Sandwich structure comprising frequency selective surface

Abstract

The invention relates to the technical field of radar detection, in particular to a sandwich structure comprising a frequency selective surface, the sandwich structure is provided with a first material layer, a second material layer, the frequency selective surface and a polyimide material layer for bearing the frequency selective surface, and the material layers are connected in a bonding mode. And only one second material layer or multiple second material layers can be selected according to requirements, so that the sandwich structure realizes different passband bandwidths, meanwhile, in the sandwich structure provided by the invention, the inner and outer edges of the Y-ring units on the frequency selection surface are arc lines, and the embodiment of the invention is specifically set to be elliptical, so that the frequency selection surface is more uniform. And the arrangement period of the Y-ring unit is limited, so that the response of an electromagnetic wave incident angle to the inner angle of the Y-ring unit is reduced. According to the sandwich structure provided by the invention, a traditional Y-ring rectangular angle is changed into a smooth structure, the response of electromagnetic waves at the right angle can be effectively reduced, the passband bandwidth is widened, the transmittance is high, and the angle stability is good.

Description

Technical Field

[0001] The invention relates to the field of radar detection technology, and in particular provides a sandwich structure comprising a frequency selective surface. Background Art

[0002] In modern defense systems, radar detection is an extremely important part. Radar detection has great limitations and threats on aircraft reconnaissance, penetration, and attack. According to radar detection theory, the effective detection distance of radar is proportional to the fourth root of the target radar cross section (RCS). Therefore, the realization of radar stealth technology, that is, the technology of reducing RCS, has become a key link that needs to be broken through in the current radar detection field.

[0003] Frequency Selective Surface (FSS) is composed of periodically arranged metal patches or aperture units of a specific shape. It has the ability to modulate electromagnetic waves. Common filtering characteristics include bandpass or bandstop characteristics.

[0004] By utilizing the spatial filtering characteristics of the frequency selective surface, the operating frequency of one's own radar antenna can be set within the wave transmission range of the frequency selective surface without introducing loading impedance, so that one's own electromagnetic wave signals can be received normally. In contrast, the operating frequency of the other party's radar detection is in the scattering range of the frequency selective surface, and the scattered electromagnetic waves will not be completely captured by the other party's radar, thereby reducing the radar scattering cross section.

[0005] Based on this principle, a radome with a low radar cross section (RCS) or a microwave absorbing structure can be manufactured to reduce the radar cross section of sensitive targets, thereby achieving electromagnetic stealth. However, in order to meet specific dynamic requirements, the radome of an aircraft is usually designed as a streamlined structure. For the frequency selective surface that follows the shape of the radome, the incident angle range of the electromagnetic wave is relatively large. Therefore, the angular stability and polarization stability of the frequency selective surface become extremely important.

[0006] At present, most of the design schemes of frequency selective surfaces only meet the stability of a small angle range under TE polarization and have complex structures and large losses. Therefore, it is very necessary to design a frequency selective surface that takes into account both angle stability and polarization stability and has good transmission characteristics.

[0007] Existing frequency selective surface design schemes cannot take into account both angle stability and polarization stability. For example, in 2020, Indian scholar Sayi Soundariya Sampath proposed a new ultra-wideband FSS with broadband band-stop characteristics. This unit shows excellent stability in polarization mode, but when the electromagnetic wave is incident at a large angle, its angle stability is poor; in 2021, Fan Yudi, Li Tianwu and others proposed an FSS with full-angle and full-polarization stability. This unit can make the incident wave change within a range of nearly 90° with excellent stability, but its metal layer structure is too complex and it is difficult to mass produce and widely use. Summary of the invention

[0008] In order to solve the above problems, the present invention provides a sandwich structure including a frequency selective surface, in which the Y-ring units are arranged into an elliptical structure and densely arranged, and a multi-layer sandwich structure is provided at the same time, thereby improving the angular stability and polarization stability and widening the passband bandwidth.

[0009] The sandwich structure including a frequency selective surface provided by the present invention comprises: two first material layers, at least one second material layer and at least one frequency selective surface; The two first material layers are respectively located at the uppermost layer and the lowermost layer of the sandwich structure; The second material layer is located between the two first material layers, arranged layer by layer; The frequency selective surface is located between two adjacent second material layers or between an adjacent first material layer and a second material layer; Y-ring units are arranged on the frequency selection surface, and the Y-ring units are arranged periodically; the Y-ring units have three branches, and the angle between the center lines of any two branches is 120°; the inner edges and outer edges of the three branches are all arc-shaped.

[0010] Preferably, the dielectric constant of the first material layer is greater than the dielectric constant of the second material layer.

[0011] Preferably, a polyimide material layer is disposed under any frequency selective surface layer.

[0012] Preferably, when the second material layer is a plurality of layers, the frequency selective surface is located between two adjacent second material layers; when the second material layer is a single layer, the frequency selective surface is located between adjacent first material layer and second material layer.

[0013] Preferably, when the second material layer is a multilayer, a frequency selective surface is disposed between every two adjacent second material layers.

[0014] Preferably, the arc is an ellipse.

[0015] Preferably, in the transverse arrangement period of the Y ring units, the center distance between any two adjacent Y ring units is greater than one times the maximum transverse dimension of the Y ring units and less than two times the maximum transverse dimension of the Y ring units.

[0016] Preferably, in the longitudinal arrangement period of the Y ring units, the center distance between any two adjacent Y ring units is less than one times the longitudinal maximum dimension of the Y ring units.

[0017] Preferably, the material of the frequency selective surface is copper.

[0018] Preferably, any adjacent material layers of the sandwich structure are connected by gluing.

[0019] Compared with the prior art, the present invention can achieve the following beneficial effects: The sandwich structure designed in the embodiment of the present invention can be selected to be a single-layer form or a multi-layer form according to user needs. Among them, the single-layer sandwich structure only has one second material layer and one frequency selective surface, and the multi-layer sandwich structure has multiple second material layers and multiple frequency selective surfaces. The single-layer sandwich structure is easy to process and has a high degree of developability, and the multi-layer sandwich structure has a wider passband bandwidth. The two schemes improve the flexibility and adaptability of the sandwich structure and can meet the various needs of different users.

[0020] At the same time, the embodiment of the present invention also designs the rectangular structure of the inner and outer edges of each branch of the traditional Y-ring unit into an arc structure. The embodiment of the present invention is specifically designed as an elliptical branch structure, which changes the right angles of the rectangle into a smooth arc, which can effectively reduce the response of the incident angle of the electromagnetic wave to the inner angle of the unit, so that the angular stability and polarization stability of the sandwich structure can be taken into account; and the present invention limits the arrangement period of the Y-ring unit to make its arrangement more dense. The densely arranged Y-ring unit arrangement improves the angular stability, improves the transmittance of the electromagnetic wave, and increases the passband bandwidth. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic diagram of a sandwich structure provided according to an embodiment of the present invention; Figure 2 is a schematic diagram of a frequency selective surface structure provided according to an embodiment of the present invention; Figure 3 is a graph of filtering characteristics of vertical polarization at different incident angles of a single-layer sandwich structure provided by an embodiment of the present invention; Figure 4 is a filtering characteristic curve diagram of horizontal polarization under different incident angles of a single-layer sandwich structure provided by an embodiment of the present invention; Figure 5 is a filtering characteristic curve diagram of vertical polarization and horizontal polarization at different incident angles of a single-layer sandwich structure provided by an embodiment of the present invention; Figure 6 is a graph of filtering characteristics of vertical polarization at different incident angles of a multi-layer sandwich structure provided by an embodiment of the present invention; Figure 7 is a filtering characteristic curve diagram of horizontal polarization under different incident angles of a multi-layer sandwich structure provided by an embodiment of the present invention; Figure 8 It is a filtering characteristic curve diagram of vertical polarization and horizontal polarization of the multi-layer sandwich structure provided by an embodiment of the present invention at different incident angles.

[0022] Reference numerals include: A first material layer 1 , a second material layer 2 , a frequency selective surface 3 , and a polyimide material layer 4 . DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the invention clearer, the invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the invention and do not constitute a limitation to the invention. Similar components in different embodiments use associated similar component numbers. In the following embodiments, many detailed descriptions are to enable the invention to be better understood. However, those skilled in the art can easily recognize that some of the features can be omitted in different situations, or can be replaced by other components, materials, and methods. In some cases, some operations related to the invention are not shown or described in the specification, in order to avoid the core part of the invention being overwhelmed by too much description, and for those skilled in the art, it is not necessary to describe these related operations in detail, and they can fully understand the related operations according to the description in the specification and the general technical knowledge in the art.

[0024] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other to form various implementation methods. At the same time, the steps or actions in the method description can also be interchanged or adjusted in a manner that is obvious to those skilled in the art. Therefore, the various sequences in the specification and the drawings are only for the purpose of clearly describing a certain embodiment and are not meant to be a necessary sequence, unless otherwise specified that a certain sequence must be followed.

[0025] In the description of the invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the invention, unless otherwise specified, the meaning of "multiple" is two or more.

[0026] In the description of the invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the invention can be understood according to specific circumstances.

[0027] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0028] like Figure 1 As shown, the present invention provides a sandwich structure including a frequency selective surface 3, the sandwich structure includes a first material layer 1, a second material layer 2, a frequency selective surface 3 and a polyimide material layer 4. The embodiment of the present invention provides two sandwich structure solutions, both of which include two first material layers 1, which are respectively located at the top and bottom of the sandwich structure, and the two first material layers 1 are made of the same material and have the same thickness.

[0029] like Figure 1 As shown in (a), in the first sandwich structure, there is one second material layer 2, one frequency selective surface 3, and one polyimide material layer 4, and the second material layer 2 is sandwiched between two first material layers 1, and the frequency selective surface 3 is sandwiched between the first material layer 1 and the second material layer 2, that is, the frequency selective surface 3 can be between the uppermost first material layer 1 and the second material layer 2, or between the second material layer 2 and the lowermost first material layer 1. Figure 1(a) shows that the frequency selective surface 3 is disposed between the second material layer 2 and the lowermost first material layer 1 .

[0030] The frequency selective surface 3 is a single-screen or multi-screen periodic array structure composed of a large number of passive resonant units. This structure can be composed of periodically arranged metal patch units or periodically arranged aperture units on a metal screen, and can present total reflection (patch type) or total transmission characteristics (aperture type) near the unit resonant frequency. The frequency selective surface 3 is usually made of metal and is a metal sheet with Y-ring units, which usually requires a bearing structure to support it. In the embodiment of the present invention, the material of the frequency selective surface 3 is copper, and the bearing structure is the polyimide material layer 4. Therefore, in the embodiment of the present invention, the polyimide material layer 4 is arranged below the frequency selective surface 3 to support the frequency selective surface 3. The embodiment of the present invention refers to the first scheme as a single-layer sandwich structure, which is easier to process and has a high degree of development.

[0031] like Figure 1 As shown in (b), in the second sandwich structure scheme, the second material layer 2 has multiple layers, the frequency selective surface 3 has multiple layers, and the polyimide material layer 4 has multiple layers, and when the second material layer 2 has multiple layers, the multiple layers of the second material layer 2 are sandwiched between two layers of the first material layer 1, arranged one after another. All frequency selective surfaces 3 are sandwiched between two adjacent layers of the second material layer 2, and a layer of frequency selective surface 3 is arranged between each two adjacent layers of the second material layer 2, and a layer of polyimide material layer 4 is arranged under each layer of frequency selective surface 3 as a bearing structure of the frequency selective surface 3. The multi-layer structure can more effectively widen the passband bandwidth. The embodiment of the present invention refers to the second scheme as a multi-layer sandwich structure. In the two solutions of the embodiments of the present invention, any two adjacent material layers are connected by pasting.

[0032] Both of the above two solutions have a frequency selective surface 3, such as Figure 2 As shown, in the embodiment of the present invention, the frequency selective surface 3 is composed of periodically arranged Y-ring units, and the Y-ring unit has three branches, which are called the first branch, the second branch and the third branch in the embodiment of the present invention. The three branches are all approximately annular structures, and the center lines of the three branches intersect at one point. The angle between the center lines of any two branches is 120°. The three branches intersect to form a "Y" shape, and the shapes and sizes of the three branches can be the same or different. Any branch has an inner edge and an outer edge, and the inner and outer edges are arcs. The arc is used to replace the traditional rectangular edge branch, and the rectangular corner is changed to a smooth structure, which can effectively reduce the response of the electromagnetic wave incident angle at a right angle. Preferably, the inner and outer edges of the embodiment of the present invention are both elliptical.

[0033] Regarding the arrangement period of the Y-ring units, the Y-ring units of the embodiments of the present invention are more densely arranged than the traditional Y-ring units. Specifically, from the perspective of the horizontal arrangement period, the center distance between any two adjacent Y-ring units is greater than one times the maximum horizontal dimension of the Y-ring unit, and less than two times the maximum horizontal dimension of the Y-ring unit; from the perspective of the vertical arrangement period, the center distance between any two adjacent Y-ring units is less than one times the maximum vertical dimension of the Y-ring unit, that is, no matter in the horizontal or vertical direction, the gap between any two adjacent Y-ring units is inserted with a branch of another Y-ring unit. By adopting a denser arrangement, the bandwidth width of the passband at -3dB can be increased, effectively improving the angle stability.

[0034] In order to verify the effect of the embodiment of the present invention, a simulation experiment is performed by giving a clear size to each structure. Figure 1 and Figure 2 , as follows: For the first solution of the embodiment of the present invention, the dielectric constant of the first material layer 1 is set to 4.2, the loss tangent is set to 0.01, and the thickness is set to The dielectric constant of the second material layer 2 is 1.1, the loss tangent is 0.005, and the thickness is 0.5 mm. 4 mm, the dielectric constant of the polyimide material layer 4 is 3, the loss tangent is 0.005, and the thickness is The three branches of the Y-ring unit on the frequency selective surface 3 have the same shape and size, wherein the periodic size of the Y-ring unit is: the distance between the centers of any two adjacent Y-ring units in the lateral direction is 6 mm, that is, , the center distance between any two adjacent Y ring units in the longitudinal direction is 3.464 mm, that is Dy=3.464mm. Among the three branches, the major axis of the outer edge ellipse is 3mm and the minor axis is 1.2mm, that is, a=6mm, b=1.2mm. The major axis of the inner edge is 2.4mm and the minor axis is 0.6mm, that is, c=2.4mm and d=0.6mm.

[0035] The simulation results are as follows Figure 3 , Figure 4 and Figure 5 As shown, Figure 3 and Figure 4 Here, TE represents the vertical polarization of the frequency selective surface 3, TM represents the horizontal polarization, 0-TE represents the vertical polarization corresponding to the incident angle of the electromagnetic wave received by the sandwich structure of 0°, 30-TM represents the horizontal polarization corresponding to the incident angle of the electromagnetic wave received by the sandwich structure of 30°, and so on. Figure 3 and Figure 4The filtering characteristic curves of TE polarization and TM polarization under different incident angles are shown. It can be seen that under TE polarization and TM polarization, the sandwich structure has higher transmittance and better angular stability. Figure 5 The following is a comparison of the filtering characteristic curves of TE and TM at different incident angles. The horizontal coordinates of all the curves are frequency (GHz) and the vertical coordinates are transmittance (%). Figure 5 It can be seen that the curves in the two polarization conditions are in good agreement, and have good polarization stability.

[0036] For the second solution of the embodiment of the present invention, the dielectric constant of the first material layer 1 is set to 4.2, the loss tangent is set to 0.01, and the thickness is set to is 0.5 mm, the dielectric constant of the second material layer 2 is 1.1, the number of layers is 3, the loss tangent is 0.005, and the thickness is 4 mm, the dielectric constant of the polyimide material layer 4 is 3, the number of layers is 3, the loss tangent is 0.005, and the thickness is The frequency selective surface 3 has three layers, and the three branches of the Y ring unit on the frequency selective surface 3 have the same shape and size, wherein the periodic size of the Y ring unit is: the center distance between any two adjacent Y ring units in the lateral direction is 10 mm, that is, , the center distance between any two adjacent Y ring units in the longitudinal direction is 5.776 mm, that is, Among the three branches, the major axis of the outer edge ellipse is 4.6 mm and the minor axis is 2.2 mm, that is, a=4.6mm, b=2.2mm, and the major axis of the inner edge is 3.8 mm and the minor axis is 1 mm, that is, c=3.8mm, d=1mm.

[0037] The simulation results are as follows Figure 6 , Figure 7 and Figure 8 As shown, the filter characteristic simulation curve is as follows Figure 6 and Figure 7 As shown, the sandwich structure has good angular stability under TE polarization and TM polarization, and because it is a multi-layer elliptical frequency selective surface 3 structure, it has a certain widening effect on the passband bandwidth. Figure 8 The polarization stability of the structure of the multilayer elliptical frequency selective surface 3 is shown. The horizontal coordinates of all the curves are frequency (GHz) and the vertical coordinates are transmittance (%). In the passband part, the polarization stability is greatly improved. At the same time, it can be seen from the curve that the multilayer sandwich structure has a wider effective bandwidth, compared with the single-layer sandwich structure, that is, the corresponding relatively smooth section on the curve is longer.

[0038] Although the embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and cannot be understood as limiting the present invention. Those skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

[0039] The above specific implementations of the present invention do not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A sandwich structure comprising a frequency selective surface, characterized in that include: two first material layers, at least one second material layer and at least one frequency selective surface; The two first material layers are respectively located at the uppermost layer and the lowermost layer of the sandwich structure; The second material layer is located between the two first material layers and arranged layer by layer; The frequency selective surface is located between two adjacent second material layers or between an adjacent first material layer and a second material layer; The frequency selection surface is provided with Y-ring units, which are arranged periodically; the Y-ring units have three branches, and the center line angle between any two branches is 120°; the inner edges and outer edges of the three branches are arc-shaped.

2. The sandwich structure comprising a frequency selective surface according to claim 1, characterized in that: The dielectric constant of the first material layer is greater than the dielectric constant of the second material layer.

3. The sandwich structure comprising a frequency selective surface according to claim 1, characterized in that: A polyimide material layer is disposed under any layer of the frequency selective surface.

4. The sandwich structure comprising a frequency selective surface according to claim 1, characterized in that: When the second material layer is a plurality of layers, the frequency selective surface is located between two adjacent second material layers; when the second material layer is a single layer, the frequency selective surface is located between adjacent first material layer and second material layer.

5. The sandwich structure comprising a frequency selective surface according to claim 4, characterized in that: When the second material layer is a multilayer, a frequency selective surface is disposed between every two adjacent second material layers.

6. The sandwich structure comprising a frequency selective surface according to claim 1, characterized in that: The arc is an ellipse.

7. The sandwich structure comprising a frequency selective surface according to claim 1, characterized in that: In the transverse arrangement period of the Y ring units, the center distance between any two adjacent Y ring units is greater than one times the maximum transverse dimension of the Y ring units and less than two times the maximum transverse dimension of the Y ring units.

8. The sandwich structure comprising a frequency selective surface according to claim 7, characterized in that: In the longitudinal arrangement period of the Y ring units, the center distance between any two adjacent Y ring units is less than one times the longitudinal maximum dimension of the Y ring units.

9. The sandwich structure comprising a frequency selective surface according to claim 1, characterized in that: The material of the frequency selective surface is copper.

10. The sandwich structure comprising a frequency selective surface according to claim 1, characterized in that: Any adjacent material layers of the sandwich structure are connected by gluing.

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