Close-range target detection method based on digitally programmable metasurface

Abstract

The present invention discloses a method for detecting close-range targets based on a digital programmable metasurface. The detection information includes the horizontal displacement of the target, the radial distance and the radial velocity. The horizontal displacement of the target is estimated by the sum and difference beams generated by the metasurface, and the difference and sum ratio is obtained by the ratio of the difference beam to the sum beam for estimation. Furthermore, beam tracking can be achieved by sum and difference beams with different directions. For radial distance and velocity estimation, a range Doppler algorithm based on two-phase coding on the sum beam is applied, wherein the two-phase coded signal is generated by the metasurface switching of the mouth-face coding of two identical radiation modes to dial the radiation phase.

Description

Technical Field

[0001] The present invention belongs to the field of wireless communication technology, and in particular relates to a close-range target detection method based on a digitally programmable metasurface. Background Art

[0002] Electromagnetic perception is considered as the focus of 6G wireless communication, which includes target positioning, imaging, tracking and classification. Target positioning refers to the detection of target distance, speed and angle. These studies are currently mainly based on traditional phased array antennas. Since the phased array system needs to install a transceiver for each antenna, its system architecture is highly complex and costly. Digital programmable metasurfaces have excellent performance in electromagnetic wave control. Compared with traditional phased arrays, metasurfaces only need one transceiver, which can greatly reduce costs and hardware complexity. In addition, metasurfaces can control electromagnetic waves by dynamically controlling the unit state of the surface, reducing the complexity of signal processing in the time domain, frequency domain and spatial domain, which greatly facilitates the application of metasurfaces in electromagnetic perception. Summary of the invention

[0003] The purpose of the present invention is to propose a close-range target detection method based on a digital programmable metasurface. The detection information includes the target horizontal displacement, radial distance and radial velocity. Among them, the target horizontal displacement estimation is completed by relying on the sum and difference beams generated by the metasurface, and the difference and sum ratio is obtained by the ratio of the difference beam to the sum beam for estimation. Furthermore, beam tracking can be achieved by sum and difference beams with different directions; for radial distance and velocity estimation, a range Doppler algorithm based on two-phase coding on the sum beam is applied, in which the two-phase coded signal is generated by the metasurface switching of the mouth-face coding of two identical radiation modes to dial the radiation phase.

[0004] The close-range target detection method based on a digitally programmable metasurface of the present invention comprises the following steps:

[0005] Step 1: The metasurface transmits a beam to illuminate the moving target, and by designing the aperture coding, the metasurface generates a sum and difference beam to detect the horizontal displacement of the moving target;

[0006] For the sum beam, the radiation pattern is described by a directional wave, which is Among them, θ and Represent the elevation angle and azimuth angle of the directional beam respectively.

[0007] For a difference beam, the radiation pattern consists of the difference of two directional beams:

[0008]

[0009] Step 2, calculate the difference and ratio R(d), as follows:

[0010]

[0011] Among them, F Δ (d) and F ∑ (d) Represents the field strength of the difference beam and sum beam at the target moving trajectory.

[0012] Step 3, for a close moving target on a horizontal line parallel to the hypersurface, the identification distance line is obtained by the difference and ratio, that is, the relationship between the difference and ratio R(d) and the horizontal displacement d is obtained, thereby obtaining the horizontal displacement.

[0013] The close-range target detection method based on digital programmable metasurface of the present invention further includes the following steps:

[0014] Step 1: Assume that the metasurface emits a directional beam with a binary radiation phase, and the transmitted signal s t (t) and the received signal s r (t) is represented by the following formula:

[0015]

[0016]

[0017] Among them, a(t) and are the amplitude and phase of the transmitted signal respectively. For a two-phase coded signal, is 0 or π, f c Indicates the carrier frequency of the signal, t r Indicates the delay from signal transmission to signal reception;

[0018] Step 2: Pulse compression technology obtains the instantaneous signal-to-noise ratio signal s through matched filtering cr (t), the radial distance of the target is estimated by pulse compression technology. The pulse compression process is given by the following formula:

[0019]

[0020] in, and They are s t (t) and s r (t) is the Fourier transform form of the signal s cr (t) at t = t r Get peak value at all times;

[0021] Step 3: For a moving target, the echo signal includes radial velocity information. Assume that the target moves at a speed v r Close to the metasurface, the initial radial distance between the target and the metasurface is R0, then the echo signal s r (t) can be expressed as:

[0022]

[0023] in, From formula (6), we can know that s r (t) contains the delay information t r and Doppler frequency f d , delay information t r and Doppler frequency f d They are related to the radial distance and radial velocity of the target respectively.

[0024] Signals rd (t,f) at t = t r ,f=f d The peak value is obtained when and d = c * t r It can estimate the radial distance and speed of moving targets.

[0025] Furthermore, f d The value of can be estimated by collecting echo signals of multiple cycles through Doppler filtering and performing Fourier transform to compress the echo signals, as described in the following formula:

[0026] s rd (t,f)=FFT[s cr (t+nT r )],n=0,1,…,N (7)

[0027] Among them, t∈(0,T r ), T r is the signal period, and N is the number of accumulated signal periods.

[0028] Beneficial effects: The metasurface controls electromagnetic waves by dynamically adjusting the unit state of the surface, achieves target positioning, reduces the complexity of signal processing in the time domain, frequency domain and spatial domain, and greatly facilitates the application of metasurface in electromagnetic sensing. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a target detection model diagram of the digital programmable metasurface on which the method of the present invention is based;

[0030] Figure 2 is a characteristic diagram of the unit structure of the metasurface;

[0031] Figure 3 This is the full-wave simulation result diagram of three groups of sum and difference beams;

[0032] Figure 4 This is the full-wave simulation result diagram of the metasurface, difference beam and range detection line;

[0033] Figure 5 It is the simulation result of estimating single-target scene and multi-target scene based on the hypersurface;

[0034] Figure 6 This is the result of the target horizontal displacement estimation and tracking experiment;

[0035] Figure 7 This is a simulation diagram for estimating the radial distance and speed of the target. DETAILED DESCRIPTION

[0036] The close-range target detection method based on digital programmable metasurface of the present invention is based on the following Figure 1 In the target detection model shown, the transmissive metasurface contains 10×10 units, which are vertically illuminated by a horn antenna that radiates 28 GHz single-frequency waves as a feed source. Figure 2 The unit structure properties of the proposed metasurface are demonstrated. Figure 2 (a) shows the structural composition of the unit cell. Figure 2 (b) is the transmission amplitude diagram of the unit in the binary state; Figure 2

[0037] (c) is the transmission phase diagram of the unit cell in the binary state.

[0038] The metasurface transmits a beam to illuminate the moving target, and by designing the aperture coding, the metasurface generates a sum and difference beam to detect the horizontal displacement of the moving target. In addition, the metasurface generates a two-phase coded signal on the sum beam through two-phase control, so the radial distance and speed of the target can be obtained through the range Doppler algorithm.

[0039] Sum and difference beams are often used in monopulse radar systems for target tracking because the echo of the sum and difference beams carries the target spatial angle information. Compared with traditional monopulse radar antennas, metasurfaces can achieve sum and difference beams by reconstructing the interface coding without the need for sum and difference networks. For sum beams, the radiation pattern can be described by directional waves, which are Among them, θ and Represent the elevation and azimuth of the directional beam respectively. For a difference beam, the radiation pattern can be constructed by the difference of two directional beams:

[0040]

[0041] When two directional beams are very close to each other, the subtraction will cause the radiation pattern to generate a notch at the pointing direction. By defining enough sum and difference beam coding, sum and difference beam steering can be achieved. The corresponding sum and difference beam aperture coding can be generated by geometric optics principles.

[0042] Figure 3The full-wave simulation results of three groups of sum and difference beams are given. Figure 3 (a)-(c) in the figure respectively give the aperture coding diagrams with beam pointing at -8.53°, 0° and 8.53°. Figure 3 (d)-(f) in the figure respectively give the aperture coding diagrams of the difference beam pointing to -8.53°, 0° and 8.53°. Figure 3 (g)-(i) in the figure respectively give the radiation patterns corresponding to the aperture coding of sum beam and difference beam pointing to -8.53°, 0° and 8.53°. The simulation results verify the feasibility of generating sum and difference beams based on metasurface.

[0043] For a close-range moving target on a horizontal line parallel to the metasurface, the method for calculating its horizontal displacement is similar to the method of using the ratio of the difference beam to the sum beam to obtain a single pulse angle detection curve. The detection range line can be obtained by the difference and sum ratio, that is, the difference and sum ratio R(d) is as follows:

[0044]

[0045] Among them, F Δ (d) and F ∑ (d) represents the field strength of the difference beam and the sum beam at the target moving track. Figure 3 The sum and difference beam coding, Figure 4 The full-wave simulation results of the metasurface and difference beam and the range detection line are given. Figure 4 (a)-(c) in the figure show the simulated field strength results of the sum and difference beams pointing at -8.53°, 0° and 8.53° on parallel lines 12 mm away from the metasurface. Figure 4 (d)-(f) in Figure 1 show the relationship between the distance line, that is, the difference and ratio R, and the horizontal displacement d. The monotonicity of these lines can be used to estimate the horizontal displacement of the moving target.

[0046] Binary phase coded signals are widely used in the field of radar detection due to their high time-bandwidth product, pulse compression and anti-interference characteristics. By switching the appropriate aperture coding, the metasurface can be phase modulated on a fixed pattern, so the binary phase coded signal can be directly generated by the metasurface. Assume that the metasurface transmits a directional beam with a binary radiation phase, and the transmitted signal s t (t) and the received signal s r (t) is represented by the following formula:

[0047]

[0048]

[0049] Among them, a(t) and are the amplitude and phase of the transmitted signal respectively. For a two-phase coded signal, is 0 or π, f c Indicates the carrier frequency of the signal, t r Indicates the delay from when a signal is transmitted to when it is received.

[0050] The pulse compression technology obtains the signal with peak instantaneous signal-to-noise ratio through matched filtering. The radial distance of the target can be estimated by pulse compression technology. The pulse compression process is given by the following formula:

[0051]

[0052] in, and They are s t (t) and s r (t) is the Fourier transform form of the signal s. cr (t) at t = t r The peak value is obtained at every moment and can be used to estimate the radial distance of the target.

[0053] For a moving target, the echo signal includes radial velocity information. Assume that the target moves at a speed v r Close to the metasurface, the initial radial distance between the target and the metasurface is R0, then the echo signal s r (t) can be expressed as:

[0054]

[0055] in, It can be seen that r (t) contains the delay information t r and Doppler frequency f d , which are related to the radial distance and radial velocity of the target respectively. d The value of can be estimated by collecting echo signals of multiple cycles through Doppler filtering and performing Fourier transform to compress the echo signals, as described in the following formula:

[0056] s rd (t,f)=FFT[s cr (t+nT r )],n=0,1,…,N (7)

[0057] Among them, t∈(0,T r ), T r is the signal period, and N is the number of accumulated signal periods. rd (t,f) at (t=t r ,f=f d ) to obtain the peak value, using and d = c * t rIt can estimate the radial distance and speed of moving targets.

[0058] To verify the theory, simulations were performed for single-target and multi-target scenarios. In the simulation, a 255-bit m-sequence was used as a two-phase coded signal, and the symbol rate of the signal was 200MHz, corresponding to the switching rate of the metasurface interface coding. In the single-target scenario, the target was set to be 2.1m away from the metasurface and approached the metasurface at a speed of 1m / s, i.e. (2.1m, 1m / s); in the multi-target scenario, three targets were set in the same direction, with the parameters of (2m, -1m / s), (4m, 1m / s) and (4m, -1m / s). Figure 5 (a) shows the estimation result in a single target scenario, with the peak at (2.1m, 1.0463m / s), which is very close to the set parameters. Figure 5 (b) shows the estimation results for three target scenarios, with peaks at (2.025m, -1.0463m / s), (4.05m, 1.0463m / s) and (4.05m, -1.0463m / s), which are also close to the set parameters. The simulation results verify the effectiveness of the 1-metasurface for radial distance and velocity estimation.

[0059] To estimate the horizontal displacement, the near field on parallel lines 1 m away from the metasurface was tested. Figure 6 (a)-(c) in the figure show the near-field measurement results of the sum and difference beams pointing to -8.53°, 0° and 8.53° respectively. It is obvious that the sum and difference beams lead to different near-field distributions, which can be used to estimate the horizontal displacement of the target. Due to multiple reflections between the metasurface and the feed horn, the measured near-field values ​​will have some jitter. Figure 6 (d)-(f) in Fig. 3 are the sum and difference beam results obtained based on equation (2). The solid lines are fitted by the least squares algorithm. The monotonicity of these lines confirms the effectiveness of the target horizontal displacement estimation.

[0060] In order to estimate the radial distance and velocity of the target, the metasurface is configured with two sets of aperture codes, which generate sum beams pointing to 0° but with opposite phase information. Figure 7 The measured near-field information is given. Figure 7 (a) shows the measurement results of the near-field amplitude and phase on a horizontal line 1m away from the metasurface. It can be seen that the amplitudes are similar but the phases are opposite, which lays the foundation for generating a two-phase coded signal. According to the m-sequence switching of the metasurface's surface coding, the target in front of the metasurface will be illuminated by the two-phase coded signal. Figure 7 (b) in the figure is the result of the range Doppler image. The estimated parameters are (1.05m, 1.0463m / s), which are very close to the set parameters (1m, 1m / s).

[0061] The present invention successfully establishes close-range target detection based on digital programmable metasurfaces, including target horizontal displacement, radial distance and radial velocity. The target horizontal displacement estimation and tracking are realized by relying on the ratio and different orientations of the metasurface and the difference beam, and the target radial distance and radial velocity estimation are realized by relying on the two-phase coded signal and the range Doppler algorithm. Both simulation and experimental results prove the effectiveness of the experiment. The present invention demonstrates the application potential of digital programmable metasurfaces in near-field detection, and hopes to further explore the application of programmable metasurfaces in the field of intelligent electromagnetic perception.

Claims

1. A close-range target detection method based on a digitally programmable metasurface, characterized in that: The detection information includes target horizontal displacement, radial distance and radial velocity. When the detection information is target horizontal displacement, the following steps are included: Step 1: The metasurface transmits a beam to illuminate the moving target, and by designing the aperture coding, the metasurface generates a sum and difference beam to detect the horizontal displacement of the moving target; For the sum beam, the radiation pattern is described by a directional wave, which is Among them, θ and Respectively represent the elevation angle and azimuth angle of the directional beam; For a difference beam, the radiation pattern consists of the difference of two directional beams: Step 2, calculate the difference and ratio R(d), as follows: Among them, F Δ (d) and F ∑ (d) represents the field strength of the difference beam and the sum beam at the target moving track; Step 3, for a close moving target on a horizontal line parallel to the hypersurface, obtain the identification distance line through the difference and ratio, that is, obtain the relationship between the difference and ratio R(d) and the horizontal displacement d, thereby obtaining the horizontal displacement; In order to estimate the radial distance and velocity of the target, the metasurface is configured with two sets of aperture codes. These two sets of codes generate sum beams pointing to 0° but with opposite phase information. When the detection information is radial distance and radial velocity, the following steps are included: Step 1: Assume that the metasurface emits a directional beam with a binary radiation phase, and the transmitted signal s t (t) and the received signal s r (t) is represented by the following formula: Among them, a(t) and are the amplitude and phase of the transmitted signal respectively; for a two-phase coded signal, is 0 or π, f c Indicates the carrier frequency of the signal, t r Indicates the delay from signal transmission to signal reception; Step 2: Pulse compression technology obtains the instantaneous signal-to-noise ratio signal s through matched filtering cr (t), the radial distance of the target is estimated by pulse compression technology. The pulse compression process is given by the following formula: in, and They are s t (t) and s r (t) is the Fourier transform form of the signal s cr (t) at t = t r Get peak value at all times; Step 3: For a moving target, the echo signal includes radial velocity information; assuming that the target moves at a speed v r Close to the metasurface, the initial radial distance between the target and the metasurface is R0, then the echo signal s r (t) can be expressed as: in, From formula (6), we can know that s r (t) contains the delay information t r and Doppler frequency f d , delay information t r and Doppler frequency f d are related to the radial distance and radial velocity of the target, respectively; Signals rd (t,f) at t = t r ,f=f d The peak value is obtained when and d = c * t r It can estimate the radial distance and speed of moving targets; d The value of can be estimated by collecting echo signals of multiple cycles through Doppler filtering and performing Fourier transform to compress the echo signals, as described in the following formula: s rd (t,f)=FFT[s cr (t+nT r )],n=0,1,…,N (7) Among them, t∈(0,T r ), T r is the signal period, and N is the number of accumulated signal periods.

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