Electromagnetic metamaterial-based array radar space-time coding digital regulation anti-jamming method

Abstract

The application provides an electromagnetic metamaterial-based array radar space-time coding digital regulation anti-interference method, which is based on search results, determines time domain coding coefficients of each false target according to the conditions of the occurrence of the zero points of a transmission beam pattern and the maximum allowed deviation of each false target relative to a mismatched frequency, further determines a weight vector of a beam former and constructs the beam former, compensates an original transmission signal to form a first transmission signal according to the maximum allowed deviation of each false target relative to the mismatched frequency, widens each zero point region according to the transmission spatial frequency of the zero point region corresponding to each false target, the maximum allowed deviation of each false target relative to the mismatched frequency and the first transmission signal, obtains a target weight vector corresponding to each widened zero point region, determines a second transmission signal according to each target weight vector, and further determines the phases of each space domain coding unit in the electromagnetic metamaterial-based array radar based on preset phase constraint conditions, and constructs the radar, so that the anti-interference capability of the radar is improved.

Description

Technical Field

[0001] This invention relates to the field of radar technology, and specifically to an anti-jamming method for array radar based on electromagnetic metamaterials with space-time coding digital modulation. Background Technology

[0002] In today's diverse use of information technology, deceptive and suppressive information interference restricts the accurate detection of targets by radar.

[0003] Interference sources in array radar can be classified in many ways according to different criteria. For airspace interference signals, they can be divided into main lobe interference and side lobe interference based on whether the interference signal is located within the main lobe of the beam. The presence of these types of interference will affect the detection and processing of the desired signal.

[0004] Current research on sidelobe interference suppression has been quite in-depth, with methods such as generalized sidelobe cancellation and adaptive beamforming achieving good sidelobe interference suppression results. However, research on main lobe interference is relatively limited. When interference falls into the main lobe region of the array beam, because the main lobe interference is located within the main lobe and close to the target signal, directly applying traditional adaptive beamforming algorithms will lead to increased sidelobe levels, main lobe beam distortion, and peak shift, resulting in an increased false alarm rate for the radar and affecting target detection. Furthermore, during radar angle measurement, the main lobe distortion and peak shift caused by main lobe interference will severely affect the radar's angle measurement accuracy. Summary of the Invention

[0005] To address the aforementioned problems in existing technologies, this invention provides a space-time coded digital modulation anti-jamming method for array radar based on electromagnetic metamaterials. Specifically, it includes:

[0006] In a first aspect, the present invention provides a space-time coded digital modulation anti-jamming method for array radar based on electromagnetic metamaterials, comprising:

[0007] Based on the target search results in the target airspace, the time-domain coding coefficients of each false target are determined according to the conditions for the occurrence of null points in the transmitted beam pattern and the maximum permissible deviation of each false target relative to the mismatch frequency.

[0008] Based on the time-domain coding coefficients, the weight vector of the beamformer is determined, and the beamformer is constructed based on the weight vector of the beamformer.

[0009] Based on the maximum permissible deviation of each dummy target relative to the mismatch frequency, the original transmitted signal is compensated to form the first transmitted signal;

[0010] Based on the transmission spatial frequency of the null region corresponding to each false target and the maximum permissible deviation relative to the mismatch frequency, and the first transmission signal, the null region of the transmission beam diagram of each false target is widened to obtain the target weight vector corresponding to each widened null region.

[0011] The second transmission signal is determined based on the weight vectors of each target.

[0012] Based on the second transmitted signal and the preset phase constraint conditions, the phase of each spatial coding unit in the array radar based on electromagnetic metamaterials is determined;

[0013] Based on the phase and beamformer of each spatial coding unit, an array radar based on electromagnetic metamaterials is constructed. The array radar based on electromagnetic metamaterials is used to generate and transmit a second transmitted signal, and to suppress interference of the received signal through the beamformer.

[0014] Secondly, the present invention also provides an array radar based on electromagnetic metamaterials, comprising:

[0015] Beamformer and multiple spatial coding units based on electromagnetic metamaterials;

[0016] The process of building a beamformer includes:

[0017] Based on the target search results in the target airspace, the time-domain coding coefficients of each false target are determined according to the conditions for the occurrence of null points in the transmit beam pattern and the maximum permissible deviation of each false target relative to the mismatch frequency. Based on each time-domain coding coefficient, the weight vector of the beamformer is determined, and the beamformer is constructed based on the weight vector of the beamformer.

[0018] The process of determining the phase of each spatial coding unit includes:

[0019] Based on the maximum permissible deviation of each false target relative to the mismatch frequency, the original transmitted signal is compensated to form a first transmitted signal; based on the transmitted spatial frequency of the null region corresponding to each false target and the maximum permissible deviation relative to the mismatch frequency, and the first transmitted signal, the null region of the transmitted beam pattern of each false target is widened to obtain the target weight vector corresponding to each widened null region; based on each target weight vector, a second transmitted signal is determined; based on the second transmitted signal and the preset phase constraint conditions, the phase of each spatial coding unit in the array radar based on electromagnetic metamaterials is determined.

[0020] Thirdly, the present invention provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements any of the methods provided in the first aspect.

[0021] Fourthly, the present invention provides a program product comprising computer program instructions that, when executed, can implement any of the methods provided in the first aspect.

[0022] The beneficial effects of this invention are:

[0023] The present invention provides an anti-jamming method for array radar based on electromagnetic metamaterials with space-time coding digital control. This method determines the time-domain coding coefficients of each false target based on target search results in the target spatial domain, according to the conditions for the occurrence of null points in the transmitted beam pattern and the maximum permissible deviation of each false target relative to the mismatch frequency. Based on these time-domain coding coefficients, the weight vector of the beamformer is determined, and a beamformer is constructed using this weight vector. A first transmitted signal is formed after compensating the original transmitted signal based on the maximum permissible deviation of each false target relative to the mismatch frequency. Finally, the transmitted beam pattern of each false target is widened based on the transmitted spatial frequency of the null region corresponding to each false target, the maximum permissible deviation relative to the mismatch frequency, and the first transmitted signal. The zero-point regions are obtained, and the target weight vectors corresponding to each widened zero-point region are obtained. Based on each target weight vector, the second transmitted signal is determined. Based on the second transmitted signal and the preset phase constraint conditions, the phase of each spatial coding unit in the electromagnetic metamaterial-based array radar is determined. Based on the phase of each spatial coding unit and the beamformer, the electromagnetic metamaterial-based array radar is constructed. The electromagnetic metamaterial-based array radar is used to generate and transmit the second transmitted signal, and the beamformer suppresses interference on the received signal. It can combine time-domain coding and spatial coding to achieve space-time coding digital control, improve the anti-interference capability of the electromagnetic metamaterial-based array radar, enhance the anti-main lobe interference performance, and improve the signal-to-interference-plus-noise ratio.

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0025] Figure 1 A flowchart illustrating an anti-interference method for array radar based on electromagnetic metamaterials using space-time coding digital modulation.

[0026] Figure 2 A schematic diagram of the spatial coding unit structure of an electromagnetic metasurface for an array radar based on electromagnetic metamaterials, provided by the present invention;

[0027] Figure 3 A schematic diagram of an experimental scenario provided by the present invention;

[0028] Figure 4a A transmission pattern provided by the present invention;

[0029] Figure 4b A transmission pattern provided by the present invention;

[0030] Figure 5 This invention provides a schematic diagram showing the distribution of the target and interference before anti-interference measures are implemented.

[0031] Figure 6 This invention provides a schematic diagram showing the distribution of the target and interference after anti-interference measures are implemented.

[0032] Figure 7 This is a comparison chart of the signal-to-interference-plus-noise ratio (SIR) of an array radar based on electromagnetic metamaterials provided by this invention and a MIMO radar based on general materials. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0034] To address the challenge of enhancing radar anti-jamming capabilities under complex electromagnetic interference, it is imperative to conduct research on key anti-jamming technologies for new radar systems from a technical perspective. This research aims to achieve new anti-jamming gains across the entire radar signal transmission and reception chain. This approach inspires us to explore new methods that combine radar transmit waveform design with array receiver optimization. Future anti-jamming development will not only require innovation at the technical level but also necessitate the integration of novel theoretical frameworks to drive continuous innovation in radar systems. New radar systems based on novel electromagnetic information theories are expected to generate coded, numerically controlled multi-channel array pattern characteristics under a unified space-time coding system, enabling precise interference suppression or cancellation in the spatial domain. Constructing transmit and receive waveforms with pulse phase encoding and decoding for array elements will filter interference in the joint transmit and receive domain. Combined with traditional signal processing gains, this is expected to overcome the performance bottlenecks of traditional radar systems in anti-jamming.

[0035] Figure 1 A flowchart illustrating an anti-jamming method for space-time coding digital control of array radar based on electromagnetic metamaterials provided by this invention is shown below. Figure 1 As shown, the method includes:

[0036] S101. Based on the target search results in the target airspace, determine the time-domain coding coefficients of each false target according to the conditions for the occurrence of the null point in the transmitted beam pattern and the maximum permissible deviation of each false target relative to the mismatch frequency.

[0037] The transmit beammap corresponding to the false target is the transmit beammap of the false target in the transmit space frequency domain. In one possible implementation, based on the target search results in the target spatial domain, and according to the conditions for the occurrence of nulls in the transmit beammap and the maximum permissible deviation of each false target relative to the mismatch frequency, the time-domain coding coefficients of each false target are determined, including:

[0038] For any q-th false target, adjust the time-domain coding coefficients of the q-th false target so that the transmission spatial frequency corresponding to the q-th false target is equal to the maximum permissible deviation of the q-th false target from the mismatch frequency, so that the transmission beam pattern of the q-th false target has a null point, and obtain the final time-domain coding coefficients of the q-th false target. The final time-domain coding coefficients of the q-th false target are expressed as:

[0039]

[0040] Where γ represents the time-domain coding coefficient, and p represents the difference in the number of delayed pulses between the q-th false target and the real target.

[0041] A crucial prerequisite for EPC-MIMO radar to achieve false target suppression is that prior coarse knowledge of the target, such as the number of delayed pulses, is available during the radar search phase. Optionally, the expression for the normalized equivalent transmit beam pattern of the q-th false target in the transmit space frequency domain, i.e., the transmit beam pattern of the q-th false target, is:

[0042]

[0043] in, P T (f Tq f represents the transmission beam pattern of the q-th dummy target. Tq Let f represent the spatial frequency of the q-th false target, T represent the duration of the radar pulse, M represent the number of transmitting elements, and f' represent the frequency of the transmitted pulse. T Let γ represent the launch frequency of the real target, e represent the exponential function, j represent the complex number, and γ represent the launch frequency of the real target. p =γp, where γ represents the time-domain coding coefficient, p represents the difference in the number of delayed pulses between the q-th false target and the real target, d represents the element spacing, λ0 represents the wavelength of the transmitted signal, θ represents the beam angle, and θ0 represents the target angle.

[0044] The emission beam pattern of the q-th dummy target shows a zero point, that is, a concave surface.

[0045] The conditions for the null point of the transmission beam pattern of the q-th dummy target are: the numerator of the expression of the transmission beam pattern of the q-th dummy target is zero and the denominator is not zero. At this time, the transmission spatial frequency corresponding to the q-th dummy target is equal to the maximum permissible deviation of the q-th dummy target relative to the mismatch frequency.

[0046] When the transmit beam pattern of the q-th dummy target has a null point, its corresponding transmit spatial frequency is expressed as:

[0047]

[0048] Among them, f nullThis represents the transmission spatial frequency corresponding to the occurrence of a zero point, k = 1, 2, ..., M-1, where M represents the number of transmission array elements.

[0049] This method, by designing time-domain coding coefficients, makes the transmission spatial frequency corresponding to the false target equal to its maximum allowable deviation relative to the mismatch frequency. Thus, when the false target is exactly at the zero point of the equivalent transmission beam pattern, the false target can be suppressed.

[0050] S102. Determine the weight vector of the beamformer based on each time-domain coding coefficient, and construct the beamformer based on the weight vector of the beamformer.

[0051] In one possible implementation, the weight vector of the beamformer is expressed as:

[0052]

[0053] Where θ0 represents the target direction, b(θ0) represents the receiving guidance vector, and γ s =γp s p s The pulse delay number represents the real target, and s represents the real target. This represents the launch guidance vector of the actual target after compensating for the phase difference between array elements. It represents the Kronecker product, and EPC stands for Element-pulse-coding.

[0054] Furthermore, the normalized receiver pattern is represented as:

[0055]

[0056] Among them, P R (f R ) represents the normalized receiver pattern, f R The received spatial frequency is represented by N, and the number of receiving array elements is represented by f. Rq Let represent the received spatial frequency of the q-th dummy target, e represent the exponential function, j represent the complex number, d represent the element spacing, λ0 represent the wavelength of the transmitted signal, θ represent the direction of the received beam, and θ0 represent the direction of the target.

[0057] Therefore, the two-way transmission and reception pattern can be represented as:

[0058]

[0059] Among them, f Tq Let P represent the spatial frequency of the q-th dummy target. T (f Tq P represents the normalized equivalent transmit beammap in the transmit space frequency domain of the q-th dummy target.R (f R ) represents the normalized receiver pattern.

[0060] S103. Based on the maximum permissible deviation of each dummy target relative to the mismatch frequency, the original transmission signal is compensated to form the first transmission signal.

[0061] S104. Based on the transmission spatial frequency of the null region corresponding to each false target and the maximum permissible deviation relative to the mismatch frequency, and the first transmission signal, widen the null region of the transmission beam diagram of each false target to obtain the target weight vector corresponding to each widened null region.

[0062] When EPC-MIMO radar suppresses main lobe deception interference using a transmit-receive beamformer, the transmit spatial frequency of the false target is related to its delayed pulse number and time-domain coding coefficients. Therefore, there is no mismatch caused by range quantization error. That is, if the radar system parameters and configuration remain unchanged within a coherent processing time, the configuration of the false target generator also remains unchanged, and the transmit frequency of the false target is a fixed value. By designing appropriate time-domain coding coefficients, the false target can be positioned precisely at the null point of the equivalent transmit beammap, thereby suppressing the false target. However, in real-world scenarios, errors in the angle measurement process may cause the false target to be not precisely positioned in the assumed direction, resulting in a slight deviation between the false target and its assumed null point in the equivalent transmit beammap. Therefore, the performance of suppressing deception interference using only the false target's prior data for independent beamforming may be degraded. To address this issue, the notch of the EPC-MIMO radar beammap needs to be widened to mitigate potential angular deviations.

[0063] In one possible implementation, based on the transmission spatial frequency of the null region corresponding to each dummy target and the maximum permissible deviation relative to the mismatch frequency, and the first transmitted signal, the null region of the transmission beam pattern of each dummy target is widened, as shown below:

[0064]

[0065] in, The vector represents the weight vector, and the superscript H indicates the conjugate transpose. q Represents Θ q Any transmission spatial frequency in, a(f q ) represents any steering vector in the q-th zero region, ·2 represents the Euclidean norm, ξ represents the predefined zero depth, and w opt This represents the final optimized target weight vector. This represents the launch guidance vector of the real target after compensation. Indicates the actual launch frequency of the target after compensation. Θ represents the actual transmission spatial frequency of the q-th dummy target. q Let Δf represent the set of transmitted spatial frequencies in the q-th null region. T This represents the maximum permissible deviation relative to the mismatch frequency. The subscript T indicates the pulse duration, M indicates the number of transmit array elements, and st indicates the constraint condition.

[0066] Specifically, in the above optimization problem, the actual emission spatial frequency of the q-th dummy target can be expressed as:

[0067]

[0068] Where Δθ represents the angular offset of mismatch in the direction-of-arrival estimation, p represents the difference in the number of delayed pulses between the q-th false target and the real target, γ represents the time-domain coding coefficient, λ0 represents the wavelength of the transmitted signal, d represents the element spacing, and θ0 represents the direction of the target.

[0069] The mismatch frequency can be expressed as:

[0070]

[0071] Where D0 represents the equivalent angle corresponding to the mismatch frequency.

[0072] The arbitrary steering vector of the q-th zero-point region can be expressed as:

[0073]

[0074] Where e represents an exponential function, j represents a complex number, the superscript T represents the pulse duration, and the superscript M represents the number of transmitting array elements.

[0075] The compensated launch steering vector can be expressed as:

[0076]

[0077] Furthermore, the above optimization problem is solved using the preset broadened nulling beamformer (PBN-BF) algorithm.

[0078] The PBN-BF algorithm is designed by applying artificial disturbances of appropriate power around the null point of the dummy target. The PBN-BF algorithm is explained in detail below:

[0079] (1) The interference plus noise covariance matrix is ​​composed of artificial interference rather than real data.

[0080] (2) The artificial interference is irrelevant, while the false targets generated by the same false target generator are relevant. This is feasible because the distance and angle information of the real target is known and available, while the information of the false target is predictable.

[0081] (3) Since the array’s response to interference depends on the intensity of the interference, the power of artificial interference is calculated in a closed form based on a predefined desired depth.

[0082] (4) In real-world environments, the exact information about the false target generator is unknown. Therefore, all possible notches should be enlarged to fully suppress false targets and improve anti-interference performance.

[0083] Specifically, in the first stage, the initial interference plus noise covariance matrix is ​​calculated by continuously applying artificial interference, and it can be expressed as:

[0084]

[0085] in, R represents the steering vector of the first artificial interference, the superscript H indicates the conjugate transpose, and R0 represents the initial interference plus noise covariance matrix.

[0086] Let V be the variance of the Gaussian white noise.

[0087] The power of the first interference can be expressed as:

[0088]

[0089] When the Qth artificial interference signal is applied, the final interference plus noise covariance matrix with continuous artificial interference structure is updated as follows:

[0090]

[0091] The power of the qth interference is calculated as follows:

[0092]

[0093] Where a0 represents the launch guidance vector of the compensated target.

[0094] Specifically,

[0095] Therefore, the obtained interference plus noise covariance matrix is ​​R j+n =R Q .

[0096] The weight vector calculated using the minimum variance distortionless response (MVDR) beamforming method is as follows:

[0097]

[0098] However, when continuous artificial interference is applied, it is necessary to calculate the interference plus noise covariance matrix Q times. To reduce the number of calculations and simplify the operation, this invention adopts a synchronous artificial interference construction method. The construction of the interference plus noise covariance matrix is ​​as follows:

[0099]

[0100] The interference-to-noise ratio (JNR) matrix is ​​defined as follows:

[0101]

[0102] Then, the inverse of the interference plus noise covariance matrix is ​​calculated as follows:

[0103]

[0104] The formula for calculating the weight vector w is:

[0105]

[0106] Where Λ represents the normalization coefficient, which can be expressed as:

[0107]

[0108] Where, β 0J The spatial correlation vector can be represented as:

[0109]

[0110] Therefore, the weight vector can be obtained as:

[0111]

[0112] Define a function to represent the positive difference in the l-th iteration:

[0113]

[0114] Among them, f i (i = 1, 2, ..., F) represents the discretized spatial frequency, and F represents Θ. q The total number of frequencies in the discretized space, function P d (f i) represents f i The beam pattern response of the site design, Δf T This represents the maximum permissible frequency deviation, requiring D to... l ≤ε. When D l When the value is greater than ε, the iteration process continues.

[0115] The main computational complexity of the PBN-BF algorithm lies in calculating the inverse of the interference plus noise covariance matrix of the equivalent emission pattern, i.e., O(LQM). 2 L represents the total number of iterations. The PBN-BF algorithm can be used to obtain a preset equivalent transmit beam pattern with a widened notch.

[0116] Finally, the weight vector can be represented as:

[0117]

[0118] When angle estimation error exists, the output signal-to-interference-plus-noise ratio (SINNR) after using the PBN-BF algorithm is:

[0119]

[0120] in, Indicates the power of the signal.

[0121] This method allows for flexible adjustment of the zero point position and width of the radiation pattern, reducing the impact of angle estimation errors on interference suppression.

[0122] S105. Determine the second transmission signal based on the weight vectors of each target.

[0123] The second transmitted signal, determined based on the target weight vector, has a wider zero-point range and stronger fault tolerance compared to any previous transmitted signal.

[0124] S106. Determine the phase of each spatial coding unit in the array radar based on electromagnetic metamaterials according to the second transmitted signal and the preset phase constraint conditions.

[0125] Electromagnetic metamaterial-based array radars are array radars equipped with electromagnetic metasurfaces. For example, the basic spatial coding structure of the phase gradient electromagnetic metasurface used in such array radars is the simplest square patch structure. The reflection phase of the metasurface spatial coding unit is controlled by changing the size of the square metal patch. The structure of the 2-bit phase metasurface spatial coding unit is as follows: Figure 2 The dimensions of the spatial coding unit and the metal sheet are shown in Table 1. Different metal sheets correspond to different reflection phases, and the reflection phases of 2-bit phase metamaterial units, i.e., adjacent spatial coding units, differ by 90°.

[0126] Table 1. Size of spatial coding and size of metal sheet

[0127]

[0128] When an excitation electromagnetic wave signal is incident on a reflective metasurface, each coded supercell will have a reflected response. The far-field modes of the metasurface are thus superimposed on each supercell. Based on this characteristic, the derivation of the far-field modes of the metasurface can be analogous to the derivation of the far-field function of an array radar. The pattern product theorem of array radar can be used to derive the field function of the metasurface. The pattern product theorem is an important tool for deriving the pattern function of an array antenna. It describes how the field function of the entire array can be derived from the field function of a single element and the arrangement of the elements. That is, the total pattern of the antenna array is equal to the pattern (direction function) of a single antenna multiplied by the pattern of the array factors (array functions) of the array.

[0129] The coded metasurface is simulated as a two-dimensional planar array antenna, where the spacing between array elements is the size of the metacell. Accordingly, in one possible implementation, the phase of each spatial coded cell in the array radar based on the electromagnetic metamaterial is determined according to the second transmitted signal and preset phase constraint conditions, including the following steps A1-A4:

[0130] A1. Based on the pattern product theorem for array antennas, the field function of the coded metasurface of an array radar based on electromagnetic metamaterials is determined as follows:

[0131]

[0132] Where f() represents the field function of the coded metasurface of the array radar based on electromagnetic metamaterials, f e () represents the field function of each supercell, and θ represents the elevation angle of the reflected beam. The azimuth angle of the reflected beam is represented by m and n, which correspond to the transverse and longitudinal sequence numbers of the supercell, respectively. Let P represent the reflection phase of the coding unit with sequence number (m,n), P represent the supercell period, k represent the spatial wave number, N represent the number of array elements, i represent a complex number, and exp represent an exponential function.

[0133] A2. Based on the field function of the coded metasurface, determine the direction coefficients of the coded metasurface, expressed as:

[0134]

[0135] Where Dir() represents the orientation coefficient of the encoded metasurface.

[0136] As can be seen from the scattering function and the field directivity coefficient, when a certain spatial coding unit size and coding sequence are designed, the field radiation pattern is the superposition of the field radiation patterns of each array element.

[0137] A3. Determine the initial phase of each spatial coding unit in an array radar based on electromagnetic metamaterials, based on the field function and direction coefficient of the coding metasurface.

[0138] When another set of coded sequences is superimposed on an existing code, the radiation pattern corresponding to the original coded sequence will be deflected according to the latter's pattern. This theorem, when applied to the coded numbers, results in the mathematical addition of the coded numbers. Therefore, in one possible implementation, the initial phase of the spatial coding unit (m,n) is represented as:

[0139] Φ c (m,n)=Φ r (m,n)+Φ f (m,n),

[0140] Where, Φ c (m,n) represents the phase of the spatial coding unit (m,n), Φ r (m,n) represents the uncompensated phase of the spatial coding unit (m,n), Φ f (m,n) represents the compensated phase of the feed analog plane wave corresponding to the spatial coding unit (m,n).

[0141] Specifically, when a coordinate system is established with the geometric center of the metasurface as the origin, the direction of the main lobe is... The phase requirement with respect to the spatial coding unit (m,n) can be expressed as:

[0142]

[0143] Where θ represents the azimuth angle of the main lobe of the beam. The pitch angle indicating the direction of the main lobe of the beam, (x m ,y n ) represents the geometric coordinates of the spatial coding unit (m,n) relative to the origin, and k0 represents the wave vector in free space.

[0144] The relationship between k0 and the selected operating wavelength λ is as follows:

[0145]

[0146] The compensated phase of the feed-simulated plane wave corresponding to the spatial coding unit (m,n) can be expressed as:

[0147]

[0148] Where F represents the feed height, This represents the phase difference caused by the height of the feed source to the metasurface.

[0149] A4. Discretize the initial phase of each spatial coding unit according to the preset discretization criteria to obtain the phase of each spatial coding unit.

[0150] Since the initial phase of the spatial coding unit calculated in the above steps is continuous, while the phase of the spatial coding unit applicable to the electromagnetic metamaterial-based array radar provided by this invention is discrete, it is necessary to discretize the obtained initial phase.

[0151] In one possible implementation, the preset discretization criterion is:

[0152]

[0153] Where, Φ d Φ represents the discretized phase. c This indicates the actual phase of the coding unit.

[0154] Based on this criterion, it can be guaranteed that the phase difference between adjacent spatial coding units is 90°, which meets the 2-bit phase coding requirement.

[0155] S107. Based on the phase and beamformer of each spatial coding unit, construct an array radar based on electromagnetic metamaterials. The array radar based on electromagnetic metamaterials is used to generate and transmit a second transmitted signal, and to suppress interference of the received signal through the beamformer.

[0156] It is understandable that building an array radar based on electromagnetic metamaterials can be either building a real radar or building a simulation model.

[0157] The present invention provides an anti-jamming method for array radar based on electromagnetic metamaterials using space-time coding digital modulation. This method determines the time-domain coding coefficients of each false target based on target search results in the target spatial domain, according to the conditions for the occurrence of null points in the transmitted beammaps of each false target in the target spatial domain and the maximum permissible deviation of each false target relative to the mismatch frequency. Based on these time-domain coding coefficients, the weight vector of the beamformer is determined, and a beamformer is constructed using these weight vectors. A first transmitted signal is formed after compensating the original transmitted signal based on the maximum permissible deviation of each false target relative to the mismatch frequency. The transmission steering vector of the first transmitted signal is determined, and the method is based on the maximum permissible deviation of the transmitted spatial frequency and mismatch frequency in the null region of the transmitted beammaps of each false target, as well as the first transmitted signal... The transmission steering vector is used to widen the null regions of the transmission beammaps of each false target, obtaining the target weight vectors corresponding to each widened null region. Based on each target weight vector, the second transmission signal is determined. Based on the second transmission signal and preset phase constraints, the phase of each spatial coding unit in the electromagnetic metamaterial-based array radar is determined. Based on the phase of each spatial coding unit and the beamformer, an electromagnetic metamaterial-based array radar is constructed. This array radar generates and transmits the second transmission signal and suppresses interference in the received signal through the beamformer. It can combine time-domain coding and spatial coding to achieve space-time coding digital control, improving the anti-interference capability of the electromagnetic metamaterial-based array radar, enhancing its anti-main lobe interference performance, and increasing the signal-to-interference-plus-noise ratio.

[0158] To further demonstrate the beneficial effects of the present invention, a set of experimental data is also provided, as follows:

[0159] Experimental site such as Figure 3 As shown, the radar is mounted on the top of a building, while the target and jammer are positioned approximately 2 km away on the road. The target (with jamming) has a movement range of 170m-550m. The structure of the array unit based on electromagnetic metamaterials is as follows: Figure 2 As shown, this is the classic "T" shaped structure. The basic structural parameters are shown in Table 1, and the structural parameters and reflection phases corresponding to different coding units are shown in Table 2.

[0160] Table 2. Structural parameters and reflection phases for different coding units.

[0161] Metal sheet gap g / mm Reflection Phase / ° Corresponding numerical code 0.5 -238 00 2 -146 01 3 -54 10 5.5 45 11

[0162] Figure 4a and Figure 4bThe figure shows the emission pattern after being modulated by the method provided by this invention. In the figure, Frequency represents the frequency, Main lobe magnitude represents the main lobe amplitude, Main lobe direction represents the main lobe direction, Angular width represents the main lobe width, Side lobe level represents the side lobe level, dB represents decibels, deg represents degrees, farfield represents the far field, and Theta Degree vs. dB represents the angle in decibels (Theta - dB). Figure 4a The zero point is at 5.5°. Figure 4b The zero point is approximately -6°, and as Figure 2 The reflection loss of the array element shown is close to 0, which proves that the multi-channel array radar combined with digitally coded metamaterials can achieve flexible control of the main lobe null position while minimizing the loss of transmitted signal energy. Figure 5 , Figure 6 The distribution of the target and the interference before and after the anti-jamming of the array radar based on electromagnetic metamaterials provided by this invention is shown, proving that the system can effectively resist main lobe interference. Figure 7 The comparison of the signal-to-interference-plus-noise ratio (SIR) of the array radar based on electromagnetic metamaterials provided by this invention with that of MIMO radar based on conventional materials demonstrates that this invention can effectively improve the SIR.

[0163] This invention also provides an array radar based on electromagnetic metamaterials, comprising:

[0164] Beamformer and multiple spatial coding units based on electromagnetic metamaterials.

[0165] The process of building a beamformer includes:

[0166] Based on the target search results in the target airspace, the time-domain coding coefficients of each false target are determined according to the conditions for the occurrence of null points in the transmit beam pattern corresponding to each false target in the target airspace and the maximum permissible deviation of each false target relative to the mismatch frequency. Based on each time-domain coding coefficient, the weight vector of the beamformer is determined, and the beamformer is constructed based on the weight vector of the beamformer.

[0167] The process of determining the phase of each spatial coding unit includes:

[0168] Based on the maximum permissible deviation of each false target relative to the mismatch frequency, the original transmitted signal is compensated to form a first transmitted signal; the transmission steering vector of the first transmitted signal is determined, and based on the maximum permissible deviation of the transmission spatial frequency and mismatch frequency of the null region of each false target's transmission beammap, as well as the transmission steering vector of the first transmitted signal, the null region of each false target's transmission beammap is widened to obtain the target weight vector corresponding to each widened null region; based on each target weight vector, a second transmitted signal is determined; based on the second transmitted signal and preset phase constraint conditions, the phase of each spatial coding unit in the array radar based on electromagnetic metamaterials is determined.

[0169] The present invention also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps provided in the above-described method embodiments.

[0170] The present invention also provides a program product that, when executed by a processor, implements the steps provided in the above method embodiments.

[0171] For embodiments of devices / electronic devices / storage media / program products, since they are basically similar to method embodiments, the description is relatively simple. For specific details and beneficial effects, please refer to the description of the method embodiments.

[0172] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0173] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A space-time coded digital modulation anti-interference method for array radar based on electromagnetic metamaterials, characterized in that, include: Based on the target search results in the target airspace, the time-domain coding coefficients of each false target are determined according to the conditions for the occurrence of null points in the transmitted beam pattern and the maximum permissible deviation of each false target relative to the mismatch frequency. Based on each of the time-domain coding coefficients, the weight vector of the beamformer is determined, and the beamformer is constructed based on the weight vector of the beamformer. Based on the maximum permissible deviation of each of the dummy targets relative to the mismatch frequency, the original transmitted signal is compensated to form the first transmitted signal; Based on the transmission spatial frequency of the null region corresponding to each of the false targets and the maximum permissible deviation relative to the mismatch frequency, and the first transmission signal, the null region of the transmission beam pattern of each of the false targets is widened to obtain the target weight vector corresponding to each widened null region. The second transmission signal is determined based on the target weight vectors described above; According to the pattern product theorem for array antennas, the field function of the coded metasurface of the electromagnetic metamaterial-based array radar is determined as follows: ， in, This represents the field function of the coded metasurface in an array radar based on electromagnetic metamaterials. This represents the field function of each superunit. Indicates the elevation angle of the reflected beam. Indicates the azimuth angle of the reflected beam. and These correspond to the number of sequences in the horizontal and vertical directions of the superunit, respectively. Indicates the sequence number is The reflection phase of the coding unit, Indicates the supercell period. Represents the space wavenumber. Indicates the number of array elements. To represent a complex number, Represents an exponential function; Based on the field function of the coded metasurface, the direction coefficients of the coded metasurface are determined, and are expressed as follows: ， in, Indicates the orientation coefficient of the encoded metasurface; The initial phase of each spatial coding unit in the electromagnetic metamaterial-based array radar is determined based on the field function and the direction coefficient of the coding metasurface. The initial phase of each spatial coding unit is discretized according to a preset discretization criterion to obtain the phase of each spatial coding unit. The electromagnetic metamaterial-based array radar is constructed based on the phase of each spatial coding unit and the beamformer. The electromagnetic metamaterial-based array radar is used to generate and transmit the second transmitted signal, and to suppress interference in the received signal through the beamformer.

2. The method according to claim 1, characterized in that, The target search results based on the target spatial domain, according to the conditions for the occurrence of null points in the transmit beammap and the maximum permissible deviation of each false target relative to the mismatch frequency, determine the time-domain coding coefficients of each false target, including: For any number A false goal: Adjust the first The temporal coding coefficients of the first false target make the first false target... The emission spatial frequency corresponding to the first dummy target is equal to the first... The maximum permissible deviation of the dummy target relative to the mismatch frequency makes the first... The emission beam pattern of the first dummy target shows a null point, thus obtaining the first... The final temporal coding coefficients of the dummy targets, The first The final temporal coding coefficients of the dummy targets are expressed as: ， in, Represents the time-domain coding coefficients. Indicates the first The difference in the number of delayed pulses between a false target and a real target. , This indicates the number of transmitting array elements.

3. The method according to claim 1 or 2, characterized in that, The weight vector of the beamformer is expressed as: ， in, Indicates the direction of the target. Indicates the receiving guide vector. , Represents the time-domain coding coefficients. The number of pulse delays representing the actual target. Represent the true objective. This represents the launch guidance vector of the actual target after compensating for the phase difference between array elements. Represents the Kronecker product. This indicates the pulse coding method of the array elements.

4. The method according to claim 1, characterized in that, The method involves widening the null regions of the transmission beammaps of each false target based on the transmission spatial frequency of the null region corresponding to each false target, the maximum permissible deviation relative to the mismatch frequency, and the first transmission signal, to obtain the target weight vector corresponding to each widened null region, expressed as: ， ， in, , Represents the weight vector, with superscript. This indicates the conjugate transpose. express Any transmission frequency in the space, Indicates the first Arbitrary directional vectors in zero-point regions Describes the Euclidean norm. Indicates the predefined zero-point depth. This represents the final optimized target weight vector. This represents the launch guidance vector of the real target after compensation. Indicates the actual launch frequency of the target after compensation. Indicates the first The actual launch frequency of the dummy target Indicates the first The set of transmission spatial frequencies in the zero-point region Indicates the maximum permissible deviation relative to the mismatch frequency, subscript Indicates the pulse duration. Indicates the number of transmitting array elements. This indicates a constraint condition.

5. The method according to claim 4, characterized in that, The preset discretization criterion is: ， in, Represents the discretized phase. This indicates the actual phase of the coding unit.

6. The method according to claim 4, characterized in that, Spatial coding unit The initial phase is expressed as: ， in, Spatial coding unit phase, Spatial coding unit The phase without compensation, Spatial coding unit The corresponding feed simulation plane wave compensation phase ， ， Describes the wave vector in free space. Spatial coding unit Geometric coordinates relative to the origin This indicates the azimuth angle to which the main lobe of the beam points. This indicates the pitch angle pointing to the main lobe of the beam. Indicates the feed height. This represents the phase difference caused by the height of the feed source to the metasurface.

7. An array radar based on electromagnetic metamaterials, characterized in that, include: Beamformer and multiple spatial coding units based on electromagnetic metamaterials; The process of constructing the beamformer includes: Based on the target search results in the target airspace, the time-domain coding coefficients of each false target are determined according to the conditions for the occurrence of null points in the transmit beam pattern and the maximum permissible deviation of each false target relative to the mismatch frequency; the weight vector of the beamformer is determined according to the time-domain coding coefficients, and the beamformer is constructed according to the weight vector of the beamformer. The process of determining the phase of each of the spatial coding units includes: Based on the maximum permissible deviation of each dummy target relative to the mismatch frequency, the original transmitted signal is compensated to form a first transmitted signal; based on the transmitted spatial frequency of the null region corresponding to each dummy target and the maximum permissible deviation relative to the mismatch frequency, and the first transmitted signal, the null region of the transmitted beam pattern of each dummy target is widened to obtain the target weight vector corresponding to each widened null region; based on each target weight vector, a second transmitted signal is determined. According to the pattern product theorem for array antennas, the field function of the coded metasurface of the electromagnetic metamaterial-based array radar is determined as follows: ， in, This represents the field function of the coded metasurface in an array radar based on electromagnetic metamaterials. This represents the field function of each superunit. Indicates the elevation angle of the reflected beam. Indicates the azimuth angle of the reflected beam. and These correspond to the number of sequences in the horizontal and vertical directions of the superunit, respectively. Indicates the sequence number is The reflection phase of the coding unit, Indicates the supercell period. Represents the space wavenumber. Indicates the number of array elements. To represent a complex number, Represents an exponential function; Based on the field function of the coded metasurface, the direction coefficients of the coded metasurface are determined, and are expressed as follows: ， in, Indicates the orientation coefficient of the encoded metasurface; The initial phase of each spatial coding unit in the electromagnetic metamaterial-based array radar is determined based on the field function and the direction coefficient of the coding metasurface. The initial phase of each spatial coding unit is discretized according to a preset discretization criterion to obtain the phase of each spatial coding unit.

8. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, implements the method described in any one of claims 1-6.

9. A program product, characterized in that, The program product includes computer program instructions, which, when executed, enable the implementation of the method as described in any one of claims 1-6.

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