An antenna for generating an orbital angular momentum beam

Abstract

The application provides an antenna for generating an orbital angular momentum beam. The antenna adopts a holographic metasurface antenna integrating a monopole feed and a metasurface unit network, wherein the monopole feed is a coaxial feeding monopole located at the center of a lower metal plate and used for generating a reference wave. A vortex wave propagating along the normal direction of the antenna is taken as a target wave, a hologram function is calculated in combination with the reference wave, and then a surface phase distribution is obtained. The gap state of the metasurface unit network is modulated by using the phase distribution to provide required phase compensation, the modulated unit interacts with the reference wave, and finally an orbital angular momentum beam of a specified mode is generated. The application integrates a monopole feed and a metasurface through a holographic principle, omits a complex feeding network and an external transmitting source, has advantages of simple structure, low profile, easy miniaturization and the like, and effectively overcomes the problems of large space occupation and complex design in the prior art.

Description

Technical Field

[0001] This application belongs to the field of antennas, and in particular relates to an antenna that generates orbital angular momentum beams. Background Technology

[0002] Various antenna schemes for generating orbital angular momentum (OAM) beams are proposed to improve spectral efficiency and system capacity in wireless communication by utilizing vortex electromagnetic waves. As the number of wireless communication users increases, spectral efficiency approaches the Shannon limit. Vortex electromagnetic waves carry orbital angular momentum (OAM), and their wavefront phase is helical. Different OAM modes are orthogonal to each other and interference-free, exhibiting high spectral efficiency and anti-interference capabilities, bringing new degrees of freedom to wireless communication.

[0003] Existing technologies include microstrip patch antennas, array antennas, traveling-wave antennas, and metasurface antennas. For example, array antennas use complex feeding networks to provide corresponding vortex phases for antenna elements in different regions to generate high-gain OAM beams. Metasurface antennas, based on the generalized Snell's law, generate OAM beams by controlling the geometric parameters and spatial arrangement of the element structure at the subwavelength scale to precisely control the amplitude, phase, and polarization of electromagnetic waves. These methods can achieve broadband, high-mode-purity beam generation; for instance, reflective / transmissive metasurfaces provide phase compensation through element design.

[0004] However, in the existing technology, the process of using a feeding network or an external transmitter has drawbacks such as large antenna footprint, high design complexity, and difficulty in miniaturization and integration because array antennas require complex feeding network designs and reflection / transmission antennas require an external transmitter. Utility Model Content

[0005] The purpose of this application is to overcome the deficiencies in the prior art and provide an antenna for generating orbital angular momentum beams.

[0006] This application provides an antenna for generating orbital angular momentum beams, comprising: a monopole feed and a metasurface element network;

[0007] The monopole feed is a coaxially fed monopole antenna inserted at the center of the lower metal plate;

[0008] The metasurface unit network comprises multiple units, each unit having an adjustable gap;

[0009] The monopole feed is located at the center of the lower metal plate and is used to generate a reference wave.

[0010] The metasurface unit network is arranged above the monopole feed to modulate the state of the tunable slit based on the surface phase distribution, so as to provide phase compensation.

[0011] By coordinating the monopole feed and the metasurface unit network, an orbital angular momentum beam of a specified mode is generated.

[0012] Optionally, the metasurface unit network is arranged above the monopole feed, comprising:

[0013] The cells in the metasurface unit network are placed in a predetermined pattern based on the surface phase distribution;

[0014] The predetermined pattern is used to couple each unit to the reference wave of the desired phase.

[0015] Optionally, the cells in the metasurface unit network include adjustable gaps, comprising:

[0016] The adjustable slot is configured to provide orthogonal polarization phase compensation;

[0017] The orthogonal polarization phase compensation includes x-polarization phase compensation and y-polarization phase compensation.

[0018] Optionally, the monopole feed is disposed at the center of the lower metal plate and is used to generate a reference wave, including:

[0019] The monopole feed generates a cylindrical wave as the reference wave;

[0020] The magnetic field distribution of the cylindrical wave has x-components and y-components, which are generated based on the cylindrical wave function.

[0021] Optionally, in the state of modulating the adjustable slit based on the surface phase distribution, the surface phase distribution conforms to the vortex factor;

[0022] The vortex factor is the product of an exponential function and the number of modes and the azimuth angle, where the number of modes is an integer and the azimuth angle is the azimuth angle of the unit position.

[0023] The beneficial effects of this application are:

[0024] This application provides an antenna for generating an orbital angular momentum beam, comprising: a monopole feed and a metasurface element network; the monopole feed is a coaxially fed monopole antenna inserted at the center of a lower metal plate; the metasurface element network comprises multiple elements, each element having an adjustable slot; wherein, the monopole feed is disposed at the center of the lower metal plate for generating a reference wave; the metasurface element network is arranged above the monopole feed for modulating the state of the adjustable slot based on the surface phase distribution to provide phase compensation; through the coordinated arrangement of the monopole feed and the metasurface element network, an orbital angular momentum beam of a specified mode is generated. This application, by integrating a monopole feed with a holographic metasurface, calculates the interference phase distribution of the reference wave and the target wave based on the holographic principle, eliminating the need for a complex feed network and an external transmitter, thus achieving a simplified antenna structure, low profile height, and ease of miniaturization and integration, overcoming the shortcomings of large space occupation and complex design in existing technologies. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the process for generating the orbital angular momentum beam in this application;

[0026] Figure 2 This is a schematic diagram of the antenna used to generate the orbital angular momentum beam in this application;

[0027] Figure 3 This is a schematic diagram of the phase distribution of the x-component of the reference wave in this application;

[0028] Figure 4 This is a schematic diagram of the phase distribution of the reference wave y-component in this application;

[0029] Figure 5 This is a schematic diagram of the phase distribution of the x-component of the target wave in this application;

[0030] Figure 6 This is a schematic diagram of the phase distribution of the y-component of the target wave in this application;

[0031] Figure 7 This is a schematic diagram of the holographic phase x-component distribution in this application;

[0032] Figure 8 This is a schematic diagram of the holographic phase y-component distribution in this application;

[0033] Figure 9 This is a schematic diagram of the simulated distribution of the vortex phase in this application;

[0034] Figure 10 This is a schematic diagram of the metasurface antenna structure in this application. Detailed Implementation

[0035] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it is to be understood that various forms of implementation of the present disclosure are intended and should not be limited to the embodiments set forth herein. Rather, the embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0036] Please refer to Figure 2 As shown, this application provides an antenna for generating orbital angular momentum beams, comprising:

[0037] A monopole feed is provided, which is a coaxially fed monopole antenna inserted at the center of the lower metal plate to generate a reference wave. The monopole feed is the main excitation component of the antenna, inserted coaxially at the center of the lower metal plate to generate a cylindrical reference wave. This reference wave is used for subsequent interaction with the metasurface element network.

[0038] Specifically, the monopole feed has a simple structure, which helps to reduce the overall profile height of the antenna and facilitates miniaturized integration with other devices.

[0039] For example, in one embodiment, the monopole feed is in the form of a coaxial probe, directly welded to the lower metal plate to ensure stable electrical connection and mechanical fixation.

[0040] As shown in Figure 10, a metasurface unit network is provided, comprising a plurality of units, each having an adjustable slot, wherein the metasurface unit network is arranged above a monopole feed for modulating the state of the adjustable slot based on the surface phase distribution to provide phase compensation.

[0041] The metasurface element network is the antenna radiating component, composed of multiple subwavelength elements. Each element couples electromagnetic waves from a monopole feed via an adjustable slot. The metasurface element network adjusts the adjustable slot state of each element based on a calculated surface phase distribution, thereby providing the necessary phase compensation to generate the target beam. For example, in one embodiment, the metasurface element network employs a three-layer parallel plate waveguide structure, with the top and bottom layers being copper plates and the middle layer being a dielectric substrate with a dielectric constant ε. r =3. Rogers 3003 material with loss tangent tanδ = 0.001 and height h1 = 1.5mm to ensure operation in the 24GHz band.

[0042] By coordinating a monopole feed and a metasurface element network, an orbital angular momentum beam of a specified mode is generated. This coordinating arrangement refers to the interaction between the reference wave generated by the monopole feed and the metasurface element network, which, through the holographic principle, produces an orbital angular momentum beam of the specified mode in the desired spatial direction.

[0043] Specifically, the reference wave generated by the monopole feed propagates on the metasurface plane and couples with the cell arrangement designed according to the hologram, thereby radiating a vortex beam carrying orbital angular momentum. For example, in an embodiment, the mode number l of the target beam can be set to 1, generating an orbital angular momentum beam of l=1, with the beam direction propagating along the antenna normal (z-axis).

[0044] In a metasurface element network, elements are placed in a predetermined pattern based on a surface phase distribution. This predetermined pattern is used to couple each element to a reference wave of the desired phase. The predetermined pattern is an interferometric hologram calculated using holographic principles, which contains superposition information of the reference wave generated by the feed and the orbital angular momentum beam of the desired topological mode. The elements are arranged in a specific pattern according to the surface phase distribution, ensuring that each element can couple to a reference wave of the desired phase, thereby precisely modulating the wavefront. For example, in one embodiment, the predetermined pattern is a holographic phase distribution Φ_s calculated using a MATLAB script, which is mapped to the geometric position of each element, causing the elements to be arranged in a vortex pattern within the network.

[0045] The metasurface unit cell network includes adjustable slots configured to provide orthogonal polarization phase compensation, which includes x-polarization phase compensation and y-polarization phase compensation. The adjustable slot is a slotted structure on each unit cell, providing phase compensation for the x- and y-polarization components by changing the state of the slot (e.g., shape, size, or orientation), thereby supporting the generation of circularly polarized orbital angular momentum beams. Specifically, the adjustable slot achieves independent control of orthogonal polarization by coupling a reference wave and adjusting the phase response. For example, in an embodiment, the phase adjustment capability of the adjustable slot is verified by HFSS simulation, providing phase compensation in the range of 0 to 2π to meet holographic requirements.

[0046] The reference wave is generated by a monopole feed, and its magnetic field distribution on the metasurface can be expressed as:

[0047]

[0048] Among them, H ref H represents the magnetic field distribution of the reference wave. x H represents the x-component of the magnetic field distribution. y The y-component represents the distribution of the magnetic field. Let k represent the first kind of Hankel function. g The wave number in the medium is represented by r, and the radial distance from the element to the feed point is represented by r. Indicates the azimuth angle.

[0049] The target wave is the desired orbital angular momentum beam, and its target field distribution on the metasurface is as follows:

[0050]

[0051] Among them, P obj The field distribution of the target wave is represented by j, where j represents the imaginary unit, and l represents the number of modes in OAM. Indicates the azimuth angle, and Where x and y represent the coordinates of the element on the hypersurface.

[0052] The interference principle of holographic metasurfaces requires that the surface hologram contain information about the target wave and the conjugate reference wave. The hologram function M is expressed as:

[0053] Wherein, M represents the hologram function, P_obj represents the target wave, and H_ref^* represents the conjugate of the reference wave.

[0054] To directly generate the distribution used for phase modulation of the control unit, the required surface phase distribution Φ_s is calculated:

[0055]

[0056] Where Φ_s represents the surface phase distribution, the phase function represents taking the complex phase value, and P obj This represents the field distribution of the target wave. It represents the conjugate of the magnetic field distribution of the reference wave.

[0057] The two linear polarization components of a circularly polarized orbital angular momentum beam are expressed as follows:

[0058]

[0059] Among them, P x P represents the field distribution of the x-polarization component. y The field distribution of the y-polarization component is represented by k0, the free space wavenumber is represented by theta0, the elevation angle of the plane wave is represented by phi0, the azimuth angle of the plane wave is represented by x_center and y_center, the center coordinates of the element and phi, the azimuth angle of the element position is represented by phi.

[0060] The simulation partially simulates the direction of plane wave propagation, determined by theta0 and phi0, e j*1*phi Partially generated OAM target wave vortex factor with l=1.

[0061] This invention employs a joint MATLAB-HFSS automated design process. The MATLAB script main program is responsible for calculating the holographic phase distribution Φ_s, mapping the phase values ​​to the specific geometric parameters of each element, and automatically generating an HFSSVBScript script containing the geometric models of all elements. By running this script, a complete antenna model is automatically built in HFSS, greatly improving design efficiency. Single-feed excitation simplifies the antenna structure, eliminating the need for complex multi-channel feed networks and reducing the complexity and design cost of vortex antennas.

[0062] Please refer to Figure 1 This application provides a method for generating orbital angular momentum beams, applied in the field of holographic metasurface antennas, to solve the problems of complex structure, high profile, and low design efficiency of existing antennas. The method includes:

[0063] S101. A reference wave is generated by the monopole feed, wherein the monopole feed is a coaxially fed monopole antenna inserted at the center of the lower metal plate.

[0064] The monopole feed, serving as the excitation source, is integrated into the antenna structure. Specifically, the holographic metasurface antenna employs a three-layer parallel plate waveguide structure, with the top and bottom layers being copper plates and the middle layer being a dielectric substrate. The dielectric substrate uses a dielectric constant ε. r =3. Rogers 3003 material with loss tangent tanδ = 0.001 and height h1 = 1.5mm, a monopole antenna is inserted into the center of the lower metal plate and generates electromagnetic waves through coaxial feeding.

[0065] The reference wave generated by the monopole feed is a cylindrical wave, and its magnetic field distribution on the metasurface can be expressed by the formula:

[0066]

[0067] Among them, H ref H represents the magnetic field distribution of the reference wave. x H represents the x-component of the magnetic field distribution. y The y-component represents the distribution of the magnetic field. Let k represent the first kind of Hankel function. g The wave number in the medium is represented by r, and the radial distance from the element to the feed point is represented by r. Indicates the azimuth angle.

[0068] This formula describes the spatial distribution characteristics of the reference wave on the metasurface. The phase distributions of the x and y components correspond to different sine and cosine functions, respectively, thus forming a cylindrical wavefront. Generating the reference wave using a monopole feed avoids the use of complex feeding networks, simplifies the antenna structure, reduces the profile height, and facilitates miniaturization and integration.

[0069] The antenna proposed in this application integrates the monopole feed and the radiating surface, which helps to reduce the overall profile height of the antenna and makes it easier to miniaturize and integrate with other devices. Because it utilizes surface wave excitation and designs the arrangement of the surface radiating elements based on holographic principles, the overall antenna structure is simple, eliminating the need for a complex feed network and improving antenna design efficiency.

[0070] Specifically, a linearly polarized holographic metasurface antenna operating at 24 GHz was created. This antenna employed a single-feed excitation system, resulting in an extremely simplified structure. It abandoned complex multi-channel feeding networks, using only a simple coaxial probe-type monopole antenna as the feed. The phase distributions of the x and y components of the reference wave are as follows: Figure 3 and attached Figure 4 As shown, Figure 3 The phase distribution pattern of the x-component of the reference wave is shown. Figure 4 The phase distribution patterns of the y-component of the reference wave are shown. These distributions are generated based on cylindrical wave functions and reflect the spatial characteristics of the reference wave.

[0071] S102. Target wave based on orbital angular momentum mode, wherein the target wave is a vortex beam propagating along the antenna normal.

[0072] The target wave is a beam carrying orbital angular momentum (OAM) that is desired to be radiated. Its propagation direction is along the antenna normal (z-axis), and it possesses a specific topological mode. The phase distribution of the target wave conforms to the vortex factor. The phase change characteristics, where l is the number of OAM modes, which is an integer. It is the azimuth angle, that is, the azimuth angle of the location of each unit. The calculation formula is:

[0073] The field distribution of the target wave on the metasurface can be expressed by the formula:

[0074]

[0075] Among them, P obj The field distribution of the target wave is represented by j, where j represents the imaginary unit, and l represents the number of modes in OAM. Indicates the azimuth angle.

[0076] like Figure 5 and Figure 6 As shown, this formula reflects the vortex phase characteristics of the target wave. The phase distribution exhibits a typical "vortex" pattern, meaning it increases linearly with the azimuth angle, thus generating a beam carrying orbital angular momentum. When the target wave is a circularly polarized orbital angular momentum beam, it is necessary to calculate the phase distributions of the x-polarized component and the y-polarized component separately to accurately determine the target wave.

[0077] The phase distribution of the x-polarization component is generated based on the plane wave propagation direction and vortex factor, while the phase distribution of the y-polarization component is generated based on the plane wave propagation direction, orthogonal phase shift, and vortex factor. The specific formulas are as follows:

[0078]

[0079] Among them, P x P represents the field distribution of the x-polarization component. y The field distribution of the y-polarization component is represented by k0, the free space wavenumber is represented by theta0, the elevation angle of the plane wave is represented by phi0, the azimuth angle of the plane wave is represented by x_center and y_center, the center coordinates of the element and phi, the azimuth angle of the element position is represented by phi.

[0080] The simulation partially simulates the direction of plane wave propagation, determined by theta0 and phi0, e j*1*phi Partially generated OAM target wave vortex factor with l=1.

[0081] By calculating these components, the target wave can be fully circularly polarized, ensuring that the beam has the required orbital angular momentum characteristics.

[0082] Unlike holographic antennas that generate pencil beams, this application aims to design holographic antennas that generate vortex beams carrying orbital angular momentum. The phase distribution of the target wave in the proposed circularly polarized holographic metasurface antenna exhibits a typical "vortex" pattern.

[0083] The target wave is based on the vortex factor, where the mode number l is an integer and the azimuth angle is... The azimuth angle of the unit position.

[0084] S103. Calculate the hologram function based on the reference wave and the target wave.

[0085] The holographic function is generated based on the principle of interference, and it contains superposition information of the reference wave and the target wave.

[0086] The interference principle of holographic metasurfaces requires that the surface hologram contain all information of the target wave and the conjugate reference wave. Therefore, the hologram function is obtained by calculating the product of the target wave and the conjugate reference wave, and the specific formula is as follows:

[0087]

[0088] Where M represents the hologram function, P obj This represents the field distribution of the target wave. It represents the conjugate of the magnetic field distribution of the reference wave.

[0089] By substituting the magnetic field distribution formula on the metasurface and the field distribution formula of the target wave on the metasurface into this formula, the holographic function M can be obtained, which reflects the interference pattern of the reference wave and the target wave on the metasurface.

[0090] By calculating the hologram function, a foundation was laid for subsequent phase distribution calculations, ensuring that the antenna's radiation characteristics could accurately match the design objectives.

[0091] The calculation of the hologram function is directly based on the principle of interference. The hologram contains the superposition information of the reference wave generated by the feed source and the OAM beam of the desired topological mode, which lays the foundation for subsequent phase extraction.

[0092] S104. Calculate the surface phase distribution based on the hologram function.

[0093] The surface phase distribution is the phase value extracted from the hologram function and is used to guide the modulation of the metasurface units. Specifically, the surface phase distribution is obtained by calculating the phase of the hologram function, as shown in the formula:

[0094]

[0095] Where Φ_s represents the surface phase distribution, the phase function represents taking the complex phase value, and P obj This represents the field distribution of the target wave. It represents the conjugate of the magnetic field distribution of the reference wave.

[0096] This formula extracts phase information from the holographic function M, yielding a continuous phase distribution Φ_s, which represents the required phase compensation value for each element, ranging from 0 to 2π. Calculating the surface phase distribution is a crucial step in generating the hologram, directly transforming interference theory into a feasible phase pattern.

[0097] The calculation of the surface phase distribution is the core of generating the interferometric hologram. By accurately calculating the required phase for each element, an interferometric hologram is generated. This hologram already contains the superposition information of the reference wave generated by the feed and the OAM beam of the desired topological mode.

[0098] S105. Modulate the cells in the metasurface unit network according to the surface phase distribution, and provide phase compensation by changing the cell gap state.

[0099] The metasurface unit cell network is a discrete array of units on an upper metal plate, with each unit coupling electromagnetic waves through a slit. The modulation process is based on the surface phase distribution Φ_s, and discrete metasurface units are designed to provide phase compensation.

[0100] Each element couples to a reference wave by being placed at different locations. Specifically, the element placement is determined based on the surface phase distribution to couple each element to a reference wave with the desired phase. Changing the element slot state can provide a specific polarization phase response; for example, the phase delay can be altered by adjusting the slot geometry (such as length, width, or shape). The element structure is subwavelength-scale, with each element mapped to specific geometric parameters based on its phase value, thus achieving precise coupling and phase modulation of the reference wave. This step is implemented through a MATLAB-HFSS joint automated design flow. The MATLAB script is responsible for calculating the phase distribution, mapping the geometric parameters, and automatically generating the HFSS script, which is then used to build the antenna model in HFSS, improving design efficiency.

[0101] like Figure 7 and Figure 8 As shown, this application employs a combined MATLAB-HFSS automated design flow. The MATLAB script main program is responsible for calculating the holographic phase distribution Φ_s, and automatically generating an HFSSVBScript script containing the geometric models of all elements based on the phase values ​​mapped to the specific geometric parameters of each element. By running this script, a complete antenna model is automatically built in HFSS, greatly improving design efficiency.

[0102] S106. The modulated metasurface unit network interacts with the reference wave to generate an orbital angular momentum beam of a specified mode.

[0103] like Figure 9 As shown, the modulated metasurface element network interacts with a reference wave generated by a monopole feed. The reference wave, acting as an excitation source, couples with the elements on the holographic surface, ultimately generating a trajectory angular momentum beam of a specified mode in the desired spatial direction (e.g., the antenna normal). Since the hologram already contains the superposition information of the reference and target waves, the interaction process gives the radiated beam vortex phase characteristics, thus generating a beam carrying trajectory angular momentum. This method avoids complex feed networks, utilizes surface wave excitation and holographic principles, simplifies the antenna structure, reduces the complexity and design cost of vortex antennas, and achieves miniaturized integration.

[0104] The single-feed excitation method greatly simplifies the antenna structure. This application abandons the complex multi-channel feed network and uses only a simple coaxial probe-type monopole antenna as the feed source. This helps to reduce the overall profile height of the antenna and makes it easier to integrate with other devices in a miniaturized manner. Because it utilizes surface wave excitation and designs the arrangement of surface radiating elements based on holographic principles, the overall antenna structure is simple, greatly reducing the complexity and design cost of the vortex antenna. By using the reference wave from the feed source to interact with the entire holographic surface, a target OAM beam of a specified mode can be generated in the desired spatial direction.

[0105] The above description of the embodiments is provided to enable those skilled in the art to understand and apply this application. Those skilled in the art will readily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without inventive effort. Therefore, this application is not limited to the above embodiments, and any improvements and modifications made to this application based on the disclosure thereof should be within the scope of protection of this application.

Claims

1. An antenna for generating an orbital angular momentum beam, characterized in that, include: Monopole feed and metasurface unit network; The monopole feed is a coaxially fed monopole antenna inserted at the center of the lower metal plate; The metasurface unit network comprises multiple units, each unit having an adjustable gap; The monopole feed is located at the center of the lower metal plate and is used to generate a reference wave. The metasurface unit network is arranged above the monopole feed to modulate the state of the tunable slit based on the surface phase distribution, so as to provide phase compensation. By coordinating the monopole feed and the metasurface unit network, an orbital angular momentum beam of a specified mode is generated.

2. The antenna according to claim 1, characterized in that, The metasurface unit network is arranged above the monopole feed and includes: The cells in the metasurface unit network are placed in a predetermined pattern based on the surface phase distribution; The predetermined pattern is used to couple each unit to the reference wave of the desired phase.

3. The antenna according to claim 1, characterized in that, The cells in the metasurface unit network include adjustable gaps, including: The adjustable slot is configured to provide orthogonal polarization phase compensation; The orthogonal polarization phase compensation includes x-polarization phase compensation and y-polarization phase compensation.

4. The antenna according to claim 1, characterized in that, The monopole feed is located at the center of the lower metal plate and is used to generate a reference wave, including: The monopole feed generates a cylindrical wave as the reference wave; The magnetic field distribution of the cylindrical wave has x-components and y-components, which are generated based on the cylindrical wave function.

5. The antenna according to claim 1, characterized in that, In the state of the adjustable slit modulated based on the surface phase distribution, the surface phase distribution conforms to the vortex factor; The vortex factor is the product of an exponential function and the number of modes and the azimuth angle, where the number of modes is an integer and the azimuth angle is the azimuth angle of the unit position.

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