Radar detection method for active electromagnetic regulation and control target

Abstract

The invention discloses a radar detection method for an active electromagnetic regulation and control target. The method comprises the following steps: modeling a radar receiving echo signal after a radar transmitting signal is reflected by an electromagnetic metasurface arranged on a to-be-detected target; carrying out carrier frequency removal and frequency modulation preprocessing on the echo signal, and then carrying out phase unwrapping processing to obtain an absolute phase; performing windowing segmentation processing on the absolute phase, estimating the slope of each segmented phase, and taking the slope average value of the segmented phases as the slope estimation result of the absolute phase; constructing a phase distribution linear function by using the slope estimation result of the absolute phase, and subtracting the absolute phase from the phase distribution linear function to obtain a jump phase item estimation value of the electromagnetic metasurface; constructing a time domain phase compensation function according to the hopping phase item estimation value, and multiplying the time domain phase compensation function by the radar receiving echo signal to obtain a reconstruction signal; and performing matched filtering processing on the reconstructed signal to obtain an output signal.

Description

Technical Field

[0001] The present invention relates to the field of radar signal processing and target detection, and in particular to a radar detection method for active electromagnetic control targets. Background Art

[0002] As an active electromagnetic target detection equipment, radar has all-day and all-weather detection and perception capabilities, and is an important means of battlefield situation perception and target monitoring in the air, land, and sea. In modern electronic warfare, quickly and accurately perceiving the enemy's situation is the core of victory. At present, stealth technology has developed in the direction of wide operating frequency band, large stealth range and integrated stealth deception. The development of radar equipment with resistance to active control interference is the key to comprehensive and accurate perception of battlefield situation in high-dynamic and strong game electronic confrontation scenarios.

[0003] The electromagnetic metasurface based on phase characteristic time-varying modulation can perform specific modulation on the radar incident electromagnetic wave, and has the characteristics of flexible and diverse modulation parameters, time-varying modulation process, and fast modulation response speed, and can change the distribution of radar echo signals in time domain, frequency domain, time-frequency domain, etc. The time-varying metasurface directly changes the phase characteristics of the radar transmitted electromagnetic wave, and generates an echo signal at the radar receiving end that is a multiplicative aliasing of the transmitted signal waveform and the metasurface time-varying reflection coefficient, resulting in a large number of phase mutation points in the time domain of the radar echo signal, and spectrum aliasing and spectrum shifting in the echo frequency domain, which seriously weakens the target signal energy in the real distance unit after radar matched filtering processing, thereby seriously affecting the target detection performance of the radar equipment.

[0004] Existing aliasing signal separation methods are mostly applied to scenarios where signals and interference are additively aliased, and the commonly used signal separation methods have the following technical difficulties: 1) The radar echo reflected by the time-modulated metasurface is a multiplicative superposition of the useful signal and the interference signal. The kernel function and transform domain in the existing signal separation algorithm are not suitable for the separation of such aliasing signals; 2) In actual working scenarios, the time-varying phase coding modulation of the metasurface has phase errors and is affected by the incident angle and the operating frequency of the metasurface. When estimating the aliasing signal parameters, it is necessary not only to estimate the modulation parameters of the metasurface, but also to estimate the random dynamic errors, which seriously restricts its application in practice.

[0005] To sum up, considering the technical difficulties of active control interference such as "difficulty in separating multiplicative interference" and "difficulty in estimating parameters in real time", it is urgently necessary to carry out research on radar detection methods for active electromagnetic control targets, solve technical problems such as separation of multiplicative aliasing echo signals and estimation of modulation parameters of non-cooperative modulation parties, and enhance the radar's perception and detection capabilities for new active electromagnetic control targets. Summary of the invention

[0006] The purpose of the present invention is to provide a radar detection method for active electromagnetic control targets, which is used to estimate the modulation parameters and separate the signals of the multiplicative aliasing echo signals generated by the phase characteristic modulation of the radar incident electromagnetic signal by the time-modulated metasurface stealth target.

[0007] In order to achieve the above tasks, the present invention adopts the following technical solutions:

[0008] A radar detection method for an active electromagnetic control target, comprising:

[0009] Modeling the radar received echo signal after the radar transmit signal is reflected by the electromagnetic metasurface set on the target to be detected; pre-processing the echo signal by removing the carrier frequency and demodulating the frequency based on the parameters of the radar transmit signal; performing phase unwrapping processing on the pre-processed echo signal to obtain the absolute phase of the echo signal;

[0010] The absolute phase of the echo signal is processed by windowing and segmenting, and the slope of each segment phase is estimated by the least square method. After the slopes of all segment phases are estimated, the average value is taken as the slope estimation result of the absolute phase;

[0011] Constructing a phase distribution linear function using the slope estimation result of the absolute phase, and subtracting the absolute phase from the phase distribution linear function to obtain an estimated value of the jump phase term of the electromagnetic metasurface;

[0012] A time domain phase compensation function is constructed according to the estimated value of the jump phase term, and the time domain phase compensation function is multiplied by the radar receiving echo signal to obtain a reconstructed signal;

[0013] The reconstructed signal is processed by matched filtering to obtain an output signal.

[0014] Furthermore, the radar receiving echo signal after the radar transmitting signal is reflected by the electromagnetic metasurface set on the target to be detected is modeled as follows:

[0015] The target surface to be detected is equipped with an electromagnetic metasurface, and the radar transmits a signal s t (t) is a linear frequency modulation signal, and the time-varying reflection coefficient of the metasurface is Γ(t), then the radar received echo signal expression r(t):

[0016]

[0017] Where t is the time parameter, rect(·) is the rectangular window function, is the time delay corresponding to the target to be detected at the distance R0, c is the speed of light, T p is the pulse width, K p is the modulation frequency, f0 is the carrier frequency, and j is the imaginary unit;

[0018] The expression of the metasurface time-varying reflection coefficient Γ(t) is:

[0019]

[0020] Where l = {0, 1, 2, ... L-1}, is the reflection coefficient Γ(t) at pulse width T p The number of phase changes within a period, l represents the lth change; T b For each phase state φ in the reflection coefficient Γ(t) l The duration of l ∈{0,π}.

[0021] Further, the method of preprocessing the echo signal by removing the carrier frequency and demodulating the frequency based on the parameters of the radar transmission signal; and performing phase unwrapping processing on the preprocessed echo signal to obtain the absolute phase of the echo signal includes:

[0022] After preprocessing the echo signal r(t) by removing the carrier frequency and demodulating the frequency, we can get s d (t):

[0023]

[0024] Among them, exp(jπK p Δτ 2 ), exp(-j2πf0Δτ) is a constant term independent of time t;

[0025] After phase unwrapping, s d The absolute phase of (t) is expressed as

[0026]

[0027] Further, the absolute phase of the echo signal is subjected to windowing and segmentation processing, comprising:

[0028] For absolute phase After windowing and segmentation processing, we can get:

[0029]

[0030] in, is the mth segment phase obtained after segmenting the absolute phase, m = 1, 2, ..., M; M is the total number of absolute phase segments; T win is the segment length of each segment phase after segmentation, and T win <T b , w m (t) is the window function.

[0031] Furthermore, the method of estimating the slope of each segmented phase by the least square method, and taking the average value as the slope estimation result of the absolute phase after the slopes of all segmented phases are estimated, includes:

[0032] Absolute Phase After segmentation processing, the discretization table of the segmented phase can be obtained:

[0033]

[0034] Where N = T p ·F s is the pulse width T p The number of all discrete sampling points within, the sampling rate is F s ; w m [n] is the segment phase Window function w m The discretized form of (t), n represents the nth sampling point;

[0035] The mth segment phase and the corresponding window function are calculated using the least squares method. The slope k m Perform fitting;

[0036] The absolute phase The final slope estimation result K esti for:

[0037]

[0038] Furthermore, the fitting result of the slope by the least square method is expressed as:

[0039]

[0040] Furthermore, the use of the slope estimation result of the absolute phase to construct a phase distribution function, and subtracting the absolute phase from the phase distribution function to obtain an estimated value of the jump phase term of the electromagnetic metasurface includes:

[0041] The final slope estimation result K of the absolute phase is used esti Construct a phase distribution function (i.e., a slant line), where the intercept b of the phase distribution function is esti By absolute phase The decision expression is:

[0042]

[0043] Where t0 is the reference time delay;

[0044] Using the slope K esti and intercept besti Constructed phase distribution linear function The expression is:

[0045]

[0046] Will With absolute phase After subtraction, the estimated value of the jump phase term can be obtained Its expression is:

[0047]

[0048] Further, constructing a time domain phase compensation function according to the estimated value of the jump phase term, and multiplying the time domain phase compensation function with the radar received echo signal to obtain a reconstructed signal includes:

[0049] Using the jump phase term Construct the time domain phase compensation function H com (t):

[0050]

[0051] in, is the slope estimation error;

[0052] The phase compensation function H com (t) is multiplied with the echo signal r(t) to reconstruct the signal; the reconstructed signal is expressed as:

[0053]

[0054] A radar adopts the radar detection method for active electromagnetic control targets to detect the echo signal of a target with an electromagnetic metasurface.

[0055] A terminal device comprises a processor, a memory and a computer program stored in the memory; when the processor executes the computer program, the radar detection method for active electromagnetic control targets is implemented.

[0056] A computer-readable storage medium stores a computer program; when the computer program is executed by a processor, the radar detection method for active electromagnetic control targets is implemented.

[0057] Compared with the prior art, the present invention has the following technical features:

[0058] The method of the present invention can estimate the time-varying reflection coefficient of the metasurface with "unknown phase modulation parameters" and "variable phase modulation error", and reconstruct the aliased echo signal, so as to achieve effective target detection. When the radar receives the echo reflected by the time-varying reflection coefficient of the metasurface, the present invention uses the known parameter information of the transmission waveform, eliminates the influence of the carrier frequency and the quadratic term on the phase through digital down-conversion and demodulation processing, and uses the phase unwrapping processing to restore the absolute phase of the echo, and uses the least squares fitting method to obtain the slope and intercept information in the linear function of the aliased echo phase through the characteristics of the absolute phase changing with time, and constructs the interference-free phase distribution consistent with the slope of each phase distribution in the absolute phase segmented function based on this, and then subtracts the absolute phase from the reconstructed interference-free phase to obtain the interference phase distribution, and uses the interference phase distribution to construct a phase compensation function, demodulates the aliased echo received by the radar, and finally reconstructs the echo signal with the phase jump restored. By processing the measured data of metasurface reflection and performing matched filtering on the reconstructed echo signal, the target energy within the real distance unit is effectively improved while the harmonic energy generated by the metasurface feature modulation is suppressed, ultimately achieving effective detection of metasurface targets. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 is a flow chart of the method of the present invention;

[0060] Figure 2 is a schematic diagram of aliased echoes received by the radar in an example of the present invention;

[0061] Figure 3 (a) is the absolute phase after echo down-conversion and demodulation in the example of the present invention, (b) is the slope fitted after the slope and intercept estimation operation in the example of the present invention, (c) is the residual phase solved in the example of the present invention; (d) is the phase distribution after the absolute phase is compensated by the residual phase in the example of the present invention;

[0062] Figure 4 (a) is the spectrum of the metasurface reflected echo received by the radar in the example of the present invention, and (b) is the spectrum of the echo after the useful signal is reconstructed by using the proposed method in the example of the present invention;

[0063] Figure 5 is the matched filtering result before and after the reconstruction of the aliased echo in the example of the present invention; DETAILED DESCRIPTION

[0064] The present invention provides an accurate, effective and practical active electromagnetic control target detection method, which can accurately estimate the modulation parameters under the non-ideal working state of the metasurface, is not affected by the metasurface modulation error, and can quickly and accurately restore the multiplicative aliasing echo, effectively improving the radar's ability to resist new active control electromagnetic interference; see attached Figure 1 A radar detection method for an active electromagnetic control target of the present invention comprises the following steps:

[0065] Step 1: Model the radar received echo signal after the radar transmit signal is reflected by the electromagnetic metasurface set on the target to be detected; based on the parameters of the radar transmit signal, pre-process the echo signal by removing the carrier frequency and demodulating the frequency; perform phase unwrapping processing on the pre-processed echo signal to obtain the absolute phase of the echo signal.

[0066] 1.1 Radar receives echo signals for modeling.

[0067] The target surface to be detected is equipped with an electromagnetic metasurface, and the radar transmits a signal s t (t) is a linear frequency modulation signal, and the time-varying reflection coefficient of the metasurface is Γ(t), then the radar received echo signal expression r(t):

[0068]

[0069] Where t is the time parameter, rect(·) is the rectangular window function, is the time delay corresponding to the target to be detected at the distance R0, c is the speed of light, T p is the pulse width, K p is the modulation frequency, f0 is the carrier frequency, and j is the imaginary unit.

[0070] The expression of the metasurface time-varying reflection coefficient Γ(t) is:

[0071]

[0072] Where l = {0, 1, 2, ... L-1}, is the reflection coefficient Γ(t) at pulse width T p The number of phase changes within a period, l represents the lth change; T b For each phase state φ in the reflection coefficient Γ(t) l The duration of l ∈{0,π}.

[0073] 1.2 Preprocessing of echo signals to eliminate the influence of quadratic terms in echo signals on echo phase.

[0074] After preprocessing the echo signal r(t) by removing the carrier frequency and demodulating the frequency, we can get s d (t):

[0075]

[0076] Among them, exp(jπK p Δτ 2) and exp(-j2πf0Δτ) are constant terms that are independent of time t and can be ignored.

[0077] 1.3 Phase unwrapping processing.

[0078] Considering that the actual measured phase is limited to between -π and π, phase unwrapping is performed to restore the real phase information; after phase unwrapping, s d The absolute phase of (t) is expressed as

[0079]

[0080] Step 2, perform windowing and segmentation processing on the absolute phase of the echo signal, use the least squares method to estimate the slope of each segment phase, and after the slopes of all segment phases are estimated, take the average value as the slope estimation result of the absolute phase.

[0081] 2.1 Windowing and segmentation of absolute phase.

[0082] Since the phase state φ in the reflection coefficient l Randomly selecting values ​​between {0,π} will make the preprocessed echo signal s d The absolute phase of (t) The change curve is a superposition of two parts: one part has a slope of -2πK p The linear slope of Δτ and the other part are b A broken line segment with phase jumps at all times; absolute phase It is composed of multiple line segments, and each line segment has the same slope.

[0083] For absolute phase After windowing and segmentation processing, we can get:

[0084]

[0085] in, is the mth segment phase obtained after segmenting the absolute phase, m = 1, 2, ..., M; M is the total number of absolute phase segments; T win is the segment length of each segment phase after segmentation, and T win <T b , w m (t) is the window function.

[0086] 2.2 Slope estimation of absolute phase.

[0087] Absolute Phase After segmentation processing, each segment phase has no phase jump point; the discretization table of the segment phase can be obtained:

[0088]

[0089] Where N = T p ·F s is the pulse width T p The number of all discrete sampling points within, the sampling rate is F s ; w m [n] is the segment phase Window function w m (t), where n represents the nth sampling point.

[0090] The mth segment phase and the corresponding window function are calculated using the least squares method. The slope k m Fitting and calculation can be obtained:

[0091]

[0092] The absolute phase The final slope estimation result K esti for:

[0093]

[0094] Step 3, construct a phase distribution linear function using the slope estimation result of the absolute phase, and subtract the absolute phase from the phase distribution linear function to obtain an estimated value of the jump phase term of the electromagnetic metasurface.

[0095] The final slope estimation result K of the absolute phase is used esti Construct a phase distribution function (i.e., a slant line), where the intercept b of the phase distribution function is esti By absolute phase The decision expression is:

[0096]

[0097] Where t0 is the reference time delay, usually τ<t0< <T p .

[0098] Using the slope K esti and intercept b esti Constructed phase distribution linear function The expression is:

[0099]

[0100] Will With absolute phase After subtraction, the estimated value of the jump phase term can be obtained Its expression is:

[0101]

[0102] Step 4: construct a time domain phase compensation function according to the estimated value of the jump phase term, and multiply the time domain phase compensation function with the radar received echo signal to obtain a reconstructed signal.

[0103] Using the jump phase term Construct the time domain phase compensation function H com (t):

[0104]

[0105] in, is the slope estimation error.

[0106] The phase compensation function H com The signal can be reconstructed by multiplying the echo signal r(t) to restore the jump phase changed by the metasurface modulation, thus realizing the effective detection of the active electromagnetic control target. The reconstructed signal is expressed as:

[0107]

[0108] Step 5: reconstruct the signal s re (t) is processed by matched filtering to obtain the output signal y(t). The specific operation is as follows:

[0109]

[0110] Wherein, h(t) is the reference signal in the matched filtering process.

[0111] Example:

[0112] The measured data comes from the X-band radar echo, where the time width of the transmitted signal is T p =100μs, bandwidth 400MHz, frequency modulation K p =4×10 12 , sampling frequency F s =500MHz, carrier frequency f0 = 10GHz, the distance between the radar and the metasurface is 12.6m, and the corresponding time delay Δτ = 8.4×10 -8 s, the angle between the radar incident electromagnetic wave and the normal of the metasurface is 5.2194°, and the time-varying reflection coefficient Γ(t) of the electromagnetic metasurface adopts periodic phase modulation with a modulation frequency of 1 MHz. The modulation phase has two states, 0 and π, and the duration of each state is 1 us.

[0113] The method of the present invention is used to process the example, where φ l ∈{0,π},L=100,T b =1us, absolute phase The slope is -2.1112×10 6 , the total number of segments M = 200, segment length T win = 0.5us, the number of all discrete sampling points within the pulse width N = 50000, Reference time delay t0 = 4 × 10 -7 s, is the slope estimation error.

[0114] After the radar received aliased echo is processed by the proposed algorithm, the peak position after matched filtering is 8.4×10 -8 s, and the measured target distance is 12.6m.

[0115] 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, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These 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 all be included in the protection scope of the present application.

Claims

1. A radar detection method for active electromagnetic control targets, characterized in that: include: Modeling the radar receiving echo signal after the radar transmitting signal is reflected by the electromagnetic metasurface set on the target to be detected; Based on the parameters of the radar transmission signal, the echo signal is pre-processed by removing the carrier frequency and demodulating the frequency; Performing phase unwrapping processing on the preprocessed echo signal to obtain the absolute phase of the echo signal; The absolute phase of the echo signal is processed by windowing and segmenting, and the slope of each segment phase is estimated by the least square method. After the slopes of all segment phases are estimated, the average value is taken as the slope estimation result of the absolute phase; Constructing a phase distribution linear function using the slope estimation result of the absolute phase, and subtracting the absolute phase from the phase distribution linear function to obtain an estimated value of the jump phase term of the electromagnetic metasurface; A time domain phase compensation function is constructed according to the estimated value of the jump phase term, and the time domain phase compensation function is multiplied by the radar receiving echo signal to obtain a reconstructed signal; The reconstructed signal is processed by matched filtering to obtain an output signal.

2. The radar detection method for active electromagnetic control targets according to claim 1 is characterized in that: The radar receiving echo signal after the radar transmitting signal is reflected by the electromagnetic metasurface set on the target to be detected is modeled as follows: The target surface to be detected is equipped with an electromagnetic metasurface, and the radar transmits a signal s t (t) is a linear frequency modulation signal, and the time-varying reflection coefficient of the metasurface is Γ(t), then the radar received echo signal expression r(t): Where t is the time parameter, rect(·) is the rectangular window function, is the time delay corresponding to the target to be detected at the distance R0, c is the speed of light, T p is the pulse width, K p is the modulation frequency, f0 is the carrier frequency, and j is the imaginary unit; The expression of the metasurface time-varying reflection coefficient Γ(t) is: Where l = {0, 1, 2, ... L-1}, is the reflection coefficient Γ(t) at pulse width T p The number of phase changes within a period, l represents the lth change; T b For each phase state φ in the reflection coefficient Γ(t) l The duration of l ∈{0,π}.

3. The radar detection method for active electromagnetic control targets according to claim 1 is characterized in that: The preprocessing of removing carrier frequency and demodulating frequency of the echo signal is performed based on the parameters of the radar transmission signal; Perform phase unwrapping processing on the preprocessed echo signal to obtain the absolute phase of the echo signal, including: After preprocessing the echo signal r(t) by removing the carrier frequency and demodulating the frequency, we can get s d (t): Among them, exp(jπK p Δτ 2 ), exp(-j2πf0Δτ) is a constant term independent of time t; After phase unwrapping, s d The absolute phase of (t) is expressed as 4. The radar detection method for active electromagnetic control targets according to claim 1 is characterized in that: The absolute phase of the echo signal is subjected to windowing and segmentation processing, comprising: For absolute phase After windowing and segmentation processing, we can get: in, is the mth segment phase obtained after segmenting the absolute phase, m = 1, 2, ..., M; M is the total number of absolute phase segments; T win is the segment length of each segment phase after segmentation, and T win <T b , w m (t) is the window function.

5. The radar detection method for active electromagnetic control targets according to claim 1, characterized in that: The method of estimating the slope of each segment phase by the least square method and taking the average value as the slope estimation result of the absolute phase after the slopes of all segment phases are estimated includes: Absolute Phase After segmentation processing, the discretization table of the segmented phase can be obtained: Where N = T p ·F s is the pulse width T p The number of all discrete sampling points within, the sampling rate is F s ; w m [n] is the segment phase Window function w m The discretized form of (t), n represents the nth sampling point; The mth segment phase and the corresponding window function are calculated using the least squares method. The slope k m Perform fitting; The absolute phase The final slope estimation result K esti for:

6. The radar detection method for active electromagnetic control targets according to claim 1, characterized in that: The fitting result of the slope by the least square method is expressed as:

7. The radar detection method for active electromagnetic control targets according to claim 1 is characterized in that: The method of constructing a phase distribution linear function by using the slope estimation result of the absolute phase, and subtracting the absolute phase from the phase distribution linear function to obtain an estimated value of a jump phase term of the electromagnetic metasurface includes: The final slope estimation result K of the absolute phase is used esti Construct a phase distribution function (i.e., a slant line), where the intercept b of the phase distribution function is esti By absolute phase The decision expression is: Where t0 is the reference time delay; Using the slope K esti and intercept b esti Constructed phase distribution linear function The expression is: Will With absolute phase After subtraction, the estimated value of the jump phase term can be obtained Its expression is:

8. The radar detection method for active electromagnetic control targets according to claim 1, characterized in that: The time domain phase compensation function is constructed according to the estimated value of the jump phase term, and the time domain phase compensation function is multiplied by the radar receiving echo signal to obtain a reconstructed signal. include: Using the jump phase term Construct the time domain phase compensation function H com (t): in, is the slope estimation error; The phase compensation function H com (t) is multiplied with the echo signal r(t) to reconstruct the signal; the reconstructed signal is expressed as:

9. A radar, characterized in that: The radar uses a radar detection method for active electromagnetic control targets according to any one of claims 1 to 8 to detect the echo signal of a target with an electromagnetic metasurface.

10. 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 radar detection method for active electromagnetic control targets according to any one of claims 1 to 8 is implemented.

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