Low-Profile Frequency Selective Surface with Out-of-Band Harmonic Suppression

Abstract

The present invention discloses a low-profile frequency selective surface with out-of-band harmonic suppression, which includes a plurality of resonant units arranged according to a preset rule. The resonant unit includes: a first metal patch, a second metal patch, a first dielectric substrate, a third metal patch, a first dielectric substrate and a second dielectric substrate; wherein, the first metal patch is located on the surface of the first dielectric substrate away from the second dielectric substrate, the second metal patch is located between the first dielectric substrate and the second dielectric substrate, and the third metal patch is located on the surface of the second dielectric substrate away from the second metal patch; along the direction perpendicular to the plane where the resonant unit is located, the orthographic projection of the second metal patch is a cross shape. By adopting the cascading method of double-layer band-pass frequency selective surfaces, the present invention can not only maintain the original passband performance, but also suppress the high-order harmonics outside the band; in addition, since only two types of band-pass frequency selective surfaces are adopted, the profile thickness is greatly reduced, and it has high angular stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of antennas, and particularly relates to a low-profile frequency selective surface with out-of-band harmonic suppression. Background Art

[0002] FSS (Frequency Selective Surface) is usually a single-layer or multi-layer periodic structure formed by arranging metal patches (or apertures on a metal screen) according to a certain rule. FSS is often used in the military field. Since the radar antennas at the front ends of aircraft, ship masts, or missiles and other aircraft are themselves relatively large electromagnetic scattering sources, it is difficult to reduce this electromagnetic scattering using traditional dielectric radomes, and it is also impossible to reduce the RCS (Radar Cross Section). Therefore, an absorbing material can also be loaded on the dielectric radome to reduce the backscattered electromagnetic wave, so as to achieve the purpose of reducing the RCS. However, the use of absorbing materials will seriously affect the normal communication and detection performance of the aircraft. Therefore, at present, the method of loading FSS with band-pass filtering characteristics on the dielectric radome as the radome is mostly adopted to effectively reduce the RCS of the radar antenna without affecting the normal operation of the system. After loading the FSS, the electromagnetic wave signals within the operating frequency band of the radar antenna can pass through the radome without loss, while the electromagnetic wave signals outside the operating frequency band of the radar antenna are almost all reflected. At the same time, combined with the low-scattering shape of the fuselage, the detection waves of the other party can be scattered in other directions, and the echo signal generated by the fuselage is very weak, greatly reducing the possibility of being detected and located by the detection radar of the other party, thus achieving the purpose of stealth.

[0003] For the FSS radomes at the front ends of aircraft such as fighter jets, ship masts, and missiles, since they need to be conformal with the front end, the electromagnetic waves received and transmitted by our communication system are incident at a relatively large angle with respect to the FSS radome. If the designed FSS radome has poor angular stability, it will seriously affect the communication quality of our communication system. At the same time, with the development of detection technology, the detectable frequency range is getting wider and wider. Most of the existing frequency selective surfaces have a narrow out-of-band suppression range. Due to the appearance of harmonics in the higher frequency band, they cannot maintain the reflection characteristics, greatly reducing the stealth performance of the aircraft. As the incident angle of the detected electromagnetic wave increases, the already not excellent out-of-band suppression characteristics of the existing frequency selective surface radome will deteriorate even more.

[0004] It can be seen that most of the existing frequency selective surfaces with out-of-band harmonic suppression adopt cascaded double-layer band-stop frequency selective surfaces or cascaded double-layer capacitive surface layers to suppress high-frequency harmonics. The double-layer cascade technology is mainly to expand the suppression bandwidth. However, generally speaking, the double-layer cascade needs to be spaced by a quarter of a wavelength, which will bring the problem of too high a profile and is not suitable for aircraft and other carrier platforms with very limited space resources. Summary of the Invention

[0005] To solve the above problems existing in the prior art, the present invention provides a low-profile frequency selective surface with out-of-band harmonic suppression. The technical problems to be solved by the present invention are achieved through the following technical solutions:

[0006] The present invention provides a low-profile frequency selective surface with out-of-band harmonic suppression, including a plurality of resonant units arranged according to a preset rule. The resonant unit includes: a first metal patch, a second metal patch, a first dielectric substrate, a third metal patch, a first dielectric substrate and a second dielectric substrate; wherein,

[0007] The first metal patch is located on the surface of the first dielectric substrate away from the second dielectric substrate, the second metal patch is located between the first dielectric substrate and the second dielectric substrate, and the third metal patch is located on the surface of the second dielectric substrate away from the second metal patch;

[0008] In the direction perpendicular to the plane where the resonant unit is located, the orthographic projection of the second metal patch is a cross shape.

[0009] In an embodiment of the present invention, the materials of the first dielectric substrate and the second dielectric substrate include polytetrafluoroethylene F4b.

[0010] In an embodiment of the present invention, the size of the first dielectric substrate is 28mm×28mm×0.1mm, and the size of the second dielectric substrate is 28mm×28mm×0.5mm.

[0011] In an embodiment of the present invention, the third metal patch includes a hollowed-out area; in the direction perpendicular to the plane where the resonant unit is located, the orthographic projection of the hollowed-out area is a grid shape.

[0012] In an embodiment of the present invention, the low-profile frequency selective surface includes a plurality of first lines arranged along a first direction and extending along a second direction, and a plurality of second lines arranged along the second direction and extending along the first direction. The first lines and the second lines intersect to form a plurality of intersection points; wherein, the first direction is perpendicular to the second direction, and the geometric centers of the plurality of resonant units respectively coincide with the intersection points.

[0013] In an embodiment of the present invention, the geometric centers of the first metal patch, the second metal patch, the first dielectric substrate, the third metal patch and the second dielectric substrate all coincide with the geometric center of the resonant unit.

[0014] In an embodiment of the present invention, the materials of the first metal patch, the second metal patch and the third metal patch include copper.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] In the low-profile frequency selective surface provided by the present invention, the first metal patch, the first dielectric substrate and the second metal patch form a non-resonant frequency selective surface, and the second dielectric substrate and the third metal patch form a band-pass frequency selective surface. The cascaded double-layer band-pass frequency selective surface can not only maintain the original passband performance, but also suppress the high-order harmonics outside the band. In addition, since only two types of band-pass frequency selective surfaces are used, the profile thickness is greatly reduced, which is more suitable for application scenarios with limited space resources. And because the two types of band-pass frequency selective surfaces used have high angular stability, the overall frequency selective surface after cascading also has high angular stability.

[0017] The present invention will be further described in detail below with reference to the drawings and embodiments. Description of the Drawings

[0018] Figure 1 is a schematic structural diagram of a low-profile frequency selective surface with out-of-band harmonic suppression provided by an embodiment of the present invention;

[0019] Figure 2 is a cross-sectional view of the resonant unit along the AA' direction provided by an embodiment of the present invention;

[0020] Figure 3 is a top view of the second metal patch provided by an embodiment of the present invention;

[0021] Figure 4 is a top view of the third metal patch provided by an embodiment of the present invention. Detailed Embodiments

[0022] The present invention will be further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0023] In the related art, the center frequency of the passband of a band-pass frequency selective surface will shift as the incident angle of the electromagnetic wave increases. At the same time, harmonics will appear in the reflection band outside the passband as the incident angle of the electromagnetic wave increases. An ideal band-pass frequency selective surface should have the characteristics of transmitting waves within the band and completely reflecting outside the band, and its performance should not deteriorate with the change of the incident angle of the electromagnetic wave. Since the frequency selective surface radome used for in-band communication and out-of-band stealth can only maintain the normal use of our communication system when the passband center is stable, and at the same time, the absence of harmonics outside the band can combine with the low-scattering shape of the carrier platform to achieve the stealth performance. However, the space resources on the carrier platform are very limited. Frequency selective surfaces operating at lower frequencies are difficult to conform to our carrier platform due to their large volume. This requires that the frequency selective surface be thin and light while meeting the required electrical performance, that is, requirements are made for the low-profile characteristics of frequency selection.

[0024] In view of this, an embodiment of the present invention provides a low-profile frequency selective surface with out-of-band harmonic suppression.

[0025] Figure 1 FIG. is a schematic structural diagram of a low-profile frequency selective surface with out-of-band harmonic suppression provided by an embodiment of the present invention. Figure 2 FIG. is a sectional view of the resonant unit along the AA' direction provided by an embodiment of the present invention. Figure 3 FIG. is a top view of the second metal patch provided by an embodiment of the present invention. Please refer to Figures 1 - 3 An embodiment of the present invention provides a low-profile frequency selective surface with out-of-band harmonic suppression, including a plurality of resonating units 1 arranged periodically. The resonating unit 1 includes: a first metal patch 10, a second metal patch 30, a first dielectric substrate 20, a third metal patch 50, a first dielectric substrate 20, and a second dielectric substrate 40. Among them,

[0026] The first metal patch 10 is located on the surface of the first dielectric substrate 20 away from the second dielectric substrate 40, the second metal patch 30 is located between the first dielectric substrate 20 and the second dielectric substrate 40, and the third metal patch 50 is located on the surface of the second dielectric substrate 40 away from the second metal patch 30.

[0027] In the direction perpendicular to the plane where the resonating unit 1 is located, the orthographic projection of the second metal patch 30 is a cross shape.

[0028] It should be understood that the frequency selective surface itself does not absorb electromagnetic waves. It will exhibit the characteristics of complete reflection (band-stop) or complete transmission (band-pass) near the resonant frequency. That is to say, the performance of the frequency selective surface is equivalent to a filter, which plays a role of selective filtering for electromagnetic waves in space. Compared with ordinary filters, the frequency response of the frequency selective surface is not only related to its own structure, but also closely related to the operating frequency, the polarization mode of the incident electromagnetic wave, and the incident angle, etc.

[0029] In this embodiment, the low-profile frequency selective surface with out-of-band harmonic suppression includes a plurality of first lines arranged in a first direction and extending in a second direction, and a plurality of second lines arranged in the second direction and extending in the first direction. The first lines and the second lines intersect to form a plurality of intersection points. Among them, the first direction is perpendicular to the second direction, and the geometric centers of the plurality of resonant units 1 coincide with the intersection points respectively.

[0030] Specifically, Figure 1 From the perspective shown, the low-profile frequency selective surface includes a plurality of first lines extending longitudinally and a plurality of second lines extending transversely. The distances between any two adjacent first lines are equal, and the distances between any two adjacent second lines are equal. That is to say, the first lines and the second lines divide the frequency selective surface into a plurality of checkerboard-shaped squares, and the plurality of resonant units 1 are distributed at the vertices of these squares. Exemplarily, the geometric center of each resonant unit 1 coincides with the intersection point of the first line and the second line.

[0031] It should be noted that actually, the low-profile frequency selective surface with out-of-band harmonic suppression provided by the present invention does not contain the first lines and the second lines. The reason for introducing the first lines and the second lines in this embodiment is only to facilitate the description of the arrangement rule of the resonant units 1.

[0032] As Figure 2 shown, each resonant unit 1 includes, from top to bottom in sequence: a first metal patch 10, a first dielectric substrate 20, a second metal patch 30, a second dielectric substrate 40, and a third metal patch 50. That is to say, the first metal patch 10 is printed on the upper surface of the first dielectric substrate 20, and the second metal patch 30 is printed on the lower surface of the first dielectric substrate 20. The third metal patch 50 is printed on the lower surface of the second dielectric substrate 40.

[0033] Exemplarily, as Figure 3 shown, the first metal patch 10 is square, with a size of 24 mm × 24 mm. The positive projection of the second metal patch 30 in the direction perpendicular to the plane where the resonant unit 1 is located is cross-shaped. This metal patch is composed of a metal strip with a length of 28 mm and a width of 0.2 mm and another metal strip with a length of 0.2 mm and a width of 28 mm.

[0034] Figure 4 is the top view of the third metal patch provided by the embodiment of the present invention. Further, as Figure 4 shown, in this embodiment, the third metal patch 50 includes a hollowed-out area. The positive projection of the hollowed-out area in the direction perpendicular to the plane where the resonant unit 1 is located is cross-shaped. As Figure 3As shown, the third metal patch 50 is formed by removing a well-shaped closed figure from a square metal patch. Among them, the side length p of the third metal patch 50 is 28 mm, L = 18 mm, w1 = 2 mm, and s = 1 mm in the well-shaped closed figure.

[0035] It can be seen that in the low-profile frequency selective surface provided by the present invention, the first metal patch 10, the first dielectric substrate 20, and the second metal patch 30 form a non-resonant type frequency selective surface, and the second dielectric substrate 40 and the third metal patch 50 form a band-pass type frequency selective surface. These two different types of band-pass type frequency selective surfaces have the same passband and different out-of-band harmonics. After cascading, the resonant unit 1 can not only maintain the original passband performance, but also suppress the out-of-band high-order harmonics generated at high frequencies with each other, that is, the way of cascading two-layer band-pass type frequency selective surfaces is used to suppress the out-of-band high-order harmonics. In addition, since the above low-profile frequency selective surface does not use a band-stop type frequency selective surface and only uses two band-pass type frequency selective surfaces, the profile is very low, only 1% of the wavelength of the center frequency of the passband, which is more suitable for application scenarios with limited space resources. And because the two band-pass type frequency selective surfaces used have high angular stability, the overall frequency selective surface after cascading also has high angular stability.

[0036] In this embodiment, the materials of the first dielectric substrate 20 and the second dielectric substrate 40 include polytetrafluoroethylene F4b. The relative dielectric constant of polytetrafluoroethylene F4b is 2.65, and the loss tangent is 0.006. The size of the first dielectric substrate 20 is 28 mm × 28 mm × 0.1 mm, and the size of the second dielectric substrate 40 is 28 mm × 28 mm × 0.5 mm.

[0037] In this embodiment, the geometric centers of the first metal patch 10, the second metal patch 30, the first dielectric substrate 20, the third metal patch 50, and the second dielectric substrate 40 all coincide with the geometric center of the resonant unit 1. Exemplarily, the materials of the first metal patch 10, the second metal patch 30, and the third metal patch 50 include copper.

[0038] From the above embodiments, it can be seen that the beneficial effects of the present invention are as follows:

[0039] In the low-profile frequency selective surface provided by the present invention, the first metal patch, the first dielectric substrate and the second metal patch form a non-resonant frequency selective surface, and the second dielectric substrate and the third metal patch form a band-pass frequency selective surface. The cascaded double-layer band-pass frequency selective surface can not only maintain the original passband performance, but also suppress the high-order harmonics outside the band. In addition, since only two types of band-pass frequency selective surfaces are used, the profile thickness is greatly reduced, which is more suitable for application scenarios with limited space resources. Moreover, since the two types of band-pass frequency selective surfaces used have high angular stability, the overall frequency selective surface after cascading also has high angular stability.

[0040] In the description of the present invention, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality" means two or more, unless otherwise specifically defined.

[0041] In the description of this specification, the description with reference to the terms "an embodiment", "some embodiments", "example", "specific example", or "some examples", etc. means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine the different embodiments or examples described in this specification.

[0042] Although the present application has been described in conjunction with various embodiments herein, however, in the process of implementing the claimed present application, those skilled in the art can understand and realize other variations of the disclosed embodiments by viewing the accompanying drawings, the disclosure, and the appended claims.

[0043] The above content is a further detailed description of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention pertains, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should all be regarded as belonging to the protection scope of the present invention.

Claims

1. A low-profile frequency selective surface with out-of-band harmonic suppression, characterized in that, It includes a plurality of resonant units arranged according to a preset rule. The resonant unit includes: a first metal patch, a second metal patch, a first dielectric substrate, a third metal patch, a first dielectric substrate, and a second dielectric substrate. Among them, The first metal patch is located on the surface of the first dielectric substrate away from the second dielectric substrate, the second metal patch is located between the first dielectric substrate and the second dielectric substrate, and the third metal patch is located on the surface of the second dielectric substrate away from the second metal patch. The third metal patch includes a hollowed-out area. Along the direction perpendicular to the plane where the resonant unit is located, the orthographic projection of the second metal patch is cross-shaped, and the orthographic projection of the hollowed-out area is well-shaped. Among them, The third metal patch is formed by removing a well-shaped closed figure from a square metal patch. The first metal patch is square, and the geometric centers of the first metal patch, the first dielectric substrate, the second metal patch, the second dielectric substrate, and the third metal patch all coincide with the geometric center of the resonant unit.

2. The low-profile frequency selective surface with out-of-band harmonic suppression according to claim 1, wherein The materials of the first dielectric substrate and the second dielectric substrate include polytetrafluoroethylene F4b.

3. The low-profile frequency selective surface with out-of-band harmonic suppression according to claim 2, wherein The size of the first dielectric substrate is 28mm × 28mm × 0.1mm, and the size of the second dielectric substrate is 28mm × 28mm × 0.5mm.

4. The low-profile frequency selective surface with out-of-band harmonic suppression according to claim 1, characterized in that, The low-profile frequency selective surface includes a plurality of first lines arranged along a first direction and extending along a second direction, and a plurality of second lines arranged along the second direction and extending along the first direction. The first lines and the second lines intersect to form a plurality of intersection points. Among them, the first direction is perpendicular to the second direction, and the geometric centers of the plurality of resonant units respectively coincide with the intersection points.

5. The low-profile frequency selective surface with out-of-band harmonic suppression according to claim 1, characterized in that, The materials of the first metal patch, the second metal patch, and the third metal patch include copper.

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