A radar detection method for active electromagnetic regulation target

Abstract

The application discloses a radar detection method for active electromagnetic regulation and control targets, comprising the following steps: modeling a radar receiving echo signal after a radar transmitting signal is reflected by an electromagnetic super surface arranged on a target to be detected; performing pretreatment on the echo signal to remove a carrier frequency and a frequency modulation, and then performing phase unwrapping processing to obtain an absolute phase; performing window segmentation processing on the absolute phase, estimating a slope of each segmented phase, and taking an average value of the slope of the segmented phase as a slope estimation result of the absolute phase; constructing a phase distribution first-order function by using the slope estimation result of the absolute phase, and subtracting the absolute phase from the phase distribution first-order function to obtain an estimated value of a jump phase term of the electromagnetic super surface; constructing a time-domain phase compensation function according to the estimated value of the jump phase term, multiplying the time-domain phase compensation function with the radar receiving echo signal to obtain a reconstructed 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 fields of radar signal processing and target detection, and in particular to a radar detection method for active electromagnetically controlled targets. Background Art

[0002] Radar, as an active electromagnetic target detection device, possesses all-day, all-weather detection and perception capabilities, making it a crucial means of battlefield situational awareness and target surveillance in the air, land, and sea. In modern electronic warfare, rapid and accurate perception of enemy situational awareness is crucial for success. Currently, stealth technology is developing towards wide operating frequency bands, wide stealth ranges and viewing angles, and integrated stealth and deception capabilities. Developing radar equipment with robust resistance to active interference control is crucial for comprehensive and accurate battlefield situational awareness in highly dynamic and intense electronic warfare scenarios.

[0003] Electromagnetic metasurfaces based on time-varying modulation of phase characteristics can specifically modulate radar incident electromagnetic waves. They feature flexible and diverse modulation parameters, a time-varying modulation process, and a fast modulation response. They can alter the distribution of radar echo signals in the time, frequency, and time-frequency domains. By directly altering the phase characteristics of the radar's transmitted electromagnetic waves, the time-varying metasurface generates an echo signal at the radar receiver that is a multiplicative mixture of the transmitted signal waveform and the metasurface's time-varying reflection coefficient. This results in a large number of phase mutation points in the radar echo signal's time domain, as well as spectral aliasing and shifting in the echo's frequency domain. This severely weakens the target signal energy within the true range unit after radar matched filtering processing, significantly impacting the radar's target detection performance.

[0004] Existing aliasing signal separation methods are mostly applied to scenarios where signals and interference are additively aliased, and 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 improve 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 aliased echo signals generated by the time-modulated metasurface stealth target modulating the phase characteristics of the radar incident electromagnetic signal.

[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; preprocessing the echo signal by removing the carrier frequency and demodulating the frequency based on the parameters of the radar transmit signal; performing phase unwrapping on the preprocessed echo signal to obtain the absolute phase of the echo signal;

[0010] The absolute phase of the echo signal is windowed and segmented, and the slope of each segment phase is estimated using the least squares method. After the slopes of all segment phases are estimated, the average value is taken as the absolute phase slope estimation result;

[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 received echo signal to obtain a reconstructed signal;

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

[0014] Furthermore, the radar receiving echo signal after the radar transmitting signal is reflected by the electromagnetic metasurface provided 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) is:

[0016]

[0017] Among them, t is the time parameter, rect(·) is the rectangular window function, is the time delay corresponding to the target to be detected at the position 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 Duration, φ l ∈{0,π}.

[0021] Furthermore, the method of pre-processing 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 pre-processed echo signal to obtain the absolute phase of the echo signal includes:

[0022] After pre-processing the echo signal r(t) to remove the carrier frequency and demodulate the frequency, we can get s d (t):

[0023]

[0024] Among them, exp(jπK p Δτ 2 ), exp(-j2πf0Δτ) is a constant term that has nothing to do with time t;

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

[0026]

[0027] Furthermore, the performing windowing and segmentation processing on the absolute phase of the echo signal includes:

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

[0029]

[0030] in, is the mth segment phase obtained by 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 using the least squares method and taking the average value of the slopes of all segmented phases as the slope estimation result of the absolute phase after the slopes 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 sample 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 using the least squares method is expressed as:

[0039]

[0040] Furthermore, the method of 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 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 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] Furthermore, 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 by 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 by 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 includes 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 a metasurface with unknown phase modulation parameters and a variable phase modulation error, and reconstruct the aliased echo signal, thereby achieving effective target detection. When a radar receives an echo modulated by the time-varying reflection coefficient of the metasurface, the method uses the known parameter information of the transmitted waveform to eliminate the influence of the carrier frequency and quadratic term on the phase through digital down-conversion and demodulation processing, and uses phase unwrapping processing to restore the absolute phase of the echo. Based on the time-varying characteristics of the absolute phase, the slope and intercept information in the linear function of the aliased echo phase are obtained using the least squares fitting method. Based on this, an interference-free phase distribution is constructed with the same slope as the phase distribution of each segment in the absolute phase piecewise function. The absolute phase is then subtracted from the reconstructed interference-free phase to obtain an interference phase distribution. The interference phase distribution is then used to construct a phase compensation function to demodulate the aliased echo received by the radar, and finally reconstruct an echo signal with restored phase jumps. 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 slope and intercept estimation in the example of the present invention, (c) is the residual phase obtained 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 using the proposed method in the example of the present invention;

[0063] Figure 5 is the matched filtering result before and after 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, and is not affected by the metasurface modulation error, and can quickly and accurately recover the multiplicative aliasing echo, effectively improving the radar's ability to resist new active electromagnetic interference. Figure 1 The present invention provides a radar detection method for an active electromagnetic control target, comprising 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, preprocess the echo signal by removing the carrier frequency and demodulating the frequency; and perform phase unwrapping processing on the preprocessed 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) is:

[0068]

[0069] Among them, t is the time parameter, rect(·) is the rectangular window function, is the time delay corresponding to the target to be detected at the position 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 Duration, φ 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 pre-processing the echo signal r(t) to remove the carrier frequency and demodulate the frequency, we can get s d (t):

[0075]

[0076] Among them, exp(jπK p Δτ 2), exp(-j2πf0Δτ) is a constant term 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 true phase information; after phase unwrapping, s d The absolute phase of (t) is expressed as

[0079]

[0080] Step 2: Perform windowing and segmenting processing on the absolute phase of the echo signal, and use the least squares method to estimate the slope of each segment phase. After the slopes of all segment phases are estimated, the average value is taken as the absolute phase slope estimation result.

[0081] 2.1 Windowing and segmentation of absolute phase.

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

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

[0084]

[0085] in, is the mth segment phase obtained by 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 sample 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 Perform fitting and calculate:

[0091]

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

[0093]

[0094] Step 3: Use the slope estimation result of the absolute phase to construct a phase distribution linear function, 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 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 based on the estimated value of the jump phase term, and multiply the time domain phase compensation function with the radar received echo signal to obtain the 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) with the phase shift phase changed by the metasurface modulation to achieve effective detection of active electromagnetic control targets. 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 operations are 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 metasurface normal 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 receives the aliased echo and 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 various embodiments of the present application, and should all be included in the scope of protection of the present application.

Claims

1. A radar detection method for active electromagnetic control targets, characterized in that: include: Modeling 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 transmission signal, the echo signal is pre-processed by removing the carrier frequency and demodulating the frequency; Performing phase unwrapping processing on the pre-processed echo signal to obtain the absolute phase of the echo signal; The absolute phase of the echo signal is windowed and segmented, and the slope of each segment phase is estimated using the least squares method. After the slopes of all segment phases are estimated, the average value is taken as the absolute phase slope estimation result; 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 received echo signal to obtain a reconstructed signal; The reconstructed signal is processed by matched filtering to obtain the output signal.

2. The radar detection method for active electromagnetic control targets according to claim 1, 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 is a linear frequency modulation signal, and the time-varying reflection coefficient of the metasurface is , then the radar receives the echo signal expression : in, is the time parameter, is a rectangular window function, For distance The time delay corresponding to the target to be detected at the position, is the speed of light, is the pulse width, To adjust the frequency, is the carrier frequency, j is an imaginary unit; Time-varying reflection coefficient of metasurface The expression is: in, , is the reflection coefficient In pulse width The number of phase changes within Indicates the l times change; is the reflection coefficient Each phase state duration, .

3. The radar detection method for active electromagnetic control targets according to claim 2, characterized in that: The echo signal is pre-processed by removing the carrier frequency and demodulating the frequency based on the parameters of the radar transmission signal; Perform phase unwrapping on the pre-processed echo signal to obtain the absolute phase of the echo signal, including: Echo signal After pre-processing of removing carrier frequency and demodulating frequency, we can get : in, For time irrelevant constant terms; After phase unwrapping, The absolute phase is expressed as : 。 4. The radar detection method for active electromagnetic control targets according to claim 3 is characterized in that: The windowing and segmenting processing of the absolute phase of the echo signal includes: Absolute phase After windowing and segmentation processing, we can get: in, is the first segment obtained after segmenting the absolute phase m Segment phase, ; is the total number of absolute phase segments; is the segment length of each segment phase after segmentation, and , is the window function.

5. The radar detection method for active electromagnetic control targets according to claim 4, characterized in that: The method of estimating the slope of each segment phase by the least square method and taking the average value of the slopes of all segment phases as the slope estimation result of the absolute phase after the slope estimation is completed includes: Absolute Phase After segmentation processing, the discretization table of the segmented phase can be obtained: in, Pulse width The number of all discrete sampling points within the sampling rate is ; 、 Segmented phase , window function The discretized form of n Indicates the n sampling points; Using the least squares method, m Segmented phase and corresponding window function The slope Perform fitting; The absolute phase The final slope estimate result for: 。 6. The radar detection method for active electromagnetic control targets according to claim 5, 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 5, characterized in that: The method comprises: 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 the jump phase term of the electromagnetic metasurface. The final slope estimation result using the absolute phase Construct a phase distribution function, that is, a slant line; the intercept of the phase distribution function is By absolute phase The decision expression is: in, is the reference time delay; Using slope and intercept 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 , whose expression is: 。 8. The radar detection method for active electromagnetic control targets according to claim 7, 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 received echo signal to obtain a reconstructed signal. include: Using the jump phase term Constructing time domain phase compensation function : in, is the slope estimation error; The phase compensation function With echo signal Multiply 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 storing a computer program; wherein: 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.

Images