Ultra-wideband low-RCS metasurface based on polarization conversion unit

Abstract

The invention provides an ultra-wide-band low-RCS metasurface based on polarization conversion units. The ultra-wide-band low-RCS metasurface is formed by rotating the polarization conversion units at different positions by a specific angle and arranging the polarization conversion units. According to the invention, the polarization conversion rate under the broadband is mainly improved, and the RCS is reduced; according to the scheme, the wavefront phase of the incident electromagnetic wave can be changed, so that the reflected electromagnetic wave carries the vortex phase; by utilizing the characteristic of the phase singular point of the vortex wave, the amplitude of the electric field at the center of the reflected wave is zero, and the metasurface shows obvious RCS reduction along the propagation axis. In addition, based on the broadband design of the polarization conversion unit, RCS reduction in an ultra-wideband range is finally realized.

Description

Technical Field

[0001] The present invention belongs to the field of electromagnetic metamaterials, and in particular relates to an ultra-wideband low RCS metasurface based on a polarization conversion unit. Background Art

[0002] With the continuous advancement of science and technology, electromagnetic waves have been applied to every aspect of life and are an indispensable component in the military. Effective control of electromagnetic waves on the battlefield is a key factor in determining the outcome of modern warfare, and stealth technology is a crucial component. Radar cross section (RCS), a physical quantity that characterizes the intensity of the echo produced by an object when illuminated by electromagnetic waves, is a key technical indicator of stealth performance. Stealth performance is largely determined by its RCS (Remote Cross Section), with a smaller RCS indicating a stronger stealth capability.

[0003] Traditional RCS reduction methods primarily include surface shaping, radar absorbing material loading, and active and passive cancellation. These methods, however, face limitations in practical applications due to design difficulties, bulky size, and narrow operating bandwidth. Metamaterials are artificial composite materials that possess electromagnetic properties unattainable by traditional materials. They can effectively manipulate properties such as the polarization, phase, and propagation direction of electromagnetic waves, enabling previously unattainable functions and playing a significant role in the field of stealth. Metasurfaces, a special type of metamaterial, reduce design and manufacturing complexity while maintaining their unique electromagnetic properties, making them a valuable tool for practical applications. Compared to other metamaterials, metasurfaces offer advantages such as low profile, ease of fabrication, and low loss, offering broad application potential for RCS reduction. Over the past few decades, RCS reduction technologies based on metasurfaces have made significant progress. Electromagnetic metasurfaces used to achieve targeted RCS reduction primarily include electromagnetic bandgap structures, frequency selective surfaces, artificial magnetic conductors, phase gradient metasurfaces, and coding metasurfaces. However, existing technologies have problems such as low polarization conversion rate and high RCS in wide bandwidth, which cannot meet application requirements. Summary of the Invention

[0004] In order to overcome the shortcomings of the existing technology, improve the polarization conversion rate under wide bandwidth and reduce RCS, the present invention provides an ultra-wideband low RCS metasurface based on a polarization conversion unit.

[0005] An ultra-wideband low RCS metasurface based on a polarization conversion unit comprises a plurality of polarization conversion units; the polarization conversion unit comprises a unit patch, a dielectric layer, an air layer and a reflective layer in order from top to bottom; the unit patch is arranged on the top surface of the dielectric layer; a gap is provided between the dielectric layer and the reflective layer; the gap is the air layer; coaxial through holes are respectively provided on the dielectric layer and the reflective layer, and nylon columns are provided in the through holes to support and fix the polarization conversion unit; the centers of the dielectric layer and the unit patch coincide; the unit patch comprises an inner patch and an outer patch; the inner patch and the outer patch are cocentric; the inner patch is nested in the outer patch, and the inner patch and the outer patch are coplanar; the inner patch is in the shape of a ring; the outer patch is in the shape of a ring; A first short stub 5, a second short stub 6, a third short stub 7 and a fourth short stub 8 are evenly arranged clockwise along the inner circumference of the external patch; the first short stub, the second short stub, the third short stub and the fourth short stub are respectively pointed to the center in the radial direction; a coordinate system is established with the line through the center of the second short stub 6 and the fourth short stub 8 as the X-axis, and the line through the center of the first short stub 5 and the third short stub 7 as the Y-axis; the external patch is provided with a pair of radial external patch gaps; the angle between the line through the center of the pair of external patch gaps and the X-axis is 135 degrees; the internal patch is provided with a pair of radial internal patch gaps; the angle between the line through the center of the pair of internal patch gaps and the X-axis is 135 degrees; the multiple polarization units are rotated to form an ultra-wideband low RCS metasurface.

[0006] Furthermore, the steps of rotating the polarization unit to form an ultra-wideband low RCS metasurface are as follows: The reflection phase of the metasurface satisfies The vortex distribution characteristics of the metasurface are taken as the origin, the z-axis is perpendicular to the metasurface, and the coordinate system is established according to the right-hand rule. The coordinates of any polarization unit are ,like is the azimuth, then ; Then the angle of the polarization unit rotating in the counterclockwise direction is ,in is the imaginary part, is the order of the vortex wave.

[0007] Furthermore, the dielectric layer and the reflective layer are both square in shape; the side lengths of the dielectric layer and the air layer are p=9.2 mm, the height of the dielectric layer is h1=1 mm, and the height of the air layer is h2=2 mm.

[0008] Furthermore, the outer ring radius of the inner patch is r1=1mm, the difference between the outer ring radius and the inner ring radius of the inner patch is w1=0.2mm, the arc length of the inner patch gap is l1=0.2mm, the outer ring radius of the outer patch is r2=4.1mm, the difference between the outer ring radius and the inner ring radius of the outer patch is w2=1mm, and the arc length of the outer patch gap is l2=0.8mm.

[0009] Furthermore, the width w3 of the first short stub, the second short stub, the third short stub and the fourth short stub are all the same; the length l3 of the first short stub, the second short stub, the third short stub and the fourth short stub are all the same; w3=1mm, l3=1.1mm; Furthermore, the dielectric layer is a Rogers RT5880LZ substrate with a dielectric constant of 1.8 and a loss tangent of 0.0021.

[0010] Furthermore, the unit patch and the reflective layer are both metal copper foils; the conductivity of the metal copper foil is 5.8×10 7 S / m, the thickness of the metal copper foil is 0.017mm.

[0011] Furthermore, the metasurface is a square, and the side length of the metasurface is 193 mm×193 mm.

[0012] Furthermore, the shape of the inner patch includes a square metal ring; the shape of the outer patch includes a square metal ring.

[0013] The beneficial effects of the present invention are as follows: the polarization conversion unit designed by the present invention introduces multiple resonant frequency points by means of opening, attaching open-circuit stubs and nesting, thereby broadening the polarization conversion bandwidth of the unit and realizing ultra-wideband polarization conversion in the range of 8.2-26.9GHz, with a relative bandwidth of 106% and a polarization conversion rate of more than 90%. Based on the ultra-wideband polarization conversion unit, a metasurface composed of a vortex phase arrangement is used to achieve an RCS reduction of more than 10dB in the range of 8.3-26.8GHz, with a relative bandwidth of 105%, which basically covers the entire polarization conversion bandwidth of the polarization conversion unit. The present invention has the advantages of simple preparation process, low processing cost, flexible and adjustable parameters, etc., and can be applied to different usage scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of the three-dimensional structure of the RCS reduction metasurface of the present invention; Figure 2 Schematic diagram of the three-dimensional structure of the polarization conversion unit of the present invention; Figure 3 Schematic diagram of the dimensions of the polarization conversion unit of the present invention, wherein (a) is a top view; (b) is a side view; Figure 4 is a graph showing the co-polarization coefficient and cross-polarization coefficient of the polarization conversion unit of the present invention; Figure 5 This is a polarization conversion rate curve of the polarization conversion unit of the present invention; Figure 6 This is a comparison graph of the RCS of the RCS-reduced metasurface of the present invention and the PEC plate of the same size; Figure 7 is a graph showing RCS reduction of the RCS reduction metasurface of the present invention; Figure 8 The three-dimensional far-field radiation patterns of the RCS reduction metasurface of the present invention; (a) is the three-dimensional far-field radiation pattern at 9 GHz; (b) is the three-dimensional far-field radiation pattern at 14 GHz; (c) is the three-dimensional far-field radiation pattern at 22 GHz; and (d) is the three-dimensional far-field radiation pattern at 26 GHz. Among them, 1-unit patch; 2-dielectric layer; 3-air layer; 4-reflection layer; 5-first short stub; 6-second short stub; 7-third short stub; 8-fourth short stub; - the arc length of the internal patch gap; - the arc length of the external patch gap; - the length of the first stub; - radius of the inner patch outer ring; - the outer ring radius of the outer patch; -The difference between the outer and inner ring radii of the inner patch; - The difference between the outer and inner ring radii of the outer patch; -The width of the first stub; the side length of the p-dielectric layer; - the height of the dielectric layer; -Height of the air layer. DETAILED DESCRIPTION

[0015] While metasurface-based RCS reduction technology has made significant progress over the past few decades, many challenges remain. For example, current design methods cannot fully meet the requirements for broadband RCS reduction. In modern warfare, enemy radars typically use multiple frequency bands to increase the probability of target detection. By broadening the RCS reduction bandwidth, weapons and equipment can achieve stealth across a wider frequency range, reducing the risk of detection by multi-band radars and significantly enhancing their survivability and combat effectiveness in complex electromagnetic environments.

[0016] The present invention solves the technical problem by adopting an ultra-wideband low RCS metasurface based on polarization conversion units, wherein the ultra-wideband low RCS metasurface includes a plurality of polarization conversion units; The polarization conversion unit includes, from top to bottom, a unit patch, a dielectric layer, an air layer, and a reflective layer; the unit patch is arranged on the top surface of the dielectric layer; a gap is provided between the dielectric layer and the reflective layer; the gap is the air layer; coaxial through holes are respectively provided on the dielectric layer and the reflective layer, and nylon columns are provided in the through holes to support and fix the polarization conversion unit; the centers of the dielectric layer and the unit patch coincide.

[0017] The unit patch includes an inner patch and an outer patch; the inner patch and the outer patch are co-centered; the inner patch is nested in the outer patch, and the inner patch and the outer patch are coplanar; The inner patch is in the shape of a circular ring or a square metal ring; the outer patch is in the shape of a circular ring or a square metal ring; A first short stub 5, a second short stub 6, a third short stub 7 and a fourth short stub 8 are evenly arranged clockwise along the inner circumference of the external patch; the first short stub, the second short stub, the third short stub and the fourth short stub are respectively pointed to the center in the radial direction; a coordinate system is established with the line through the center of the second short stub 6 and the fourth short stub 8 as the X-axis, and the line through the center of the first short stub 5 and the third short stub 7 as the Y-axis; the external patch is provided with a pair of radial external patch gaps; the angle between the line through the center of the pair of external patch gaps and the X-axis is 135 degrees; the internal patch is provided with a pair of radial internal patch gaps; the angle between the line through the center of the pair of internal patch gaps and the X-axis is 135 degrees; Due to the anisotropy of the polarization conversion unit, the reflected wave produces a 180-degree phase difference in two perpendicular directions, thus achieving the polarization conversion effect. At the same time, because the unit patch adopts an open design, attached open-circuit short-circuit wires, and adopts an inner and outer ring nesting design, the unit patch can support multiple modes and generate four different resonance points, thereby achieving ultra-wideband polarization conversion. The steps of rotating the polarization units to form a metasurface are as follows: The reflection phase of the metasurface satisfies The vortex distribution characteristics of the metasurface are taken as the origin, the z-axis is perpendicular to the metasurface, and the coordinate system is established according to the right-hand rule. The coordinates of any polarization unit are ,like is the azimuth, then ; Then the angle of the polarization unit rotating in the counterclockwise direction is ,in is the imaginary part, is the order of the vortex wave; By utilizing the characteristics of the vortex wave phase singularity, the purpose of RCS reduction can be achieved. These different reflection phases are the PB phases generated by rotating the polarization conversion unit. According to the PB phase theory, if a unit can produce a reflection effect with the same reflection amplitude and a phase difference of 180° for the incident orthogonal linear polarization electromagnetic wave, then when the left-handed circularly polarized wave is incident on the metasurface unit, by rotating the unit counterclockwise, the left-handed circularly polarized wave will be reflected by the unit. Angle, the reflected left-hand circularly polarized wave will produce This characteristic can be used to easily form the desired metasurface.

[0018] The dielectric layer and the reflective layer are both square in shape; The side length of the dielectric layer and the air layer is p = 9.2 mm, the height of the dielectric layer is h1 = 1 mm, and the height of the air layer is h2 = 2 mm; The outer ring radius of the inner patch is r1=1mm, the difference between the outer ring radius and the inner ring radius of the inner patch is w1=0.2mm, and the arc length of the inner patch gap is l1=0.2mm. The outer ring radius of the outer patch is r2=4.1mm, the difference between the outer ring radius and the inner ring radius of the outer patch is w2=1mm, and the arc length of the outer patch gap is l2=0.8mm. The width w3 of the first short stub, the second short stub, the third short stub, and the fourth short stub are all the same; the length l3 of the first short stub, the second short stub, the third short stub, and the fourth short stub are all the same; w3=1mm, l3=1.1mm; The dielectric layer is a Rogers RT5880LZ substrate with a dielectric constant of 1.8 and a loss tangent of 0.0021; The unit patch and the reflective layer are both metal copper foils; the conductivity of the metal copper foil is 5.8×10 7 S / m, the thickness of the metal copper foil is 0.017mm.

[0019] The metasurface is square, and the side length of the metasurface is 193 mm×193 mm.

[0020] The present application will be described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application.

[0021] like Figure 1 As shown, the present invention proposes an ultra-wideband low RCS metasurface based on polarization conversion units, including 21×21 polarization conversion units. The polarization conversion units generate different reflection phases by rotating, so that the reflection phase of the metasurface satisfies the vortex characteristics of exp(ilϕ). In the present invention, l=2.

[0022] like Figure 2 As shown, the polarization conversion unit has a four-layer structure, consisting of a unit patch, a dielectric layer, an air layer, and a reflective layer from top to bottom. The unit patch is attached to the upper surface of the dielectric layer, and the reflective layer is located on the lower surface of the air layer. Vias are punched in the reflective layer and the dielectric layer, and nylon posts are inserted into the vias to fix the structure. The unit patch consists of an inner patch and an outer patch, with the inner patch nested within the outer patch. The inner patch is an open circular ring, while the outer patch is an open circular ring with an open stub attached to the inside. The opening positions of the inner and outer patches are both diagonal lines with a 135-degree angle between the line connecting the stub 7 and the stub 5. Because the unit patch adopts an opening, an attached open stub, and a nested inner and outer ring design, the unit patch can support multiple modes, thereby effectively broadening the polarization conversion bandwidth of the unit.

[0023] Reference Figure 3 , the side length of the dielectric layer and the air layer of the present invention is p=9.2mm, the height of the dielectric layer is h1=1mm, and the height of the air layer is h2=2mm. The outer radius of the inner open circular ring is r1=1mm, the width between the inner and outer circles is w1=0.2mm, and the opening length is l1=0.2mm. The outer radius of the outer open circular ring is r2=4.1mm, the width between the inner and outer circles is w2=1mm, and the opening length is l2=0.8mm. The width of the attached open short stub is w3=1mm, and the length is l3=1.1mm. The dielectric layer is a RogersRT5880LZ substrate with a dielectric constant of 1.8 and a loss tangent of 0.0021. The unit patch and the reflective layer are made of a conductive material of 5.8×10 7 It is composed of S / m metal copper foil with a thickness of 0.017mm.

[0024] like Figure 4 As shown, taking the x-polarized wave incident as an example, the reflection coefficient curve of the polarization conversion unit includes the co-polarization reflection coefficient r xx Curve and cross-polarization reflection coefficient r yx Curve. Among them, the co-polarization reflection coefficient r xx Four resonance points are generated at 8.95GHz, 14.67GHz, 22.15GHz, and 25.82GHz, and are all less than -10dB in the frequency band of 8.2-26.9GHz. The cross-polarization reflection coefficient r yx In this range, it is close to 0dB. Therefore, in this frequency band, most of the energy of the incident x-polarized wave is converted into the energy of the y-polarized wave. Figure 5 It can be seen that within the frequency band of 8.2-26.9 GHz, the polarization conversion rate of the polarization conversion unit exceeds 90%, achieving ultra-wideband polarization conversion.

[0025] The radar cross section of the present invention is compared with the radar cross section of the PEC plate of the same size. Figure 6 As shown in the figure, by comparison, it can be seen that the designed metasurface has good RCS reduction performance in the 8.3-26.8GHz frequency band. Figure 7 ,It can be seen that in the frequency band range of 8.3-26.8 GHz, the RCS reduction values ​​of the designed metasurface are all greater than 10 dB.

[0026] In addition, the far-field radiation patterns at four frequencies, 9 GHz, 14 GHz, 22 GHz, and 26 GHz, are selected to explain the mechanism of RCS reduction by the designed metasurface. Figure 8 As shown in Figure 1, when an incident electromagnetic wave is reflected by the metasurface, the reflected electromagnetic wave takes the form of a vortex wave. A void, or radiation null point, can be observed at the center of the beam. Therefore, the metasurface of the present invention can achieve RCS reduction when a plane wave is incident perpendicularly.

Claims

1. An ultra-wideband low RCS metasurface based on a polarization conversion unit, characterized by: The ultra-wideband low RCS metasurface includes several polarization conversion units; The polarization conversion unit includes, from top to bottom, a unit patch, a dielectric layer, an air layer, and a reflective layer; the unit patch is arranged on the top surface of the dielectric layer; a gap is provided between the dielectric layer and the reflective layer; the gap is the air layer; the centers of the dielectric layer and the unit patch coincide; The unit patch includes an inner patch and an outer patch; the inner patch is in the shape of a ring; the outer patch is in the shape of a ring; the inner patch and the outer patch are concentric; the inner patch is nested inside the outer patch, and the inner patch and the outer patch are coplanar; a first short stub, a second short stub, a third short stub and a fourth short stub are evenly arranged clockwise along the inner edge of the outer patch; the first short stub, the second short stub, the third short stub and the fourth short stub are respectively pointed to the center in the radial direction; the second short stub is arranged in the shape of a ring; the second short stub is arranged in the shape of a ring; the second short stub is arranged in the shape of a ring; the second short stub is arranged in the shape of a ring; the second short stub is arranged in the shape of a ring A coordinate system is established with the line connecting the short stub and the fourth short stub through the center as the X-axis, and the line connecting the first short stub and the third short stub through the center as the Y-axis; the external patch is provided with a pair of radial external patch gaps; the angle between the line connecting the pair of external patch gaps through the center and the X-axis is 135 degrees; the internal patch is provided with a pair of radial internal patch gaps; the angle between the line connecting the pair of internal patch gaps through the center and the X-axis is 135 degrees; the multiple polarization units are rotated to form an ultra-wideband low RCS metasurface.

2. The ultra-wideband low RCS metasurface based on a polarization conversion unit according to claim 1, characterized in that: The steps of rotating the polarization unit to form an ultra-wideband low RCS metasurface are as follows: The reflection phase of the ultra-wideband low RCS metasurface satisfies The vortex distribution characteristics of the ultra-wideband low RCS metasurface are taken as the origin, the z-axis is perpendicular to the ultra-wideband low RCS metasurface, and the coordinate system is established according to the right-hand rule. The coordinates of any polarization unit are ,like is the azimuth, then ; Then the angle of the polarization unit rotating in the counterclockwise direction is ,in is the imaginary part, is the order of the vortex wave.

3. The ultra-wideband low RCS metasurface based on a polarization conversion unit according to claim 1, characterized in that: The dielectric layer and the reflective layer are both square in shape; the side lengths of the dielectric layer and the air layer are both 9.2 mm, the height of the dielectric layer is 1 mm, and the height of the air layer is 2 mm.

4. The ultra-wideband low RCS metasurface based on a polarization conversion unit according to claim 1, characterized in that: The dielectric layer is a Rogers RT5880LZ substrate with a dielectric constant of 1.8 and a loss tangent of 0.0021.

5. The ultra-wideband low RCS metasurface based on a polarization conversion unit according to claim 1, characterized in that: The unit patch and the reflective layer are both metal copper foils; the conductivity of the metal copper foil is 5.8×10 7 S / m, the thickness of the metal copper foil is 0.017mm.

6. The ultra-wideband low RCS metasurface based on a polarization conversion unit according to claim 1, characterized in that: The ultra-wideband low RCS metasurface is square, and the side length of the metasurface is 193 mm×193 mm.

7. The ultra-wideband low RCS metasurface based on a polarization conversion unit according to claim 1, characterized in that: The outer ring radius of the inner patch is r1, which is 1 mm. The difference between the outer ring radius and the inner ring radius of the inner patch is w1, which is 0.2 mm. The arc length l1 of the inner patch gap is 0.2 mm. The outer ring radius r2 of the outer patch is 4.1 mm. The difference between the outer ring radius and the inner ring radius of the outer patch is w2, which is 1 mm. The arc length l2 of the outer patch gap is 0.8 mm.

8. The ultra-wideband low RCS metasurface based on a polarization conversion unit according to claim 1, characterized in that: The width of the first short stub, the width of the second short stub, the width of the third short stub and the width of the fourth short stub are all the same; the length of the first short stub, the length of the second short stub, the length of the third short stub and the length of the fourth short stub are all the same; the width of the first short stub is 1 mm; the length of the first short stub is 1.1 mm.

9. The ultra-wideband low RCS metasurface based on a polarization conversion unit according to claim 1, characterized in that: The inner patch is in the shape of a square metal ring; the outer patch is in the shape of a square metal ring.

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