Imaging radar confrontation method based on amplitude programmable metasurface

Abstract

The invention discloses an imaging radar confrontation method based on an amplitude programmable metasurface, and relates to the field of artificial electromagnetic meta-structure materials, and the method comprises the steps: determining the operation parameters of an imaging radar and a regulation mode selected by a user; a modulation gene sequence is generated according to the operation parameters and the selected regulation and control mode, and a corresponding voltage waveform is generated according to the modulation gene sequence and input into the amplitude programmable metasurface; the amplitude programmable metasurface switches reflection and absorption states according to an input signal to interfere with a radar echo signal. According to the method, diversified amplitude programmable metasurface modulation strategies are constructed, and key technical support is provided for construction of a new-generation intelligent electromagnetic war system.

Description

Technical Field

[0001] The present invention relates to the technical field of artificial electromagnetic metamaterials, and more specifically to an imaging radar countermeasure method based on an amplitude-programmable metasurface. Background Art

[0002] Radar imaging technology has the characteristics of all-weather, all-day, and high precision, and can depict fine geometric features such as the size, external contour, and posture of a target, playing an important role in military and civilian scenarios such as military reconnaissance, situation awareness, and remote sensing mapping. High-value targets on the ground face the risk of being exposed during peacetime and wartime. How to control the radar characteristics of high-value targets to deceive and interfere with radars has become a key topic and urgent task in the field of radar electronic countermeasures.

[0003] Existing imaging radar jamming technologies mainly include two categories: active jamming and passive jamming. Active jamming relies on a high-power transmitter to actively emit electromagnetic waves to suppress the radar with noise, deceive the radar in a large scene, etc. On the one hand, it relies on the emission of high-power signals, which requires high costs and is prone to exposure under aerospace reconnaissance conditions; on the other hand, it highly depends on the accuracy of reconnaissance information, requires high capabilities for acquiring and processing information, and has a high computational cost. Passive jamming does not actively emit electromagnetic signals and mainly achieves the purpose of disrupting radar reconnaissance by generating false echoes, high-intensity echoes, or weakening reflected echoes in multiple ways such as reflecting radar signals. Currently, commonly used passive protection systems mainly include chaff, corner reflectors, camouflage nets, absorbing materials, etc. However, once they are manufactured, their electromagnetic scattering characteristics are relatively fixed, and it is impossible to achieve real-time, flexible, and complex regulation of radar echoes. Due to its flexible electromagnetic regulation characteristics, the electromagnetic metasurface can combine the two traditional methods to construct a simple and lightweight radar jamming architecture, realizing the regulation of the radar characteristics of real targets and the generation of false targets, and overcoming problems such as power consumption, cost, and efficiency of traditional methods.

[0004] However, existing electromagnetic metasurface solutions mostly weaken or enhance echo signals from a single dimension of energy regulation or spatial coding, lacking targeted analysis of radar operating modes and signal characteristics, and it is difficult to adapt to the countermeasure requirements of multiple types of detection systems. Secondly, existing research on time-modulated metasurfaces focuses on velocity deception or the generation of one-dimensional range image false targets, but its theoretical model is usually based on ideal assumptions of normal incidence of electromagnetic waves and single polarization. In actual electronic countermeasure scenarios, radars often use oblique incidence detection and full-polarization transceiver modes, and the interference efficiency of metasurface units decreases or even fails due to changes in the incident angle or polarization sensitivity. In addition, existing time modulation schemes are mostly limited to periodic square wave switching within a single radar pulse, lacking in-depth exploration of inter-pulse agile coding, intra-pulse - inter-pulse joint modulation, and aperiodic sequences, which results in too high temporal correlation of interference signals and is easily detected or suppressed by the radar terminal.

[0005] Therefore, how to solve the problems of angular stability and polarization sensitivity in metasurface regulation, so as to realize diversified radar jamming modes, is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the present invention provides an imaging radar countermeasure method based on an amplitude-programmable metasurface, which solves the problems of angular sensitivity and polarization sensitivity of the programmable metasurface, and constructs diversified modulation strategies, providing key technical support for the construction of a new generation of intelligent electromagnetic warfare systems.

[0007] In order to achieve the above object, the present invention provides the following technical solutions: The present invention discloses an imaging radar countermeasure method based on an amplitude-programmable metasurface, and the specific steps are as follows: Determine the operating parameters of the imaging radar and the regulation method selected by the user; Generate a modulation gene sequence according to the operating parameters and the selected regulation method, and generate a corresponding voltage waveform according to the modulation gene sequence and input it into the amplitude-programmable metasurface; The amplitude-programmable metasurface switches between reflection and absorption states according to the input signal to interfere with the radar echo signal.

[0008] Furthermore, the amplitude-programmable metasurface has a two-layer structure, and an air spacer layer is also provided between the first layer structure and the second layer structure; The top layer of the first layer structure is composed of two four-open metal rings. A PIN diode and a resistor are provided at each opening of the two four-open metal rings, and the four-open metal rings are connected in series to form a complete ring. The inner and outer rings are connected by an inductor; the lower layer of the first layer structure is a dielectric substrate; The top layer of the second layer structure is composed of a four-open metal ring. A PIN diode and a resistor are provided at each opening of the four-open metal ring, and the four-open metal ring is connected in series to form a complete ring; the middle layer of the second layer structure is a dielectric substrate; the lower layer of the second layer structure is a metal bottom plate; By controlling the on and off states of the PIN diodes of each of the four-open metal rings, the coding state of the amplitude-programmable metasurface is controlled.

[0009] Furthermore, the operating parameters include: the starting working frequency , bandwidth B, pulse width , frequency sampling points N , the distance where the metasurface is placed , the moving length of the imaging radar slide rail L , moving speed v , total number of pulses M; The mathematical expression of the radar transmitted signal is: ; Where, represents the fast time within a pulse, represents the slow time between pulses, j is the imaginary unit, represents the chirp rate, rect represents the rectangular pulse window function; The undisturbed baseband echo signal is expressed as: ; Where, represents the total time of radar imaging, c represents the speed of light.

[0010] Furthermore, the regulation methods include: The first regulation method: control the amplitude-programmable metasurface to be in the wave-absorbing state through a DC voltage, absorb the electromagnetic wave energy under the conditions of an imaging radar to reduce the target scattering intensity, and achieve radar stealth; The second regulation method: apply the same regulated voltage waveform to the amplitude-programmable metasurface within each pulse of the imaging radar to generate false targets in the range direction of the imaging radar; The third regulation method: apply different regulated voltages to the amplitude-programmable metasurface between pulses of the imaging radar, make the amplitude-programmable metasurface be in a relatively static state of absorption or reflection within each pulse, and generate false targets in the azimuth direction of the imaging radar; The fourth regulation method: conduct regulation simultaneously within and between pulses of the imaging radar, apply the same regulated voltage waveform within pulses with a quantity of to make the reflection amplitude of the amplitude-programmable metasurface switch rapidly, apply a DC regulated voltage within pulses with a quantity of to make the amplitude-programmable metasurface maintain a relatively static state of reflection or absorption, and generate false targets in the range and azimuth directions of the imaging radar; The fifth regulation method: conduct non-periodic random sequence regulation within and between pulses of the imaging radar, generate an amplitude coding sequence according to probability, make the amplitude-programmable metasurface randomly modulate the imaging radar reflection signal, generate a large number of dense dot targets in the azimuth and range directions of the imaging radar, and achieve the stealth of its own target under the imaging radar; The sixth regulation method: conduct modulation with frequency agility of the voltage waveform within and between pulses of the imaging radar, each pulse corresponds to a voltage modulation waveform with a different frequency, and the frequencies of the voltage waveforms are different between different pulses, and generate diverse two-dimensional false targets on the imaging radar.

[0011] Furthermore, in the first regulation method, the expression of the modulation gene is: ; where, A represents the reflection amplitude of the metasurface, taking values of 0 or 1; the modulation gene sequence of the first modulation method is expressed as: , with a size of M ; The expression of the baseband signal after modulation by the first modulation method is: ; The expression of the final radar image result of the first modulation method is: ; where, represents the sinc function, represents the azimuth modulation frequency, represents the total radar imaging time.

[0012] Furthermore, in the second modulation method, the in-pulse metasurface modulation signal is a periodic voltage modulation signal, using one of a square wave, a triangular wave, a sawtooth wave, and a sequence pulse. Expanded by the Fourier series, the mathematical expression is: ; where, represents the modulation frequency, n is the order of the Fourier series, represents the coupling coefficient of the Fourier series coefficient and the reflection amplitude of the amplitude-programmable metasurface, including the information of the Fourier series and the state of the metasurface reflection amplitude; The modulation gene sequence of the second modulation method is expressed as: , with a size of M ; The expression of the baseband signal after modulation by the second modulation method is: ; where, represents the undisturbed baseband echo signal; After being processed by the range-direction matching filter, the mathematical expression is: ; After being processed by migration correction and azimuth-direction matching filter, the expression of the final radar image result of the second modulation method is: ; where, is the phase of the signal after range-direction matching filtering; is the coefficient representing the intensity of the peak, represents the sinc function, represents the azimuth modulation frequency, represents the total radar imaging time.

[0013] Further, in the third modulation method, a periodic square wave or periodic sequence is selected for the inter-pulse modulation of the imaging radar. When the state of the square wave or periodic sequence for inter-pulse modulation is 1, it indicates that the amplitude-programmable metasurface is in the reflection state within the corresponding pulse; when the state of the square wave or periodic sequence for inter-pulse modulation is 0, it indicates that the amplitude-programmable metasurface is in the wave-absorbing state within the corresponding pulse. The modulation gene sequence of the third modulation method is expressed as: , with a size of M , where is the reflection amplitude in the reflection state, is the reflection amplitude in the wave-absorbing state; The mathematical expression for the Fourier series expansion of the periodic modulation signal between pulses is: ; Among them, represents the coupling coefficient between the Fourier series coefficient of the inter-pulse signal and the reflection amplitude of the amplitude-programmable metasurface, m is the order of the Fourier series, is the frequency of the inter-pulse modulation; The expression of the baseband signal after modulation by the third modulation method is: ; Among them, represents the baseband echo signal without interference; The expression of the final radar image result of the third modulation method is: ; Among them, represents the phase value of the radar imaging result, is the coefficient representing the intensity of the peak, represents the sinc function, represents the azimuth modulation frequency, represents the total radar imaging time.

[0014] Further, in the fourth modulation method, one of the waveforms of a square wave or a triangular wave is selected as the radar intra-pulse modulation waveform gene , and the mathematical expression for its Fourier series expansion is: ; Among them, represents the modulation frequency, z is the order of the Fourier series, represents the coupling coefficient between the Fourier series coefficient and the reflection amplitude of the amplitude-programmable metasurface, including the information of the Fourier series and the state of the metasurface reflection amplitude; Select a periodic square wave or periodic sequence for imaging radar inter-pulse modulation. When the state of the square wave or periodic sequence for inter-pulse modulation is 1, it indicates that intra-pulse modulation is performed within the corresponding pulse; when the state of the square wave or periodic sequence for inter-pulse modulation is 0, it indicates that intra-pulse modulation is not required within the corresponding pulse, and it is in a relatively stationary wave-absorbing or reflecting state; the periodic modulation signal between pulses The mathematical expression for Fourier series expansion is: ; where represents the coupling coefficient between the Fourier series coefficient of the inter-pulse signal and the reflection amplitude of the amplitude-programmable metasurface, m is the order of the Fourier series, is the frequency of inter-pulse modulation; The modulation gene sequence of the fourth modulation method is expressed as: , with a size of M ; The expression of the baseband signal after modulation by the fourth modulation method is: ; The expression of the final radar image result of the fourth modulation method is: ; where F represents the amplitude value of the radar imaging result, represents the phase value of the radar imaging result, represents the sinc function, represents the azimuth modulation frequency, represents the total radar imaging time.

[0015] Furthermore, in the fifth modulation method, the random sequence signal within the o th radar pulse is denoted as , and the radar pulse is divided into parts, with a time length of . Within each pulse width and appear with probabilities of P and 1 - P , represents the time-domain function with a reflection coefficient of represents the time-domain function with a reflection coefficient of , and the sequence signal within the pulse is expressed as: ; where ; The modulation gene sequence of the fifth modulation method is expressed as: , with a size ofM 。

[0016] Further, in the sixth regulation method, a voltage regulation waveform is randomly selected from a square wave, triangular wave, and sawtooth wave waveform library, and a modulation frequency and duty cycle are randomly selected from a waveform parameter library to obtain the voltage modulation signal within the m th radar pulse , and the voltage regulation signals corresponding to M pulses are combined to obtain the modulation gene sequence of the sixth regulation method: ; The expression of the baseband signal after modulation by the sixth regulation method is: 。

[0017] As can be seen from the above technical solutions, compared with the prior art, the present invention discloses an imaging radar countermeasure method based on an amplitude-programmable metasurface, and its beneficial effects are as follows: 1. Considering the scenarios of radar oblique incidence and full-polarization detection, the metasurface unit maintains stable amplitude switching under oblique incidence and full polarization. The metasurface has a reflection state and an absorbing state, with the dual interference effects of direct stealth in the absorbing state and reflection-absorbing time-modulated deception; 2. For high-precision imaging radars, a multi-dimensional interference fusion framework of intra-pulse, inter-pulse, and combined timing modulation is built. Combining periodic sequences, random sequences, and frequency-agile waveforms, a gene library of modulation waveforms is formed. Through the combination of different modulation waveform genes, the generation and deformation of false targets in the two-dimensional imaging domain can be realized. The present invention constructs a diversified amplitude-programmable metasurface modulation strategy, providing key technical support for the construction of a new generation of intelligent electromagnetic warfare systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0019] Figure 1 It is a schematic diagram of the overall process of an embodiment of the present invention.

[0020] Figure 2a It is a top view of the first layer structure of the unit of the amplitude-programmable metasurface according to an embodiment of the present invention.

[0021] Figure 2b It is a top view of the second layer structure of the unit of the amplitude-programmable metasurface according to an embodiment of the present invention.

[0022] Figure 2cSide view of the overall unit structure of the amplitude-programmable metasurface according to an embodiment of the present invention.

[0023] Figure 3 Schematic diagram of the reflection amplitude response curve of the metasurface according to an embodiment of the present invention in the on and off states of the PIN diode.

[0024] Figure 4 Schematic diagram of the imaging radar simulation results of the amplitude-programmable metasurface in the total reflection state according to an embodiment of the present invention.

[0025] Figure 5 Schematic diagram of the imaging radar simulation results of the amplitude-programmable metasurface in the wave-absorbing state according to an embodiment of the present invention.

[0026] Figure 6 Schematic diagram of the imaging radar simulation results of the amplitude-programmable metasurface with in-pulse periodic sequence modulation according to an embodiment of the present invention.

[0027] Figure 7 Schematic diagram of the imaging radar simulation results of the amplitude-programmable metasurface with inter-pulse periodic sequence modulation according to an embodiment of the present invention.

[0028] Figure 8 Schematic diagram of the imaging radar simulation results of the amplitude-programmable metasurface with in-pulse modulation and inter-pulse intermittent two-dimensional modulation according to an embodiment of the present invention.

[0029] Figure 9 Schematic diagram of the imaging radar simulation results of the amplitude-programmable metasurface with in-pulse and inter-pulse two-dimensional aperiodic random sequence modulation according to an embodiment of the present invention.

[0030] Figure 10 Schematic diagram of the imaging radar simulation results of the amplitude-programmable metasurface with in-pulse modulation and inter-pulse voltage waveform frequency agility two-dimensional modulation according to an embodiment of the present invention.

[0031] In the figure, 1. resistor; 2. inductor; 3. PIN diode; 4. dielectric substrate; 5. air spacer; 6. metal bottom plate. Detailed implementation manners

[0032] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0033] An embodiment of the present invention discloses an imaging radar countermeasure method based on an amplitude-programmable metasurface, as Figure 1 shown, and the specific steps are as follows: Determine the operating parameters of the imaging radar and the control method selected by the user; Generate a modulated gene sequence according to the operating parameters and the selected control method, and generate a corresponding voltage waveform input to the amplitude programmable metasurface according to the modulated gene sequence; The amplitude programmable metasurface switches between reflection and absorption states according to the input signal to interfere with the radar echo signal.

[0034] In a specific embodiment, such as Figure 2a 、 Figure 2b 、 Figure 2c As shown, the amplitude programmable metasurface is a two-layer structure, and an air spacer layer 5 is also provided between the first layer structure and the second layer structure; The top layer of the first layer structure is composed of two four-open metal rings. A PIN diode 3 and a resistor 1 are provided at each opening of the two four-open metal rings to connect the four-open metal rings in series into a complete ring, and the inner and outer rings are connected by an inductor 2; the lower layer of the first layer structure is a dielectric substrate 4; The top layer of the second layer structure is composed of a four-open metal ring. A PIN diode 3 and a resistor 1 are provided at each opening of the four-open metal ring to connect the four-open metal rings in series into a complete ring; the middle layer of the second layer structure is a dielectric substrate 4; the lower layer of the second layer structure is a metal bottom plate 6; By controlling the on and off states of the PIN diodes 3 of each four-open metal ring, the coding state of the amplitude programmable metasurface is controlled.

[0035] Specifically, the amplitude programmable metasurface as a whole includes basic units. The entire metasurface has a total of n control links. The m units in each column share the same control link in series. The control link is composed of a field programmable gate array FPGA and a voltage amplifier. The two metal four-open rings on the top layer of the first layer structure of the amplitude programmable metasurface are printed on an F4B350 dielectric substrate 4 with a dielectric constant of 3.5, a loss tangent of 0.001, and a thickness of ; a PIN diode 3 (model: SMP1320-079LF) and a resistor 1 (resistance value: 130 ohms) are welded side by side at the ring opening, and an inductor 2 (inductance value: 12 nH) is welded between the inner and outer rings. The top layer of the second layer structure consists of a metal four-open ring, which is printed on an F4B350 dielectric substrate 4 with a dielectric constant of 3.5, a loss tangent of 0.001, and a thickness of ; the device mounting at the opening is the same as that of the first layer structure, and the bottom layer is a metal bottom plate 6; the middle of the two layers is an air spacer layer 5 with a height of . Among them, the side length p of the metasurface unit is 15 mm; the radii of the two metal four-open rings in the first layer structure are respectively , ; The radius of the metal four-open-ring in the second layer structure is ; The line width of the metal four-open-ring is , the opening width , the line width at the opening , the length of the opening gap .

[0036] When the amplitude-programmable metasurface is under incident angles from 0° to 45°, the reflection amplitudes of the PIN diodes in different states are as Figure 3 shown. In the figure, (a) is the result of horizontal polarization, and (b) is the result of vertical polarization. Under horizontal polarization, the metasurface can achieve amplitude encoding of reflection and wave absorption states within 6.5 GHz to 8.8 GHz; under vertical polarization, the metasurface can achieve amplitude encoding of reflection and wave absorption states within 7.6 GHz to 10.1 GHz.

[0037] In a specific embodiment, the operating parameters include: the starting frequency of the LFM signal of the imaging radar, the bandwidth B, the pulse width , the number of frequency sampling points N , the distance where the metasurface is placed , the moving length of the imaging radar sliding rail L , the moving speed v , the total number of pulses M ; The mathematical expression of the radar transmitted signal is: ; Among them, represents the fast time within the pulse, represents the slow time between pulses, j is the complex unit, represents the frequency modulation rate, rect represents the rectangular pulse window function.

[0038] The undisturbed baseband echo signal is expressed as: ; Among them, represents the total radar imaging time, c represents the speed of light.

[0039] In a specific embodiment, the regulation methods include: The first regulation method is to control the amplitude-programmable metasurface to be in the wave absorption state through a DC voltage, absorb the electromagnetic wave energy under the imaging radar conditions to reduce the target scattering intensity, and achieve radar stealth; The second regulation method is to apply the same regulated voltage waveform to the amplitude-programmable metasurface within each pulse of the imaging radar to generate false targets in the range direction of the imaging radar; The third control method is to apply different control voltages to the amplitude-programmable metasurface during the inter-pulse period of the imaging radar, keeping the amplitude-programmable metasurface in a relatively static state of absorption or reflection within each pulse, and generating false targets in the azimuth direction of the imaging radar. The fourth control method is to perform control simultaneously during the intra-pulse and inter-pulse periods of the imaging radar. Apply the same control voltage waveform within the pulses with a quantity of to make the amplitude of the amplitude-programmable metasurface reflect quickly switch, and apply a DC control voltage within the pulses with a quantity of to keep the amplitude-programmable metasurface in a relatively static state of reflection or absorption, and generate false targets in the range and azimuth directions of the imaging radar. The fifth control method is to perform non-periodic random sequence control during the intra-pulse and inter-pulse periods of the imaging radar, generating an amplitude coding sequence according to probability, making the amplitude-programmable metasurface randomly modulate the reflected signal of the imaging radar, generating a large number of dense dot targets in the azimuth and range directions of the imaging radar, and achieving the stealth of its own target under the imaging radar. The sixth control method is to perform modulation with frequency agility of the voltage waveform during the intra-pulse and inter-pulse periods of the imaging radar. Each pulse corresponds to a voltage modulation waveform with a different frequency, and the frequencies of the voltage waveforms are different between different pulses, generating diverse two-dimensional false targets on the imaging radar.

[0040] In a specific embodiment, in the first control method, using the amplitude-programmable metasurface, according to the control waveform genome: without voltage waveform modulation, making it in the wave-absorbing state, absorbing electromagnetic wave energy under the imaging radar conditions to achieve radar stealth.

[0041] Specifically, after determining the radar transmit signal expression, determine the waveform of the metasurface modulation. At this time, for M pulses, the state of the metasurface within the pulse is the wave-absorbing or reflecting state, and the corresponding intra-pulse modulation waveform is a 0V or 36V DC voltage. Use this waveform as the modulation gene to form a gene sequence of size M to control the amplitude-programmable metasurface. The expression of the modulation gene is: ; where A represents the reflection amplitude of the metasurface, taking values of 0 or 1; the modulation gene sequence of the first control method is expressed as: , with a size of M.

[0042] After being modulated by the amplitude-programmable metasurface, the radar echo is mixed from radio frequency to intermediate frequency and band-pass filtered to obtain the baseband signal. The expression of the baseband signal after modulation by the first control method is: ; After being modulated by the amplitude-programmable metasurface, after range-direction matched filtering, azimuth-direction FFT, range migration correction, and azimuth-direction matched filtering, the final image result expression of the radar by the first control method is: ; in, represents the Symle function, Indicates the azimuth modulation frequency, Indicates the total radar imaging time.

[0043] like Figure 4 As shown, when the modulation genomes of the amplitude programmable metasurface are all in the reflective state, , we can analyze the location of the super surface as , the strong reflection points caused by the metasurface can be observed in the image; Figure 5 As shown in Figure 2, when the modulation genomes of the amplitude programmable metasurface are all in the wave absorbing state, , the strong reflection points on the image disappear and invisibility is achieved.

[0044] In a specific embodiment, in the second control method, an amplitude-programmable metasurface is used, and according to the control waveform genome: the same control voltage waveform is applied in each pulse to achieve the generation of false targets in the imaging radar range upward.

[0045] Specifically, the radar detection method, basic parameters, signal expression and metasurface placement are consistent with the first control method. For the case of modulation within the imaging radar pulse, the reflection state of the amplitude programmable metasurface changes according to the change of voltage, and its change law is the same within M pulses. The metasurface modulation signal within the pulse It is a periodic voltage modulation signal, using one of square wave, triangle wave, sawtooth wave, and sequence pulse. Using Fourier series expansion, the mathematical expression is: ; in, represents the modulation frequency, n is the order of the Fourier series, The coupling coefficient representing the Fourier series coefficient and the reflection amplitude of the amplitude programmable metasurface contains the information of the Fourier series and the state of the reflection amplitude of the metasurface.

[0046] The determined periodic voltage modulation waveform is used as a gene. Since each pulse is modulated by the amplitude programmable metasurface according to the same rule, the modulation gene sequence of the second control mode is expressed as: , the size is M .

[0047] When the modulation frequency When it is smaller than the bandwidth of the intermediate frequency bandpass filter of the receiver, the expression of the baseband signal modulated by the second control mode is: ;in, Represents the baseband echo signal without interference.

[0048] After being processed by the range-matching filter, the mathematical expression is: ; After being further processed by migration correction and azimuth-matching filter, the expression of the final radar image result of the second control method is: ; Wherein, is the phase of the signal after range-matching filtering; is the coefficient representing the intensity of the peak, represents the sinc function, represents the azimuth frequency modulation rate, represents the total radar imaging time.

[0049] According to the final imaging result, based on the sinc characteristics of the function envelope, the peak will appear at , Therefore, the distance interval and between any-order false targets can be calculated. In this embodiment, the starting working frequency of the radar, the bandwidth B = 200 MHz, the pulse width , two metasurfaces are placed. One amplitude-programmable metasurface is in the reflection state during the radar operation, and the other amplitude-programmable metasurface is regulated by a square-wave voltage with a frequency and a duty cycle of 0.5, so as to generate false targets arranged at a certain interval in the range direction of the imaging radar as shown in Figure 6 .

[0050] In a specific embodiment, in the third control method, an amplitude-programmable metasurface is used to generate false targets in the azimuth direction of the imaging radar according to the regulation waveform genome: different regulation voltages are applied between pulses, and the reflection state of the metasurface within each pulse is in a relatively static state of absorption or reflection.

[0051] Specifically, for the modulation between radar pulses, a periodic square wave or periodic sequence is selected for the modulation between radar pulses. When the state of the periodic square wave or periodic sequence of the modulation between pulses is 1, it means that the amplitude-programmable metasurface is in the reflection state within the corresponding pulse; when the state of the periodic square wave or periodic sequence of the modulation between pulses is 0, it means that the amplitude-programmable metasurface is in the wave-absorbing state within the corresponding pulse. The modulation gene sequence of the third control method is expressed as: , with a size of M , where is the reflection amplitude in the reflection state, is the reflection amplitude in the wave-absorbing state; The periodic modulation signal The mathematical expression for Fourier series expansion is as follows: ; where represents the coupling coefficient between the Fourier series coefficient of the inter-pulse signal and the reflection amplitude of the amplitude-programmable metasurface, m is the order of the Fourier series, is the frequency of the inter-pulse modulation.

[0052] The expression of the baseband signal after being modulated by the third modulation method is: ; where represents the baseband echo signal without interference.

[0053] After the reflected signal passes through range-direction matching filtering, migration correction, and azimuth-direction matching filtering, the expression of the final radar image result of the third modulation method is: ; where represents the phase value of the imaging result, is the coefficient representing the intensity of the peak, represents the sinc function, represents the azimuth modulation frequency, represents the total radar imaging time.

[0054] According to sinc the envelope characteristics of the function, false targets may appear in the azimuth direction with the same distance as the original target. The interval distance between false targets of any order and . In this embodiment, the starting frequency of the radar is B = 200 MHz, the bandwidth , the pulse width v = 200 m / s; Two metasurfaces are placed. One amplitude-programmable metasurface is in the reflection state during the radar operation, and the other amplitude-programmable metasurface is regulated by a square-wave voltage with a pulse-interval modulation frequency and a duty cycle of 0.5, so as to generate false targets arranged at a certain interval in the azimuth direction of the imaging radar as shown in Figure 7 .

[0055] In a specific embodiment, in the fourth modulation method, an amplitude-programmable metasurface is used. According to the modulation waveform genome: the same modulation voltage waveform is applied within the pulses with the modulation quantity of both within the pulse and between pulses, so that its reflection amplitude can be quickly switched. A DC modulation voltage is applied within the pulses with the quantity of to keep it in a relatively static state of reflection or absorption, thus realizing the generation of false targets in the range and azimuth directions of the imaging radar.

[0056] Specifically, for the intra-pulse modulation of radar, select one of the square wave or triangular wave as the intra-pulse modulation waveform gene of the radar , and the mathematical expression for the Fourier series expansion is: ; where represents the modulation frequency, z is the order of the Fourier series, represents the coupling coefficient between the Fourier series coefficient and the reflection amplitude of the amplitude-programmable metasurface, including the information of the Fourier series and the state of the metasurface reflection amplitude; For the inter-pulse modulation of radar, select a periodic square wave or periodic sequence for the imaging radar inter-pulse modulation. When the state of the square wave or periodic sequence of the inter-pulse modulation is 1, it means that the intra-pulse modulation is performed within the corresponding pulse; when the state of the square wave or periodic sequence of the inter-pulse modulation is 0, it means that the intra-pulse modulation is not required within the corresponding pulse, and it is in a relatively static wave-absorbing or reflecting state; the periodic modulation signal between pulses The mathematical expression for the Fourier series expansion is: ; where represents the coupling coefficient between the Fourier series coefficient of the inter-pulse signal and the reflection amplitude of the amplitude-programmable metasurface, m is the order of the Fourier series, is the frequency of the inter-pulse modulation; The modulation gene sequence of the fourth control method is expressed as: , with a size of M . The expression of the baseband signal after modulation by the fourth control method is: .

[0057] After the reflected signal passes through range migration correction and azimuth matched filtering, the expression of the final radar image result of the fourth control method is: ; where represents the amplitude value of the imaging result, represents the phase value of the radar imaging result, represents the sinc function, represents the azimuth chirp rate, represents the total time of radar imaging.

[0058] Finally, the azimuth distribution and range distribution of the false targets can be obtained. The interval distance and between the false targets of order , the distance interval and between the false targets of order . In this embodiment, the starting operating frequency of the radar , the bandwidth B = 200 MHz, the pulse width , the flight speed of the radar v = 200 m / s; Two metasurfaces are placed. One amplitude-programmable metasurface is in a reflective state during the operation of the radar, and the other amplitude-programmable metasurface is regulated by a square-wave voltage with an inter-pulse modulation frequency and a duty cycle of 0.5, and is regulated by a square-wave voltage with a frequency and a duty cycle of 0.5 within the pulse, so as to generate false targets arranged at certain intervals in the range direction and azimuth direction of the imaging radar as shown in Figure 8 .

[0059] In a specific embodiment, in the fifth regulation method, an amplitude-programmable metasurface is used to perform non-periodic random sequence regulation in the pulse and between pulses according to the regulation waveform genome, and an amplitude coding sequence is generated according to the probabilities and to achieve the stealth of the target under the imaging radar.

[0060] Specifically, the random sequence signal within the o th radar pulse is denoted as , the pulse of the radar is divided into parts, the time length is , and the probabilities of and appearing within each pulse width are P and 1 - P , represents the time-domain function with a reflection coefficient of , represents the time-domain function with a reflection coefficient of , so the sequence signal within the pulse is expressed as: ; where ; The mathematical expression of its power spectrum is: ; Among them, f represents the echo spectrum, represents the spectral width of the time-domain function of the reflection coefficient, represents the waveform spectrum loaded with the reflection coefficient , represents the waveform spectrum loaded with the reflection coefficient , is the unit impulse function.

[0061] The modulation gene sequence of the fifth modulation method is expressed as: , with a size of M .

[0062] The signal modulated by this random sequence, after range - direction matched filtering, migration correction, and azimuth - direction matched filtering, will generate a large number of dense dot - like targets in the azimuth and range directions. Since the energy is distributed at many false positions, the energy of the original target will be reduced, and its amplitude is related to the probability and the frequency - domain distribution of the modulation waveform. In this embodiment, the starting operating frequency of the radar , bandwidth , pulse width , the flight speed of the radar ; Place two metasurfaces. One amplitude - programmable metasurface is in the reflection state during the radar operation, and the other amplitude - programmable metasurface is modulated by the reflection or absorption state with a probability of 50%. The modulation pulse width , to achieve the generation of false targets arranged at certain intervals in the range and azimuth directions of the imaging radar as shown in Figure 9 .

[0063] In a specific embodiment, in the sixth modulation method, an amplitude - programmable metasurface is used to modulate the voltage waveform frequency agility intra - pulse and inter - pulse according to the modulation waveform genome, and different - frequency voltage modulation waveforms correspond to each pulse, realizing the diversified generation of two - dimensional false targets of the imaging radar.

[0064] Specifically, randomly select the voltage modulation waveform from the waveform libraries of square wave, triangular wave, and sawtooth wave, and randomly select the modulation frequency and duty cycle from the waveform parameter library to obtain the voltage modulation signal m within the th radar pulse. Combine the voltage modulation signals corresponding to the M pulses to obtain the modulation gene sequence of the sixth modulation method: ; The expression of the baseband signal modulated by the sixth modulation method is: .

[0065] Since this modulation modulates different waveforms intra - pulse, false targets will be generated in the range direction. At the same time, there are differences in the modulation waveforms between different pulses in the azimuth direction, so false targets at different positions will also be generated in the azimuth direction. In this embodiment, the intra - pulse modulation of the amplitude - programmable metasurface is a square wave, but with different modulation frequencies. This genome can be quantified from the frequency type as [5, 4, 5, 8, 5, 3, … repeating …, 5, 4, 5, 8, 5, 3], to achieve as shown in Figure 10As shown, false targets with diverse arrangements are generated in the range and azimuth directions of the imaging radar.

[0066] In this specification, each embodiment is described in a progressive manner. The key point of each embodiment is the difference from other embodiments. For the same or similar parts among the embodiments, reference can be made to each other. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple. For the relevant parts, reference can be made to the description in the method section.

[0067] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An imaging radar countermeasure method based on amplitude-programmable metasurface, characterized in that, The specific steps are as follows: Determine the operating parameters of the imaging radar and the control method selected by the user; Generate a modulation gene sequence according to the operating parameters and the selected control method, and generate a corresponding voltage waveform according to the modulation gene sequence and input it into the amplitude-programmable metasurface; The amplitude-programmable metasurface switches between reflection and absorption states according to the input signal to interfere with the radar echo signal.

2. The imaging radar countermeasure method based on an amplitude-programmable metasurface according to claim 1, wherein The amplitude-programmable metasurface has a two-layer structure, and an air spacer layer is also provided between the first layer structure and the second layer structure; The top layer of the first layer structure is composed of two four-open metal rings. A PIN diode and a resistor are provided at each opening of the two four-open metal rings, and the four-open metal rings are connected in series to form a complete ring. The inner and outer rings are connected by an inductor; the lower layer of the first layer structure is a dielectric substrate; The top layer of the second layer structure is composed of a four-open metal ring. A PIN diode and a resistor are provided at each opening of the four-open metal ring, and the four-open metal ring is connected in series to form a complete ring; the middle layer of the second layer structure is a dielectric substrate; the lower layer of the second layer structure is a metal bottom plate; By controlling the on and off states of the PIN diodes of each of the four-open metal rings, the coding state of the amplitude-programmable metasurface is controlled.

3. A method for imaging radar countermeasure based on amplitude-programmable metasurface according to claim 1, characterized in that, The operating parameters include: the starting frequency of the LFM signal of the imaging radar , the bandwidth B, the pulse width , the number of frequency sampling points N , the distance where the metasurface is placed , the moving length of the imaging radar slide rail L , the moving speed v , the total number of pulses M ; The mathematical expression of the radar transmitted signal is: ； Among them, represents the fast intra-pulse time, represents the slow inter-pulse time, j is a complex unit, represents the chirp rate, rect represents the rectangular pulse window function; The undisturbed baseband echo signal is expressed as: ； Among them, represents the total radar imaging time, c represents the speed of light.

4. A method for imaging radar countermeasure based on amplitude-programmable metasurface according to claim 3, characterized in that The control methods include: The first control method: control the amplitude-programmable metasurface to be in the wave-absorbing state through a DC voltage, absorb electromagnetic wave energy under the conditions of the imaging radar to reduce the target scattering intensity, and achieve radar stealth; The second control method: apply the same control voltage waveform to the amplitude-programmable metasurface within each pulse of the imaging radar to generate false targets in the range direction of the imaging radar; The third control method: apply different control voltages to the amplitude-programmable metasurface between pulses of the imaging radar, and make the amplitude-programmable metasurface in a relatively static state of absorption or reflection within each pulse to generate false targets in the azimuth direction of the imaging radar; The fourth control method is to perform control both within and between pulses of the imaging radar. Apply the same control voltage waveform within the pulses with a quantity of to cause the reflection amplitude of the amplitude-programmable metasurface to switch rapidly. Apply a DC control voltage within the pulses with a quantity of to keep the amplitude-programmable metasurface in a relatively static state of reflection or absorption, and generate false targets in the range and azimuth directions of the imaging radar; The fifth control method: perform non-periodic random sequence control within and between pulses of the imaging radar, generate an amplitude coding sequence according to probability, make the amplitude-programmable metasurface randomly modulate the imaging radar reflection signal, and generate a large number of dense dot targets in the azimuth and range directions of the imaging radar to achieve the stealth of its own target under the imaging radar; The sixth control method: perform modulation with frequency agility of the voltage waveform within and between pulses of the imaging radar. Each pulse corresponds to a voltage modulation waveform with a different frequency, and the frequencies of the voltage waveforms between different pulses are different, generating diverse two-dimensional false targets on the imaging radar.

5. A method for imaging radar countermeasure based on amplitude-programmable metasurface according to claim 4, characterized in that, In the first regulation method, the expression formula of the modulation gene is: ; where A represents the reflection amplitude of the metasurface, and its value is 0 or 1; the modulation gene sequence of the first regulation method is expressed as: , with a size of M ; The expression of the baseband signal after modulation by the first control method is: ； The expression of the final radar image result of the first control method is: ； Among them, represents the sinc function, represents the azimuth modulation frequency, represents the total radar imaging time.

6. A method for imaging radar countermeasure based on an amplitude-programmable metasurface according to claim 4, characterized in that, In the second regulation method, the on-pulse metasurface modulation signal is a periodic voltage modulation signal, which is one of square wave, triangular wave, sawtooth wave, and sequence pulse. Using Fourier series expansion, the mathematical expression is as follows: ； Among them, represents the modulation frequency, n is the order of the Fourier series, represents the coupling coefficient between the Fourier series coefficient and the reflection amplitude of the amplitude-programmable metasurface, including the information of the Fourier series and the state of the metasurface reflection amplitude; The regulatory gene sequence of the second regulation method is represented as: , with a size of M ; The expression of the baseband signal after modulation by the second control method is: ； Among them, represents the undisturbed baseband echo signal; After being processed by the range-matching filter, the mathematical expression is as follows: ; After migration correction and azimuth matching filter processing, the expression of the final radar image result in the second control mode is: ; Among them, is the phase of the signal after range-direction matched filtering; is the coefficient representing the intensity of the peak, represents the sinc function, represents the azimuth frequency modulation rate, represents the total radar imaging time.

7. A method for imaging radar countermeasure based on an amplitude-programmable metasurface according to claim 4, characterized in that, In the third control method, a periodic square wave or periodic sequence is selected for imaging radar inter-pulse modulation. When the state of the square wave or periodic sequence of the inter-pulse modulation is 1, it means that the amplitude-programmable metasurface is in the reflection state within the corresponding pulse; when the state of the square wave or periodic sequence of the inter-pulse modulation is 0, it means that the amplitude-programmable metasurface is in the wave-absorbing state within the corresponding pulse. The modulation gene sequence of the third control method is expressed as: , with a size of M , where is the reflection amplitude in the reflection state, and is the reflection amplitude in the wave-absorbing state; Periodic modulation signal between pulses The mathematical expression for Fourier series expansion is as follows: ； Among them, represents the coupling coefficient between the Fourier series coefficients of the inter-pulse signal and the reflection amplitude of the amplitude-programmable metasurface, m is the order of the Fourier series, is the frequency of the inter-pulse modulation; The expression of the baseband signal after modulation by the third control method is: ； Among them, represents the undisturbed baseband echo signal; The expression of the final radar image result of the third control method is: ； Among them, represents the phase value of the radar imaging result, is the coefficient representing the intensity of the peak value, represents the sinc function, represents the azimuth modulation frequency, represents the total radar imaging time.

8. A method for imaging radar countermeasure based on an amplitude-programmable metasurface according to claim 4, characterized in that In the fourth control method, a waveform of either a square wave or a triangular wave is selected as the radar intra-pulse modulation waveform gene , and the mathematical expression for Fourier series expansion is: ; where represents the modulation frequency, z is the order of the Fourier series, represents the coupling coefficient between the Fourier series coefficient and the reflection amplitude of the amplitude-programmable metasurface, and contains the information of the Fourier series and the state of the metasurface reflection amplitude; Select a periodic square wave or periodic sequence for imaging radar inter-pulse modulation. When the state of the square wave or periodic sequence of inter-pulse modulation is 1, it means that intra-pulse modulation is performed within the corresponding pulse; when the state of the square wave or periodic sequence of inter-pulse modulation is 0, it means that intra-pulse modulation is not required within the corresponding pulse, and it is in a relatively stationary wave-absorbing or reflecting state; the periodic modulation signal between pulses The mathematical expression for Fourier series expansion is: ; where represents the coupling coefficient between the Fourier series coefficient of the inter-pulse signal and the reflection amplitude of the amplitude-programmable metasurface, m is the order of the Fourier series, is the frequency of inter-pulse modulation; The regulatory gene sequence of the fourth regulatory method is represented as: , with a size of M ; The expression of the baseband signal after modulation by the fourth control method is: ； The expression of the final radar image result of the fourth control method is: ； in, F Represents the amplitude value of the radar imaging result, Represents the phase value of the radar imaging result, represents the Symle function, Indicates the modulation frequency. Indicates the total radar imaging time.

9. A method for imaging radar countermeasure based on amplitude-programmable metasurface according to claim 4, characterized in that In the fifth control method, the random sequence signal within the o th radar pulse is denoted as . The radar pulse is divided into parts, with a time length of . Within each pulse width and appear with probabilities of P and 1 - P . represents the time-domain function with a reflection coefficient of . represents the time-domain function with a reflection coefficient of . The in-pulse sequence signal is expressed as: ； Among them ; The modulation gene sequence of the fifth control method is expressed as: , with a size of M .

10. A method for imaging radar countermeasure based on an amplitude-programmable metasurface according to claim 4, characterized in that, In the sixth regulation method, a voltage regulation waveform is randomly selected from a square wave, triangular wave, and sawtooth wave waveform library, and a modulation frequency and duty cycle are randomly selected from a waveform parameter library to obtain a voltage modulation signal within the m th radar pulse . The voltage regulation signals corresponding to M pulses are combined to obtain a modulation gene sequence for the sixth regulation method: ； The expression of the baseband signal after being modulated by the sixth modulation method is as follows: 。

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