A dual-side steep drop wide passband angle-stable frequency selective surface

Abstract

The application discloses a wide-passband angle-stable frequency selective surface with double-side steep drop, and a unit structure of the frequency selective surface comprises, from top to bottom, a first metal layer, a first dielectric substrate, a second metal layer, a second dielectric substrate and a third metal layer; the unit structure of the frequency selective surface is a regular hexagon, and the units are closely arranged in the form of an equilateral triangle grid; the first metal layer and the third metal layer are completely identical in structure and are composed of six rotationally symmetrical identical petal-shaped metal patches; the second metal layer is a regular hexagonal ring; and the overall structure is symmetrical about the second metal layer. The application realizes wide-passband filtering while taking into account the double-side steep drop characteristic of the passband, can maintain stable passband characteristics in the case of oblique incidence, and has a relatively low profile and is easy to conform to a curved surface.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic field technology, specifically relating to a frequency selective surface with a wide passband angle stability and a steeply sloping double-sided gradient. Background Technology

[0002] A frequency selective surface (FSS) is typically a two-dimensional periodic array structure that can effectively control the reflection and transmission of electromagnetic waves. Due to its unique spatial filtering properties, FSS is widely used in radar stealth, electromagnetic shielding, wireless communication, and electronic warfare.

[0003] In recent years, with the continuous development of radar and other systems, higher demands have been placed on stealth and anti-stealth technologies. The need for wide passband and strong out-of-band stealth has made the design of wide passband Fast Sensing Surfaces (FSS) with steeply sloping passband sides a research hotspot. A FSS with steeply sloping passband sides typically refers to an FSS whose transmission response exhibits a flat passband and steeply sloping out-of-band suppression characteristics. This structure enables precise frequency selection and shielding, reduces signal interference, improves electromagnetic compatibility, and ensures efficient system operation. Due to its broad prospects, wideband frequency selective surfaces with steeply sloping passband sides have become a research focus and development trend in the electromagnetic field.

[0004] Currently, the main techniques for achieving steep passband sag on both sides include constructing resonant cavities (such as substrate-integrated waveguides, ring resonators, etc.), multi-layer cascading (such as cascaded resonant or non-resonant layers, introducing coupling holes, etc.), and 3D structures (such as slot lines, microstrip lines, etc.). Among these, the FSS structure based on resonant cavities has a relatively narrow transmission bandwidth, currently reaching a maximum of 16.7%, thus limiting its application scope. Multi-layer cascaded FSSs can achieve higher-order filtering responses, which can extend the transmission bandwidth to some extent. However, such structures can only achieve steep sag characteristics in a single sideband (high-frequency transmission band) while achieving a wide passband. If a steep sag on both sides is achieved, the passband bandwidth is limited, reaching a maximum of 29.3%. 3D FSS structures can achieve broadband transmission characteristics with steep sag on both sides due to their unique spatial dimension. However, as the incident electromagnetic wave angle increases, the passband bandwidth of such structures changes drastically with the incident angle, greatly affecting their out-of-band stealth characteristics when electromagnetic waves are obliquely incident. In addition, the overall thickness of such structures is relatively thick, which is not conducive to conformal application in curved surfaces such as radomes.

[0005] The patent "A Wide-Passband 3D Frequency Selective Surface" discloses a wide-passband 3D FSS structure. Its purpose is to design a wide-passband FSS with steep edge drops and a certain degree of angular stability. The unit comprises five dielectric substrates and four metal layers. The metal layers include four trapezoidal ring structures on the upper surface of the upper dielectric substrate and the lower surface of the lower dielectric substrate; square metal ring structures formed by the upper and lower surfaces of the middle dielectric substrate surrounding the four edges of the dielectric substrate; and two sets of 2×2 square ring structures inside the square metal rings. The center of the first set of square ring structures is located at the four diagonal positions of the dielectric substrate, and the center of the second set of rings is located at the midpoint of the line connecting the centers of adjacent first sets of rings. The trapezoidal ring structures on the upper surface of the upper dielectric substrate and the lower surface of the lower dielectric substrate are connected correspondingly by wires. At a 0° incident angle, its transmission coefficient bandwidth is 6.27-13.30 GHz, with a relative bandwidth of 71.4%. The steep edges of the wide passband are 8.6% and 2.5% respectively, exhibiting good steep-drop characteristics. At a 45° incident angle, its bandwidth becomes 5.23-14.16 GHz, with a relative bandwidth of 92.1%. The bandwidth of this structure changes drastically with the incident angle, resulting in a deterioration in out-of-band stealth performance. The overall thickness of this structure is 0.2λ (λ is the low-frequency operating wavelength in the passband).

[0006] Therefore, how to design a low-profile FSS structure that balances steep descent on both sides, wide bandwidth, and angular stability is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies, this invention provides a wide-passband angle-stable frequency selective surface with a steeply tapered passband on both sides. Its unit structure, from top to bottom, includes: a first metal layer, a first dielectric substrate, a second metal layer, a second dielectric substrate, and a third metal layer. The frequency selective surface units are regular hexagons, and the units are closely arranged in an equilateral triangular grid pattern. The first and third metal layers have identical structures, consisting of six rotationally symmetrical, identical petal-shaped metal patches. The second metal layer is a regular hexagonal ring. The overall structure is symmetrical about the second metal layer. This invention achieves wide-passband filtering while also maintaining a steeply tapered passband on both sides. It maintains stable passband characteristics even under oblique incidence conditions. Furthermore, this invention has a low profile, facilitating conformal surface design.

[0008] The technical solution adopted by this invention to solve its technical problem is as follows:

[0009] A frequency selective surface with a wide passband angle stability and steeply sloping sides comprises, from top to bottom: a first metal layer, a first dielectric substrate, a second metal layer, a second dielectric substrate, and a third metal layer;

[0010] The frequency selective surface has a regular hexagonal structure, and the regular hexagonal units are arranged in an equilateral triangular grid shape.

[0011] The first metal layer is printed on the upper surface of the first dielectric substrate, and the third metal layer is printed on the lower surface of the second dielectric substrate; the second metal layer is sandwiched between the first dielectric substrate and the second dielectric substrate, and the entire frequency selection surface structure is symmetrical about the second metal layer;

[0012] The first metal layer and the third metal layer have the same structure, and each has six identical petal-shaped metal patches printed on it. The petal-shaped metal patches are rotated 60 degrees clockwise or counterclockwise with the center point as the center point and then overlap with the adjacent metal patches.

[0013] The first metal layer and the third metal layer are connected in the vertical direction by six metal vias that penetrate the first dielectric substrate and the second dielectric substrate.

[0014] Preferably, both the first dielectric substrate and the second dielectric substrate are made of F4B material with a thickness of 4.3 mm, a dielectric constant of 2.55, and a loss tangent of 0.001.

[0015] Preferably, the second metal layer is composed of regular hexagonal rings.

[0016] Preferably, the petal-shaped metal patch is derived from an equilateral triangle; wherein the base adjacent to the unit periodic boundary protrudes outward, and the two sides adjacent to the same patch are recessed inward.

[0017] Preferably, the metal vias are of the same size, and after rotating 60 degrees clockwise or counterclockwise around the center point, they coincide with the adjacent metal vias.

[0018] Preferably, the unit period side length p of the frequency selective surface is in the range of 0.1λ-0.2λ, where λ is the passband low-frequency operating wavelength.

[0019] Preferably, the width w of the regular hexagonal ring of the second metal layer ranges from 0.017λ to 0.028λ.

[0020] Preferably, the gap length l1 between the bottom edge of the petal-shaped metal patch of the first metal layer and the boundary of the unit period is 0.08λ-0.09λ, and the width d3 is 0.011λ-0.017λ; the arc-shaped gap length l2 between the metal patches is 0.08λ-0.09λ, the minimum width d1 is 0.006λ-0.011λ, and the maximum width d2 is 0.015λ-0.02λ.

[0021] Preferably, the distance d between the metal via and another metal via that is symmetrical to the center is in the range of 0.025λ-0.03λ; the diameter r is in the range of 0.001λ-0.005λ.

[0022] The beneficial effects of this invention are as follows:

[0023] 1. This invention expands the passband bandwidth and improves the performance of the double-sided steep descent. This invention generates four transmission poles and two transmission zeros, achieving a relative passband bandwidth of 101.6%, with wide passband left and right edge steep descents of 3.9% and 2%, respectively.

[0024] 2. The unit structure adopted in this invention is arranged in an equilateral triangular grid to achieve a compact array structure, thereby obtaining a frequency response characteristic with stable angle. The passband bandwidth is stable within the incident angle range of 0°-45°, ensuring the out-of-band stealth characteristics when electromagnetic waves are obliquely incident.

[0025] 3. The present invention comprises 3 metal layers and 2 dielectric layers, with a low overall thickness (thickness of 0.095λ) and a simple unit form that is easy to process and design. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the overall structure of the frequency selective surface of the present invention.

[0027] Figure 2 This is a schematic diagram of the first and third metal layers of the frequency selective surface array unit of the present invention.

[0028] Figure 3 This is a schematic diagram of the second metal layer of the frequency selective surface array unit of the present invention.

[0029] Figure 4 This is a side view of the frequency selective surface array unit of the present invention.

[0030] Figure 5 This is the equivalent circuit diagram of the frequency selective surface array unit of the present invention.

[0031] Figure 6(a) is a side-view current diagram of the frequency selective surface of the present invention at the first transmission zero F01 = 3.14 GHz when electromagnetic waves are incident perpendicularly; Figure 6(b) is a side-view current diagram of the frequency selective surface of the present invention at the first transmission pole Fp1 = 3.48 GHz when electromagnetic waves are incident perpendicularly; Figure 6(c) is a side-view current diagram of the frequency selective surface of the present invention at the fourth transmission pole Fp4 = 10 GHz when electromagnetic waves are incident perpendicularly; Figure 6(d) is a side-view current diagram of the frequency selective surface of the present invention at the second transmission zero F02 = 10.49 GHz when electromagnetic waves are incident perpendicularly.

[0032] Figure 7 These are simulation curves of the transmission coefficient and reflection coefficient of the frequency selective surface in an embodiment of the present invention when electromagnetic waves are incident perpendicularly;

[0033] Figure 8This is a simulation curve of the transmission coefficient of the frequency selective surface in an embodiment of the present invention when electromagnetic waves are obliquely incident at different angles (θ).

[0034] Figure description: 1-First metal layer, 2-First dielectric substrate, 3-Second metal layer, 4-Second dielectric substrate, 5-Third metal layer, 6-Metal via. Detailed Implementation

[0035] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0036] To address the shortcomings of existing technologies, this invention provides a wide-bandwidth, angle-stable, low-profile FSS structure with steeply sloping sides, achieving the characteristics of steeply sloping sides, wide bandwidth, angle stability, and low profile simultaneously. The structure is simple and easy to manufacture.

[0037] To achieve the above objectives, the technical solution of the present invention is as follows:

[0038] A wide passband and angle-stable frequency selective surface with steeply tapered sides comprises, from top to bottom: a first metal layer, a first dielectric substrate, a second metal layer, a second dielectric substrate, and a third metal layer;

[0039] Both the first and second dielectric substrates are made of F4B material with a thickness of 4.3 mm, a dielectric constant of 2.55, and a loss tangent of 0.001.

[0040] The second metal layer is mainly composed of regular hexagonal rings;

[0041] The first metal layer and the third metal layer have the same structure, and each has six identical petal-shaped metal patches printed on it. The petal-shaped metal patches are rotated 60 degrees clockwise or counterclockwise with the center as the center point and then overlap with the adjacent metal patches.

[0042] The structure of the frequency selective surface is a regular hexagon, with the units arranged in a compact equilateral triangular grid shape.

[0043] The first metal layer is printed on the upper surface of the first dielectric substrate, and the third metal layer is printed on the lower surface of the second dielectric substrate.

[0044] The entire frequency-selective surface structure is symmetrical about the second metal layer;

[0045] The petal-shaped metal patch is based on the deformation of an equilateral triangle; the base adjacent to the unit period boundary protrudes slightly outward, and the two sides adjacent to the same patch are slightly concave inward.

[0046] The first and third metal layers are connected in the vertical direction by six metal vias that penetrate the first dielectric substrate and the second dielectric substrate.

[0047] Metal vias of the same size will overlap with adjacent metal vias after being rotated 60 degrees clockwise or counterclockwise around the center point.

[0048] The edge length p of the unit period of the frequency-selective surface ranges from 0.1λ to 0.2λ.

[0049] The width w of the regular hexagonal ring in the second metal layer ranges from 0.017λ to 0.028λ;

[0050] The gap length l1 between the bottom edge of the petal-shaped metal patch of the first and third metal layers and the boundary of the unit period ranges from 0.08λ to 0.09λ, and the width d3 ranges from 0.011λ to 0.017λ; the arc-shaped gap length l2 between the metal patches ranges from 0.08λ to 0.09λ, the minimum width d1 ranges from 0.006λ to 0.011λ, and the maximum width d2 ranges from 0.015λ to 0.02λ.

[0051] The distance d between the metal via and another metal via that is symmetrical to the center ranges from 0.025λ to 0.03λ; the diameter r ranges from 0.001λ to 0.005λ.

[0052] Example:

[0053] Figure 1 This is a schematic diagram of the overall structure of a frequency selective surface according to an embodiment of the present invention. The present invention discloses a wide-bandwidth, angle-stable frequency selective surface with steeply sloping sides. The structure of the frequency selective surface is a regular hexagon, with the units arranged compactly in an equilateral triangular grid shape. From top to bottom, the structure includes: a first metal layer, a first dielectric substrate, a second metal layer, a second dielectric substrate, and a third metal layer.

[0054] Figure 2 This is a schematic diagram of the first and third metal layers of a frequency selective surface array unit according to an embodiment of the present invention. The first metal layer is printed on the upper surface of a first dielectric substrate, and the third metal layer is printed on the lower surface of a second dielectric substrate. The first and third metal layers have identical structures, each printed with six centrally symmetrical, identical petal-shaped metal patches. The petal-shaped metal patches are based on the deformation of an equilateral triangle, wherein the base adjacent to the boundary of the unit period slightly protrudes outward, and the two sides adjacent to the same patch are slightly concave inward. After rotating 60 degrees clockwise or counterclockwise around the center, they coincide with the adjacent metal patches. In the attached figure, p = 9.7 mm, l1 = 7.11 mm, l2 = 7.24 mm, d1 = 0.95 mm, d2 = 1.4 mm, and d3 = 1.1 mm.

[0055] Figure 3This is a schematic diagram of the second metal layer of a frequency-selective surface array unit according to an embodiment of the present invention. The second metal layer is mainly composed of regular hexagonal rings. In the figure, w = 2.25 mm, d = 2.65 mm.

[0056] Figure 4 This is a side view of the frequency selective surface array unit according to an embodiment of the present invention. Both the first and second dielectric substrates are made of F4B material with a thickness of 4.3 mm, a dielectric constant of 2.55, and a loss tangent of 0.001. In the figure, r = 0.3 mm. The overall structural thickness is 8.6 mm (i.e., a cross-sectional height of 0.095λ).

[0057] The entire frequency-selective surface structure is symmetrical about the second metal layer. The first and third metal layers are connected vertically by six metal vias penetrating the first and second dielectric substrates. These metal vias are of the same size and overlap with their adjacent vias after rotating 60 degrees clockwise or counterclockwise around their center.

[0058] Figure 5 This is an equivalent circuit diagram of the frequency-selective surface array unit according to an embodiment of the present invention. The dielectric substrate can be equivalently represented as a segment of length h with impedance h. The transmission line, where Z0 represents the wave impedance in free space, with a value of 377Ω, ε r Let C be the relative permittivity of the dielectric layer. Due to the symmetry of the structure, the first and third metal layers are composed of C with the same parameters. T1 -C T2 (or C) B1 -C B2 It consists of a series resonant network, where C T1 Or C B1 C represents the equivalent inductance of the gap between the petal-shaped metal patches of adjacent cells. T2 Or C B2 The first metal layer represents the equivalent inductance of the gap between the petal-shaped metal patches within the same unit; the second metal layer is equivalent to inductance L in the circuit. via C represents the equivalent inductance of a portion of the metal via in the first or second dielectric substrate. via This represents the equivalent capacitance of the mutual coupling between adjacent metal vias.

[0059] The equivalent capacitance and inductance of metal vias introduce a new design dimension to the multi-layered cascaded two-dimensional frequency selective surface. A pair of transmission zeros and poles are introduced at the top and bottom of the passband of the high-order filter response, respectively, expanding the operating bandwidth and improving the performance of the bilateral steep sag. Figure 6(a) is a side-view current diagram of the frequency selective surface of the embodiment of the present invention at the first transmission zero when electromagnetic waves are incident perpendicularly; Figure 6(b) is a side-view current diagram of the frequency selective surface of the embodiment of the present invention at the first transmission pole when electromagnetic waves are incident perpendicularly; Figure 6(c) is a side-view current diagram of the frequency selective surface of the embodiment of the present invention at the fourth transmission pole when electromagnetic waves are incident perpendicularly; Figure 6(d) is a side-view current diagram of the frequency selective surface of the embodiment of the present invention at the second transmission zero when electromagnetic waves are incident perpendicularly. It can be seen that the metal vias are used to connect the first and third metal layers, constructing a new current path; on the other hand, they are also part of the resonant structure, extending the effective resonant length while the capacitance and inductance effects also participate in the resonance.

[0060] To verify that the proposed frequency-selective surface has a wideband characteristic with steep descent on both sides, simulations were performed on the transmission and reflection curves of electromagnetic waves incident perpendicularly according to the embodiments of the present invention. The results are as follows: Figure 7 As shown.

[0061] Figure 7 Simulated curves of the transmission and reflection coefficients for perpendicular electromagnetic wave incidence are presented. It can be seen that the four transmission poles are located at 3.48 GHz, 4.5 GHz, 7.67 GHz, and 10 GHz, forming a flat, wide passband. The center frequency is 6.77 GHz, with a relative bandwidth of up to 101.6%, and the maximum insertion loss within the band is less than 1 dB. Furthermore, the transmission zeros on both sides of the passband are located at 3.14 GHz and 10.49 GHz, respectively, significantly improving the out-of-band cutoff capability. The wide passband exhibits steep drops of 3.9% and 2% at the left and right edges, respectively, and the rectangularity coefficient of the transmission window, K = 1.02, approaches 1, demonstrating excellent bilateral steep drops.

[0062] To verify that the proposed frequency-selective surface has incident angle stability characteristics, the transmission curves of electromagnetic waves incident at different angles according to the embodiments of the present invention were simulated. The results are as follows: Figure 8 As shown.

[0063] Figure 8 Simulated transmission coefficient curves are shown for TE-polarized electromagnetic waves incident at different angles. It can be seen that as the angle of the incident electromagnetic wave increases to 45°, the transmission passband of the structure maintains the same bandwidth as that of vertical incident waves while retaining its steeply sloping bilateral characteristics. At 45° incident angle, the maximum insertion loss within the passband is less than 3dB, demonstrating excellent angle stability.

Claims

1. A frequency selective surface with a wide passband angle stability and a steeply sloping design on both sides, characterized in that, From top to bottom, it includes: a first metal layer, a first dielectric substrate, a second metal layer, a second dielectric substrate, and a third metal layer; The frequency selective surface has a regular hexagonal structure, and the regular hexagonal units are arranged in an equilateral triangular grid shape. The first metal layer is printed on the upper surface of the first dielectric substrate, and the third metal layer is printed on the lower surface of the second dielectric substrate; the second metal layer is sandwiched between the first dielectric substrate and the second dielectric substrate, and the entire frequency selectivity surface structure is symmetrical about the second metal layer; the second metal layer is composed of regular hexagonal rings. The first metal layer and the third metal layer have the same structure, and each has six identical petal-shaped metal patches printed on them. The petal-shaped metal patches are rotated 60 degrees clockwise or counterclockwise around the center as the origin and then overlap with the adjacent metal patches. The petal-shaped metal patches are based on the deformation of an equilateral triangle. The base of the patch adjacent to the unit period boundary protrudes outward and the two sides adjacent to the same patch are recessed inward. The first metal layer and the third metal layer are connected in the vertical direction by six metal vias that penetrate the first dielectric substrate and the second dielectric substrate.

2. The frequency selective surface with a steeply sloping, wide-passband angle-stabilized design according to claim 1, characterized in that, Both the first and second dielectric substrates are made of F4B material with a thickness of 4.3 mm, a dielectric constant of 2.55, and a loss tangent of 0.

001.

3. The frequency selective surface with a steeply sloping, wide-passband angle-stabilized design according to claim 1, characterized in that, The metal vias are of the same size, and after rotating 60 degrees clockwise or counterclockwise around the center, they coincide with the adjacent metal vias.

4. A frequency selective surface with a steeply sloping, wide-passband angle-stabilized design according to claim 1, characterized in that, The unit period side length p of the frequency selective surface ranges from 0.1λ to 0.2λ, where λ is the low-frequency operating wavelength of the passband.

5. A frequency selective surface with a steeply sloping, wide-passband angle-stabilized design according to claim 1, characterized in that, The width w of the regular hexagonal ring in the second metal layer ranges from 0.017λ to 0.028λ.

6. A frequency selective surface with a steeply sloping double-sided wide passband angle stability according to claim 1, characterized in that, The gap length l1 between the bottom edge of the petal-shaped metal patch of the first metal layer and the boundary of the unit period is 0.08λ-0.09λ, and the width d3 is 0.011λ-0.017λ. The arc-shaped gap length l2 between the metal patches is 0.08λ-0.09λ, the minimum width d1 is 0.006λ-0.011λ, and the maximum width d2 is 0.015λ-0.02λ.

7. A frequency selective surface with a steeply sloping double-sided wide passband angle stability according to claim 1, characterized in that, The distance d between the metal via and another metal via that is symmetrical to the center ranges from 0.025λ to 0.03λ; the diameter r ranges from 0.001λ to 0.005λ.

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