Ultra wide band linear circular polarization converter based on wheel-shaped metasurface

Abstract

The invention belongs to the technical field of microwaves, and discloses a wheel-shaped metasurface-based ultra-wideband linear circular polarization converter, the linear circular polarization converter is composed of reflection-type polarization conversion units which are periodically arranged, and each reflection-type polarization conversion unit comprises an upper wheel-shaped metal pattern layer, a middle dielectric substrate and a bottom metal layer, the upper surface of the middle dielectric substrate is tightly connected with the upper wheel-shaped metal pattern layer, the lower surface of the middle dielectric substrate is tightly combined with the bottom metal layer, and the upper wheel-shaped metal pattern layer, the middle dielectric substrate and the bottom metal layer act synergistically to realize a polarization regulation and control function. Through the design of the wheel-shaped metal pattern, efficient conversion from linear polarized waves to circular polarized waves is achieved, the ultra-wide frequency band characteristic and excellent angle stability are guaranteed, meanwhile, the technology advantages of being simple in structure and convenient and fast to machine are achieved, and good application prospects and development potential are achieved in the technical fields of communication, microwaves and the like.

Description

Technical Field

[0001] This application belongs to the field of microwave technology, and specifically relates to an ultra-wideband linear-to-circular polarization converter based on a wheel-shaped metasurface. Background Art

[0002] Electromagnetic wave regulation technology, especially electromagnetic wave polarization regulation, has always been a research focus in the field of electromagnetic wave propagation. Common electromagnetic wave polarization forms mainly include linear polarization, circular polarization, and elliptical polarization. Different polarization methods have their unique advantages and practical values in specific application scenarios. Taking circularly polarized waves as an example, their anti-interference ability in complex electromagnetic environments is particularly significant: in satellite communication scenarios, the signal reflection by the ionosphere is prone to cause multipath effects, and circularly polarized waves can effectively suppress the interference of reflected signals due to their rotation direction characteristics; in 5G base station communication, circularly polarized waves can alleviate signal fading caused by environments such as rain and fog, thus ensuring the stability and reliability of information transmission in a strong interference environment. Therefore, it has become the key to improving the performance of modern communication systems. As the core device for realizing circularly polarized waves, the linear-to-circular polarization converter has broad application potential in fields such as microwave communication, microscopy imaging, and radio and television.

[0003] In the early days, traditional polarization converters mainly relied on the optical rotation effect of natural materials to achieve electromagnetic wave polarization regulation, but generally suffered from problems such as narrow bandwidth, poor angular stability, large volume, and low integration. These problems severely restricted their application and promotion in actual scenarios. Compared with traditional solutions, metasurface polarization converters can efficiently regulate the phase and polarization characteristics of electromagnetic waves through precise design of unit structures, and have unique electromagnetic response characteristics such as anisotropy, extraordinary reflection / transmission. In addition, this type of converter also has significant advantages such as small volume, thin thickness, light weight, low loss, and easy integration with other components, becoming an ideal solution to solve the defects of traditional polarization converters.

[0004] Although certain progress has been made in the research of metasurface polarization converters, their large-scale application still faces multiple challenges: First, existing converters are mostly targeted at a single frequency band such as the Ku band from 12 GHz to 18 GHz, and it is difficult to meet the full coverage requirements of the C / Ku / K band, that is, from 4 GHz to 27 GHz, resulting in limited bandwidth; Second, the angular stability of existing metasurface polarization converters is insufficient. When the incident angle increases, the axial ratio deteriorates significantly, restricting their application in wide-angle scanning scenarios such as phased array radars; Third, the process cost is a key factor restricting the industrialization of metasurface technology. Especially for sub-wavelength metal patterns, the processing accuracy needs to be controlled within ±5 μm, and the cost of high-performance dielectric substrates is relatively high. Therefore, it is of great practical significance to develop a linear-to-circular polarization converter with wide bandwidth, high angular stability, and low cost. Summary of the Invention

[0005] In view of the technical limitations of existing linear-to-circular polarization converters in aspects such as bandwidth expansion, angular stability, and processing complexity, this application proposes an ultra-wideband linear-to-circular polarization converter based on a wheel-shaped metasurface. Through the innovative design of the wheel-shaped metal pattern, this application successfully realizes the efficient conversion of linearly polarized waves to circularly polarized waves. While significantly improving the working bandwidth and angular stability, it still retains the core advantages of simple structure and convenient processing, and has important theoretical research value and engineering application potential.

[0006] To achieve the above object, this application is realized through the following technical solutions:

[0007] This application is an ultra-wideband linear-to-circular polarization converter based on a wheel-shaped metasurface

[0008] This application is an ultra-wideband linear-to-circular polarization converter based on a wheel-shaped metasurface. The ultra-wideband linear-to-circular polarization converter based on a wheel-shaped metasurface is composed of periodically arranged reflective polarization conversion units, and each reflective polarization conversion unit adopts a stacked structure. Each of the reflective polarization conversion units includes an upper wheel-shaped metal pattern layer, an intermediate dielectric substrate, and a bottom metal layer. The upper surface of the intermediate dielectric substrate is tightly connected to the upper wheel-shaped metal pattern layer, and the lower surface of the intermediate dielectric substrate is tightly combined with the bottom metal layer. The upper wheel-shaped metal pattern layer, the intermediate dielectric substrate, and the bottom metal layer cooperate to achieve the polarization regulation function. Specifically, when a linearly polarized wave is incident on the polarization converter, the upper wheel-shaped metal pattern layer converts the incident linearly polarized wave into a circularly polarized wave, the intermediate dielectric substrate extends the transmission path of the linearly polarized wave and generates resonance, and the bottom metal layer is used to reflect the incident linearly polarized wave.

[0009] A further improvement of this application lies in that: the upper wheel-shaped metal pattern layer is of a wheel-shaped structure and is composed of a cross-shaped metal sheet, a circular metal sheet, and rectangular metal strips. Among them, the cross-shaped metal sheets are symmetrically distributed along the diagonal direction with the center of the surface of the reflective polarization conversion unit as the symmetry point. The cross-shaped metal sheet includes a long-axis direction metal sheet and a short-axis direction metal sheet that are orthogonal to each other. The short-axis direction metal sheet is vertically overlapped at the center point of the surface of the reflective polarization conversion unit. Two circular metal sheets are symmetrically arranged at the ends of the long-axis direction metal sheet, and the centers of the two circular metal sheets are located on the diagonal line of the reflective polarization conversion unit. Six rectangular metal strips of the same size are provided on each of the circular metal sheets, and each of the rectangular metal strips is rotationally symmetrically distributed at an equal angular interval of 30° with the center of the circular metal sheet as the center.

[0010] A further improvement of the present application lies in that: the length L1 of the metal sheet in the long-axis direction is 6.2 mm, the width W1 is 0.3 mm, the length L2 of the metal sheet in the short-axis direction is 0.8 mm, the width W2 is 0.4 mm, the distance between the center of the circular metal sheet and the center of the surface of the reflective polarization conversion unit is 3.1 mm, the diameter D of each circular metal sheet is 1.6 mm, the length L3 of each rectangular metal strip is 2 mm, and the width W3 is 0.3 mm.

[0011] A further improvement of the present application lies in that: the intermediate dielectric substrate is made of FR4 dielectric material with a relative dielectric constant = 4.3 and a loss tangent = 0.025, and the size of the intermediate dielectric substrate is length × width × thickness = 8.2 mm × 8.2 mm × 2.4 mm.

[0012] A further improvement of the present application lies in that: both the upper layer wheel-shaped metal pattern layer and the bottom metal layer are prepared from metal copper material and have the same thickness, which is 0.035 mm.

[0013] A further improvement of the present application lies in that: the side length p of the reflective polarization conversion unit is 8.2 mm

[0014] The beneficial effects of the present application are as follows: (1) By using a unique wheel-shaped metal pattern, the present application successfully realizes the efficient conversion of linearly polarized waves to circularly polarized waves. (2) In the frequency range from 7.05 GHz to 18.91 GHz, the present application can convert vertically incident linearly polarized waves into circularly polarized waves, and the 3 dB axial ratio bandwidth is 91.37%, featuring an ultra-wide frequency band characteristic. (3) When the incident angle is 40°, the bandwidth of the converter can be maintained within 7.05 to 15.34 GHz, and the 3 dB axial ratio bandwidth is 74.05%, showing good angular stability. (4) The phase difference of the electric vector components of the reflected electromagnetic wave is stable, and the amplitudes of the two components are almost equal. (5) The structure of the present invention is simple and small in size, specifically 0.355 λ 0.355 λ 0.104 λ. (6) The present application uses a single-layer FR4 dielectric substrate, which has a low profile, is easy to fabricate and produce, and has a low production cost. Description of the Drawings

[0015] Figure 1 is a three-dimensional structure schematic diagram of the structure of the ultra-wideband linear-circular polarization converter unit of the present application.

[0016] Figure 2 is a dimensional drawing of the structure of the ultra-wideband linear-circular polarization converter unit of the present application.

[0017] Figure 3 It is the amplitude and phase difference diagram of the reflection coefficient when the y-polarized wave is vertically incident in the ultra-wideband line circular polarization converter of this application.

[0018] Figure 4 It is the 3 dB axial ratio diagram when the y-polarized wave is incident at incident angles of 0°, 20°, and 40° in the ultra-wideband line circular polarization converter of this application.

[0019] Figure 5 It is the amplitude diagram of the reflection coefficient when the u-polarized wave and the v-polarized wave are incident in the ultra-wideband line circular polarization converter of this application.

[0020] Figure 6 It is the phase and phase difference diagram of the reflection coefficient when the u-polarized wave and the v-polarized wave are incident in the ultra-wideband line circular polarization converter of this application.

[0021] Among them, 1 - upper layer wheel-shaped metal pattern layer; 2 - intermediate dielectric substrate; 3 - bottom metal layer. Detailed implementation manners

[0022] The following will disclose the implementation manners of the present invention with diagrams. For the sake of clear illustration, many practical details will be described together in the following narrative. However, it should be understood that these practical details are not used to limit the present invention. That is to say, in some implementation manners of the present invention, these practical details are not necessary. In addition, for the sake of simplifying the diagrams, some conventional structures and components will be shown in a simple schematic manner in the diagrams.

[0023] As Figure 1-2 shown, this application is an ultra-wideband line circular polarization converter based on a wheel-shaped metasurface, and the side length p of the reflection-type polarization conversion unit is 8.2 mm. The ultra-wideband line circular polarization converter based on the wheel-shaped metasurface is composed of periodically arranged reflection-type polarization conversion units, and each reflection-type polarization conversion unit adopts a stacked structure. Each reflection-type polarization conversion unit includes an upper layer wheel-shaped metal pattern layer 1, an intermediate dielectric substrate 2, and a bottom metal layer 3. The upper surface of the intermediate dielectric substrate 2 is tightly connected to the upper layer wheel-shaped metal pattern layer 1, and the lower surface of the intermediate dielectric substrate 2 is tightly combined with the bottom metal layer 3.

[0024] The upper layer wheel-shaped metal pattern layer 1, the intermediate dielectric substrate 2, and the bottom metal layer 3 cooperate to achieve the polarization regulation function with ultra-wideband and high angle stability. Specifically, when a linearly polarized wave is incident on the polarization converter, the upper layer wheel-shaped metal pattern layer 1 decomposes the incident linearly polarized wave into two orthogonal polarization components, introduces a 90° phase difference, and realizes the conversion from a linearly polarized wave to a circularly polarized wave. The intermediate dielectric substrate 2 prolongs the transmission path of the linearly polarized wave through dielectric regulation and generates resonance. The bottom metal layer 3 is used to reflect the incident linearly polarized wave.

[0025] Among them, the upper wheel-shaped metal pattern layer 1 is made of metallic copper with a thickness of 0.035 mm. The upper wheel-shaped metal pattern layer 1 is of a wheel-shaped structure and is composed of a cross-shaped metal sheet, a circular metal sheet, and a rectangular metal strip. The cross-shaped metal sheets are symmetrically distributed along the diagonal direction with the center of the surface of the reflective polarization conversion unit as the symmetry point. The cross-shaped metal sheet includes a metal sheet in the long-axis direction and a metal sheet in the short-axis direction that are orthogonal to each other. The length L1 of the metal sheet in the long-axis direction is 6.2 mm, and the width W1 is 0.3 mm. The metal sheet in the short-axis direction perpendicularly overlaps the center point of the surface of the reflective polarization conversion unit. The length L2 of the metal sheet in the short-axis direction is 0.8 mm, and the width W2 is 0.4 mm. Two circular metal sheets are symmetrically arranged at the ends of the metal sheet in the long-axis direction. The distance from the center of the circular metal sheet to the center of the surface of the reflective polarization conversion unit is 3.1 mm. The centers of the two circular metal sheets are located on the diagonal of the reflective polarization conversion unit. The diameter D of each circular metal sheet is 1.6 mm. Six rectangular metal strips with the same size are provided on each circular metal sheet. The length L3 of each rectangular metal strip is 2 mm, and the width W3 is 0.3 mm. Each rectangular metal strip is rotationally symmetrically distributed at an equal angular interval of 30° with the center of the circular metal sheet as the center.

[0026] The intermediate dielectric substrate 2 is selected as an FR4 dielectric material with a relative dielectric constant = 4.3 and a loss tangent = 0.025. This dielectric material is inexpensive and easy to process. The size of the intermediate dielectric substrate 2 is length × width × thickness = 8.2 mm × 8.2 mm × 2.4 mm.

[0027] The bottom metal layer 3 is a complete metal panel, which is closely attached to the lower surface of the intermediate dielectric substrate 2 and is used to reflect the incident ray polarization wave. The bottom metal layer 3 is made of copper material with a thickness of 0.035 mm. This thickness is the standard PCB copper foil thickness, which conforms to the industrial processing specifications and is convenient for large-scale production.

[0028] Due to the symmetry of the metasurface unit structure, for the vertically incident x-polarized wave and y-polarized wave, they have the same polarization rotation characteristics. In this embodiment, taking the y-polarized wave as an example, the reflected electric field can be expressed as:

[0029]

[0030] Among them, and respectively represent the cross-polarization and co-polarization reflection coefficients, and are their corresponding phases. When , and When the reflection wave is a circularly polarized wave, n is an integer.

[0031] As Figure 3 shown, in a very wide frequency range, and are almost equal and the phase difference is approximately equal to 90°. In this range, the polarization converter converts the incident linearly polarized wave into a circularly polarized wave.

[0032] As Figure 4 shown, when the incident angle is 0°, the linear-to-circular converter can maintain the axial ratio of the reflection wave below 3 dB in the frequency range from 7.05 GHz to 18.91 GHz, and the bandwidth reaches 91.37%. When the incident angle is 20°, the linear-to-circular converter can maintain the axial ratio of the reflection wave below 3 dB in the frequency range from 7.05 GHz to 16.56 GHz, and the bandwidth reaches 80.56%. When the incident angle is 40°, the bandwidth of the converter can still be maintained within 7.05 to 15.34 GHz, and the relative bandwidth is 74.05%. This shows that the polarization converter has an extremely wide bandwidth and good angular stability.

[0033] To further explain the mechanism of polarization conversion, the xy coordinate system is rotated counterclockwise by 45° to obtain the uv coordinate system. In the uv coordinate system, the incident field can be expressed as: . The reflected field can be expressed as:

[0034]

[0035] where , , , are the reflection coefficients when the u-polarized and v-polarized incident waves are incident, respectively, and , , , are their corresponding phases. When , and the reflection wave is a circularly polarized wave, and n is an integer.

[0036] As Figure 5 and 6 shown, in a very wide frequency range, and are approximately equal to 0, and are approximately equal to 1 and the phase difference is close to 90° or -270°. In this range, the polarization converter converts the incident linearly polarized wave into a circularly polarized wave.

[0037] The above are only the embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the scope of the claims of the present invention.

Claims

1. An ultra-wideband linear-to-circular polarization converter based on a wheel-shaped metasurface, characterized in that: The ultra-wideband linear-to-circular polarization converter based on the wheel-shaped metasurface is composed of periodically arranged reflective polarization conversion units, and each reflective polarization conversion unit adopts a stacked structure. Each reflective polarization conversion unit includes an upper wheel-shaped metal pattern layer (1), a middle dielectric substrate (2), and a bottom metal layer (3). The upper surface of the middle dielectric substrate (2) is tightly connected to the upper wheel-shaped metal pattern layer (1), and the lower surface of the middle dielectric substrate (2) is tightly bonded to the bottom metal layer (3). The upper wheel-shaped metal pattern layer (1), the middle dielectric substrate (2), and the bottom metal layer (3) cooperate to achieve the polarization regulation function. Specifically, when a linearly polarized wave is incident on the ultra-wideband linear-to-circular polarization converter, the upper wheel-shaped metal pattern layer (1) converts the incident linearly polarized wave into a circularly polarized wave, the middle dielectric substrate (2) extends the transmission path of the linearly polarized wave and generates resonance, and the bottom metal layer (3) is used to reflect the incident linearly polarized wave.

2. The ultra-wideband line circular polarization converter based on a wheel-shaped metasurface according to claim 1, wherein: The upper wheel-shaped metal pattern layer (1) has a wheel-shaped structure and is composed of a cross-shaped metal sheet, a circular metal sheet, and a rectangular metal strip. Among them, the cross-shaped metal sheets are symmetrically distributed along the diagonal direction with the center of the surface of the reflective polarization conversion unit as the symmetry point. The cross-shaped metal sheet includes a major-axis direction metal sheet and a minor-axis direction metal sheet that are orthogonal to each other. The minor-axis direction metal sheet is vertically overlapped at the center point of the surface of the reflective polarization conversion unit. Two circular metal sheets are symmetrically arranged at the ends of the major-axis direction metal sheet. The centers of the two circular metal sheets are located on the diagonal line of the reflective polarization conversion unit. Six rectangular metal strips with the same size are provided on each circular metal sheet. Each rectangular metal strip is rotationally symmetrically distributed at an equal angle interval of 30° with the center of the circular metal sheet as the center.

3. The ultra-wideband line circular polarization converter based on a wheel-shaped metasurface according to claim 2, characterized in that: The length L1 of the major-axis direction metal sheet is 6.2 mm, the width W1 is 0.3 mm, the length L2 of the minor-axis direction metal sheet is 0.8 mm, the width W2 is 0.4 mm, the distance between the center of the circular metal sheet and the center of the surface of the reflective polarization conversion unit is 3.1 mm, the diameter D of each circular metal sheet is 1.6 mm, the length L3 of each rectangular metal strip is 2 mm, and the width W3 is 0.3 mm.

4. The ultra-wideband line-to-circular polarization converter based on a wheel-shaped metasurface according to claim 1, wherein: The intermediate dielectric substrate (2) is selected as an FR4 dielectric material with a relative dielectric constant = 4.3 and a loss tangent = 0.

025. The size of the intermediate dielectric substrate (2) is length × width × thickness = 8.2 mm × 8.2 mm × 2.4 mm.

5. The ultra-wideband line circular polarization converter based on a wheel-shaped metasurface according to claim 1, wherein: Both the upper wheel-shaped metal pattern layer (1) and the bottom metal layer (3) are prepared from copper material, and the upper wheel-shaped metal pattern layer (1) and the bottom metal layer (3) have the same thickness, both being 0.035 mm.

6. The ultra-wideband line circular polarization converter based on a wheel-shaped metasurface according to claim 1, characterized in that: The side length p of the reflective polarization conversion unit is 8.2 mm.

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