Bidirectional Multi-Mode Terahertz Orbital Angular Momentum Antenna

Abstract

The present invention belongs to the field of communication technologies, and specifically relates to a bidirectional multi-mode orbital angular momentum wave antenna. The antenna of the present invention is composed of a two-dimensional array formed by periodically extending metamaterial units after rotating them by different angles and a spiral metasurface; the spiral metasurface is a spiral phase plate that rotates around the center and whose height increases step by step as the rotation angle increases, and is located at the center of the antenna; the two-dimensional array of metamaterial units is divided into eight sub-arrays; these eight sub-arrays are arranged in sequence in eight azimuths around the spiral metasurface to form a square antenna; the metamaterial unit is composed of a metal patch, a dielectric substrate and a metal ground stacked together; the antenna of the present invention can convert a plane wave incident in a circular polarization mode into an orbital angular momentum wave, and form a bidirectional multi-mode orbital angular momentum wave through reflection and transmission modes. By changing the arrangement mode of the metamaterial units or the height of the spiral phase plate, orbital angular momentum waves of different modes can be formed, which has the advantages of multi-mode multiplexing, flexible design, simple structure, etc.

Description

Technical Field

[0001] The present invention belongs to the field of communication technologies, and particularly relates to an antenna capable of generating bidirectional multi-mode terahertz orbital angular momentum waves. Background Art

[0002] With the rapid development of contemporary technological levels, especially the increasing demand in the field of communication, higher bandwidth utilization and channel capacity have become current popular development directions. Orbital angular momentum (OAM), due to its topological charges carrying mutually orthogonal characteristics, can maintain independent phase transmission for each, improving the bandwidth utilization while effectively enhancing the anti-interference ability of the beam.

[0003] When an electromagnetic wave carries orbital angular momentum, it becomes a vortex electromagnetic wave. The phase wavefront of the vortex electromagnetic wave will be helically distorted along the propagation direction, and a central point with low or zero intensity will be generated in the vortex beam. There are currently many research methods for generating OAM, mainly using circular array antennas, spiral phase plates, spiral reflectors, or metasurfaces. However, using an array antenna to generate OAM in the terahertz frequency band requires a very complex feeding network, and other methods have limitations in generating multi-mode terahertz OAM waves at a single frequency point. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies and defects existing in the prior art, and provide an antenna capable of generating bidirectional multi-mode terahertz orbital angular momentum (OAM) waves, also known as a bidirectional multi-mode terahertz orbital angular momentum antenna.

[0005] The antenna provided by the present invention that can generate bidirectional multi-mode terahertz orbital angular momentum (OAM) waves converts a circularly polarized incident plane wave into a bidirectional multi-mode terahertz OAM wave, and its structure is as Figure 1 shown. The antenna consists of a two-dimensional array of metasurface units formed by rotating the metasurface units by different angles and periodically extending, and a spiral metasurface. The spiral metasurface is a spiral phase plate that rotates around the center and whose height increases step by step as the rotation angle increases. It is square-shaped and is located at the center of the entire antenna. The two-dimensional array of metasurface units is divided into eight sub-arrays, and the size of each sub-array matches the size of the spiral metasurface. These eight sub-arrays are arranged in sequence in eight azimuths around the spiral metasurface, thus forming a square antenna.

[0006] The spiral metasurface is a spiral phase plate that rotates around the center and whose height increases step by step as the rotation angle increases. There are a total of eight gradient surfaces with spiral increase. The adjacent gradient surfaces increase by the same height in sequence. That is, for the eight gradient surfaces of the spiral phase plate, the central angle corresponding to each gradient surface is 45 degrees. And the eight gradients of the spiral phase plate increase synchronously from low to high.

[0007] The metamaterial unit is composed of a layer of metal patch, a layer of dielectric substrate, and a layer of metal ground, which are stacked in sequence from top to bottom. For the structural decomposition, please refer to Figure 2 as shown. Among them, the metal patch is oval, and a fork-shaped (i.e., cross-shaped) groove is opened at the center part.

[0008] Furthermore, the eight sub-arrays of the two-dimensional array of the metamaterial units, each sub-array has 8*8 = 64 metamaterial units, and the eight sub-arrays have a total of 64*8 = 512 metamaterial units.

[0009] The eight sub-arrays of the two-dimensional array of the metamaterial units are formed by extending the metamaterial units after rotating different angles; specifically, with the center of the metal patch as the origin, rotating around the z-axis and rotating a certain angle in the horizontal plane of the metasurface The rotation angle has a linear relationship with the phase change, and can cover a phase change range of 0 degrees to 360 degrees when rotating from 0 degrees to 180 degrees; then the rotated units are translated and extended by equal intervals in the horizontal plane of the metasurface until the entire sub-array is formed (covered); all sub-arrays form a two-dimensional array of metamaterial units; the circularly polarized incident wave irradiated on the unit will be reflected as a circularly polarized wave with the same sense of rotation.

[0010] Furthermore:

[0011] The major axis range of the metal patch in the metamaterial unit is 290 - 310um, the minor axis range is 220 - 230um, the length of the fork-shaped groove at the center of the metal patch is 185 - 188um, and the width is 13 - 15um;

[0012] The metal patch is made of copper foil with a thickness of 18 - 20um;

[0013] The lowest step height of the spiral phase plate position is 137.5 - 139um; the highest step height is 1101 - 1104um;

[0014] The length of the spiral phase plate position is 3745 - 3755um, and the width is 3740 - 3745um.

[0015] In the embodiment:

[0016] The major axis of the metal patch in the metamaterial unit is 299.2um, the minor axis is 224.4um, the length of the fork-shaped groove at the center of the metal patch is 187um, and the width is 14.96um;

[0017] The metal patch is made of copper foil with a thickness of 17um;

[0018] The lowest step height of the spiral phase plate position is 138 um; the highest step height is 1103.9 um;

[0019] The length of the spiral phase plate position is 3750.1 mm, and the width is 3742.5 mm.

[0020] In the present invention, the material of the spiral phase plate dielectric substrate can adopt RO3010 material with a dielectric constant of 11.2 and a loss tangent of 0.0035.

[0021] In the present invention, the material of the metamaterial unit dielectric substrate can adopt Polymide material with a dielectric constant of 3.5, a loss tangent of 0.004, and a size of 10777.2×10777.2×112.2 um 3 (length × width × height).

[0022] In the present invention, the metamaterial units in the eight regions have the same metal patch structure and size, the difference lies in the different rotation angles of the metal patches. The metal patches are all elliptical shapes with a fork-shaped groove in the middle. By changing the rotation angle, the phase delay of the incident wave passing through the metamaterial surface can be changed, and an OAM wave can be obtained after reflection.

[0023] In the present invention, the phase delay of the incident wave changes with the change of the height gradient of the spiral phase plate, and an OAM wave can be obtained after transmission.

[0024] Specifically, with the center of the metal patch as the origin, the basic unit rotates around the z-axis and rotates a certain angle Φ in the horizontal plane of the metasurface. The rotation angle Φ has a linear relationship with the phase change, which can make the phase delay of the incident wave change in the range of 0° to 360° with the change of the patch unit size, and the basic unit can cover the phase transformation range of 0° to 360° when rotating from 0 degrees to 180 degrees; by arranging sub-arrays composed of units with different rotation angles clockwise or counterclockwise to form a two-dimensional metasurface array, when the phase delay after arrangement is a multiple of 360 degrees, different modulus OAM waves can be obtained after reflection; at the same time, when the dielectric substrate of the spiral phase plate is determined, its height change will cause different optical path differences for the incident wave, and has a linear relationship with the mode of the OAM wave, thereby causing the phase delay of the incident wave. When the phase delay is a multiple of 360 degrees, different modulus OAM waves can be obtained after transmission; therefore, the incident wave can form a bidirectional multi-mode OAM wave after reflection by the metasurface and transmission by the spiral phase plate.

[0025] The simulation results show that the metamaterial surface can convert the incident circularly polarized wave at 220 GHz into a bidirectional multi-mode OAM wave. By changing the unit rotation angle of the eight regions on the metamaterial surface and the height of the spiral phase plate, OAM waves of different modes can be obtained. When the unit rotation angles of the metamaterials distributed in the eight regions on the metamaterial surface are all different and exactly make the adjacent phase delay difference 45°, and the eight increasing steps of the spiral phase plate exactly make the adjacent phase delay difference 90°, the incident plane wave can be reflected and converted into a +1 mode and transmitted and converted into a +2 mode bidirectional multi-mode OAM wave at the same time.

[0026] The antenna designed in the present invention can convert the plane wave incident in a circular polarization manner into an orbital angular momentum wave, and can form a bidirectional multi-mode orbital angular momentum wave through reflection and transmission. By changing the arrangement mode of the metamaterial units or the height of the spiral phase plate, orbital angular momentum waves of different modes can be formed, which has the advantages of multi-mode multiplexing, flexible design, simple structure, low cost, etc.

[0027] The literature retrieval results show that no antenna has used this structure to achieve the conversion of a circularly polarized incident plane wave into a bidirectional multi-mode OAM wave at 220 GHz. Brief Description of the Drawings

[0028] Figure 1 It is a top view of the overall structure of the antenna surface for converting a circularly polarized incident plane wave into a bidirectional multi-mode terahertz orbital angular momentum wave according to the present invention.

[0029] Figure 2 It is an exploded view of the unit structure of the metamaterial surface of the antenna for converting a circularly polarized incident plane wave into a bidirectional multi-mode terahertz orbital angular momentum wave according to the present invention.

[0030] Figure 3 It is a diagram of the rotation angle and phase relationship of the unit structure of the metamaterial surface of the antenna for converting a circularly polarized incident plane wave into a bidirectional multi-mode terahertz orbital angular momentum wave according to the present invention at 220 GHz.

[0031] Figure 4 It is a +1 mode phase distribution diagram generated in the near field of the front surface when a 220 GHz circularly polarized plane wave is incident on the antenna for converting a circularly polarized incident plane wave into a bidirectional multi-mode terahertz orbital angular momentum wave according to the present invention.

[0032] Figure 5 It is a +1 mode amplitude distribution diagram generated in the near field of the front surface when a 220 GHz circularly polarized plane wave is incident on the antenna for converting a circularly polarized incident plane wave into a bidirectional multi-mode terahertz orbital angular momentum wave according to the present invention.

[0033] Figure 6The phase distribution diagram of the +2 mode generated in the near field on the back when the antenna of the present invention converts a circularly polarized incident plane wave into a bidirectional multi-mode terahertz orbital angular momentum wave is irradiated by a 220 GHz circularly polarized plane wave.

[0034] Figure 7 The phase distribution diagram of the +2 mode generated in the near field on the back when the antenna of the present invention converts a circularly polarized incident plane wave into a bidirectional multi-mode terahertz orbital angular momentum wave is irradiated by a 220 GHz circularly polarized plane wave. Detailed implementation manners

[0035] The present invention will be further described below in conjunction with the accompanying drawings and embodiments; the embodiments give detailed implementation manners and specific operation processes, but the protection scope of the present invention is not limited to the following embodiments.

[0036] As Figure 1 shown, the present invention provides a metamaterial surface capable of converting a circularly polarized incident plane wave into a bidirectional multi-mode terahertz orbital angular momentum wave, with a center frequency of 220 GHz and an overall size of 10777.2×10777.2×212.2 um 3 (length × width × height). This embodiment includes: an antenna that simultaneously generates bidirectional +1 mode and +2 mode OAM waves, composed of eight metamaterial units rotated at different angles in the outer layer and a spiral phase plate in the inner layer.

[0037] As Figure 1 and Figure 2 shown, the metamaterial unit described in this embodiment is composed of a layer of metal patch, a layer of dielectric substrate, and a layer of metal ground laminated from top to bottom; the metal patch is an ellipse with a fork-shaped slot in the center, and the fork-shaped slot is formed by a long strip-shaped slit with a length of 187 um and a width of 14.96 um rotating ±45° at the center to form a slot combination that intersects at the center. By scanning and simulating the size of the metal patch at 220 GHz, the results are as Figure 3 shown. When the rotation range of the ellipse of the metal patch changes from 0° to 180°, the phase difference change range is from 0° to 360°. According to this simulation result, the metal patch size and rotation angle of the metamaterial unit that meet the requirements can be determined; the lowest step height of the spiral phase plate is 138 um, and the highest step height is 1103.9 um, so that the phase difference change range is from 0° to 720°. The metamaterial unit and the spiral phase plate form a bidirectional multi-mode OAM wave antenna.

[0038] The bidirectional OAM wave antenna implementing the +1 mode and +2 mode in this embodiment consists of an outer layer of eight metamaterial unit sub-arrays and an inner layer of a spiral phase plate. The major axis of the metal patch of the eight metamaterial units is 299.2um, the minor axis is 224.4mm, the slot length is 187um, and the width is 14.96um. A Polymide material substrate with a thickness of 112.2um and a metal floor with a thickness of 100um are selected, and the overall size is 10777.2×10777.2×212.2um 3 (length × width × height). The length of the spiral phase plate is 3750.1um, the width is 3742.5um, the lowest step height is 138um, and the highest step height is 1103.9um. RO3010 is selected as the dielectric material.

[0039] As Figure 4 、 6 shown, for the near-field phase distribution characteristics of the OAM wave described in this embodiment, at the near-field plane 40mm away from the front of the antenna, a square with a width of 40mm is selected to collect the electromagnetic field of the reflected beam. For the metamaterial surface generating the OAM wave of the +1 mode, it can be seen from the near-field phase distribution obtained by simulation that the reflected wave is a vortex beam carrying the orbital angular momentum of the +1 mode. At the near-field plane 40mm away from the back of the antenna, a square with a width of 40mm is selected to collect the electromagnetic field of the transmitted beam. For the metamaterial surface generating the OAM wave of the +2 mode, it can be seen from the near-field phase distribution obtained by simulation that the transmitted wave is a vortex beam carrying the orbital angular momentum of the +2 mode.

[0040] As Figure 5 、 7 shown, for the near-field amplitude distribution characteristics of the OAM wave described in this embodiment, at the near-field plane 40mm away from the front of the antenna, a square with a width of 40mm is selected to collect the electromagnetic field of the reflected beam. For the metamaterial surface generating the OAM wave of the +1 mode, it can be seen from the near-field amplitude distribution obtained by simulation that the reflected wave is a vortex beam carrying the orbital angular momentum of the +1 mode. At the near-field plane 40mm away from the back of the antenna, a square with a width of 40mm is selected to collect the electromagnetic field of the transmitted beam. For the metamaterial surface generating the OAM wave of the +2 mode, it can be seen from the near-field amplitude distribution obtained by simulation that the transmitted wave is a vortex beam carrying the orbital angular momentum of the +2 mode.

[0041] The technical solution of the present invention is not limited to the limitations of the above specific embodiments. For example, the present invention is an antenna combining a metamaterial unit and a spiral phase plate that can convert a circularly polarized incident plane wave into a bidirectional multi-mode OAM wave working at 220GHz, and can generate OAM waves of bidirectional +1 mode and +2 mode simultaneously. Any technical deformation made according to the technical solution of the present invention falls within the protection scope of the present invention.

Claims

1. A bidirectional multi-mode terahertz orbital angular momentum antenna, characterized in that It converts the incident circularly polarized plane wave into a bidirectional multi-mode terahertz OAM wave through the reflection of the outer metasurface and the transmission of the central spiral phase plate; the antenna consists of a two-dimensional array of metasurface units formed by rotating the metasurface units at different angles and periodically extending, and a spiral metasurface; the spiral metasurface is a spiral phase plate that rotates around the center and the height increases step by step as the rotation angle increases, which is square-shaped and located at the center of the whole antenna; the two-dimensional array of metasurface units is divided into eight sub-arrays, and the size of each sub-array matches the size of the spiral metasurface; these eight sub-arrays are arranged in turn in eight azimuths around the spiral metasurface to form a square antenna. In the spiral metasurface, there are a total of eight spiral-increasing gradient surfaces, and the adjacent gradient surfaces increase by the same height in turn; that is, for the eight gradient surfaces of the spiral phase plate, the central angle corresponding to each gradient surface is 45 degrees; moreover, the eight gradients of the spiral phase plate increase synchronously from low to high. The metasurface unit is composed of a layer of metal patch, a layer of dielectric substrate, and a layer of metal ground stacked from top to bottom in sequence; among them, the metal patch is oval-shaped, and a fork-shaped groove is opened in the center part.

2. The bidirectional multi-mode terahertz orbital angular momentum antenna according to claim 1, wherein For the eight sub-arrays of the two-dimensional array of metasurface units, each sub-array has 8×8 = 64 metasurface units, and the eight sub-arrays have a total of 64×8 = 512 metasurface units.

3. The bidirectional multi-mode terahertz orbital angular momentum antenna according to claim 2, wherein The eight sub-arrays of the two-dimensional array of metamaterial units are formed by extending the metamaterial units after rotating them by different angles. Specifically, with the center of the metal patch as the origin, it rotates around the z-axis and rotates a certain angle in the horizontal plane of the metasurface. The rotation angle shows a linear relationship with the phase change, and can cover a phase change range of 0 degrees to 360 degrees when rotating from 0 degrees to 180 degrees. Then, the rotated units are translated and extended at equal intervals in the horizontal plane of the metasurface until the entire sub-array is covered. All sub-arrays form a two-dimensional array of metamaterial units. When a circularly polarized incident wave irradiates the unit, it will be reflected into a circularly polarized wave with the same chirality.

4. The bidirectional multi-mode terahertz orbital angular momentum antenna according to claim 2, wherein In the metasurface unit, the major axis of the oval metal patch is 290 - 310 μm, the minor axis is 220 - 230 μm, the length of the fork-shaped groove in the center of the metal patch is 185 - 188 μm, and the width is 13 - 15 μm.

5. The bidirectional multi-mode terahertz orbital angular momentum antenna according to claim 4, characterized in that The metal patch is made of copper foil with a thickness of 18 - 20 μm.

6. The bidirectional multi-mode terahertz orbital angular momentum antenna according to claim 1, wherein The lowest step height of the spiral phase plate is 137.5 - 139 μm; the highest step height is 1101 - 1104 μm.

7. The bidirectional multi-mode terahertz orbital angular momentum antenna according to claim 6, wherein The length of the spiral phase plate is 3745 - 3755 μm, and the width is 3740 - 3745 μm.

8. The bidirectional multi-mode terahertz orbital angular momentum antenna according to any one of claims 1-7, characterized in that, The antenna converts the incident circularly polarized plane wave at 220 GHz into a bidirectional multi-mode OAM wave through the reflection of the outer metasurface and the transmission of the central spiral phase plate, and different modes of OAM waves can be obtained by changing the rotation angle of the units in the eight regions of the metasurface or the height of the spiral phase plate.

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