Parasitic time-varying phase modulation interference suppression method

Abstract

The invention discloses a parasitic time-varying phase modulation interference suppression method, and the method comprises the steps: receiving an aliasing echo signal from a target, and carrying out the modeling and preprocessing of the aliasing echo signal; wherein the target is provided with an adjustable electromagnetic material surface; and judging the energy intensity of the fundamental component and the energy intensity of the first-order harmonic component in the aliasing echo signal, and executing a corresponding processing strategy. For the condition that radar emission signals are incident to the surface of the adjustable electromagnetic material at different angles, the method can effectively suppress two types of interference, realizes recovery and reconstruction of real fundamental wave energy by moving and modulating harmonic components, realizes estimation and separation of interference characteristics and recovery of real target energy, and has good application prospects. And finally, the signal-to-interference ratio required by target detection is effectively improved.

Description

Technical Field

[0001] The present invention relates to the field of radar signal processing and electromagnetic interference countermeasure, and in particular to a method for suppressing parasitic harmonic interference generated when a time-varying phase modulated electromagnetic material is arranged on a target surface. Background Art

[0002] Radar, as an active microwave target detection device, has the ability to detect and perceive targets at all times and in all weather conditions. It is an important means of situational awareness in the air, land, and sea battlefields, and plays an irreplaceable role in various surveillance systems. The core of modern electronic warfare lies in how to obtain accurate target information. At present, interference technology has developed in the direction of rapid parameter modulation and smart feature deception. The development of radar anti-interference equipment with the ability to quickly demodulate interference parameters and restore true features is the key to winning in complex dynamic electromagnetic confrontation environments.

[0003] Parasitic harmonic interference is a type of coherent interference generated by the phase modulation of the radar incident electromagnetic wave by the adjustable electromagnetic material. Since the impedance coefficient of the adjustable electromagnetic material has a time-varying characteristic, when the radar incident signal reaches its surface, the electromagnetic wave will undergo a specific parameter modulation, thereby changing the phase characteristics of the incident electromagnetic wave. In practice, the adjustable electromagnetic material is usually placed at the key position of the target. The echo signal received by the radar includes not only the harmonic interference component generated by the modulation of the incident electromagnetic wave by the adjustable electromagnetic material, but also the non-modulated signal reflected by the real target, that is, the fundamental component. After pulse compression processing is performed on the echo with two parts of the 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 false target energy, which poses a great threat to radar detection.

[0004] The existing distance deception interference suppression method cannot directly deal with parasitic harmonic interference, and the commonly used anti-interference means have the following technical difficulties:

[0005] 1) For the case of passive interference, it is generated by modulating the phase parameters of the radar incident signal. The harmonic component is formed by shifting the fundamental component corresponding to the real signal. At the same time, the harmonic component can form a distance-dimensional deceptive false target after pulse compression. If it is directly separated and filtered in the transform domain, not only the energy of the real target component cannot be restored, but also a large amount of useful signals are lost.

[0006] 2) Harmonic interference echo is a part of the real target echo itself, which is a coherent interference. After pulse accumulation, the interference component can also achieve the effect of energy concentration. It is impossible to use the energy characteristics to identify the real and false targets in the pulse dimension.

[0007] In summary, considering the technical bottlenecks of existing anti-interference methods in parasitic harmonic interference scenarios, it is urgent to carry out research on periodic phase modulation harmonic interference suppression technology to solve technical problems such as "target energy is weakened", "interference and target are strongly coupled", and "interference and target are strongly similar". Effectively improve the radar's interference perception and target detection capabilities in high-dynamic and strong game electronic confrontation scenarios. Summary of the invention

[0008] In view of the problem that existing anti-interference technology is unable to cope with parasitic harmonic interference, the purpose of the present invention is to provide a parasitic time-varying phase modulation interference suppression method, which can suppress the false target component formed by the harmonic component under different incident conditions, and at the same time restore the weakened real signal energy, thereby effectively improving the signal-to-interference ratio required for radar detection.

[0009] In order to achieve the above tasks, the present invention adopts the following technical solutions:

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

[0011] 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;

[0012] If the energy of the fundamental component is weaker than the first-order harmonic component, the radar transmits the signal vertically into the adjustable electromagnetic material surface of the target; at this time, the phase information of the processed time domain data of the aliased echo signal is first solved and a phase sequence is formed, and then the phase jump information is obtained through differential transformation, and the modulation period and initial jump time of the phase modulation sequence are estimated by outlier detection, and 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 restored;

[0013] If the energy of the fundamental component is stronger than the first-order harmonic component, the radar transmits a signal obliquely into the adjustable electromagnetic material surface of the incident target; at this time, the frequency information of the fundamental component is first extracted and reconstructed according to 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 the periodic phase modulation, and then the phase is subjected to time domain difference processing to obtain the phase modulation information, and the harmonic component is restored using the constructed phase modulation sequence.

[0014] Furthermore, the aliased echo signal is modeled as follows:

[0015] s j (t) = a 1 ·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), a 1 ,a 2 are the signal amplitudes corresponding to the non-modulated part and the modulated part respectively, and p(t) is the periodic phase modulation interference sequence generated by the time-varying impedance on the surface of the adjustable electromagnetic material. Its signal expression is:

[0017]

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

[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 energy of the fundamental wave component is weaker than the first-order harmonic component, the radar transmits the signal vertically into the adjustable electromagnetic material surface of the target, and the processing process is:

[0023] Step 201: pre-processed aliased echo signal It consists of two parts: non-modulation part and modulation part; considering a 1 <a 2 ,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 the phase is transformed into time domain difference, we can get:

[0024]

[0025] Where ∠(·) represents the phase extraction operation, φ 1 [n] is A phase sequence composed of time domain phase information;

[0026] Step 202: extract the phase sequence φ from step 201. 1 [n] The time domain difference transformation is performed as follows:

[0027]

[0028] in,[·] (1) represents the differential operation, d 1 [n] is the phase sequence φ 1 The difference transformed sequence of [n];

[0029] Step 203, the sequence d after the difference transformation 1 [n] is a set of periodic impulse sequences in the time domain, and the impulse moment corresponds to the phase jump moment of the periodic phase modulation sequence p[n]; for sequence d 1 After outlier detection on [n], the modulation period T of p[n] is p and the initial position T start Estimation; detection threshold T s The calculation formula is as follows:

[0030] T s =μ s +3σ s

[0031] Among them, μ s and σ s Sequence d 1 The mean and standard deviation of [n];

[0032] If d 1 [i]>T s ,but 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, is the estimated time of the pth phase jump;

[0035] Using the estimated series Get an estimate of the modulation period and an estimate of the initial position

[0036]

[0037] Reconstructed periodic modulation sequence for:

[0038]

[0039] Wherein, L is a positive integer;

[0040] Step 204, demodulating the aliased echo signal using the reconstructed periodic modulation sequence, the specific operation is:

[0041]

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

[0043] Step 205: Perform matched filtering on the demodulated signal to obtain an output signal y 1 [n], the specific operations are as follows:

[0044]

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

[0046] Furthermore, if the energy of the fundamental wave component is stronger than the first-order harmonic component, the radar transmits the signal obliquely to the adjustable electromagnetic material surface of the incident target. At this time, the processing process is:

[0047] Step 211: preprocessed aliased echo signal It consists of two parts: non-modulation part and modulation part; considering a 1 >a 2 ,right Perform Fourier transform, and reconstruct and separate the fundamental component based on the symmetry of the harmonic components and the characteristic that the fundamental component is higher than each order of harmonics;

[0048] Fourier transform of The expression is as follows:

[0049]

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

[0051] Frequency parameter estimate corresponding to the fundamental component for:

[0052]

[0053] in, To find the function with the largest independent variable, F s is the sampling frequency;

[0054] Amplitude parameter estimate corresponding to the fundamental component for:

[0055]

[0056] Using the estimated frequency values Amplitude value The frequency K of the known radar transmission signal parameters LFM , the reconstructed fundamental component It is expressed as:

[0057]

[0058] 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

[0059]

[0060] Step 212: The harmonic components obtained after the cancellation process Demodulate and sample at the sampling frequency F s After sampling, we get Determine the reconstructed periodic modulation sequence use For harmonic components Perform demodulation and harmonic shifting:

[0061]

[0062] in, is the restored harmonic component, for With sampling frequency F s The time domain sampling sequence obtained after sampling;

[0063] Step 213, reconstructing the fundamental component in step 211 and the harmonic components recovered in step 212 Perform matched filtering to obtain the output signal y 2 [n], the specific operations are as follows:

[0064]

[0065] in, for With sampling frequency F s The time domain sampling sequence obtained after sampling, 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 the interference of aliased echo signals of targets with adjustable electromagnetic material surfaces.

[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 invention has the following technical features:

[0070] 1. The parasitic harmonic interference suppression method proposed in the present invention can cope with different types of harmonic interference existing in the received echo when the radar observes the target covered by the adjustable electromagnetic material at different angles; when the radar transmitting signal is vertically incident on the surface of the adjustable electromagnetic material, the present invention uses the known parameter information of the transmitting signal to eliminate the influence of the carrier frequency term and the phase quadratic term through digital down-conversion and demodulation frequency preprocessing, and combines the time domain difference result of the extracted phase sequence with the characteristics of the impulse function to estimate the modulation start time and modulation period of the periodic phase modulation sequence, and uses the reconstructed periodic phase modulation sequence to realize the movement and compensation of the harmonic modulation term; when the radar transmitting signal is obliquely incident on the surface of the adjustable electromagnetic material, the present invention can extract and reconstruct the frequency information of the fundamental component according to the symmetric characteristics of the harmonic component in the Fourier transform domain after demodulation frequency processing, and then cancel 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 situation where the energy of the fundamental component is weaker than the first-order harmonic component. The interference suppression processing steps used in the vertical incidence case are executed to reconstruct the periodic phase modulation sequence and complete the harmonic shift compensation processing.

[0071] 2. When the radar transmission signal is incident on the surface of the adjustable electromagnetic material at different angles, the present invention can effectively suppress both types of interference that occur, and realize the recovery and reconstruction of the true fundamental wave energy by moving the modulated harmonic components, thereby realizing the estimation and separation of interference characteristics and the recovery of the true target energy, and ultimately effectively improving the signal-to-interference ratio required for target detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Figure 1 is a flow chart of the method of the present invention;

[0073] Figure 2 It is a schematic diagram of the process of modulation of radar transmission signal by the adjustable electromagnetic material surface in an example of the present invention;

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

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

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

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

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

[0079] In actual scenarios, the adjustable electromagnetic material is only set at the key position of the target instead of covering the entire target surface. The radar received echo consists of two parts: the non-modulated signal reflected by the target (i.e., the fundamental component) and the modulated signal reflected by the surface of the adjustable electromagnetic material (i.e., the harmonic component). The present invention mainly utilizes the energy difference between the fundamental and harmonic components in the aliased echo to perform interference suppression processing on the received echo under two incidence conditions, namely, vertical incidence and oblique incidence.

[0080] See attached Figure 1 The present invention provides a parasitic time-varying phase modulation interference suppression method, comprising the following steps:

[0081] Receive the aliased echo signal from the target, model and pre-process the aliased echo signal, and determine the energy of the fundamental component and the first-order harmonic component in the aliased echo signal to determine the subsequent processing method; wherein the target is set with an adjustable electromagnetic material surface;

[0082] Case 1: If the fundamental wave component is weaker than the first-order harmonic component, the radar transmits a signal perpendicular to the target's adjustable electromagnetic material surface; at this time, the aliased echo signal received by the radar generates multiple peaks in the distance dimension after matched filtering, and the peak amplitude formed by the false target is higher than that of the real target. The modulated signal component in the aliased echo plays a dominant role;

[0083] For this situation, first, the phase information of the processed time domain data of the aliased echo signal is solved and a phase sequence is formed. Then, the phase jump information is obtained through differential transformation, and the modulation period and initial jump time of the phase modulation sequence are estimated by outlier detection. The phase modulation sequence is reconstructed according to the estimated parameters and the modulated harmonic components are compensated. Finally, the weakened true fundamental component is effectively restored, thereby improving the signal-to-interference ratio required for target detection.

[0084] Case 2: If the fundamental wave component energy is stronger than the first-order harmonic component, the radar transmits the signal obliquely into the adjustable electromagnetic material surface of the target; the fundamental wave energy in the echo after phase modulation is stronger than the first-order harmonic component. Although the energy of the real target formed by the radar receiving echo after matched filtering is higher than the false target generated by the harmonic component, the false target formed by the harmonic component has high fidelity and low signal-to-interference ratio due to the coherence of the harmonic component.

[0085] In this case, the frequency information of the fundamental component is first extracted and reconstructed according to 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 differentially processed in the time domain to obtain the phase modulation information, and the harmonic component is restored using the constructed phase modulation sequence, ultimately improving the signal-to-interference ratio after pulse compression processing.

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

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

[0088] In actual scenarios, the adjustable electromagnetic material is only set at the key position of the real target instead of covering the entire target surface. The aliased echo signal received by the radar contains harmonic modulation components and non-modulated fundamental components. When the radar transmits a signal s t When (t) is a linear frequency modulation signal, its expression is:

[0089]

[0090] Among them, t is the time parameter, rect(·) is the rectangular window function, T d is the duration of the transmitted pulse, K LFM is the modulation frequency, f 0 is the carrier frequency, c is the speed of light, λ is the wavelength of the transmitted signal, and j is the imaginary unit.

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

[0092] s j (t) = a 1 ·s t (t)+a 2 ·s p (t) = a 1 ·s t (t)+a 2 ·s t (t)·p(t)

[0093] Among them, 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), a 1 ,a 2 are the signal amplitudes corresponding to the non-modulated part and the modulated part respectively, and p(t) is the periodic phase modulation interference sequence generated by the time-varying impedance on the surface of the adjustable electromagnetic material. Its signal expression is:

[0094]

[0095] Among them, e is a natural constant, w p =2π / T p is the period T of the modulation coding sequence on the surface of the tunable electromagnetic material p Determined angular frequency, Am is the Fourier series coefficient corresponding to the mth-order harmonic generated by the time-varying impedance response of the adjustable electromagnetic material surface, expressed as follows:

[0096]

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

[0098] According to the known parameters of the radar transmission signal, the aliased echo signal s j (t) After preprocessing, including digital down-conversion and de-linear frequency modulation, we can get:

[0099]

[0100] 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.

[0101] As the relative angle between the radar and the detected target changes, the energy of the harmonic components generated by the adjustable electromagnetic material will change accordingly, and the corresponding interference suppression methods will also have corresponding differences. After downsampling and demodulation frequency conversion of the received wave, the fundamental component corresponding to the real target appears in the form of a single spectrum line in the frequency domain and is located near the zero frequency, while the harmonic component is symmetrical, and its frequency domain distribution is two symmetrical spectrum lines centered on the zero frequency. When the signal amplitude corresponding to the single spectrum line near the zero frequency is greater than the amplitude of all harmonic components, it corresponds to situation 2, and vice versa, it corresponds to situation 1.

[0102] Step 2: According to the difference in amplitude between the fundamental wave energy corresponding to the non-modulated part and the maximum harmonic energy corresponding to the modulated part, the following two cases are classified:

[0103] Case 1: The radar transmission signal is incident vertically on the surface of the adjustable electromagnetic material, and the fundamental wave component energy is weaker than the first-order harmonic component, that is, a 1 <a 2 .

[0104] Step 201: pre-processed aliased echo signal It consists of two parts: non-modulation part and modulation part; considering a 1 <a 2 ,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 the phase is transformed into time domain difference, we can get:

[0105]

[0106] Where ∠(·) represents the phase extraction operation, φ 1 [n] is A phase sequence composed of time domain phase information.

[0107] Step 202: extract the phase sequence φ from step 201. 1 [n] The time domain difference transformation is performed as follows:

[0108]

[0109] in,[·] (1) represents the differential operation, d 1 [n] is the phase sequence φ 1 The sequence after the difference transformation of [n].

[0110] Step 203, the sequence d after the difference transformation 1 [n] is a set of periodic impulse sequences in the time domain, and the impulse moment corresponds to the phase jump moment of the periodic phase modulation sequence p[n]; for sequence d 1 After outlier detection on [n], the modulation period T of p[n] is p and the initial position T start Estimation; detection threshold T s The calculation formula is as follows:

[0111] T s =μ s +3σ s

[0112] Among them, μ s and σ s Sequence d 1 The mean and standard deviation of [n].

[0113] If d 1 [i]>T s ,but Then the estimated sequence obtained after threshold detection is:

[0114]

[0115] 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.

[0116] Considering that the phase jump points of the periodic modulation sequence are regular, only the modulation period T p and the initial position T startThe complete modulation sequence can be reconstructed; therefore, the estimated sequence is used Get an estimate of the modulation period and an estimate of the initial position

[0117]

[0118] Reconstructed periodic modulation sequence for:

[0119]

[0120] Wherein, L is a positive integer.

[0121] Step 204, demodulating the aliased echo signal using the reconstructed periodic modulation sequence, the specific operation is:

[0122]

[0123] in, is the result of demodulation of the interfered echo, sj[n] is s j (t) The result after discrete sampling.

[0124] Step 205: Perform matched filtering on the demodulated signal to obtain an output signal y 1 [n], the specific operations are as follows:

[0125]

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

[0127] Case 2: The radar transmit signal is incident obliquely on the surface of the adjustable electromagnetic material, and the fundamental wave component is stronger than the first-order harmonic component, that is, a 1 >a 2 .

[0128] Step 211: preprocessed aliased echo signal It consists of two parts: non-modulation part and modulation part; considering a 1 >a 2 ,right Fourier transform is performed, and based on the symmetry of the harmonic components and the fact that the fundamental component is higher than each order of harmonics, the fundamental component is reconstructed and separated.

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

[0130]

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

[0132] Frequency parameter estimate corresponding to the fundamental component for:

[0133]

[0134] in, To find the function with the largest independent variable, F s is the sampling frequency.

[0135] Amplitude parameter estimate corresponding to the fundamental component for:

[0136]

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

[0138] Using the estimated frequency values Amplitude value The frequency K of the known radar transmission signal parameters LFM , the reconstructed fundamental component It can be expressed as:

[0139]

[0140] 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 The specific operation process is as follows:

[0141]

[0142] Step 212: The harmonic components obtained after the cancellation process Demodulate and sample at the sampling frequency F s After sampling, we get According to step 201 to step 203, The same processing process is used to obtain the reconstructed periodic modulation sequence use For harmonic components Perform demodulation and harmonic shifting. The specific operations are as follows:

[0143]

[0144] in, is the restored harmonic component, for With sampling frequency F s The time domain sampling sequence obtained after sampling.

[0145] Step 213, reconstructing the fundamental component in step 211 and the harmonic components recovered in step 212 Perform matched filtering to obtain the output signal y 2 [n], the specific operations are as follows:

[0146]

[0147] in, for With sampling frequency F s The time domain sampling sequence obtained after sampling, h[n] is the reference signal used for matched filtering.

[0148] Example:

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

[0150] Case 1: The parameter used for threshold detection is μ s =0.0031 and σ s =0.1674, and the detection threshold Ts = 0.5052. Estimated value of the modulation period The corresponding modulation frequency is 1.0504MHz, and the initial position of the jump is

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

[0152] Case 2: Sampling frequency F s =500MHz, Fourier transform points N FT =50000, T d =200us, K LFM=4×10 12 , μ s =1.44×10 -4 and σ s =0.3484, and the detection threshold T is obtained s =1.0454; estimated value of modulation period The corresponding modulation frequency is 1.0204MHz, and the initial position of the jump is

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

[0154] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions 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 parasitic time-varying phase modulation interference suppression method, 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 energy of the fundamental component is weaker than the first-order harmonic component, the radar transmits the signal vertically into the adjustable electromagnetic material surface of the target; at this time, the phase information of the processed time domain data of the aliased echo signal is first solved and a phase sequence is formed, and then the phase jump information is obtained through differential transformation, and the modulation period and initial jump time of the phase modulation sequence are estimated by outlier detection, and 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 restored; If the energy of the fundamental component is stronger than the first-order harmonic component, the radar transmits a signal obliquely into the adjustable electromagnetic material surface of the incident target; at this time, the frequency information of the fundamental component is first extracted and reconstructed according to 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 the periodic phase modulation, and then the phase is subjected to time domain difference processing to obtain the phase modulation information, and the harmonic component is restored using the constructed phase modulation sequence.

2. The parasitic time-varying phase modulation interference suppression method according to claim 1, characterized in that: 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 on the surface of the adjustable electromagnetic material. Its signal expression is: Among them, e is a natural constant, w p =2π / T p is the period T of the modulation coding sequence on the surface of the tunable electromagnetic material p Determined angular frequency, A m It is the Fourier series coefficient corresponding to the mth-order harmonic generated by the time-varying impedance response of the adjustable electromagnetic material surface.

3. The parasitic time-varying phase modulation interference suppression method according to claim 1, characterized in that: For aliased echo signal s j (t) After preprocessing, including digital down-conversion and de-linear frequency modulation, we can get: 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 parasitic time-varying phase modulation interference suppression method according to claim 1, characterized in that: If the fundamental wave component is weaker than the first-order harmonic component, the radar transmits the signal vertically into the adjustable electromagnetic material surface of the target. At this time, the processing process is: 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 the phase is transformed into time domain difference, we can get: Where ∠(·) represents the phase extraction operation and φ1[n] is A phase sequence composed of time domain phase information; Step 202, performing time domain differential transformation processing on the phase sequence φ1[n] extracted in step 201 is as follows: d1[n]=ϕ1 (1) [n] in,[·] (1) represents the differential operation, d1[n] is the sequence after the 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 moment corresponds to the phase jump moment 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 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, demodulating the aliased echo signal using the reconstructed periodic modulation sequence, the specific operation is: in, is the result of demodulation of the interfered echo, s j [n] is s j (t) The result after discrete sampling; Step 205, performing matched filtering on the demodulated signal to obtain an output signal y1[n], the specific operation is as follows: Wherein, 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 parasitic time-varying phase modulation interference suppression method according to claim 1, characterized in that: 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: Step 211: preprocessed 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 characteristic that the fundamental component is higher than each order of 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 estimate corresponding to the fundamental component for: in, To find the function with the largest independent variable, F s is the sampling frequency; Amplitude parameter estimate corresponding to the fundamental component for: Using the estimated frequency values Amplitude value The frequency K of the known radar transmission signal parameters LFM , the reconstructed fundamental component It is 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 Demodulate and sample at the sampling frequency 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, reconstructing the fundamental component 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 for 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 parasitic time-varying phase modulation interference suppression method according to any one of claims 1 to 5 is implemented.

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

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