Frequency selective surface with steep bilateral drop, wide passband and stable angle

Abstract

The invention discloses a bilateral steep-drop wide-passband frequency selective surface with a stable angle. The unit structure of the frequency selective surface sequentially comprises a first metal layer, a first dielectric substrate, a second metal layer, a second dielectric substrate and a third metal layer from top to bottom, the frequency selective surface units are regular hexagons, and the units are closely arranged in an equilateral triangle grid form; the first metal layer and the third metal layer are identical in structure and are composed of six identical petal-shaped metal patches which are in rotational symmetry. The second metal layer is a regular hexagonal ring; the overall structure is symmetrical about the second metal layer. According to the invention, while wide-passband filtering is realized, the bilateral steep drop characteristic of the passband is considered, the stable passband characteristic can be maintained under the condition of oblique incidence, and in addition, the filter has a relatively low section and is easy for curved surface conformal.

Description

Technical Field

[0001] The invention belongs to the technical field of electromagnetic fields, and in particular relates to a frequency selective surface with a wide passband and stable angle and a double-sided steep drop. Background Art

[0002] Frequency Selective Surface (FSS) is usually 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, electronic countermeasures and other fields.

[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 demand for wide passband and strong out-of-band stealth has made the design of wide passband FSS structures with steep bilateral dips gradually become a research hotspot. FSS with steep passband bilateral dips usually refers to FSS with a flat passband and steep out-of-band suppression characteristics. This structure can achieve precise frequency selection and shielding, reduce signal interference, improve electromagnetic compatibility, and ensure efficient operation of the system. Due to its broad prospects, broadband frequency selective surfaces with steep bilateral dips have become a research focus and development trend in the electromagnetic field.

[0004] At present, the technical means to achieve the steep drop in the passband on both sides mainly include constructing a resonant cavity (such as substrate integrated waveguide, ring resonator, etc.), multi-layer cascading (such as cascaded resonant layer or non-resonant layer, introduction of coupling holes, etc.) and 3D structure (such as slot line, microstrip line, etc.). Among them, the FSS structure based on the resonant cavity has a narrow wave transmission bandwidth, which can currently reach up to 16.7%, so the application scope of this technology is limited. Multi-layer cascaded FSS can achieve high-order filtering response, which can expand the wave transmission bandwidth to a certain extent. However, this type of structure can only achieve the steep drop characteristics of the single sideband (high-frequency wave transmission band) while achieving a wide passband. If the steep drop in both sides is achieved, the passband bandwidth is limited, which can reach up to 29.3%. The 3D FSS structure can achieve broadband wave transmission characteristics with steep drop in both sides due to its unique spatial dimension. However, as the angle of the incident electromagnetic wave increases, the passband bandwidth of this structure changes dramatically with the incident angle, which greatly affects its out-of-band stealth characteristics when the electromagnetic wave is obliquely incident. In addition, the overall thickness of this type of structure is relatively thick, which is not conducive to its conformal performance in curved applications 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 drop and certain angle stability. Its unit includes five dielectric plates and four metal layers. The metal layer includes four trapezoidal ring structures on the upper surface of the upper dielectric plate and the lower surface of the lower dielectric plate, a square metal ring structure formed by the upper and lower surfaces of the middle dielectric plate around the four edges of the dielectric plate, and two groups of 2×2 square ring structures inside the square metal ring. The center of the first group of square ring structures is at the four diagonal positions of the dielectric plate, and the center of the second group of rings is at the midpoint of the line connecting the centers of the adjacent first groups of rings. The trapezoidal ring structures on the upper surface of the upper dielectric plate and the lower surface of the lower dielectric plate are connected to each other through wires. At an incident angle of 0°, the bandwidth of its transmission coefficient is 6.27-13.30GHz, the relative bandwidth is 71.4%, and the steep drop of the left and right edges of the wide passband is 8.6% and 2.5% respectively, which has good steep drop characteristics. At an incident angle of 45°, its bandwidth becomes 5.23-14.16 GHz, with a relative bandwidth of 92.1%. As the incident angle changes, the bandwidth of the structure changes dramatically, and the out-of-band stealth performance deteriorates. The overall thickness of the structure is 0.2λ (λ is the passband low-frequency operating wavelength).

[0006] Therefore, how to design a low-profile FSS structure that takes into account bilateral steepness, wide passband, and angular stability is a technical problem that needs to be urgently solved in this field. Summary of the invention

[0007] In order to overcome the shortcomings of the prior art, the present invention provides a frequency selective surface with a bilateral steep drop and a wide passband and a stable angle, and its unit structure includes, from top to bottom, the first metal layer, the first dielectric substrate, the second metal layer, the second dielectric substrate, and the third metal layer; the frequency selective surface unit is a regular hexagon, and the units are closely arranged in the form of an equilateral triangle grid; the first and third metal layers have exactly the same structure, and are composed of six identical rotationally symmetrical 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 present invention realizes wide passband filtering while taking into account the bilateral steep drop characteristics of the passband, and can maintain a stable passband characteristic under oblique incidence conditions. In addition, the present invention has a lower cross-section and is easy to conform to the curved surface.

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

[0009] A frequency selective surface with a wide passband and a stable angle with a double-sided steep drop, comprising, 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 structure of the frequency selective surface is a regular hexagon, and the regular hexagonal units are arranged in an equilateral triangle 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 selective surface structure is symmetrical about the second metal layer;

[0012] The first metal layer and the third metal layer have the same structure, and are respectively printed with six identical, centrally symmetrical petal-shaped metal patches; the petal-shaped metal patches are rotated 60 degrees clockwise or counterclockwise with the center as the dot to 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 penetrating the first dielectric substrate and the second dielectric substrate.

[0014] Preferably, the first dielectric substrate and the second dielectric substrate are both 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 deformed based on an equilateral triangle, wherein the bottom edge adjacent to the unit period boundary protrudes outward, and the two sides adjacent to the same patch are recessed inward.

[0017] Preferably, the metal vias have the same size and overlap with the adjacent metal vias after rotating 60 degrees clockwise or counterclockwise with the center as a circle point.

[0018] Preferably, the unit period side length p of the frequency selective surface ranges from 0.1λ to 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 third metal layer and the unit period boundary is in the range of 0.08λ-0.09λ, and the width d3 is in the range of 0.011λ-0.017λ; the arc gap length l2 between the metal patches is in the range of 0.08λ-0.09λ, the minimum width d1 is in the range of 0.006λ-0.011λ, and the maximum width d2 is in the range of 0.015λ-0.02λ.

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

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

[0023] 1. The present invention expands the passband bandwidth and improves the performance of bilateral steep drop. The present invention generates four transmission poles and two transmission zeros, the relative passband bandwidth reaches 101.6%, and the steep drop of the left and right edges of the wide passband is 3.9% and 2% respectively.

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

[0025] 3. The present invention comprises three metal layers and two dielectric plates, the overall thickness is relatively low (the thickness is 0.095λ), and the unit form is simple and easy to process and design. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0027] Figure 2 It 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 It is a schematic diagram of the second metal layer of the frequency selective surface array unit of the present invention.

[0029] Figure 4 It is a side schematic diagram of the frequency selective surface array unit of the present invention.

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

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

[0032] Figure 7 is a simulation curve of transmission coefficient and reflection coefficient of the frequency selective surface of the embodiment of the present invention when the electromagnetic wave is incident vertically;

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

[0034] Description of the drawings: 1-first metal layer, 2-first dielectric substrate, 3-second metal layer, 4-second dielectric substrate, 5-third metal layer, 6-metal via. DETAILED DESCRIPTION

[0035] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0036] In view of the defects of the prior art, the present invention provides a FSS structure with a wide passband, angle stability and low profile with a steep drop on both sides, so as to achieve the characteristics of steep drop on both sides, wide passband, angle stability and low profile at the same time, and the structure is simple and easy to process.

[0037] In order to achieve the above object, the technical solution of the present invention is as follows:

[0038] A frequency selective surface with a wide passband and stable angle, comprising, 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] The first dielectric substrate and the second dielectric substrate are both 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 are respectively printed with six identical, centrosymmetrical petal-shaped metal patches; the petal-shaped metal patches are rotated 60 degrees clockwise or counterclockwise with the center as the dot to overlap with the adjacent metal patches;

[0042] The structure of the frequency selective surface is a regular hexagon, and the units are compactly arranged in an equilateral triangle 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 deformed based on an equilateral triangle, wherein the bottom edge adjacent to the unit period boundary is slightly convex 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 penetrating the first dielectric substrate and the second dielectric substrate;

[0047] The metal vias have the same size, and they overlap with the adjacent metal vias after rotating 60 degrees clockwise or counterclockwise from the center;

[0048] The unit period side length p of the frequency selective surface ranges from 0.1λ to 0.2λ;

[0049] The width w of the regular hexagonal ring of 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 unit period boundary is in the range of 0.08λ-0.09λ, and the width d3 is in the range of 0.011λ-0.017λ; the arc gap length l2 between the metal patches is in the range of 0.08λ-0.09λ, the minimum width d1 is in the range of 0.006λ-0.011λ, and the maximum width d2 is in the range of 0.015λ-0.02λ;

[0051] The distance d between the metal via and another metal via 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;

[0052] Example:

[0053] Figure 1 The overall structure diagram of the frequency selective surface of the embodiment of the present invention. The present invention discloses a frequency selective surface with a wide passband and stable angle with a steep bilateral drop. The structure of the frequency selective surface is a regular hexagon, and the units are compactly arranged in an equilateral triangle grid shape. The structure includes, 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.

[0054] Figure 2 This is a schematic diagram of the first and third metal layers of the frequency selective surface array unit of an embodiment of the present invention. 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 first metal layer and the third metal layer have exactly the same structure, and are respectively printed with six identical, centrosymmetrical petal-shaped metal patches; the petal-shaped metal patches are deformed based on an equilateral triangle, wherein the bottom edge adjacent to the unit periodic boundary protrudes slightly outward, and the two sides adjacent to the same patch are slightly concave inward, and the metal patches adjacent to the patch are overlapped after rotating 60 degrees clockwise or counterclockwise with the center as the center. In the attached figure, p=9.7mm, l1=7.11mm, l2=7.24mm, d1=0.95mm, d2=1.4mm, and d3=1.1mm.

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

[0056] Figure 4 The side view of the frequency selective surface array unit of the embodiment of the present invention. The first dielectric substrate and the second dielectric substrate are both 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 structure thickness is 8.6 mm (i.e., a cross-sectional height of 0.095 λ).

[0057] The entire frequency selective surface structure is symmetrical about the second metal layer. 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. The metal vias have the same size and overlap with the adjacent metal vias after rotating 60 degrees clockwise or counterclockwise with the center as the circle point.

[0058] Figure 5 is an equivalent circuit diagram of the frequency selective surface array unit of the embodiment of the present invention. The dielectric substrate can be equivalent to a section with a length of h and an impedance of The transmission line, where Z0 represents the wave impedance in free space, is 377Ω, and ε r is the relative dielectric constant of the dielectric layer. Due to the symmetry of the structure, the first and third metal layers have the same parameters C T1 -C T2 (or C B1 -C B2 ) series resonant network, where C T1 or C B1 Represents the equivalent inductance of the gap between the petal-shaped metal patches between adjacent units, C T2 or C B2 Represents the equivalent inductance of the gap between the petal-shaped metal patches in the same unit; the second metal layer is equivalent to the inductor L in the circuit. L via represents the equivalent inductance of some metal vias in the first or second dielectric substrate, C via 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 for the multi-layer cascaded two-dimensional frequency selective surface, and introduce a pair of transmission zeros and transmission poles at the upper and lower ends of the passband of the high-order filter response, which expands the working bandwidth and improves the performance of bilateral steep drop. Figure 6 (a) is a side view current diagram of the frequency selective surface at the first transmission zero point when the electromagnetic wave is vertically incident; Figure 6 (b) is a side view current diagram of the frequency selective surface at the first transmission pole when the electromagnetic wave is vertically incident; Figure 6 (c) is a side view current diagram of the frequency selective surface at the fourth transmission pole when the electromagnetic wave is vertically incident; Figure 6 (d) is a side view current diagram of the frequency selective surface at the second transmission zero point when the electromagnetic wave is vertically incident. It can be seen that the metal via is used to connect the first and third metal layers to construct a new current path on the one hand; on the other hand, it is also part of the resonant structure itself. While extending the effective resonant length, the capacitance and inductance effects also participate in the resonance.

[0060] In order to verify that the proposed frequency selective surface has a broadband characteristic with a steep decline on both sides, the transmission curve and reflection curve of the electromagnetic wave vertically incident on the embodiment of the present invention are simulated. The results are as follows: Figure 7 shown.

[0061] Figure 7 The simulation curves of transmission coefficient and reflection coefficient when electromagnetic wave is incident vertically are shown. It can be seen that the four transmission poles are located at 3.48GHz, 4.5GHz, 7.67GHz and 10GHz, forming a flat wide passband. The center frequency is 6.77GHz, the relative bandwidth is as high as 101.6%, and the maximum insertion loss in the band is less than 1dB. In addition, the transmission zero points on both sides of the passband are located at 3.14GHz and 10.49GHz, which greatly improves the out-of-band cutoff capability. The left and right edges of the wide passband drop sharply by 3.9% and 2% respectively, and the rectangular coefficient of the wave-transmitting window K=1.02 is close to 1, showing excellent bilateral steepness.

[0062] In order to verify that the proposed frequency selective surface has the characteristic of stable incident angle, the transmission curves of electromagnetic waves with different oblique incident angles of the embodiment of the present invention are simulated. The results are as follows: Figure 8 shown.

[0063] Figure 8 The simulation curves of transmission coefficients corresponding to different oblique incident angles of TE polarized electromagnetic waves are shown. It can be seen that as the oblique incident electromagnetic wave angle increases to 45°, the transmission passband of the structure maintains the same passband bandwidth as the vertical incidence while maintaining the bilateral steep drop characteristics. The maximum insertion loss in the band is less than 3dB at 45° incidence, showing excellent angular stability characteristics.

Claims

1. A wide passband angle-stable frequency selective surface with a double-sided steep drop, characterized in that: The invention 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 structure of the frequency selective surface is a regular hexagon, and the regular hexagonal units are arranged in an equilateral triangle 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 selective surface structure is symmetrical about the second metal layer; The first metal layer and the third metal layer have the same structure, and are respectively printed with six identical, centrally symmetrical petal-shaped metal patches; the petal-shaped metal patches are rotated 60 degrees clockwise or counterclockwise with the center as the dot to overlap with the adjacent metal patches; The first metal layer and the third metal layer are connected in the vertical direction by six metal vias penetrating the first dielectric substrate and the second dielectric substrate.

2. The double-sided steep-drop wide-passband angle-stable frequency selective surface according to claim 1, characterized in that: The first dielectric substrate and the second dielectric substrate are both 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 double-sided steep-drop wide-passband angle-stable frequency selective surface according to claim 1, characterized in that: The second metal layer is composed of regular hexagonal rings.

4. The double-sided steep-drop wide-passband angle-stable frequency selective surface according to claim 1, characterized in that: The petal-shaped metal patch is deformed based on an equilateral triangle, wherein the bottom edge adjacent to the unit period boundary protrudes outward, and the two sides adjacent to the same patch are recessed inward.

5. The double-sided steep-drop wide-passband angle-stable frequency selective surface according to claim 1, characterized in that: The metal vias have the same size and overlap with the adjacent metal vias after rotating 60 degrees clockwise or counterclockwise with the center as a circle point.

6. The double-sided steep-drop wide-passband angle-stable frequency selective surface according to claim 1, characterized in that: The unit period side length p of the frequency selective surface has a value range of 0.1λ-0.2λ, where λ is the passband low-frequency operating wavelength.

7. The double-sided steep-drop wide-passband angle-stable frequency selective surface according to claim 1, characterized in that: The width w of the regular hexagonal ring of the second metal layer ranges from 0.017λ to 0.028λ.

8. The double-sided steep-drop wide-passband angle-stable frequency selective surface 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 third metal layer and the unit period boundary is in the range of 0.08λ-0.09λ, and the width d3 is in the range of 0.011λ-0.017λ; the arc gap length l2 between the metal patches is in the range of 0.08λ-0.09λ, the minimum width d1 is in the range of 0.006λ-0.011λ, and the maximum width d2 is in the range of 0.015λ-0.02λ.

9. The double-sided steep-drop wide-passband angle-stable frequency selective surface according to claim 1, characterized in that: The distance d between the metal via and another metal via symmetrical to the center is in the range of 0.025λ-0.03λ; and the diameter r is in the range of 0.001λ-0.005λ.

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