A method for target detection using amplitude-coded modulation linear frequency modulation signals

Abstract

This invention discloses a target detection method using amplitude-coded modulated linear frequency (LFM) signals, comprising: first, amplitude-coded modulation of the LFM signal; second, frequency shift processing using a matched filter; third, harmonic pulse compression processing; and fourth, energy compensation, thereby obtaining a high-resolution range image consistent with the matched filter output of the original signal. This invention utilizes its spectral shifting characteristics to provide a foundation for subsequent target detection. A reference signal is obtained for subsequent pulse compression processing. Pulse compression processing of the amplitude-coded modulated LFM signal is achieved, resulting in a high-resolution range image of the target echo at the harmonic components. The amplitude loss of the matched filter output caused by amplitude-coded modulation is eliminated, resulting in a high-resolution range image consistent with the amplitude of the original LFM signal. A simulation experiment of target detection using amplitude-coded modulated LFM signals has been completed.

Description

[Technical Field]

[0001] This invention relates to a target detection method using amplitude-coded modulation of linear frequency modulated signals, belonging to the field of radar signal processing. Specifically, it relates to amplitude-coded modulation of linear frequency modulated signals and the use of the modulated signal to achieve a high-precision target range image acquisition method. [Background Technology]

[0002] In modern warfare, radar has become an indispensable electronic device, but its vulnerability to jamming is a fatal weakness. Since radar receivers only receive signals within their operating frequency band, suppressing and jamming the radar's operating frequency is currently the most widely used jamming method. Among these, targeted jamming uses jamming signals with a bandwidth only slightly larger than the radar receiver's operating bandwidth, resulting in concentrated jamming power, a narrow jamming bandwidth, high power utilization, and good jamming effect. Determining the appropriate countermeasures and target information acquisition has always been a hot research topic in the field of radar target detection.

[0003] Current research on anti-targeting jamming mainly focuses on radar signal frequency design, with frequency agility and intra-pulse multi-carrier (IPM) being among the most widely studied. Frequency agility signals can achieve wide-bandwidth frequency hopping, making it difficult for reconnaissance aircraft to accurately identify radar radiation source parameters. Furthermore, carrier frequency hopping can effectively reduce jamming power density, but it is not easily compatible with moving target indication (MTI) and pulse-Doppler systems. IPM multi-carrier signals cause reconnaissance aircraft to mistakenly perceive the sub-pulse width as the entire pulse width, thus allowing jamming equipment to target only one sub-pulse. Even after removing the jammed sub-pulse, good detection performance is still maintained.

[0004] This invention utilizes amplitude-coded modulation (AMCM) signals to modulate linear frequency modulated (LFM) signals. By designing AMCM signals, the spectrum of radar signals is shifted. A matched filter is then frequency-shifted based on the modulation signal parameters to obtain a reference signal for harmonic pulse compression. Subsequently, harmonic pulse compression is performed to obtain a one-dimensional range profile of the target echo at the harmonic locations. Energy compensation is then used to compensate for the energy loss caused by AMCM modulation, thus obtaining a one-dimensional range profile of the target consistent with the original signal echo. [Summary of the Invention]

[0005] The technical problem to be solved by this invention is: to design an amplitude-coded modulation signal to modulate a linear frequency modulated signal; and to use the spectrum shifting characteristics of the modulated signal to perform pulse compression and energy compensation processing on the harmonics by frequency shifting through a matched filter when the main period of the echo spectrum is suppressed, thereby obtaining a high-resolution range image of the target.

[0006] This invention relates to a target detection method for amplitude-coded modulated linear frequency modulated signals, and the technical solution adopted is as follows:

[0007] The first step is to perform amplitude encoding modulation of the linear frequency modulated signal.

[0008] The envelope of the amplitude-coded modulated signal is a rectangular pulse train p(t), with amplitude modulation of [0,1]. In the time domain, this is represented by dividing a complete pulse into several sub-pulses through the modulation pulse.

[0009] The linear frequency modulated signal transmitted by the radar is represented as s(t). By using p(t) to perform amplitude coding modulation on s(t), the modulated signal x(t) = p(t)s(t) can be obtained. If the modulation frequency of p(t) is set to be greater than the bandwidth of the s(t) signal, then x(t) in the frequency domain will behave as if the spectrum of the linear frequency modulated signal has been shifted to both sides according to the modulation frequency.

[0010] The second step is frequency shift processing of the matched filter.

[0011] When the dominant period of the echo spectrum is suppressed, the matched filter is frequency-shifted so that its spectrum is located at the unsuppressed harmonic components, thus obtaining the frequency-shifted reference signal s. f (t).

[0012] The third step is harmonic pulse compression processing.

[0013] Based on steps two and three, and using the reference signal s f (t), pulse compression processing is performed on x(t) to obtain a high-precision range image of the target echo at the harmonic components.

[0014] The fourth step is energy compensation.

[0015] Since the amplitude of the matched filter output of the signal is attenuated after amplitude coding modulation, a high-resolution range image consistent with the matched filter output of the original signal can be obtained by compensating for it with a compensation coefficient.

[0016] The specific process of the second step is as follows:

[0017] The expression for a linear frequency modulated signal is:

[0018]

[0019] Among them, T p Where f is the pulse width, f0 = 0 is the carrier frequency, and μ = B / T p Let B be the modulation slope, B be the signal bandwidth, and j be a complex number.

[0020] When the dominant period of the echo spectrum is suppressed, the matched filter is frequency-shifted, that is, the reference signal carrier frequency f0 is shifted to the harmonic position. If it is the first harmonic, the frequency-shifted reference signal is:

[0021]

[0022] The specific process of the third step is as follows:

[0023] For a radar system with transmitted signal g(t), its matched filter can be expressed as:

[0024] h(t)=g*(t0-t) (3)

[0025] Where * denotes the conjugate operation, and t0 is a constant that makes h(t) physically realizable. If t0 = 0, then h(t) can be written as:

[0026] h(t)=g*(-t) (4)

[0027] The output of the radar signal after matched filtering is:

[0028]

[0029] Performing a Fourier transform on equation (4), the spectrum of the matched filter output is obtained as follows:

[0030] Y(f)=G(f)H(f)=G(f)G*(f) (6)

[0031] Substituting the result of the first step of amplitude coding modulation into equation (6), we obtain the matched filter output spectrum of x(t) as follows:

[0032]

[0033] Performing an inverse Fourier transform on equation (7), the matched filter output of x(t) is obtained as follows:

[0034]

[0035] Based on reference signal s f By performing pulse compression processing on x(t), a high-precision range image of the target echo at the harmonic components can be obtained.

[0036] The specific process of the fourth step is as follows:

[0037] make

[0038] a n =τf s sinc(nf s τ) (9)

[0039] Equation (8) can then be written as:

[0040]

[0041] As can be seen from equation (10), the matched filter output of the amplitude-coded modulated signal has different frequency shifts nf.s The linear superposition of the original signal's matched filter outputs, with amplitude weighting coefficient a. n Let D be the duty cycle of p(t), then we have Equation (9) can then be written as:

[0042]

[0043] As can be seen from equation (11), the attenuation amplitude of the matched filter output of the amplitude-coded modulated signal follows a sinc function related to D.

[0044] In particular, when When p(t) transforms into a square wave pulse train, the equation can be written as:

[0045]

[0046] When n = 0, When n is a non-zero even number, a n =0; when n is odd, That is, |a n As |n| increases, it approximates... Attenuation, or energy compensation coefficient, is |n|π. By compensating for this coefficient, a high-resolution range image with the same amplitude as the original linear frequency modulated signal can be obtained.

[0047] The main beneficial effects of this invention include:

[0048] First, an amplitude-coded modulation (ACDM) linear frequency modulated signal was designed. Its spectrum-shifting characteristics provided a foundation for subsequent target detection.

[0049] Second, frequency shifting of the matched filter was performed to obtain the reference signal for subsequent pulse compression processing.

[0050] Third, based on the frequency-shifted reference signal, pulse compression processing of the amplitude-coded modulated linear frequency modulation signal was realized, resulting in a high-resolution range image of the target echo at the harmonic components.

[0051] Fourth, through energy compensation, the amplitude loss of the matched filter output caused by amplitude coding modulation is eliminated, resulting in a high-resolution range image with the same amplitude as the original linear frequency modulated signal.

[0052] Fifth, a simulation experiment on target detection using amplitude-coded modulated linear frequency (AM) signals was completed. This verified that AM-coded modulated AM signals possess excellent target detection capabilities. [Attached Image Description]

[0053] Figure 1 This is a flowchart of the method of the present invention.

[0054] Figure 2This is a schematic diagram of an amplitude-coded modulation signal.

[0055] Figure 3 This is the spectrum of the linear frequency modulated signal after amplitude coding modulation.

[0056] Figure 4(a) is the spectrum of the original reference signal.

[0057] Figure 4(b) is the spectrum of the reference signal after frequency shifting.

[0058] Figure 5(a) is a high-resolution range image of the target echo of a linear frequency modulated signal.

[0059] Figure 5(b) is a high-resolution range image of the target echo of the suppressed linear frequency modulated signal.

[0060] Figure 5(c) shows the high-resolution range image of the target echo at the harmonic components.

[0061] Figure 5(d) shows the high-resolution range image of the target echo at the harmonic components after energy compensation.

Detailed Implementation Methods

[0062] The invention will be further described below with reference to the accompanying drawings. The invention relates to a target detection method for amplitude-coded modulated linear frequency modulated signals, such as... Figure 1 As shown, the steps are as follows:

[0063] The first step is to perform amplitude encoding modulation of the linear frequency modulated signal.

[0064] like Figure 2 As shown, the amplitude-coded modulation signal waveform is a rectangular pulse train with a modulation period of T. s The pulse width is τ, and τ is in For any value within a range, the expression can be written as:

[0065]

[0066] In the formula, rect(·) is a rectangle function. δ(·) represents the convolution operation, δ(·) is the unit impulse function, n is the number of pulses, and t represents time.

[0067] And there are:

[0068]

[0069] Performing a Fourier transform on the equation, we obtain the spectral expression for the amplitude-coded modulation signal as follows:

[0070]

[0071] in, For the modulation (sampling) frequency, sinc(x) = sin(πx) / πx is the sinc function.

[0072] As can be seen from the equation, the spectrum of the amplitude-coded modulation signal p(t) is composed of a series of equally spaced impulse functions superimposed, and the shifting distance is determined by f. s It is determined that the amplitudes of each order follow a sinc function. Based on this characteristic, if an amplitude-coded modulation signal is used to modulate the radar signal, it is equivalent to discrete modulation of the radar signal in the frequency domain.

[0073] For a linear frequency modulated signal s(t) transmitted by radar, after amplitude coding modulation, it can be expressed as:

[0074] x(t)=p(t)s(t) (4)

[0075] Performing a Fourier transform on the equation yields the spectrum of the modulated signal:

[0076]

[0077] Where P(f) and S(f) are the spectra of p(t) and s(t), respectively.

[0078] Substituting the equation into the expression, we get:

[0079]

[0080] As can be seen from the formula, when f s When the signal bandwidth is greater than s(t), the spectrum of the amplitude-coded modulated signal is nf s To uniformly shift the original signal spectrum at intervals, such as Figure 3 As shown.

[0081] The second step is frequency shift processing of the matched filter.

[0082] The expression for a linear frequency modulated signal is:

[0083]

[0084] Among them, T p Where f is the pulse width, f0 = 0 is the carrier frequency, and μ = B / T p Let B be the modulation slope, B be the signal bandwidth, and j be a complex number.

[0085] As shown in Figures 4(a) and (b), when the main period of the echo spectrum is suppressed, the matched filter is frequency-shifted, that is, the reference signal carrier frequency f0 is shifted to the harmonic position. Taking the first harmonic as an example, the frequency-shifted reference signal is:

[0086]

[0087] The third step is harmonic pulse compression processing.

[0088] For a radar system with transmitted signal g(t), its matched filter can be expressed as:

[0089] h(t)=g*(t0-t) (9)

[0090] Where * denotes the conjugate operation, and t0 is a constant that makes h(t) physically realizable. Without loss of generality, let t0 = 0, then h(t) can be written as:

[0091] h(t)=g*(-t) (10)

[0092] The output of the radar signal after matched filtering is:

[0093]

[0094] Performing a Fourier transform on the equation yields the spectrum of the matched filter output:

[0095] Y(f)=G(f)H(f)=G(f)G*(f) (12)

[0096] Substituting the equation into the given equation, we obtain the matched filter output spectrum of x(t) as follows:

[0097]

[0098] Performing an inverse Fourier transform on the equation, the matched filter output of x(t) is obtained as follows:

[0099]

[0100] Based on reference signal s f By performing pulse compression processing on x(t), a high-precision range image of the target echo at the harmonic components can be obtained.

[0101] The fourth step is energy compensation.

[0102] make

[0103] a n =τf s sinc(nf s τ) (15)

[0104] The formula can be written as:

[0105]

[0106] As can be seen from the equation, the matched filter output of the amplitude-coded modulated signal has different frequency shifts nf. s The linear superposition of the original signal's matched filter outputs, with amplitude weighting coefficient a. n Let D be the duty cycle of p(t), then we have The formula can be written as:

[0107]

[0108] As can be seen from the equation, the attenuation amplitude of the matched filter output of the amplitude-coded modulated signal follows a sinc function related to D.

[0109] In particular, when When p(t) transforms into a square wave pulse train, the equation can be written as:

[0110]

[0111] When n = 0, When n is a non-zero even number, a n =0; when n is odd, That is, |a n As |n| increases, it approximates... Attenuation, or energy compensation coefficient, is |n|π. By compensating for this coefficient, a high-resolution range image with the same amplitude as the original linear frequency modulated signal can be obtained.

[0112] Example: Simulation Experiment of Target Detection with Amplitude-Coded Modulated Linear Frequency Modulated Signal

[0113] Set radar signal parameters and perform target detection analysis and comparison on amplitude-coded modulated linear frequency modulation signals.

[0114] The radar parameter settings are shown in Table 1 below:

[0115]

[0116] Table 1

[0117] As shown in Table 1, the distances of the three point targets from the radar are 1500 meters, 3500 meters, and 8500 meters, respectively. Figure 5(a) shows the high-resolution range profile of the linear frequency modulated (LFM) signal echo, demonstrating that the radar accurately detected the three point targets. Figure 5(b) shows the high-resolution range profile of the suppressed LFM signal echo, indicating that the radar echo was contaminated by noise and could not detect the targets. Matching filtering was performed on the amplitude-coded modulated LFM signal and the frequency-shifted reference signal to obtain the high-resolution range profile with sidelobe matched filtering, as shown in Figure 5(c). This shows that the radar accurately detected the positions of the three point targets, with only a loss in amplitude. The high-resolution range profile after energy compensation is shown in Figure 5(d), showing that the compensated high-resolution range profile is consistent with the high-resolution range profile of the LFM signal echo.

Claims

1. A target detection method using amplitude-coded modulated linear frequency modulation (LFM) signals, characterized in that: The method includes the following steps: The first step is to perform linear frequency modulation (LFM) signal amplitude coding. The envelope of the amplitude-coded modulated signal is a rectangular pulse train. Its amplitude is modulated in the range of [0,1], and in the time domain, it is represented by dividing a complete pulse into several sub-pulses through the modulation pulse; The linear frequency modulated signal transmitted by the radar is represented as ,Will Used for Amplitude coding modulation is performed to obtain the modulated signal. ;Will The modulation frequency is set to be greater than Signal bandwidth, at this time In the frequency domain, this manifests as shifting the spectrum of a linear frequency modulated signal to both sides according to the modulation frequency; The second step is frequency shift processing of the matched filter. When the dominant period of the echo spectrum is suppressed, the matched filter is frequency-shifted so that its spectrum is located at the unsuppressed harmonic components, thus obtaining the frequency-shifted reference signal. ; The third step is harmonic pulse compression processing. Based on steps two and three, and the reference signal ,right Pulse compression processing is performed to obtain a high-precision range image of the target echo at the harmonic components; Step 4, Energy Compensation Since the amplitude of the matched filter output of the signal is attenuated after amplitude coding modulation, it is compensated by a compensation coefficient to obtain a high-resolution range image that is consistent with the matched filter output of the original signal.

2. The target detection method for amplitude-coded modulation linear frequency modulated signals according to claim 1, characterized in that: The specific process of the second step is as follows: The expression for a linear frequency modulated signal is: (1) in, For pulse width, For carrier frequency, The modulation slope, For signal bandwidth, j To represent a complex number; When the dominant period of the echo spectrum is suppressed, the matched filter is frequency-shifted, i.e., the reference signal carrier frequency is... If the frequency is shifted to the harmonic level and it is the first harmonic, then the reference signal after the frequency shift is: (2)。 3. The target detection method for amplitude-coded modulation linear frequency modulation signal according to claim 1, characterized in that: The specific process of the third step is as follows: For the transmitted signal is For a radar system, its matched filter is expressed as: (3) Where * denotes the conjugate operation. In order to make The physical realization constant, let ,but Written as: (4) The output of the radar signal after matched filtering is: (5) Performing a Fourier transform on equation (4), the spectrum of the matched filter output is obtained as follows: (6) Substituting the result of the first step amplitude coding modulation into equation (6), we get The matched filter output spectrum is: (7) Performing an inverse Fourier transform on equation (7) yields... The output of the matched filter is: (8) Based on reference signal ,right Pulse compression processing is performed to obtain a high-precision range image of the target echo at the harmonic components.

4. The target detection method for amplitude-coded modulation linear frequency modulated signals according to claim 1, Its features are: The specific process of the fourth step is as follows: make (9) Then equation (8) can be written as: (10) From equation (10), the matched filter output of the amplitude-coded modulated signal has different frequency shifts. The linear superposition of the original signal's matched filter outputs, with amplitude weighting coefficients as follows: ,make for The duty cycle has Then equation (9) can be written as: (11) From equation (11), the attenuation amplitude of the matched filter output of the amplitude-coded modulated signal follows the same principle as... Related function; when hour, If it is transformed into a square wave pulse train, then equation (15) can be written as: (12) when hour, ;when n When it is a non-zero even number, ; when n When it is an odd number, ,Right now along with The increase is approximated by Attenuation, i.e., energy compensation coefficient is Through coefficient compensation, a high-resolution range image with the same amplitude as the original linear frequency modulated signal is obtained.

Images