Anti-chaff interference method for LFMCW millimeter wave fuze based on FPGA

Abstract

The invention relates to an FPGA (Field Programmable Gate Array)-based chaff interference resisting method for an LFMCW (Linear Frequency Modulated Continuous Wave) millimeter wave fuze. The chaff interference resisting method is used for solving the problem that the existing millimeter wave fuze possibly has failure modes such as early explosion and the like under chaff interference. The method comprises the following steps: sampling received difference frequency echo signals, completing analog-to-digital conversion, performing synchronous control and FIFO (First In First Out) caching on the acquired two paths of signals through synchronous pulses, performing FIR (Finite Impulse Response) digital filtering, calculating a polarization ratio mean value of output signals, and judging whether chaff interference is detected at the moment; if chaff interference is detected, oblique projection polarization filtering processing is carried out on one path of signals, then spectrum analysis is completed, and distance information of an effective target is output; if the chaff interference does not exist in the detection result, directly performing spectrum analysis to obtain the distance information of the target. And finally, range judgment is performed on the distance, and when the target is within the fixed-distance range of the fuze detection system, an execution-level signal is output.

Description

Technical Field

[0001] The invention belongs to the technical field of fuze anti-interference, and in particular relates to an FPGA-based anti-chaff interference method for LFMCW millimeter wave fuze. Background Art

[0002] As a type of proximity fuze, radio fuze has the advantages of long detection distance, high ranging accuracy and high target recognition rate. In recent years, in order to improve the accuracy of proximity fuzes, the application frequency band of radio fuzes has gradually developed towards millimeter waves. However, millimeter-wave fuzes are very prone to failure modes such as "premature explosion" under the interference of chaff. The appearance of chaff interference greatly affects the performance of missile-borne fuzes. Therefore, it is urgent to improve the ability of millimeter-wave fuzes to resist chaff interference.

[0003] At present, the technology of anti-chaff interference can be roughly divided into the following six categories: (1) recognition method based on echo signal waveform characteristics; (2) recognition method based on echo signal time domain characteristics; (3) recognition method based on echo signal frequency domain characteristics; (4) recognition method based on echo signal Doppler characteristics; (5) recognition method based on polarization domain information; (6) recognition method based on composite guidance. The polarization characteristics reflect the inherent physical properties of the target and can provide more target information for the fuze. The difference in polarization characteristics between the target and the interference can further improve the fuze's ability to identify and suppress interference.

[0004] However, in the existing research on using polarization information to counter chaff interference, on the one hand, only the situation where the target and chaff interference appear separately within the fuze detection range is considered, and on the other hand, there is a lack of hardware implementation verification. Summary of the invention

[0005] In order to solve the influence of the current chaff interference on the LFMCW millimeter wave fuze, the present invention proposes an anti-chaff interference method for the LFMCW millimeter wave fuze based on FPGA.

[0006] The technical solution of the present invention to solve the above problems is:

[0007] An anti-chaff interference method for LFMCW millimeter wave fuze based on FPGA, characterized in that it comprises the following steps:

[0008] 1) AD data collection output

[0009] The ADC is used to sample the two-way difference frequency echo signals of the horizontal polarization channel and the vertical polarization channel to complete the analog-to-digital conversion;

[0010] 2) Synchronous pulse

[0011] The two collected echo signals are synchronously controlled by using synchronization pulses;

[0012] 3) FIFO buffer and FIR digital filter

[0013] The two echo signals controlled by the synchronous pulse are cached in FIFO, and then the filter design is completed using the FIR IP core;

[0014] 4) Polarization identification

[0015] 4.1) Utilization To calculate the polarization ratio of the i-th echo signal in step 3), where A HH and A HV Represents the amplitude of two echo signals, i = 1, 2, ..., N, N is the number of statistical echo signals;

[0016] 4.2) After the polarization ratios of the N echo signals are calculated respectively, their mean is calculated to determine whether the mean is greater than the discrimination threshold of the polarization ratio mean. The thresholds of different aircraft targets are different. In practical applications, the mean polarization ratio of the aircraft needs to be determined in advance. The calculation method is the same as step 4.1), and this mean is used as the discrimination threshold of the polarization ratio mean;

[0017] 4.3) When the mean value of the polarization ratio of the echo signal is less than or equal to the discrimination threshold value, it is determined that there is chaff interference, and it is necessary to suppress the chaff interference signal, and enter step 5; when the mean value is greater than the discrimination threshold value, it is determined that there is only an aircraft target, and the target distance information can be directly analyzed and entered into step 6;

[0018] 5) Oblique projection polarization filtering

[0019] 5.1) The echo signal with foil interference determined by polarization identification is used as the input signal. The input signal is the echo signal of the dual-polarization fuze. First, the polarization angle γ of the echo signal is calculated by the following formula: J The polarization angle difference is φ J Perform polarization parameter estimation to determine the polarization state of the foil strip:

[0020]

[0021] φ J =arg[E JV (t)]-arg[E JH (t)]

[0022] Among them, E JV (t) represents the echo signal amplitude of the vertical polarization channel, E JH (t) represents the echo signal amplitude of the horizontal polarization channel, arg[g] represents the signal phase angle;

[0023] The polarization state of the aircraft target needs to be determined in advance in practical applications. The calculation method is the same as step 5.1) to calculate the polarization state of the foil strip, and the aircraft polarization angle γ can also be obtained. S and the aircraft polarization angle difference φ S ;

[0024] 5.2) The oblique projection operator is calculated according to the polarization parameters estimated in step 5.1) by the following formula:

[0025]

[0026]

[0027]

[0028] Among them, [g] T represents the transpose operation of the matrix, [g] H represents the conjugate transpose of the matrix, S represents the polarization subspace of the aircraft signal, J represents the polarization subspace of the chaff signal, and E SJ is the oblique projection operator, is the orthogonal projection operator of J orthogonal complement space, I is the identity matrix;

[0029] 5.3) multiplying the oblique projection operator in step 5.2) by the input signal of any polarization channel to obtain the target echo signal after suppressing the interference of the chaff strips;

[0030] 6) FFT transformation

[0031] Call the FFT IP core to transform the echo signal processed by step 4.3 or step 5 from a time domain signal to a frequency domain signal;

[0032] 7) Distance estimation and detonation control

[0033] The frequency domain signal obtained in step 6) is the effective target echo signal after suppressing the interference of the foil strip. For the LFMCW millimeter wave fuze, the target distance can be calculated by the following formula using the spectral line number corresponding to the spectrum peak:

[0034]

[0035] Among them, f beat_up and f beat_down are the difference frequency signals of the upper and lower sweep frequency bands of the moving target, c is the speed of light, T M is the modulation period of the LFMCW signal, ΔF M is the modulation bandwidth of the LFMCW signal;

[0036] When the target is within the fixed distance range of the LFMCW millimeter wave fuze detection system, an execution level signal is output. After the previous steps, the execution level signal obtained is more reliable, reducing the probability of the fuze being misfired.

[0037] Compared with the prior art, the advantages of the present invention are:

[0038] 1. The processing of the echo signal in the present invention is completed in the polarization domain. Polarization domain processing, as a supplementary form of time domain, frequency domain and spatial domain signal processing, can solve problems that cannot be solved by the above three domains;

[0039] 2. The present invention integrates the detection of whether there is foil strip interference in the echo signal with the suppression of foil strip interference, and is a more complete anti-interference method. The advantage of the oblique projection polarization filtering used therein compared with other traditional filtering methods is that it has no effect on the amplitude and phase information of the target, and filtering can be performed when there is a difference in the polarization angle and polarization angle between the target and the interference. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The present invention is a flow chart of the method.

[0041] Figure 2 It is a flow chart of the polarization identification method in the present invention.

[0042] Figure 3 This is a flow chart of the oblique projection polarization filtering in the present invention. DETAILED DESCRIPTION

[0043] An FPGA-based anti-chaff interference method for LFMCW millimeter wave fuze includes the following steps:

[0044] 1) AD data collection output

[0045] The ADC is used to sample the two-way difference frequency echo signals of the horizontal polarization channel and the vertical polarization channel to complete the analog-to-digital conversion;

[0046] 2) Synchronous pulse

[0047] The two collected echo signals are synchronously controlled by using synchronization pulses;

[0048] 3) FIFO buffer and FIR digital filter

[0049] The two echo signals controlled by the synchronous pulse are cached in FIFO, and then the filter design is completed using the FIR IP core;

[0050] 4) Polarization identification

[0051] 4.1) Utilization To calculate the polarization ratio of the i-th echo signal in step 3), where AHH and A HV Represents the amplitude of two echo signals, i = 1, 2, ..., N, N is the number of statistical echo signals;

[0052] 4.2) After the polarization ratios of the N echo signals are calculated respectively, their mean is calculated to determine whether the mean is greater than the discrimination threshold of the polarization ratio mean. The thresholds of different aircraft targets are different. In practical applications, the mean polarization ratio of the aircraft needs to be determined in advance. The calculation method is the same as step 4.1), and this mean is used as the discrimination threshold of the polarization ratio mean;

[0053] 4.3) When the mean value of the polarization ratio of the echo signal is less than or equal to the discrimination threshold value, it is determined that there is chaff interference, and it is necessary to suppress the chaff interference signal, and enter step 5; when the mean value is greater than the discrimination threshold value, it is determined that there is only an aircraft target, and the target distance information can be directly analyzed and entered into step 6;

[0054] 5) Oblique projection polarization filtering

[0055] 5.1) The echo signal with foil interference is used as the input signal after polarization identification. The input signal is the echo signal of the dual-polarization fuze. First, the polarization angle γ of the echo signal is calculated by the following formula: J The polarization angle difference is φ J Perform polarization parameter estimation to determine the polarization state of the foil strip:

[0056]

[0057] φ J =arg[E JV (t)]-arg[E JH (t)]

[0058] Among them, E JV (t) represents the echo signal amplitude of the vertical polarization channel, E JH (t) represents the echo signal amplitude of the horizontal polarization channel, and arg[g] represents the signal phase angle.

[0059] The polarization state of the aircraft target needs to be determined in advance in practical applications. The calculation method is the same as that of the foil polarization state in step 5.1). The γ S Aircraft polarization angle and φ S The polarization angle of the aircraft is different.

[0060] 5.2) The oblique projection operator is calculated according to the polarization parameters estimated in step 5.1) by the following formula:

[0061]

[0062]

[0063]

[0064] Among them, [g] T represents the transpose operation of the matrix, [g] H represents the conjugate transpose of the matrix, S represents the polarization subspace of the aircraft signal, J represents the polarization subspace of the chaff signal, and E SJ is the oblique projection operator, is the orthogonal projection operator of J orthogonal complement space, and I is the identity matrix.

[0065] 5.3) Multiply the oblique projection operator in step 5.2) by the input signal of any polarization channel to obtain the target echo signal after suppressing the foil interference.

[0066] 6) FFT transformation

[0067] Call the FFT IP core to transform the echo signal processed by step 4.3 or step 5 from a time domain signal to a frequency domain signal;

[0068] 7) Distance estimation and detonation control

[0069] The frequency domain signal obtained in step 6) is the effective target echo signal after suppressing the interference of the foil strip. For the LFMCW millimeter wave fuze, the target distance can be calculated by the following formula using the spectral line number corresponding to the spectrum peak:

[0070]

[0071] Among them, f beat_up and f beat_down are the difference frequency signals of the upper and lower sweep frequency bands of the moving target, c is the speed of light, T M is the modulation period of the LFMCW signal, ΔF M is the modulation bandwidth of the LFMCW signal.

[0072] When the target is within the fixed distance range of the LFMCW millimeter wave fuze detection system, an execution level signal is output. After the previous steps, the execution level signal obtained is more reliable, reducing the probability of the fuze being misfired.

[0073] It should be understood that the above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. An anti-chaff interference method for LFMCW millimeter wave fuze based on FPGA, characterized in that: The following steps are involved: 1) AD data collection output The ADC is used to sample the two-way difference frequency echo signals of the horizontal polarization channel and the vertical polarization channel to complete the analog-to-digital conversion; 2) Synchronous pulse The two collected echo signals are synchronously controlled by using synchronization pulses; 3) FIFO buffer and FIR digital filter The two echo signals controlled by the synchronous pulse are cached in FIFO, and then the filter design is completed using the FIRIP core; 4) Polarization identification, including the following steps: 4.1) Utilization To calculate the polarization ratio of the i-th echo signal in step 3), where A HH and A HV Represents the amplitude of two echo signals, i=1,2,...,N, where N is the number of statistical echo signals; 4.2) After the polarization ratios of the N echo signals are calculated respectively, their mean is calculated to determine whether the mean is greater than the discrimination threshold of the polarization ratio mean, and the polarization ratio mean of the aircraft calculated in step 4.1) is used as the discrimination threshold of the polarization ratio mean; 4.3) When the mean value of the polarization ratio of the echo signal is less than or equal to the discrimination threshold value, it is determined that there is chaff interference, and the chaff interference signal is suppressed, and the process goes to step 5; when the mean value is greater than the discrimination threshold value, it is determined that there is only an aircraft target, and the target distance information is directly analyzed and the process goes to step 6; 5) Oblique projection polarization filtering, including the following steps: 5.1) The echo signal with foil interference determined by polarization identification is used as the input signal. The input signal is the echo signal of the dual-polarization fuze. First, the polarization angle γ of the echo signal is calculated by the following formula: J and the polarization angle difference φ J Perform polarization parameter estimation to determine the polarization state of the foil strip: φ J Arg[E JV (t)]-arg[E JH (t)] Among them, E JV (t) represents the echo signal amplitude of the vertical polarization channel, E JH (t) represents the echo signal amplitude of the horizontal polarization channel, arg[g] represents the signal phase angle; The polarization state of the aircraft target needs to be determined in advance. The calculation method is the same as step 5.1) to calculate the polarization state of the foil strip to obtain the aircraft polarization angle γ S and the aircraft polarization angle difference φ S ; 5.2) The oblique projection operator is calculated according to the polarization parameters estimated in step 5.1) by the following formula: Among them, [g] T represents the transpose operation of the matrix, [g] H represents the conjugate transpose of the matrix, S represents the polarization subspace of the aircraft signal, J represents the polarization subspace of the chaff signal, and E SJ is the oblique projection operator, is the orthogonal projection operator of J orthogonal complement space, I is the identity matrix; 5.3) multiplying the oblique projection operator in step 5.2) by the input signal of any polarization channel to obtain the target echo signal after suppressing the interference of the chaff strips; 6) FFT transformation Call the FFT IP core to transform the echo signal processed by step 4.3 or step 5 from a time domain signal to a frequency domain signal; 7) Distance estimation and detonation control The frequency domain signal obtained in step 6) is the effective target echo signal after suppressing the interference of the foil strip. For the LFMCW millimeter wave fuze, the target distance is calculated by the following formula using the spectral line number corresponding to the spectrum peak: Among them, f beat_up and f beat_down are the difference frequency signals of the upper and lower sweep frequency bands of the moving target, c is the speed of light, T M is the modulation period of the LFMCW signal, ΔF M is the modulation bandwidth of the LFMCW signal; When the target is within the range of the LFMCW millimeter wave fuze detection system, an execution level signal is output.

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