), k = 1, 2, ..., N is the corresponding harmonic number, N is the signal length; Step 1.2 Extract the modulus of the Fourier transform result: FM fuse difference frequency signal x Δf The Fourier transform result X(kf m ) is in complex form, extract the Fourier transform result X(kf m ) modulus value |X(kf m )|, as shown in formula (5): Among them, Re[X(kf m )] is the Fourier transform result X(kf m ), Im[X(kf m )] is the Fourier transform result X(kf m ) Step 1.3 Extract the harmonic envelopes of different periods: Repeat steps 1.1 and 1.2 for the frequency modulation fuze difference frequency signal data of each period during the missile-target rendezvous process. The modulus value of each harmonic in different periods is the harmonic envelope, as shown in formula (6):

3. The method for anti-interference of FM fuze based on harmonic envelope adaptive weighting according to claim 2, characterized in that: Step 2 specifically includes the following sub-steps: Step 2.1 Extract the harmonic envelope corresponding to the predetermined explosion height and its adjacent higher harmonic envelopes: According to the actual process of the missile-target intersection from far to near and the difference frequency of the FM fuze difference frequency signal corresponding to the predetermined explosion height, the corresponding harmonic envelope in step 1 and its adjacent high-order harmonic envelope are extracted at the same time. According to formula (6), the relationship between the predetermined explosion height and the harmonic order k of the harmonic envelope peak in the FM fuze difference frequency signal is shown in formula (7): Where R is the predetermined explosion height, c is the propagation speed of electromagnetic waves in free space; Step 2.2: Low-pass filtering of two harmonic envelopes: Perform low-pass filtering on the harmonic envelope corresponding to the predetermined explosion height extracted in step 2.1 and its adjacent higher-order harmonic envelope to reduce the impact of abnormal peaks caused by background noise.

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