Dual-polarization three-dimensional frequency selective surface suitable for large incident angle

Abstract

The invention discloses a dual-polarization three-dimensional frequency selective surface suitable for a large incident angle, the three-dimensional frequency selective surface is formed by periodically arranging a plurality of three-dimensional frequency selective surface units with the same structure, and each three-dimensional frequency selective surface unit comprises an outer layer medium, the polygonal metal ring and the multi-bending metal ring are embedded in the outer layer medium, the polygonal metal ring is of an axial symmetry structure, the multi-bending metal ring is of a central symmetry structure, the two ends of the polygonal metal ring and the two ends of the multi-bending metal ring are in contact connection, the polygonal metal ring and the multi-bending metal ring are perpendicular to each other, and dual-polarization filtering under the large incident angle is achieved. According to the three-dimensional frequency selective surface, through the combined action of the two metal rings and the dielectric layer, the frequency selective surface can achieve a large passband and low insertion loss under the condition of large-angle incidence of electromagnetic waves.

Description

Technical Field

[0001] The present invention relates to the technology of aircraft frequency selective radomes, and particularly to a dual-polarized three-dimensional frequency selective surface applicable to large incident angles. Background Art

[0002] Generally, the normal incidence effect is an important index for evaluating the performance of frequency selective surfaces. However, in practical applications, most are large-angle incidences. For example, since the relative distance between a radar and an aircraft is usually much larger than the relative height between the radar and the aircraft, the electromagnetic wave can be regarded as irradiating the aircraft along a direction parallel to the ground, and part of the fuselage is in the situation of being incident by the electromagnetic wave at a large angle. However, in the current research on frequency selective surfaces, traditional two-dimensional frequency selective surfaces adopt single-layer or multi-layer planar unit structures, mostly metal patterns printed on dielectric substrates, whose structural plane and periodic plane are in the same plane. Under the condition of large incident angles, their regulation ability is limited, and there are often problems such as frequency response drift and increased insertion loss, which cannot meet the high-performance requirements of today's communication and radar systems, restricting their application in high-performance communication systems. Summary of the Invention

[0003] Object of the Invention: The object of the present invention is to provide a dual-polarized three-dimensional frequency selective surface applicable to large incident angles, achieving a larger passband and lower insertion loss.

[0004] Technical Solution: The dual-polarized three-dimensional frequency selective surface applicable to large incident angles of the present invention is composed of a plurality of three-dimensional frequency selective surface units with the same structure arranged periodically. The three-dimensional frequency selective surface unit includes an outer layer of dielectric, and a polygonal metal ring and a multi-bent metal ring embedded in the outer layer of dielectric. The polygonal metal ring is an axisymmetric structure, and the multi-bent metal ring is a centrosymmetric structure. The two ends of the polygonal metal ring and the multi-bent metal ring are in contact connection, and the polygonal metal ring and the multi-bent metal ring are perpendicular to each other to achieve dual-polarized filtering under large incident angles.

[0005] Optionally, the polygonal metal ring is a quadrilateral metal ring, a hexagonal metal ring or an octagonal metal ring.

[0006] Optionally, the multi-bent metal ring includes a first bent metal strip and a second bent metal strip, and the first bent metal strip and the second bent metal strip are bent multiple times in sequence to be in a shape similar to an "M".

[0007] Optionally, the polygonal metal ring is cut from a complete rectangular sheet.

[0008] Optionally, the multi-bent metal ring is cut from a complete metal sheet, and then divided into two parts, which are respectively pasted on both sides of the polygonal metal ring to form a closed metal ring.

[0009] Optionally, the three-dimensional frequency selective surface is composed of a periodic array arrangement of N×N three-dimensional frequency selective surface units, where N is a natural number greater than or equal to 1.

[0010] Optionally, the outer medium is made of a non-magnetic material with a dielectric constant in the range of 2.0 to 2.5 and a loss angle in the range of 0.008 to 0.02.

[0011] Optionally, the material of the polygonal metal ring is a conductive metal.

[0012] Optionally, the material of the multi-bent metal ring is a conductive metal.

[0013] Optionally, the three-dimensional frequency selective surface is applicable to the frequency selective cover of an aircraft.

[0014] Advantageous effects: Compared with the prior art, the remarkable technical effects of the present invention are as follows: In the case of large-angle incidence of electromagnetic waves, the 3D structure of the present invention makes the present invention insensitive to large-angle incidence. The equivalent sizes of the polygonal metal ring and the multi-bent metal ring are matched, avoiding the frequency shift of the resonance point and the change of the overall impedance of the three-dimensional frequency selective surface caused by the change of the equivalent inductance or capacitance value, thereby avoiding the reduction of the bandwidth or the increase of the in-band insertion loss, and achieving a larger passband and a lower insertion loss. Description of the Drawings

[0015] Figure 1 It is a schematic three-dimensional structure diagram of a dual-polarized three-dimensional frequency selective surface unit with a large incident angle in a specific embodiment of the present invention;

[0016] Figure 2 It is a front view of a dual-polarized three-dimensional frequency selective surface unit with a large incident angle in a specific embodiment of the present invention;

[0017] Figure 3 It is a left view of a dual-polarized three-dimensional frequency selective surface unit with a large incident angle in a specific embodiment of the present invention;

[0018] Figure 4 It is a top view of a dual-polarized three-dimensional frequency selective surface unit with a large incident angle in a specific embodiment of the present invention;

[0019] Figure 5 It is a frequency response diagram of a dual-polarized three-dimensional frequency selective surface unit applicable to a large incident angle of the present invention. Specific Embodiments

[0020] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention and the corresponding drawings. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of this application.

[0021] The following will describe in detail the technical solutions provided by the embodiments of this application with reference to the drawings.

[0022] The dual-polarized three-dimensional frequency selective surface applicable to large incident angles in the present invention is composed of a periodic array of N×N three-dimensional frequency selective surface unit cells, where N is a natural number greater than or equal to 1. The unit structure of the dual-polarized three-dimensional frequency selective surface for large incident angles includes an external dielectric layer and two metal rings. In the case of large-angle incidence, the three-dimensional frequency selective surface avoids the frequency shift of the resonance point and the change of the overall impedance of the three-dimensional frequency selective surface caused by the change of the equivalent inductance or capacitance value, thereby avoiding the reduction of the bandwidth or the increase of the in-band insertion loss, and achieving a larger passband and a lower insertion loss.

[0023] Refer to Figure 1 , Figure 1 which is a schematic diagram of the three-dimensional structure of an optional dual-polarized three-dimensional frequency selective surface unit in the specific embodiment of the present invention; the three-dimensional frequency selective surface is formed by periodically arranging a number of three-dimensional frequency selective surface units with the same structure. The three-dimensional frequency selective surface unit includes an outer dielectric layer 1, a polygonal metal ring 2, and a multi-bent metal ring 3. The polygonal metal ring 2 and the multi-bent metal ring 3 are both embedded in the outer dielectric layer 1, and the two ends of the polygonal metal ring 2 and the multi-bent metal ring 3 are connected.

[0024] Refer to Figure 2 , Figure 2 which is a front view of an optional dual-polarized three-dimensional frequency selective surface unit with a large incident angle in the specific embodiment of the present invention. In the figure: the polygonal metal ring 2 and the multi-bent metal ring 3 are perpendicular to each other to meet the requirements of dual-polarized filtering. The perpendicular metal rings form independent periodic structures in two perpendicular directions. For horizontally polarized waves, the metal rings in the vertical direction can control the resonance frequency by adjusting their lengths and spacings; conversely, the metal rings in the horizontal direction can regulate the response of vertically polarized waves. Moreover, the symmetry of the perpendicular structure reduces the coupling between polarizations. When electromagnetic waves are incident in a certain polarization direction, the corresponding metal ring dominates its response, and the structure in the orthogonal direction has little influence on the other polarized wave. This decoupling effect avoids the generation of cross-polarization components and ensures that the filtering performances of the two polarization modes do not interfere with each other. Therefore, the two metal rings being perpendicular to each other can meet the requirements of dual-polarized filtering.

[0025] Refer toFigure 3 , Figure 3 This is the left view of a dual-polarized three-dimensional frequency selective surface unit with a large incident angle, which is an optional one in the specific embodiments of the present invention. In the figure: The polygonal metal ring 2 has an axisymmetric structure, and the three-dimensional annular structure of the polygonal metal ring 2 satisfies the equivalent size matching. From the direction of electromagnetic wave incidence, the three-dimensional annular structure is different from the planar structure. When designing, the shape of the metal ring can be adjusted in the vertical space according to different electromagnetic wave incident angles to meet the equivalent size matching.

[0026] In this embodiment, the polygonal metal ring 2 is a quadrilateral metal ring, which is cut from a complete rectangular sheet and is included in the outer layer medium 1. The polygonal metal ring 2 can also be a hexagonal metal ring, an octagonal metal ring, etc.

[0027] Refer to Figure 4 , which is the top view of a dual-polarized three-dimensional frequency selective surface unit with a large incident angle, which is an optional one in the specific embodiments of the present invention. In the figure: The multi-bent metal ring 3 has a centrosymmetric structure, and the three-dimensional annular structure of the multi-bent metal ring 3 satisfies the equivalent size matching. Adding two bends is for better matching. The multi-bent metal ring 3 is cut from a complete metal sheet, and then divided into two parts, which are respectively attached to both sides of the polygonal metal ring 2 to form a closed metal ring, and is included in the outer layer medium 1. In this embodiment, the multi-bent metal ring 3 includes a first bent metal strip and a second bent metal strip. After the first bent metal strip and the second bent metal strip are bent multiple times in sequence, they are in a shape similar to an "M".

[0028] In this embodiment, the outer layer medium 1 uses a non-magnetic material, the dielectric constant ranges from 2.0 to 2.5, and the loss angle ranges from 0.008 to 0.02. The materials of the polygonal metal ring 2 and the multi-bent metal ring 3 are both conductive metals.

[0029] The three-dimensional frequency selective surface (FSS) enables a larger passband and lower insertion loss under large-angle incidence of electromagnetic waves through the combined action of two metal rings and an outer dielectric. Electromagnetic waves in space are generally divided into two polarization modes: TE mode and TM mode. Under different polarization modes, as the incident angle changes, the free-space wave impedance of the mode will change. Under large-angle incidence of electromagnetic waves, the equivalent size of the structure will be distorted due to the incident angle. Also, since the free-space wave impedance of different polarization modes also varies with the incident angle, the equivalent inductance or capacitance value will change, which will cause a frequency shift of the resonance point and a change in the overall impedance of the frequency selective surface, thereby leading to impedance mismatch, resulting in a reduction in bandwidth or an increase in in-band insertion loss. Compared with the two-dimensional FSS, the three-dimensional FSS is more likely to achieve equivalent size matching under large-angle incidence, avoiding the frequency shift of the resonance point and the change in the overall impedance of the three-dimensional FSS caused by the change in the equivalent inductance or capacitance value under large incident angles, thus avoiding a reduction in bandwidth or an increase in in-band insertion loss and achieving a larger passband and lower insertion loss.

[0030] In a two-dimensional frequency selective surface, generally, when the electric field direction is parallel to the metal strip, the metal strip supports current flow and exhibits inductance. When the electric field direction is perpendicular to the metal strip, the gap between the metal strips forms a capacitor and exhibits capacitance. The parameters of the equivalent LC resonance circuit will change significantly due to the change in the incident angle, resulting in a resonance frequency shift. The three-dimensional structure, through vertical layering, introduces additional equivalent circuit elements (such as the bends of the multi-bent metal ring 3), reducing the dependence of the total impedance on the incident angle. At the same time, in the three-dimensional space, during the design of the three-dimensional structure, the structure of the two metal rings can be adjusted to meet the equivalent size matching, avoiding the change in the equivalent inductance or capacitance directly caused by the increase in the incident angle, thus avoiding the frequency shift of the resonance point and the change in the overall impedance of the frequency selective surface. Additionally, in the vertical direction, the three-dimensional structure design enables the electromagnetic field energy to be more evenly distributed in the three-dimensional space rather than concentrated on the surface. This distribution is less sensitive to the change in the incident angle, thereby reducing the resonance frequency shift.

[0031] The three-dimensional frequency selective surface solves the problems existing in the traditional two-dimensional frequency selective surface, such as frequency response drift and increased insertion loss, and is applicable to applications such as aircraft frequency selective radomes.

[0032] To further illustrate the technical effects of this solution, based on the foregoing solution settings, a simulation analysis was carried out to examine the performance of the three-dimensional frequency selective surface with dual polarization under large-angle incidence; see Figure 5As shown, 65° incidence is selected, and the frequency response at 65° incidence is given. The bandwidth range evaluated by the insertion loss of 1 dB is approximately 6.3 - 13.2 GHz, with a width of 6.9 GHz and a relative bandwidth of approximately 71%.

[0033] The above content is only an example of the specific solution of the present invention. For the devices and structures not described in detail therein, it should be understood that the existing general devices and general methods in the art are adopted for implementation.

[0034] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A dual-polarization three-dimensional frequency selective surface suitable for large incident angles, characterized in that: The three-dimensional frequency selective surface is formed by a periodic arrangement of a plurality of three-dimensional frequency selective surface units with the same structure. The three-dimensional frequency selective surface unit comprises an outer layer medium (1), and a polygonal metal ring (2) and a multi-bend metal ring (3) embedded in the outer layer medium (1). The polygonal metal ring (2) is an axisymmetric structure, and the multi-bend metal ring (3) is a centrosymmetric structure. The two ends of the polygonal metal ring (2) and the multi-bend metal ring (3) are in contact and connected, and the polygonal metal ring (2) and the multi-bend metal ring (3) are perpendicular to each other, so as to realize dual polarization filtering under a large incident angle.

2. The dual-polarization three-dimensional frequency selective surface suitable for large incident angles according to claim 1, characterized in that: The polygonal metal ring (2) is a quadrilateral metal ring, a hexagonal metal ring or an octagonal metal ring.

3. The dual-polarization three-dimensional frequency selective surface suitable for large incident angles according to claim 1, characterized in that: The multi-bend metal ring (3) comprises a first bent metal strip and a second bent metal strip, and the first bent metal strip and the second bent metal strip are bent multiple times in sequence to form an "M" shape.

4. The dual-polarization three-dimensional frequency selective surface suitable for large incident angles according to claim 1, characterized in that: The polygonal metal ring (2) is cut from a complete rectangular sheet.

5. The dual-polarization three-dimensional frequency selective surface suitable for large incident angles according to claim 1, characterized in that: The multi-bend metal ring (3) is cut from a complete metal sheet, which is then divided into two parts and respectively attached to the two sides of the polygonal metal ring (2) to form a closed metal ring.

6. The dual-polarization three-dimensional frequency selective surface suitable for large incident angles according to claim 1, characterized in that: The three-dimensional frequency selective surface is composed of a periodic array of N×N three-dimensional frequency selective surface units, where N is a natural number greater than or equal to 1.

7. The dual-polarization three-dimensional frequency selective surface suitable for large incident angles according to claim 1, characterized in that: The outer layer medium (1) is made of non-magnetic material, with a dielectric constant ranging from 2.0 to 2.5 and a loss angle ranging from 0.008 to 0.

02.

8. The dual-polarization three-dimensional frequency selective surface suitable for large incident angles according to claim 1, characterized in that: The material of the polygonal metal ring (2) is conductive metal.

9. The dual-polarization three-dimensional frequency selective surface suitable for large incident angles according to claim 1, characterized in that: The material of the multi-bend metal ring (3) is conductive metal.

10. The dual-polarization three-dimensional frequency selective surface suitable for large incident angles according to claim 1, characterized in that: The three-dimensional frequency selective surface is suitable for an aircraft frequency selective cover.

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