Miniaturized active frequency selective surface based on curling structure

Abstract

The invention belongs to the technical field of electronic functional materials, and particularly relates to a miniaturized active frequency selective surface based on a curling structure. According to the invention, two different types of cross curling structure frequency selection surfaces of a communication type and an interval type are cascaded up and down, so that double wave-transparent frequency bands are generated at low frequency; the frequency selective surface with a centrosymmetric pattern is adopted, and polarization stability is achieved; and a fractal structure FSS is used for loading a PIN diode, so that dual-band electromagnetic on / off active regulation and control can be realized at low frequency. The invention further provides a scheme adopting a Wheatstone bridge feed circuit, and electromagnetic coupling between the feed circuit and the structure is reduced. The first working frequency band is in the P and L wave bands, the second working frequency band is in the S wave band, the working range covers the P wave band to the S wave band, and the antenna has excellent angle stability and has great potential in application in the aspects of electromagnetic transmission regulation and control, low-frequency communication and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of electronic functional materials, and specifically is a miniaturized active frequency selective surface based on a curling structure, which is mainly used for low-frequency radar communication and electromagnetic control. Background Art

[0002] In the past decade, due to the space limitations in practical applications, miniaturized frequency selective surfaces (FSS) for low-frequency communications have attracted widespread attention. By utilizing the FSS of miniaturized components, enough periodic resonant units can be accommodated in a limited space to achieve the characteristics of a bandpass filter. Compared with traditional FSS, micro-component FSS exhibits better resonance stability under oblique incidence conditions, which helps to improve the antenna performance within the operating frequency band, and at the same time can move the grating area away from the operating frequency band to improve the out-of-band stealth shielding or stealth performance.

[0003] A variety of methods have been proposed to reduce the unit size of FSS, including loading lumped elements, using fractal patterns and metamaterial-based elements, bending interdigitation technology, and 2.5-dimensional and 3-dimensional FSS structures. Among them, loading lumped elements is considered to be an effective way. Active components are often used in FSS structure design to achieve electrically controlled regulation characteristics due to their advantages in high switching speed, compact size and low cost. At present, most electromagnetic switch designs are only targeted at a single low-frequency band, making it difficult to achieve simultaneous regulation of multiple low-frequency bands, and there is a disadvantage of poor angular stability. In addition, the electromagnetic coupling between the additional feeding line and the structure of the traditional external excitation source will affect the performance of the electromagnetic switch. Therefore, it is a key task in this field to design and prepare an electromagnetic switch that works in the low-frequency range, reduces the influence of the feeding line, and achieves independent regulation of electromagnetic wave reflection / shielding in multiple frequency bands, and has excellent angular stability, low profile thickness, and light weight. Summary of the invention

[0004] In view of the above-mentioned problems or shortcomings, in order to solve the problems of single function, narrow control band and optimization of external excitation feeding line of current low-frequency electromagnetic switch, and to improve the control performance of current AFSS (active frequency selective surface) electromagnetic switch at low frequency; the present invention provides a miniaturized active frequency selective surface based on a curled structure, which has the characteristics of miniaturization, light weight, low profile, polarization insensitivity and excellent incident angle stability. The AFSS electromagnetic switch can realize active control switching of low-frequency single / dual-band electromagnetic passband on / off.

[0005] To achieve the above-mentioned purpose of the invention, the technical solution of the present invention is as follows:

[0006] A miniaturized active frequency selective surface based on a curled structure is arranged with a square with a period of P as a structural unit. The structural unit includes a five-layer structure of a connected cross-curled structure frequency selective surface, a first dielectric layer, a spaced cross-curled structure frequency selective surface, a second dielectric layer and a fractal structure active frequency selective surface stacked in sequence from top to bottom. The physical centers of the layers coincide in the thickness direction, and the projection of the entire structural unit in the thickness direction is a square with a side length of P.

[0007] The first and second dielectric layers are both square dielectrics with a side length of P (ie, the range of the structural unit period P), and are completely overlapped in the thickness direction. The three-layer frequency selective surface is isolated by the first and second dielectric layers.

[0008] The connected cross-curled frequency selective surface is a layer of metal pattern centrally arranged on the first dielectric layer, the metal pattern has four identical rectangular ends, each of which is arranged in a manner that its two adjacent sides are adaptively aligned with the two corner sides of one corner of the first dielectric layer; the center of the metal pattern is a metal pattern of a cross structure, the four branch metal lines of the cross structure are all S3 in width and S4 in length, and are respectively perpendicular to one side of the square dielectric, and respectively extend along the four branch metal lines in a right-angle curling manner to the perpendicular square dielectric side until they are connected with the rectangular end, and the ends of the four branch metal lines correspond to the four rectangular ends; the curling gap distance of the four branch metal lines, the closest gap distance between adjacent branch metal lines, and the distance between the outermost branch metal line and the nearest square dielectric side after extension are all S2. The length of one side of the rectangular end is S1, and the length of the other side is S2+S3, and the wide side of the outermost branch metal line is finally adaptively aligned with the side of the rectangular end with a length of S2+S3.

[0009] The spaced cross-curled structure frequency selective surface is a layer of metal pattern centrally arranged between the first dielectric layer and the second dielectric layer. Compared with the metal pattern of the connected cross-curled structure frequency selective surface, the metal pattern only lacks a rectangular end. The distance between the wide side of the end of the four branch metal lines and the nearest square dielectric side is d, 0<d<2(S2+S3).

[0010] The fractal structure active frequency selection surface is a layer of metal pattern centrally arranged under the second dielectric layer, including four completely identical metal pattern fractal units and four PIN diodes; the fractal unit is an L-shape with two equal right angles widened to l1, and is arranged in a manner that the two long right angles of the L-shape are adaptively aligned with the two angles of one corner of the second dielectric layer, and the four fractal units are aligned one by one with the four corners of the second dielectric layer; the four fractal units are centrally symmetrical about the center point of the second dielectric layer, the wide sides of two adjacent fractal units are parallel sides with a spacing of l2, l2>0, and the wide sides of two adjacent fractal units are bridged by a PIN diode, with a total of four PIN diodes; one selected fractal unit is connected to the positive electrode of the PIN diode, and the fractal units at the diagonal positions are connected to the negative electrode of the PIN diode.

[0011] The arrangement cycle is specifically as follows: the structural units are tightly arranged in a matrix manner to form an n×m matrix, and then the metal graphic fractal units of the outermost fractal structure active frequency selective surface are respectively connected to the positive feed line and the negative feed line, and then connected to the external bias power supply through the circuit wire, thus forming an AFSS active frequency selective surface electromagnetic switch, where n and m are both greater than 2.

[0012] Furthermore, the metal materials of the three frequency selective surfaces are selected from copper, aluminum, gold or silver.

[0013] Furthermore, the material of the first dielectric layer and the second dielectric layer is selected from one of a polytetrafluoroethylene dielectric substrate, a polyimide dielectric substrate, a glass fiber reinforced epoxy resin dielectric substrate and a polyethylene terephthalate dielectric substrate.

[0014] Furthermore, after the structural units are closely arranged in a matrix to form an n×m matrix, structural units are added outwardly on the four sides of the n×m matrix in a row-by-row / row-by-row gradient decreasing manner, and then the positive feed line and the negative feed line are connected to achieve a better external excitation feed line.

[0015] Furthermore, the row-by-row / line-by-row gradient reduction is performed on at least two of the four edges of the n×m matrix.

[0016] Furthermore, the gradient is decreased in such a way that both ends of each added row / column are decreased in gradient.

[0017] Furthermore, the gradient is decreased in such a way that both ends of each added row / column are decreased in gradient, and the number of decreases is one at each end.

[0018] Furthermore, both ends of each added row / column are gradually decreased until the number of structural units in the outermost row / column is 1 or 2.

[0019] In summary, compared with the traditional low-frequency electromagnetic switch AFSS, the structural unit of the present invention adopts two different types of cross-curled structure frequency selection surfaces, connected type and spaced type, cascaded up and down, so that it can produce dual-wave transmission bands at low frequency, solving the problem of difficulty in realizing multi-band electromagnetic passband on / off active regulation at low frequency; because the three layers of frequency selection surfaces are all centrally symmetrical patterns, it has the polarization stability of the overall structural unit; and supplemented by the fractal structure FSS loaded with PIN diodes, it can realize dual-band electromagnetic on / off regulation at low frequency. Through simulation experiments, it is shown that the first working frequency band is in the P and L bands, and the second working frequency band is in the S band. The working range covers the P to S bands and has excellent angular stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the overall three-dimensional structure of the structural unit of the present invention;

[0021] Figure 2 It is a schematic structural diagram of a frequency selective surface of a connected cross-curled structure according to the present invention;

[0022] Figure 3 It is a schematic structural diagram of the frequency selective surface of the interval type cross curl structure of the present invention;

[0023] Figure 4 It is a structural schematic diagram of the fractal structure active frequency selective surface of the present invention;

[0024] Figure 5 is a schematic structural diagram of an AFSS active frequency selective surface electromagnetic switch according to an embodiment;

[0025] Figure 6 is a transmission characteristic curve variation diagram of the AFSS on / off state under different incident angles in the TE polarization mode of the embodiment;

[0026] Figure 7 1 is a graph showing the change in transmission characteristic curves of the AFSS on / off state at different incident angles in the TM polarization mode of the embodiment.

[0027] Figure numerals: 1-connected cross-curled structure frequency selective surface, 2-first dielectric layer, 3-interval cross-curled structure frequency selective surface, 4-second dielectric layer, 5-fractal structure active frequency selective surface, 51-fractal unit, 52-PIN diode, 61-bias power supply, 62-circuit conductor, 63-positive feeding line, 64-negative feeding line. DETAILED DESCRIPTION

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

[0029] Example

[0030] A miniaturized active frequency selective surface based on a curled structure is arranged with a square as a structural unit. The structural unit includes a five-layer structure of a connected cross-curled structure frequency selective surface, a first dielectric layer, a spaced cross-curled structure frequency selective surface, a second dielectric layer and a fractal structure active frequency selective surface stacked in sequence from top to bottom. The physical centers of the layers coincide in the thickness direction, and the projection of the entire structural unit in the thickness direction is a square with a side length of P.

[0031] The overall three-dimensional structure of the structural unit is as follows Figure 1 shown. Figure 2 This is a schematic diagram of the structure of a connected cross-curled frequency selective surface. Figure 3 This is a schematic diagram of the structure of the frequency selective surface with an interval cross-curl structure. Figure 4 It is a structural schematic diagram of a fractal structure active frequency selective surface.

[0032] In this embodiment: copper is selected as the material of the three frequency selective surfaces; the dielectric layer is selected from Rogers 4350B dielectric substrate, with a dielectric constant of 3.48 and a loss tangent of 0.0037; the thickness of the first dielectric layer 2 is 1.2 mm, and the thickness of the second dielectric layer 4 is 0.254 mm. The model of the PIN diode is SMPA1345-040LF; a miniaturized active frequency selective surface based on a curled structure with an area of ​​300 mm×300 mm is manufactured.

[0033] Arrangement cycle: Arrange the structural units to form a 3×3 matrix, and add a centered structural unit outward in the row and column directions of the matrix. After the arrangement, the bottom fractal structure active frequency selective surface is used as a schematic diagram; then the metal graphic fractal unit of the fractal structure active frequency selective surface at the outermost edge is connected to the positive feed line and the negative feed line respectively, and then connected to the external bias power supply through the circuit wire to form the AFSS active frequency selective surface electromagnetic switch of the embodiment, such as Figure 5 shown.

[0034] The other detailed structural parameters of the miniaturized active frequency selective surface based on the curled structure of this embodiment are as follows:

[0035]

[0036] Figure 6It is a transmission characteristic curve variation diagram of the AFSS on / off state under different incident angles of the TE polarization mode of this embodiment; it can be seen that under TE polarization, as the incident angle of the electromagnetic wave increases, the transmission coefficient of the AFSS off state decreases slightly, but the transmission pole remains unchanged, and the transmission poles are 1.09GHz and 2.33GHz respectively. The transmission coefficient of the AFSS on state also decreases slightly with the increase of the incident angle. When the incident angle is 0°, the difference between the AFSS on / off state at the first transmission pole is 22.75dB, and the difference at the second transmission pole is 18.40dB; when the incident angle is 60°, the difference between the AFSS on / off state at the first transmission pole is 26.17dB, and the difference at the second transmission pole is 21.78dB, indicating that the AFSS has good switching characteristics.

[0037] Figure 7 It is a transmission characteristic curve variation diagram of the AFSS on / off state under different incident angles of the TM polarization mode of this embodiment; it can be seen that under TM polarization, as the incident angle of the electromagnetic wave increases, the transmission coefficient of the AFSS off state increases slightly, but the transmission pole remains unchanged, and the transmission poles are 1.09GHz and 2.33GHz respectively. The transmission coefficient of the AFSS on state also increases slightly with the increase of the incident angle. When the incident angle is 0°, the difference between the AFSS on / off state at the first transmission pole is 22.75dB, and the difference at the second transmission pole is 18.40dB; when the incident angle is 60°, the difference between the AFSS on / off state at the first transmission pole is 14.56dB, and the difference at the second transmission pole is 10.67dB, indicating that the AFSS has good switching characteristics.

[0038] It can be seen from the above embodiments that the structural unit of the present invention adopts two different types of cross-curled structure frequency selection surfaces, connected type and spaced type, cascaded up and down, so that it produces dual wave transmission bands at low frequency, solving the problem that it is difficult to realize active regulation of multi-band electromagnetic passband on / off at low frequency; because three layers of frequency selection surfaces are used, which are all centrally symmetrical patterns, it has the polarization stability of the overall structural unit; and supplemented by fractal structure FSS loaded PIN diodes, it can achieve switching of electromagnetic wave reflection / shielding at low frequency. It also further provides a solution using a Wheatstone bridge feed line to reduce the electromagnetic coupling between the feed line and the structure. The first working frequency band is in the P and L bands, and the second working frequency band is in the S band. The working range covers the P to S bands, and has excellent angle stability and good polarization insensitivity; it has great potential for application in electromagnetic transmission regulation, low-frequency communication, etc.

Claims

1. A miniaturized active frequency selective surface based on a curled structure, characterized in that: The structure unit is composed of a square with a period of P, and the structure unit includes a five-layer structure of a connected cross-curled structure frequency selective surface, a first dielectric layer, a spaced cross-curled structure frequency selective surface, a second dielectric layer and a fractal structure active frequency selective surface stacked in sequence from top to bottom, the physical center of each layer coincides in the thickness direction, and the projection of the entire structure unit in the thickness direction is a square with a side length of P; The first and second dielectric layers are both square dielectrics with a side length of P, and completely overlap in the thickness direction, and the three-layer frequency selective surface is isolated by the first and second dielectric layers; The connected cross-curled structure frequency selective surface is a layer of metal graphics centrally arranged on the first dielectric layer, the metal graphics has four identical rectangular ends, and each rectangular end is arranged in a manner that its two adjacent sides are adaptively aligned with the two corner sides of a corner of the first dielectric layer; the center of the metal graphics is a cross-structured metal graphics, and the four branch metal lines of the cross structure are all S3 in width and S4 in length, and are respectively perpendicular to one side of the square dielectric, and respectively extend along the four branch metal lines in a right-angle curling manner to the perpendicular square dielectric side until they are connected with the rectangular end, and the ends of the four branch metal lines correspond to the four rectangular ends; the curling gap distance of the four branch metal lines, the closest gap distance between adjacent branch metal lines, and the distance between the outermost branch metal line and the nearest square dielectric side after extension are all S2; the length of one side of the rectangular end is S1, and the length of the other side is S2+S3, and the wide side of the outermost branch metal line is finally adaptively aligned and connected with the side of the rectangular end with a length of S2+S3; The interval type cross curl structure frequency selective surface is a layer of metal pattern centrally arranged between the first dielectric layer and the second dielectric layer. Compared with the metal pattern of the connected cross curl structure frequency selective surface, the metal pattern lacks only a rectangular end. The distance between the wide side of the end of the four branch metal lines and the nearest square dielectric side is d, 0<d<2(S2+S3); The fractal structure active frequency selective surface is a layer of metal pattern centrally arranged under the second dielectric layer, including four completely identical metal pattern fractal units and four PIN diodes; the fractal unit is an L-shape with two equal right angles widened to l1, and the two long right angles of the L-shape are arranged in a manner of adaptively aligning the two angles of one corner of the second dielectric layer, and the four fractal units are aligned one by one with the four corners of the second dielectric layer; the four fractal units are centrally symmetrical about the center point of the second dielectric layer, the wide sides of two adjacent fractal units are parallel sides with a spacing of l2, l2>0, and the wide sides of two adjacent fractal units are bridged by a PIN diode, with a total of four PIN diodes; one fractal unit is selected to be connected to the positive electrode of the PIN diode, and the fractal units at the diagonal positions are connected to the negative electrode of the PIN diode; The arrangement cycle is specifically as follows: the structural units are tightly arranged in a matrix manner to form an n×m matrix, and then the metal graphic fractal units of the outermost fractal structure active frequency selective surface are respectively connected to the positive feed line and the negative feed line, and then connected to the external bias power supply through the circuit wire, thus forming an AFSS active frequency selective surface electromagnetic switch, where n and m are both greater than 2.

2. The miniaturized active frequency selective surface based on the curled structure as claimed in claim 1, characterized in that: The metal materials of the three frequency selective surfaces are selected from copper, aluminum, gold or silver.

3. The miniaturized active frequency selective surface based on the curled structure as claimed in claim 1, characterized in that: The material of the first dielectric layer and the second dielectric layer is selected from one of a polytetrafluoroethylene dielectric substrate, a polyimide dielectric substrate, a glass fiber reinforced epoxy resin dielectric substrate and a polyethylene terephthalate dielectric substrate.

4. The miniaturized active frequency selective surface based on the curled structure as claimed in claim 1, characterized in that: After the structural units are closely arranged in a matrix to form an n×m matrix, structural units are added outwardly on the four sides of the n×m matrix in a row-by-row / line-by-line gradient decreasing manner, and then the positive feed line and the negative feed line are connected.

5. The miniaturized active frequency selective surface based on the curled structure as claimed in claim 4, characterized in that: The row-by-row / line-by-line gradient reduction is performed by selecting at least two of the four edges.

6. The miniaturized active frequency selective surface based on the curled structure as claimed in claim 4, characterized in that: The gradient is decreased in such a way that both ends of each added row / column are decreased in gradient.

7. The miniaturized active frequency selective surface based on the curled structure as claimed in claim 4, characterized in that: The gradient is decreased in such a way that both ends of each added row / column are decreased in gradient, and the number of decreased gradients is one at each end.

8. The miniaturized active frequency selective surface based on the curled structure as claimed in claim 4, characterized in that: Both ends of each added row / column are gradually decreased until the number of structural units in the outermost row / column is 1 or 2.

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