A method for suppressing parasitic time-varying phase modulation interference

Abstract

The application discloses a kind of parasitic time-varying phase modulation interference suppression methods, comprising: receiving from the alias echo signal of target, and alias echo signal is modeled and preprocessed;Wherein, the target sets adjustable electromagnetic material surface;The energy of fundamental wave component in alias echo signal, the energy intensity of first harmonic component is judged, and corresponding processing strategy is executed.For the case that radar transmitting signal is incident to adjustable electromagnetic material surface at different angles, the application can effectively suppress the two types of interference that appear, restore and reconstruct the real fundamental wave energy by shifting modulation harmonic component, realize interference characteristic estimation and separation, real target energy recovery, finally effectively improve the signal-to-interference ratio required for target detection.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of radar signal processing and electromagnetic interference countermeasures, and particularly relates to a method for suppressing parasitic harmonic interference generated when time-varying phase modulation electromagnetic materials are arranged on a target surface. BACKGROUND

[0002] As an active microwave target detection device, radar has the ability to detect and perceive targets at all times and in all weather, and is an important means of space-time-ground-sea battlefield situation awareness, and plays an irreplaceable role in various monitoring systems. The core of modern electronic warfare is how to obtain accurate target information. At present, interference technology has developed in the direction of fast parameter modulation and feature deception. Developing radar anti-jamming equipment with the ability of fast interference parameter demodulation and real feature recovery is the key to winning in a complex dynamic electromagnetic countermeasure environment.

[0003] Parasitic harmonic interference is a kind of coherent interference generated when radar incident electromagnetic waves are phase-modulated by tunable electromagnetic materials. Because the impedance coefficient of tunable electromagnetic materials has time-varying characteristics, when the radar incident signal reaches its surface, the electromagnetic wave will be modulated with specific parameters, thereby changing the phase characteristics of the incident electromagnetic wave. In practice, tunable electromagnetic materials are usually placed at key positions of the target. The return signal received by the radar not only includes the harmonic interference component generated by the modulation of the incident electromagnetic wave by the tunable electromagnetic material, but also contains the non-modulated signal reflected by the real target, i.e. the fundamental component. After pulse compression processing of the mixed return signal with modulated and non-modulated signals, the distance dimension not only contains the real distance information corresponding to the non-modulated part, but also contains a large amount of false distance information. At the same time, the signal energy at the real distance position may be much smaller than the energy of the false target, thereby posing a great threat to radar detection.

[0004] Existing distance deception jamming suppression methods cannot directly deal with parasitic harmonic interference, and the commonly used anti-jamming means has the following technical difficulties:

[0005] 1) For the case of passive interference type, the harmonic component is formed by shifting the fundamental component corresponding to the real signal, which is generated by modulating the phase parameters of the radar incident signal. After pulse compression, the harmonic component can form a distance dimension deception false target. If direct separation filtering processing is performed in the transform domain, not only the energy of the real target component cannot be recovered, but also a large amount of useful signals are lost.

[0006] 2) The harmonic interference return is part of the real target return itself, and is a coherent interference. After inter-pulse accumulation, the interference component can also achieve the effect of energy aggregation, and cannot use the energy feature to distinguish between real and false targets in the pulse dimension.

[0007] In summary, considering the technical bottlenecks of the existing anti-jamming methods in the parasitic harmonic interference scene, it is urgent to carry out the research on the periodic phase modulation harmonic interference suppression technology, to solve the technical problems such as 'target energy is weakened','strong coupling between interference and target','strong similarity between interference and target', and effectively improve the interference perception and target detection ability of radar in the high dynamic strong game electronic countermeasure scene. SUMMARY

[0008] In view of the problem that the existing anti-interference technology cannot cope with parasitic harmonic interference, the purpose of the present application is to provide a parasitic time-varying phase modulation interference suppression method, which can suppress the false target components formed by the harmonic components under different incidence conditions, and at the same time restore the real signal energy weakened, effectively improve the signal-to-interference ratio required for radar detection.

[0009] In order to achieve the above task, the present application adopts the following technical scheme:

[0010] A parasitic time-varying phase modulation interference suppression method, comprising:

[0011] Receiving the aliasing echo signal from the target, and modeling and preprocessing the aliasing echo signal, and determining the energy of the fundamental component and the energy strength of the first-order harmonic component in the aliasing echo signal; wherein the target is provided with a tunable electromagnetic material surface;

[0012] If the fundamental component energy is weaker than the first-order harmonic component, the radar transmitting signal is perpendicular to the tunable electromagnetic material surface of the target; at this time, first, the phase information of the time domain data of the aliasing echo signal after processing is solved and a phase sequence is composed, then the phase jump information is obtained by difference transformation, and the modulation period and initial jump time of the phase modulation sequence are estimated by using outlier detection, the phase modulation sequence is reconstructed according to the estimated parameters and the modulation harmonic component is compensated, and finally the real fundamental component weakened is recovered;

[0013] If the fundamental component energy is stronger than the first-order harmonic component, the radar transmitting signal is obliquely incident on the tunable electromagnetic material surface of the target; at this time, first, the frequency information of the fundamental component is extracted and reconstructed according to the symmetry characteristics of the harmonic component after Fourier transform, then the aliasing echo signal and the fundamental component are processed to obtain the harmonic component generated by the periodic phase modulation, and then the phase modulation information is obtained after the time domain difference processing of the phase, and the harmonic component is recovered by using the constructed phase modulation sequence.

[0014] Further, the aliasing echo signal is modeled as:

[0015] s j (t)=a1·s t (t)+a2·s p (t)

[0016] Among them, s p (t) = s t (t)·p(t),s t (t) represents the linear radar transmission signal, s j (t) is the aliased echo signal received by the radar, which contains the non-modulated part s corresponding to the fundamental component. t (t) The modulation part corresponding to the harmonic component s p (t), a1 and a2 are the signal amplitudes corresponding to the non-modulation part and the modulation part respectively, and p(t) is the periodic phase modulation interference sequence generated by the time-varying impedance of the adjustable electromagnetic material surface. Its signal expression is:

[0017]

[0018] Among them, e is a natural constant, w p =2π / T p is the period of the modulation coding sequence on the surface of the tunable electromagnetic material T p Determined angular frequency, A m is the Fourier series coefficient corresponding to the mth-order harmonic generated by the time-varying impedance response of the tunable electromagnetic material surface.

[0019] Furthermore, for the aliased echo signal s j (t) After preprocessing, including digital down-conversion and de-linear frequency modulation, we can obtain:

[0020]

[0021] in, is the DC component obtained after down-conversion and de-frequency modulation of the aliased echo signal, T s is the sampling period, N is the total number of sampling points, n=1,2,…,N is the sampling time domain sequence, and p[n] is the periodic phase modulation sequence.

[0022] Furthermore, if the fundamental wave component energy is weaker than the first-order harmonic component, the radar transmit signal is perpendicular to the target's adjustable electromagnetic material surface. In this case, the processing process is:

[0023] Step 201: pre-processed aliased echo signal It consists of two parts: non-modulation part and modulation part; considering a1<a2, and contains only the DC component, The phase jump of is consistent with the phase jump of the periodic phase modulation sequence p[n], then After performing time domain difference transformation on the phase of , we can get:

[0024]

[0025] where ∠(·) represents a phase extraction operation, and φ1[n] is a phase sequence composed of the time-domain phase information of

[0026] Step 202, the phase sequence φ1[n] extracted in step 201 is processed by time-domain difference transformation as follows:

[0027]

[0028] where [·] (1) represents a difference operation, and d1[n] is a sequence after difference transformation of the phase sequence φ1[n];

[0029] Step 203, the sequence d1[n] after difference transformation is a group of periodic impulse sequences in the time domain, and the impulse time corresponds to the phase jump time of the periodic phase modulation sequence p[n]; after performing outlier detection on the sequence d1[n], the modulation period T p and the initial position T start of p[n] are estimated; the calculation formula of the detection threshold T s is as follows:

[0030] T s = μ s + 3σ s

[0031] where μ s and σ s are the mean and standard deviation of the sequence d1[n], respectively;

[0032] If d1[i] > T s , then The estimated sequence obtained after threshold detection is:

[0033]

[0034] where i = 1, 2,..., n, p is the total number of phase jumps of the periodic modulation sequence p[n] within the total number of sampling points N, and T is the estimated time of the pth phase jump.

[0035] The estimated value of the modulation period T and the estimated value of the initial position T are obtained using the estimated sequence

[0036]

[0037] The reconstructed periodic modulation sequence is:

[0038] ​

[0039] wherein L is a positive integer;

[0040] Step 204, demodulating the aliasing echo signal by using the reconstructed periodic modulation sequence, and the specific operation is as follows:

[0041]

[0042] wherein, is the result of demodulation of the interfered echo, and sj[n] is s j (t) is the result of discrete sampling;

[0043] Step 205, performing matched filtering processing on the demodulated signal to obtain an output signal y1[n], and the specific operation is as follows:

[0044]

[0045] wherein h[n] is a reference signal used for matched filtering, and DFT[·] and IDFT[·] are discrete Fourier transform and inverse discrete Fourier transform operations respectively.

[0046] Further, if the fundamental component energy is stronger than the first harmonic component, the radar transmitting signal is incident on the surface of the tunable electromagnetic material at an angle, and at this time, the processing process is as follows:

[0047] Step 211, pre-processing the aliasing echo signal is composed of a non-modulation part and a modulation part; considering that a1>a2, the non-modulation part is is Fourier transformed, and according to the symmetry of the harmonic components and the characteristic that the fundamental component is higher than each order harmonic, the fundamental component is reconstructed and separated;

[0048] Fourier transform of is expressed as follows:

[0049]

[0050] wherein FT[·] is Fourier transform, N FT is the number of Fourier transform points, and k represents the kth sampling point;

[0051] The frequency parameter estimation value corresponding to the fundamental component is :

[0052]

[0053] wherein, is a function of finding the maximum of the independent variable, F s is a sampling frequency;

[0054] amplitude parameter estimation value corresponding to the fundamental component is:

[0055]

[0056] using the estimated frequency value amplitude value and the known radar transmission signal parameter frequency modulation rate K LFM , the reconstructed fundamental component is expressed as:

[0057]

[0058] using the reconstructed fundamental component and the radar received aliasing echo signal s j (t) to obtain the harmonic component generated by the periodic modulation interference

[0059]

[0060] Step 212, the harmonic component obtained after the cancellation processing is de-linear modulated and sampled at a sampling frequency F s After sampling, the time domain sampling sequence is determined using the harmonic component is demodulated and harmonic shifted:

[0061]

[0062] wherein, is the recovered harmonic component, is the time domain sampling sequence obtained after sampling at a sampling frequency F s ;

[0063] Step 213, the reconstructed fundamental component in step 211 is matched filtered with the recovered harmonic component in step 212 to obtain an output signal y2[n], the specific operation is as follows:

[0064]

[0065] wherein, is the time domain sampling sequence obtained after sampling at a sampling frequency F s , and h[n] is the reference signal used for matched filtering.

[0066] A radar adopts the parasitic time-varying phase modulation interference suppression method to suppress aliasing echo signals of a target with a surface of tunable electromagnetic material.

[0067] A terminal device comprises a processor, a memory and a computer program stored in the memory; when the processor executes the computer program, the parasitic time-varying phase modulation interference suppression method is implemented.

[0068] A computer readable storage medium stores a computer program; when the computer program is executed by a processor, the parasitic time-varying phase modulation interference suppression method is implemented.

[0069] Compared with the prior art, the present application has the following technical features:

[0070] 1. The parasitic harmonic interference suppression method can cope with different types of harmonic interference existing in the received echo when the radar observes the target covered by the tunable electromagnetic material at different angles; when the radar transmitting signal is vertically incident on the surface of the tunable electromagnetic material, the present application uses the known parameter information of the transmitting signal, eliminates the influence of the carrier frequency term and the phase quadratic term through digital down-conversion and demodulation frequency preprocessing, estimates the modulation starting time and modulation period of the periodic phase modulation sequence by combining the time domain difference results of the extracted phase sequence with the characteristics of the impulse function, and realizes the shift and compensation of the harmonic modulation term by using the reconstructed periodic phase modulation sequence; when the radar transmitting signal is obliquely incident on the surface of the tunable electromagnetic material, the present application can extract and reconstruct the frequency information of the fundamental component according to the symmetry characteristics of the harmonic component after the demodulation frequency processing in the Fourier transform domain, and then performs cancellation processing on the aliasing echo and the fundamental component to obtain the harmonic component generated by the periodic phase modulation. Since the cancellation operation has largely eliminated the influence of the fundamental component, it can be equivalent to the case where the energy of the fundamental component is weaker than that of the first-order harmonic component, and the interference suppression processing steps used in the vertical incidence case are performed, so that the periodic phase modulation sequence is reconstructed to complete the harmonic shift compensation processing.

[0071] 2. For the case that the radar transmitting signal is incident on the surface of the tunable electromagnetic material at different angles, the present application can effectively suppress both types of interference, realize the recovery and reconstruction of the real fundamental energy by shifting the modulation harmonic component, realize the interference feature estimation and separation, the real target energy recovery, and finally effectively improve the signal-to-interference ratio required for target detection. BRIEF DESCRIPTION OF DRAWINGS

[0072] Figure 1 is a flowchart of the method of the present application;

[0073] Figure 2 is a schematic diagram of the modulation process of the radar transmitting signal by the surface of the tunable electromagnetic material in the example of the present application.

[0074] Figure 3 (a) is the frequency spectrum diagram of the radar echo after digital down conversion and demodulation frequency processing when the radar transmitting signal is vertically incident in the example of the present application; (b) is the frequency spectrum diagram of the radar echo after digital down conversion and demodulation frequency processing when the radar transmitting signal is obliquely incident in the example of the present application;

[0075] Figure 4 (a) is the time-domain waveform of the radar echo after digital down conversion and demodulation frequency processing when the radar transmitting signal is vertically incident in the example of the present application; (b) is the result of phase sequence difference after the radar transmitting signal is vertically incident in the example of the present application; (c) is the result of time-domain mutation point detection when the radar transmitting signal is vertically incident in the example of the present application; (d) is the reconstructed periodic phase modulation sequence when the radar transmitting signal is vertically incident in the example of the present application;

[0076] Figure 5 is the comparison result before and after the interference suppression processing when the radar transmitting signal is vertically incident in the example of the present application;

[0077] Figure 6 (a) is the time-domain waveform of the harmonic signal component after demodulation frequency processing when the radar transmitting signal is obliquely incident in the example of the present application; (b) is the result of phase sequence difference after the harmonic component is obtained after the fundamental wave cancellation when the radar transmitting signal is obliquely incident in the example of the present application; (c) is the result of time-domain mutation point detection of the reconstructed harmonic when the radar transmitting signal is obliquely incident in the example of the present application; (d) is the reconstructed periodic phase modulation sequence when the radar transmitting signal is obliquely incident in the example of the present application;

[0078] Figure 7 is the comparison result before and after the interference suppression processing when the radar transmitting signal is obliquely incident in the example of the present application. DETAILED DESCRIPTION

[0079] In actual scenarios, the tunable electromagnetic material is only arranged at the key position of the target instead of covering the entire target surface, and the radar receives the echo composed of two parts: the non-modulated signal (i.e. the fundamental wave component) reflected by the target and the modulated signal (i.e. the harmonic component) reflected by the surface of the tunable electromagnetic material. The present application mainly utilizes the energy difference between the fundamental wave and the harmonic component in the aliasing echo to perform interference suppression processing on the received echo under two kinds of incident conditions, i.e. vertical incidence and oblique incidence.

[0080] Referring to FIG. 1, Figure 1 The present application provides a parasitic time-varying phase modulation interference suppression method, which comprises the following steps:

[0081] The mixed echo signal from the target is received, the mixed echo signal is modeled and preprocessed, and the energy of the fundamental component and the energy of the first-order harmonic component in the mixed echo signal are determined to determine the subsequent processing mode; wherein the target is provided with an adjustable electromagnetic material surface;

[0082] Case 1: If the fundamental component energy is weaker than the first-order harmonic component, the radar transmitting signal is vertically incident on the adjustable electromagnetic material surface of the target; at this time, the mixed echo signal received by the radar produces multiple sharp peaks in the distance dimension after matched filter processing, and the peak value of the false target is higher than that of the real target, and the modulated signal component in the mixed echo signal plays a dominant role;

[0083] For this case, first, the phase information of the time domain data of the processed mixed echo signal is solved and a phase sequence is formed, then the phase jump information is obtained by difference transformation, and the modulation period and initial jump time of the phase modulation sequence are estimated by using outlier detection, the phase modulation sequence is reconstructed according to the estimated parameters and the modulated harmonic component is compensated, and finally the weakened real fundamental component is effectively recovered and the signal-to-interference ratio required for target detection is improved.

[0084] Case 2: If the fundamental component energy is stronger than the first-order harmonic component, the radar transmitting signal is obliquely incident on the adjustable electromagnetic material surface of the target; the fundamental energy in the echo after phase modulation is stronger than the first-order harmonic component, and although the real target energy formed after matched filter processing of the received echo is higher than that of the harmonic component false target, the harmonic component has a high degree of realism and a low signal-to-interference ratio due to its phase correlation;

[0085] For this case, first, the frequency information of the fundamental component is extracted and reconstructed according to the symmetry of the harmonic component after Fourier transform, then the mixed echo signal is processed to eliminate the fundamental component to obtain the harmonic component generated by periodic phase modulation, and then the phase modulation information is obtained by time domain difference processing, and finally the harmonic component is recovered using the constructed phase modulation sequence to improve the signal-to-interference ratio after pulse compression processing.

[0086] The specific implementation process of each step is further described below.

[0087] Step 1, the radar receives the mixed echo signal from the target, and models and preprocesses the mixed echo signal.

[0088] In actual scenarios, the adjustable electromagnetic material is only arranged at the key position of the real target instead of covering the entire target surface, and the mixed echo signal received by the radar contains harmonic modulation components and non-modulated fundamental components; when the radar transmitting signal s t When the linear frequency modulation signal (t) is used, its expression is:

[0089]

[0090] where t is time parameter, rect(·) is rectangular window function, T d is the duration of the transmitted pulse, K LFM is the frequency modulation rate, f0is the carrier frequency, c is the speed of light, λ is the wavelength of the transmitted signal, j is the imaginary unit.

[0091] The mixed echo signal received by radar is modeled as follows:

[0092] s j (t) = a1·s t (t) + a2·s p (t) = a1·s t (t) + a2·s t (t)·p(t)

[0093] where s j (t) is the mixed echo signal received by radar, which contains the non-modulated part s t (t) corresponding to the fundamental component and the modulated part s p (t) corresponding to the harmonic component, a1, a2 are the signal amplitudes corresponding to the non-modulated part and the modulated part respectively, p(t) is the periodic phase modulation interference sequence generated by the time-varying impedance of the tunable electromagnetic material surface, and its signal expression is:

[0094]

[0095] where e is the natural constant, w p = 2π / T p is the angular frequency determined by the modulation code sequence period T p of the tunable electromagnetic material surface, A m is the Fourier series coefficient corresponding to the mth harmonic generated by the time-varying impedance response of the tunable electromagnetic material surface, which is expressed as:

[0096]

[0097] where, x is the independent variable of the function.

[0098] According to the known parameters of the radar transmitted signal, the mixed echo signal s j (t) is preprocessed, including digital down conversion and linear frequency modulation processing, and the following can be obtained:

[0099]

[0100] where, T is the DC component obtained after down-conversion and de-chirp of the aliasing echo signal s is the sampling period, N is the total number of sampling points, n = 1, 2, …, N is the sampling time sequence, and p[n] is the periodic phase modulation sequence.

[0101] With the continuous change of the relative angle between the radar and the detected target, the energy of the harmonic component generated by the tunable electromagnetic material will change accordingly, and the corresponding interference suppression method also has corresponding differences. After down-sampling and de-chirp transformation of the received echo, the fundamental component corresponding to the real target presents a single spectral line in the frequency domain, and is located near zero frequency, while the harmonic component has symmetry, and its frequency domain distribution is two spectral lines symmetrically centered on zero frequency. When the signal amplitude corresponding to the single spectral line near zero frequency is greater than the amplitude of all harmonic components, it corresponds to case 2, and vice versa, it corresponds to case 1.

[0102] Step 2, according to the amplitude difference between the fundamental energy corresponding to the non-modulation part and the maximum harmonic energy corresponding to the modulation part, it is divided into the following two cases:

[0103] Case 1: The radar transmitted signal is perpendicular to the surface of the tunable electromagnetic material, and the fundamental component energy is weaker than the first-order harmonic component, i.e. a1

[0104] Step 201, the aliasing echo signal after preprocessing is composed of non-modulation part and modulation part; considering that a1 contains only DC component, the phase jump condition is consistent with that of the periodic phase modulation sequence p[n], then the phase of can be obtained after time domain difference transformation:

[0105]

[0106] Where ∠(·) represents the phase extraction operation, and φ1[n] is the phase sequence composed of the time domain phase information of .

[0107] Step 202, the phase sequence φ1[n] extracted in step 201 is processed by time domain difference transformation as follows:

[0108]

[0109] Where [·] (1) represents the difference operation, and d1[n] is the sequence after difference transformation of the phase sequence φ1[n].

[0110] Step 203, the differential transformed sequence d1[n] is a group of periodic impulse sequences in time domain, and the impulse time corresponds to the phase jump time of the periodic phase modulation sequence p[n]; after performing outlier detection on the sequence d1[n], the modulation period T p and the initial position T start are estimated; the detection threshold T s is calculated as follows:

[0111] T s = μ s + 3σ s

[0112] wherein μ s and σ s are the mean value and standard deviation of the sequence d1[n], respectively.

[0113] If d1[i] > T s , then The estimated sequence obtained after threshold detection is:

[0114]

[0115] wherein i = 1, 2,..., n, p is the total number of phase jumps of the periodic modulation sequence p[n] within the total sampling point number N, is the estimated time of the pth phase jump.

[0116] Considering that the phase jump points of the periodic modulation sequence have regularity, only the modulation period T p and the initial position T start are needed to reconstruct the complete modulation sequence; therefore, the estimated value of the modulation period T and the estimated value of the initial position T are obtained by using the estimated sequence

[0117]

[0118] The reconstructed periodic modulation sequence is:

[0119]

[0120] wherein L is a positive integer.

[0121] Step 204, the reconstructed periodic modulation sequence is used to demodulate the aliasing echo signal, and the specific operation is as follows:

[0122]

[0123] wherein, is the result of the disturbed echo after demodulation, and sj[n] is thej (t) the result after discrete sampling.

[0124] Step 205, the demodulated signal is matched filtered to obtain the output signal y1[n], the specific operation is as follows:

[0125]

[0126] Wherein, h[n] is the reference signal used for matched filtering, DFT[·] and IDFT[·] are discrete Fourier transform and inverse discrete Fourier transform operation respectively.

[0127] Case 2: the radar transmitting signal is obliquely incident on the surface of the tunable electromagnetic material, and the energy of the fundamental component is stronger than that of the first harmonic component, that is, a1>a2.

[0128] Step 211, the preprocessed aliasing echo signal Composed of non-modulated part and modulated two parts; considering a1>a2, the Fourier transform is carried out on , and according to the symmetry of harmonic components and the characteristic that the fundamental component is higher than each order harmonic, the fundamental component is reconstructed and separated.

[0129] Fourier transform of The expression is as follows:

[0130]

[0131] Wherein, FT[·] is the Fourier transform, N FT is the number of points of Fourier transform, k represents the kth sampling point.

[0132] The frequency parameter estimation value corresponding to the fundamental component is:

[0133]

[0134] Wherein, is the function of finding the maximum of independent variable, F s is the sampling frequency.

[0135] The amplitude parameter estimation value corresponding to the fundamental component is:

[0136]

[0137] Wherein, max(·) is the maximum value.

[0138] The estimated frequency value The amplitude value And the known radar transmitting signal parameter frequency K LFM, the reconstructed fundamental component may be expressed as:

[0139]

[0140] with the reconstructed fundamental component and the aliasing echo signal s received by the radar j (t) to obtain the harmonic component generated by the periodic modulation interference The specific operation process is as follows:

[0141]

[0142] Step 212, the harmonic component obtained after the cancellation processing is demodulated and sampled at a sampling frequency F s After sampling, the time-domain sampling sequence is obtained which is processed according to the same process in steps 201 to 203 to obtain the reconstructed periodic modulation sequence with the reconstructed periodic modulation sequence The harmonic component is demodulated and the harmonic is shifted, and the specific operation is as follows:

[0143]

[0144] wherein, is the recovered harmonic component, is the time-domain sampling sequence obtained after sampling at a sampling frequency F s .

[0145] Step 213, the reconstructed fundamental component in step 211 is matched with the recovered harmonic component in step 212 to obtain the output signal y2[n], and the specific operation is as follows:

[0146]

[0147] wherein, is the time-domain sampling sequence obtained after sampling at a sampling frequency F s .

[0148] Embodiment:

[0149] In one example of the present application, the measured data is derived from X-band radar received echoes, wherein the transmitted signal has a time width of 100 us, a bandwidth of 400 MHz, a sampling frequency of 500 MHz, a carrier frequency of 10 GHz, a pulse repetition time of 200 us, a distance between the radar and the target of 12.9 m, and the adjustable electromagnetic material surface installed on the target is modulated at a 1 MHz period with a duty cycle of 50%, as shown in Figure 3

[0150] Case 1: the parameters used in the threshold detection are μ s = 0.0031 and σ s = 0.1674, and the detection threshold Ts = 0.5052 is obtained. The estimated value of the modulation period corresponds to a modulation frequency of 1.0504 MHz, and the initial position of the jump is

[0151] As shown in Figure 4 and Figure 5 , before the interference suppression processing, the ratio of the real signal energy corresponding to the fundamental wave to the false target energy corresponding to the first-order harmonic in the one-dimensional range profile is -11.02 dB, and after the interference suppression processing, the point with the highest energy in the one-dimensional range profile is located at 12.9 m, consistent with the distance of the real target, and the ratio of the real target energy to the false target energy corresponding to the first-order harmonic is 17.27 dB, and the signal-to-interference ratio is improved by 28.29 dB after the interference suppression processing.

[0152] Case 2: the sampling frequency rate F s = 500 MHz, the Fourier transform point number N FT = 50000, T d = 200 us, K LFM = 4 x 10 12 , μ s = 1.44 x 10 -4 and σ s = 0.3484, and the detection threshold T s = 1.0454 is obtained; the estimated value of the modulation period corresponds to a modulation frequency of 1.0204 MHz, and the initial position of the jump is

[0153] As shown in Figure 6 and Figure 7 , before the interference suppression processing, the ratio of the real signal energy corresponding to the fundamental wave to the false target energy corresponding to the first-order harmonic in the one-dimensional range profile is 8.83 dB, and after the interference suppression processing, the point with the highest energy in the one-dimensional range profile is located at 12.9 m, consistent with the distance of the real target, and the ratio of the real target energy to the false target energy corresponding to the first-order harmonic is 28.19 dB, and the signal-to-interference ratio is improved by 19.36 dB after the interference suppression processing.​

[0154] The above examples are only used to illustrate the technical solutions of the present application, but not to limit the same; although the present application has been described in detail with reference to the foregoing examples, those ordinarily skilled in the art should understand: the technical solutions recorded in the foregoing examples can still be modified, or some technical features can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. A method for suppressing parasitic time-varying phase modulation interference, characterized in that: include: Receiving an aliased echo signal from a target, modeling and preprocessing the aliased echo signal, and determining the energy strength of the fundamental component and the first-order harmonic component in the aliased echo signal; wherein the target is provided with an adjustable electromagnetic material surface; If the fundamental component is weaker than the first-order harmonic component, the radar transmits a signal perpendicular to the target's adjustable electromagnetic material surface. First, the phase information of the processed time-domain data of the aliased echo signal is calculated to form a phase sequence. Phase transition information is then acquired through differential transformation, and outlier detection is used to estimate the modulation period and initial transition moment of the phase modulation sequence. The phase modulation sequence is reconstructed based on the estimated parameters, and the modulated harmonic components are compensated, ultimately restoring the weakened true fundamental component. If the energy of the fundamental component is stronger than the first-order harmonic component, the radar transmit signal will be tilted to the adjustable electromagnetic material surface of the incident target; at this time, the frequency information of the fundamental component is first extracted and reconstructed based on the symmetry characteristics of the harmonic component after Fourier transform, and then the aliased echo signal and the fundamental component are canceled to obtain the harmonic component generated by periodic phase modulation. The phase is then subjected to time domain difference processing to obtain the phase modulation information, and the constructed phase modulation sequence is used to restore the harmonic component.

2. The method for suppressing parasitic time-varying phase modulation interference according to claim 1, wherein: The aliased echo signal is modeled as follows: s j (t)=a1·s t (t)+a2·s p (t) Among them, s p (t) = s t (t)·p(t),s t (t) represents the linear radar transmission signal, s j (t) is the aliased echo signal received by the radar, which contains the non-modulated part s corresponding to the fundamental component. t (t) The modulation part corresponding to the harmonic component s p (t), a1 and a2 are the signal amplitudes corresponding to the non-modulation part and the modulation part respectively, and p(t) is the periodic phase modulation interference sequence generated by the time-varying impedance of the adjustable electromagnetic material surface. Its signal expression is: Among them, e is a natural constant, w p =2π / T p is the period of the modulation coding sequence on the surface of the tunable electromagnetic material T p Determined angular frequency, A m is the Fourier series coefficient corresponding to the mth-order harmonic generated by the time-varying impedance response of the tunable electromagnetic material surface.

3. The method for suppressing parasitic time-varying phase modulation interference according to claim 1, wherein: For aliased echo signal s j (t) After preprocessing, including digital down-conversion and de-linear frequency modulation, we can obtain: in, is the DC component obtained after down-conversion and de-frequency modulation of the aliased echo signal, T s is the sampling period, N is the total number of sampling points, n=1,2,…,N is the sampling time domain sequence, and p[n] is the periodic phase modulation sequence.

4. The method for suppressing parasitic time-varying phase modulation interference according to claim 1, wherein: If the fundamental wave component is weaker than the first-order harmonic component, the radar transmits the signal perpendicularly to the target's adjustable electromagnetic material surface. The processing process is as follows: Step 201: pre-processed aliased echo signal It consists of two parts: non-modulation part and modulation part; considering a1<a2, and contains only the DC component, The phase jump of is consistent with the phase jump of the periodic phase modulation sequence p[n], then After performing time domain difference transformation on the phase of , we can get: Where ∠(·) represents the phase extraction operation, and φ1[n] is A phase sequence composed of the time domain phase information; Step 202: Perform time domain differential transformation on the phase sequence φ1[n] extracted in step 201 as follows: d1[n]=φ1 (1) [n] in,[·] (1) represents the differential operation, d1[n] is the sequence after differential transformation of the phase sequence φ1[n]; Step 203: The sequence d1[n] after differential transformation is a set of periodic impulse sequences in the time domain, and the impulse moments correspond to the phase jump moments of the periodic phase modulation sequence p[n]. After performing outlier detection on the sequence d1[n], the modulation period T of p[n] is calculated. p and the initial position T start Estimation; detection threshold T s The calculation formula is as follows: T s =μ s +3s s Among them, μ s and σ s are the mean and standard deviation of the sequence d1[n] respectively; If d1[i]>T s ,but Then the estimated sequence obtained after threshold detection is: Where i = 1, 2, ..., n, p is the total number of phase jumps of the periodic modulation sequence p[n] within the total number of sampling points N, is the estimated time of the pth phase jump; Using the estimated series Get an estimate of the modulation period and an estimate of the initial position Reconstructed periodic modulation sequence for: Wherein, L is a positive integer; Step 204: demodulate the aliased echo signal using the reconstructed periodic modulation sequence. The specific operations are: in, is the result of demodulation of the interfered echo, s j [n] is s j (t) The result after discrete sampling; Step 205: Perform matched filtering on the demodulated signal to obtain an output signal y1[n]. The specific operation is as follows: Where h[n] is the reference signal used in matched filtering, DFT[·] and IDFT[·] are discrete Fourier transform and inverse discrete Fourier transform operations, respectively.

5. The method for suppressing parasitic time-varying phase modulation interference according to claim 1, wherein: If the fundamental wave component is stronger than the first-order harmonic component, the radar transmits the signal at an angle to the adjustable electromagnetic material surface of the incident target. The processing process is as follows: Step 211: pre-processed aliased echo signal It consists of two parts: non-modulation part and modulation part; considering a1>a2, Perform Fourier transform and reconstruct and separate the fundamental component based on the symmetry of the harmonic components and the fact that the fundamental component is higher than all other harmonics. Fourier transform of The expression is as follows: Where FT[·] is the Fourier transform, N FT is the number of Fourier transform points, k represents the kth sampling point; Frequency parameter estimation corresponding to the fundamental component for: in, To find the function with the largest independent variable, F s is the sampling frequency; Amplitude parameter estimation corresponding to the fundamental component for: Using estimated frequency values Amplitude value Frequency modulation K with known radar transmission signal parameters LFM , the reconstructed fundamental component Expressed as: Using the reconstructed fundamental component The aliased echo signal s received by the radar j (t) Cancellation processing can be performed to obtain the harmonic components generated by periodic modulation interference Step 212: The harmonic components obtained after the cancellation process are Demodulate and sample at F s After sampling, we get Determine the reconstructed periodic modulation sequence use For harmonic components Perform demodulation and harmonic shifting: in, is the restored harmonic component, for With sampling frequency F s The time domain sampling sequence obtained after sampling; Step 213, the fundamental component reconstructed in step 211 and the harmonic components recovered in step 212 Perform matched filtering to obtain the output signal y2[n]. The specific operations are as follows: in, for With sampling frequency F s The time domain sampling sequence obtained after sampling, h[n] is the reference signal used in matched filtering.

6. A radar, characterized in that: The radar uses the parasitic time-varying phase modulation interference suppression method according to any one of claims 1 to 5 to suppress interference of aliased echo signals of targets with adjustable electromagnetic material surfaces.

7. A terminal device comprising a processor, a memory, and a computer program stored in the memory; characterized in that: When the processor executes the computer program, the method for suppressing parasitic time-varying phase modulation interference according to any one of claims 1 to 5 is implemented.

8. A computer-readable storage medium storing a computer program; wherein: When the computer program is executed by a processor, the method for suppressing parasitic time-varying phase modulation interference according to any one of claims 1 to 5 is implemented.

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