A nonlinear radar speed and distance measurement method based on Costas frequency modulation coded signal

Abstract

The present application relates to a nonlinear radar speed and ranging method based on a Costas frequency modulation coded signal. A nonlinear radar echo signal model based on the Costas frequency modulation coded signal is established. The multi-order nonlinear effects of the nonlinear radar are comprehensively considered, and a nonlinear frequency change is proposed. An expression for the echo phase is obtained, which has important value for the signal processing and application of nonlinear radar systems. The present application proposes a nonlinear radar echo phase compensation method for the Costas frequency modulation coded signal. By formula derivation, a phase compensation method for the frequency modulation signal is obtained, including delay redundancy compensation and Doppler redundancy compensation, and nonlinear radar speed and ranging information of the Costas frequency modulation coded signal is obtained.

Description

Technical Field

[0001] The present application relates to the field of radar technology, and in particular to a nonlinear radar speed and distance measurement method based on Costas frequency modulation coded signals. Background Art

[0002] Nonlinear radar exploits the nonlinear characteristics of a target and detects harmonic components scattered by it. Unlike fundamental radar, which only receives reflected signals from the fundamental wave, nonlinear radar receives the second and third harmonics excited by the target. This allows nonlinear radar to effectively search for and identify nonlinear targets. Compared to fundamental radar, nonlinear radar features a novel detection mechanism and strong clutter immunity, making it a novel radar technology with significant application value. Its outstanding advantages include strong clutter immunity, anti-stealth capabilities, and excellent recognition performance, and it demonstrates great potential for military applications in areas such as surface target detection. However, research on speed and ranging methods for target detection is still incomplete. In particular, when the transmitted signal is coded, methods for measuring speed and ranging using nonlinear radar echo signals are largely unavailable. Summary of the Invention

[0003] In order to overcome at least one deficiency in the prior art, the present application provides a nonlinear radar speed and ranging method based on Costas frequency modulation coded signals.

[0004] In a first aspect, a nonlinear radar speed and ranging method based on a Costas frequency modulation coded signal is provided, comprising:

[0005] Transmit Costas frequency-modulated coded signals to nonlinear targets and obtain echo signals reflected by the nonlinear targets; the echo signals include linear echoes, second harmonics, and third harmonics;

[0006] Preprocessing the echo signal to obtain a preprocessed signal; the preprocessing includes digital down-conversion and band-pass filtering;

[0007] Performing phase compensation on the preprocessed signal to obtain a compensated signal; the phase compensation includes compensating for delay redundancy and compensating for Doppler redundancy;

[0008] Perform inverse fast Fourier transform on the compensated signal to transform the data in the signal from the frequency domain to the fast time domain, and determine the distance between the radar and the nonlinear target based on the data in the fast time domain;

[0009] The compensated signal is subjected to discrete Fourier transform to convert the data in the signal from the slow time domain to the Doppler frequency domain, and the speed of the nonlinear target is determined according to the data in the Doppler frequency domain.

[0010] In one embodiment, the echo signal reflected by the nonlinear target is:

[0011]

[0012] Among them, s D is the echo signal reflected by the nonlinear target, r is the order of the echo signal, a r is the amplitude factor of the rth order echo signal, f is the carrier frequency of the pth pulse, t is the time, β is the phase, λ is the wavelength and l is the distance between the radar and the nonlinear target.

[0013] In one embodiment, the band-pass filtering uses three band-pass filters to perform band-pass filtering on the linear echo, the second harmonic, and the third harmonic respectively;

[0014] When performing bandpass filtering on the linear echo, the center frequency of the bandpass filter is the same as the center frequency of the transmitted signal, and the bandwidth of the bandpass filter is the same as the bandwidth of the transmitted signal;

[0015] When band-pass filtering is performed on the second harmonic, the center frequency of the band-pass filter is twice the center frequency of the transmitted signal, and the bandwidth of the band-pass filter is twice the bandwidth of the transmitted signal;

[0016] When band-pass filtering is performed on the third harmonic, the center frequency of the band-pass filter is three times the center frequency of the transmitted signal, and the bandwidth of the band-pass filter is three times the bandwidth of the transmitted signal.

[0017] In one embodiment, performing phase compensation on the preprocessed signal includes performing phase compensation on the second harmonic and the third harmonic in the preprocessed signal respectively;

[0018] The delay redundancy term of the second harmonic is exp{-j4πf n τ0}, the Doppler redundancy term is Among them, f n is the coding carrier frequency, τ0 is the pulse width, f c is the fixed carrier frequency of the transmitted signal; v is the speed of the nonlinear target, n is the discrete sampling time, T r is the pulse repetition period, c is the speed of light;

[0019] The delay redundancy term of the third harmonic is exp{-j6πf n τ0}, the Doppler redundancy term is

[0020]

[0021] In one embodiment, performing a discrete Fourier transform on the compensated signal includes performing discrete Fourier transform on the second harmonic and the third harmonic in the compensated signal respectively;

[0022] The transformation factor used in the discrete Fourier transform of the second harmonic is Among them, f n is the code carrier frequency, f c is the fixed carrier frequency of the transmitted signal, v is the speed of the nonlinear target, n is the discrete sampling time, T r is the pulse repetition period, c is the speed of light;

[0023] The transformation factor used in the discrete Fourier transform of the third harmonic is

[0024]

[0025] In a second aspect, a nonlinear radar speed and ranging system based on a Costas frequency modulation coded signal is provided, comprising:

[0026] a transmitter for transmitting a Costas frequency modulation coded signal to a non-linear target;

[0027] A receiver is used to obtain an echo signal reflected by a nonlinear target; the echo signal includes a linear echo, a second harmonic, and a third harmonic;

[0028] A preprocessing module is used to preprocess the echo signal to obtain a preprocessed signal; the preprocessing includes digital down-conversion and band-pass filtering;

[0029] A phase compensation module is used to perform phase compensation on the preprocessed signal to obtain a compensated signal; the phase compensation includes compensation for delay redundancy and compensation for Doppler redundancy;

[0030] The ranging module is used to perform inverse fast Fourier transform on the compensated signal, transform the data in the signal from the frequency domain to the fast time domain, and determine the distance between the radar and the nonlinear target based on the data in the fast time domain;

[0031] The speed measurement module is used to perform discrete Fourier transform on the compensated signal, convert the data in the signal from the slow time domain to the Doppler frequency domain, and determine the speed of the nonlinear target based on the data in the Doppler frequency domain.

[0032] In one embodiment, the pre-processing module includes a mixer and three band-pass filters, the mixer is used to digitally down-convert the echo signal, and the three band-pass filters are used to band-pass filter the linear echo, the second harmonic, and the third harmonic respectively;

[0033] When performing bandpass filtering on the linear echo, the center frequency of the bandpass filter is the same as the center frequency of the transmitted signal, and the bandwidth of the bandpass filter is the same as the bandwidth of the transmitted signal;

[0034] When band-pass filtering is performed on the second harmonic, the center frequency of the band-pass filter is twice the center frequency of the transmitted signal, and the bandwidth of the band-pass filter is twice the bandwidth of the transmitted signal;

[0035] When band-pass filtering is performed on the third harmonic, the center frequency of the band-pass filter is three times the center frequency of the transmitted signal, and the bandwidth of the band-pass filter is three times the bandwidth of the transmitted signal.

[0036] Compared with the prior art, this application has the following beneficial effects:

[0037] 1. A nonlinear radar echo signal model based on Costas frequency modulation coded signal was established. The multi-order nonlinear effects of nonlinear radar were comprehensively considered, the nonlinear frequency change was proposed, and the expression of echo phase was obtained, which has important value for the signal processing and application of nonlinear radar system.

[0038] 2. A nonlinear radar echo phase compensation method for Costas FM coded signals is proposed. By formula derivation, the phase compensation method of FM signals is obtained, including delay redundancy compensation and Doppler redundancy compensation, and the nonlinear radar speed and ranging information of Costas FM coded signals is obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The present application may be better understood by referring to the following description in conjunction with the accompanying drawings, which together with the following detailed description are incorporated into and form a part of this specification. In the drawings:

[0040] Figure 1 A flow chart of a nonlinear radar speed and distance measurement method based on Costas frequency modulation coded signals is shown;

[0041] Figure 2 Shows a schematic diagram of nonlinear radar signal transmission and reception;

[0042] Figure 3 The Costas matrix of the encoding sequence {4 7 1 6 5 2 3} is shown;

[0043] Figure 4 Figure 2 shows the different harmonic range-Doppler effects obtained using Costas-coded frequency-modulated signals, where (a) shows the effect of pulse Doppler processing of the fundamental echo, (b) shows the effect of pulse Doppler processing of the quadratic nonlinear radar echo, and (c) shows the effect of pulse Doppler processing of the cubic nonlinear radar echo.

[0044] Figure 5The figure shows the accumulation effect under different input signal-to-noise ratios, where (a) is the multi-pulse accumulation effect diagram for SNR = -30dB, (b) is the multi-pulse accumulation effect diagram for SNR = 0dB, and (c) is the multi-pulse accumulation effect diagram for SNR = 10dB.

[0045] Figure 6 The distance and speed error curves under different input signal-to-noise ratios are shown, where (a) is the distance error curve and (b) is the speed error curve. DETAILED DESCRIPTION

[0046] Exemplary embodiments of the present application are described below with reference to the accompanying drawings. For the sake of clarity and conciseness, not all features of actual embodiments are described in this specification. However, it should be understood that in the process of developing any such actual embodiment, many implementation-specific decisions may be made to achieve the developer's specific goals, and these decisions may vary from one implementation to another.

[0047] It is also necessary to explain here that, in order to avoid obscuring the present application due to unnecessary details, the accompanying drawings only show the device structure closely related to the solution according to the present application, while other details that are not closely related to the present application are omitted.

[0048] It should be understood that the present application is not limited to the described embodiments due to the following description with reference to the accompanying drawings. In this document, where feasible, the embodiments may be combined with each other, features between different embodiments may be replaced or borrowed, and one or more features may be omitted in one embodiment.

[0049] The embodiment of the present application provides a nonlinear radar speed and ranging method based on Costas frequency modulation coded signals, establishes a nonlinear radar echo signal model based on Costas frequency modulation coded signals, comprehensively considers the multi-order nonlinear effects of the nonlinear radar, proposes nonlinear frequency changes, and obtains an expression for the echo phase, which is of great value to the signal processing and application of nonlinear radar systems.

[0050] Figure 1 A flow chart of a nonlinear radar speed and distance measurement method based on Costas frequency modulation coded signals is shown. Figure 1 , the method mainly includes the following steps:

[0051] Step S1: First, a nonlinear radar detection model is established.

[0052] A Costas frequency-modulated signal is transmitted to a nonlinear target, and an echo signal reflected by the nonlinear target is obtained; the echo signal includes a linear echo, a second harmonic, and a third harmonic.

[0053] Figure 2The figure shows a schematic diagram of nonlinear radar signal transmission and reception. Nonlinear radar technology exploits the nonlinear characteristics of the target and receives the nonlinear components of the target's scattering for target detection. The system transmits a baseband signal and receives the secondary / third-order nonlinear scattered signals. The radar simultaneously receives the secondary / third-order nonlinear radar echo signals and processes them to measure the range and velocity of moving targets. When operating in the transmitting state, microwave signals are transmitted toward the target through the entire antenna. When receiving, the signals are transmitted through three receiving channels.

[0054] The expression of the transmitted Costas frequency modulation coded signal is:

[0055]

[0056] Where u(t) is the transmitted Costas frequency modulation coded signal, u1(t) is the sub-pulse envelope, t is the time, N is the number of pulses, i is the pulse number, T r is the pulse repetition period, f c Fixed carrier frequency for transmitting signal, b n is the Costas coding sequence, and Δf is the frequency modulation unit interval.

[0057] Construct Costas coding sequence based on finite field Golomb. Suppose GF(q)(q=p n , p is a prime number, n is a positive integer, q is the order), α and β are primitive roots of GF(q) if and only if α j +β j =1, A ij =1, otherwise A ij = 0. This method can be used to obtain the Costas matrix of order q-2, A ij is the element in the i-th row and j-th column of the Costas matrix. If α + β = 1, then the first row and first column of the matrix can be removed to obtain a q-3 order Costas matrix. Figure 3 The Costas matrix of the encoding sequence {4 7 1 65 2 3} is shown.

[0058] See also Figure 3 , analyze the signal of each node. In order to simplify the analysis process, consider the pth pulse of Costas frequency modulation coded pulse signal. Assuming that the carrier frequency of the pulse signal is f, the signal s at point A is A It can be expressed as:

[0059] s A =m(t)exp(j2πft)

[0060] Where m(t) is the baseband linear frequency modulation signal. f = f c +m p Δf, where f cFixed carrier frequency for the transmitted signal, m p is the coding symbol of the p-th pulse, and Δf is the frequency modulation unit interval.

[0061] The signal amplitude is normalized to 1. In addition, for simplicity, the subsequent analysis only considers the phase change of the signal and ignores the baseband signal m t From A to B, the signal propagates electromagnetically for a distance l, so the signal s at point B is B for:

[0062]

[0063] Where l is the distance between the radar and the nonlinear target, c is the speed of light, β is the phase, λ is the wavelength.

[0064] The signal from point B to point C is reflected by the nonlinear target, so the signal at point C is s C It is the superposition of linear echo signal and non-primary nonlinear signal. The specific expression is:

[0065]

[0066] Among them, a r is the amplitude factor of the rth order echo signal, r is the order of the echo signal, r = 1, 2, 3, r = 1 corresponds to linear echo, r = 2 corresponds to second harmonic, r = 3 corresponds to third harmonic.

[0067] Will s B =exp[j(2πft-βl)] Substituting into the above formula, we can get the signal s at point C C for:

[0068]

[0069] Among them, β r is the phase of the r-th order echo signal.

[0070] According to the working mechanism of target transmission and reception delay, β r l=rβl, substituting into the above formula, we can get the echo signal of a single pulse at the radar receiver:

[0071]

[0072] Among them, s D is the echo signal reflected by the nonlinear target, r is the order of the echo signal, a r is the amplitude factor of the rth order echo signal, f is the carrier frequency of the pth pulse, t is the time, β is the phase, λ is the wavelength and l is the distance between the radar and the nonlinear target.

[0073] The second harmonic phase is twice the linear echo phase, the third harmonic phase is three times the linear echo phase, and so on. A nonlinear target will cause the phase of the rth order harmonic echo component to change to a multiple of the corresponding harmonic order.

[0074] Step S2, preprocessing the echo signal to obtain a preprocessed signal; the preprocessing includes digital down conversion and bandpass filtering.

[0075] Specifically, the echo signal is down-converted in a mixer, and the carrier frequency component is removed to obtain a baseband signal.

[0076] By analyzing the transmitted signal, we know that the pulse signal carrier frequency is f, f = f c +m p Δf, bandwidth B = NΔf;

[0077] The band-pass filtering uses three band-pass filters to perform band-pass filtering on the linear echo, the second harmonic, and the third harmonic respectively; the three band-pass filters are band-pass filter 1, band-pass filter 2, and band-pass filter 3.

[0078] Bandpass filter 1: When performing bandpass filtering on the linear echo, the center frequency of bandpass filter 1 is the same as the center frequency of the transmitted signal, and the bandwidth of the bandpass filter is the same as the bandwidth of the transmitted signal;

[0079] Bandpass filter 2: When bandpass filtering is performed on the second harmonic, the center frequency of bandpass filter 2 is twice the center frequency of the transmitted signal, and the bandwidth of the bandpass filter is twice the bandwidth of the transmitted signal;

[0080] Bandpass filter 3: When performing bandpass filtering on the third harmonic, the center frequency of bandpass filter 3 is three times the center frequency of the transmitted signal, and the bandwidth of the bandpass filter is three times the bandwidth of the transmitted signal.

[0081] Step S3, performing phase compensation on the preprocessed signal to obtain a compensated signal; the phase compensation includes compensating for delay redundancy and compensating for Doppler redundancy.

[0082] Due to its frequency modulation characteristics, the frequency-modulated coded signal will introduce an additional phase term during Doppler processing, making the echo pulse phase incoherent, making it impossible to obtain the target velocity through accumulation. Therefore, the additional phase term needs to be compensated before multi-pulse accumulation.

[0083] Here, performing phase compensation on the preprocessed signal includes performing phase compensation on the second harmonic and the third harmonic in the preprocessed signal respectively.

[0084] The signal phase φ2 of the second harmonic after down-conversion mixing and sub-pulse matched filtering mainly includes the following items:

[0085]

[0086] Among them, f n is the coding carrier frequency, τ0 is the pulse width, f c is the fixed carrier frequency of the transmitted signal; v is the speed of the nonlinear target, n is the discrete sampling time, T r is the pulse repetition period, c is the speed of light;

[0087] By analyzing the above phase term, we can see that the delay redundancy term caused by frequency modulation is exp{-j4πf n τ0}, the Doppler redundancy term caused by frequency modulation is In order to achieve coherent phase accumulation, the delay redundancy of the frequency modulation can be compensated first, that is, the compensation factor exp{j4πf n τ0} eliminates the impact of this term.

[0088] The signal phase φ3 of the third harmonic after down-conversion mixing and sub-pulse matched filtering mainly includes the following items:

[0089]

[0090] The delay redundancy caused by frequency modulation is exp{-j6πf n τ0}, the Doppler redundancy term caused by frequency modulation is In order to achieve coherent phase accumulation, the delay redundancy of the frequency modulation can be compensated first, that is, the compensation factor exp{j6πf n τ0} eliminates the impact of this term.

[0091] Step S4: Perform an inverse fast Fourier transform on the compensated signal to convert the signal data from the frequency domain to the fast time domain. The fast time domain data is used to determine the distance between the radar and the nonlinear target. The fast time domain data can be used to determine the time at which the echo signal was received, and thus the distance between the radar and the nonlinear target.

[0092] Step S5: Perform a discrete Fourier transform on the compensated signal to convert the signal data from the slow time domain to the Doppler frequency domain. The velocity of the nonlinear target is determined based on the Doppler frequency domain data. Determining the velocity of the nonlinear target based on the Doppler frequency domain data is a conventional technique in the art and will not be further described.

[0093] Specifically, performing discrete Fourier transform on the compensated signal, including performing discrete Fourier transform on the second harmonic and the third harmonic in the compensated signal respectively;

[0094] The transformation factor used in the discrete Fourier transform of the second harmonic is Among them, f n is the code carrier frequency, f c is the fixed carrier frequency of the transmitted signal, v is the speed of the nonlinear target, n is the discrete sampling time, T r is the pulse repetition period, c is the speed of light;

[0095] The transformation factor used in the discrete Fourier transform of the third harmonic is

[0096]

[0097] The following further illustrates the technical effects of the method of the present application through simulation data.

[0098] The specific simulation parameters are as follows:

[0099] Table 1 FM coded signal simulation parameters

[0100]

[0101]

[0102] Figure 4 The figure shows the different harmonic distance-Doppler effect diagrams obtained by using Costas coded frequency modulation signals, where (a) is the fundamental wave echo pulse Doppler processing effect diagram, (b) is the quadratic nonlinear radar echo pulse Doppler processing effect diagram, and (c) is the cubic nonlinear radar echo pulse Doppler processing effect diagram. Figure 4 It can be seen that with the increase of harmonic order, the target velocity resolution effect is also significantly improved.

[0103] In order to quantitatively analyze the distance and speed measurement effects, Figure 5 The accumulation effects under different input signal-to-noise ratios are shown, where (a) is a diagram of multi-pulse accumulation effects when SNR=-30dB, (b) is a diagram of multi-pulse accumulation effects when SNR=0dB, and (c) is a diagram of multi-pulse accumulation effects when SNR=10dB. Figure 6 The distance and speed error curves under different input signal-to-noise ratios are shown, where (a) is the distance error curve and (b) is the speed error curve.

[0104] Simulation results show that when the input signal-to-noise ratio is too low, the noise floor in the environment is too high, causing the target to be buried in the noise and making it impossible to detect the target's distance and position. As the signal-to-noise ratio increases, the target detection effect improves significantly. When the input signal-to-noise ratio is less than -20dB, the target distance and speed measurement errors are large due to the influence of noise. When the input signal-to-noise ratio is greater than or equal to -20dB, the target distance and speed can be accurately measured.

[0105] Using the same inventive concept as the nonlinear radar speed and ranging method based on Costas FM coded signals, this embodiment also provides a corresponding nonlinear radar speed and ranging system based on Costas FM coded signals, including:

[0106] a transmitter for transmitting a Costas frequency modulation coded signal to a non-linear target;

[0107] A receiver is used to obtain an echo signal reflected by a nonlinear target; the echo signal includes a linear echo, a second harmonic, and a third harmonic;

[0108] A preprocessing module is used to preprocess the echo signal to obtain a preprocessed signal; the preprocessing includes digital down-conversion and band-pass filtering;

[0109] Specifically, the pre-processing module includes a mixer and three band-pass filters. The mixer is used to digitally down-convert the echo signal, and the three band-pass filters perform band-pass filtering on the linear echo, second harmonic, and third harmonic respectively.

[0110] When performing bandpass filtering on the linear echo, the center frequency of the bandpass filter is the same as the center frequency of the transmitted signal, and the bandwidth of the bandpass filter is the same as the bandwidth of the transmitted signal;

[0111] When band-pass filtering is performed on the second harmonic, the center frequency of the band-pass filter is twice the center frequency of the transmitted signal, and the bandwidth of the band-pass filter is twice the bandwidth of the transmitted signal;

[0112] When band-pass filtering is performed on the third harmonic, the center frequency of the band-pass filter is three times the center frequency of the transmitted signal, and the bandwidth of the band-pass filter is three times the bandwidth of the transmitted signal.

[0113] A phase compensation module is used to perform phase compensation on the preprocessed signal to obtain a compensated signal; the phase compensation includes compensation for delay redundancy and compensation for Doppler redundancy;

[0114] The ranging module is used to perform inverse fast Fourier transform on the compensated signal, transform the data in the signal from the frequency domain to the fast time domain, and determine the distance between the radar and the nonlinear target based on the data in the fast time domain;

[0115] The speed measurement module is used to perform discrete Fourier transform on the compensated signal, convert the data in the signal from the slow time domain to the Doppler frequency domain, and determine the speed of the nonlinear target based on the data in the Doppler frequency domain.

[0116] The nonlinear radar speed and ranging system based on Costas FM coded signals in this embodiment has the same inventive concept as the nonlinear radar speed and ranging method based on Costas FM coded signals described above. Therefore, the specific implementation method of the device can be seen in the embodiment section of the nonlinear radar speed and ranging method based on Costas FM coded signals described above, and its technical effects correspond to the technical effects of the above-mentioned method, which will not be repeated here.

[0117] The above descriptions are merely examples of various embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any modifications or substitutions that can be readily conceived by a person skilled in the art within the technical scope disclosed in the present application should be included within the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A nonlinear radar speed and distance measurement method based on Costas frequency modulation coded signal, characterized in that: include: transmitting a Costas frequency modulation coded signal to a nonlinear target and acquiring an echo signal reflected by the nonlinear target; The echo signal includes a linear echo, a second harmonic and a third harmonic; Preprocessing the echo signal to obtain a preprocessed signal; the preprocessing includes digital down conversion and bandpass filtering; Performing phase compensation on the preprocessed signal to obtain a compensated signal; the phase compensation includes compensating for a delay redundancy item and compensating for a Doppler redundancy item; Performing an inverse fast Fourier transform on the compensated signal to transform data in the signal from a frequency domain to a fast time domain, and determining the distance between the radar and the nonlinear target based on the data in the fast time domain; The compensated signal is subjected to discrete Fourier transform to convert data in the signal from a slow time domain to a Doppler frequency domain, and the speed of the nonlinear target is determined based on the data in the Doppler frequency domain.

2. The method according to claim 1, wherein The echo signal reflected by the nonlinear target is: Among them, s D is the echo signal reflected by the nonlinear target, r is the order of the echo signal, a r is the amplitude factor of the rth order echo signal, f is the carrier frequency of the pth pulse, t is the time, β is the phase, λ is the wavelength and l is the distance between the radar and the nonlinear target.

3. The method according to claim 1, wherein The band-pass filtering uses three band-pass filters to perform band-pass filtering on the linear echo, the second harmonic and the third harmonic respectively; When performing bandpass filtering on the linear echo, the center frequency of the bandpass filter is the same as the center frequency of the transmitted signal, and the bandwidth of the bandpass filter is the same as the bandwidth of the transmitted signal; When band-pass filtering is performed on the second harmonic, the center frequency of the band-pass filter is twice the center frequency of the transmitted signal, and the bandwidth of the band-pass filter is twice the bandwidth of the transmitted signal; When band-pass filtering is performed on the third harmonic, the center frequency of the band-pass filter is three times the center frequency of the transmitted signal, and the bandwidth of the band-pass filter is three times the bandwidth of the transmitted signal.

4. The method according to claim 1, wherein in, Performing phase compensation on the preprocessed signal, including performing phase compensation on the second harmonic and the third harmonic in the preprocessed signal respectively; The delay redundancy term of the second harmonic is exp{-j4πf n τ0}, the Doppler redundancy term is Among them, f n is the coding carrier frequency, τ0 is the pulse width, f c is the fixed carrier frequency of the transmitted signal; v is the speed of the nonlinear target, n is the discrete sampling time, T r is the pulse repetition period, c is the speed of light; The delay redundancy term of the third harmonic is exp{-j6πf n τ0}, the Doppler redundancy term is 5. The method according to claim 1, wherein in, performing discrete Fourier transform on the compensated signal, including performing discrete Fourier transform on the second harmonic and the third harmonic in the compensated signal respectively; The transformation factor used in the discrete Fourier transform of the second harmonic is Among them, f n is the code carrier frequency, f c is the fixed carrier frequency of the transmitted signal, v is the speed of the nonlinear target, n is the discrete sampling time, T r is the pulse repetition period, c is the speed of light; The transformation factor used in the discrete Fourier transform of the third harmonic is 6. A nonlinear radar speed and distance measurement system based on Costas frequency modulation coded signal, characterized in that: include: a transmitter for transmitting a Costas frequency modulation coded signal to a non-linear target; a receiver, configured to obtain an echo signal reflected by the nonlinear target; The echo signal includes a linear echo, a second harmonic and a third harmonic; A preprocessing module, configured to preprocess the echo signal to obtain a preprocessed signal; the preprocessing includes digital down-conversion and band-pass filtering; A phase compensation module, configured to perform phase compensation on the preprocessed signal to obtain a compensated signal; the phase compensation includes compensating for delay redundancy and Doppler redundancy; a ranging module, configured to perform an inverse fast Fourier transform on the compensated signal, transform the data in the signal from the frequency domain to the fast time domain, and determine the distance between the radar and the nonlinear target based on the data in the fast time domain; The speed measurement module is used to perform discrete Fourier transform on the compensated signal, convert the data in the signal from the slow time domain to the Doppler frequency domain, and determine the speed of the nonlinear target according to the data in the Doppler frequency domain.

7. The system according to claim 6, wherein: The pre-processing module includes a mixer and three band-pass filters, the mixer is used to perform digital down-conversion on the echo signal, and the three band-pass filters respectively perform band-pass filtering on the linear echo, the second harmonic and the third harmonic; When performing bandpass filtering on the linear echo, the center frequency of the bandpass filter is the same as the center frequency of the transmitted signal, and the bandwidth of the bandpass filter is the same as the bandwidth of the transmitted signal; When band-pass filtering is performed on the second harmonic, the center frequency of the band-pass filter is twice the center frequency of the transmitted signal, and the bandwidth of the band-pass filter is twice the bandwidth of the transmitted signal; When band-pass filtering is performed on the third harmonic, the center frequency of the band-pass filter is three times the center frequency of the transmitted signal, and the bandwidth of the band-pass filter is three times the bandwidth of the transmitted signal.

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