Construction method and system of multifunctional self-adaptive direction backtracking Doppler invisible cloak

Abstract

The invention discloses a method and system for constructing a multifunctional self-adaptive direction backtracking Doppler invisible cloak, and the method specifically comprises the steps: constructing a two-bit phase shifter based on a reconfigurable microstrip transmission line, and regulating and controlling the length of the microstrip transmission line, so that the phase shifter achieves four discrete phase states; the method comprises the following steps: analyzing a generalized conjugate relation between a receiving phase and a radiation phase of an array element in an antenna array, constructing a reconfigurable Van Atta array model based on a 2-bit phase shifter, and realizing adaptive direction backtracking in four discrete phase states; time modulation is introduced into the reconfigurable Van Atta array model, Doppler frequency compensation of adaptive direction backtracking is realized, and a Doppler cloak is obtained; spatial modulation is introduced into the reconfigurable Van Atta array model, the radar cross-sectional area RCS of self-adaptive direction backtracking is reduced, and the multifunctional Doppler stealth cloak is obtained. The efficiency of multifunctional self-adaptive direction regulation and control of the Doppler invisible cloak can be remarkably improved.

Description

Technical Field

[0001] The present invention relates to the field of space-time modulation metasurface technology, and in particular to a method and system for constructing a multifunctional adaptive directional backtracking Doppler stealth cloak. Background Art

[0002] The Doppler effect is one of the most basic concepts in physics. When there is relative motion between the source and the observer, the received electromagnetic waves will have a frequency shift compared to the radiated electromagnetic waves. In order to compensate for the Doppler frequency shift effect caused by relative motion, the team of Professor F. Bilotti of the University of Rome Tre proposed the concept of Doppler cloak based on time-modulated metasurface (D. Ramaccia, D. L. Sounas, A. Alu, A. Toscano, F. Bilotti, Metasurface-based Doppler cloaks: Time- varying metasurface profile to achieve perfect frequency mixing, IEEE 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials), pp. 331-333, 2018.). It mainly uses the abnormal interaction between the incident electromagnetic wave and the time-space modulated metasurface. By properly regulating the electromagnetic properties of the metasurface, a perfect mixing effect can be achieved, so that the reflected electromagnetic wave produces a frequency shift, which can compensate for the Doppler frequency shift caused by motion, thereby avoiding the detection of the target's motion speed (D. Ramaccia, D. L. Sounas, A. Alu, A. Toscano, F. Bilotti, Phase-induced frequency conversion and Doppler effect with time-modulated metasurfaces,IEEE Transactions on Antennas and Propagation, vol.68,no.pp.1607-1617,2019.). In addition to the above applications, Doppler cloaks can also be used in the field of antennas, for example, to restore the matching of narrowband mobile antennas (D. Ramaccia, A. Toscano, F. Bilotti, Non-reciprocity and control of Doppler effect in antenna systems induced by active time-varying metamaterials and metasurfaces,IEEE 2019 European Microwave Conference in Central Europe (EuMCE), pp.1-1,2019.) and so on.

[0003] However, the traditional planar Doppler cloak based on time-modulated metasurface (B.Liu, Y. He, SWong, Y.Li, "Experimental demonstration of a time-domain digital-coding metasurfacefor a Doppler cloak," Optics Express, vol.29, no.2, pp.740-750, 2021; XGZhang, YL Sun, Q.Yu, Q.Cheng, WXJiang, CWQiu, TJCui, Smart Doppler cloak operatingin broad band and full polarizations, Advanced Materials, vol.33, Art.no.2007966, 2021.) only provides normal Doppler compensation. In oblique incidence single-station observation, the scattered energy is mainly along the direction of mirror reflection, and there is a problem that effective Doppler compensation cannot be achieved under oblique incidence conditions. The self-adaptive retro-reflective Doppler cloak based on planar space-time modulated metasurfaces (X. Fang, M. Li, D. Ramaccia, A. Toscano, F. Bilotti, D. Ding, Self-adaptive retro-reflective Doppler cloak based on planar space-time modulated metasurfaces, Applied Physics Letters 9 January 2023; 122 (2): 021702.) solves the problem of inability to achieve effective Doppler compensation under oblique incidence, but its structure is complex and the working bandwidth is narrow, which makes it difficult to implement. Summary of the invention

[0004] The object of the present invention is to provide a method and system for constructing a multifunctional adaptive directional backtracking Doppler stealth cloak, so as to improve the efficiency of the multifunctional adaptive directional control of the Doppler stealth cloak.

[0005] The technical solution to achieve the purpose of the present invention is: a method for constructing a multifunctional adaptive direction-tracing Doppler stealth cloak, comprising the following steps:

[0006] Step 1: construct a 2-bit phase shifter based on a reconfigurable microstrip transmission line, and adjust the length of the microstrip transmission line so that the phase shifter can achieve four discrete phase states;

[0007] Step 2: Analyze the generalized conjugate relationship between the receiving phase and the radiation phase of the array elements in the antenna array, construct a reconfigurable Van Atta array model based on a 2-bit phase shifter, and realize adaptive directional tracing in four discrete phase states;

[0008] Step 3, introducing time modulation into the reconfigurable Van Atta array model to achieve Doppler frequency compensation with adaptive directional retrieval and obtain the Doppler cloak;

[0009] Step 4: Introduce spatial modulation into the reconfigurable Van Atta array model to achieve adaptive directional backtracking radar cross-sectional area (RCS) reduction and obtain a multifunctional Doppler stealth cloak.

[0010] A multifunctional adaptive directional back-tracing Doppler stealth cloak construction system is used to implement the multifunctional adaptive directional back-tracing Doppler stealth cloak construction method. The system includes a phase shifter construction module, an array model construction module, a time modulation module and a space modulation module. The functions of each module are as follows:

[0011] Phase shifter construction module, which builds a 2-bit phase shifter based on a reconfigurable microstrip transmission line and adjusts the length of the microstrip transmission line to enable the phase shifter to achieve four discrete phase states;

[0012] The array model building module analyzes the generalized conjugate relationship between the receiving phase and the radiation phase of the array elements in the antenna array, builds a reconfigurable Van Atta array model based on a 2-bit phase shifter, and realizes adaptive directional tracing in four discrete phase states;

[0013] The time modulation module introduces time modulation into the reconfigurable Van Atta array model to achieve adaptive directional backtracking Doppler frequency compensation and obtain the Doppler cloak;

[0014] The spatial modulation module introduces spatial modulation into the reconfigurable Van Atta array model to achieve adaptive directional backtracking radar cross-sectional area (RCS) reduction and obtain a multifunctional Doppler stealth cloak.

[0015] A multifunctional adaptive directional back-tracing Doppler stealth cloak is constructed based on the construction method of the multifunctional adaptive directional back-tracing Doppler stealth cloak.

[0016] A mobile terminal comprises a memory, a processor and a computer program stored in the memory and executable on the processor. When the processor executes the program, the method for constructing a multifunctional adaptive direction-tracing Doppler stealth cloak is implemented.

[0017] Compared with the prior art, the present invention has the following significant advantages:

[0018] (1) The generalized conjugate relationship between the receiving phase and the radiation phase of the array elements in the antenna array is analyzed, and a reconfigurable Van Atta array model based on a 2-bit phase shifter is constructed. Time modulation is introduced to achieve Doppler frequency compensation with adaptive directional tracing.

[0019] (2) Introducing spatial modulation into the reconfigurable Van Atta array to achieve adaptive directional backtracking radar cross-sectional area (RCS) reduction and obtain a multifunctional Doppler stealth cloak;

[0020] (3) It can significantly improve the efficiency of the multifunctional adaptive directional control of the Doppler stealth cloak, and solve the problem that the traditional planar Doppler stealth cloak is not applicable in the case of single-station oblique incidence observation.

[0021] The present invention is further described in detail below in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of a 2-bit phase shifter in the present invention.

[0023] Figure 2 FIG. 1 is an equivalent circuit diagram of a PIN diode used in a 2-bit phase shifter of the present invention.

[0024] Figure 3a It is a frequency-amplitude diagram of transmission coefficient simulation of four states of the 2-bit phase shifter in the present invention.

[0025] Figure 3b The simulated frequency-phase diagram of the transmission coefficient of the four states of the 2-bit phase shifter in the present invention.

[0026] Figure 4 This is an analysis diagram of the working principle of the directional backtracking array in the present invention.

[0027] Figure 5 This is a schematic diagram of the multifunctional adaptive directional backtracking Doppler stealth cloak in the present invention.

[0028] Figure 6 This is a bottom view of the Van Atta array designed in the present invention.

[0029] Figure 7 This is a top view of the Van Atta array designed in the present invention.

[0030] Figure 8 It is a side view of the Van Atta array designed in the present invention.

[0031] Fig. 9 This is a comparison chart of the single-station RCS far-field results of an equal-sized metal plate and a directional back-tracking Doppler stealth cloak at 0°-60° at 10GHz in the present invention.

[0032] Fig.10 This is a diagram showing the amplitude difference between the 0th and 1st order harmonic spectrums of the directional retrospective Doppler stealth cloak under time modulation at different angles and working frequencies.

[0033] Fig.11a Normalized directivity pattern of spatial modulation of the directional retro-Doppler stealth cloak at an incident angle of 0°.

[0034] Fig.11b Normalized directivity pattern of the spatially modulated directional Doppler cloak at an incident angle of 15°.

[0035] Fig.11c Normalized directivity pattern of the spatially modulated directional Doppler cloak at an incident angle of 30°.

[0036] Fig.11d Normalized directivity pattern of the spatially modulated directional Doppler cloak at an incident angle of 45°. DETAILED DESCRIPTION

[0037] The present invention provides a method for constructing a multifunctional adaptive directional backtracking Doppler stealth cloak, which mainly includes: constructing a 2-bit phase shifter based on a reconfigurable microstrip transmission line, adjusting the length of the microstrip transmission line so that the phase shifter realizes four discrete phase states; analyzing the generalized conjugate relationship between the receiving phase and the radiation phase of the array element in the antenna array, constructing a reconfigurable Van Atta array model based on the 2-bit phase shifter, and realizing adaptive directional backtracking in four discrete phase states; introducing time modulation in the reconfigurable Van Atta array model to realize Doppler frequency compensation of adaptive directional backtracking, and obtaining a Doppler cloak; introducing space modulation in the reconfigurable Van Atta array to realize RCS reduction of adaptive directional backtracking, and obtaining a multifunctional Doppler stealth cloak. The method of the present invention can significantly improve the efficiency of multifunctional adaptive directional control of the Doppler stealth cloak.

[0038] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It is easy to understand that, based on the technical solution of the present invention, without changing the essential spirit of the present invention, a person skilled in the art can imagine a variety of implementations of the present invention. Therefore, the following specific implementations and drawings are only exemplary descriptions of the technical solution of the present invention, and should not be regarded as the entirety of the present invention or as a limitation or restriction to the technical solution of the present invention.

[0039] Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present invention unless otherwise specifically stated.

[0040] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses.

[0041] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered as part of the specification.

[0042] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0043] The present invention provides a method for constructing a multifunctional adaptive direction-tracing Doppler stealth cloak, comprising the following steps:

[0044] Step 1: construct a 2-bit phase shifter based on a reconfigurable microstrip transmission line, and adjust the length of the microstrip transmission line so that the phase shifter can achieve four discrete phase states;

[0045] Step 2: Analyze the generalized conjugate relationship between the receiving phase and the radiation phase of the array elements in the antenna array, construct a reconfigurable Van Atta array model based on a 2-bit phase shifter, and realize adaptive directional tracing in four discrete phase states;

[0046] Step 3, introducing time modulation into the reconfigurable Van Atta array model to achieve Doppler frequency compensation with adaptive directional retrieval and obtain the Doppler cloak;

[0047] Step 4: Introduce spatial modulation into the reconfigurable Van Atta array model to achieve adaptive directional backtracking radar cross-sectional area (RCS) reduction and obtain a multifunctional Doppler stealth cloak.

[0048] As a specific example, in step 1, a 2-bit phase shifter based on a reconfigurable microstrip transmission line is constructed, and the length of the microstrip transmission line is adjusted so that the phase shifter can achieve four discrete phase states; Figure 1 The schematic diagram of the 2-bit phase shifter is shown in the figure. Figure 2 The equivalent circuit diagram of the PIN transistor used in the 2-bit phase shifter is shown in FIG. Figure 3a , Figure 3b The transmission coefficient simulation diagram of the four states of the bit shifter shown is as follows:

[0049] The reconfigurable microstrip transmission line is Figure 1 As shown in FIG. 1 , it is composed of microstrip lines of different electrical lengths and PIN diodes; the DC bias voltage is controlled according to the preset voltage coding, the on-off state of the PIN diodes loaded at both ends of the microstrip lines of different electrical lengths is changed, and the electrical length of the transmission line is adjusted, so that the phase state of the phase shifter changes. Figure 2As shown, the diode model used is MA4FCP305. When the PIN diode is turned on, it can be equivalent to a The resistance and a When the PIN is turned off, it can be equivalent to a The capacitance and a inductors in series.

[0050] The 2-bit phase shifter based on reconfigurable microstrip transmission line is composed of two sets of transmission lines in cascade, each set of transmission lines is composed of two microstrip lines of unequal electrical lengths.

[0051] The electrical length difference of the first group of microstrip lines ,in is the phase wavelength of the microstrip line, that is, the microstrip line satisfies the phase difference ; The electrical length difference of the second group of microstrip lines , that is, the microstrip line satisfies the phase difference ;

[0052] PIN diodes are used at both ends of the microstrip line as connecting input and output ports, and the DC bias voltage is adjusted to control the on and off of the PIN diodes, so as to select the path between the input and output ports, thereby controlling the phase change between the input and output ports;

[0053] Finally, four phase states are obtained, namely , to achieve 2-bit phase shift. Figure 3a , Figure 3b As shown, the 2-bit phase shifter designed in the X-band can achieve four phase states, and the amplitudes of the four states are basically consistent.

[0054] As a specific example, in step 2, the generalized conjugate relationship between the receiving phase and the radiation phase of the array element in the antenna array is analyzed, and a reconfigurable Van Atta array model based on a 2-bit phase shifter is constructed to achieve adaptive directional tracing in four discrete phase states; combined with Figure 4 The working principle analysis diagram of the directional traceback array is shown. Figure 5 The schematic diagram of the multifunctional adaptive directional backtracking Doppler bucket is shown. Figure 6 The bottom view of the Van Atta array is shown. Figure 7 The top view of the Van Atta array is shown. Figure 8 Side view of the Van Atta array shown, Fig. 9 The comparison of the far-field RCS results of a large metal plate and a directional Doppler bucket at 0°-60° at 10GHz is shown in the figure, specifically:

[0055] Step 2.1, determine the generalized conjugate relationship between the receiving phase and the radiation phase of the array element in the directional traceback antenna array;

[0056] like Figure 4 As shown, suppose there is a rectangular coordinate system O-xyz in the three-dimensional space. The source , electromagnetic waves propagate outward as spherical waves, and are approximately plane waves under far-field conditions; in space, there is The antenna array is composed of array elements. The position of the array element is recorded as , ;

[0057] Assume that the signal radiated to the array element is simple harmonic and its amplitude is , the angular frequency is , the initial phase is zero, then The array element at time Received signal It is expressed as:

[0058] (1)

[0059] (2)

[0060] in, For time, is the attenuation factor of the radiation signal propagating in space; The radiation signal propagates in space to the The receiving phase when the array element is Array elements and source points The wave distance between The phase lag caused by is the wavelength of electromagnetic waves in space, is the speed of light, is the electromagnetic wave carrier frequency, ;

[0061] No. After receiving the radiation signal, the array element reflects the signal, and the reflected signal propagates to the space at The venue Time, field Received signal It is expressed as:

[0062] (3)

[0063] (4)

[0064] in, is the attenuation factor of the reflected signal propagating in space, is the initial phase of the reflected signal in space, For the Array elements and field points The wave distance between The phase lag caused by

[0065] In the far field condition, the field point Total field received equal The superposition of the fields of the array elements at this point, equation (3) is expressed by the superposition theorem as:

[0066] (5)

[0067] Ignoring the array size under far-field conditions, , Is only with distance Related functions require the array to implement the direction backtracking function, that is, When the total field is superimposed in phase, the field strength is the largest. Then according to formula (5), we can get:

[0068] (6)

[0069] in, is a constant term, representing the reference value of the phase shift, is an arbitrary integer, representing a multiple of the phase period. According to equations (2) and (4), equation (6) can be written as:

[0070] (7)

[0071] That is, the receiving phase of the array element Phase with radiation Satisfy the generalized phase conjugation relationship;

[0072] when and When , equation (7) obtains the phase conjugate relationship in the complex frequency domain:

[0073] (8)

[0074] Step 2.2, determining the generalized conjugate relationship between the receiving phase and the echo phase of the array element in the one-dimensional Van Atta array based on the 2-bit phase shifter;

[0075] For a one-dimensional Van Atta array based on a 2-bit phase shifter, such as Figure 5 As shown, the number of array elements is an even number, and the array element spacing is , then in the case of plane wave incidence, there is a fixed phase difference between two adjacent array elements ;No. The array element and The electrical length between the array elements is The microstrip transmission line and phase shifter are connected, so there is The array elements are connected to each other; The receiving phase of each element and The receiving phase of each element will be exchanged; taking the first array element as the reference array element, and It is expressed as:

[0076] (9)

[0077] (10)

[0078] Electrical length The microstrip transmission line produces a delayed phase , the phase shifter produces a delayed phase ,in is determined by the phase shifter state, and The states of the group phase shifters remain the same, ; then The echo phase of an array element is , then The sum of the receiving phase and the echo phase of each array element is a constant, satisfying the generalized phase conjugate relationship:

[0079] (11)

[0080] Step 2.3, in the case of oblique incidence of broadband signals, determine the generalized conjugate relationship between the receiving phase and the echo phase of the array element in the one-dimensional Van Atta array based on the 2-bit phase shifter;

[0081] In the case of broadband signals, the frequency of the radiation signal changes with time. Assume that the broadband radiation signal is a linear frequency modulation signal:

[0082] (12)

[0083] in, is the linear frequency modulation period, is the linear frequency-varying coefficient. When the radiation signal is incident obliquely, there is a fixed time delay between two adjacent array elements. , radiating to the The delay difference between the array element and the reference array element , delay difference This causes different frequencies when incident on different array elements, thus causing additional phase , No. The array elements pass through phase shifters and the electrical length is The microstrip transmission line and The array elements exchange phases and generate a delayed phase , No. The receiving phase and echo phase of each array element are and ; The additional phase is linearly related to the frequency, that is, , is the linear phase change coefficient, is the frequency difference caused by the additional phase. The change in frequency is linearly related to time, that is, , is the time delay difference caused by the frequency difference, then the additional phase Delay Difference The linear relationship , then The sum of the received phase of each array element and the echo phase satisfies the generalized phase conjugation principle:

[0084] (13)

[0085] That is, directional tracing is independent of frequency and has no dispersion characteristics. The working bandwidth of the Van Atta array is limited by the working bandwidth of the array elements and the transmission lines.

[0086] As a specific example, in step 2, a reconfigurable Van Atta array model based on a 2-bit phase shifter is constructed to achieve adaptive directional tracing in four discrete phase states, as follows:

[0087] Take the X-band electromagnetic wave Van Atta array as an example. Figure 6 , Figure 7 , Figure 8 As shown in the figure, the designed reconfigurable Van Atta array model is a multi-layer structure, which is composed of 8 basic array elements. The side length of the basic array element is 15 mm, and it includes six layers from top to bottom, among which:

[0088] The first layer is the patch antenna layer. The patch antenna is composed of rectangular metal patches placed symmetrically in the center. The length of the square metal patch is 9 mm and the width is 8 mm.

[0089] The second layer is the first dielectric substrate layer, the dielectric substrate material is F4B, the dielectric constant is 2.65, the dielectric loss tangent is 0.0027, and the thickness is 2 mm;

[0090] The third layer is the second dielectric substrate layer, the dielectric material is FR-4, the dielectric constant is 4.3, the dielectric loss tangent is 0.025, and the thickness is 0.1 mm;

[0091] The fourth layer is a metal grounding layer with a thickness of 0.035 mm, which serves as the grounding plate of the microstrip line structure;

[0092] The fifth layer is the third dielectric substrate layer, the dielectric material is Rogers RO4350B, the dielectric constant is 3.66, the dielectric loss tangent is 0.0037, the thickness is 0.254 mm, and it serves as the dielectric substrate of the microstrip line structure;

[0093] The sixth layer is a microstrip line structure with a microstrip line width of 0.5 mm and a thickness of 0.035 mm. There are 4 groups of microstrip transmission lines of equal length and 2-bit phase shifters are connected in the middle. In order to provide a DC bias voltage to the PIN diode, two DC feed lines are set at both ends of the phase shifter, and a radial stub is set at a quarter wavelength of the DC feed line to isolate the AC signal. The patch antenna of the first layer is connected to the microstrip line structure of the sixth layer through a coaxial feed line, and the bottom feed line can reduce the additional electromagnetic scattering interference caused by the feed line on the same layer.

[0094] By performing full-wave simulation on the designed directional Doppler stealth cloak, we can obtain the RCS far-field comparison between the large metal plate and the directional Doppler stealth cloak at 0°-60° at 10GHz, as shown in the figure below. Fig. 9 As shown in the figure, compared with the metal plate of the same size, the directional backtracking Doppler stealth cloak in the four states still maintains a higher RCS value as the angle increases.

[0095] As a specific example, in step 3, time modulation is introduced into the reconfigurable Van Atta array model to achieve Doppler frequency compensation for adaptive directional retrieval and obtain a Doppler cloak; combined with Fig.10 , the 0th and 1st order harmonic spectrum amplitude difference diagrams of the time modulation of the directional back-tracing Doppler stealth cloak at different angles and working frequencies are as follows:

[0096] Assume that the signal source is is the direction of arrival incident on the linear array elements, with the rightmost element as the reference element, and no loss in the radiation process, then The signal received by each array element is expressed as:

[0097] (14)

[0098] in, is the time delay from the signal source to the reference array element, is the distance from the signal source to the reference array element, The signal source reaches The time delay of an array element relative to the reference array element is The time delay caused by the microstrip transmission line and phase shifter is ;

[0099] Then, the array element The radiated signal is expressed as:

[0100] (15)

[0101] in, is the transmission coefficient of the array element, is the reflection coefficient of the array element, is the transmission loss coefficient of the microstrip transmission line, is a time-varying periodic function of the phase shifter that changes periodically over time, is the modulation frequency, and Due to the performance of the patch, within the working bandwidth of the reconfigurable Van Atta array model , for the point frequency signal , then the signal radiated by the array is expressed as:

[0102] (16)

[0103] From formula (16), we can see that the reconfigurable Van Atta array model realizes the Doppler frequency compensation of adaptive directional retrieval and obtains the Doppler cloak.

[0104] Perform Fourier transform on the modulated echo signal to obtain its spectrum diagram. ) and fundamental frequency ( ) by subtracting the amplitude of the Doppler cloak at different frequencies and incident angles, we can obtain the modulation effect of the directional Doppler stealth cloak at different frequencies and incident angles, such as Fig.10 shown.

[0105] As a specific example, in step 4, spatial modulation is introduced into the reconfigurable Van Atta array model to achieve adaptive directional backtracking radar cross-sectional area RCS reduction, and obtain a multifunctional Doppler stealth cloak; combined with Fig.11a , Fig.11b , Fig.11c , Fig.11d , the normalized directional pattern of the directional back-tracing Doppler stealth cloak for spatial modulation at different angles is:

[0106] According to the array factor theory, for a one-dimensional linear array, the beam direction of the linear array can be determined based on the phase gradient maintained between the array elements. ; Assume that the linear array has Array element, is a positive even number, according to the phase cancellation technique, select The array element increases the phase , backscattering will occur. A beam notch is generated at

[0107] For the reconfigurable Van Atta array model, the phase delay of the transmission line is controlled by adjusting the phase shifter to achieve Transmission lines and other The delay phase difference of the transmission line , thus satisfying the phase cancellation principle and achieving RCS reduction;

[0108] (17)

[0109] From equation (17), according to the requirements of phase cancellation technology, control Transmission lines and other The delay phase difference of the transmission line , then there exists Combinations, according to formula (18) as the standard, The direction of the backtracking array is Under RCS, For the phase cancellation array The RCS under each combination has a minimum difference between the two linear array RCSs within the scanning angle range. The combination with the largest minimum difference is taken as the optimal combination for RCS reduction:

[0110] (18)

[0111] The reconfigurable Van Atta array model that meets the optimal combination of RCS reduction is the Doppler stealth cloak.

[0112] like Figure 11a~Figure 11d As shown, the directional back-tracking Doppler stealth cloak achieves RCS reduction after spatial modulation based on phase cancellation, and the normalized radiation pattern at incident angles of 0°, 15°, 30°, and 45°.

[0113] In one embodiment, a multifunctional adaptive directional back-tracing Doppler stealth cloak construction system is provided, and the system is used to implement the multifunctional adaptive directional back-tracing Doppler stealth cloak construction method. The system includes a phase shifter construction module, an array model construction module, a time modulation module and a space modulation module. The functions of each module are as follows:

[0114] Phase shifter construction module, which builds a 2-bit phase shifter based on a reconfigurable microstrip transmission line and adjusts the length of the microstrip transmission line to enable the phase shifter to achieve four discrete phase states;

[0115] The array model building module analyzes the generalized conjugate relationship between the receiving phase and the radiation phase of the array elements in the antenna array, builds a reconfigurable Van Atta array model based on a 2-bit phase shifter, and realizes adaptive directional tracing in four discrete phase states;

[0116] The time modulation module introduces time modulation into the reconfigurable Van Atta array model to achieve adaptive directional backtracking Doppler frequency compensation and obtain the Doppler cloak;

[0117] The spatial modulation module introduces spatial modulation into the reconfigurable Van Atta array model to achieve adaptive directional backtracking radar cross-sectional area (RCS) reduction and obtain a multifunctional Doppler stealth cloak.

[0118] In one embodiment, a multifunctional adaptive directional back-tracing Doppler stealth cloak is provided. The stealth cloak is constructed based on the construction method of the multifunctional adaptive directional back-tracing Doppler stealth cloak.

[0119] In one embodiment, a mobile terminal is provided, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the method for constructing the multifunctional adaptive directional backtracking Doppler stealth cloak when executing the program.

[0120] In summary, the present invention can significantly improve the efficiency of the multifunctional adaptive direction control of the Doppler stealth cloak, and solve the problem that the traditional planar Doppler stealth cloak is not applicable in the case of single-station oblique incidence observation.

[0121] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

[0122] It should be understood that in order to simplify the present invention and help those skilled in the art understand the various aspects of the present invention, in the above description of the exemplary embodiments of the present invention, the various features of the present invention are sometimes described in a single embodiment or described with reference to a single figure. However, the present invention should not be interpreted as the features included in the exemplary embodiments are all necessary technical features of the patent claims.

Claims

1. A method for constructing a multifunctional adaptive directional backtracking Doppler stealth cloak, characterized in that: The following steps are involved: Step 1: construct a 2-bit phase shifter based on a reconfigurable microstrip transmission line, and adjust the length of the microstrip transmission line so that the phase shifter can achieve four discrete phase states; Step 2: Analyze the generalized conjugate relationship between the receiving phase and the radiation phase of the array elements in the antenna array, construct a reconfigurable Van Atta array model based on a 2-bit phase shifter, and realize adaptive directional tracing in four discrete phase states; Step 3, introducing time modulation into the reconfigurable Van Atta array model to achieve Doppler frequency compensation with adaptive directional retrieval and obtain the Doppler cloak; Step 4: Introduce spatial modulation into the reconfigurable Van Atta array model to achieve adaptive directional backtracking radar cross-sectional area (RCS) reduction and obtain a multifunctional Doppler stealth cloak.

2. The method for constructing a multifunctional adaptive directional backtracking Doppler stealth cloak according to claim 1 is characterized in that: The reconfigurable microstrip transmission line described in step 1 is composed of microstrip lines of different electrical lengths and PIN diodes; the DC bias voltage is controlled according to a preset voltage code, the on-off state of the PIN diodes loaded at both ends of the microstrip lines of different electrical lengths is changed, and the electrical length of the transmission line is adjusted, so that the phase state passing through the phase shifter is changed.

3. The method for constructing a multifunctional adaptive directional backtracking Doppler stealth cloak according to claim 2 is characterized in that: In step 1, a 2-bit phase shifter based on a reconfigurable microstrip transmission line is constructed, and the length of the microstrip transmission line is adjusted so that the phase shifter can achieve four discrete phase states, specifically: The 2-bit phase shifter based on reconfigurable microstrip transmission line is composed of two sets of transmission lines in cascade, each set of transmission lines is composed of two microstrip lines of unequal electrical lengths. The electrical length difference of the first group of microstrip lines ,in is the phase wavelength of the microstrip line, that is, the microstrip line satisfies the phase difference ; The electrical length difference of the second group of microstrip lines , that is, the microstrip line satisfies the phase difference ; PIN diodes are used at both ends of the microstrip line as connecting input and output ports, and the DC bias voltage is adjusted to control the on and off of the PIN diodes, so as to select the path between the input and output ports, thereby controlling the phase change between the input and output ports; Finally, four phase states are obtained, namely , achieving 2-bit phase shift.

4. The method for constructing a multifunctional adaptive directional backtracking Doppler stealth cloak according to claim 3 is characterized in that: In step 2, the generalized conjugate relationship between the receiving phase and the radiation phase of the array element in the antenna array is analyzed, specifically: Step 2.1, determine the generalized conjugate relationship between the receiving phase and the radiation phase of the array element in the directional traceback antenna array; Suppose there is a rectangular coordinate system in three-dimensional space The source , electromagnetic waves propagate outward as spherical waves, and are approximately plane waves under far-field conditions; in space, there is The antenna array is composed of array elements. The position of the array element is recorded as , ; Assume that the signal radiated to the array element is simple harmonic and its amplitude is , the angular frequency is , the initial phase is zero, then The array element at time Received signal It is expressed as: (1) (2) in, For time, is the attenuation factor of the radiation signal propagating in space; The radiation signal propagates in space to the The receiving phase when the array element is Array elements and source points The wave distance between The phase lag caused by is the wavelength of electromagnetic waves in space, is the speed of light, is the electromagnetic wave carrier frequency, ; No. After receiving the radiation signal, the array element reflects the signal, and the reflected signal propagates to the space at The venue Time, field Received signal It is expressed as: (3) (4) in, is the attenuation factor of the reflected signal propagating in space, is the initial phase of the reflected signal in space, For the Array elements and field points The wave distance between The phase lag caused by In the far field condition, the field point Total field received equal The superposition of the fields of the array elements at this point, equation (3) is expressed by the superposition theorem as: (5) Ignoring the array size under far-field conditions, , Is only with distance Related functions require the array to implement directional backtracking, that is, When the total field is superimposed in phase, the field strength is the largest. Then according to formula (5), we can get: (6) in, is a constant term, indicating the reference value of the phase shift; is an arbitrary integer, representing a multiple of the phase period; according to equations (2) and (4), equation (6) is written as: (7) The receiving phase of the array element Phase with radiation Satisfy the generalized phase conjugation relationship; when and When , equation (7) obtains the phase conjugate relationship in the complex frequency domain: (8) Step 2.2, determining the generalized conjugate relationship between the receiving phase and the echo phase of the array element in the one-dimensional Van Atta array based on the 2-bit phase shifter; For a one-dimensional Van Atta array based on a 2-bit phase shifter, the number of array elements is is an even number, and the array element spacing is , then in the case of plane wave incidence, there is a fixed phase difference between two adjacent array elements ;No. The array element and The electrical length between the array elements is The microstrip transmission line and phase shifter are connected, so there is a total of The array elements are connected to each other; The receiving phase of each element and The receiving phase of each element will be exchanged; taking the first array element as the reference array element, and It is expressed as: (9) (10) Electrical length The microstrip transmission line produces a delayed phase , the phase shifter produces a delayed phase ,in is determined by the phase shifter state, and The states of the group phase shifters remain the same, ; then The echo phase of an array element is , then The sum of the receiving phase and the echo phase of each array element is a constant, satisfying the generalized phase conjugate relationship: (11) Step 2.3, in the case of oblique incidence of broadband signals, determine the generalized conjugate relationship between the receiving phase and the echo phase of the array element in the one-dimensional Van Atta array based on the 2-bit phase shifter; In the case of broadband signals, the frequency of the radiation signal changes with time. Assume that the broadband radiation signal is a linear frequency modulation signal: (12) in, is the linear frequency modulation period, is the linear frequency-varying coefficient. When the radiation signal is incident obliquely, there is a fixed time delay between two adjacent array elements. , radiating to the The delay difference between the array element and the reference array element , delay difference This causes different frequencies when incident on different array elements, thus causing additional phase , No. The array elements pass through phase shifters and the electrical length is The microstrip transmission line and The array elements exchange phases and generate a delayed phase , No. The receiving phase and echo phase of each array element are and ; The additional phase is linearly related to the frequency, that is, , is the linear phase change coefficient, is the frequency difference caused by the additional phase; the change in frequency is linearly related to time, that is, , is the time delay difference caused by the frequency difference, then the additional phase Delay Difference The linear relationship , then The sum of the received phase of each array element and the echo phase satisfies the generalized phase conjugation principle: (13) That is, directional tracing is independent of frequency and has no dispersion characteristics. The working bandwidth of the Van Atta array is limited by the working bandwidth of the array elements and the transmission lines.

5. The method for constructing a multifunctional adaptive directional backtracking Doppler stealth cloak according to claim 4 is characterized in that: In step 2, a reconfigurable Van Atta array model based on a 2-bit phase shifter is constructed to achieve adaptive directional tracing in four discrete phase states, as follows: For the X-band electromagnetic wave Van Atta array, the reconfigurable Van Atta array model is designed as a multi-layer structure, which is composed of 8 basic array elements. The side length of the basic array element is 15 mm, and it includes six layers from top to bottom, including: The first layer is the patch antenna layer. The patch antenna is composed of rectangular metal patches placed symmetrically in the center. The length of the square metal patch is 9 mm and the width is 8 mm. The second layer is the first dielectric substrate layer, the dielectric substrate material is F4B, the dielectric constant is 2.65, the dielectric loss tangent is 0.0027, and the thickness is 2 mm; The third layer is the second dielectric substrate layer, the dielectric material is FR-4, the dielectric constant is 4.3, the dielectric loss tangent is 0.025, and the thickness is 0.1 mm; The fourth layer is a metal grounding layer with a thickness of 0.035 mm, which serves as the grounding plate of the microstrip line structure; The fifth layer is the third dielectric substrate layer, the dielectric material is Rogers RO4350B, the dielectric constant is 3.66, the dielectric loss tangent is 0.0037, the thickness is 0.254 mm, and it serves as the dielectric substrate of the microstrip line structure; The sixth layer is a microstrip line structure with a microstrip line width of 0.5 mm and a thickness of 0.035 mm. There are 4 groups of microstrip transmission lines of equal length and 2-bit phase shifters are connected in the middle. In order to provide a DC bias voltage to the PIN diode, two DC feed lines are set at both ends of the phase shifter, and a radial stub is set at a quarter wavelength of the DC feed line to isolate the AC signal. The patch antenna of the first layer is connected to the microstrip line structure of the sixth layer through a coaxial feed line.

6. The method for constructing a multifunctional adaptive directional backtracking Doppler stealth cloak according to claim 5 is characterized in that: In step 3, time modulation is introduced into the reconfigurable Van Atta array model to achieve Doppler frequency compensation with adaptive directional retrieval and obtain the Doppler cloak, specifically: Assume that the signal source is is the direction of arrival incident on the linear array elements, with the rightmost element as the reference element, and no loss in the radiation process, then The signal received by each array element is expressed as: (14) in, is the time delay from the signal source to the reference array element, is the distance from the signal source to the reference array element, The signal source reaches The time delay of an array element relative to the reference array element is The time delay caused by the microstrip transmission line and phase shifter is ; Then, the array element The radiated signal is expressed as: (15) in, is the transmission coefficient of the array element, is the reflection coefficient of the array element, is the transmission loss coefficient of the microstrip transmission line, is a time-varying periodic function of the phase shifter that changes periodically over time, is the modulation frequency, and Due to the performance of the patch, within the working bandwidth of the reconfigurable Van Atta array model , for the point frequency signal , then the signal radiated by the array is expressed as: (16) From formula (16), we know that the reconfigurable Van Atta array model can realize the Doppler frequency compensation of adaptive directional retrieval and obtain the Doppler cloak.

7. The method for constructing a multifunctional adaptive directional backtracking Doppler stealth cloak according to claim 6 is characterized in that: In step 4, spatial modulation is introduced into the reconfigurable Van Atta array model to achieve adaptive directional backtracking radar cross-sectional area RCS reduction and obtain a multifunctional Doppler stealth cloak, specifically: According to the array factor theory, for a one-dimensional linear array, the beam direction of the linear array can be determined based on the phase gradient maintained between the array elements. ; Assume that the linear array has Array elements, is a positive even number, according to the phase cancellation technique, select The phase of each array element increases , backscattering will occur. A beam notch is generated at For the reconfigurable Van Atta array model, the phase delay of the transmission line is controlled by adjusting the phase shifter to achieve Transmission lines and other The delay phase difference of the transmission line , thus satisfying the phase cancellation principle and achieving RCS reduction; (17) From equation (17), according to the requirements of phase cancellation technology, control Transmission lines and other The delay phase difference of the transmission line , then there exists Combinations, according to formula (18) as the standard, The direction of the backtracking array is Under RCS, For the phase cancellation array The RCS under each combination has a minimum difference between the two linear array RCSs within the scanning angle range. The combination with the largest minimum difference is taken as the optimal combination for RCS reduction: (18) The reconfigurable Van Atta array model that meets the optimal combination of RCS reduction is the Doppler stealth cloak.

8. A multifunctional adaptive direction-tracing Doppler stealth cloak construction system, characterized in that: The system is used to implement the method for constructing a multifunctional adaptive directional backtracking Doppler stealth cloak according to any one of claims 1 to 7. The system includes a phase shifter construction module, an array model construction module, a time modulation module and a space modulation module. The functions of each module are as follows: Phase shifter construction module, which builds a 2-bit phase shifter based on a reconfigurable microstrip transmission line and adjusts the length of the microstrip transmission line to enable the phase shifter to achieve four discrete phase states; The array model building module analyzes the generalized conjugate relationship between the receiving phase and the radiation phase of the array elements in the antenna array, builds a reconfigurable Van Atta array model based on a 2-bit phase shifter, and realizes adaptive directional tracing in four discrete phase states; The time modulation module introduces time modulation into the reconfigurable Van Atta array model to achieve adaptive directional backtracking Doppler frequency compensation and obtain the Doppler cloak; The spatial modulation module introduces spatial modulation into the reconfigurable Van Atta array model to achieve adaptive directional backtracking radar cross-sectional area (RCS) reduction and obtain a multifunctional Doppler stealth cloak.

9. A multifunctional adaptive directional Doppler cloak, characterized in that: The invisible cloak is constructed based on the construction method of the multifunctional adaptive directional backtracking Doppler invisible cloak described in any one of claims 1 to 7.

10. A mobile terminal comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the program, the method for constructing the multifunctional adaptive direction-tracing Doppler stealth cloak as described in any one of claims 1 to 7 is implemented.

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