A Vortex Wave Generation Structure and Design Method Based on a Multifunctional Shared Aperture Metasurface

Abstract

The present invention discloses a vortex wave generation structure and a design method based on a multifunctional shared-aperture metasurface, which relates to the technical field of novel artificial electromagnetic materials. It can realize the generation of vortex waves with different polarizations and different modes working in different wide frequency bands. The technical solution of the present invention is as follows: The vortex wave generation structure includes a multifunctional shared-aperture metasurface, and the multifunctional shared-aperture metasurface includes a plurality of shared-aperture basic unit structures. The shared-aperture basic unit structure sequentially includes a top pattern layer, an intermediate dielectric layer, and a bottom metal layer from top to bottom; the top pattern layer includes a right-handed circular polariton unit formed by embedding a hollow cross ring in a square split-ring resonator, a vertical polariton unit in an "I" shape structure, and a horizontal polariton unit in an "I" shape structure. The overall design idea is novel, simple and feasible, and the structure of this case is stable and the working effect is good.

Description

Technical Field

[0001] The present invention relates to the technical field of novel artificial electromagnetic materials, and particularly relates to a design of a vortex wave generation structure based on a multi-functional shared aperture metasurface. Background Art

[0002] As is well known, the development of the characteristics of traditional electromagnetic waves such as polarization, frequency, amplitude, and phase in improving the channel capacity has reached a threshold, and it is very difficult to further improve the spectrum utilization rate. Due to the inherent orthogonality and infinity of orbital angular momentum, it has become a new physical parameter dimension for electromagnetic wave multiplexing and manipulation, and has great potential in the development of a new generation of communication systems.

[0003] Two-dimensional metamaterials, namely artificial electromagnetic metasurfaces, have the characteristics of light weight, low profile, and simple manufacturing, and have electromagnetic characteristics that are difficult to achieve by natural materials. By reasonably designing parameters such as the period, structure, thickness, and material of the basic unit of the metasurface, the free and independent control of the phases of electromagnetic waves with multiple polarizations and multiple frequency bands can be achieved under the same unit aperture. By arranging and combining such shared aperture basic units, vortex wave generation, beam scanning, beam anomalous reflection, beam focusing, polarization conversion, RCS (radar cross section) reduction, etc. can be achieved in the field of electromagnetic waves.

[0004] In the microwave and millimeter wave bands, earlier methods for realizing vortex waves include spiral phase plates, planar phase plates, parabolic antennas, etc., which have great limitations in manufacturing processes and working bandwidths. In recent years, antenna arrays, cavity structures, and metasurface structures have been mostly used to realize the generation of vortex waves. Among them, metasurfaces have great advantages in combining the orbital angular momentum of vortex waves with traditional physical parameters. However, most of the research on multi-functional vortex waves based on metasurfaces stays at generating dual-band and dual-polarization vortex waves, and uses multi-layer technology or sub-array technology, which will lead to an increase in preparation difficulty and too low aperture efficiency. In addition, since the design difficulty of multi-functional metasurfaces is to ensure that the coupling effects between polarization sub-units working in each wide frequency band are small, it is more difficult to achieve multi-function on a single-layer structure than on a multi-layer structure. In summary, it is necessary to find a clever structure combination and space allocation method to design a single-layer shared aperture multi-polarization multi-frequency band reflective metasurface, so as to realize the independent control of the phases of different polarization reflected waves working in different wide frequency bands. Summary of the Invention

[0005] In view of the above problems, the present invention proposes a vortex wave generation structure and design method based on a multi-functional shared aperture metasurface, which can generate vortex waves of different polarizations and different modes working in different wide frequency bands. Finally, a single-layer reflective metasurface that can generate right-handed circularly polarized vortex waves with l = 1, vertically polarized vortex waves with l = -1, and horizontally polarized vortex waves with l = -2 at working frequencies of 7.15 - 9.07 GHz, 14 - 17 GHz, and 21 - 25 GHz is achieved.

[0006] The technical solution of the present invention is as follows: The vortex wave generation structure includes a multi-functional shared aperture metasurface, and the multi-functional shared aperture metasurface includes a plurality of shared aperture basic unit structures. The shared aperture basic unit structure sequentially includes a top pattern layer, an intermediate dielectric layer, and a bottom metal layer that are fixedly connected from top to bottom;

[0007] The intermediate dielectric layer and the bottom metal layer have the same period;

[0008] The top pattern layer includes a right-handed circularly polarized sub-unit 3 formed by embedding a hollow cross-ring 2 in a square split-ring resonator 1, a vertically polarized sub-unit 4 in an "I" shape structure, and a horizontally polarized sub-unit 5 in an "I" shape structure. The vertically polarized sub-unit 4 is perpendicular to the horizontally polarized sub-unit 5, and both are within the hollow cross-ring 2.

[0009] Further, the vertically polarized sub-unit 4 is composed of a metal strip with a width of w y and the horizontally polarized sub-unit 5 is composed of a metal strip with a width of w x , w y > w x .

[0010] Further, the intermediate dielectric layer is composed of a low-loss material with a relative dielectric constant of 2.2 - 2.65, and the metal of the bottom metal layer and the top pattern layer is composed of a metal material with a reflectivity approximately equal to 1.

[0011] Further, the periods of the bottom metal layer and the intermediate dielectric layer are both 7 mm, and the thickness of the central dielectric layer is 2 mm; both the bottom metal layer and the top metal pattern layer are composed of copper with a conductivity of 5.8×10 7 S / m, and the dielectric layer is composed of F4B with a relative dielectric constant of 2.65 and a loss tangent of 0.0009.

[0012] Further, the overall thickness of the multi-functional shared aperture metasurface is less than one-tenth of the longest operating wavelength of the three polarizations.

[0013] It is designed according to the following steps: It is required to design three sub-units that can independently control the right-handed circularly polarized wave, the vertically polarized wave, and the horizontally polarized wave, and adopt a suitable spatial distribution method so that a shared aperture basic unit structure reasonably distributes the sub-units of the three polarizations, realizing the shared aperture of the three sub-units. The shared aperture basic unit structure successively includes a top metal pattern layer, a middle dielectric layer, and a bottom metal layer from top to bottom;

[0014] Step 1: First, according to the requirements of the amplitude and phase of the basic unit structure for the vortex wave generating reflection, the rotation angle and slot width of the slotted strip of the right-handed circularly polarized sub-unit 3 in the shared aperture basic unit structure are used as optimization variables to optimize the size parameters of the right-handed circularly polarized sub-unit 3 structure. The rotation angle takes values from -90° to 90° at intervals of 5°. Different rotation angles respectively correspond to the slot widths required for the fixed resonance frequency points, and a total of 37 basic states are obtained, realizing that the co-polarization reflection coefficient is greater than 0.935 and the phase span is 347°; the length of the central metal strip of the vertically polarized sub-unit 4 in the shared aperture basic unit structure is used as an optimization variable to optimize the size parameters of the vertically polarized sub-unit 4 structure. Taking the phase interval of 90° required by the 2-bit coded metasurface as the optimization factor, a total of 4 basic states are obtained, realizing that the co-polarization reflection coefficient is approximately equal to 1 and the phase interval is approximately equal to 90°; the length of the central metal strip of the horizontally polarized sub-unit 5 in the shared aperture basic unit structure is used as an optimization variable to optimize the size parameters of the horizontally polarized sub-unit 5 structure. Similarly, taking the phase interval of 90° required by the 2-bit coded metasurface as the optimization factor, a total of 4 basic states are obtained, realizing that the co-polarization reflection coefficient is approximately equal to 1 and the phase interval is approximately equal to 90°;

[0015] Step 2: According to Step 1, the shared aperture basic unit structure has a total of 37×4×4 basic states. Among them, the 37 structural states of the right-handed circularly polarized sub-unit 3 correspond to 37 phase responses, realizing the phenomenon of the multiple relationship between the unit rotation angle and the phase response of the PB-like phase. The 4 structural states of the vertically polarized sub-unit 4 and the horizontally polarized sub-unit 5 respectively correspond to 4 phase responses with a phase interval of approximately 90 degrees, realizing the phase gradient required by the 2-bit coded metasurface;

[0016] According to the Helmholtz equation in free space, the electric field expression of the vortex wave propagating along the electromagnetic wave transmission direction is derived. The phases of the vortex beam modes reflected in the vertical direction for different polarizations are used as the output phases of the metasurface, and the output phase formula of each unit on the metasurface is obtained;

[0017] Then, according to the incident field source, the input phase of the metasurface is obtained. Among them, the incident right-handed circularly polarized wave is a plane wave, and the incident vertically polarized and horizontally polarized waves are both spherical waves. Furthermore, the compensation phases that need to be provided by the polarization sub-unit structures on the metasurface are obtained;

[0018] Step 3: According to the compensation phase formula, use the MATLAB program to establish the correspondence between the phase of each polariton unit structure of the shared aperture basic unit structure and the compensation phase, obtain the form of the compensation phase required by different polariton unit structures of the entire metasurface, and then obtain the arrangement rule of all shared aperture basic units of the metasurface that generates different polarized different-mode vortex waves. According to the principle of the phase gradient metasurface, the right-handed circularly polarized unit selects the structural state corresponding to the phase value closest to the required phase among 37 phase states, the vertical polarized unit arrangement uses a 90° phase gradient, and the horizontal polarized unit arrangement uses a 90° phase gradient. Fill the right-handed circularly polarized unit (3), the vertical polarized unit (4), and the horizontal polarized unit (5) into each local position of the overall metasurface according to the required phase, so as to obtain a reflective multi-functional vortex wave generating metasurface.

[0019] The shared aperture basic unit structure designed based on this method can maintain the polarization conversion efficiency of circular polarization above 90% within the relative bandwidth of 23.67% in the C and X bands (7.15 - 9.07 GHz), realize the reflection of the same polarization and can achieve a phase span of 347°; within the relative bandwidth of 19.35% in the Ku band (14 - 17 GHz), the vertical polarization reflection coefficient is approximately equal to 1, realizing the reflection of the same polarization and realizing a 2-bit digital coding metasurface; within the relative bandwidth of 17.39% in the K band (21 - 25 GHz), the horizontal polarization reflection coefficient is approximately equal to 1, realizing the reflection of the same polarization and realizing a 2-bit digital coding metasurface. Through the theoretical derivation of the vortex wave compensation phase and the correlation of the corresponding phase responses of each sub-unit structure of the shared aperture unit, using the right-handed circularly polarized plane wave, the vertical polarized spherical wave, and the horizontal polarized spherical wave as the field sources of the three polarizations, a single-layer reflective metasurface that can generate a right-handed circularly polarized vortex wave with l = 1, a vertical polarized vortex wave with l = -1, and a horizontal polarized vortex wave with l = -2 at the operating frequencies of 7.15 - 9.07 GHz, 14 - 17 GHz, and 21 - 25 GHz is designed. The proposed scheme is simulated and designed through full-wave simulation, and finally the multi-functional vortex wave metasurface structure is experimentally verified, which is in line with the simulation results.

[0020] Overall, this case can ultimately achieve the generation of vortex waves in different modes with different polarizations operating in different wide frequency bands. Finally, a single-layer reflective metasurface can generate right-handed circularly polarized vortex waves with \(l = 1\), vertically polarized vortex waves with \(l=-1\), and horizontally polarized vortex waves with \(l = -2\) at working frequencies of 7.15 - 9.07 GHz, 14 - 17 GHz, and 21 - 25 GHz. The overall design concept is novel, simple and feasible. Moreover, the structure of this case is stable and has good working effects. Through ingenious structural combinations and spatial distributions, the single-layer multi-polarization multi-band reflective metasurface with a shared aperture realizes the purpose of independent phase regulation of reflected waves with different polarizations operating in different wide frequency bands. Description of the Drawings

[0021] Figure 1 Side view of the basic unit of the shared aperture of the metasurface for realizing multi-polarization multi-band multi-mode vortex waves in the embodiment;

[0022] Figure 2 Top view of the basic unit of the shared aperture of the metasurface for realizing multi-polarization multi-band multi-mode vortex waves in the embodiment, with the structural parameters of the square split ring resonator marked;

[0023] Figure 3 Top view of the basic unit of the shared aperture of the metasurface for realizing multi-polarization multi-band multi-mode vortex waves in the embodiment, with the structural parameters of the hollow cross ring marked;

[0024] Figure 4 Top view of the basic unit of the shared aperture of the metasurface for realizing multi-polarization multi-band multi-mode vortex waves in the embodiment, with the structural parameters of the orthogonally placed "I"-shaped structure marked;

[0025] Where: 1 - square split ring resonator, 2 - hollow cross ring, 3 - right-handed circular polarization sub-unit, 4 - vertical polarization sub-unit, 5 - horizontal polarization sub-unit; \(p\) is the periodic side length of the basic unit, \(h\) is the thickness of the dielectric plate of the basic unit, \(o\) is the outer side length of the square split ring resonator, \(i\) is the inner side length of the square split ring resonator, \(g\) is the slot width of the square split ring resonator, \(\alpha\) is the rotation angle of the slotted strip, \(a\) o is the outer side length in the vertical direction of the hollow cross ring, \(a\) i is the inner side length in the vertical direction of the hollow cross ring, \(b\) o is the outer side length in the horizontal direction of the hollow cross ring, \(b\) i is the inner side length in the horizontal direction of the hollow cross ring; \(d\) is the distance of the vertical ring from the vertical (horizontal) polarization sub-unit in the horizontal (vertical) direction, \(d\) y is the arm length of the upper and lower horizontal arms of the larger-sized "I"-shaped structure, \(w\) y is the width of the metal strip of the larger-sized "I"-shaped structure, \(l\) y is the side length of the central metal strip of the larger-sized "I"-shaped structure, \(d\)x is the arm length of the left and right vertical arms of the smaller-sized "I"-shaped structure, w x is the width of the metal strip of the smaller-sized "I"-shaped structure, l x is the side length of the central metal strip of the smaller-sized "I"-shaped structure.

[0026] Figure 5 are the performance results of the shared aperture basic unit of the embodiment, Figure 5 (a) are the co-polarization reflection coefficient and phase of the right-handed circularly polarized unit, Figure 5 (b) are the co-polarization reflection coefficient and phase of the vertically polarized unit, Figure 5 (c) are the co-polarization reflection coefficient and phase of the horizontally polarized unit;

[0027] Figure 6 are the final compensated phase distributions of the metasurface calculated in MATLAB for the generation of different modal vortex waves of three polarizations working in different wide frequency bands in the embodiment: from left to right are right-handed circular polarization, vertical polarization, and horizontal polarization;

[0028] Figure 7 is the test sample for generating multi-polarization, multi-band, and multi-modal vortex waves prepared by the printed circuit board process in the embodiment;

[0029] Figure 8 are the phase and amplitude results of the multi-polarization, multi-band, and multi-modal vortex waves simulated and tested in the embodiment, Figure 8 (a) are the phase and amplitude results of the right-handed circularly polarized wave in the xoy plane at a far-field distance from the metasurface when an 8 GHz right-handed circularly polarized wave is incident, Figure 8 (b) are the phase and amplitude results of the vertically polarized wave in the xoy plane at a distance of 450 mm from the metasurface when a 15 GHz vertically polarized wave is incident, Figure 8 (c) are the phase and amplitude results of the horizontally polarized wave in the xoy plane at a distance of 450 mm from the metasurface when a 22 GHz horizontally polarized wave is incident. Detailed implementation mode

[0030] To clearly illustrate the technical features of this patent, the following will elaborate on this patent in detail through specific implementation modes and in conjunction with its attached drawings.

[0031] In this embodiment: The vortex wave generation structure includes a feed source and a multi-functional shared aperture metasurface. The feed source generates a vortex wave after being incident on the multi-functional shared aperture metasurface. The feed source includes a right-handed circularly polarized plane wave, a horizontally polarized spherical wave, and a vertically polarized spherical wave. The multi-functional shared aperture metasurface includes a plurality of shared aperture basic unit structures, and the shared aperture basic unit structures sequentially include a top pattern layer, an intermediate dielectric layer, and a bottom metal layer fixedly connected from top to bottom;

[0032] The period p of the intermediate dielectric layer and the bottom metal layer of the shared aperture basic unit ( Figure 1 ) is 7 mm, and the thickness h of the intermediate dielectric layer is 2 mm; both the bottom metal layer and the top pattern layer are made of metallic copper with a conductivity of 5.8×10 7 S / m, and the central dielectric layer is made of F4B with a relative dielectric constant of 2.65 and a loss tangent of 0.0009;

[0033] The overall size of the multifunctional metasurface is 224 mm×224 mm, which is composed of 32×32 shared aperture basic units distributed in an array.

[0034] It is required to design three sub-units that can independently control the right-handed circularly polarized wave, the vertically polarized wave, and the horizontally polarized wave, and adopt a suitable spatial distribution method so that the sub-units of the three polarizations are reasonably distributed in a shared aperture basic unit structure to achieve the shared aperture of the three sub-units. The shared aperture basic unit structure includes a top metal pattern layer, an intermediate dielectric layer, and a bottom metal layer from top to bottom in sequence;

[0035] Step 1: First, according to the requirements of the amplitude and phase of the basic unit structure for the vortex wave that generates reflection, the rotation angle and slot width of the slotted strip of the right-handed circularly polarized sub-unit 3 in the shared aperture basic unit structure are used as optimization variables to optimize the size parameters of the right-handed circularly polarized sub-unit 3 structure. The slot width of the slot opened on the square resonant ring by the slotted strip after rotating α is g, thus forming a square split-ring resonator 1. The rotation angle takes values from -90° to 90° at intervals of 5°. Different rotation angles respectively correspond to the slot widths required for fixed resonant frequencies, and a total of 37 basic states are obtained, achieving a co-polarization reflection coefficient greater than 0.935 and a phase span of 347°; the length of the central metal strip of the vertically polarized sub-unit 4 in the shared aperture basic unit structure is used as an optimization variable to optimize the size parameters of the vertically polarized sub-unit 4 structure. Taking the phase interval of 90° required by the 2-bit coded metasurface as the optimization factor, a total of 4 basic states are obtained, achieving a co-polarization reflection coefficient approximately equal to 1 and a phase interval approximately equal to 90°; the length of the central metal strip of the horizontally polarized sub-unit 5 in the shared aperture basic unit structure is used as an optimization variable to optimize the size parameters of the horizontally polarized sub-unit 5 structure. Similarly, taking the phase interval of 90° required by the 2-bit coded metasurface as the optimization factor, a total of 4 basic states are obtained, achieving a co-polarization reflection coefficient approximately equal to 1 and a phase interval approximately equal to 90°;

[0036] Specifically, the shared-aperture basic unit is designed on the principle that the coupling between the circularly polarized and linearly polarized sub-units is less affected. The structure of the circularly polarized sub-unit is modeled and optimized in CST. The basic unit structure includes a bottom metal layer, an intermediate dielectric layer, and a top metal pattern layer. The intermediate dielectric layer and the bottom metal layer have the same period. The top pattern layer is composed of a square split-ring resonator 1 combined with a hollow cross-ring 2 as the right-handed circularly polarized sub-unit 3, a larger-sized "I"-shaped structure as the vertical polarized sub-unit 4, and a smaller-sized "I"-shaped structure as the horizontal polarized sub-unit.

[0037] As Figure 2 shown, in the right-handed circularly polarized sub-unit 3, the outer side length o of the square split-ring resonator 1 is 6.4 mm, the inner side length i is 6 mm, the rotation angle α of the slotted strip is variable from -90° to 90°, and the slotted width g is variable from 1.3 - 2.35 mm. Both are optimization variables.

[0038] As Figure 3 shown, the outer side length a of the hollow cross-ring in the vertical direction o is 5.6 mm, and the inner side length a i is 5.2 mm. The outer side length b of the hollow cross-ring in the horizontal direction o is 5.6 mm, and the inner side length b i is 5.2 mm;

[0039] As Figure 4 shown, the hollow cross-ring includes a vertical ring and a horizontal ring. The distance d between the vertical ring and the vertical polarized sub-unit 4 in the horizontal direction is 0.2 mm, and the distance d between the horizontal ring and the horizontal polarized sub-unit 5 in the vertical direction is 0.2 mm. The arm length d of the upper and lower horizontal arms of the vertical polarized sub-unit 4 y is 3 mm, the width w of the metal strip y is 0.4 mm, and the length l of the central metal strip y varies in the range of 1.5 - 4.39 mm, which is an optimization variable. The arm length d of the left and right vertical arms of the horizontal polarized sub-unit 5 x is 1.2 mm, the width w of the metal strip x is 0.2 mm, and the length l of the central metal strip x varies in the range of 0.5 - 4.76 mm, which is an optimization variable;

[0040] Step 2: According to the shared-aperture basic unit structure obtained in Step 1, there are a total of 37×4×4 basic states. Among them, the 37 structural states of the right-handed circularly polarized sub-unit 3 correspond to 37 phase responses, realizing the phenomenon of the multiple relationship between the unit rotation angle and the phase response of the PB-like phase. The 4 structural states of the vertical polarized sub-unit 4 and the horizontal polarized sub-unit 5 respectively correspond to 4 phase responses with a phase interval of approximately 90 degrees, realizing the phase gradient required by the 2-bit encoded metasurface.

[0041] Specifically, according to the amplitude and phase requirements for realizing vortex waves, during the CST optimization process, for the right-handed circularly polarized sub-unit 3, the rotation angle and slot width of the slotted strip in the square split-ring resonator 1 are selected as optimization variables. The phase modulation principle of the right-handed circularly polarized sub-unit 3 is similar to the basic principle of PB phase, but technically, while adjusting the rotation angle of the slotted strip, the slot width needs to be adjusted to keep the resonance frequency unchanged, and 37 basic states with a phase span of 347° can be optimized, so that the circular polarization conversion rate is greater than 90% in the frequency range of 7.15 - 9.07 GHz (C and X bands). For the vertical polarized sub-unit 4, the length of the central metal strip is selected as the optimization variable to ensure that the co-polarization reflection coefficient is approximately equal to 1 when the vertically polarized wave is incident in the frequency range of 14 - 17 GHz, and 4 basic states with a phase span of approximately 270° are realized, with a phase gradient of 90°. For the horizontally polarized sub-unit 5, the length of the central metal strip is selected as the optimization variable to ensure that the co-polarization reflection coefficient is approximately equal to 1 when the horizontally polarized wave is incident in the frequency range of 21 - 25 GHz, and 4 basic states with a phase span of approximately 270° are realized, with a phase gradient approximately equal to 90°.

[0042] According to the above three principles, the rotation angles α and slot widths g of the 37 basic states of the right-handed circular polarizer unit 3 are as follows: -90°, 2.35 mm; -85°, 2.30879 mm; -80°, 2.18317 mm; -75°, 1.99024 mm; -70°, 1.95809 mm; -65°, 1.87574 mm; -60°, 1.84752 mm; -55°, 1.87999 mm; -50°, 1.44415 mm; -45°, 1.3 mm; -40°, 1.44415 mm; -35°, 1.6491 mm; -30°, 1.90526 mm; -25°, 1.98609 mm; -20°, 1.88359 mm; -15°, 1.8635 mm; -10°, 1.92931 mm; -5°, 1.96749 mm; 0°, 2 mm; 5°, 1.96749 mm; 10°, 1.92931 mm; 15°, 1.8635 mm; 20°, 1.88359 mm; 25°, 1.98609 mm; 30°, 1.90526 mm; 35°, 1.649 mm; 40°, 1.44415 mm; 45°, 1.3 mm; 50°, 1.44415 mm; 55°, 1.87999 mm; 60°, 1.84752 mm; 65°, 1.87574 mm; 70°, 1.95809 mm; 75°, 1.95809 mm; 80°, 2.18317 mm; 85°, 2.30879 mm; 90°, 2.35 mm; The right-handed circular polarization reflection coefficients of these 37 basic states are all above 0.935, and the phase span can reach 347°( Figure 5 (a)). The lengths l of the central metal strips of the 4 basic states of the vertical polarizer unit 4 y are 1.5 mm, 1.97 mm, 2.16 mm, and 2.78 mm respectively; the vertical polarization reflection coefficients of these 4 basic states are approximately equal to 1, and the phase intervals are approximately equal to 90 degrees( Figure 5 (b)). The lengths l of the central metal strips of the 4 basic states of the horizontal polarizer unit 5 x are 0.61 mm, 2.06 mm, 3.06 mm, and 4.76 mm respectively; the horizontal polarization reflection coefficients of these 4 basic states are approximately equal to 1, and the phase intervals are approximately equal to 90 degrees( Figure 5 (c));

[0043] According to the Helmholtz equation in free space, the electric field expression of the vortex wave propagating along the electromagnetic wave transmission direction is derived:

[0044]

[0045] where l is the OAM mode number, is the azimuth angle of the unit at the coordinate position (x, y) relative to the origin, k0 is the free-space wave number, and E0 is a constant vector. The input phase of the metasurface is obtained from the incident field source. Since the incident right-handed circularly polarized wave is a plane wave and no phase compensation is required, the phase compensation formula for the circular polariton unit on the metasurface is:

[0046]

[0047] Both the incident vertically polarized and horizontally polarized waves are spherical waves, and spherical wave phase compensation is required. Then, the phase compensation formulas for the two linearly polarized polariton units on the metasurface are obtained:

[0048]

[0049] where is the position vector of the m-th unit on the x-axis and the n-th unit on the y-axis, is the position vector of the feed antenna, and k represents the wave number in vacuum at the center frequency point.

[0050] Step 3: According to the compensation phase formulas (2) and (3), use the MATLAB program to establish the correspondence between the phase of each polariton unit structure and the compensation phase of the shared aperture basic unit structure of the metasurface, and the required compensation phase forms for different polariton unit structures of the entire metasurface can be obtained. Then, the arrangement rules of all shared aperture basic units of the metasurface that generate different polarized different-mode vortex waves ( Figure 6 ) are obtained, that is, in the MATLAB program, calculate α, g, and l of each shared aperture basic unit in the 32x32 shared aperture basic units according to the compensation phase formulas (2) and (3) y 、l x . The right-handed circularly polarized polariton unit 3 (select the structure state corresponding to the phase value closest to the required phase from 37 phase states), the vertically polarized polariton unit 4 (the structure state with a 90-degree phase gradient), and the horizontally polarized polariton unit 5 (the structure state with a 90° phase gradient) are filled into the respective local positions of the overall metasurface according to the arrangement rules corresponding to right-handed circular polarization, vertical polarization, and horizontal polarization according to the required phase, so as to obtain the reflective multifunctional vortex wave generation metasurface.

[0051] Step 4: Modeling and simulation in CST: Based on the hyper-surface compensation phase program obtained from MATLAB, joint modeling and simulation are carried out in CST. It is determined that the simulation working frequency band for the right-handed circular polarization part is 7.15 - 9.07 GHz, the simulation working frequency band for the vertical polarization part is 14 - 17 GHz, and the simulation working frequency band for the horizontal polarization part is 21 - 25 GHz. The right-handed circular polarization plane wave, vertical polarization spherical wave, and horizontal polarization spherical wave are respectively selected as the field sources for simulation calculation. The spherical wave feed is 100 mm away from the hyper-surface. Analyze the electric field amplitude and phase in the near field. For the sampling planes of vertical polarization and horizontal polarization, they are both set on a 200 mm × 200 mm plane 450 mm away from the hyper-surface;

[0052] Step 5: As Figure 7 shown, prepare the sample through the PCB printed circuit board process and complete the test in the microwave anechoic chamber to observe the effects achieved by the device; obtain the test results of 8 GHz right-handed circular polarization ( Figure 8 (a)), the simulation test results of 15 GHz vertical polarization and 22 GHz horizontal polarization ( Figure 8 (b) and (c)). It can be seen that the effects of the electric field amplitude and phase are basically the same. The right-handed circular polarization has the vortex wave phase effect of l = 1 (counterclockwise single-arm helix), the vertical polarization has the vortex wave phase effect of l = -1 (clockwise single-arm helix), and the horizontal polarization has the vortex wave phase effect of l = -2 (clockwise double-arm helix). The effects are consistent with the expectations, verifying the feasibility of the structure;

[0053] In summary, based on the single-layer multi-polarization multi-band shared aperture basic unit, the present invention designs a structure for generating multi-polarization multi-band multi-mode vortex waves, which can be preferably applied to the expansion directions of frequency diversity and polarization diversity in the communication system based on orbital angular momentum.

[0054] There are many specific implementation ways for the present invention. The above description is only the preferred implementation manner of the present invention. It should be pointed out that for those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements can still be made, and these improvements should also be regarded as the protection scope of the present invention.

Claims

1. A vortex wave generation structure based on a multi-functional shared aperture metasurface, characterized in that The vortex wave generation structure includes a multi-functional shared aperture metasurface, which includes a plurality of shared aperture basic unit structures. The shared aperture basic unit structure successively includes a top pattern layer, a middle dielectric layer, and a bottom metal layer from top to bottom; The middle dielectric layer and the bottom metal layer have the same period; The top pattern layer includes a right-handed circular polariton unit (3) formed by embedding a hollow cross ring (2) in a square split ring resonator (1), a vertical polariton unit (4) in an "I" shape structure, and a horizontal polariton unit (5) in an "I" shape structure. The vertical polariton unit (4) is perpendicular to the horizontal polariton unit (5), and both are within the hollow cross ring (2).

2. The vortex wave generation structure based on a multifunctional shared-aperture metasurface according to claim 1, wherein The vertical polariton unit (4) is composed of metal strips with a width of w y and the horizontal polariton unit (5) is composed of metal strips with a width of w x . w y > w x .

3. The vortex wave generation structure based on a multifunctional shared-aperture metasurface according to claim 1, wherein The periods of both the bottom metal layer and the middle dielectric layer are 7 mm, and the thickness of the central dielectric layer is 2 mm; both the bottom metal layer and the top metal pattern layer are composed of metallic copper with a conductivity of 5.8×10 7 S / M, and the dielectric layer is composed of F4B with a relative permittivity of 2.65 and a loss tangent of 0.0009.

4. A vortex wave generation structure based on a multi-functional shared aperture metasurface according to claim 1, characterized in that, The overall thickness of the multi-functional shared aperture metasurface is less than one-tenth of the longest operating wavelength of the three polarizations.

5. A design method of the multifunctional shared-aperture metasurface described in claim 1, characterized in that, It is designed according to the following steps: Step 1: First, according to the requirements of the amplitude and phase of the basic unit structure for generating the reflected vortex wave, the rotation angle and groove width of the slotted strip of the right-handed circular polariton unit (3) in the shared aperture basic unit structure are used as optimization variables to optimize the size parameters of the right-handed circular polariton unit (3) structure. The rotation angle is taken from -90° to 90° at intervals of 5°. Different rotation angles respectively correspond to the slot widths required for fixed resonance frequencies, and a total of 37 basic states are obtained, realizing that the co-polarization reflection coefficient is greater than 0.935 and the phase span is 347°; the length of the central metal strip of the vertical polariton unit (4) in the shared aperture basic unit structure is used as an optimization variable to optimize the size parameters of the vertical polariton unit (4) structure. Taking the phase interval of 90° required by the 2-bit coded metasurface as the optimization factor, a total of 4 basic states are obtained, realizing that the co-polarization reflection coefficient is approximately equal to 1 and the phase interval is approximately equal to 90°; the length of the central metal strip of the horizontal polariton unit (5) in the shared aperture basic unit structure is used as an optimization variable to optimize the size parameters of the horizontal polariton unit (5) structure. Similarly, taking the phase interval of 90° required by the 2-bit coded metasurface as the optimization factor, a total of 4 basic states are obtained, realizing that the co-polarization reflection coefficient is approximately equal to 1 and the phase interval is approximately equal to 90°. Step 2: According to Step 1, the shared aperture basic unit structure has a total of 37×4×4 basic states. Among them, the 37 structural states of the right-handed circular polariton unit (3) correspond to 37 phase responses, realizing the phenomenon of the multiple relationship between the unit rotation angle and the phase response of the PB-like phase. The 4 structural states of each of the vertical polariton unit (4) and the horizontal polariton unit (5) respectively correspond to 4 phase responses with a phase interval of approximately 90 degrees, realizing the phase gradient required by the 2-bit coded metasurface; According to the Helmholtz equation in free space, the electric field expression of the vortex wave propagating along the electromagnetic wave transmission direction is derived. The phases of different modes of the vortex beam reflected in the vertical direction for different polarizations are used as the output phases of the metasurface, and the output phase formula of each unit on the metasurface is obtained; Then, the input phase of the metasurface is obtained according to the incident field source, where the incident right-handed circularly polarized wave is a plane wave, and the incident vertically polarized and horizontally polarized waves are both spherical waves, and then the compensation phases required by each polariton unit structure on the metasurface are obtained; Step 3: According to the compensation phase formula, use the MATLAB program to establish the correspondence between the phase of each polariton unit structure of the shared aperture basic unit structure and the compensation phase, obtain the compensation phase forms required by different polariton unit structures of the entire metasurface, and then obtain the arrangement rules of all shared aperture basic units of the metasurface that generate different polarization different-mode vortex waves; According to the principle of the phase gradient metasurface, the right-handed circular polariton unit selects the structural state corresponding to the phase value closest to the required phase among 37 phase states, the vertically polarized unit arrangement uses a 90° phase gradient, and the horizontally polarized unit arrangement uses a 90° phase gradient. Fill the right-handed circular polariton unit (3), the vertically polarized unit (4), and the horizontally polarized unit (5) into the respective local positions of the overall metasurface according to the required phase, so as to obtain a reflective multi-functional vortex wave generating metasurface.

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