Anti-folding clutter method based on staggered MTI
By employing an anti-folding clutter method based on staggered MTI, and utilizing frequency-modulated agile radar design and alternating positive and negative pulse slopes, the problem of clutter aliasing in low-altitude slow-speed target detection by radar is solved, achieving effective suppression of far-field clutter and clear separation of target signals.
Patent Information
- Application Number
- CN202511788064.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-01
- Publication Date
- 2026-02-13
AI Technical Summary
Modern radars face severe ground/sea clutter interference in airborne or spaceborne down-looking detection, especially when detecting low-altitude, slow-moving, small targets. The weak echo overlaps with the Doppler frequency of the clutter main lobe, leading to a decrease in the detection performance of traditional Doppler filters. Far-field folded clutter and near-range target echoes are mixed, increasing the difficulty of detection. Moreover, existing solutions are costly and difficult to implement in engineering.
An anti-folding clutter method based on staggered MTI is adopted. By establishing a slow-time total echo model of frequency-modulated agile airborne radar, the signal is down-converted and matched-filtered. After extracting the slow-time series, staggered MTI filtering and coherent accumulation are performed. The far-field folding clutter is suppressed by using pulse design with alternating positive and negative slopes.
It effectively suppresses far-field folded clutter, maintains target detection performance, significantly reduces clutter influence, and achieves effective separation and detection of target signals.
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Figure CN121522582A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to aluminum plastic door and window related methods, in particular to an anti-folding clutter method based on staggered MTI. BACKGROUND
[0002] Modern radars face serious ground / sea clutter interference in down-looking detection under airborne or spaceborne, especially when detecting low-altitude slow-moving small targets (such as unmanned aerial vehicles, cruise missiles), the weak echo and the main lobe Doppler frequency of the clutter overlap, resulting in the decline of the detection performance of traditional Doppler filtering. The far-zone folding clutter is formed due to the problem of range ambiguity: the echo of a far-distance target is folded to a near-distance cell, mixed with the real target, increasing the detection difficulty. The traditional fixed PRF (Pulse Repetition Frequency) system cannot meet the needs of range measurement and velocity measurement, and the staggered PRF technology improves the velocity measurement performance through a multi-cycle pulse sequence, but introduces folding clutter, which makes the far-zone clutter and the echo of a near-distance target mixed in the range dimension, drowning the weak small target. Existing solutions include methods based on high-PRF super-resolution signal processing (such as compressed sensing, matrix filling), which can recover the ambiguity-free range-Doppler spectrum from undersampled data, but the requirements for signal sparsity and system linearity are extremely high, making it difficult to implement in engineering and costly; another type of dual-frequency alternate transmission mode solves the real range through the difference in frequency points, but it compresses the Doppler bandwidth, which is not conducive to slow target detection, and requires consistent target scattering characteristics, which is strict on the radar frequency conversion capability. SUMMARY
[0003] The purpose of the present application is to provide an anti-folding clutter method based on staggered MTI, comprising the following steps: step S100, establishing a slow-time total echo model of a frequency-modulated agile airborne radar in a clutter environment, and performing down-conversion processing on the signal; step S200, performing pulse compression on the target echo signal processed by the down-conversion, and performing matched filtering through positive and negative filters; step S300, extracting the slow-time sequence of the matched filtered target echo signal; step S400, performing staggered MTI filtering processing on the slow-time sequences of the two groups of echo signals; step S500, performing coherent accumulation processing on the echo signals processed by the staggered MTI filtering; step S600, performing non-coherent accumulation processing on the echo signals processed by the coherent accumulation and not having other strong interference signals; step S700, performing folding clutter rejection processing on the echo signals processed by the non-coherent accumulation, and finally outputting the signal result.
[0004] Further, step S100 comprises:
[0005] Step S101, establishing a slow-time total echo model of a frequency-modulated agile airborne radar in a clutter environment,
[0006] ,
[0007] wherein A is the target complex amplitude, is the frequency modulation slope of the i-th pulse, is the echo time delay of the target i-th pulse, is the carrier frequency, t is the time variable, is the pulse width;
[0008] Step S102, the target echo signal is processed by digital down conversion, the local oscillation signal is , then the echo signal of the target signal of the i-th pulse after down conversion processing is represented as
[0009] ,
[0010] wherein, is the target amplitude after digital down conversion processing;
[0011] Step S103, the echo signal during the entire CPI is represented as a set of all pulse echo signals,
[0012] .
[0013] Further, step S300 includes:
[0014] Step S301, extracting the positive slope group slow time sequence,
[0015] ,
[0016] wherein, is the distance gate, ;
[0017] Step S302, extracting the negative slope group slow time sequence,
[0018] ,
[0019] wherein .
[0020] Further, step S400 includes:
[0021] Step S401, MTI processing is performed on the positive slope group slow time sequence,
[0022] ;
[0023] Step S402, MTI processing is performed on the negative slope group slow time sequence,
[0024] .
[0025] Further, step S500 includes:
[0026] Step S501, MTD processing, i.e. coherent accumulation processing, is performed on the slow-time sequence of the positive slope group,
[0027] ;
[0028] Step S502, MTD processing, i.e. coherent accumulation processing, is performed on the slow-time sequence of the negative slope group,
[0029] .
[0030] Further, step S700 comprises:
[0031] Step S701, two complete range-Doppler spectra, , are obtained for each range cell , the amplitude difference of the Doppler cells corresponding to the positive and negative slope groups is calculated,
[0032] ,
[0033] wherein, represents the modulus (amplitude) of a complex number;
[0034] Step S702, the amplitude difference threshold is set, which is determined by the following formula,
[0035] ,
[0036] wherein, is an adjustment factor, taking 2-3, is the system noise level, is the time-bandwidth product,
[0037] or an adaptive threshold is used,
[0038] ,
[0039] wherein, is a proportional coefficient, taking 1.5-2.0;
[0040] Step S703, when , the amplitude difference is less than the threshold, it is determined as a target signal, and target signal processing is performed,
[0041] ,
[0042] ;
[0043] Step S704, the output signal result is,
[0044] 。
[0045] Compared with the prior art, the present application has the following advantages: by orthogonalizing the front and rear repeated cycles of pulses, using the method of alternately changing the positive and negative slopes of the waveforms and changing the repetition frequency to suppress the far-zone folded clutter, the suppression characteristics of the positive and negative slope frequency-modulated pulses on the folded clutter are effectively utilized, the influence of the folded clutter is significantly reduced while the target detection performance is maintained.
[0046] The present application will be further described below in conjunction with the accompanying drawings of the specification. BRIEF DESCRIPTION OF DRAWINGS
[0047] Figure 1 It is an algorithm flow diagram.
[0048] Figure 2 It is a single CPI internal reference staggered waveform arrangement diagram.
[0049] Figure 3 It is a distance-amplitude diagram of the positive slope group MTI.
[0050] Figure 4 It is a distance-amplitude diagram of the negative slope group MTI.
[0051] Figure 5 It is a distance-amplitude diagram of the positive slope group MTD.
[0052] Figure 6 It is a distance-amplitude diagram of the negative slope group MTD.
[0053] Figure 7 It is a folded clutter suppression algorithm diagram. DETAILED DESCRIPTION
[0054] In combination Figure 1 , an anti-folded clutter method based on staggered MTI, the specific steps are as follows: step S100, a slow-time total return model of a frequency-modulated agile airborne radar in a clutter environment is established, and the signal is down-converted; step S100 includes:
[0055] Step S101, an inter-pulse agile single-target slow-time return model based on wide speed coverage is established, it is assumed that the airborne radar transmits P pulses in a CPI, the bandwidth is B, the intermediate frequency carrier frequency is , and the frequency-modulated slope and the carrier frequency of the pulse train exist inter-pulse agility. In the 1st, 3rd, 5th, …, P-1th pulses, the linear frequency-modulated signal slope is positive, that is , in the 2nd, 4th, 6th, …, Pth pulses, the linear frequency-modulated signal slope is negative, that is . Then the model of the slow-time return signal of a single target in the ith pulse is represented as:
[0056] (1)
[0057] where A is the target complex amplitude, is the frequency modulation slope of the i-th pulse, is the echo time delay of the i-th pulse, is the carrier frequency, and t is the time variable.
[0058] Step S102, the target echo signal is down-converted, and the local oscillation signal is .
[0059] The echo signal of the i-th pulse after the target signal is down-converted is represented as:
[0060] (2)
[0061] where, is the target amplitude after digital down-conversion.
[0062] Step S103, the echo signal during the entire CPI can be represented as a set of all pulse echo signals:
[0063] (3)
[0064] Step S200, the down-converted target echo signal is pulse compressed, and matched filtering is performed through positive and negative filters;
[0065] For a linear frequency modulation signal, the maximum output of the matched filter occurs at the time t equal to the target time delay . Matched filtering provides pulse compression gain, and the peak amplitude is proportional to the signal energy and the energy of the matched filter coefficient.
[0066] By grouping the echo signals of the entire CPI, the positive and negative echo signals are set, and when the positive slope echo signal enters the negative slope matched filter, the pulse compression gain will be greatly reduced due to the mismatch of the frequency modulation slope, and the peak power will be reduced.
[0067] The peak amplitude of the pulse compression output under the matched condition is:
[0068] (4)
[0069] where A is the target complex amplitude, is the frequency modulation slope, is the pulse width.
[0070] And in the mismatch case (positive slope signal using negative slope matched filter), the peak amplitude is:
[0071] (5)
[0072] The ratio of peak amplitude in the matched case to that in the mismatch case is:
[0073] (6)
[0074] Where D is the time-bandwidth product, when the time-bandwidth product D is very large (which is the typical case for pulse compression radar), Therefore:
[0075] (7)
[0076] This shows that the filter mismatch causes a large loss of signal amplitude compared to the matched case. Therefore, for the target signal, the matched filter can improve the compression gain. And for the folding clutter, when the positive slope pulse signal enters the negative slope pulse receiving section (or the negative slope pulse signal enters the positive slope pulse receiving section), the signal will be suppressed to a low amplitude noise floor after the matched filter, so as to achieve the purpose of suppressing the folding clutter.
[0077] Step S300, extracting the slow time sequence of the matched filtered target echo signal;
[0078] After matched filtering, the slow time sequence is extracted for each range gate (corresponding to the fast time ):
[0079] Step S301, extracting the slow time sequence of the positive slope group:
[0080] (8)
[0081] Where .
[0082] Step S302, extracting the slow time sequence of the negative slope group:
[0083] (9)
[0084] Where .
[0085] Step S400, performing staggered MTI filtering processing on the slow time sequences of the two groups of echo signals;
[0086] Step S401, performing MTI processing on the slow time sequence of the positive slope group:
[0087] (10)
[0088] Step S402, MTI is performed on the slow-time sequence of the negative slope group:
[0089] (11)
[0090] Step S500, coherent accumulation processing is performed on the echo signal that has been subjected to the incoherent MTI filtering processing;
[0091] Step S501, MTD processing is performed on the slow-time sequence of the positive slope group:
[0092] (12)
[0093] Step S502, MTD processing is performed on the slow-time sequence of the negative slope group:
[0094] (13)
[0095] Through the MTI and MTD processing, the clutter can be further suppressed and the Doppler frequency of the moving target can be detected.
[0096] Step S600, non-coherent accumulation processing is performed on the echo signal that has been subjected to the coherent accumulation processing and does not have other strong interference signals;
[0097] Step S700, folding clutter rejection processing is performed on the echo signal that has been subjected to the non-coherent accumulation processing, and a final signal result is output;
[0098] The amplitude difference calculation and threshold decision are performed on the two groups of signals after the MTD,
[0099] Step S701, two complete range-Doppler spectra are obtained after the MTD processing of step S500: , For each range unit , the amplitude difference of the Doppler unit corresponding to the positive and negative slope groups is calculated:
[0100] (14)
[0101] wherein represents the modulus (amplitude) of a complex number.
[0102] Step S702, an amplitude difference threshold is set, which can be determined in the following manner:
[0103] (15)
[0104] wherein: is an adjustment factor, usually 2~3, is the system noise level, is the time-bandwidth product.
[0105] Or use adaptive threshold:
[0106] (16)
[0107] Wherein: is a proportionality coefficient, usually 1.5~2.0.
[0108] Fold clutter rejection algorithm, for each distance-Doppler unit , the following decision and processing:
[0109] Step S703, when The amplitude difference is small, and the target signal is determined, and the target signal processing is performed:
[0110] (17)
[0111] Where the maximum comparison is based on the amplitude value:
[0112] (18) When The amplitude difference is large, and the folded clutter is determined, and the folded clutter processing is performed:
[0113] (19)
[0114] Where the minimum comparison is based on the amplitude value:
[0115] (20)
[0116] Step S704, the output signal result is:
[0117] (21)
[0118] The algorithm effectively utilizes the suppression characteristics of positive and negative slope frequency modulation pulses on folded clutter, while maintaining target detection performance, significantly reducing the influence of folded clutter. The overall algorithm implementation process is shown in Figure 1 .
[0119] Embodiment: In view of the poor suppression effect of MTI filter on far-zone distance folded clutter, a design method of anti-folded clutter based on uneven MTI is proposed.
[0120] Refer to Figure 2The simulation experiment is as follows: by combining the modulation domain slope agility and the folding clutter elimination method, the long-distance folding distance Doppler spread clutter is effectively suppressed, and the target signal submerged by the distance folding clutter is successfully separated.
[0121] The overall waveform adopts a multi-parameter alternating pulse repetition period arrangement, and the overall contains 32 pulse repetition periods. The waveform of every two PRTs forms a small group. The PRTs in the small group are positively and negatively frequency-modulated and orthogonally isolated, and the carrier frequency is agile. , , , Four small groups of 8 pulses (PRTs) form a cycle, and there are a total of four cycles. , , , , , , ,
[0122] The radar system parameters of the simulation are shown in Table 1.
[0123] Table 1 Radar system parameters
[0124] Radar system parameters Values Signal carrier frequency 150 MHz Signal bandwidth 10 MHz T [1334, 1204, 1139, 1123] us Target range 32 km PRT [774, 560, 563, 579, 644] us range expansion variance 3 km Doppler spread variance 10 Hz Folded clutter range [3.9, 23.4, 33.1, 35.5, 36.0] km
[0125] Referring to Figures 3-6 , the results after grouping MTI and MTD, wherein Figure 3 , Figure 4 is a range-amplitude graph of the positive slope group MTI and the positive slope group MTD, Figure 5 , Figure 6 is a range-amplitude graph of the positive slope group MTI and the positive slope group MTD. Due to the slope agility and the carrier frequency agility, when the positive slope pulse enters the negative slope pulse receiving section, after passing through the matched filter, the positive slope pulse will be suppressed to a low-amplitude noise floor due to the low positive and negative slope cross-correlation, and vice versa, thereby suppressing the folding clutter. From Figure 3 , Figure 5 it can be seen that there is a 3.9 km folding clutter, but the remaining folding clutters are suppressed. From Figure 4 , Figure 6 it can be seen that there are 23.4, 33.1, 35.5, and 36.0 km folding clutters, but the 3.9 km folding clutter is suppressed. Therefore, it can be seen that the folding clutters are all suppressed and can be eliminated through subsequent algorithm processing.
[0126] Referring to Figure 7 , Figure 7 For the right, negative slope group MTD after the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the suppression of the result of the
Claims
1. A method for resisting folded clutter based on staggered MTI, characterized in that, Includes the following steps: Step S100: Establish a slow-time total echo model for frequency-modulated agile airborne radar under clutter conditions, and perform down-conversion processing on the signal. Step S200: The target echo signal after down-conversion is over-pulse compressed and then matched and filtered by positive and negative filters. Step S300: Extract the slow time series from the target echo signal of the matched filter; Step S400: Perform staggered MTI filtering on the slow time series of the two sets of echo signals. Step S500: Perform coherent accumulation processing on the echo signal that has undergone staggered MTI filtering; Step S600: Perform non-coherent accumulation processing on the echo signal that has undergone coherent accumulation processing and does not have other strong interference signals; Step S700: The echo signal that has undergone noncoherent accumulation processing is subjected to folding clutter removal processing, and the final output signal result is obtained.
2. The method according to claim 1, characterized in that, Step S100 includes: Step S101: Establish a slow-time total echo model for frequency-modulated agile airborne radar under clutter conditions. ， Where A is the target complex amplitude. Let be the frequency modulation slope of the i-th pulse. Let the echo delay of the target i-th pulse be , Where t is the carrier frequency, and t is the time variable. The pulse width; Step S102: Perform digital down-conversion processing on the target echo signal, with the local oscillation signal being... Then, the echo signal of the target signal of the i-th pulse after down-conversion processing is represented as follows: ， in, The target amplitude after digital down-conversion processing; Step S103: Represent the echo signal during the entire CPI period as a set of all pulse echo signals. 。 3. The method according to claim 1, characterized in that, Step S300 includes: Step S301: Extract the slow time series of the positive slope group. ， in, For distance gate, ; Step S302: Extract the slow time series of the negative slope group. ， in .
4. The method according to claim 1, characterized in that, Step S400 includes: Step S401: Perform MTI processing on the slow time series of the positive slope group. ； Step S402: Perform MTI processing on the slow time series of the negative slope group. 。 5. The method according to claim 1, characterized in that, Step S500 includes: Step S501: Perform MTD processing, i.e., coherent accumulation processing, on the slow time series of the positive slope group. ； Step S502: Perform MTD processing, i.e., coherent accumulation processing, on the slow time series of the negative slope group. 。 6. The method according to claim 1, characterized in that, Step S700 includes: Step S701, convert the two sets of complete distance-Doppler spectra. , For each distance unit Calculate the amplitude difference between the Doppler elements corresponding to the positive and negative slope groups. ， in, Indicates the modulus (amplitude) of a complex number; Step S702: Set the amplitude difference threshold This threshold is determined by the following formula: ， in, As an adjustment factor, take a value of 2 to 3. This represents the system noise level. It is the time-bandwidth product. Alternatively, an adaptive threshold can be used. ， in, This is a proportionality coefficient, ranging from 1.5 to 2.0; Step S703, when When the amplitude difference is less than the threshold, it is determined to be a target signal and target signal processing is performed. ， ； Step S704, the output signal result is, 。