Method and system for constructing a multifunctional adaptive direction-tracking Doppler stealth cloak

Abstract

The present invention discloses a method and system for constructing a multifunctional adaptive directional backtracking Doppler stealth cloak. Specifically, the method comprises: 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 achieves four discrete phase states; analyzing the generalized conjugate relationship between the receiving phase and the radiating phase of the array elements in the antenna array, constructing a reconfigurable Van Atta array model based on the 2-bit phase shifter, and achieving adaptive directional backtracking in the four discrete phase states; introducing time modulation into the reconfigurable Van Atta array model to achieve Doppler frequency compensation for the adaptive directional backtracking, thereby obtaining a Doppler cloak; and introducing spatial modulation into the reconfigurable Van Atta array model to achieve radar cross-section (RCS) reduction during the adaptive directional backtracking, thereby obtaining a multifunctional Doppler stealth cloak. This method can significantly improve the efficiency of the multifunctional adaptive directional control of the Doppler stealth cloak.

Description

Technical Field

[0001] The present invention relates to the field of spatiotemporal 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 produce a frequency shift compared to the radiated electromagnetic waves. In order to compensate for the Doppler 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.). This concept mainly utilizes the abnormal interaction between the incident electromagnetic wave and the time-varying metasurface. By properly controlling the electromagnetic properties of the metasurface, a perfect mixing effect can be achieved, causing the reflected electromagnetic wave to produce a frequency shift, which can compensate for the Doppler frequency shift caused by motion and thus avoid 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 In addition to the above applications, Doppler cloaking 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).

[0003] However, traditional planar Doppler cloaks based on time-modulated metasurfaces (B.Liu, Y. He, SWWong, 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, YLSun, 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 provide normal Doppler compensation. In oblique-incidence single-station observations, the scattered energy is mainly along the direction of specular reflection, and there is a problem that effective Doppler compensation cannot be achieved under oblique-incidence conditions. 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, 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 purpose 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-retracing 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 radiating phase of the antenna array elements, construct a reconfigurable Van Atta array model based on a 2-bit phase shifter, and implement adaptive directional retrieval in four discrete phase states;

[0008] Step 3: Introduce time modulation into the reconfigurable Van Atta array model to achieve adaptive directional backtracking Doppler frequency compensation and obtain a Doppler cloak;

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

[0010] A multifunctional adaptive directional retrospective Doppler stealth cloak construction system is used to implement the multifunctional adaptive directional retrospective Doppler stealth cloak construction method. The system includes a phase shifter construction module, an array model construction module, a time modulation module, and a spatial 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. The length of the microstrip transmission line is adjusted to enable the phase shifter to achieve four discrete phase states.

[0012] The array model construction module analyzes the generalized conjugate relationship between the receiving phase and the radiating phase of the antenna array elements, constructs a reconfigurable Van Atta array model based on a 2-bit phase shifter, and implements adaptive directional tracking 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 a Doppler cloak;

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

[0015] A multifunctional self-adaptive directional retrospective Doppler stealth cloak is constructed based on the method for constructing a multifunctional self-adaptive directional retrospective 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) Analyze the generalized conjugate relationship between the receiving phase and the radiating phase of the antenna array elements, construct a reconfigurable Van Atta array model based on a 2-bit phase shifter, and introduce time modulation to achieve Doppler frequency compensation with adaptive directional retracement;

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

[0020] (3) It 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.

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

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

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

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

[0025] Figure 3b The figure shows the frequency-phase diagram of the transmission coefficient simulation 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 principle 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 A top view of the Van Atta array designed in the present invention.

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

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

[0032] Figure 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 operating frequencies.

[0033] Figure 11a Normalized directivity pattern of the spatially modulated directional retro-Doppler stealth cloak at an incident angle of 0°.

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

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

[0036] Figure 11d Normalized directivity pattern of the spatially modulated directional retro-Doppler stealth 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. The method 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 achieves four discrete phase states; analyzing the generalized conjugate relationship between the receiving phase and the radiation phase of the array elements in the antenna array, constructing a reconfigurable Van Atta array model based on the 2-bit phase shifter, and achieving adaptive directional backtracking in the four discrete phase states; introducing time modulation into the reconfigurable Van Atta array model to achieve Doppler frequency compensation for the adaptive directional backtracking, thereby obtaining a Doppler cloak; and introducing spatial modulation into the reconfigurable Van Atta array to achieve radar cross-section (RCS) reduction for the adaptive directional backtracking, thereby obtaining a multifunctional Doppler stealth cloak. The method of the present invention can significantly improve the efficiency of the multifunctional adaptive directional control of the Doppler stealth cloak.

[0038] The present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments. It will be readily understood that, based on the technical solutions of the present invention, a person of ordinary skill in the art can devise various embodiments of the present invention without altering the essential spirit of the present invention. Therefore, the following specific embodiments and drawings are merely illustrative of the technical solutions of the present invention and should not be construed as the entirety of the present invention or as limiting or restricting the technical solutions 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 unless otherwise specifically stated, 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.

[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 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-retracing 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 radiating phase of the antenna array elements, construct a reconfigurable Van Atta array model based on a 2-bit phase shifter, and implement adaptive directional retrieval in four discrete phase states;

[0046] Step 3: Introduce time modulation into the reconfigurable Van Atta array model to achieve adaptive directional backtracking Doppler frequency compensation and obtain a Doppler cloak;

[0047] Step 4: Introduce spatial modulation into the reconfigurable Van Atta array model to achieve adaptive directional backtracking radar cross-section (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; combined with 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 the figure. Figure 3a 、 Figure 3b The transmission coefficient simulation diagram of the four states of the bit shifter is shown as follows:

[0049] The reconfigurable microstrip transmission line is as follows Figure 1 As shown in the figure, 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 lines is composed of two cascaded transmission lines, each of which consists 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 to connect the input and output ports. The DC bias voltage is adjusted to control the on and off of the PIN diodes, selecting 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 realize 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 retracement in four discrete phase states; combined with Figure 4 The working principle analysis diagram of the directional backtracking array shown in the figure is as follows: Figure 5 The principle diagram of the multifunctional adaptive directional backtracking Doppler bucket is shown. Figure 6 Bottom view of the Van Atta array shown, Figure 7 The top view of the Van Atta array is shown. Figure 8 Side view of the Van Atta array shown, Figure 9 The following is a comparison of the far-field RCS results of a large metal plate and a directional Doppler bucket at 0°-60° at 10GHz, specifically:

[0055] Step 2.1, determine the generalized conjugate relationship between the receiving phase and the radiating 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. 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 elements at time Received signal 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 range 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 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 range 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 in phase with the superposition field strength, 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: Determine the generalized conjugate relationship between the receive 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 The electrical length between the array elements is The microstrip transmission line and phase shifter are connected, and there is a total of The array elements are connected to each other; The receiving phase of each element Hedi The receiving phase of each element will be exchanged; take the first array element as the reference array element, and 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: Under the condition 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 results in different frequencies incident on different array elements, causing additional phase , No. The array elements are connected through phase shifters and an electrical length of 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 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 retracement is independent of frequency and has no dispersion characteristics. The operating bandwidth of the Van Atta array is limited by the operating bandwidth of the array elements and 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 retrieval 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. It includes six layers from top to bottom, among which:

[0088] The first layer is the patch antenna layer. The patch antenna consists of rectangular metal patches placed symmetrically around 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, with a dielectric constant of 2.65, a dielectric loss tangent of 0.0027, and a thickness of 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 ground layer with a thickness of 0.035 mm, which serves as the ground plane of the microstrip line structure;

[0092] The fifth layer is the third dielectric substrate layer. The dielectric material is Rogers RO4350B, with a dielectric constant of 3.66, a dielectric loss tangent of 0.0037, and a thickness of 0.254 mm. 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. It is equipped with four groups of equal-length microstrip transmission lines, each of which is connected to a 2-bit phase shifter. In order to provide a DC bias voltage for the PIN diode, two DC feed lines are set at both ends of the phase shifter, and radial stubs are set at a quarter wavelength of the DC feed line to isolate the AC signal. The patch antenna on the first layer is connected to the microstrip line structure on the sixth layer via a coaxial feed line. 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 retrospective Doppler stealth cloak, we can obtain the RCS far-field comparison between the large metal plate and the directional retrospective Doppler stealth cloak at 0°-60° at 10GHz, as shown in the following figure: Figure 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 with adaptive directional retrieval and obtain a Doppler cloak; Figure 10 , the 0th and 1st order harmonic spectrum amplitude difference diagrams of the time modulation of the directional retrospective 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 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 can realize the Doppler frequency compensation of adaptive directional retrieval and obtain the Doppler cloak.

[0104] Perform Fourier transform on the modulated echo signal to obtain its spectrum diagram, and perform Fourier transform on the first-order harmonic ( ) and fundamental frequency ( ) by making a difference in the amplitude of the retracement Doppler stealth cloak at different frequencies and different incident angles, such as Figure 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 Figure 11a 、 Figure 11b 、 Figure 11c 、 Figure 11d , the normalized directional pattern of the direction-retracing Doppler stealth cloak for spatial modulation at different angles is as follows:

[0106] According to the array factor theory, for a one-dimensional linear array, the beam pointing 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 technology, 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] According to formula (17), according to the requirements of phase cancellation technology, control Transmission lines and other The delay phase difference of the transmission line , then there are Combinations, according to formula (18) as the standard, The direction of the backtracking array is Under RCS, For phase cancellation array The RCS under each combination of two linear arrays has a minimum difference in 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 to Figure 11d As shown, the directional retrospective 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 system for constructing a multifunctional adaptive directional retrospective Doppler stealth cloak is provided. The system is used to implement the method for constructing a multifunctional adaptive directional retrospective Doppler stealth cloak. The system includes a phase shifter construction module, an array model construction module, a time modulation module, and a spatial 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. The length of the microstrip transmission line is adjusted to enable the phase shifter to achieve four discrete phase states.

[0115] The array model construction module analyzes the generalized conjugate relationship between the receiving phase and the radiating phase of the antenna array elements, constructs a reconfigurable Van Atta array model based on a 2-bit phase shifter, and implements adaptive directional tracking 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 a Doppler cloak;

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

[0118] In one embodiment, a multifunctional adaptive directional retrospective Doppler stealth cloak is provided. The stealth cloak is constructed based on the method for constructing the multifunctional adaptive directional retrospective 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 when the processor executes the program, the method for constructing a multifunctional adaptive directional backtracking Doppler stealth cloak is implemented.

[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 embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection 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, 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 if all the features included in the exemplary embodiments are essential technical features of the claims of this patent.

Claims

1. A method for constructing a multifunctional adaptive direction-tracking 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. Adjust the length of the microstrip transmission line so that the phase shifter can achieve four discrete phase states: The 2-bit phase shifter based on reconfigurable microstrip transmission lines is composed of two cascaded transmission lines, each of which consists 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 to connect the input and output ports. The DC bias voltage is adjusted to control the on and off of the PIN diodes, selecting 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; Step 2: Analyze the generalized conjugate relationship between the receiving phase and the radiating phase of the antenna array elements, construct a reconfigurable Van Atta array model based on a 2-bit phase shifter, and implement adaptive directional retrieval in four discrete phase states, as follows: For the X-band electromagnetic wave Van Atta array, a 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 consists of rectangular metal patches placed symmetrically around 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, with a dielectric constant of 2.65, a dielectric loss tangent of 0.0027, and a thickness of 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 ground layer with a thickness of 0.035 mm, which serves as the ground plane of the microstrip line structure; The fifth layer is the third dielectric substrate layer. The dielectric material is Rogers RO4350B, with a dielectric constant of 3.66, a dielectric loss tangent of 0.0037, and a thickness of 0.254 mm. It serves as the dielectric substrate of the microstrip line structure. The sixth layer is a microstrip structure with a width of 0.5 mm and a thickness of 0.035 mm. It features four sets of microstrip transmission lines of equal length, each connected to a 2-bit phase shifter. To provide a DC bias voltage for the PIN diodes, two DC feed lines are placed at each end of the phase shifters, and radial stubs are placed at a quarter wavelength of the DC feed line to isolate the AC signal. The patch antenna on the first layer is connected to the microstrip structure on the sixth layer via a coaxial feed line. Step 3: Introduce time modulation into the reconfigurable Van Atta array model to achieve adaptive directional backtracking Doppler frequency compensation and obtain a Doppler cloak; Step 4: Introduce spatial modulation into the reconfigurable Van Atta array model to achieve adaptive directional backtracking radar cross-section (RCS) reduction and obtain a multifunctional Doppler stealth cloak.

2. The method for constructing a multifunctional adaptive direction-tracking Doppler stealth cloak according to claim 1, 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 to change the on-off state of the PIN diodes loaded at both ends of the microstrip lines of different electrical lengths, thereby regulating the electrical length of the transmission line and changing the phase state of the phase shifter.

3. The method for constructing a multifunctional adaptive direction-tracking Doppler stealth cloak according to claim 2 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 radiating phase of the array element in the directional traceback antenna array; Suppose there is a rectangular coordinate system in three-dimensional space 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 elements at time Received signal 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 range 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 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 range 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 the direction backtracking function, that is, When the total field is in phase with the superposition field strength, the field strength is the largest. Then according to formula (5), we can get: (6) in, is a constant term, which represents 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: (7) That is, 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: Determine the generalized conjugate relationship between the receive 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 The electrical length between the array elements is The microstrip transmission line and phase shifter are connected, and there is a total of The array elements are connected to each other; The receiving phase of each element Hedi The receiving phase of each element will be exchanged; take the first array element as the reference array element, and 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: Under the condition 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 results in different frequencies incident on different array elements, causing additional phase , No. The array elements are connected through phase shifters and an electrical length of The microstrip transmission line and the 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 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 retracement is independent of frequency and has no dispersion characteristics. The operating bandwidth of the Van Atta array is limited by the operating bandwidth of the array elements and transmission lines.

4. The method for constructing a multifunctional adaptive directional retrospective Doppler stealth cloak according to claim 3 is characterized in that: In step 3, time modulation is introduced into the reconfigurable Van Atta array model to achieve adaptive directional Doppler frequency compensation 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 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 Equation (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.

5. The method for constructing a multifunctional adaptive directional retrospective Doppler stealth cloak according to claim 4 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-section (RCS) reduction and obtain a multifunctional Doppler stealth cloak. Specifically: According to the array factor theory, for a one-dimensional linear array, the beam pointing 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 technology, select The array element increases the phase , 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) According to formula (17), according to the requirements of phase cancellation technology, control Transmission lines and other The delay phase difference of the transmission line , then there are Combinations, according to formula (18) as the standard, The direction of the backtracking array is Under RCS, For phase cancellation array The RCS under each combination of two linear arrays has a minimum difference in 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.

6. A multifunctional adaptive directional backtracking Doppler stealth cloak construction system, characterized by: The system is used to implement the method for constructing a multifunctional adaptive directional retrospective Doppler stealth cloak as described in any one of claims 1 to 5. The system includes a phase shifter construction module, an array model construction module, a time modulation module, and a spatial 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. The length of the microstrip transmission line is adjusted to enable the phase shifter to achieve four discrete phase states. The array model construction module analyzes the generalized conjugate relationship between the receiving phase and the radiating phase of the antenna array elements, constructs a reconfigurable Van Atta array model based on a 2-bit phase shifter, and implements adaptive directional tracking 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 a Doppler cloak; The spatial modulation module introduces spatial modulation into the reconfigurable Van Atta array model to achieve adaptive directional backtracking radar cross-section RCS reduction and obtain a multifunctional Doppler stealth cloak.

7. A multifunctional adaptive directional backtracking Doppler stealth cloak, characterized by: The invisible cloak is constructed based on the construction method of the multifunctional adaptive direction-tracking Doppler invisible cloak according to any one of claims 1 to 5.

8. A mobile terminal comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the program, the method for constructing the multifunctional adaptive direction-retracing Doppler stealth cloak according to any one of claims 1 to 5 is implemented.

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