Moire smart reflective surface for enabling beamforming

Abstract

The invention discloses a Moore intelligent reflecting surface for realizing beam forming. The Moore intelligent reflecting surface is structurally composed of four layers of materials, wherein the first layer and the second layer are periodic metal pattern layers which have different rotational symmetry and are tightly attached, the third layer is a dielectric material isolation layer, and the fourth layer is a metal backboard layer. The Moore intelligent reflecting surface can reflect a vertical incident wave, surface impedance distribution can be adjusted by changing the style of the metal pattern layer, and beamforming of the reflected wave is achieved. By endowing the two layers of periodic metal patterns with different rotational symmetry, single-beam, two-beam and three-beam far-field directional diagrams can be formed; the two layers of metal patterns are mutually rotated along the central axis, so that continuous scanning adjustment can be carried out on the pitch angle of a reflected wave beam within the range of 0-60 degrees and the azimuth angle within the range of 0-360 degrees. The design does not need an active device, and compared with a beam forming mode of a traditional active device, the beam forming device has the advantages of being low in cost, low in power consumption, low in profile, high in reliability, not prone to breakdown and the like.

Description

Technical Field

[0001] The present invention belongs to the intersection of new artificial electromagnetic materials and wireless communication technology, and relates to a passive Moore intelligent reflective surface capable of realizing dynamic beam forming. More specifically, it relates to an intelligent reflective passive electromagnetic metasurface that realizes beam azimuth and pitch angle scanning, as well as beam quantity and shape switching through mechanical rotation. Background Art

[0002] In recent years, information metamaterials have become a research hotspot in the electromagnetic field. Reconfigurable smart metasurfaces have become the focus of cross-border innovation between artificial electromagnetic metamaterials and modern mobile communication technologies. By dynamically controlling the reflection / transmission phase of the array with a given bit accuracy, highly flexible real-time control of the incident wave is achieved, thereby achieving the goal of high-speed scanning and switching of far-field beams. Traditional reconfigurable smart metasurfaces have high requirements for unit control, which will produce many unfavorable factors, including high cost, difficulty in large-scale commercial deployment, poor stability, and output power limitations. Therefore, it is of vital strategic significance to seek a low-cost, low-profile, lightweight, and multi-purpose beam-reconfigurable reflector antenna that can replace traditional phased array antennas and reflector antennas based on active elements in military application scenarios such as radar detection, target tracking, satellite communications, and RCS reduction. In the past decade, twistronics has rapidly become a research hotspot in the field of condensed matter. This is a new research field that changes the electrical properties of materials by adjusting the twist angle between two layers of two-dimensional materials. Specifically, when two pieces of two-dimensional materials are close together and rotated, the energy band characteristics of the composite structure composed of the two layers of materials will change wonderfully and lead to strange physical behaviors, such as high-temperature superconductivity. The close fit and twisting between two layers of electromagnetic metasurfaces with different periodic structures and different symmetries can produce special beamforming functions for incident electromagnetic waves. By stacking two layers of metasurfaces with high-frequency spatial periods closely and rotating them relative to each other along an axis perpendicular to the surface, a superimposed pattern that changes with the twist angle can be formed, including the pattern period size and pattern style, and a radiation beam pointing to a specific angle can be formed. This method of twisting and superimposing metasurfaces provides a low-cost implementation solution for beam-reconfigurable Moore smart reflective surfaces. More importantly, this design solution is different from traditional metasurfaces from theoretical analysis to design optimization, and will open up new ideas for theoretical analysis and design of metasurfaces. Summary of the invention

[0003] Technical problem: The present invention provides a Moore smart reflection surface for realizing beamforming, which can meet the demand for beam reconfigurable antennas in high-power microwave application scenarios. By closely fitting two layers of periodic metal patterns with completely different rotational symmetries, a pattern with a larger common period is superimposed to change the surface equivalent impedance distribution, realize the wavefront control of the incident wave, and then achieve the purpose of controlling the far-field radiation pattern. The single beam, two beams and three beams formed by the reflection of the Moore smart reflection surface can be continuously scanned within the range of 0° to 60° in elevation angle and 0° to 360° in azimuth angle. The present invention overcomes the problems of high cost and easy breakdown of reflective surface array antennas based on active devices, and has the advantages of low cost, low power consumption, low profile and high reliability.

[0004] Technical solution: The overall structure of the Moore smart reflective surface of the present invention includes four layers. The first and second layers are periodic metal pattern layers with rotational symmetry, the third layer is a dielectric material isolation layer, and the fourth layer is an all-metal reflective layer. The two layers of different metal patterns can rotate around an axis passing through the center points of the two layers of patterns. By giving different rotational symmetries to the first and second layers of metal patterns, single-beam, two-beam and three-beam far-field radiation patterns can be achieved. By adjusting the relative rotation angle of the two layers of metal patterns, the pitch angle of the reflected beam can be freely scanned in the upper half space, realizing a Moore smart reflective surface with dynamic beamforming.

[0005] in,

[0006] The two-layer metal pattern may have any one of C2, C3, C4 or C6 rotational symmetry.

[0007] The two layers of metal patterns have different rotational symmetries at their highest weights. By combining patterns with different rotational symmetries, effective control of the number of beams can be achieved.

[0008] The two-layer metal pattern is not unique under the condition of satisfying the specified rotational symmetry, and can be selected from the corresponding planar space group pattern.

[0009] The electrical thickness of the periodic metal pattern is 0.0001 wavelength to 0.01 wavelength.

[0010] The periodic metal pattern is processed on a dielectric substrate with any dielectric constant, and the electrical thickness of the dielectric substrate ranges from 0.0001 wavelength to 0.01 wavelength.

[0011] The dielectric constant and dielectric loss of the material used in the dielectric material isolation layer are close to the relevant parameters of air. Its electrical dimension thickness should be 0.001 wavelength to 0.5 wavelength.

[0012] The material of the metal backplane layer has strong conductivity, and its electrical dimension thickness is greater than 0.0001 wavelength.

[0013] The overall appearance of the smart reflective surface is of any shape.

[0014] Beneficial effects: Compared with the prior art, the present invention has the following advantages

[0015] 1. Compared with the traditional two-layer twisted metasurface with the same symmetry, the present invention can control the number and radiation state of reflected electromagnetic wave beams by selecting the rotational symmetry of the single-layer metasurface. In the case of a vertically incident circularly polarized beam, it can achieve full coverage of reflected single-beam, two-beam, and three-beam at pitch angles of 0° to 60° and azimuth angles of 0° to 360°.

[0016] 2. Compared with the method of using programmable metamaterials with active devices (such as switching diodes and varactor diodes) to control beamforming, the present invention eliminates the active devices and peripheral circuits. Only by superimposing and rotating two layers of passive metasurfaces, the shape and number of beams can be efficiently controlled, greatly reducing costs.

[0017] 3. Active antenna arrays such as programmable metamaterials and massive MIMO antennas using active devices contain a large number of switching diodes or varactor diodes, as well as peripheral circuits. During the operation of beamforming, the parameters of all diodes need to be controlled and adjusted, and the control process is very complicated and cumbersome. The present invention adopts a passive method, and only the torsion angle needs to be adjusted to achieve beamforming and adjust the number of beams, and has a larger beam radiation coverage.

[0018] 4. Since the present invention does not include active devices such as switching diodes or varactor diodes, it is less affected by interference during operation and has higher working stability. Therefore, it can work in high-power microwave scenarios such as radar detection and electronic countermeasures.

[0019] 5. The present invention is applicable to the optimization of channel blind area coverage of wireless communication systems. Beamforming is achieved by relative rotation of two layers of patterns, and base station signals are reflected to weak channel areas and blind areas, thereby improving channel coverage quality. Compared with smart reflective surfaces based on active devices, the present invention does not require active devices and control circuits, greatly reduces costs, has higher economic benefits, and is suitable for large-scale commercial deployment. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the structure of the molar intelligent reflective surface.

[0021] Figure 2 It is a moiré intelligent reflective surface with C3 rotational symmetry and C4 rotational symmetry.

[0022] Figure 3 It is a molar intelligent reflective surface with C2 rotational symmetry and C4 rotational symmetry.

[0023] Figure 4 It is a molar intelligent reflective surface with C3 rotational symmetry and C6 rotational symmetry.

[0024] Figure 5 are examples of different patterns with C2 rotational symmetry.

[0025] Figure 6 are examples of different patterns with C3 rotational symmetry.

[0026] Figure 7 are examples of different patterns with C4 rotational symmetry.

[0027] Figure 8 are examples of different patterns with C6 rotational symmetry.

[0028] Fig. 9 The simulation results of the 3D far-field pattern of the single-beam moiré smart reflector when the twist angle ψ = 0°, 2°, 4°, 6°, 8°, and 10°. The solid line indicates the fluctuation range of the normalized intensity of all beam amplitudes.

[0029] Fig.10 It is the beam peak angle trajectory of the single-beam smart reflector when the twist angle rotates counterclockwise from 0° to 12° (step size 0.25°).

[0030] Fig.11 The simulation results of the three-dimensional far-field pattern of the two-beam smart reflector when the twist angle ψ = 0°, 2°, 4°, 6°, 8°, and 10°. The solid line represents the fluctuation range of the normalized intensity of all beam amplitudes.

[0031] Fig.12 It is the beam peak angle trajectory of the two-beam smart reflector when the twist angle rotates counterclockwise from 0° to 12° (step size 0.25°).

[0032] Fig.13 The simulation results of the three-dimensional far-field pattern of the three-beam Moore smart reflector when the twist angle ψ = 0°, 2°, 4°, 6°, 8°, and 10°. The solid line represents the fluctuation range of the normalized intensity of all beam amplitudes.

[0033] Fig.14 It is the beam peak angle trajectory of the three-beam smart reflector when the twist angle rotates counterclockwise from 0° to 12° (step size 0.25°). DETAILED DESCRIPTION

[0034] The present invention is used to realize a low-cost moiré intelligent reflective surface for beamforming. The moiré pattern formed by the relative rotation of two layers of periodic metal patterns can be used to adjust the surface impedance distribution, thereby realizing the wavefront control of the incident wave and achieving the purpose of dynamic beamforming. At present, asymmetric single beam, asymmetric three beams, and symmetric two beams have been realized. The research has broken through the technical difficulties of high cost, high power consumption, and high-power breakdown of reconfigurable reflective surfaces based on active devices, and proposed an innovative point of wavefront control based on the moiré principle.

[0035] Figure 1 A structural schematic diagram of a Moore smart reflective surface is given, which includes, from top to bottom, two tightly fitted and relatively rotatable metal layer metasurfaces 1 and 2 with periodic patterns, a dielectric isolation layer 3, and a metal backplane 4. All layers are tightly fitted in sequence. The styles of the two layers of periodic metal patterns can be arbitrarily and independently selected from a two-dimensional space group; at the same time, the two layers of periodic patterns have different rotational symmetries. When the two layers of tightly fitted periodic metal patterns are tightly fitted, a Moore periodic pattern will be formed in the overlapping area, thereby changing the surface impedance distribution of the metasurface, so that the wavefront of the incident wave obtains the expected amplitude and phase distribution, thereby achieving the purpose of arbitrary regulation of the far field. By rotating the two layers of tightly fitted periodic metal patterns, the Moore pattern will change continuously, so that the continuous regulation of the far-field pattern can be achieved, achieving the purpose of dynamic beamforming.

[0036] Figure 2 , Figure 3 and Figure 4 Specific example schematic diagrams of three types of Moore smart reflective surfaces are shown, corresponding to the reflective surface designs for generating asymmetric single beam, symmetric two-beam and asymmetric three-beam, respectively. Figure 2 The moiré smart reflective surface pattern shown adopts an asymmetric single-beam design, with the first metal layer having C3 rotational symmetry and the second layer having C4 rotational symmetry, and the relative rotation angle between the two layers of the metasurface is set to ψ = 10°. From the figure, the moiré pattern formed by the overlapping part of the two layers of pattern can be intuitively observed. This difference in rotational symmetry between the upper and lower layers gives the reflective surface a unique moiré pattern feature, which is in sharp contrast to the traditional metasurface design. Unlike the traditional design of periodic unit or super subunit patterns, the moiré smart reflective surface produces special performance through the unique overlapping structure of the two layers of pattern. Figure 3 A symmetric two-beam moiré smart reflective surface is shown. The regular triangle pattern has a regular hexagonal periodic structure. By changing the number and distribution of regular triangles, the following structures can be formed: Figure 3 The combination of the C6 symmetric pattern and the C3 symmetric pattern is shown. The relative rotation angle ψ is also set to 10°. This design forms a clearly visible moiré pattern and realizes the dynamic shaping of the two beams through precise beam control. Figure 4 This corresponds to the schematic diagram of the asymmetric three-beam Moore smart reflective surface. Figure 2 and Figure 3 Similarly, the two-layer pattern has different planar distribution to achieve asymmetric three-beam. To this end, the upper layer design adopts C3 rotational symmetry, and the lower layer adopts C6 rotational symmetry, and maintains a relative rotation angle of ψ = 10°. This design also produces a significant moiré pattern through the unique rotational symmetry difference between the two layers, meeting the needs of multi-beamforming.

[0037] Figure 5-Figure 8 Other alternative examples with different plane rotational symmetries are given, which are different patterns satisfying C2, C3, C4 and C6 rotational symmetries.

[0038] Through the time-domain simulation solver of the full-wave simulation software CST Studio Suite, a systematic simulation calculation was carried out for three types of Moore smart reflective surfaces with different rotational symmetries. In view of the fact that Moore smart reflective surfaces are usually anisotropic in a rectangular coordinate system, a left-handed circularly polarized plane wave was used as the excitation source to ensure the accuracy of the simulation results. Since the lossless reflective metasurface has chiral symmetry, the response of the Moore smart reflective surface to right-handed and left-handed circularly polarized plane waves is symmetrical, and only the polarization direction is flipped. In order to achieve the comparison of results at different incident angles, all far-field scattering results were normalized. The normalized benchmark uses the backscattering of a metal plate of the same size under the same excitation conditions, thereby ensuring the comparability of the results at different angles.

[0039] In order to ensure that the patterns can overlap at any rotation angle, the model is designed to be circular with a diameter of 250mm. The isolation layer material is polymethacrylimide (PMI) foam, which has a refractive index close to that of air. The two layers of metasurface are processed using conventional printed circuit board (PCB) technology on a 40-micron thick flexible polyimide dielectric layer (dielectric constant is about 3.1).

[0040] Fig. 9 It is the simulation result of the three-dimensional far-field pattern (left-hand circularly polarized component) of the single-beam smart reflector when the torsion angle ψ = 0°, 2°, 4°, 6°, 8°, and 10°. The solid line represents the fluctuation range of the normalized intensity of all beam amplitudes. It can be seen from the figure that the single beam at all rotation angles has a stable beam intensity. This feature can also be seen from the average value of the beam intensity at each torsion angle (double solid line). Here, we define the normalized beam intensity as the beam efficiency. It can be seen that the beam efficiency at all torsion angles is greater than 0.4. It is worth pointing out that this beam efficiency is higher than the beam efficiency of traditional metasurfaces.

[0041] Fig.10The beam trajectory is further shown when the twist angle increases from 0° to 10° (step size 0.2°). As the twist angle increases, the single beam trajectory moves accordingly. The asymmetric single beam trajectory changes very steadily. As the twist angle increases, there is no obvious sudden change in the azimuth and elevation angles.

[0042] Fig.11 The simulation results of the three-dimensional far-field pattern (left-hand circular polarization component) of the Moore smart reflection surface that can generate symmetrical dual beams at ψ = 0°, 2°, 4°, 6°, 8°, and 10°. When the torsion angle is 0, there is almost no beam splitting effect, and a certain diffraction component is generated. It can be seen from the figure that as the torsion angle ψ gradually increases in the range of 0° to 10°, the pitch angle of the symmetrical two beams will gradually increase. Consistent with the previous simulation results, the peak intensity of the two beams will also gradually decrease with the increase of the pitch angle. It can be observed that when ψ = 10°, the beam changes from a dual beam to a triple beam. This is because at this torsion angle, the surface current distribution caused by the Moore pattern of the Moore smart reflection surface undergoes a sudden change. Compared with the single beam case, the beam efficiency is slightly reduced, and the overall efficiency remains above 0.3.

[0043] Fig.12 The figure is a schematic diagram of the trajectory of the peak angle of the beam simulated by the two-beam pattern. It can be seen from the figure that the two beams obtained by the two-beam pattern simulation have the characteristics of symmetrical distribution, and the angle between the beams is approximately 180°. The change of the torsion angle will not cause a sudden change in the pitch angle, which shows that even if the rotational symmetry of the two-layer structure is different, the change of the moiré pattern can still remain stable.

[0044] By using a combination of different symmetries, an asymmetric three-beam system can also be achieved. Fig.13 The full-wave simulation results of the three-beam pattern are given, and it can be seen from the figure that when the twist angle between the two metasurfaces changes from ψ = 0° to 10°, the left-hand circularly polarized reflected wave will have three obvious beams and the pitch angle of the beam will gradually increase.

[0045] Fig.14 The trajectory diagram of the peak angle of the three-beam pattern simulation beam is given. The angle between the three beams is about 120°, and as the twist angle increases, there will be no obvious mutation in the azimuth and elevation angles.

[0046] Due to the significant advantages of Moore's smart reflective surface in cost and power consumption, it has broad prospects for large-scale application in the next generation of mobile communications. Specifically, in indoor scenes, Moore's smart reflective surface can be cleverly hidden in the ceiling, furniture surface, wall or behind decorative paintings; in outdoor scenes, it can also be integrated into the facade of the building, light boxes and billboards, thereby greatly improving the communication performance without affecting the beauty of the environment. Although the dynamic control of the beam by Moore's smart reflective surface is mainly achieved through mechanical rotation, its control speed is slightly inferior to the programmable metamaterial loaded with diodes, and it cannot achieve the level of real-time response, but it is still applicable in many communication scenarios that only require channel control in seconds or minutes. In addition, due to its purely passive characteristics, Moore's smart reflective surface will not produce additional noise effects on the channel, ensuring signal quality. In addition, Moore's smart reflective surface also has broad application prospects in the field of radar detection. For example, by designing a purely planar parabolic antenna, Moore's smart reflective surface can provide excellent beamforming effects while maintaining an ultra-low profile appearance. This ultra-low profile structure is not only easy to install, but also flexible to conformal requirements. Its passive characteristics have unique advantages in applications such as electronic countermeasures that need to withstand high power.

[0047] It should be noted that the above is only a preferred embodiment of the present invention. Since the present invention uniquely utilizes two layers of passive materials with different rotational symmetries to form a moiré pattern and thus realizes continuous regulation of the far-field pattern, it has the characteristics of being easy to implement and imitate. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A Moore's smart reflective surface for realizing beamforming, characterized in that: the overall structure of the reflective surface comprises four layers, the first and second layers are periodic metal pattern layers with rotational symmetry, the third layer is a dielectric material isolation layer, and the fourth layer is an all-metal reflective layer; the two layers of different metal patterns can rotate around an axis passing through the center points of the two layers of patterns; by giving different rotational symmetries to the first and second layers of metal patterns, single-beam, two-beam and three-beam far-field radiation patterns are realized; by adjusting the relative rotation angle of the two layers of metal patterns, the pitch angle of the reflected beam can be freely scanned in the upper half space, thereby realizing a Moore's smart reflective surface with dynamic beamforming.

2. The moiré smart reflective surface for realizing beamforming according to claim 1, characterized in that: The two-layer metal pattern has any one of C2, C3, C4 or C6 rotational symmetry.

3. The moiré smart reflective surface for realizing beamforming according to claim 1, characterized in that: The highest rotational symmetries of the two layers of metal patterns are different. By combining patterns with different rotational symmetries, effective control of the number of beams can be achieved.

4. The moiré smart reflective surface for realizing beamforming according to claim 1, characterized in that: The two-layer metal pattern, while satisfying the specified rotational symmetry condition, is not unique and is selected from the corresponding planar space group pattern.

5. The moiré smart reflective surface for realizing beamforming according to claim 1, characterized in that: The electrical thickness of the periodic metal pattern is 0.0001 wavelength to 0.01 wavelength.

6. The moiré smart reflective surface for realizing beamforming according to claim 1, characterized in that: The periodic metal pattern is processed on a dielectric substrate with any dielectric constant, and the electrical thickness of the dielectric substrate ranges from 0.0001 wavelength to 0.01 wavelength.

7. The moiré smart reflective surface for implementing beamforming according to claim 1, characterized in that: The dielectric constant and dielectric loss of the material used in the dielectric material isolation layer are close to the relevant parameters of air, and the electrical dimension thickness thereof is 0.001 wavelength to 0.5 wavelength.

8. The moiré smart reflective surface for implementing beamforming according to claim 1, characterized in that: The material of the metal backplane layer is conductive, and its electrical thickness is greater than 0.0001 wavelength.

9. The moiré smart reflective surface for implementing beamforming according to claim 1, characterized in that: The overall appearance of the smart reflective surface is of any shape.

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