An imaging radar countermeasure method based on amplitude programmable metasurface

Abstract

This invention discloses an imaging radar countermeasure method based on an amplitude-programmable metasurface, relating to the field of artificial electromagnetic metamaterials. The method comprises: determining the operating parameters of the imaging radar and the user-selected control method; generating a modulation gene sequence based on the operating parameters and the selected control method; generating a corresponding voltage waveform based on the modulation gene sequence and inputting it into the amplitude-programmable metasurface; and finally, switching the amplitude-programmable metasurface between reflection and absorption based on the input signal, thereby interfering with the radar echo signal. This invention establishes a diverse modulation strategy for the amplitude-programmable metasurface, providing key technical support for the construction of a new generation of intelligent electromagnetic warfare systems.

Description

Technical Field

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

[0002] Radar imaging technology boasts all-day, all-weather, and high-precision capabilities, capable of depicting detailed geometric features such as target size, outline, and posture. It plays a vital role in military reconnaissance, situational awareness, and remote sensing mapping, among other military and civilian applications. High-value ground targets face the risk of being exposed in both peacetime and wartime. Controlling their radar signatures to deceive and jam radars has become a critical and pressing issue in the field of radar electronic countermeasures.

[0003] Existing imaging radar jamming technologies fall into two main categories: active jamming and passive jamming. Active jamming relies on high-power transmitters to actively transmit electromagnetic waves, achieving radar noise suppression and large-scale deception. On the one hand, its reliance on high-power signal transmission imposes high costs and is easily exposed in aerospace reconnaissance environments. On the other hand, it relies heavily on the accuracy of reconnaissance information, requiring high capabilities for acquiring and processing information and posing a high computational cost. Passive jamming, on the other hand, does not actively transmit electromagnetic signals. Instead, it disrupts radar reconnaissance by reflecting radar signals to generate false echoes, high-intensity echoes, or attenuated reflected echoes. Currently, commonly used passive protection systems include chaff, corner reflectors, camouflage nets, and absorbing materials. However, once manufactured, these systems have relatively fixed electromagnetic scattering properties, making them incapable of real-time, flexible, and complex control of radar echoes. Due to their flexible electromagnetic control properties, electromagnetic metasurfaces can combine these two traditional methods to create a simple and lightweight radar jamming architecture that can manipulate the radar signatures of real targets and generate false targets, overcoming the power consumption, cost, and efficiency issues of traditional methods.

[0004] However, existing electromagnetic metasurface solutions mostly weaken or enhance echo signals from a single dimension of energy control or spatial coding, lacking targeted analysis of radar operating modes and signal characteristics, making it difficult to adapt to the countermeasure requirements of multiple types of detection systems. Secondly, existing time-modulated metasurface research has focused on speed deception or one-dimensional range image false target generation, but its theoretical models are usually based on the ideal assumptions of normal incidence and single polarization of electromagnetic waves. In actual electronic countermeasure scenarios, radars often use oblique incidence detection and full polarization transmission and reception modes. The interference efficiency of metasurface units is reduced 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 non-periodic sequences. This results in excessively high time domain correlation of interference signals, making them easily detected or suppressed by the radar end.

[0005] Therefore, how to solve the problems of angular stability and polarization sensitivity of metasurface regulation to achieve diversified radar interference patterns is an urgent problem that technicians in this field need to solve. Summary of the Invention

[0006] In view of this, the present invention provides an imaging radar countermeasure method based on amplitude programmable metasurface to solve the problems of angular sensitivity and polarization sensitivity of programmable metasurface, and construct a diversified modulation strategy to provide 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:

[0008] The present invention discloses an imaging radar countermeasure method based on amplitude programmable metasurface, the specific steps of which are as follows:

[0009] Determine the operating parameters of the imaging radar and the control method selected by the user;

[0010] Generate a modulation gene sequence according to the operating parameters and the selected control method, and generate a corresponding voltage waveform input amplitude programmable metasurface according to the modulation gene sequence;

[0011] The amplitude-programmable metasurface switches between reflection and absorption states according to an input signal, thereby interfering with radar echo signals.

[0012] Furthermore, the amplitude programmable metasurface has a two-layer structure, and an air spacer is provided between the first layer structure and the second layer structure;

[0013] The top layer of the first layer structure is composed of two four-opening metal rings, each opening of which is provided with a PIN diode and a resistor. The four-opening metal rings are connected in series to form a complete ring, and the inner and outer rings are connected by an inductor; the lower layer of the first layer structure is a dielectric substrate;

[0014] The top layer of the second layer structure is composed of a metal ring with four openings, each opening of which is provided with a PIN diode and a resistor, and the four metal rings are connected in series to form a complete ring; the middle layer of the second layer structure is a dielectric substrate; and the lower layer of the second layer structure is a metal bottom plate;

[0015] By controlling the on and off states of each PIN diode of each of the four open metal rings, the coding state of the amplitude programmable metasurface is controlled.

[0016] Furthermore, the operating parameters include: the operating starting frequency of the imaging radar LFM signal , bandwidth B, pulse width , frequency sampling pointsN , the distance between the metasurfaces , the motion length of the imaging radar slide L , movement speed v , total number of pulses M ;The mathematical expression of the radar transmission signal is:

[0017] ;

[0018] in, Indicates the fast time in the pulse, Indicates the slow time between pulses, j is a plural unit, Indicates frequency modulation. rect represents the rectangular pulse window function;

[0019] The baseband echo signal without interference is expressed as:

[0020] ;

[0021] in, represents the total radar imaging time, c Represents the speed of light.

[0022] Furthermore, the control method includes:

[0023] The first control mode is to control the amplitude programmable metasurface to be in an absorbing state by DC voltage, so as to absorb electromagnetic wave energy under imaging radar conditions to reduce the target scattering intensity and achieve radar stealth;

[0024] A second control mode is to apply the same control voltage waveform to the amplitude programmable metasurface in each pulse of the imaging radar to generate a false target in the range upward of the imaging radar;

[0025] A third control mode is to apply different control voltages to the amplitude programmable metasurface between pulses of the imaging radar, so that the amplitude programmable metasurface is in a relatively static state of absorption or reflection within each pulse, thereby generating a false target in the azimuth direction of the imaging radar;

[0026] The fourth control method is to control the imaging radar both within the pulse and between pulses at the same time. The same control voltage waveform is applied within the pulse of , so that the amplitude programmable metasurface reflection amplitude is quickly switched. applying a DC control voltage within the pulse to keep the amplitude programmable metasurface in a relatively static state of reflection or absorption, thereby generating a false target in the range and azimuth of the imaging radar;

[0027] The fifth control method is to perform non-periodic random sequence control within and between pulses of the imaging radar, generate an amplitude coding sequence according to probability, and make the amplitude programmable metasurface randomly modulate the imaging radar reflection signal, thereby generating a large number of dense point targets in the azimuth and range directions of the imaging radar, thereby achieving the stealth of the target itself under the imaging radar;

[0028] The sixth control method is to perform frequency-agile modulation of the voltage waveform within and between pulses of the imaging radar. Each pulse corresponds to a voltage modulation waveform of a different frequency, and the frequency of the voltage waveform is different between different pulses, thereby generating diversified two-dimensional false targets on the imaging radar.

[0029] Furthermore, in the first regulation mode, the expression of the modulated gene is: ;in, A Indicates the reflection amplitude of the metasurface, which takes a value of 0 or 1. The modulation gene sequence of the first control mode is expressed as: , the size is M ;

[0030] The expression of the baseband signal after modulation in the first control mode is:

[0031] ;

[0032] The final radar image result expression of the first control mode is:

[0033] ;

[0034] in, represents the Sigmoid function, Indicates the azimuth frequency modulation, Indicates the total radar imaging time.

[0035] Furthermore, in the second control mode, the metasurface modulation signal in the pulse It is a periodic voltage modulation signal, using one of the square wave, triangle wave, sawtooth wave, and sequence pulse. Using Fourier series expansion, the mathematical expression is:

[0036] ;

[0037] in, represents the modulation frequency, n is the order of the Fourier series, The coupling coefficient representing the Fourier series coefficient and the amplitude-programmable metasurface reflection amplitude contains the information of the Fourier series and the state of the metasurface reflection amplitude;

[0038] The modulation gene sequence of the second regulation mode is expressed as: , the size is M ;

[0039] The expression of the baseband signal after modulation in the second control mode is:

[0040] ;

[0041] in, Represents the baseband echo signal without interference;

[0042] After being processed by the range matched filter, the mathematical expression is:

[0043] After the migration correction and azimuth matched filter processing, the final radar image result expression of the second control mode is:

[0044] ;

[0045] in, is the phase of the signal after range-matched filtering; is the coefficient representing the intensity of the peak, represents the Sigmoid function, Indicates the azimuth frequency modulation, Indicates the total radar imaging time.

[0046] Furthermore, in the third control mode, a periodic square wave or periodic sequence is selected for inter-pulse modulation of the imaging radar. When the state of the inter-pulse modulated square wave or periodic sequence is 1, it indicates that the amplitude programmable metasurface within the corresponding pulse is in a reflecting state; when the state of the inter-pulse modulated square wave or periodic sequence is 0, it indicates that the amplitude programmable metasurface within the corresponding pulse is in an absorbing state. The modulation gene sequence of the third control mode is expressed as: , the size is M ,in is the reflection amplitude in the reflection state, is the reflection amplitude in the absorbing state;

[0047] Pulse-to-pulse periodic modulation signal The mathematical expression for Fourier series expansion is:

[0048] ;

[0049] in, 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 interpulse modulation;

[0050] The expression of the baseband signal after modulation by the third control mode is:

[0051] ;

[0052] in, Represents the baseband echo signal without interference;

[0053] The final radar image result expression of the third control method is:

[0054] ;

[0055] in, Represents the phase value of radar imaging result, is the coefficient representing the intensity of the peak, represents the Sigmoid function, Indicates the azimuth frequency modulation, Indicates the total radar imaging time.

[0056] Furthermore, in the fourth control mode, a square wave or a triangle wave is selected as the radar intra-pulse modulation waveform gene , the mathematical expression for Fourier series expansion is: ;in, represents the modulation frequency, z is the order of the Fourier series, The coupling coefficient representing the Fourier series coefficient and the amplitude-programmable metasurface reflection amplitude contains the information of the Fourier series and the state of the metasurface reflection amplitude;

[0057] Select a periodic square wave or periodic sequence for interpulse modulation of the imaging radar. When the state of the interpulse modulated square wave or periodic sequence is 1, it means that the pulse modulation is performed in the corresponding pulse; when the state of the interpulse modulated square wave or periodic sequence is 0, it means that the corresponding pulse does not need to be modulated and is in a relatively static absorption or reflection state; the periodic modulation signal between pulses The mathematical expression for Fourier series expansion is: ;in, 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 interpulse modulation;

[0058] The modulation gene sequence of the fourth regulation mode is expressed as: , the size is M ;

[0059] The expression of the baseband signal after modulation in the fourth control mode is:

[0060] ;

[0061] The final radar image result expression of the fourth control method is:

[0062] ;

[0063] in, F Indicates the amplitude value of the radar imaging result, Represents the phase value of the radar imaging result, represents the Sigmoid function, Indicates the azimuth frequency modulation, Indicates the total radar imaging time.

[0064] Furthermore, in the fifth control method, o The random sequence signal within a radar pulse is recorded as , the radar pulse is divided into The duration is , within each pulse width and The probability of occurrence is P and 1- P , The reflection coefficient is The reflection coefficient is The time domain function of the pulse sequence signal is expressed as:

[0065] ;

[0066] in ;

[0067] The modulation gene sequence of the fifth regulation mode is expressed as:

[0068] , the size is M .

[0069] Furthermore, in the sixth control mode, a voltage control waveform is randomly selected from a square wave, a triangle wave and a sawtooth wave waveform library, and a modulation frequency and a duty cycle are randomly selected from a waveform parameter library to obtain the first control waveform. m Voltage modulated signal within a radar pulse ,Will M The voltage control signals corresponding to the pulses are combined to obtain the modulation gene sequence of the sixth control mode:

[0070] ;

[0071] The expression of the baseband signal after modulation in the sixth control mode is:

[0072] .

[0073] Through the above technical solutions, it can be seen that compared with the prior art, the present invention discloses an imaging radar countermeasure method based on amplitude programmable metasurface, which has the following beneficial effects: 1. Taking into account the radar oblique incidence and full polarization detection scenarios, the metasurface unit maintains stable amplitude switching under oblique incidence and full polarization, and the metasurface has a reflective state and an absorbing state, with dual interference effects of direct stealth in the absorbing state and deception by time modulation of the reflected absorbing state; 2. For high-precision imaging radar, a multi-dimensional interference fusion framework of intra-pulse, inter-pulse and joint timing modulation is established, combining periodic sequences, random sequences and frequency agile waveforms to form a gene library of modulation waveforms. Through the combination of different modulation waveform genes, the generation and deformation of false targets in the two-dimensional imaging domain can be achieved. 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

[0074] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0075] Figure 1 Schematic diagram of the overall process of an embodiment of the present invention.

[0076] Figure 2a This is a top view of the first-layer structure of a unit cell of the amplitude programmable metasurface according to an embodiment of the present invention.

[0077] Figure 2b This is a top view of the second-layer structure of a unit cell of the amplitude programmable metasurface according to an embodiment of the present invention.

[0078] Figure 2c A side view of the overall unit structure of the amplitude programmable metasurface according to an embodiment of the present invention.

[0079] Figure 3 Schematic diagram of the reflection amplitude response curve of the metasurface of an embodiment of the present invention when the PIN diode is in the on and off states.

[0080] Figure 4 Schematic diagram of the imaging radar simulation results of the amplitude-programmable metasurface in a total reflection state according to an embodiment of the present invention.

[0081] Figure 5 Schematic diagram of imaging radar simulation results of an amplitude-programmable metasurface in an absorbing state according to an embodiment of the present invention.

[0082] Figure 6 Schematic diagram of the simulation results of imaging radar with periodic sequence modulation within the pulse of the amplitude-programmable metasurface according to an embodiment of the present invention.

[0083] Figure 7 Schematic diagram of the simulation results of the imaging radar using the amplitude-programmable metasurface pulse period sequence modulation according to an embodiment of the present invention.

[0084] Figure 8 This is a schematic diagram of the imaging radar simulation results of the amplitude-programmable metasurface intra-pulse modulation and inter-pulse interval two-dimensional modulation according to an embodiment of the present invention.

[0085] Figure 9 This is a schematic diagram of the imaging radar simulation results of the amplitude-programmable metasurface with intra-pulse and inter-pulse two-dimensional non-periodic random sequence modulation according to an embodiment of the present invention.

[0086] Figure 10 This is a schematic diagram of the imaging radar simulation results of the amplitude-programmable metasurface intra-pulse modulation and inter-pulse voltage waveform frequency agility two-dimensional modulation according to an embodiment of the present invention.

[0087] In the figure, 1. resistor; 2. inductor; 3. PIN diode; 4. dielectric substrate; 5. air spacer; 6. metal base plate. DETAILED DESCRIPTION

[0088] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0089] The embodiment of the present invention discloses an imaging radar countermeasure method based on amplitude programmable metasurface, such as Figure 1 The specific steps are as follows:

[0090] Determine the operating parameters of the imaging radar and the control method selected by the user;

[0091] Generate a modulation gene sequence according to the operating parameters and the selected control method, and generate a corresponding voltage waveform input amplitude programmable metasurface according to the modulation gene sequence;

[0092] The amplitude-programmable metasurface switches between reflective and absorbing states according to the input signal, interfering with the radar echo signal.

[0093] In a specific embodiment, Figure 2a 、 Figure 2b 、 Figure 2cAs shown, the amplitude programmable metasurface is a two-layer structure, and an air spacer layer 5 is provided between the first layer structure and the second layer structure;

[0094] The top layer of the first layer is composed of two four-opening metal rings. Each opening of the two four-opening metal rings is provided with a PIN diode 3 and a resistor 1. The four open metal rings are connected in series to form a complete ring. The inner and outer rings are connected by an inductor 2. The lower layer of the first layer is a dielectric substrate 4.

[0095] The top layer of the second layer structure is composed of a four-opening metal ring. Each opening of the four-opening metal ring is provided with a PIN diode 3 and a resistor 1. The four open metal rings are connected in series to form 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.

[0096] By controlling the on and off states of each PIN diode 3 of each of the four open metal rings, the coding state of the amplitude programmable metasurface is controlled.

[0097] Specifically, the amplitude programmable metasurface as a whole includes The entire metasurface has n control links, and each column of m units shares the same control link in series. The control link consists 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 of the amplitude programmable metasurface are printed on a dielectric constant of 3.5, a loss tangent of 0.001, and a thickness of On the F4B350 dielectric substrate 4; a PIN diode 3 (model: SMP1320-079LF) and a resistor 1 (resistance: 130 ohms) are soldered in parallel at the ring opening, and an inductor 2 (inductance: 12nH) ​​is soldered between the inner and outer rings. The top layer of the second layer structure consists of a metal four-open ring printed on a dielectric constant of 3.5, a loss tangent of 0.001, and a thickness of On the F4B350 dielectric substrate 4, the device mounting at the opening is consistent with the first layer structure, and the bottom layer is the metal base plate 6; the middle of the two layers is the height The air gap layer 5. Among them, the side length of the metasurface unit p = 15mm; the radii of the two metal four-opening rings in the first layer structure are , ; The radius of the metal four-opening ring in the second layer structure is ; The line width of the metal four-opening ring is , opening width , opening line width , opening gap length .

[0098] When the amplitude programmable metasurface is incident at 0° to 45°, the reflection amplitude of the PIN tube in different states is as follows: Figure 3 As shown in the figure, (a) shows the result of horizontal polarization, and (b) shows the result of vertical polarization. Under horizontal polarization, the metasurface can achieve amplitude encoding of the reflection and absorption states between 6.5 GHz and 8.8 GHz; under vertical polarization, the metasurface can achieve amplitude encoding of the reflection and absorption states between 7.6 GHz and 10.1 GHz.

[0099] In a specific embodiment, the operating parameters include: the operating starting frequency of the imaging radar LFM signal , bandwidth B, pulse width , frequency sampling points N , the distance between the metasurfaces , the motion length of the imaging radar slide L , movement speed v , total number of pulses M ;The mathematical expression of the radar transmission signal is:

[0100] ;

[0101] in, Indicates the fast time in the pulse, Indicates the slow time between pulses, j is a plural unit, Indicates frequency modulation. rect Represents a rectangular pulse window function.

[0102] The baseband echo signal without interference is expressed as:

[0103] ;

[0104] in, represents the total radar imaging time, c Represents the speed of light.

[0105] In a specific embodiment, the control method includes:

[0106] The first control method uses DC voltage to control the amplitude programmable metasurface to be in an absorbing state. Under imaging radar conditions, it absorbs electromagnetic wave energy to reduce the target scattering intensity and achieve radar stealth.

[0107] The second control method applies the same control voltage waveform to the amplitude programmable metasurface in each pulse of the imaging radar, generating a false target in the upward direction of the imaging radar range;

[0108] The third control method applies different control voltages to the amplitude programmable metasurface between pulses of the imaging radar, placing the amplitude programmable metasurface in a relatively static state of absorption or reflection within each pulse, thereby generating a false target in the azimuth direction of the imaging radar.

[0109] The fourth control method is to control the imaging radar both within the pulse and between pulses at the same time. The same control voltage waveform is applied in the pulse of , which makes the amplitude programmable metasurface reflection amplitude switch quickly. A DC control voltage is applied within the pulse to keep the amplitude programmable metasurface in a relatively static state of reflection or absorption, thereby generating a false target in the range and azimuth of the imaging radar;

[0110] The fifth control method is to perform non-periodic random sequence control within and between pulses of the imaging radar, generate amplitude coding sequences according to probability, and make the amplitude programmable metasurface randomly modulate the imaging radar reflection signal, thereby generating a large number of dense point targets in the azimuth and range directions of the imaging radar, thus achieving the stealth of the target itself under the imaging radar;

[0111] The sixth control method is to perform frequency-agile modulation of the voltage waveform within and between pulses of the imaging radar. Each pulse corresponds to a voltage modulation waveform of a different frequency, and the frequency of the voltage waveform is different between different pulses, thereby generating diversified two-dimensional false targets on the imaging radar.

[0112] In a specific embodiment, in the first control method, an amplitude-programmable metasurface is used, and according to the control waveform genome: no voltage waveform modulation is performed, so that it is in a wave-absorbing state, and electromagnetic wave energy is absorbed under imaging radar conditions to achieve radar stealth.

[0113] Specifically, after determining the radar transmission signal expression, the metasurface modulation waveform is determined. At this time, for M pulses, the metasurface is in an absorbing or reflecting state within the pulse, and the corresponding intra-pulse modulation waveform is a 0V or 36V DC voltage. This waveform is used as a modulation gene to form a gene sequence of size M to control the amplitude programmable metasurface. The expression of the modulation gene is: ; Wherein, A represents the reflection amplitude of the metasurface, which takes a value of 0 or 1; the modulation gene sequence of the first control mode is expressed as: , size is M.

[0114] After being modulated by the amplitude-programmable metasurface, the radar echo is mixed from the RF to the IF and bandpass filtered to obtain the baseband signal. The expression of the modulated baseband signal in the first control mode is:

[0115] ;

[0116] After amplitude programmable metasurface modulation, range matched filtering, azimuth FFT, range migration correction, and azimuth matched filtering, the final radar image result expression of the first control method is: ;

[0117] in, represents the Sigmoid function, Indicates the azimuth frequency modulation, Indicates the total radar imaging time.

[0118] like Figure 4 As shown, when the modulation genomes of the amplitude programmable metasurface are all in the reflective state, , we can analyze the position of the metasurface as , the strong reflection points caused by the metasurface can be observed in the image; Figure 5 As shown, when the modulation genomes of the amplitude programmable metasurface are all in the absorbing state, , the strong reflection points on the image disappear and achieve invisibility.

[0119] In a specific embodiment, in the second control mode, 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.

[0120] 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 pattern is the same within M pulses. The metasurface modulation signal within the pulse is It is a periodic voltage modulation signal, using one of the square wave, triangle wave, sawtooth wave, and sequence pulse. Using Fourier series expansion, the mathematical expression is:

[0121] ;

[0122] 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 metasurface reflection amplitude.

[0123] 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 .

[0124] 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 after modulation by the second control mode is: ;in, Represents the baseband echo signal without interference.

[0125] After being processed by the range matched filter, the mathematical expression is:

[0126] After the migration correction and azimuth matched filter processing, the final radar image result expression of the second control mode is:

[0127] ;in, is the phase of the signal after range-matched filtering; is the coefficient representing the intensity of the peak, represents the Sigmoid function, Indicates the azimuth frequency modulation, Indicates the total radar imaging time.

[0128] According to the final imaging results, sinc The peak value will appear at the , Therefore, any order can be solved and Distance interval between false targets In this embodiment, the radar's operating starting frequency ,bandwidth B =200MHz, pulse width , two metasurfaces are placed, one amplitude programmable metasurface is in a reflective state during radar operation, and the other amplitude programmable metasurface is in a reflective state according to the frequency , square wave voltage control with a duty cycle of 0.5 is implemented as follows Figure 6 As shown, false targets are generated at certain intervals in the upward direction of the imaging radar range.

[0129] In a specific embodiment, in the third control method, an amplitude-programmable metasurface is used, and according to the control waveform genome, different control voltages are applied between pulses. The reflection state of the metasurface in each pulse is in a relatively static state of absorption or reflection, thereby realizing the generation of false targets in the azimuth direction of the imaging radar.

[0130] Specifically, for the modulation between radar pulses, a periodic square wave or periodic sequence is selected for imaging radar inter-pulse modulation. When the state of the inter-pulse modulated square wave or periodic sequence is 1, it indicates that the amplitude programmable metasurface is in a reflecting state within the corresponding pulse; when the state of the inter-pulse modulated square wave or periodic sequence is 0, it indicates that the amplitude programmable metasurface is in an absorbing state within the corresponding pulse. The modulation gene sequence of the third control method is expressed as: , the size is M ,in is the reflection amplitude in the reflection state, is the reflection amplitude in the absorbing state;

[0131] Pulse-to-pulse periodic modulation signal The mathematical expression for Fourier series expansion is: ;in, 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 pulse modulation.

[0132] The expression of the baseband signal after modulation by the third control mode is: ;in, Represents the baseband echo signal without interference.

[0133] After the reflected signal undergoes range-direction matched filtering, migration correction, and azimuth-direction matched filtering, the final radar image expression of the third control method is:

[0134] ;

[0135] in, Represents the phase value of the imaging result, is the coefficient representing the intensity of the peak, represents the Sigmoid function, Indicates the azimuth frequency modulation, Indicates the total radar imaging time.

[0136] according to sinc Due to the envelope characteristics of the function, the false target may appear in the same direction as the original target. and The distance between false targets In this embodiment, the radar's operating starting frequency ,bandwidth B =200MHz, pulse width , the radar's flight speed v=200m / s; place two metasurfaces, one amplitude programmable metasurface is in a reflective state during radar operation, and the other amplitude programmable metasurface is in an interpulse modulation frequency , square wave voltage control with a duty cycle of 0.5 is implemented as follows Figure 7 As shown, false targets are generated at certain intervals in the azimuth direction of the imaging radar.

[0137] In a specific embodiment, in the fourth control mode, the amplitude programmable metasurface is used to control the waveform genome: the number of controls within and between pulses is The same control voltage waveform is applied in the pulse to make the reflection amplitude switch quickly. A DC control voltage is applied to the pulse to keep it in a relatively static state of reflection or absorption, thereby realizing the generation of false targets in the range and azimuth of the imaging radar.

[0138] Specifically, for radar intra-pulse modulation, a square wave or a triangle wave is selected as the radar intra-pulse modulation waveform gene , the mathematical expression for Fourier series expansion is: ;in, represents the modulation frequency, z is the order of the Fourier series, The coupling coefficient representing the Fourier series coefficient and the amplitude-programmable metasurface reflection amplitude contains the information of the Fourier series and the state of the metasurface reflection amplitude;

[0139] For radar interpulse modulation, a periodic square wave or periodic sequence is selected for imaging radar interpulse modulation. When the state of the interpulse modulated square wave or periodic sequence is 1, it means that the pulse modulation is performed in the corresponding pulse; when the state of the interpulse modulated square wave or periodic sequence is 0, it means that the corresponding pulse does not need to be modulated and is in a relatively static absorption or reflection state; the periodic modulation signal between pulses The mathematical expression for Fourier series expansion is: ;in, 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 interpulse modulation;

[0140] The modulation gene sequence of the fourth regulation mode is expressed as: , the size is M The expression of the baseband signal after modulation by the fourth control mode is:

[0141] .

[0142] After the reflected signal undergoes range-direction matched filtering, migration correction, and azimuth-direction matched filtering, the final radar image expression of the fourth control method is:

[0143] ;

[0144] in, Indicates the amplitude value of the imaging result, Represents the phase value of the radar imaging result, represents the Sigmoid function, Indicates the azimuth frequency modulation, Indicates the total radar imaging time.

[0145] Finally, we can get the azimuth and distance distribution of the false target, the order and The distance between false targets , order and Distance interval between false targets In this embodiment, the radar's operating starting frequency ,bandwidth B =200MHz, pulse width , the radar's flight speed v =200m / s; place two metasurfaces, one amplitude programmable metasurface is in a reflective state during radar operation, and the other amplitude programmable metasurface is in an interpulse modulation frequency , the duty cycle is 0.5 square wave voltage control, according to the frequency , square wave voltage control with a duty cycle of 0.5 is implemented as follows Figure 8 As shown, false targets are generated in a certain interval in the range and azimuth directions of the imaging radar.

[0146] In a specific embodiment, in the fifth control mode, the amplitude programmable metasurface is used to control the waveform genome: non-periodic random sequence control within and between pulses, according to the probability and Generate amplitude coding sequences to achieve target stealth under imaging radar.

[0147] Specifically, the o The random sequence signal within a radar pulse is recorded as , the radar pulse is divided into The duration is , within each pulse width and The probability of occurrence is P and 1- P , The reflection coefficient is The time domain function of The reflection coefficient is The time domain function of , so the sequence signal in the pulse is expressed as:

[0148] ;

[0149] in ;

[0150] The mathematical expression of its power spectrum is:

[0151] ;

[0152] in, f represents the echo spectrum, represents the spectrum width of the reflection coefficient time domain function, Represents the loading reflection coefficient The waveform spectrum, Represents the loading reflection coefficient The waveform spectrum, is the unit impulse function.

[0153] The modulation gene sequence of the fifth regulation mode is expressed as:

[0154] , the size is M .

[0155] After the signal modulated by the random sequence undergoes range-wise matched filtering, migration correction, and azimuth-wise matched filtering, a dense number of point-like targets will be generated in both azimuth and range directions. Since the energy is distributed over 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 radar's operating starting frequency is ,bandwidth , pulse width , the radar's flight speed Place two metasurfaces, one amplitude programmable metasurface is in the reflection state during radar operation, and the other amplitude programmable metasurface is modulated by the reflection or absorption state with a probability of 50%, and the modulation pulse width , to achieve Figure 9 As shown, false targets are generated in a certain interval in the range and azimuth directions of the imaging radar.

[0156] In a specific embodiment, in the sixth control method, an amplitude-programmable metasurface is used to control the waveform genome: the voltage waveform frequency is agilely modulated within and between pulses, and each pulse corresponds to a voltage modulation waveform of a different frequency, thereby realizing the diversified generation of two-dimensional false targets of the imaging radar.

[0157] Specifically, the voltage control waveform is randomly selected from the square wave, triangle wave and sawtooth wave waveform library, and the modulation frequency and duty cycle are randomly selected from the waveform parameter library to obtain the first m Voltage modulated signal within a radar pulse ,Will M The voltage control signals corresponding to the pulses are combined to obtain the modulation gene sequence of the sixth control mode:

[0158] ;

[0159] The expression of the baseband signal after modulation in the sixth control mode is:

[0160] .

[0161] Since the modulation modulates the pulse with different waveforms, false targets will be generated in the range direction. At the same time, the modulation waveforms between different pulses in the azimuth direction are different, so false targets at different positions will also be generated in the azimuth direction. In this embodiment, the pulse modulation of the amplitude programmable metasurface is a square wave, but with different modulation frequencies. The frequency type can be quantized as [5, 4, 5, 8, 5, 3, ... repeat ..., 5, 4, 5, 8, 5, 3], so as to achieve the following: Figure 10 As shown, various false targets are generated in the range and azimuth directions of the imaging radar.

[0162] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method description.

[0163] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to 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 input amplitude programmable metasurface according to the modulation gene sequence; The amplitude programmable metasurface switches between reflection and absorption states according to an input signal, thereby interfering with the radar echo signal; The amplitude programmable metasurface has a two-layer structure, and an air spacer is provided between the first layer and the second layer; The top layer of the first layer structure is composed of two four-opening metal rings, each opening of which is provided with a PIN diode and a resistor. The four-opening metal rings are connected in series to form a complete ring, and 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 metal ring with four openings, each opening of which is provided with a PIN diode and a resistor, and the four metal rings are connected in series to form a complete ring; the middle layer of the second layer structure is a dielectric substrate; and the lower layer of the second layer structure is a metal bottom plate; By controlling the on and off states of each PIN diode of each of the four open metal rings, the coding state of the amplitude programmable metasurface is controlled.

2. The imaging radar countermeasure method based on amplitude programmable metasurface according to claim 1, characterized in that: The operating parameters include: the operating starting frequency of the imaging radar LFM signal , bandwidth B, pulse width , frequency sampling points N , the distance between the metasurfaces , the motion length of the imaging radar slide L , movement speed v , total number of pulses M ;The mathematical expression of the radar transmission signal is: ； in, Indicates the fast time in the pulse, Indicates the slow time between pulses, j is a plural unit, Indicates frequency modulation. rect represents the rectangular pulse window function; The baseband echo signal without interference is expressed as: ； in, represents the total radar imaging time, c Represents the speed of light.

3. The imaging radar countermeasure method based on amplitude programmable metasurface according to claim 2, characterized in that: The control methods include: The first control mode is to control the amplitude programmable metasurface to be in an absorbing state by DC voltage, so as to absorb electromagnetic wave energy under imaging radar conditions to reduce the target scattering intensity and achieve radar stealth; A second control mode is to apply the same control voltage waveform to the amplitude programmable metasurface in each pulse of the imaging radar to generate a false target in the range upward of the imaging radar; A third control mode is to apply different control voltages to the amplitude programmable metasurface between pulses of the imaging radar, so that the amplitude programmable metasurface is in a relatively static state of absorption or reflection within each pulse, thereby generating a false target in the azimuth direction of the imaging radar; The fourth control method is to control the imaging radar both within the pulse and between pulses at the same time. The same control voltage waveform is applied within the pulse of , so that the amplitude programmable metasurface reflection amplitude is quickly switched. applying a DC control voltage within the pulse to keep the amplitude programmable metasurface in a relatively static state of reflection or absorption, thereby generating a false target in the range and azimuth of the imaging radar; The fifth control method is to perform non-periodic random sequence control within and between pulses of the imaging radar, generate an amplitude coding sequence according to probability, and make the amplitude programmable metasurface randomly modulate the imaging radar reflection signal, thereby generating a large number of dense point targets in the azimuth and range directions of the imaging radar, thereby achieving the stealth of the target itself under the imaging radar; The sixth control method is to perform frequency-agile modulation of the voltage waveform within and between pulses of the imaging radar. Each pulse corresponds to a voltage modulation waveform of a different frequency, and the frequency of the voltage waveform is different between different pulses, thereby generating diversified two-dimensional false targets on the imaging radar.

4. The imaging radar countermeasure method based on amplitude programmable metasurface according to claim 3, characterized in that: In the first regulation mode, the expression of the modulated gene is: ;in, A Indicates the reflection amplitude of the metasurface, which takes a value of 0 or 1. The modulation gene sequence of the first control mode is expressed as: , the size is M ; The expression of the baseband signal after modulation in the first control mode is: ； The final radar image result expression of the first control mode is: ； in, represents the Sigmoid function, Indicates the azimuth frequency modulation, Indicates the total radar imaging time.

5. The imaging radar countermeasure method based on amplitude programmable metasurface according to claim 3, characterized in that: In the second control mode, the metasurface modulation signal in the pulse It is a periodic voltage modulation signal, using one of the 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 amplitude-programmable metasurface reflection amplitude contains the information of the Fourier series and the state of the metasurface reflection amplitude; The modulation gene sequence of the second regulation mode is expressed as: , the size is M ; The expression of the baseband signal after modulation in the second control mode is: ； in, Represents the baseband echo signal without interference; After being processed by the range matched filter, the mathematical expression is: After the migration correction and azimuth matched filter processing, the final radar image result expression of the second control mode is: ； in, is the phase of the signal after range-matched filtering; is the coefficient representing the intensity of the peak, represents the Sigmoid function, Indicates the azimuth frequency modulation, Indicates the total radar imaging time.

6. The imaging radar countermeasure method based on amplitude programmable metasurface according to claim 3, characterized in that: In the third control mode, a periodic square wave or periodic sequence is selected for inter-pulse modulation of the imaging radar. When the state of the inter-pulse modulated square wave or periodic sequence is 1, it indicates that the amplitude programmable metasurface within the corresponding pulse is in a reflecting state; when the state of the inter-pulse modulated square wave or periodic sequence is 0, it indicates that the amplitude programmable metasurface within the corresponding pulse is in an absorbing state. The modulation gene sequence of the third control mode is expressed as: , the size is M ,in is the reflection amplitude in the reflection state, is the reflection amplitude in the absorbing state; Pulse-to-pulse periodic modulation signal The mathematical expression for Fourier series expansion is: ； in, 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 interpulse modulation; The expression of the baseband signal after modulation by the third control mode is: ； in, Represents the baseband echo signal without interference; The final radar image result expression of the third control method is: ； in, Represents the phase value of radar imaging result, is the coefficient representing the intensity of the peak, represents the Sigmoid function, Indicates the azimuth frequency modulation, Indicates the total radar imaging time.

7. The imaging radar countermeasure method based on amplitude programmable metasurface according to claim 3, characterized in that: In the fourth control mode, a square wave or a triangle wave is selected as the radar intra-pulse modulation waveform gene. , the mathematical expression for Fourier series expansion is: ;in, represents the modulation frequency, z is the order of the Fourier series, The coupling coefficient representing the Fourier series coefficient and the amplitude-programmable metasurface reflection amplitude contains the information of the Fourier series and the state of the metasurface reflection amplitude; Select a periodic square wave or periodic sequence for interpulse modulation of the imaging radar. When the state of the interpulse modulated square wave or periodic sequence is 1, it means that the pulse modulation is performed in the corresponding pulse; when the state of the interpulse modulated square wave or periodic sequence is 0, it means that the corresponding pulse does not need to be modulated and is in a relatively static absorption or reflection state; the periodic modulation signal between pulses The mathematical expression for Fourier series expansion is: ;in, 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 interpulse modulation; The modulation gene sequence of the fourth regulation mode is expressed as: , the size is M ; The expression of the baseband signal after modulation in the fourth control mode is: ； The final radar image result expression of the fourth control method is: ； in, F Indicates the amplitude value of the radar imaging result, Represents the phase value of the radar imaging result, represents the Sigmoid function, Indicates frequency modulation. Indicates the total radar imaging time.

8. The imaging radar countermeasure method based on amplitude programmable metasurface according to claim 3, characterized in that: In the fifth control method, o The random sequence signal within a radar pulse is recorded as , the radar pulse is divided into The duration is , within each pulse width and The probability of occurrence is P and 1- P , The reflection coefficient is The time domain function of The reflection coefficient is The time domain function of the pulse sequence signal is expressed as: ； in ; The modulation gene sequence of the fifth regulation mode is expressed as: , the size is M .

9. The imaging radar countermeasure method based on amplitude programmable metasurface according to claim 3, characterized in that: In the sixth control mode, a voltage control waveform is randomly selected from a square wave, triangle wave and sawtooth wave waveform library, and a modulation frequency and a duty cycle are randomly selected from a waveform parameter library to obtain the first m Voltage modulated signal within a radar pulse ,Will M The voltage control signals corresponding to the pulses are combined to obtain the modulation gene sequence of the sixth control mode: ； The expression of the baseband signal after modulation in the sixth control mode is: 。

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