Luneberg lens reflector loaded with conformal reconfigurable metasurface

Abstract

The invention belongs to the field of radar, and particularly relates to a Luneberg lens reflector loaded with conformal reconfigurable metasurfaces, the Luneberg lens reflector comprises a Luneberg lens and a reflector conformally arranged on the Luneberg lens, the reflector is composed of a plurality of reconfigurable metasurface arrays, the edge of each reconfigurable metasurface array is provided with a combination element, and the edge of each reconfigurable metasurface array is provided with a coupling element. The reconfigurable metasurface arrays are tightly arranged through combining elements, so that an uncontrollable area without a reconfigurable metasurface is effectively reduced; the tangent point of each reconfigurable metasurface array and the luneberg lens is located in the center of the reconfigurable metasurface array. By changing the bias voltage on the reconfigurable array, the working state of the reconfigurable metasurface is switched to wave absorption or reflection. The reconfigurable metasurface arrays are arranged on the luneberg lens reflector in a conformal mode after being tightly arranged through the combination elements, and the RCS regulation and control capacity and range of the luneberg lens reflector are effectively improved.

Description

Technical Field

[0001] The present invention belongs to the field of radar, and in particular relates to a Luneburg lens reflector loaded with a conformal reconfigurable metasurface. Background Art

[0002] The Luneburg lens is a gradient refractive index lens, generally composed of multiple layers of spherical shells with different dielectric constants. Its characteristic is that it can focus the incident plane wave to the back of the lens. When a metal spherical shell is loaded on the local surface of the Luneburg lens, the incident wave can be focused and reflected, thereby obtaining a large radar cross section (RCS). In the field of radar, the Luneburg lens reflector can be used as an adjustment device for airborne RCS to play an interference or target display function. Generally, airborne Luneburg lens reflectors use a mechanical structure to switch RCS, but this method has certain limitations in switching speed and reliability; in order to overcome these shortcomings, Luneburg lens reflectors loaded with reconfigurable metasurfaces came into being.

[0003] The Luneburg lens reflector mainly utilizes the outermost conformal metal shell of the Luneburg sphere. If a reconfigurable metasurface is to be loaded on the Luneburg lens, the reconfigurable metasurface must be organically combined with the Luneburg lens reflector. By rationally designing the size and structure of the unit of the reconfigurable metasurface, different frequency responses, that is, changes in RCS, can be achieved. In the prior art, one method is to use a large-size square reconfigurable metasurface as a reflector for the metal shell. When the propagation direction of the transmitting antenna is perpendicular to the front of the reflector, the effect is optimal. However, when the propagation direction of the transmitting antenna and the reflector are at a certain angle θ, the RCS switching ability becomes weaker and the directivity becomes worse. Another method is to arrange multiple small-size square reconfigurable metasurfaces uniformly on the surface of the Luneburg lens and use them as reflectors. However, in the current research, the gaps between multiple small-size square reconfigurable metasurfaces are large, and a gap needs to be left between the reconfigurable metasurface and the Luneburg lens, which weakens the RCS switching ability of the Luneburg lens reflector under multiple directional beams and increases the difficulty of assembly. In addition, due to the low bandwidth of the reconfigurable metasurface array used, the operating bandwidth of the Luneburg lens reflector is also at a low level. Summary of the invention

[0004] The purpose of the present invention is to provide a Luneburg lens reflector loaded with a conformal reconfigurable metasurface to solve the problems of insufficient bandwidth and narrow available range of existing Luneburg lens reflectors when used for RCS switching applications.

[0005] To achieve the above object, the present invention adopts the following technical solution:

[0006] A Luneburg lens reflector loaded with a conformal reconfigurable metasurface, comprising a Luneburg lens and a reflector conformally arranged on the Luneburg lens;

[0007] The reflector is composed of a plurality of reconfigurable metasurface arrays, each of which has a bonding element at the edge, and the reconfigurable metasurface arrays are closely arranged through the bonding element; the tangent point of each reconfigurable metasurface array and the Luneburg lens is located at the center of the reconfigurable metasurface array; and the working state of the reconfigurable metasurface is switched to wave absorption or reflection by changing the bias voltage on the reconfigurable array.

[0008] Furthermore, the Luneburg lens is composed of multiple layers of dielectric spherical shells with progressive dielectric constants, and the dielectric constants of the spherical shells gradually decrease from the inside to the outside.

[0009] Furthermore, the dielectric constant of each dielectric spherical shell of the Luneburg lens is between 1 and 2.

[0010] Furthermore, each reconfigurable metasurface array adopts an inverted microstrip structure, including a first dielectric layer, a second dielectric layer, a first metal layer, a third dielectric layer, and a second metal layer arranged in sequence; wherein the first dielectric layer is close to the Luneburg lens, the first dielectric layer and the second dielectric layer are bonded to each other through a semi-cured sheet to form a bonding dielectric layer, and an air layer is formed between the first metal layer and the third dielectric layer.

[0011] Furthermore, the first dielectric layer, the second dielectric layer and the third dielectric layer are all made of dielectric materials, and the thickness of the three is 0.254 mm to 0.508 mm; the thickness of the bonding dielectric layer is 0.05 mm to 0.2 mm; and the thickness of the air layer is 3 mm to 10 mm.

[0012] Furthermore, the first metal layer is composed of a first metal patch and four second metal patches. The four second metal patches are arranged around the first metal patch, and are arranged side by side in pairs and cross-arranged to form a cross structure; the second metal layer is a planar layer.

[0013] Furthermore, the first metal patch is a square metal patch with a side length of 0.2mm to 1mm; the second metal patch is a rectangular metal patch, the wide side of the rectangular patch is equal to the wide side of the square metal patch, and the long side length is 3.5mm to 4.5mm, wherein the ends of two adjacent rectangular metal patches away from the square metal patch are provided with pads for mounting PIN diodes; four resistors are loaded on the two wide sides of the rectangular metal patch and on the square metal patch; the resistance of the four resistors is 50 to 200 ohms.

[0014] Furthermore, the dielectric substrate of each reconfigurable metasurface array is Rogers 5880, and the relative dielectric constant is 2.2.

[0015] Furthermore, the prepreg is FR27, and the relative dielectric constant is 2.75.

[0016] After adopting the above technical solution, the present invention has the following beneficial effects:

[0017] (1) The present invention adopts multiple reconfigurable metasurface arrays as reflectors. The edge of each reconfigurable metasurface array has a bonding element. After the reconfigurable metasurface arrays are closely arranged by the bonding element, the uncontrollable area of ​​the non-reconfigurable metasurface is effectively reduced. The original hemispherical metal reflector is replaced and conformally placed on the Luneburg lens reflector. Since each reconfigurable metasurface array is closely arranged by the bonding element, the RCS control capability and range of the Luneburg lens reflector are effectively improved.

[0018] (2) The present invention changes the reflection characteristics of the reconfigurable metasurface array by adjusting the PIN diode bias on the reconfigurable metasurface array, thereby making the Luneburg lens reflector have an RCS controllable effect. In addition, the unit size and resistance of each metasurface in the reconfigurable metasurface array are adjustable. By adjusting the unit size and the size of the resistance, the center frequency and bandwidth of the reconfigurable metasurface array can be adjusted.

[0019] (3) With respect to the reconfigurable metasurface array, the present invention adopts an inverted microstrip structure loaded with an air layer, so that the Luneburg lens reflector has a large bandwidth while being able to protect the PIN diode from damage during installation and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic structural diagram of a Luneburg lens reflector of an embodiment;

[0021] Figure 2 Schematic diagram of the hierarchical structure of the reconfigurable metasurface array in the Luneburg lens reflector of the embodiment.

[0022] Figure 3 Schematic diagram of the first metal layer structure of the reconfigurable metasurface in the Luneburg lens reflector of an embodiment.

[0023] Figure 4 Result diagram of reflection coefficient of the reconfigurable metasurface in the Luneburg lens reflector of the embodiment.

[0024] Figure 5 This is a graph showing the RCS results of the Luneburg lens reflector in the Luneburg lens reflector of the embodiment.

[0025] Reference numerals:

[0026] 1- Luneburg lens; 2- reconfigurable metasurface array; 3- first dielectric layer; 4- bonding dielectric layer; 5- second dielectric layer; 6- first metal layer; 7- air layer; 8- third dielectric layer; 9- second metal layer;

[0027] 10 - first metal patch; 20 - first rectangular metal patch; 30 - second rectangular metal patch; 40 - third rectangular metal patch; 50 - fourth rectangular metal patch; 60 - first PIN diode pad; 70 - second PIN diode pad. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0029] like Figure 1 As shown, the present embodiment provides a Luneburg lens reflector loaded with a conformal reconfigurable metasurface, including a Luneburg lens 1, and a reflector conformally arranged in a hemispherical region of the Luneburg lens.

[0030] The Luneburg lens 1 is composed of multiple layers of dielectric spherical shells with a progressive dielectric constant of 1 to 2, and the dielectric constant of each layer of the spherical shell gradually decreases from the inside to the outside. In this embodiment, the Luneburg lens is a ten-layer structure, and the outermost circle radius is 65.0mm. The radii from the outside to the inside are 65.0mm, 64.6mm, 58.2mm, 54.8mm, 51.3mm, 47.9mm, 44.5mm, 41.2mm, 37.5mm, and 34.1mm respectively. The corresponding dielectric constants are 1.051, 1.151, 1.244, 1.333, 1.416, 1.493, 1.565, 1.634, 1.696, and 1.862 respectively.

[0031] The reflector is composed of a plurality of reconfigurable metasurface arrays 2, each of which has a bonding element at the edge, through which the plurality of reconfigurable metasurface arrays 2 are spliced ​​together, and the reconfigurable metasurface arrays 2 are closely arranged, effectively reducing the uncontrollable area of ​​the non-reconfigurable metasurface. The tangent point of each reconfigurable metasurface array 2 and the Luneburg lens 1 is located at the center of the reconfigurable metasurface array 2; by changing the bias voltage on the reconfigurable metasurface array 2, the working state of the reconfigurable metasurface array 2 is switched to wave absorption or reflection.

[0032] like Figure 2 As shown, each reconfigurable metasurface array adopts an inverted microstrip structure, including a first dielectric layer 3, a second dielectric layer 5, a first metal layer 6, a third dielectric layer 8 and a second metal layer 9 arranged in sequence; wherein the first dielectric layer 3 is close to the Luneburg lens 1, the first dielectric layer 3 and the second dielectric layer 5 are bonded to form a bonding dielectric layer 4 through a semi-cured sheet, and an air layer 7 is formed between the first metal layer 6 and the third dielectric layer 8.

[0033] The first dielectric layer 3, the second dielectric layer 5 and the third dielectric layer 8 all use dielectric substrates with a dielectric constant of 2.2, and the thickness of the three is 0.508 mm. The thickness of the adhesive dielectric layer 4 is 0.11 mm, and the node constant of the semi-cured sheet used is 2.75. The thickness of the air layer 7 is 3 mm to 10 mm.

[0034] like Figure 3 As shown, the first metal layer is composed of a first metal patch 10 and four second metal patches. The four second metal patches are arranged around the first metal patch, and are arranged side by side in pairs, cross-arranged to form a cross-shaped structure; the second metal layer 9 is a planar layer.

[0035] The first metal patch 10 is a central metal patch, and its shape is a square with a side length of 0.4 mm. The four second metal patches are respectively a first rectangular metal patch 20, a second rectangular metal patch 30, a third rectangular metal patch 40, and a fourth rectangular metal patch 50. The wide side length of each rectangular metal patch is 0.4 mm, the long side length is 4.22 mm, and the gap between each rectangular metal patch and the central metal patch is 0.4 mm. A resistor is loaded on each side of the square metal patch and the narrow side of the rectangular metal patch, for a total of four resistors; the resistance of the four resistors is 200 ohms. One end of the principle square metal patch of two adjacent rectangular metal patches is provided with a pad for mounting a PIN diode; a pad 60 of a PIN diode is placed at the end of the rectangular metal patch 40, the pad size is 0.08mm*0.3mm, the pad spacing is 0.2mm, and the PIN diode is welded between the pads on both sides; a pad 70 of a PIN diode is placed at the end of the rectangular metal patch 50, the pad size is 0.08mm*0.3mm, the pad spacing is 0.2mm, and the PIN diode is welded between the pads on both sides.

[0036] like Figure 4 As shown, in the range of 12-18 GHz, when the reconfigurable metasurface array is in the reflection state, the reflection coefficient of the Luneburg lens reflector of this embodiment is in the range of -0.69 to -4.41 dB; when the reconfigurable metasurface array is in the absorption state, the reflection coefficient is in the range of -16.07 to -12.65 dB; the minimum reflection coefficient of the reconfigurable metasurface array in the reflection state and the absorption state differs by 8.24 dB, and the absorption and reflection effects of electromagnetic waves are obvious in a wide frequency band. Figure 5 As shown in Figure 2, at 12 GHz, when the reconfigurable metasurface array is in the reflective state, the RCS of the Luneburg lens reflector is 2.38 dB (m 2 ); When the reconfigurable metasurface array is in the absorbing state, the RCS facing the Luneburg lens reflector is -5.33dB (m 2); That is to say, the RCS of the reconfigurable metasurface array in the Luneburg lens reflector of this embodiment differs by 7.71 dB when it is in the reflection state and the absorption state, and has obvious absorption and reflection effects on electromagnetic waves.

[0037] In summary, the Luneburg lens reflector of this embodiment conforms multiple reconfigurable metasurface arrays to the Luneburg spherical mirror, so that electromagnetic waves can return through the original path after passing through the reconfigurable metasurface array, and a larger RCS can be achieved within a larger incident range; the RCS of the Luneburg lens reflector is significantly changed by adjusting the bias voltage of the PIN diode to change the feed on the reconfigurable metasurface; the bandwidth of the reconfigurable metasurface is effectively improved by introducing an air layer and a resistor in the reconfigurable metasurface array; the diode damage that may be caused by motion squeezing can be avoided by placing the PIN diode in an inverted microstrip structure. In addition, the metal patch size, air layer thickness, dielectric layer thickness, and device installation position in the reconfigurable metasurface array can be adjusted according to different application scenarios to meet the index requirements of the adjustable Luneburg lens reflector.

Claims

1. A Luneburg lens reflector loaded with a conformal reconfigurable metasurface, characterized in that: The Luneburg lens reflector comprises a Luneburg lens and a reflector conformally arranged on the Luneburg lens; The reflector is composed of a plurality of reconfigurable metasurface arrays, each of which has a binding element at the edge. The binding elements enable the reconfigurable metasurface arrays to be closely arranged, thereby effectively reducing the uncontrollable area of ​​the non-reconfigurable metasurface. The tangent point of each reconfigurable metasurface array and the Luneburg lens is located at the center of the reconfigurable metasurface array. By changing the bias voltage on the reconfigurable array, the working state of the reconfigurable metasurface can be switched to wave absorption or reflection.

2. The Luneburg lens reflector loaded with a conformal reconfigurable metasurface according to claim 1, characterized in that: The Luneburg lens is composed of multiple layers of dielectric spherical shells with progressive dielectric constants, and the dielectric constants of the spherical shells gradually decrease from the inside to the outside.

3. The Luneburg lens reflector loaded with a conformal reconfigurable metasurface according to claim 3, characterized in that: The dielectric constant of each dielectric spherical shell of the Luneburg lens is between 1 and 2.

4. The Luneburg lens reflector loaded with a conformal reconfigurable metasurface according to claim 1, characterized in that: Each reconfigurable metasurface array adopts an inverted microstrip structure, including a first dielectric layer, a second dielectric layer, a first metal layer, a third dielectric layer and a second metal layer arranged in sequence; wherein the first dielectric layer is close to the Luneburg lens, the first dielectric layer and the second dielectric layer are bonded to each other through a semi-cured sheet to form a bonding dielectric layer, and an air layer is formed between the first metal layer and the third dielectric layer.

5. The Luneburg lens reflector loaded with a conformal reconfigurable metasurface according to claim 4, characterized in that: The first dielectric layer, the second dielectric layer and the third dielectric layer are all made of dielectric materials, and the thickness of the three is 0.254mm-0.508mm; the thickness of the bonding dielectric layer is 0.05mm-0.2mm; and the thickness of the air layer is 3mm-10mm.

6. The Luneburg lens reflector loaded with a conformal reconfigurable metasurface according to claim 4, characterized in that: The first metal layer is composed of a first metal patch and four second metal patches. The four second metal patches are arranged around the first metal patch, and are arranged side by side in pairs and cross-arranged to form a cross-shaped structure. The second metal layer is a planar layer.

7. The Luneburg lens reflector loaded with a conformal reconfigurable metasurface according to claim 6, characterized in that: The first metal patch is a square metal patch with a side length of 0.2mm to 1mm; the second metal patch is a rectangular metal patch, the wide side of the rectangular patch is equal to the wide side of the square metal patch, and the long side length is 3.5mm to 4.5mm, wherein the ends of two adjacent rectangular metal patches away from the square metal patch are provided with pads for mounting PIN diodes; four resistors are loaded on the two wide sides of the rectangular metal patch and on the square metal patch; the resistance of the four resistors is 50 to 200 ohms.

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