Holographic metasurface antenna for multi-feed co-boresight oam mode multiplexing and design method thereof

Abstract

This invention discloses a holographic metasurface antenna with multiple feed sources and common aperture for OAM mode multiplexing, and its design method. The scheme includes: determining the position of each feed source and the corresponding target vortex beam; calculating and superimposing the impedance distribution; designing holographic metasurface elements; mapping the impedance distribution to the size of the holographic metasurface elements; constructing the holographic metasurface and placing the feed sources. Each feed source in this invention corresponds to a different OAM mode vortex beam. This novel impedance superposition method based on multiple feed sources can achieve OAM mode multiplexing by simultaneously exciting each feed source, improving aperture utilization and channel capacity of the communication system. The antenna's feeding structure is a monopole antenna embedded in the antenna array, eliminating the need for an additional horn antenna for feeding, and offering advantages such as low profile and high integration.

Description

Technical Field

[0001] This invention belongs to the field of communication technology, and more specifically relates to a holographic metasurface antenna and its design method for multi-feed common-aperture orbital angular momentum (OAM) mode multiplexing in the field of wireless communication technology. This invention can be used in multiple-input multiple-output (MIMO) wireless communication. Background Technology

[0002] With the development of modern communication, the demand for high-capacity and high-speed communication in communication networks is increasing. Vortex electromagnetic waves carrying orbital angular momentum (OAM) have a greater advantage over traditional communication technologies in increasing the information transmission capacity of communication systems due to the infinite-dimensional orthogonality between their different modes. One important application of OAM vortex electromagnetic waves in wireless communication is to improve the communication capacity and speed of communication systems through the multiplexing and transmission of multiple OAM modes.

[0003] In their paper "Biorthogonal Circularly Polarized OAM Wave Generation Based on a Miniaturized High-Efficiency Holographic Impedance Surface" (in 2023 IEEE MTT-S International Wireless Symposium (IWS), Qingdao, China, May 2023, pp. 1-4), F. Huang et al. proposed and designed a holographic metasurface antenna for single-feed dual-mode orbital angular momentum vortex waves using an impedance superposition method. The antenna consists of a holographic metasurface and a monopole antenna located at the center of the metasurface. The holographic metasurface includes a dielectric substrate, a metal ground plane on its lower surface, and several circular slotted patches on its upper surface. Compared to single-mode orbital angular momentum vortex wave holographic metasurface antennas, the holographic metasurface antenna proposed in this paper can simultaneously generate two different modes of orbital angular momentum vortex waves through a shared aperture, which improves the aperture utilization to a certain extent. However, the antenna has the following drawback: this antenna, which is designed based on the impedance superposition method of a single feed source, can only generate two modes of orbital angular momentum simultaneously or not at all, and the two generated OAM mode vortex wave beams are not in the same direction, so OAM mode multiplexing cannot be realized.

[0004] In their paper "Multi-Orbital-Angular-Momentum-Mode VortexWave Multiplexing and Demultiplexing with Shared-Aperture Reflective Metasurfaces" (Physical Review Applied, 2022, 17(3): 034017.), F. Qiang et al. proposed a novel compensated phase calculation method for designing a reflective artificial electromagnetic surface. This antenna, with its multi-feed configuration, achieves the generation of common-aperture multimode orbital angular momentum vortex electromagnetic waves, realizing OAM mode multiplexing. However, a drawback of this antenna is that the reflective artificial electromagnetic surface requires an additional horn antenna for feeding. The horn antenna cannot be integrated into the array and is often located at a certain distance from the array, resulting in a high overall antenna profile and low integration density. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of the prior art by proposing a holographic metasurface antenna and design method for multi-feed common-aperture OAM mode multiplexing. This aims to solve the problems that the existing technology cannot be used for OAM mode multiplexing, and that the artificial electromagnetic metasurface antenna has a high structural profile and low integration.

[0006] The underlying idea for achieving the objective of this invention is as follows: This invention employs a holographic metasurface antenna structure for designing multi-feed common-aperture orbital angular momentum mode multiplexing. Compared to existing multi-feed common-aperture design methods based on reflective artificial electromagnetic surfaces, the feeding structure is a monopole antenna embedded in the antenna array, eliminating the need for an additional horn antenna for feeding. This invention proposes a novel impedance superposition holographic metasurface antenna design method based on multiple feeds. In this method, each feed is used to excite and generate different OAM mode vortex beams. First, the waves generated by each feed interfere with the corresponding OAM mode vortex waves to obtain multiple impedance distributions. Then, these impedance distributions are weighted and superimposed to generate a new impedance distribution. When one of the feeds is working, its corresponding OAM mode vortex wave will also be generated, without exciting other OAM mode vortex waves. Furthermore, multiple feeds can work together to simultaneously generate multiple different OAM mode vortex waves, and all OAM mode vortex beams are generated in the same direction, achieving multiplexing of multiple signals.

[0007] To achieve the above objectives, the steps of the holographic metasurface antenna design method of the present invention include the following:

[0008] Step 1. Determine the number of feed sources q1 and the i-th orbital angular momentum mode l. iThe position of the i-th feed source (x i ,y i ,0) Beam direction of the emitted wave in spherical coordinates Where 2≤q1≤4, i=1,2,3···q1,l i ∈[±1,±2],θ i Represents the pitch angle and θ i ∈[0360°], Indicates azimuth and

[0009] Step 2. Calculate the excitation wave J generated by the i-th feed source. i and the corresponding emitted wave E of the feed source i ;

[0010] Step 3. Calculate the excitation wave J generated by the i-th feed source. i With the corresponding outgoing wave E i Tensor surface impedance distribution Z generated by interference i ;

[0011] Step 4. Superimpose all tensor surface impedance distributions to obtain the total tensor surface impedance distribution Z;

[0012] Step 5. Transform the tensor surface impedance distribution Z into an equivalent scalar surface impedance distribution Z. e ;

[0013] Step 6. Design the tensor holographic metasurface unit used in the holographic metasurface. Each metasurface unit consists of three degrees of freedom e. x e y and θ s Control its equivalent scalar surface impedance;

[0014] Step 7. Adjust the three degrees of freedom e of the tensor holographic metasurface unit at different locations on the holographic metasurface. x e y θ s This results in the holographic metasurface having the aforementioned equivalent scalar surface impedance distribution;

[0015] Step 8. Follow e x e y θ s The distribution arranges the tensor holographic metasurface units, and the holographic metasurface formed by arranging M×N tensor holographic metasurface units is the XOY surface, with the center of the array surface as the origin of the coordinate system, M,N≥40 and M≥N. The q1 feed sources are arranged according to the position information determined in step 1, and the q1 feed sources are excited at the same time to generate the orbital angular momentum vortex electromagnetic wave corresponding to each feed source.

[0016] Step 9. By simultaneously stimulating each feed source, the OAM mode can be reused.

[0017] This invention discloses a multi-feed common-aperture OAM mode multiplexing holographic metasurface antenna using a holographic metasurface antenna design method. The antenna includes a holographic metasurface and feed sources. The holographic metasurface is composed of M×N tensor holographic metasurface units arranged periodically along the x and y axes, with identical structures but different sizes. The feed sources are q3 feeding structures embedded in the holographic metasurface, each capable of exciting the entire holographic metasurface, thus achieving multi-feed common-aperture, where q3 = q1.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] First, this invention proposes a novel holographic metasurface antenna design method based on impedance superposition using multiple feed sources. In this method, each feed source corresponds to a different OAM mode vortex beam. The waves generated by each feed source interfere with the corresponding OAM mode vortex waves to obtain multiple impedance distributions. These impedance distributions are then weighted and superimposed to generate a new impedance distribution. In contrast, existing impedance superposition methods based on a single feed source first weight superimpose multiple OAM mode vortex waves, and then interfere with the waves generated by the feed sources with the superimposed OAM mode vortex waves to obtain the impedance distribution. Compared with the prior art, the novel impedance superposition method based on multiple feed sources proposed in this invention can more flexibly control the generation of multiple OAM mode vortex beams by setting the on / off state of each feed source.

[0020] Secondly, this invention proposes a novel impedance superposition method based on multiple feed sources to realize an antenna structure for multiple-feed OAM mode multiplexing under common aperture. Different feed sources can work individually to generate a single OAM mode, or work simultaneously to generate multiple different OAM modes. Moreover, all OAM mode vortex beams are generated in the same direction, realizing the multiplexing of multiple signals. Compared with the existing single-feed dual-mode orbital angular momentum vortex wave antenna structure, the antenna structure of this invention can more flexibly control the generation of vortex beams and exhibit greater channel capacity in communication systems.

[0021] Third, this invention uses a holographic metasurface antenna structure for multi-feed common aperture OAM mode multiplexing design. Compared with the existing multi-feed common aperture design method based on reflective artificial electromagnetic surfaces, the feeding structure is a monopole antenna embedded in the antenna array, without the need for an additional horn antenna to feed it. This makes the overall antenna structure of the holographic metasurface antenna of this invention have a low profile and high integration. Attached Figure Description

[0022] Figure 1This is a flowchart illustrating the implementation of the antenna design method of the present invention;

[0023] Figure 2 This is a schematic diagram of the tensor holographic metasurface unit structure in the antenna of the present invention;

[0024] Figure 3 This is a diagram showing the phase shift-frequency dispersion curves of tensor holographic metasurface units of different sizes in the antenna of this invention.

[0025] Figure 4 This is a schematic diagram of the surface impedance of tensor holographic metasurface units of different sizes in the antenna of this invention;

[0026] Figure 5 This is a holographic metasurface array distribution diagram with two feed sources in an embodiment of the antenna of the present invention;

[0027] Figure 6 This is a schematic diagram of common-aperture 2-mode OAM vortex electromagnetic wave multiplexing generation when the number of feed sources is 2 in an embodiment of the antenna of the present invention;

[0028] Figure 7 The vortex electric field distribution and OAM mode spectrum obtained by simultaneously exciting two feed sources in an embodiment of the antenna of the present invention;

[0029] Figure 8 The vortex electric field distribution and OAM mode spectrum obtained by individually exciting feed 1 in an embodiment of the antenna of the present invention;

[0030] Figure 9 The image shows the vortex electric field distribution and OAM mode spectrum obtained by individually exciting feed 2 in an embodiment of the antenna of the present invention. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] Reference Figure 1 The implementation steps of the holographic metasurface antenna design method for multi-feed common aperture OAM mode multiplexing in the embodiments of the present invention will be described in further detail.

[0033] Several tensor surface impedances centered at different feed positions are superimposed on a common aperture, so that the aperture contains information of all target OAM modes. By simultaneously exciting each feed, multi-feed common-aperture OAM mode multiplexing is achieved. The steps of this antenna design method are as follows:

[0034] Step 1: Determine the number of feed sources q1 and the i-th orbital angular momentum mode l. i The position of the i-th feed source (x i ,y i ,0), The beam direction of the emitted wave in spherical coordinates is The size of the holographic metasurface array is M×N, where 2≤q1≤4, i=1,2,3···q1,l i ∈[±1,±2],θ i Represents the pitch angle and θ i ∈[0360°], Indicates azimuth and M, N≥40 and M≥N.

[0035] In the embodiments of the antenna design method of the present invention, the following are included but not limited to determining the number of feed sources 2, the orbital angular momentum modes l1=-1, l2=1, the beam direction of the outgoing wave in the spherical coordinate system is (0,0), and the size of the holographic metasurface array is 50×50; the two feed sources are symmetrically distributed in the YOZ plane, and their position coordinates are (0,-24mm,0) and (0,24mm,0) respectively.

[0036] Step 2: Calculate the excitation wave J generated by the i-th feed source according to the following formula. i and the corresponding emitted wave E of the feed source i :

[0037]

[0038] Among them, e (·) This represents an exponential function with the natural constant e as its base, j denotes the imaginary unit sign, and k denotes the free space wavenumber. t The wave number, x, represents the wave number of an electromagnetic wave propagating on the surface of an array. mn and y mn Let r represent the x-axis and y-axis coordinates of the center of the tensor holographic metasurface cell in the m-th row and n-th column relative to the center of the tensor holographic metasurface, respectively, m = 1, 2, 3...M, n = 1, 2, 3...N, r i Indicates the i-th feed source and (x mn ,y mn The distance between holographic metasurface units at the location,

[0039] In the embodiments of the antenna design method of the present invention, the feed positions are determined as (0, -24mm, 0) and (0, 24mm, 0), respectively. The excitation waves and corresponding outgoing waves generated by the two feeds are expressed as follows:

[0040]

[0041] in,

[0042] Step 3: Calculate the excitation wave J generated by the i-th feed source according to the following formula. i With the corresponding outgoing wave E iTensor surface impedance distribution Z generated by interference i :

[0043]

[0044] Among them, Z xxi Z xyi Z yxi Z yyi The surface impedance Z of the constituent tensor i Two vectors Z xi and Z yi The components in the x and y directions, respectively, X s M0 and M0 represent the average impedance and modulation depth of the tensor holographic metasurface unit, respectively; Im(·) represents taking the value of the imaginary part of the complex number; and the superscript H indicates the conjugate transpose sign. This represents the Kronecker multiplication operation, i.e., the vector outer product.

[0045] In an embodiment of the antenna design method of the present invention, the number of feed sources is determined to be 2. The tensor surface impedance distribution generated by the interference of the excitation wave generated by the two feed sources with the corresponding outgoing wave is as follows:

[0046]

[0047] Where Z1 and Z2 represent the tensor surface impedance distributions generated by the interference of the excitation waves generated by the two feed sources with the corresponding outgoing waves.

[0048] Step 4: Superimpose all tensor surface impedance distributions to obtain the total tensor surface impedance distribution Z:

[0049]

[0050] Where q2 represents the number of tensor surface impedance distributions, and q2 = q1.

[0051] In an embodiment of the antenna design method of the present invention, the total tensor surface impedance distribution Z is:

[0052] Z = (Z1 + Z2) / 2

[0053] Where Z represents the total tensor surface impedance distribution.

[0054] Step 5: Transform the tensor surface impedance distribution Z into an equivalent scalar surface impedance distribution Z0. e :

[0055]

[0056] Where Z0 represents the wave impedance in free space, Z xx Z xy Zyx Z yy Represent the two vectors Z that make up the surface impedance Z of the tensor x and Z y The components in the x and y directions, θ t Z represents the equivalent scalar surface impedance. e Iterate through the range and retrieve values, θ t ∈[0,2π], where π represents pi.

[0057] Step 6: Design the tensor holographic metasurface unit used in the holographic metasurface. Each metasurface unit consists of three degrees of freedom e. x e y and θ s Control its equivalent scalar surface impedance.

[0058] In an embodiment of the antenna design method of the present invention, the tensor holographic metasurface unit structure is as follows: Figure 2 As shown. Figure 2 As shown in (a), the metasurface unit consists of a dielectric substrate, a metal ground plane, and an elliptical patch. The dielectric substrate is made of S7136H material with a relative permittivity of 3.7 and a loss tangent of 0.004, and its physical dimensions are 6mm × 6mm × 1.524mm. The metal ground plane and the elliptical patch are copper foils printed on the lower and upper surfaces of the dielectric substrate, respectively. The metal ground plane is square and has the same side length as the lower surface of the dielectric substrate. Figure 2 As shown in (b), the semi-major axis of the elliptical patch is e. x The semi-minor axis is e y The angle between the major axis and the positive x-axis is θ. s e x and e y All values ​​are taken within the range of 1 to 2.9 mm, and e x >e y θ s It takes values ​​between 0 and 2π.

[0059] To facilitate the extraction of the equivalent scalar surface impedance of the element, let e x =e y =r, at which point the elliptical patch becomes a circular patch, and r is the radius of the circular patch. Then, the eigenmode solver in the commercial software HFSS is used to calculate the phase shift-frequency dispersion curves of the holographic metasurface unit for different r values, as shown below. Figure 3 As shown, r takes values ​​from 1 to 2.9 mm, with intervals of 0.1 mm, and the scalar surface impedance Z for different r values ​​is calculated accordingly. s Z s The calculation formula is:

[0060]

[0061] Where f represents the antenna's operating frequency, φ represents the phase shift in the dispersion curve corresponding to the operating frequency, and c is the speed of light. r and Z s The mapping relationship is as follows Figure 4 As shown, specifically:

[0062]

[0063] For each element with different r values, the average impedance X s The impedance modulation depth M0 are respectively:

[0064]

[0065] In an embodiment of the antenna design method of the present invention, X s =165.8, M=70.

[0066] Step 7: Adjust the three degrees of freedom e of the tensor holographic metasurface unit at different locations on the holographic metasurface. x e y θ s This results in the holographic metasurface having the aforementioned equivalent scalar surface impedance distribution.

[0067] In an embodiment of the antenna design method of the present invention, e x and e y Determined by the following formula:

[0068]

[0069] Among them, Z emax and Z emin Representing the equivalent scalar surface impedance Z respectively e The maximum and minimum values, θ s Equal to Z e Get the maximum value Z emax θ corresponding to time tmax θ tmax ∈[0,2π].

[0070] Step 8, follow e x e y θ s The distribution arranges the holographic metasurface units, and the holographic metasurface formed by arranging M×N tensor holographic metasurface units is the XOY surface, with the center of the array surface as the origin of the coordinate system, M,N≥40 and M≥N. The q1 feed sources are arranged according to the position information determined in step 1, and the q1 feed sources are excited at the same time to generate the orbital angular momentum vortex electromagnetic wave corresponding to each feed source.

[0071] In an embodiment of the antenna design method of the present invention, the holographic metasurface is composed of 50×50 tensor holographic metasurface units. The position coordinates of feed 1 are (0, -24mm, 0), which is used to excite the holographic metasurface to generate a +1 mode orbital angular momentum vortex beam. The position coordinates of feed 2 are (0, 24mm, 0), which is used to excite the holographic metasurface to generate a -1 mode orbital angular momentum vortex beam.

[0072] Step 9: By simultaneously stimulating each feed source, the OAM mode is reused.

[0073] This invention discloses a multi-feed, common-aperture OAM mode-multiplexing holographic metasurface antenna using a holographic metasurface antenna design method. The antenna comprises a holographic metasurface and feed sources. The holographic metasurface is composed of M×N tensor holographic metasurface elements arranged periodically along the x and y axes, each with the same structure but different dimensions. The feed sources consist of q3 feeding structures embedded in the holographic metasurface. Each feeding structure can excite the entire holographic metasurface, achieving multi-feed, common-aperture operation, where q3 = q1.

[0074] The feed consists of q3 monopole antennas with omnidirectional radiation characteristics. The center positions of each monopole antenna are randomly distributed in the positive and negative directions of the x-axis or y-axis and are all different. The center of all monopole antennas is separated from the center of the holographic metasurface by d wavelengths, where 1.2≤d≤1.6.

[0075] In an embodiment of the antenna of the present invention, the holographic metasurface is composed of 50×50 tensor holographic metasurface elements arranged periodically along the x-axis and y-axis directions, with identical structures but different sizes. The feed source consists of two monopole antennas embedded in the holographic metasurface. The two monopole antennas are centrally symmetrical about the holographic metasurface and are separated by 1.6 wavelengths.

[0076] The tensor holographic metasurface unit comprises a dielectric substrate, a metal ground plane, and an elliptical patch. The dielectric substrate is a cuboid-shaped solid dielectric material with a side length p ranging from 0.1λ ≤ p ≤ 0.25λ, where λ is the wavelength corresponding to the operating frequency of the tensor holographic metasurface antenna. The height h of the dielectric substrate ranges from 0.524 mm ≤ h ≤ 2.54 mm. The metal ground plane and the elliptical patch are copper foils printed on the lower and upper surfaces of the dielectric substrate, respectively. The metal ground plane is square and has the same side length as the lower surface of the dielectric substrate.

[0077] In the embodiment of the antenna of the present invention, the dielectric substrate is made of S7136H material with a relative permittivity of 3.7 and a loss tangent of 0.004, with a side length p = 6 mm and a height h = 1.524 mm.

[0078] The differences among the M×N tensor holographic metasurface units of varying sizes are defined by the three degrees of freedom of the elliptical patch, e x and e y The following formula is used to calculate:

[0079]

[0080] Among them, Z emax and Z emin Representing the equivalent scalar surface impedance Z respectively e The maximum and minimum values, θ s Equal to Z e Get the maximum value Z emax θ corresponding to time tmax θ tmax ∈[0,2π].

[0081] The top layer of the holographic metasurface has M×N elliptical patches. By selectively removing some patches, the remaining elliptical patches are arranged in a circular distribution. The removal of some patches refers to taking a circle with the center of the holographic metasurface as the origin and a as the radius, and using this circle as the boundary, removing the elliptical patches located outside the circular area, where a=(N*p) / 2.

[0082] In an embodiment of the antenna of the present invention, a circle with a radius of 150 mm is taken, and the elliptical patches located outside the circular region of the 50×50 elliptical patches on the top layer of the holographic metasurface are removed. The resulting holographic metasurface antenna array is distributed as follows. Figure 5 As shown.

[0083] The technical effects of the antenna of the present invention will be further illustrated through simulation experiments below.

[0084] according to Figure 6 The dual-feed, common-aperture, two-mode orbital angular momentum vortex electromagnetic wave multiplexing generation model shown can be used to obtain the vortex electric field distribution through electromagnetic simulation in HFSS software. To calculate the OAM mode spectrum distribution of the OAM vortex electromagnetic wave, an 800mm × 800mm observation plane was established in a three-dimensional coordinate system. The observation plane was perpendicular to the Z-axis, 800mm away from the tensor holographic metasurface antenna, and its geometric center coincided with the Z-axis. Twelve points were uniformly sampled on the observation plane with the Z-axis as the center and a radius of r = 150mm as the sampling point. The OAM mode spectrum distribution was calculated using the information from these sampling points.

[0085] When two feed sources are used simultaneously to excite the holographic metasurface, two modes of OAM vortex electromagnetic waves are generated. Their spatial radiated electric field and OAM mode spectrum distribution are as follows: Figure 7 As shown. Among them, Figure 7(a) and (b) show the electric field amplitude and phase distribution, respectively. As can be seen from the figures, this is consistent with the electric field amplitude and phase distribution of the -1 and +1 mixed-mode OAM vortex electromagnetic wave. Figure 7 As can be seen from the OAM mode spectrum in (c), the purity of the -1 and +1 modes is much higher than that of other crosstalk OAM modes. This indicates that under the design of multiple feed sources with a common aperture, multiple feed sources can generate multiple OAM mode vortex beams when excited simultaneously. Moreover, the mode information carried by all OAM mode vortex beams can be analyzed on the same receiving plane, which enables the antenna of the present invention to realize the multiplexing of multiple signals.

[0086] When only feed source 1 is excited, that is, when feed source 1 is energized and feed source 2 is de-energized, a -1 mode OAM vortex electromagnetic wave is obtained, and its spatial radiation electric field distribution and OAM mode spectrum are as follows. Figure 8 As shown. Among them, Figure 8 (a) and (b) show the electric field amplitude and phase distribution, respectively. As can be seen from the figures, this matches the electric field amplitude and phase distribution of the -1 mode OAM vortex electromagnetic wave. Figure 8 As can be seen from the OAM mode spectrum in (c), the purity of the -1 mode is much higher than that of other crosstalk OAM modes. This indicates that under the design of multiple feed sources with a common aperture, when a single feed source is excited, it only generates the target OAM vortex wave corresponding to it, and does not generate the target OAM vortex wave corresponding to other feed sources. This allows the antenna of the present invention to more flexibly control the generation of multiple OAM mode vortex beams by setting the on and off of each feed source.

[0087] When only feed source 2 is excited, that is, when feed source 2 is energized and feed source 1 is de-energized, a +1 mode OAM vortex electromagnetic wave is obtained, and its spatial radiation electric field distribution and OAM mode spectrum are as follows. Figure 9 As shown. Among them, Figure 9 (a) and (b) show the electric field amplitude and phase distribution, respectively. As can be seen from the figures, this matches the electric field amplitude and phase distribution of the +1 mode OAM vortex electromagnetic wave. Figure 9 As can be seen from the OAM mode spectrum in (c), the purity of the +1 mode is much higher than that of other crosstalk OAM modes. This indicates that under the design of multiple feed sources with a common aperture, when a single feed source is excited, it only generates the target OAM vortex wave corresponding to it, and does not generate the target OAM vortex wave corresponding to other feed sources. This allows the antenna of the present invention to more flexibly control whether multiple OAM mode vortex wave beams are generated by setting the on and off of each feed source.

[0088] In summary, by controlling the two OAM modes separately—that is, by exciting only feed source 1 to obtain the first OAM mode -1 and by exciting only feed source 2 to obtain the second OAM mode +1—different information can be distinguished according to the different modes in practical applications, thus realizing signal multiplexing.

[0089] pass Figure 7 , Figure 8 , Figure 9 This indicates that OAM modes -1 and +1 can be generated independently or simultaneously reused to meet the needs of different scenarios.

[0090] The above description is only a preferred embodiment of the present invention and does not constitute a limitation on the present invention. For those skilled in the art, various modifications and improvements can be made without departing from the innovative concept of the present invention, but these changes all fall within the protection scope of the present invention.

Claims

1. A design method for a holographic metasurface antenna with multi-feed common aperture OAM mode multiplexing, characterized in that, Several tensor surface impedances centered at different feed positions are superimposed on a common aperture, so that the aperture contains information of all target OAM mode vortex beams. By simultaneously exciting each feed, multi-feed common-aperture OAM mode multiplexing is achieved. The steps of this antenna design method are as follows: Step 1. Determine the number of feed sources The i-th orbital angular momentum mode The position of the i-th feed source The beam direction of the emitted wave in spherical coordinates is ,in, , , , Indicates pitch angle and , Indicates azimuth and ; Step 2. Calculate the first... Excitation wave generated by a feed source and the corresponding emitted wave of the feed source ; Step 3. Calculate the first... Excitation wave generated by a feed source With corresponding outgoing wave Tensor surface impedance distribution generated by interference ; Step 4. Superimpose all tensor surface impedance distributions to obtain the total tensor surface impedance distribution. ; Step 5. Transform the tensor surface impedance distribution Converted into equivalent scalar surface impedance distribution ; Step 6. Design the tensor metasurface unit used in the holographic metasurface. Each metasurface unit has three degrees of freedom. , and Control its equivalent scalar surface impedance; Step 7. Adjust the three degrees of freedom of the tensor holographic metasurface units at different locations on the holographic metasurface. , , This results in the tensor holographic metasurface having the aforementioned equivalent scalar surface impedance distribution; Step 8. Follow , , The distribution arranges the tensor holographic metasurface units to... The holographic metasurface, composed of tensor holographic metasurface units arranged in a grid, is the XOY plane, with the center of the plane being the origin of the coordinate system. and ,Will Each feed source is arranged according to the location information determined in step 1, and simultaneously excites... Each feed source generates an orbital angular momentum vortex electromagnetic wave corresponding to each feed source; Step 9. By simultaneously stimulating each feed source, the OAM mode can be reused.

2. The design method for a holographic metasurface antenna with multi-feed common aperture OAM mode multiplexing according to claim 1, characterized in that, The first Excitation wave generated by a feed source and the corresponding emitted wave of the feed source It is obtained from the following formula: ； ； in, Represented by natural constant An exponential function with base 0. The symbol represents the imaginary unit, and k represents the free space wavenumber. t This represents the wave number of an electromagnetic wave propagating on the surface of an array. and Let x and y represent the x-coordinates of the center of the tensor holographic metasurface cell in the m-th row and n-th column relative to the center of the tensor holographic metasurface, respectively. , , Indicates the i-th feed source and The distance between holographic metasurface units at the location, .

3. The design method for a holographic metasurface antenna with multi-feed common aperture OAM mode multiplexing according to claim 2, characterized in that, The first step described in step 3 Excitation wave generated by a feed source With the corresponding outgoing wave Tensor surface impedance distribution generated by interference It is obtained from the following formula: ； in, , , , Represents the surface impedance of the constituent tensor Two vectors and In respectively and Components in direction, , Let these represent the average impedance and modulation depth of the tensor holographic metasurface unit, respectively. This indicates taking a value for the imaginary part of a complex number; the superscript H indicates the conjugate transpose sign. This represents the Kronecker multiplication operation, i.e., the vector outer product.

4. The design method for a holographic metasurface antenna with multi-feed common aperture OAM mode multiplexing according to claim 3, characterized in that, The tensor surface impedance distribution described in step 4 It is obtained from the following formula: ； in, This represents the number of tensor surface impedance distributions, and .

5. The design method for a holographic metasurface antenna with multi-feed common aperture OAM mode multiplexing according to claim 4, characterized in that, The equivalent scalar surface impedance distribution described in step 5 It is obtained from the following formula: ； in, Represents wave impedance in free space. , , , Represents the surface impedance of the constituent tensor Two vectors and In respectively and Components in direction, Represents the equivalent scalar surface impedance Iterate through and retrieve values ​​within this range. , It represents pi (π).

6. A holographic metasurface antenna with multi-feed common-aperture OAM mode multiplexing, employing the holographic metasurface antenna design method described in claim 1, comprising a holographic metasurface and feed sources, characterized in that: The holographic metasurface consists of periodically arranged, identical but different-sized structures along the x and y axes. It is composed of tensor holographic metasurface units; the feed source is embedded in the holographic metasurface. Each of the several feeding structures can excite the entire holographic metasurface, achieving a multi-feed source with a common aperture. .

7. The holographic metasurface antenna with multi-feed common aperture OAM mode multiplexing according to claim 6, characterized in that, The feed source is A set of monopole antennas with omnidirectional radiation characteristics. The center positions of each monopole antenna are randomly distributed along the positive and negative x-axis or y-axis, and are all different. The centers of all monopole antennas are separated from the center of the holographic metasurface by a distance of 1 / 2. One wavelength, .

8. The holographic metasurface antenna with multi-feed common aperture OAM mode multiplexing according to claim 6, characterized in that, The tensor holographic metasurface unit is composed of a dielectric substrate, a metal ground plane, and an elliptical patch. The dielectric substrate is a cuboid-shaped solid dielectric material with a side length of [missing information]. The range of values ​​is , The wavelength corresponding to the operating frequency of the tensor holographic metasurface antenna, and the height of the dielectric substrate. The range of values ​​is The metal ground plane and the elliptical patch are copper foils printed on the lower and upper surfaces of the dielectric substrate, respectively. The metal ground plane is square and has the same side length as the lower surface of the dielectric substrate.

9. The holographic metasurface antenna with multi-feed common aperture OAM mode multiplexing according to claim 8, characterized in that, The different sizes The size variation of each tensor holographic metasurface unit is defined by the three degrees of freedom of the elliptical patch. and The following formula is used to calculate: ； ； in, and Representing the equivalent scalar surface impedance respectively The maximum and minimum values, equal Get the maximum value Time corresponding , .

10. The holographic metasurface antenna with multi-feed common aperture OAM mode multiplexing according to claim 6, characterized in that, The top layer of the holographic metasurface Each elliptical patch is selectively removed, resulting in a circular distribution of the remaining elliptical patches. The removal of some patches refers to removing patches with the center of the holographic metasurface as the origin. A circle with radius is drawn, and elliptical patches located outside the circular area are removed using this circle as the boundary. .

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