Low-profile high-order filtering response tri-band frequency selective surface

Abstract

The invention discloses a low-profile high-order filtering response tri-band frequency selective surface, which comprises a plurality of resonance units arranged in an array, each resonance unit comprises three layers of metal patches and two layers of dielectric substrates, one layer of dielectric substrate is arranged between the adjacent layers of metal patches, the three layers of metal patches form a four-order dual-mode resonator, and the two layers of dielectric substrates form a four-order dual-mode resonator. The metal patches on the middle layer form a first-order resonator, and the two resonators jointly generate a five-order three-band filtering response. The antenna has a relatively thin thickness, and is easy to integrate with an advanced radar or communication system.

Description

Technical Field

[0001] The present invention relates to the field of electromagnetic field and microwave technology, and in particular to a three-band frequency selective surface with low profile and high-order filtering response. Background Art

[0002] Frequency selective surfaces (FSSs), as practical spatial filters, have been widely used in radar, antennas, absorbing materials, and electromagnetic compatibility. With the development of advanced radar and communication systems, there is a growing demand for high-performance FSSs to meet the demands of applications such as uplink and downlink frequency separation, spread-spectrum communications, and frequency-hopping communications. These applications typically require FSSs with high-order, low-profile, multi-band, dual-polarization, and relatively wide fractional bandwidth. Traditional bandpass FSSs typically utilize low-order filter responses, but their narrow relative bandwidth and other characteristics cannot meet these growing requirements. To achieve even better performance, FSSs with higher-order filter responses are an effective solution. These approaches include cascading multiple first-order FSSs, three-dimensional FSSs with multiple resonant modes, and substrate-integrated waveguide structures, all of which achieve improved out-of-band suppression and fractional bandwidth. However, these approaches all suffer from complex structures, large size, and the inability to generate multi-frequency responses.

[0003] This time, a dual-mode patch resonator (FSS) can be used to generate more poles within the same size, thereby expanding bandwidth and achieving the desired high-order filtering response. Based on this structure, with the same substrate layer, it can provide twice the number of poles as a single-mode patch resonator FSS, while also featuring a low profile and simple structure. However, existing designs based on this structure suffer from limitations such as an inability to achieve dual polarization and large unit size. Furthermore, current designs can only control either the electrical or magnetic coupling of the dual-mode patch resonator, not both simultaneously, resulting in a lack of design freedom. In some cases, due to the size limitations of the FSS, the desired coupling amplitude cannot be achieved, making it difficult to achieve multi-band filtering performance. These limitations limit their application in advanced radar, electromagnetic compatibility, and communication systems. Therefore, achieving tri-band, dual-polarization, and higher-order filtering response while maintaining a low-profile dual-mode patch resonator structure, while also simultaneously controlling the resonator's electromagnetic coupling, remains a technical bottleneck that needs to be overcome. Summary of the Invention

[0004] In order to overcome the above-mentioned shortcomings and deficiencies of the prior art, an object of the present invention is to provide a three-band frequency selective surface with a low profile and a high-order filtering response.

[0005] The present invention adopts a dual-mode patch resonator structure to achieve a three-band high-order filtering response, which can not only maintain dual polarization and wide fractional bandwidth characteristics, but also simultaneously regulate the electric coupling and magnetic coupling of the dual-mode patch resonator.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A low-profile, high-order filtering response, three-band frequency selective surface includes multiple resonant units arranged in an array. Each resonant unit includes three layers of metal patches and two layers of dielectric substrate. A layer of dielectric substrate is arranged between adjacent layers of metal patches. The three layers of metal patches form a fourth-order dual-mode resonator, and the middle layer of metal patches forms a first-order resonator. The two resonators together produce a fifth-order, three-band filtering response.

[0008] Furthermore, the three layers of metal patches are respectively a first layer of metal patches, a second layer of metal patches and a third layer of metal patches. Each layer of metal patches is provided with four sub-resonance units, and the four sub-resonance units are obtained by rotating 90°, 180° and 270° about the geometric center of each layer of metal patches.

[0009] Furthermore, the sub-resonance unit of the first layer of metal patches is composed of square patches, which adopt a third-order Minkowski fractal structure with a fractal coefficient of 0.5, including a first-order fractal square patch, a second-order fractal square patch and a third-order fractal square patch; the geometric center of the second-order fractal square patch coincides with the four corners of the first-order fractal square patch, and the geometric center of the third-order fractal square patch coincides with the four corners of the second-order fractal square patch.

[0010] Furthermore, two diagonal corners of the third-order fractal square patch are cut off, and the cut off corners are isosceles right triangles.

[0011] Furthermore, the first-order fractal square patch is provided with rectangular slots on four edges.

[0012] Furthermore, the sub-resonance unit of the second layer of metal patch includes a square patch with a rectangular groove in the middle for regulating the magnetic coupling of the dual-mode resonator. A rectangular connecting line extends from each of the four sides of the square patch and is connected to the adjacent sub-resonance unit and the edge of the metal patch for regulating the electrical coupling of the dual-mode resonator.

[0013] Furthermore, the area of ​​the rectangular slot is used to control the magnetic coupling between the dual-mode resonators, and the width of the outwardly extending rectangular connecting line and the gap size between adjacent square patches are used to control the electrical coupling between the dual-mode resonators.

[0014] Furthermore, the rectangular connecting line acts as an inductor, and the four sub-resonance units of the second layer of metal patches are equivalent to capacitors. At this time, the rectangular connecting line lowers the frequency of the first frequency band, thereby separating it from the frequencies of other frequency bands.

[0015] Furthermore, the third layer of metal patches has the same structural dimensions as the first layer of metal patches, the second layer of metal patches is smaller than the first layer of metal patches, and the third-order fractal square patches have a partial protrusion at the diagonal relative to the second layer of metal patches, which is used to enhance the electrical coupling between the first layer of metal patches and the third layer of metal patches.

[0016] Furthermore, the resonant frequency is achieved by changing the electric coupling amount and the magnetic coupling amount. Increasing the electric coupling or decreasing the magnetic coupling increases the overall coupling, which can move the resonant frequencies in the first frequency band and the second frequency band away from each other.

[0017] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0018] (1) The present invention provides a low-profile, high-order filter response, three-band frequency selective surface with a thin thickness, which is easy to integrate with advanced radar or communication systems;

[0019] (2) The embodiment of the present invention introduces fractal technology into the dual-mode patch resonator, reducing the size of the resonant unit while maintaining good triple-band filtering performance;

[0020] (3) The embodiment of the present invention utilizes a fourth-order dual-mode patch resonator and a first-order bandpass resonator to obtain a fifth-order filtering response without the need to introduce a new metal patch layer, thereby avoiding the introduction of insertion loss by the additional metal layer and the increase in processing costs;

[0021] (4) The embodiments of the present invention have a three-band filtering effect with high roll-off and good out-of-band suppression outside the passband, and at the same time have good incident angle stability. The method for achieving high-order filtering performance can control electric coupling and magnetic coupling, increase design freedom, and have a wide range of applications;

[0022] (5) The embodiment of the present invention has a symmetrical unit structure, a simple design, and can achieve dual-polarization filtering response, and has good application prospects in electromagnetic fields such as radar and communication systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a three-dimensional schematic diagram of a three-band frequency selective surface of the present invention;

[0024] Figure 2 Schematic diagram of the decomposition structure of the triple-band frequency selective surface of the present invention;

[0025] Figure 3This is a schematic structural diagram of the first layer of metal patches in the frequency selective surface periodic unit structure of the present invention;

[0026] Figure 4 This is a schematic structural diagram of the second layer of metal patches in the frequency selective surface periodic unit structure of the present invention;

[0027] Figure 5 is a reflection characteristic curve of the frequency selective surface under a certain angle of incidence in an embodiment of the present invention;

[0028] Figure 6 is a transmission characteristic curve of the frequency selective surface under a certain angle of incidence in an embodiment of the present invention. DETAILED DESCRIPTION

[0029] The present invention will be further described in detail below with reference to the examples, but the embodiments of the present invention are not limited thereto.

[0030] Example

[0031] like Figure 1-Figure 4 As shown, a low-profile, high-order filtering response, three-band frequency selective surface is designed according to specified dimensions and includes multiple resonant units arranged in an array. The resonant units comprise three layers of metal patches and two layers of dielectric substrates, with a dielectric substrate layer disposed between adjacent layers of metal patches. Specifically, the resonant units include a first metal patch layer 1, a first dielectric substrate layer 2, a second metal patch layer 3, an adhesive layer 4, a second dielectric substrate layer 5, and a third metal patch layer 6, which are bonded in sequence. The first and second dielectric substrates both have a dielectric constant of 3.5 and a thickness of 0.508 mm.

[0032] Further explanation: The adhesive layer 4 bonds the first dielectric substrate 2 and the second dielectric substrate 5 together, has a dielectric constant of 3.5, and a thickness of 0.1 mm.

[0033] The first metal patch 1, the second metal patch 3, and the third metal patch 6 form a fourth-order dual-mode resonator, while the second metal patch 3 forms a first-order resonator. Together, these two resonators produce a fifth-order, three-band filter response, with deep transmission zeros in both the passband and the transition bands outside the passband to increase the roll-off rate and improve out-of-band suppression. Because the second metal patch 3 is already included in the structure of the fourth-order dual-mode resonator, the first-order resonator constructed solely with the second metal patch 3 eliminates the need for additional metal layers, achieving low-profile and broadband characteristics.

[0034] Further explanation: the materials of the first layer of metal patches, the second layer of metal patches and the third layer of metal patches include copper or silver with good electrical conductivity.

[0035] like Figure 3As shown, each layer of metal patch is provided with four sub-resonance units, and the four sub-resonance units are obtained by rotating 90°, 180°, and 270° about the geometric center of each layer of metal patch.

[0036] The sub-resonance unit of the first layer of metal patches includes square patches, which adopt a third-order Minkowski fractal structure with a fractal coefficient of 0.5, including a first-order fractal square patch 7 (side length L), a second-order fractal square patch 8 (side length 0.5L) and a third-order fractal square patch 9 (side length 0.25L); the geometric center of the second-order fractal square patch coincides with the four corners of the first-order fractal square patch, and the geometric center of the third-order fractal square patch coincides with the four corners of the second-order fractal square patch.

[0037] It is further explained that the initial side length of the first-order square patch is L=2.93 mm.

[0038] Further explanation, such as Figure 3 As shown, the first-order fractal square patch 7 is provided with rectangular slots 10 at the edges thereof, specifically at the midpoints of the edges, so as to extend the current path and further achieve miniaturization.

[0039] The cut corners of the third-order fractal square patch 9 are isosceles right triangles, the length of the right-angled side of the isosceles right triangle is 0.7 mm, and the cut corners formed by the two isosceles triangles are located at two opposite corners of the third-order fractal square patch.

[0040] The third-order fractal square patch has a partially protruding corner relative to the second-layer metal patch, so as to enhance the electrical coupling between the first-layer metal patch and the third-layer metal patch.

[0041] like Figure 4 As shown, the four sub-resonance units of the second layer of metal patch 3 are all composed of a square patch 12 with a rectangular slot in the middle, and the rectangular slot is rotated 90°, 180°, and 270° according to the geometric center of the metal patch.

[0042] It is further explained that the geometric center of the rectangular slot 13 coincides with the geometric center of the square patch 12, and the direction is parallel to the diagonal of the square. The small rectangular connecting line 14 extending from the outside of the square patch 12 is located at the center of each side of the square patch 12 and extends outward so as to connect with the rectangular patch of the adjacent sub-resonance unit and the edge of the metal patch. The area size of the rectangular connecting line is used to control the amount of magnetic coupling between the dual-mode resonators, and the width of the outwardly extending rectangular connecting line and the size of the gap between adjacent square patches are used to control the amount of electrical coupling between the dual-mode resonators. The rectangular connecting line acts as an inductor, pulling down the frequency of the first frequency band so as to separate it from the frequencies of other frequency bands.

[0043] The resonant frequency can be achieved by changing the electric coupling amount and the magnetic coupling amount. Increasing the electric coupling or decreasing the magnetic coupling and increasing the overall coupling can make the resonant frequencies in the first frequency band and the resonant frequencies in the second frequency band move away from each other.

[0044] Further explanation: the structure, size and configuration of the third layer of metal patches are the same as those of the first layer of metal patches, and the size of the second layer of metal patches is smaller than that of the first layer of metal patches.

[0045] like Figure 5 and Figure 6 The figure shows the reflection characteristic curve and transmission coefficient curve of the three-band frequency selective surface with low profile and high-order filtering response provided by an embodiment of the present invention under a certain angle of incidence. At vertical incidence, the center frequencies of the three transmission passbands are 8.08 GHz, 9.77 GHz and 12.29 GHz, respectively. The -3dB bandwidth of the first passband is 2.34 GHz, the -3dB bandwidth of the second passband is 0.26 GHz, and the -3dB bandwidth of the third passband is 2.03 GHz, with fractional bandwidths of 28.9%, 2.7% and 16.5%, respectively. The transmission zero point frequencies outside the passband are 9.48 GHz and 10.54 GHz, with good roll-off performance. The electrical dimensions of the FSS unit in this embodiment are 0.43λ0*0.43λ0*0.027λ0, where λ0 is the free space wavelength of the center frequency of the first passband.

[0046] like Figure 5 and Figure 6 As shown, the reflection characteristic curve and transmission coefficient curve of the three-band frequency selective surface with low profile and high-order filtering response provided by the embodiment of the present invention are basically the same at an incident angle of 0-40°, indicating that the frequency selective surface has good incident angle stability.

[0047] The embodiments provided by this invention can adapt to the requirements of radar and communication systems of different frequency bands by adjusting the structural dimensions. They are particularly suitable for radomes that require multi-band filtering and integration with skins, housings, and other structures. Benefiting from its low profile, high-order filtering, and broadband characteristics, this invention is also suitable for integrated and complex scenarios involving the integration of multi-frequency, common-aperture communication antennas.

[0048] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A three-band frequency selective surface with a low-profile high-order filter response, characterized in that: It includes multiple resonant units arranged in an array, each resonant unit includes three layers of metal patches and two layers of dielectric substrates. A layer of dielectric substrate is arranged between adjacent layers of metal patches. The three layers of metal patches constitute a fourth-order dual-mode resonator, and the middle layer of metal patches constitutes a first-order resonator. The two resonators together produce a fifth-order three-band filtering response.

2. The triple-band frequency selective surface according to claim 1, wherein: The three layers of metal patches are the first layer of metal patches, the second layer of metal patches and the third layer of metal patches. Each layer of metal patches is provided with four sub-resonance units, and the four sub-resonance units are obtained by rotating 90°, 180° and 270° about the geometric center of each layer of metal patches respectively.

3. The triple-band frequency selective surface according to claim 1, wherein: The sub-resonance unit of the first layer of metal patches is composed of square patches, which adopt a third-order Minkowski fractal structure with a fractal coefficient of 0.5, including a first-order fractal square patch, a second-order fractal square patch and a third-order fractal square patch; the geometric center of the second-order fractal square patch coincides with the four corners of the first-order fractal square patch, and the geometric center of the third-order fractal square patch coincides with the four corners of the second-order fractal square patch.

4. The triple-band frequency selective surface according to claim 3, wherein: Two diagonal corners of the third-order fractal square patch are cut off, and the cut off corners are isosceles right triangles.

5. The triple-band frequency selective surface according to claim 4, characterized in that The first-order fractal square patch is provided with rectangular slots on four edges.

6. The triple-band frequency selective surface according to claim 1, wherein: The sub-resonance unit of the second layer of metal patch includes a square patch with a rectangular groove in the middle for regulating the magnetic coupling of the dual-mode resonator. A rectangular connecting line extends from each of the four sides of the square patch to connect to the adjacent sub-resonance unit and the edge of the metal patch for regulating the electrical coupling of the dual-mode resonator.

7. The triple-band frequency selective surface according to claim 6, wherein: The area of ​​the rectangular slot is used to control the magnetic coupling between the dual-mode resonators, and the width of the rectangular connecting line extending outward and the gap size between adjacent square patches are used to control the electric coupling between the dual-mode resonators.

8. The triple-band frequency selective surface according to claim 7, wherein: The rectangular connecting line acts as an inductor, and the four sub-resonant units of the second layer of metal patches are equivalent to capacitors. At this time, the rectangular connecting line lowers the frequency of the first frequency band, thereby separating it from the frequencies of other frequency bands.

9. The triple-band frequency selective surface according to claim 3, wherein: The third layer of metal patches has the same structural dimensions as the first layer of metal patches, the second layer of metal patches is smaller than the first layer of metal patches, and the third-order fractal square patches have a partial protrusion at the diagonal relative to the second layer of metal patches, which is used to enhance the electrical coupling between the first layer of metal patches and the third layer of metal patches.

10. The triple-band frequency selective surface according to claim 7, wherein: The resonant frequency is achieved by changing the electric coupling and the magnetic coupling. Increasing the electric coupling or decreasing the magnetic coupling increases the overall coupling, which can move the resonant frequencies in the first frequency band and the second frequency band away from each other.

Images