Reflection unit based on metasurface and array antenna thereof

Abstract

The invention belongs to the technical field of antennas, and discloses a reflection unit based on a metasurface and an array antenna thereof. Comprising a linear polarization horn antenna feed source and a metasurface reflection array. The array is composed of reflection units which are arranged periodically, and each reflection unit comprises a metal resonance layer, a dielectric substrate and a metal back plate from top to bottom. The metal resonance layer comprises a non-uniform line width structure formed by a central metal strip and two symmetrically connected arc-shaped metal arms, namely, the line width of the central metal strip is unequal to that of the arc-shaped metal arms, so that the loss of the reflection unit is effectively reduced, and coupling between amplitude and phase regulation is remarkably reduced. The reflection phase of the reflection unit is realized by adjusting the central angle corresponding to the arc-shaped arm, and the reflection amplitude is realized by adjusting the rotation angle of the whole metal resonance layer around the normal axis of the metal resonance layer. Through joint optimization of parameters and array arrangement of each unit, excellent performance of low sidelobe level, low cross polarization level and high aperture efficiency is finally realized.

Description

Technical Field

[0001] This invention relates to the field of antenna technology, and more specifically, to a metasurface-based reflective element and its array antenna. Background Technology

[0002] Reflector array antennas, with their high gain, low profile, and flexible beamforming capabilities, are of great value in applications such as satellite communications, mobile communications, and radar systems. However, this technology still faces several key challenges: First, factors such as reflector element loss, phase compensation error, and feed hood obstruction lead to low overall efficiency; second, their inherent narrow bandwidth characteristics limit their application in broadband scenarios; and third, due to the use of an open-feed method, it is difficult to independently control the amplitude of the reflector element after the feed hood position is fixed, which significantly restricts the ability to suppress sidelobe levels through amplitude weighting (see reference: S. Costanzo, F. Venneri, G. Di Massa, A. Borgia, and A. Raffo, “Bandwidth performances of reconfigurable reflectarrays: state of art and future challenges,” Radioengineering, vol. 27, no. 1, pp. 1–9, Apr. 2018.).

[0003] Chinese invention patent CN 117791119 B discloses a broadband reflective element with low cross-polarization and its array antenna. This design achieves low cross-polarization by incorporating metal partitions in its multi-layer structure and primarily achieves phase modulation by adjusting geometric parameters. While this scheme reduces cross-polarization to some extent, its element structure design only allows for phase modulation, thus limiting its ability to further suppress pattern sidelobes using amplitude weighting.

[0004] In recent years, the rise of metasurface technology has provided a new approach to solving the above problems. Metasurfaces have unique advantages such as subwavelength thickness and flexible control of electromagnetic wave phase, amplitude, polarization, and frequency, and have become a research hotspot in the field of electromagnetics. Combining metasurfaces with reflective arrays can break through the limitations of traditional design and has made significant progress in improving aperture efficiency, broadening the operating bandwidth, reducing sidelobe levels, realizing multi-polarization / multi-band / multi-beam functions, and dynamic reconfigurability (see reference: MK Emara, D. Kundu, K. MacDonell, LM Rufail, and S. Gupta, “Coupled resonator-based metasurface reflector with enhanced magnitude and phase coverage,” Apr. 14, 2023, Institute of Electrical and Electronics Engineers (IEEE)).

[0005] In the design strategy of realizing low sidelobe reflection arrays using metasurfaces, a common method is to utilize the characteristic of mutual conversion between the main polarization wave and the cross-polarization wave of the reflecting element for amplitude modulation (see reference: H.-P. Li, G.-M. Wang, T. Cai, J.-G. Liang, and X.-J. Gao, “Phase- and Amplitude-Control Metasurfaces for Antenna Main-Lobe and Sidelobe Manipulations,” IEEE Trans. Antennas Propagat., vol. 66, no. 10, pp. 5121–5129, Oct. 2018). However, while this method effectively suppresses the sidelobe level, it significantly increases the cross-polarization level of the antenna, making it difficult to apply to scenarios with strict cross-polarization requirements. To suppress cross-polarization, a polarization grating can be added to guide the cross-polarized wave from the reflection region to the transmission region (see reference: Y. Wang, Y. Ge, Z. Chen, and Z. Zhou, “Design of Wideband Reflectarray and Transmitarray Antennas With Low Sidelobe and Cross-Polarization Levels Using a Multifunctional Ultrathin Metasurface,” IEEE OpenJ. Antennas Propag., vol. 5, no. 3, pp. 601–611, Jun. 2024.). However, this method leads to gain loss and reduces the aperture efficiency of the reflector array. Therefore, existing techniques struggle to achieve both low sidelobes and high cross-polarization levels while maintaining high aperture efficiency.

[0006] Therefore, this invention focuses on the structural optimization of the reflector itself, aiming to improve the unit efficiency while simultaneously achieving the goals of low sidelobe, low cross-polarization, and high aperture efficiency by improving the unit design. Summary of the Invention

[0007] The purpose of this invention is to overcome the existing defects of reflective array antennas and to propose a reflective element and its array antenna based on metasurface. By improving the structure of the reflective element, the sidelobe level is reduced while maintaining a low cross-polarization level and a high aperture efficiency.

[0008] To achieve the above objectives, the present invention proposes a metasurface-based reflective element and its array antenna, wherein the metasurface-based reflective array antenna includes a feed source and a metasurface reflective array;

[0009] The feed source is a linearly polarized horn antenna positioned above the metasurface reflector array, and its position is adjustable.

[0010] The aforementioned metasurface reflective array with a circular aperture shape includes several reflective units arranged in a rectangular grid periodic pattern. Each reflective unit includes, from top to bottom, a metal resonant layer, a dielectric substrate, and a metal backplate.

[0011] The aforementioned metal resonant layer includes a central metal strip and two arc-shaped metal arms, the two arc-shaped metal arms being symmetrically connected to both ends of the central metal strip; the linewidth of the arc-shaped metal arms is... Smaller than the line width of the central metal strip This forms a non-uniform linewidth structure; the reflection phase of the reflective unit is adjusted by changing the central angle corresponding to the half-arc length of the arc-shaped metal arm. To achieve dynamic control, the central angle is adjusted. Able to achieve greater than or equal to The reflection phase adjustment range; the reflection amplitude of the reflection unit is adjusted by regulating the rotation angle of the metal resonant layer about its normal axis. Achieve dynamic control; and satisfy: when the rotation angle for At that time, the central angle Changes can cover the reflection phase to When the rotation angle for At that time, the central angle Changes can cover the reflection phase to ; while fixing the rotation angle Under the condition of adjusting the central angle At that time, the reflection amplitude fluctuation of the reflecting unit is less than or equal to ;

[0012] The metal resonant layer, dielectric substrate, and metal backplate together form a resonant structure. The dielectric substrate provides physical support and a resonant medium, while the metal backplate is used to reflect electromagnetic waves and form the bottom boundary of the resonant cavity.

[0013] The relative permittivity of the dielectric substrate is The loss tangent is substrate thickness for Both the metal resonator layer and the metal backplate are made of copper foil material, with a thickness of... for .

[0014] Preferably, the side length of the reflective unit wavelength of the center frequency one-third, that is The reflective elements are arranged in the metasurface reflective array with this side length as the period;

[0015] Preferably, the length of the central metal strip for to The line width of the central metal strip for to .

[0016] The line width of the central metal strip The line width is greater than that of the arc-shaped metal arm. ,and The ratio is to .

[0017] The design method for a metasurface-based reflective array antenna includes the following steps:

[0018] Step 1: By calculating the relationship between the position of the feed phase center, the theoretical aperture efficiency of the reflector array, and the edge level, a suitable feed position, i.e., a suitable feed height, is determined. and offset angle ;Calculate the required compensation phase for each reflection unit based on the different positions of each reflection unit and the position of the feed phase center;

[0019] Step 2: Based on the gain pattern of the feed source The coordinates of the feed phase center in the reflector array coordinate system and the position of each reflector unit It can calculate the amplitude of the feed irradiation onto each reflector element;

[0020] Step 3: Compensate for the amplitude of the feed irradiation onto each reflector to obtain the desired amplitude window, thereby further reducing the sidelobe level of the reflector array pattern.

[0021] Step 4: Based on the compensation phase calculated in Step 1 and the compensation amplitude calculated in Step 3, and considering the phase of the reflecting unit as a function of the central angle... The relationship between the changes and the magnitude of the changes with the rotation angle Based on the changing relationship, determine the central angle corresponding to each reflecting unit. and rotation angle Configure the parameters of each reflective unit to form an array.

[0022] Compared with the prior art, the advantages of the present invention are:

[0023] 1. The non-uniform linewidth design of the metasurface reflective unit described in this invention effectively reduces the loss of the reflective unit. At the center frequency, at a fixed rotation angle... for When the amplitude of the reflection coefficient of the reflecting unit is greater than .

[0024] 2. The phase adjustment and amplitude adjustment of the reflective unit described in this invention have high independence, and at a fixed rotation angle... Adjusting the central angle under certain conditions When performing phase modulation, the reflection amplitude fluctuation is less than ; at a fixed central angle Adjusting the rotation angle under certain conditions When amplitude modulation is performed, the reflection phase fluctuation is less than .

[0025] 3. The metasurface-based reflective array antenna of the present invention, by jointly optimizing the geometric parameters of the reflective element array, can significantly reduce the sidelobe level of the radiation pattern while maintaining a low cross-polarization level and a high aperture efficiency. Attached Figure Description

[0026] Figure 1 This is a three-dimensional structural schematic diagram of the metasurface reflective unit in this invention;

[0027] Figure 2 This is a top view of the metasurface reflective unit in this invention.

[0028] Figure 3 This is a schematic diagram of the overall structure of the metasurface-based reflective array antenna of the present invention;

[0029] Figure 4 The central angle of the metasurface reflective unit in this invention A graph showing the relationship between reflection phase and reflection amplitude;

[0030] Figure 5 The rotation angle of the metasurface reflective unit in this invention. A graph showing the relationship between reflection phase and reflection amplitude;

[0031] Figure 6 This is a phase distribution diagram of the reflective array antenna compensation according to the present invention;

[0032] Figure 7 This is a diagram showing the structure distribution of the phase-weighted reflection array antenna of this invention.

[0033] Figure 8 This is a simulation result diagram of the phase-weighted reflection array antenna of this invention;

[0034] Figure 9 This is a diagram showing the compensation amplitude distribution of the Taylor-weighted reflective array antenna of the present invention.

[0035] Figure 10 This is a diagram showing the structural distribution of the Taylor-weighted reflective array antenna of the present invention.

[0036] Figure 11 The figure shows the simulation results of the Taylor-weighted reflective array antenna of this invention.

[0037] Figure Labels

[0038] 1. Metal resonant layer 2. Dielectric substrate

[0039] 3. Metal backplate 4. Metasurface reflective array

[0040] 5. Feed source; 11. Center metal strip

[0041] 12. Curved metal arm Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0043] This example mainly proposes a metasurface-based reflective element and its array antenna, specifically involving a metasurface-based reflective element with the following structure: Figure 1 and Figure 2 As shown.

[0044] The metasurface reflective unit comprises, from top to bottom, a metal resonant layer 1, a dielectric substrate 2, and a metal backplate 3. The metal resonant layer 1 is composed of a central metal strip 11 symmetrically connected to two arc-shaped metal arms 12. The central angle corresponding to the half-arc length of the arc-shaped metal arms 12 can be adjusted. To achieve phase modulation of the reflection, the metal resonator layer 1 of the reflection unit rotates around the axis. Achieve amplitude control for reflection, and satisfy the following condition: when the rotation angle... for At that time, the central angle Changes can cover the reflection phase to When the rotation angle for At that time, the central angle Changes can cover the reflection phase to The key feature is the line width of the central metal strip 11. Line width of curved metal arm 12 Uneven linewidth design.

[0045] like Figure 3As shown, the metasurface-based reflective array antenna consists of two parts: a feed source 5 and a metasurface reflective array 4. The feed source 5 is a linearly polarized horn feed source placed above the metasurface reflective array 4. The metasurface reflective array 4, which has a circular aperture shape, includes metasurface reflective elements arranged in a rectangular grid periodic pattern.

[0046] By calculating the relationship between the position of the feed phase center, the theoretical aperture efficiency of the reflector array, and the edge level, a suitable position for feed 5, i.e., a suitable feed height, is determined. and offset angle The specific implementation process is as follows:

[0047] In such Figure 3 In the overall structure of the metasurface-based reflective array antenna shown, the phase center coordinates of feed 5 are: At this point, the phase center position of feed 5 and the theoretical aperture efficiency can be calculated. The relationship is expressed by the formula:

[0048] (1)

[0049] in, This shows the gain pattern of feed 5. In the relative spherical coordinate system representing feed 5, the surface of the metasurface reflective array 4... The angular coordinates corresponding to the position This represents the integration region of the metasurface reflective array 4. This indicates the aperture size of the metasurface reflective array 4. On the aperture surface of metasurface reflective array 4 The range of position is given by the formula:

[0050] (2)

[0051] in This indicates that feed 5 is illuminating the aperture of metasurface reflector array 4. The range of position, This is the gain pattern of the reflecting unit. This indicates the four surfaces of the metasurface reflective array. The angular coordinates corresponding to the position of feed source 5 in the relative coordinate system. From the feed phase center to the four surfaces of the metasurface reflective array Distance of location:

[0052] (3)

[0053] Feed phase center position and edge level The relationship can be calculated using the following formula:

[0054] (4)

[0055] in, This represents the maximum amplitude of the light emitted by feed 5 onto the aperture surface of the reflector array. The amplitude of the feed 5 illuminating the edge of the reflector aperture.

[0056] Based on the phase center position of feed 5 Compared with theoretical caliber efficiency and edge level The relationship between the feed source and the offset angle of feed 5 To retrieve values, for each The value is selected to satisfy the high theoretical aperture efficiency and the edge level is between to Required feed height Subsequently, HFSS was used to simulate the reflector array at different feed phase center positions, and the final feed phase center position was determined by comprehensively analyzing the simulation results. .

[0057] Based on the different positions of each reflecting element and the position of the feed phase center, the required compensation phase for each reflecting element can be calculated using the following formula:

[0058] (5)

[0059] in, The vacuum propagation constant at the center operating frequency; For the feed phase center and the first The distance between each reflecting unit; For the desired beam direction in spherical coordinates, For the desired polar angle, The desired azimuth angle; For the first The compensation phase required for each reflective unit.

[0060] Maintain rotation angle for Based on the compensation phase of each reflective element, the central angle of each reflective element is adjusted. This allows us to obtain a beam pointing towards the desired beam direction. At this point, the reflection amplitude of each reflecting element is determined solely by the amplitude distribution of the feed 5 illuminating each reflecting element, and the sidelobe level reflected in the final reflection array pattern is also largely determined. Optimizing the compensation phase results in a relatively small reduction in the sidelobe level.

[0061] According to the gain pattern of feed 5 The coordinates of the feed phase center in the metasurface reflective array 4-coordinate system and the position of each reflector unit The amplitude of light emanating from feed 5 onto each reflective element can be calculated using the following formula:

[0062] (6)

[0063] in, In the relative spherical coordinate system of feed 5, the metasurface reflective array 4 is... The angular coordinates corresponding to each reflecting unit; For feed source 5 to illuminate the first The amplitude of each reflecting element is calculated. Based on this, the amplitude of the feed 5 illuminating each reflecting element is compensated to obtain the desired amplitude window, thereby further reducing the sidelobe level of the reflective array pattern. The formula for calculating the compensation amplitude is:

[0064] (7)

[0065] in, The desired amplitude distribution for each reflective element depends on the amplitude window function used. Different amplitude window functions, such as Taylor windows and Chebyshev windows, can be selected to optimize the reflective array performance based on specific application requirements. The compensation amplitude for each reflective element is calculated. Combining the compensation phase calculated using formula (5) and the compensation amplitude calculated using formula (7), the central angle of each reflective element is adjusted. and rotation angle This allows us to obtain a reflected beam with a low sidelobe level that points in the direction of the desired beam.

[0066] The reflective unit adjusts the reflection phase by changing the arc length of the arc-shaped metal arm 12, employing the principle of the extension line of the reflective unit. Based on this principle, this invention effectively reduces the loss of the reflective unit by adjusting the linewidth of the arc-shaped metal arm 12 to be inconsistent with the linewidth of the middle metal strip 11, while also reducing the coupling degree between amplitude control and phase control.

[0067] To better understand the technical solution of the present invention, the present invention will be further described below with reference to examples.

[0068] This example presents an improved metasurface reflective unit that can be used in various common microwave frequency bands. Without loss of generality, taking the Ku band as an example, the reflective unit comprises, from top to bottom, a metal resonant layer 1, a dielectric substrate 2, and a metal backplate 3, as follows: Figure 1 As shown, the dielectric substrate 2 uses F4BM265 material with a relative permittivity of [value missing]. The loss tangent is substrate thickness for Both the metal resonant layer 1 and the metal backplate 3 are made of copper foil material, with a thickness of... All The metal resonant layer 1 is composed of a central metal strip 11 and two arc-shaped metal arms 12 symmetrically connected, so as to... Taking the polarized wave as the incident wave as an example for simulation, since the reflecting unit has the characteristic of polarization conversion, the principal polarization of its reflected wave is... Polarization, cross-polarization is Polarization. The dimensions after simulation optimization are: the length of the central metal strip 11. The width of the central metal strip 11 The width of the curved metal arm 12 central angle The range of regulation is to The corresponding phase modulation range covers to Rotation angle The range of regulation is to The corresponding range of amplitude adjustment is to .exist The simulation curves for phase modulation and amplitude modulation of the metasurface reflective unit are shown below. Figure 4 and Figure 5 As shown, where Indicates incident wave Polarized reflected wave The polarization of the reflection coefficient, its amplitude Indicates the amplitude and angle of reflection. This represents the reflection phase. It can be seen that at the center frequency, maintaining the rotation angle... By keeping the reflection phase constant, the amplitude of the reflection unit is adjusted. And fluctuations Maintain the central angle The reflection amplitude remains constant, while the reflection phase of the reflecting unit remains constant. fluctuations .

[0069] Using this metasurface unit, arranged in a rectangular grid, a metasurface reflective array 4 with a circular aperture is formed. The spacing between each reflective unit is The total number of reflective units is Select operating frequency The linearly polarized horn antenna is used as feed 5. The feed waveguide of feed 5 adopts BJ-140, with a gain of [missing value]. Based on the theoretical aperture efficiency and edge level, the position of the feed phase center is determined as follows: That is, the height of feed 5 is Offset angle is Set the desired beam direction as follows: This corresponds to the mirror reflection direction of the incident direction of feed 5. The result is calculated according to formula (5). Figure 6 The compensated phase distribution diagram shown is based on the central angle of the reflecting unit obtained through pre-simulation. and rotation angle Relationship with reflection amplitude and phase (e.g.) Figure 4 , Figure 5 As shown), the central angle corresponding to the half-arc length of each reflecting unit is obtained. and rotation angle From this, we can obtain the following: Figure 7 The image shows a phase-weighted reflective array antenna. A full-wave simulation of this reflective array antenna was performed; to clearly illustrate the radiation pattern characteristics, the designed beam direction is shown in the simulation results. Set as a relative coordinate system Location. For example... Figure 8 As shown, in Below, the gain of the main polarization pattern is , The sidelobe level of the surface is The cross-polarization level is ; The sidelobe level of the surface is The cross-polarization level is Based on actual caliber efficiency Calculation formula:

[0070] (8)

[0071] It can be obtained that, when only phase-weighted, the aperture efficiency of this reflective array antenna is: ,in, The gain of the radiation pattern. This refers to the aperture size of the metasurface reflective array 4. The wavelength corresponding to the center operating frequency.

[0072] Based on this, amplitude weighting is applied to the reflective array antenna. A Taylor window is used for amplitude weighting, and the sidelobe level of the reflective array is... Direction set , Direction set The expected amplitude distribution of each reflecting unit can be calculated. The compensation amplitude for each reflective element can be calculated using formulas (6) and (7). ,like Figure 9 As shown. Combined with Figure 6The compensated phase distribution of the reflective element shown is based on the central angle of the reflective element obtained through pre-simulation. and rotation angle Relationship with reflection amplitude and phase (e.g.) Figure 4 , Figure 5 As shown in the figure, the central angle corresponding to the half-arc length of each reflecting unit can be obtained. and rotation angle From this, we can obtain the following: Figure 10 The image shows an amplitude-modulated and phase-modulated reflective array antenna. A full-wave simulation of this reflective array antenna is performed, and the results are as follows... Figure 11 As shown, in Below, the gain of the main polarization pattern is , The sidelobe level of the surface is The cross-polarization level is ; The sidelobe level of the surface is The cross-polarization level is According to the aperture efficiency calculation formula (8), after amplitude and phase modulation, the aperture efficiency of the reflective array antenna is: .

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A reflective unit based on a metasurface, characterized in that, The reflective unit comprises, from top to bottom, a metal resonant layer, a dielectric substrate, and a metal backplate; The aforementioned metal resonant layer includes a central metal strip and two coaxial arc-shaped metal arms, the two arc-shaped metal arms being symmetrically connected to both ends of the central metal strip; the linewidth of the central metal strip is... The line width is greater than that of the arc-shaped metal arm. .

2. The metasurface-based reflective unit according to claim 1, characterized in that, The linewidth of the arc-shaped metal arm Line width of the central metal strip The ratio is .

3. The metasurface-based reflective unit according to claim 1, characterized in that, The length of the central metal strip for to .

4. The metasurface-based reflective unit according to claim 1, characterized in that, The side length of the aforementioned reflective unit wavelength corresponding to the center operating frequency One-third of the reflective element in the metasurface reflective array has this side length Arrange them in a periodic manner.

5. The metasurface-based reflective unit according to claim 1, characterized in that, The central angle corresponding to the semi-arc length of the arc-shaped metal arm is... ,pass The change in [the value] can adjust the reflection phase of the reflecting unit.

6. The metasurface-based reflective unit according to claim 1, characterized in that, The rotation angle of the central metal strip about its normal axis is all ,pass The change in [something] can adjust the reflection amplitude of the reflecting unit.

7. The metasurface-based reflective unit according to claim 5, characterized in that, The reflection phase can satisfy greater than or equal to Requirements.

8. A metasurface-based reflective array antenna, characterized in that, The metasurface-based reflective array antenna includes a feed source and a metasurface reflective array; The feed source is a linearly polarized horn antenna positioned above the metasurface reflector array; The metasurface reflective array comprises a number of metasurface-based reflective units as described in claims 1-7 arranged in a periodic manner.

9. The metasurface-based reflective array antenna according to claim 8, characterized in that, The aperture shape of the metasurface reflective array is circular; the reflective units are arranged in a periodic rectangular grid.

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