Beam forming antenna based on holographic tensor impedance modulation metasurface

Abstract

The invention discloses a beam forming antenna based on a holographic tensor impedance modulation metasurface and a design method thereof, and belongs to the technical field of microwave antennas. The antenna comprises a monopole feed source and a metasurface formed by a periodic array, wherein each tensor impedance unit adopts a three-layer structure comprising an upper slotted metal patch, a middle dielectric substrate and a lower metal grounding layer. A unit library of patch sizes and electromagnetic characteristics is constructed, tensor impedance distribution of each unit is calculated by adopting an iterative algorithm based on a holographic principle, and finally accurate matching with the unit library is realized. According to the invention, the surface wave can be efficiently converted into a specified target wave beam, high-gain and low-sidelobe dual-beam or flat-topped wave beam forming can be realized in a broadband, and meanwhile, the antenna has the advantages of low profile, easiness in integration and low cost, and can be widely applied to a modern wireless communication system.

Description

Technical Field

[0001] This invention belongs to the field of microwave antenna technology, and particularly relates to a beamforming antenna based on a holographic tensor impedance modulation metasurface. Background Technology

[0002] Beamforming is a key technology that uses spatially modulated antenna radiation energy distribution to directionally transmit electromagnetic energy, suppress interference, and improve link quality. It has been widely used in mobile and satellite communications. Traditional implementations rely on antenna arrays or phased arrays, using amplitude and phase weighting to achieve main lobe directionality and sidelobe control. However, these solutions generally face challenges such as large size and weight, complex feeding and phase-shifting networks, high power consumption, increased manufacturing and assembly costs, and limited reconfigurability and integration in multi-functional scenarios, making it difficult to meet the evolving demands for terminal miniaturization, platform integration, and multi-standard collaboration. Holographic impedance-modulated metasurfaces, composed of periodic or quasi-periodic units, can precisely shape phase, amplitude, and polarization at subwavelength scales. They offer advantages such as simple structure, thinness, easy integration, and low cost, making them an important candidate for novel beamforming technologies. By holographically interfering a reference wave with the desired target wavefield on the aperture plane, the spatial distribution of the equivalent surface impedance is obtained. This distribution is then used to guide the surface current to radiate a wavefront that approximates the target, thus achieving high-fidelity beamforming and path control within the aperture plane with low profile and low complexity. This approach not only enables high-precision synthesis of propagation directions but also allows for flexible setting of wavefront morphology and energy distribution on the aperture plane, making it suitable for adaptive beamforming in multi-beam, low-sidelobe, blind zone coverage, and complex scenarios. Summary of the Invention

[0003] The purpose of this invention is to design a beamforming antenna based on a holographic tensor impedance metasurface. By utilizing the anisotropy of tensor impedance and using an iterative algorithm for non-uniform modulation, the transmission amplitude and phase of surface waves and leaky waves in each element of the array are realized. The modulation coefficients at each position of the array and the tensor impedance distribution of each element are obtained through the target radiation field, thereby realizing beamforming for different target fields.

[0004] To solve the above-mentioned technical problems, the specific technical solution of the present invention is as follows: In some embodiments of this application, a beamforming antenna based on a holographic tensor impedance modulation metasurface is provided, comprising: Feed source, wherein the feed source is a monopole antenna; The metasurface is composed of M×N tensor impedance units arranged periodically, and is used to modulate and radiate the surface wave excited by the feed source into a preset target beam. Each of the tensor impedance units includes an upper metal patch, an intermediate dielectric substrate, and a lower metal ground layer stacked from top to bottom; The upper metal patch has an axisymmetric structure and is provided with a slot for introducing anisotropy. The orientation of the slot defines the principal axis direction of the unit tensor impedance.

[0005] In some embodiments of this application, the dielectric substrate is made of ROGERS4360, which has a relative permittivity of 6.15 and a thickness of 1.52 mm.

[0006] In some embodiments of this application, the upper metal patch is a circular patch with a thickness of 0.018 mm, and the width of the gap is 0.2 mm.

[0007] In some embodiments of this application, the radius of the circular metal patch is adjustable in the range of 0.2 mm to 1.6 mm.

[0008] In some embodiments of this application, M and N are both positive integers. Preferably, M and N are both 30, the unit period is 6mm, and the total size of the metasurface is 180mm×180mm.

[0009] In some embodiments of this application, a method for designing the above-described beamforming antenna is disclosed, comprising the following steps: Unit library construction steps: Through electromagnetic simulation, obtain the intrinsic frequencies and surface impedance values ​​corresponding to the upper metal patches with different structural parameters, and establish a database of mapping relationships between structural parameters and electromagnetic properties; Target field setting steps: Set the far-field radiation pattern of the desired antenna radiation as the target radiation field; Impedance distribution calculation steps: Based on the holographic principle, a physical model between the surface wave and the target radiation field is established, and the tensor impedance distribution required for each unit of the metasurface is solved by an iterative algorithm. Unit matching step: Match the calculated tensor impedance values ​​of each unit with the unit library to determine the structural parameters and slot orientation of the upper metal patch of each unit.

[0010] In some embodiments of this application, in the unit library construction step, the upper metal patch is a circular patch with a structural parameter of patch radius; during electromagnetic simulation, the phase difference between the fixed units in two orthogonal polarization directions is a predetermined value.

[0011] In some embodiments of this application, the predetermined value is 100°. In some embodiments of this application, in the impedance distribution calculation step, the iterative algorithm uses the average tensor impedance of the metasurface as the initial value for the surface wave propagation constant.

[0012] In some embodiments of this application, the target radiation field is a dual-beam or flat-top beam.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: by slotting the upper patch according to the main axis direction determined by the algorithm and constructing a patch unit library, combined with a 30×30 unit array and monopole feeding, the present invention can efficiently convert surface waves into high-precision directional dual beams or flat-top beams in a low-profile structure without complex feed grids and phase shifters, achieving superior aperture efficiency and beam control capabilities. The overall design has significant advantages of simple structure, easy integration and low cost, and is very suitable for modern communication systems with stringent requirements for antenna performance and integration. Attached Figure Description

[0014] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 This is a schematic diagram of the unit structure provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the upper patch structure provided in an embodiment of the present invention; Figure 3 A schematic diagram of the dispersion characteristics of the unit structure provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the changes in intrinsic frequency and surface impedance of a unit cell as a function of equivalent capacitance, provided in an embodiment of the present invention. Figure 5 This is a schematic diagram showing the distribution of principal axis impedance values ​​and principal axis direction corresponding to different beam deflection angles provided in an embodiment of the present invention. Figure 6 A schematic diagram showing the principal axis impedance and principal axis direction values ​​of each unit of the flat-top beamforming array provided in an embodiment of the present invention; Figure 7 This is a schematic diagram of a dual-beam array provided in an embodiment of the present invention; Figure 8 This is a schematic diagram of a flat-top beam array provided in an embodiment of the present invention; Figure 9 This is a schematic diagram of a tensor impedance surface antenna and a mounting plate provided in an embodiment of the present invention; Figure 10 A schematic diagram of the full-wave receiving antenna structure provided for an embodiment of the invention; Figure 11 A schematic diagram of a microwave anechoic chamber experimental environment provided for an embodiment of the invention. Detailed Implementation

[0015] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0016] To better understand the purpose, structure, and function of this invention, the invention will be described in further detail below with reference to the accompanying drawings.

[0017] See appendix Figures 1-11 As shown in some embodiments of this application, this application discloses a beamforming antenna based on a holographic tensor impedance modulation metasurface, including a monopole feed antenna and a tensor holographic impedance metasurface. First, while ensuring the phase difference in the x and y directions remains consistent, the eigenfrequency and surface impedance of the impedance surface are obtained. An iterative algorithm is used to calculate the modulation coefficients at each position of the array and the tensor impedance distribution of each element, and these are matched with elements in a unit library. The metasurface mainly consists of 30×30 elements. Surface waves are radiated through the loaded monopole feed antenna and transformed into target fields with dual beams and flat-top beams via the metasurface. This design aims to achieve beamforming of different target fields and improve aperture efficiency by utilizing the anisotropy of the tensor impedance surface and improving the modulation method to non-uniformly modulate the beam radiation of any single beam. It has advantages such as high gain, simple structure, easy integration, and low profile, and does not require the introduction of an additional spatial feed.

[0018] Appendix Figure 1 This paper showcases the detailed structure and dimensions of a tensor impedance cell. The cell consists of an upper metal patch, a middle dielectric layer, and a bottom ground layer. The dielectric substrate is made of ROGERS4360 with a relative permittivity of 6.15. The upper metal patch is circular with a central slot. The metal layer is 0.018 mm thick, the dielectric layer is 1.52 mm thick, and the slot width (gs) is 0.2 mm. The slot direction corresponds to the principal axis of the tensor impedance obtained through an iterative algorithm. After selecting a phase difference of 100° for the cell, the eigenmodes are solved for different patch sizes, yielding the eigenfrequency values ​​corresponding to different patch sizes after parameter scanning. By accumulating a sufficient number of values ​​for the top metal patch structure, a cell library can be built to provide options for different tensor impedance values.

[0019] Specifically, the metasurface consists of a holographic impedance surface and fed monopoles, including 30×30 tensor impedance units. Each unit comprises an upper metal patch structure, an intermediate dielectric layer, and a lower ground layer, using a ROGERS4360 dielectric substrate with a relative permittivity of 6.15. The upper metal patch is a circular patch with a slotted structure in the middle. The thickness of the metal layer is 0.018 mm, the thickness of the dielectric layer is 1.52 mm, the slot width gs = 0.2 mm, and the direction of the slot is the principal axis direction of the tensor impedance obtained by the iterative algorithm. The phase difference of the selected unit is... Then, the intrinsic modes are solved for different patch sizes, and the intrinsic frequency values ​​corresponding to different patch sizes after parameter scanning are obtained. After accumulating enough values, a patch cell library is constructed.

[0020] The metasurface unit has a size of 6mm×6mm, a dielectric layer thickness of 1.52mm, a metal layer thickness of 0.018mm, a patch slot width of 0.2mm, and a unit patch size radius of 0.2mm-1.6mm; The top metal patch and the bottom grounding layer are made of copper foil; the dielectric material is ROGERS4360 material with a dielectric constant of 6.15.

[0021] To determine the value of the tensor impedance, the relationship between the tensor impedance and the electric field is first given:

[0022] In the formula This represents the tangential electric field on the surface of the tensor impedance. This represents the tangential magnetic field of the tensor impedance surface. According to electromagnetic boundary condition theory, the difference between these two fields is the surface current. In the formula, bold text indicates that the variable type is a tensor or vector. Therefore, it can be seen from the above formula that tensor impedance... This characterizes the relationship between the tangential electric field and the surface current. If the heat loss of the metal patch is neglected, it is generally considered to be lossless; therefore, the tensor impedance matrix... It is a Hermitian matrix. The Cartesian coordinate form of the tensor impedance matrix has already been given; the tensor and matrix forms in polar coordinates are given by the following equation:

[0023] Each component can be written in the following form

[0024] in, This represents the average value of the radial direction component of the tensor impedance component. This represents the average value of the tensor impedance components in the azimuth direction. The impedance component is in the radial direction. These are the coupling impedance components in the radial and azimuth directions. This refers to the azimuth impedance component. The modulus of the radial modulation coefficient. The phase of the modulation coefficient in the radial direction. This represents the modulus of the azimuth direction modulation coefficient. The azimuth direction modulation coefficient is the phase. As can be seen from equation (3), the values ​​of each component of the tensor impedance fluctuate around the average value. The impedance surface formed by this type of tensor impedance is also called the constant average value tensor impedance surface. The advantage of doing this is that the impedance fluctuation within the entire tensor impedance surface will not be too large, that is, there will be no sudden change in the local area, so that the tensor impedance value in the entire plane maintains a certain continuity. In this way, in actual design, a uniform tensor impedance value can be used to simulate the local tensor impedance value of the tensor impedance surface, which will be discussed in the tensor impedance extraction later. Using Floquet theory, the tensor impedance is further expressed in the following exponential form:

[0025] Now, using monopole feeding, at an infinite impedance value... On the impedance surface, the excited current density can be expressed as:

[0026] To determine the initial impedance value, it is related to the propagation constant of the surface wave. related:

[0027] The remaining two parts are impedance modulation components. Since their phase velocity is greater than the speed of light, they will be modulated into leaky waves and radiated outwards. Therefore, the propagation coefficient of the surface wave will become a complex number.

[0028] The imaginary part of the propagation constant is the radiated energy. At this point, the current density in equation (5) changes to:

[0029] Since the propagation coefficient is related to the position of the impedance surface, in equation (8) It can be obtained by integral form:

[0030] Similarly, surface current density can also be written in a form similar to the expansion of the impedance surface:

[0031] Next, using the Green's function of the grounding medium The surface electric field can be expressed as:

[0032] Combining (4) and (11) to form a system of equations, we can obtain:

[0033] Let both sides of the expression contain the same With all terms having the same parameter, equation (12) can be further expanded into the following discrete form:

[0034] because Since it is an invertible matrix, the dispersion equation for the tensor impedance surface is obtained:

[0035] By solving the equation where the determinant of the matrix is ​​0, the real and imaginary parts of the formula can be separated to obtain the propagation coefficients at different positions:

[0036] in It is the change in the surface wave propagation constant after each iteration compared to the previous iteration, because It occupies most of the impedance surface, therefore It can be used as the initial value for propagation coefficient iteration.

[0037] Since the energy of the leaky wave radiation is only the n=-1 part, equation (12) is simplified and substituted into the adiabatic dispersion equation to obtain... get:

[0038] Since the goal is to make the radiation field of the leaked wave match the target field, that is... Therefore, we get:

[0039] By equating the exponents of the equations, we can obtain the phase component in the corresponding tensor impedance component variation equation:

[0040] Substituting the remaining components into equation (17) yields the modulation coefficients:

[0041] in:

[0042] Finally, the modulation coefficients at different positions are obtained, thus yielding the tensor impedance.

[0043] The propagation coefficient and modulation coefficient at each position of the array are calculated using a non-uniform impedance modulation iterative algorithm, thus obtaining the tensor impedance value of each element in polar coordinates. It is necessary to convert the tensor impedance in polar coordinates to tensor impedance in Cartesian coordinates. Furthermore, to match the surface impedance values ​​of the previously designed patch cell library, the tensor impedance needs to be converted to the corresponding scalar impedance value. When the patch size increases from 0.2mm to 1.6mm, the intrinsic frequency of the element increases from 9.5GHz to 11.5GHz, and the scalar impedance value also increases accordingly, from 280.9... Increased to 432.6 The array modulation uses an average impedance X = 335.6. The modulation depth M = 42.6.

[0044] Appendix Figure 2 With appendix Figure 3 The dispersive characteristics of the cell were demonstrated. The slit direction of the cell is the selected principal axis direction. After fixing the phase difference between the x and y directions, the intrinsic frequency of the cell is changed by altering the size of the upper metal patch, thereby changing the intrinsic impedance of the cell surface. When the cell patch size increases from 0.2 mm to 1.6 mm, the intrinsic frequency of the cell increases from 9.5 GHz to 11.5 GHz, and the scalar impedance value also increases accordingly, from 280.9 to 432.6, thus constructing a tensor impedance cell library.

[0045] Appendix Figure 4 and Figure 5 The tensor impedance distribution of the array is shown, and the tensor impedance distribution of beamforming for the dual-beam target field and the flat-top beam target field is listed. The designed holographic impedance surface is composed of 30×30 units. Due to the perfect symmetry of the circular patch, the direction of its impedance peak is the same as the direction of the patch slit, and the average impedance is 335.6.

[0046] Appendix Figure 6 and Figure 7 The specific structure of the antenna, along with physical testing and a microwave anechoic chamber environment diagram, were demonstrated. A 30×30 tensor impedance surface array, measuring 180mm×180mm, was constructed based on the results of the previous iterative calculations. Next, the simulated array was fabricated into a physical prototype for testing. During fabrication, a through-hole was drilled in the center of the array, and an RF coaxial connector was used. The rear part was connected to the feed using an SMA connector, while the front part served as a monopole antenna, radiating surface waves and leakage waves. The monopole antenna was 10mm long. The antenna array was fixed to a support on one side, fed into the feed, and a full-wave receiving antenna was used to detect the far-field radiation pattern. The experiment was conducted in a microwave anechoic chamber.

[0047] Appendix Figure 8 and Figure 9The full-wave simulation and physical test results of the antenna array for dual-beamforming and flat-top beamforming are presented. The far-field pattern of the tensor impedance surface antenna was tested using a vector network analyzer. The first three figures show that the tensor impedance surface antenna exhibits clear dual-beamforming at 9.7 GHz, 10 GHz, and 10.3 GHz, with gains exceeding 10 dB. Dual-beamforming is well achieved within the 9.7 GHz–10.3 GHz range. Under both simulation and experimental conditions, there are no large sidelobes, and gains, excluding the main lobe, are almost all below 0 dB, ensuring good directivity and accuracy. A small sidelobe is present at 0°, but its impact is minimal. As shown in the last three figures, this tensor impedance surface antenna exhibits a distinct flat-top beam at 9.7 GHz, 10 GHz, and 10.3 GHz, with a beamwidth between -12° and 12° and a gain exceeding 13 dB. It achieves good flat-top beamforming within the 9.7 GHz–10.3 GHz range. Similar to the previous dual-beam tensor impedance surface antenna, under both simulation and experimental conditions, there are no large sidelobes, and the gain, excluding the main lobe, is almost entirely below 0 dB, effectively ensuring energy directivity and accuracy. The experimental results show a reduction of approximately 1° in the flat-top beamwidth compared to the simulation results, an error within an acceptable range. In conclusion, the experimental results agree well with the simulation results.

[0048] The technical effects achieved by the above technical solution in the embodiments of this application are as follows: This application's embodiments, by utilizing the anisotropy of tensor impedance, provide more degrees of freedom for electromagnetic control than traditional scalar impedance. Through the aforementioned non-uniform iterative algorithm, the electromagnetic response of each unit cell of the metasurface can be independently and precisely controlled. The antenna employs a low-profile, planar structure, eliminating the need for the complex feed network, phase shifters, and numerous active devices found in traditional phased arrays, greatly simplifying the system architecture. By combining unit library construction with holographic iterative algorithm matching, the complex electromagnetic inverse problem (i.e., "given a target beam, find the metasurface structure") is transformed into a systematic forward design process. The antenna designed using this method shows a high degree of consistency between its measured results and full-wave simulation results, verifying the correctness and reliability of the design method and providing an effective approach for the rapid development of high-performance metasurface antennas.

[0049] In the description of this application, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0050] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0051] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0052] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0053] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A beamforming antenna based on a holographic tensor impedance modulated metasurface, characterized in that, include: Feed source, wherein the feed source is a monopole antenna; The metasurface is composed of M×N tensor impedance units arranged periodically, and is used to modulate and radiate the surface wave excited by the feed source into a preset target beam. Each of the tensor impedance units includes an upper metal patch, an intermediate dielectric substrate, and a lower metal ground layer stacked from top to bottom; The upper metal patch has an axisymmetric structure and is provided with a slot for introducing anisotropy. The orientation of the slot defines the principal axis direction of the unit tensor impedance.

2. The beamforming antenna based on a holographic tensor impedance modulation metasurface according to claim 1, characterized in that, The dielectric substrate is made of ROGERS4360, with a relative permittivity of 6.15 and a thickness of 1.52 mm.

3. A beamforming antenna based on a holographic tensor impedance modulation metasurface according to claim 1, characterized in that, The upper metal patch is a circular patch with a thickness of 0.018 mm, and the gap width is 0.2 mm.

4. A beamforming antenna based on a holographic tensor impedance modulation metasurface according to claim 3, characterized in that, The radius of the circular metal patch is adjustable within the range of 0.2 mm to 1.6 mm.

5. A beamforming antenna based on a holographic tensor impedance modulation metasurface according to claim 1, characterized in that, Both M and N are positive integers.

6. A method for designing a beamforming antenna as described in any one of claims 1-5, characterized in that, Includes the following steps: Unit library construction steps: Through electromagnetic simulation, obtain the intrinsic frequencies and surface impedance values ​​corresponding to the upper metal patches with different structural parameters, and establish a database of mapping relationships between structural parameters and electromagnetic properties; Target field setting steps: Set the far-field radiation pattern of the desired antenna radiation as the target radiation field; Impedance distribution calculation steps: Based on the holographic principle, a physical model between the surface wave and the target radiation field is established, and the tensor impedance distribution required for each unit of the metasurface is solved by an iterative algorithm. Unit matching step: Match the calculated tensor impedance values ​​of each unit with the unit library to determine the structural parameters and slot orientation of the upper metal patch of each unit.

7. The method according to claim 6, characterized in that, In the cell library construction step, the upper metal patch is a circular patch with a structural parameter of patch radius; during electromagnetic simulation, the phase difference between the fixed cells in two orthogonal polarization directions is a predetermined value.

8. The method according to claim 7, characterized in that, The predetermined value is 100°.

9. The method according to claim 6, characterized in that, In the impedance distribution calculation step, the iterative algorithm uses the average tensor impedance of the metasurface as the initial value for the surface wave propagation constant.

10. The method according to claim 6, characterized in that, The target radiation field is a dual-beam or flat-top beam.

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