A dartboard layout metasurface for RCS reduction and OAM wave generation

Abstract

This invention discloses a dartboard-style metasurface for RCS reduction and OAM wave generation, comprising: three concentric circular metasurfaces of equal width arranged sequentially from the outside to the inside, wherein the innermost ring is a circular metasurface. The three circular metasurfaces are sequentially divided into 4, 12, and 20 fan-shaped lattices of equal area from the inside to the outside, wherein the innermost circular metasurface is divided into 4 fan-shaped lattices. This invention generates P-B phase by rotating the entire periodic polarization conversion structure. This method does not change the coupling relationship between adjacent metal patches of the periodic polarization conversion structure, and therefore does not change the polarization conversion rate of the periodic polarization conversion structure. Thus, a stable P-B phase can be generated over a wide frequency band. The dartboard-style metasurface constructed in this way can not only achieve RCS reduction in the specular reflection direction over a continuous wide frequency band, but also generate OAM waves over a wide frequency band.

Description

Technical Field

[0001] This invention relates to the field of artificial electromagnetic metasurface technology, and more particularly to a dartboard layout metasurface for RCS reduction and OAM wave generation. Background Technology

[0002] Artificial electromagnetic metasurfaces are two-dimensional electromagnetic metamaterials composed of periodic artificial electromagnetic conductors. They have advantages in structure such as low profile, conformal nature, and ease of fabrication. Functionally, they can flexibly manipulate electromagnetic waves, and are therefore widely used in radar cross section (RCS) reduction and orbital angular momentum (OAM) wave generation.

[0003] Radar cross section (RCS) is a parameter that measures the electromagnetic stealth performance of military targets. Military target surfaces are typically made of metallic materials, which cause specular reflection of incident electromagnetic waves. The RCS in the specular reflection direction is very large, making the target easily detectable by radar. To improve the stealth performance of a target, a metasurface can be loaded onto its surface to redirect the scattered wave beam, thereby reducing the RCS in the specular reflection direction.

[0004] The most distinctive feature of orbital angular momentum waves is that their phase wavefront exhibits a vortex shape and contains different modes. Mode multiplexing can further improve the spectral efficiency and capacity of communication systems. Another characteristic of OAM waves is that their waveform center amplitude is zero. For reflective metasurfaces, this means that the same metasurface can both generate OAM waves and achieve RCS reduction in the specular reflection direction. Summary of the Invention

[0005] Purpose of the invention: The present invention provides a dartboard layout metasurface for RCS reduction and OAM wave generation, which can achieve both RCS reduction and OAM wave generation.

[0006] Technical solution: The present invention provides a dartboard layout metasurface for RCS reduction and OAM wave generation, comprising: three concentric circular metasurfaces of the same width arranged sequentially from the outside to the inside, wherein the innermost ring is a circular metasurface, and the three circular metasurfaces are sequentially divided into 4, 12 and 20 fan-shaped lattices of the same area from the inside to the outside, wherein the innermost circular metasurface is divided into 4 fan-shaped lattices.

[0007] Furthermore, the reflection phase of several lattices in each annular metasurface varies uniformly by 360° along the same circumference.

[0008] Furthermore, each lattice is composed of periodic polarization transition structures.

[0009] Furthermore, the periodic polarization conversion structure consists of a metal ground plane, an air layer, a dielectric substrate, and a metal patch, arranged from bottom to top.

[0010] Furthermore, the metal patch adds two symmetrical openings along a diagonal of the structural unit based on the metal ring.

[0011] Furthermore, the ring width of the three toroidal metasurfaces is equal to the width of six periodic polarization conversion structures.

[0012] Furthermore, the different reflection phases corresponding to different lattices are the PB (Pancharatnam-Berry) phases generated by rotating the entire periodic polarization conversion structure.

[0013] Furthermore, rotating the entire periodic polarization conversion structure does not change the coupling relationship between adjacent metal patches of the periodic polarization conversion structure, and therefore does not change the polarization conversion rate of the periodic polarization conversion structure. Thus, it can generate a stable PB phase over a wide frequency band.

[0014] Furthermore, the stable PB phase generated over a wide bandwidth enables the dartboard-style metasurface to not only reduce the radar cross section (RCS) in the specular reflection direction over a continuous wide bandwidth, but also to generate ±1 order orbital angular momentum (OAM) waves over a wide bandwidth.

[0015] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: The present invention generates the PB phase by rotating the entire periodic polarization conversion structure. This method does not change the coupling relationship between adjacent metal patches of the periodic polarization conversion structure, and therefore does not change the polarization conversion rate of the periodic polarization conversion structure. Therefore, a stable PB phase can be generated in a wide frequency band. The dartboard layout metasurface constructed in this way can not only achieve RCS reduction in the specular reflection direction in a continuous wide frequency band, but also generate OAM waves in a wide frequency band. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the dartboard-type metasurface of the present invention.

[0017] Figure 2(a) shows the distribution of the reflection phases of each lattice of the dart-shaped metasurface of the present invention.

[0018] Figure 2(b) is a distribution diagram of the lattice reflection phase of the dartboard-type metasurface of the present invention.

[0019] Figure 3 This is a schematic diagram of the unit structure of the periodic polarization conversion structure of the present invention.

[0020] Figure 4(a) shows the amplitude of the co-polarization reflection coefficient and the polarization conversion rate of the periodic polarization conversion structure of the present invention under the vertical incidence of x-polarized waves.

[0021] Figure 4(b) shows the amplitude of the cross-polarization reflection coefficient and the polarization conversion rate of the periodic polarization conversion structure of the present invention under the vertical incidence of x-polarized waves.

[0022] Figure 5(a) shows the amplitude of the co-polarization reflection coefficient and the reflection phase when the metal patch of each unit of the periodic polarization conversion structure is rotated in this invention and the linearly polarized wave is incident perpendicularly.

[0023] Figure 5(b) shows the amplitude of the cross-polarization reflection coefficient and the reflection phase when the metal patch of each unit of the periodic polarization conversion structure is rotated in this invention.

[0024] Figure 6(a) is a schematic diagram of rotating only the metal patch of each unit of the periodic polarization conversion structure and rotating the entire periodic polarization conversion structure in this invention.

[0025] Figure 6(b) is a schematic diagram of rotating only the metal patch of each unit of the periodic polarization conversion structure and rotating the entire periodic polarization conversion structure in this invention.

[0026] Figure 6(c) is a schematic diagram of rotating only the metal patch of each unit of the periodic polarization conversion structure and rotating the entire periodic polarization conversion structure in this invention.

[0027] Figure 7(a) shows the amplitude of the co-polarization reflection coefficient and the reflection phase when the periodic polarization conversion structure is rotated as a whole in this invention and the linearly polarized wave is incident perpendicularly.

[0028] Figure 7(b) shows the amplitude of the cross-polarization reflection coefficient and the reflection phase when the periodic polarization conversion structure is rotated as described in this invention, under perpendicular incidence of a linearly polarized wave.

[0029] Figure 8 This invention reduces the monostatic RCS of the dartboard-type metasurface under perpendicular plane wave incidence.

[0030] Figure 9(a) shows the three-dimensional bistatic RCS pattern of the dartboard-type metasurface of the present invention under vertical incidence of a linearly polarized plane wave at 7.5 GHz.

[0031] Figure 9(b) shows the three-dimensional bistatic RCS pattern of the dartboard-type metasurface of the present invention under vertical incidence of a circularly polarized plane wave at 7.5 GHz.

[0032] Figure 9(c) shows the dart-shaped metasurface of the present invention under oblique incidence of a circularly polarized plane wave at 7.5 GHz (incident angle θ). iThree-dimensional bistatic RCS pattern (30°).

[0033] Figure 10(a) shows the reduction of the RCS of the mirror reflection direction of the dartboard-type metasurface in this invention under oblique incidence of TE-polarized plane waves.

[0034] Figure 10(b) shows the reduction of the RCS of the mirror reflection direction of the dartboard-type metasurface in this invention under oblique incidence of TM polarized plane waves.

[0035] Figure 11 This is a three-dimensional far-field pattern of the dartboard-shaped metasurface in this invention under perpendicular plane wave incidence.

[0036] Figure 12 This is a three-dimensional far-field pattern of the dartboard-shaped metasurface in this invention under perpendicular incidence of circularly polarized plane waves of different frequencies. Detailed Implementation

[0037] like Figure 1 As shown, a dartboard-shaped metasurface for RCS reduction and OAM wave generation consists of M = 3 concentric ring metasurfaces with a ring width of l, wherein the first ring is a circular metasurface. The three ring metasurfaces are successively divided into N1 = 4, N2 = 12 and N3 = 20 fan-shaped lattices of equal area from the inside to the outside, wherein the innermost circular metasurface is divided into N1 = 4 fan-shaped lattices.

[0038] In the dart-shaped metasurface of this invention, the reflection phase of several lattices in each annular metasurface varies uniformly by 360° along the same circumference, that is, the reflection phase of the nth lattice in the mth ring is β. mn =β0+2π(m-1) / N m Where β0 is the reference phase. The reflection phase β of each lattice is represented by arrows pointing in different directions in Figure 2(a). mn The lattice reflection phase distribution of the dartboard-shaped metasurface is shown in Figure 2(b).

[0039] In this invention, each lattice of the dart-shaped metasurface is composed of a periodic polarization transition structure. For example... Figure 3 This is a schematic diagram of the unit structure of the periodic polarization conversion structure used, showing a square FR-4 dielectric substrate with a width of p = 10 mm and a thickness of t = 0.5 mm (relative permittivity ε). r =4.4, loss tangent is tanδ=0.02) placed above the metal floor at h=6mm, with air gap in between. The metal patch above the dielectric substrate is based on an annular metal patch with inner diameter r1=4.43mm and outer diameter r2=4.75mm, with two openings at an angle of θ=22° added along one diagonal of the structural unit.

[0040] Figure 4(a) shows the amplitude |r of the co-polarization reflection coefficient of the periodic polarization conversion structure used in this invention under perpendicular incident x-polarized wave. xx |and the magnitude of the cross-polarization reflection coefficient|r yx |wherein, in the frequency range of 4.1 GHz to 17.3 GHz, the amplitude of the co-polarized reflection coefficient is |r xx | Less than -10dB, while the amplitude of the cross-polarized reflection coefficient|r yx The value is close to 0 dB, indicating that a polarization transition has occurred in this periodic polarization conversion structure. Based on the amplitudes of the co-polarization and cross-polarization reflection coefficients in Figure 4(a), the polarization conversion efficiency PCR = |r| of the polarization conversion structure shown in Figure 4(b) is calculated. yx | 2 / |r yx | 2 +|r xx | 2 In the frequency range of 4.1 GHz to 17.3 GHz, the polarization conversion efficiency of this periodic polarization conversion structure is greater than 90%.

[0041] In this invention, the ring width *l* of the three annular metasurfaces in the dartboard-like layout metasurface is the width of six periodic polarization conversion structural units, such as... Figure 1 As shown.

[0042] To obtain the reflection phase required for different lattices, the Pancharatnam-Berry (PB) phase principle can be applied. Rotating the polarization conversion unit by an angle α results in a 2α change in reflection phase. Previous inventions typically generated the PB phase by rotating only the metal patch of each unit in the periodic polarization conversion structure. Figure 5(a) shows the result after rotating only the metal patch of each unit in the periodic polarization conversion structure by an angle α, at a polarization angle of φ. p The amplitudes of the co-polarized and cross-polarized reflection coefficients under perpendicular incidence of a linearly polarized wave of α, where the amplitude of the co-polarized reflection coefficient |r| is [value missing] in the frequency range of 9 GHz to 15 GHz. co |Greater than -10dB, while the amplitude of the cross-polarized reflection coefficient|r cr The value moves away from 0 dB, indicating a deterioration in the polarization conversion performance of the periodic polarization conversion structure. This change in polarization conversion performance means that the reflection phase of each unit metal patch, after being rotated by an angle α, will not change by 2α, meaning a stable PB phase cannot be generated. Figure 5(b) shows the reflection phase of the x-polarized wave (φ) after rotating only each unit metal patch of the periodic polarization conversion structure by an angle α. p The reflected phase under incident angle α = 0° does not change with rotation angle α.

[0043] The main reason why the above method cannot generate a stable PB phase is that rotating only the metal patch of each unit in the periodic polarization conversion structure changes the coupling relationship between adjacent unit metal patches. As shown in Figure 6(b), the 2×2 periodic polarization conversion structure is obtained by rotating the metal patch on each unit of the initial 2×2 periodic polarization conversion structure in Figure 6(a) by an angle α. To address the impact of this coupling distortion on the generation of the PB phase, a common approach is to reduce the contour of each unit metal patch to decrease the coupling between adjacent metal patches, thereby reducing the coupling distortion caused by simply rotating the metal patches. However, this method of reducing the metal patch contour inevitably leads to a reduction in the operating frequency band of the polarization conversion structure.

[0044] To address the issue of generating a stable PB phase over a wide frequency band in previous designs, this invention employs a method of rotating the entire periodic polarization conversion structure to generate the PB phase. As shown in Figure 6(c), the 2×2 periodic polarization conversion structure is obtained by rotating the initial 2×2 periodic polarization conversion structure in Figure 6(a) by an angle α. Clearly, this method does not alter the coupling relationship between adjacent metal patches of the periodic polarization conversion structure; therefore, the polarization conversion performance of the periodic polarization conversion structure remains unchanged, allowing for the generation of a stable PB phase over a wide frequency band. Figure 7(a) shows the PB phase generated after rotating the entire periodic polarization conversion structure by an angle α, at a polarization angle of φ. p The amplitudes of the co-polarization and cross-polarization reflection coefficients under perpendicular incidence of a linearly polarized wave of α are shown. These amplitudes do not change with the rotation angle α, indicating that the polarization conversion performance of the periodic polarization conversion structure remains unchanged. Figure 7(b) shows the effect of rotating the entire periodic polarization conversion structure by an angle α on the x-polarized wave (φ). p The reflected phase under incident angle α (=0°) changes by 2α with the rotation angle α, that is, a stable PB phase is generated in a wide frequency band.

[0045] When a circularly polarized wave is incident on the periodic polarization conversion structure used in this invention, the incident circularly polarized wave can be decomposed into x-polarized and y-polarized incident waves. The reflected waves of the decomposed x-polarized and y-polarized incident waves undergo polarization conversion, resulting in the electric field rotation direction of the circularly polarized reflected waves being opposite to that of the incident waves. Since the propagation direction of the reflected waves is opposite to that of the incident waves, the periodic polarization conversion structure will undergo common polarization reflection under the incident circularly polarized wave. When the entire periodic polarization conversion structure is rotated by an angle α, the phase of both the x-polarized and y-polarized reflected waves after decomposition of the circularly polarized reflected wave increases by 2α. For circularly polarized reflected waves with the same electric field rotation direction as the periodic polarization conversion structure, their reflection phase increases by 2α; while for circularly polarized reflected waves with the opposite electric field rotation direction, their reflection phase decreases by 2α. Therefore, when a circularly polarized wave is incident, rotating the entire periodic polarization conversion structure can also generate a stable PB phase over a wide frequency band.

[0046] The reflection phases of different lattices of the dart-shaped metasurface in this invention are generated by rotating the entire periodic polarization conversion structure, such as the PB phase. Figure 1 As shown.

[0047] like Figure 8 To reduce the monostatic RCS of the dartboard-type metasurface in this invention under perpendicular incidence of plane waves with different polarizations, regardless of linear polarization (φ) p Whether the incident plane wave is a left-hand circularly polarized (LCP) or right-hand circularly polarized (RCP) plane wave, this dartboard-type metasurface can achieve a monostatic RCS reduction of more than 10 dB in a wide bandwidth of 4–17.1 GHz (relative bandwidth of 124.2%). The reduction bandwidth is consistent with the PB phase bandwidth generated by rotating the entire periodic polarization conversion structure.

[0048] Figures 9(a) and (b) show the three-dimensional bistatic RCS patterns of the dartboard-type metasurface of this invention under vertical incidence of linearly polarized and circularly polarized plane waves at 7.5 GHz, respectively. Both patterns have a hole in the vertical direction, thus achieving monostatic RCS reduction in the vertical direction. Figure 9(c) shows the dartboard-type metasurface under oblique incidence of a circularly polarized plane wave at 7.5 GHz (incident angle θ). i The three-dimensional bistatic RCS pattern (=30°) contains holes pointing towards the specular reflection direction of the incident direction, so it can achieve RCS reduction in the specular reflection direction when incident at an oblique angle.

[0049] Figures 10(a) and (b) show the RCS reduction of the specular reflection direction of the dartboard-type metasurface in this invention under oblique incidence of TE and TM polarized plane waves, respectively. Regardless of whether it is a TE or TM polarized plane wave, at θ...i Within an oblique incidence angle of less than 30°, this metasurface can achieve a specular reflection direction RCS reduction of more than 10dB over a continuous wide frequency band.

[0050] like Figure 11 The diagram shows the amplitude of the three-dimensional far-field radiation pattern of the dartboard-shaped metasurface in this invention under perpendicular incidence of a 7.5 GHz plane wave, as well as the amplitude and phase of its left-hand and right-hand circularly polarized components. (a) to (e) represent right-hand circularly polarized plane wave incidence, and (f) to (j) represent linearly polarized plane wave incidence. When a right-hand circularly polarized plane wave is incident, the left-hand circularly polarized component of the three-dimensional far-field radiation pattern is almost zero, while the amplitude of the right-hand circularly polarized component is almost the same as the total field amplitude. Furthermore, the phase of the right-hand circularly polarized component changes uniformly by 360° counterclockwise along the circumference, which is precisely the far-field characteristic of a first-order OAM wave. Therefore, this metasurface can generate a first-order OAM wave when a right-hand circularly polarized plane wave is incident, and similarly, it can generate a -1st-order OAM wave when a left-hand circularly polarized plane wave is incident. When a linearly polarized plane wave is incident, the left-hand and right-hand circularly polarized components of the three-dimensional far-field pattern have the same amplitude, which is half the amplitude of the total field. The phases of the left-hand and right-hand circularly polarized components change uniformly by 360° along the clockwise and counterclockwise directions of the circumference, respectively. This is because a linearly polarized incident plane wave can be decomposed into two left-hand and right-hand circularly polarized plane waves with the same amplitude. Therefore, the far field of this metasurface when a linearly polarized plane wave is incident can be decomposed into first-order and -1-order OAM waves.

[0051] like Figure 12 The amplitude of the three-dimensional far-field radiation pattern of the dartboard-shaped metasurface in this invention under the perpendicular incidence of circularly polarized plane waves at different frequencies is shown. The beamwidth of the generated OAM wave narrows as the frequency increases, and the waveform of the generated OAM wave improves as the RCS reduction increases, that is, the beam of the OAM wave is more uniformly distributed along the circumference, and the holes in the beam are closer to the center.

[0052] In summary, this invention generates the PB phase by rotating the entire periodic polarization conversion structure. This method does not alter the coupling relationship between adjacent metal patches of the periodic polarization conversion structure, thus maintaining the polarization conversion rate of the structure and enabling the generation of a stable PB phase over a wide bandwidth. The dartboard-style metasurface constructed in this manner not only achieves RCS reduction in the specular reflection direction over a continuous wide bandwidth but also generates OAM waves over the same bandwidth.

Claims

1. A dartboard-patterned metasurface for RCS reduction and OAM wave generation, characterized in that, include: Three concentric ring metasurfaces of equal width are arranged sequentially from the outside to the inside, with the innermost ring being a circular metasurface. The three ring metasurfaces are successively divided into 4, 12, and 20 fan-shaped lattices of equal area from the inside to the outside, with the innermost circular metasurface being divided into 4 fan-shaped lattices. The reflection phase of several lattices in each ring metasurface varies uniformly by 360° along the same circumference. Each lattice is composed of a periodic polarization conversion structure. The ring width of the three ring metasurfaces is the width of 6 periodic polarization conversion structures. The different reflection phases corresponding to different lattices are the PB phases generated by rotating the entire periodic polarization conversion structure. The periodic polarization conversion structure is rotated to generate a stable PB phase over a wide bandwidth. The stable PB phase generated over a wide bandwidth then generates ±1 order orbital angular momentum (OAM) waves over a wide bandwidth. The periodic polarization conversion structure consists of a metal ground plane, an air layer, a dielectric substrate, and a metal patch from bottom to top. The metal patch is based on a metal ring with two symmetrical openings added along one diagonal of the structural unit.

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