Ultrathin single-layer dual-passband frequency selective surface structure

Abstract

The invention discloses an ultrathin single-layer dual-passband frequency selective surface structure, and belongs to the field of electromagnetic fields and microwaves. The frequency selective surface structure is formed by periodically arranging the same unit structures, and each unit structure comprises a single-layer dielectric substrate and a single-layer metal layer loaded on the upper surface of the dielectric substrate; the single-layer metal layer is formed by sequentially nesting three concentric annular patches, and the three concentric annular patches are respectively a metal mesh tightly attached to the boundary of the unit, four square metal rings bent outwards and arranged in the metal mesh, and four circular metal rings bent outwards and arranged in the square metal rings from outside to inside. The ultra-thin single-layer dual-passband frequency selective surface structure can form two passbands with high relative bandwidths when electromagnetic waves are incident, has excellent angle stability under TE and TM polarization, and can be used for improving the performance of the antenna by changing the size parameters of the square metal ring and the circular metal ring. The two transmission zero points can be regulated and controlled, so that the position of the passband is adjusted.

Description

Technical Field

[0001] The present invention relates to the field of electromagnetic fields and microwaves, and particularly to an ultra-thin single-layer dual-band frequency selective surface structure. Background Art

[0002] A frequency selective surface (FSS) is a periodic structure that can make different selections for incident electromagnetic waves in different environments, and can transmit or reflect them according to the frequency, polarization mode, and incident angle of the electromagnetic waves. In recent decades, frequency selective surfaces have received a great deal of attention due to their unique electromagnetic space adjustment ability and anti-interference ability, and they have been widely used in various fields such as wireless communication and radar radomes. With the continuous increase in the multi-band working requirements of wireless communication and radar systems, FSSs with ultra-thin dual-band characteristics have attracted much attention because they can ensure accurate and stable frequency responses while maintaining a smaller volume.

[0003] From the perspective of existing FSS design methods, FSSs can be structurally divided into three-dimensional (3D), 2.5D, and two-dimensional (2D) structures. Among them, although 3D and 2.5D structures can achieve a relatively stable dual-band effect by introducing structures such as coupling slots and internal through-holes, they generally have a narrow bandwidth, cannot meet the requirements of broadband communication systems, and have a large unit thickness, complex structures, and high production costs, making it difficult to be widely applied in conformal design, aerospace, and other scenarios with high requirements for the toughness and volume of FSSs.

[0004] In contrast, the existing 2D multi-layer or single-layer dual-band FSSs can simplify the structural complexity and reduce the production cost to a certain extent. Through reasonable design, they can perform excellently in one of the important FSS indicators such as bandwidth, angle stability, and size and volume, but they cannot achieve all-round optimization. To address these problems, the design of a single-layer dual-band FSS with an ultra-wide dual-band, excellent angle stability, and ultra-thin characteristics is a research with great development potential and practical application value. Summary of the Invention

[0005] Object of the Invention: Aiming at the above problems, the object of the present invention is to provide an ultra-thin single-layer dual-band frequency selective surface structure that realizes dual-band transmission while ensuring a high -3dB relative bandwidth, has an ultra-thin single-layer structure and stable frequency response characteristics under large-angle incident waves, can adjust the working frequency band by adjusting the parameters of the metal ring, does not require complex designs such as drilling, is easy to process, has low costs, and can be effectively applied to fields such as conformal design, wireless communication, and even radar radomes.

[0006] Technical solution: A kind of ultra-thin single-layer double-passband frequency selective surface structure of the present invention, the frequency selective surface structure is composed of the same unit structures arranged periodically, and the unit structure includes a single-layer dielectric substrate and a single-layer metal layer loaded on the upper surface of the dielectric substrate; The single-layer metal layer is composed of three concentric ring-shaped patches nested in sequence. From the outside to the inside, they are a metal mesh grid close to the unit boundary, a square metal ring with four outward bends inside the metal mesh grid, and a circular metal ring with four outward bends inside the square metal ring.

[0007] Furthermore, the dielectric substrate is made of a flexible material, and the thickness range is 0.05~0.11mm.

[0008] Furthermore, the single-layer metal layer selects copper as the material, and the thickness range is 0.012~0.035mm.

[0009] Furthermore, the width of the outermost metal mesh grid is smaller than the widths of the middle square metal ring and the inner circular metal ring.

[0010] Furthermore, the bending parts of the square metal ring and the circular metal ring present a 45° angle.

[0011] Furthermore, by changing the size parameters of the square metal ring and the circular metal ring, the equivalent inductance and equivalent capacitance values of the frequency selective surface structure can be adjusted, so as to respectively control the positions of the two transmission zeros. The formula is: , , In the formula, f z1 is the position of the first transmission zero, f z2 is the position of the second transmission zero, C1 represents the gap capacitance of the bending part of the square metal ring, C2 represents the gap capacitance between the square metal ring and the outermost mesh grid, C3 represents the gap capacitance of the bending part of the circular metal ring, C4 represents the gap capacitance between the circular metal ring and the square metal ring, L2 represents the equivalent inductance of the linear part of the square metal ring, and L3 represents the equivalent inductance of the linear part of the circular metal ring.

[0012] Beneficial effects: Compared with the prior art, the remarkable advantages of the present invention are: 1. By loading a single metal layer composed of three concentric ring-shaped patches on a flexible dielectric substrate, the present invention shows ultra-thin characteristics. The absolute thickness is only 0.068mm. Taking the wavelength corresponding to the center frequency point of the low-frequency passband as the standard, the relative thickness is only 0.0015 , avoiding additional operations such as coupling slots and internal punching, and having significant advantages in conformal design and many fields with strict requirements for spatial dimensions; 2. Under normal incident electromagnetic waves, the present invention can achieve an absolute - 3dB bandwidth of up to 4.66 GHz and 5.28 GHz, and the relative - 3dB bandwidths are up to 72.25% and 34.99% respectively. Moreover, it still exhibits excellent transmission characteristics under large - angle incident waves, providing a new idea for realizing multi - band broadband transmission. 3. By respectively nesting a square metal ring and a circular metal ring with outward bends in a metal mesh grid with low - resistance and high - pass characteristics, the present invention introduces two transmission zeros, thus achieving a dual - passband effect. By changing the size parameters of the square metal ring and the circular metal ring, independent regulation of the transmission zeros can be achieved within a certain range, thereby flexibly adjusting the transmission passband, and it can be applied to more extensive and complex scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a schematic structural diagram of the unit structure; Figure 2 is a schematic structural diagram of the upper surface of the unit structure; Figure 3 is the transmission / reflection coefficient curve of the frequency - selective surface structure under normal incident electromagnetic waves; Figure 4 is the transmission coefficient curve of the frequency - selective surface structure at various angles under TE polarization; Figure 5 is the transmission coefficient curve of the frequency - selective surface structure at various angles under TM polarization; Figure 6 is the transmission coefficient curve of the frequency - selective surface structure with different size parameters l1; Figure 7 is the transmission coefficient curve of the frequency - selective surface structure with different size parameters k; Figure 8 is the transmission coefficient curve of the frequency - selective surface structure in non - bent and bent cases.

[0014] Among them, 1 is the dielectric substrate, 2 is the metal mesh grid, 3 is the square metal ring, and 4 is the circular metal ring. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0015] In order to make the objectives, technical solutions, and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments.

[0016] An ultra - thin single - layer dual - passband frequency - selective surface structure described in this embodiment is composed of the same unit structures arranged periodically, as Figure 1 shown. The unit structure includes a single - layer dielectric substrate 1 and a single - layer metal layer loaded on the upper surface of the dielectric substrate 1. The single-layer metal layer is composed of three concentric circular patch arrays nested in sequence. From the outside to the inside, they are the metal mesh grating 2 closely attached to the unit boundary, the square metal ring 3 with four outward-bent sections located inside the metal mesh grating 2, and the circular metal ring 4 with four outward-bent sections located inside the square metal ring 3.

[0017] Furthermore, the dielectric substrate is made of a flexible material with high strength and high toughness, and its thickness ranges from 0.05 to 0.11 mm.

[0018] Furthermore, the single-layer metal layer selects copper as the material, and its thickness ranges from 0.012 to 0.035 mm.

[0019] Furthermore, the width of the outermost metal mesh grating is smaller than the widths of the middle square metal ring and the inner circular metal ring.

[0020] Furthermore, the bending parts of the square metal ring and the circular metal ring are oriented at a 45° angle.

[0021] Furthermore, by changing the size parameters of the square metal ring and the circular metal ring, their equivalent inductance and equivalent capacitance values can be adjusted, thereby respectively controlling the positions of the two transmission zeros. The formula is: , , where f z1 is the position of the first transmission zero, f z2 is the position of the second transmission zero, C1 represents the gap capacitance of the bending part of the square metal ring, C2 represents the gap capacitance between the square metal ring and the outermost grating, C3 represents the gap capacitance of the bending part of the circular metal ring, C4 represents the gap capacitance between the circular metal ring and the square metal ring, L2 represents the equivalent inductance of the linear part of the square metal ring, and L3 represents the equivalent inductance of the linear part of the circular metal ring.

[0022] For the case where the parameters are known, the relationship between the physical structure and the equivalent circuit parameters can be obtained through the following formula: , , where t is the length of the metal linear patch, b is the width of the metal linear patch, g is the length of the metal patches above and below the gap, s is the width of the gap between the metal patches, represents the vacuum permeability, represents the vacuum permittivity, represents the relative permittivity of the dielectric substrate.

[0023] The inductance element L1 can be synthesized by the outermost square-ring-shaped metal mesh structure of the unit. For a square ring with bends, it can be equivalent to a parallel inductance L2 and a capacitance C1, and the gap between it and the metal mesh is equivalent to a series capacitance C2. Similarly, the inner circular-ring structure can be equivalent to a parallel inductance L3 and a capacitance C3, and the gap between the inner circular ring and the middle square ring can be equivalent to a series capacitance C4.

[0024] A kind of ultra-thin single-layer dual-band frequency selective surface structure proposed by the present invention is a single-layer metal loaded on the upper surface of a single-layer dielectric substrate, which consists of three concentric ring-shaped patches with different sizes, and there is a certain interval between each ring-shaped patch. Combining Figure 1 As shown, its unit structure is a square structure. The dielectric substrate 1 uses polyimide (PI) material. The metal mesh 2 is on the outermost side. The square metal ring 3 with four outward bends is located inside the metal mesh 2. The circular metal ring 4 with four outward bends is located inside the square metal ring 3. The metal material is copper. The four bent parts of the circular metal ring 4 and the four bent parts of the square metal ring 3 are symmetric about the center of the metal layer in terms of orientation, and there is a 45° angle between them.

[0025] As Figure 2 shown, in an example, the side length P of the unit structure is 9.2 mm, the width w of the metal mesh 2 is 0.1 mm, the side length a of the square metal ring 3 is 6.6 mm, the outward bending length l1 of the square ring is 1.5 mm, the outer diameter r1 of the circular metal ring 4 is 2.2 mm, the inner diameter r2 is 1.8 mm, the width k of the bent part is 1.2 mm, and the length l2 from the center is 3 mm.

[0026] Figure 3 is the transmission / reflection coefficient curve of the ultra-thin single-layer dual-band frequency selective surface described in this example under normal-incidence electromagnetic waves. It can be seen from the figure that for the electromagnetic waves under normal incidence, this unit structure can effectively achieve dual-band transmission. The first passband is 4.12 GHz - 8.78 GHz, the -3dB absolute bandwidth in this interval is 4.66 GHz, and the -3dB relative bandwidth is as high as 72.25%. The second passband is 12.45 GHz - 17.73 GHz, the -3dB absolute bandwidth in this interval is 5.28 GHz, and the -3dB relative bandwidth reaches 34.99%. Taking the wavelength corresponding to the center frequency point of the first passband as the standard, Figure 2 the unit thickness in is only 0.0015

[0027] Figures 4 to 5They are the transmission coefficient curves corresponding to different incident angles under TE / TM polarization, including 0°, 15°, 30°, 45°, 60° and 70°. It can be seen that as the deflection angle of the incident wave increases, the transmission frequency band under TE polarization shows a shrinking trend. On the contrary, the transmission frequency band under TM polarization is broadened. Even when the angle increases to 70°, the unit structure can still ensure stable transmission near the transmission poles under both polarizations, with excellent angular stability, which can meet the requirements of most practical applications.

[0028] Figure 6 They are the transmission coefficient curves of the ultra-thin single-layer dual-band frequency selective surface described in this example under different size parameters l1, including 0.7 mm, 0.9 mm, 1.1 mm and 1.3 mm. By changing the length l1 of the outward bending of the square metal ring, with the second transmission zero point remaining almost unchanged, the first transmission zero point shifts to lower frequencies as l1 increases, so that the frequency points at the right boundary of the first transmission passband and the left boundary of the second transmission passband move to lower frequencies.

[0029] Figure 7 They are the transmission coefficient curves of the ultra-thin single-layer dual-band frequency selective surface described in this example under different size parameters k, including 1.05 mm, 1.15 mm, 1.25 mm and 1.35 mm. As the width k of the bent part increases, the first transmission zero point remains almost unchanged, and the second transmission zero point shifts to lower frequencies, which can move the frequency point at the right boundary of the second transmission passband to lower frequencies without affecting the first transmission passband.

[0030] Figure 8 They are the transmission coefficient curves of the ultra-thin single-layer dual-band frequency selective surface described in this embodiment under non-bent and bent (bending radius is 200 mm) conditions. The left boundary of the first passband under the bent condition is slightly shifted compared with the non-bent condition, while the position of the second passband remains almost unchanged, which basically coincides with the transmission coefficient curve under the non-bent condition. The overall performance is stable, and it has the characteristics suitable for conformal applications on curved surfaces.

Claims

1. An ultra-thin single-layer dual-band frequency selective surface structure, characterized in that, The frequency selective surface structure is composed of the periodic arrangement of the same unit structures, and each unit structure includes a single-layer dielectric substrate and a single-layer metal layer loaded on the upper surface of the dielectric substrate; The single-layer metal layer is composed of three concentric ring-shaped patches nested in sequence. From the outside to the inside, they are a metal mesh closely attached to the unit boundary, a square metal ring with four outward bends inside the metal mesh, and a circular metal ring with four outward bends inside the square metal ring.

2. The ultra-thin single-layer dual-band frequency selective surface structure according to claim 1, characterized in that, The dielectric substrate is made of a flexible material, and the thickness range is 0.05 - 0.11 mm.

3. An ultra-thin single-layer dual-band frequency selective surface structure according to claim 1, characterized in that, The single-layer metal layer is made of copper as the material, and the thickness range is 0.012 - 0.035 mm.

4. A kind of ultra-thin single-layer double-passband frequency selective surface structure according to claim 1, characterized in that The width of the outermost metal mesh is smaller than the widths of the middle square metal ring and the inner circular metal ring.

5. An ultra-thin single-layer dual-band frequency selective surface structure according to claim 1, characterized in that, The bending parts of the square metal ring and the circular metal ring present a 45° angle in orientation.

6. The ultra-thin single-layer dual-band frequency selective surface structure according to claim 1, characterized in that, By changing the size parameters of the square metal ring and the circular metal ring, the equivalent inductance and equivalent capacitance values of the frequency selective surface structure are adjusted, so as to control the positions of the two transmission zeros respectively. The formula is: ， ， where f z1 is the position of the first transmission zero, f z2 is the position of the second transmission zero, C1 represents the gap capacitance of the bent part of the square metal ring, C2 represents the gap capacitance between the square metal ring and the outermost grid, C3 represents the gap capacitance of the bent part of the circular metal ring, C4 represents the gap capacitance between the circular metal ring and the square metal ring, L2 represents the equivalent inductance of the linear part of the square metal ring, and L3 represents the equivalent inductance of the linear part of the circular metal ring.

Images