Wave-absorbing and wave-transmitting integrated frequency selective surface with out-of-band harmonic suppression characteristics

Abstract

The present invention discloses an integrated frequency selective surface (FSS) with out-of-band harmonic suppression characteristics. The surface comprises a plurality of periodically arranged resonant units of identical structure. Each resonant unit comprises a first dielectric substrate, a second dielectric substrate, a third dielectric substrate, and a fourth dielectric substrate, arranged sequentially from top to bottom, with an air layer disposed between adjacent dielectric substrates. A first impedance surface and a second impedance surface are orthogonally printed on the upper and lower surfaces of the first dielectric substrate. A bandpass frequency selective unit is printed on the upper surface of the second dielectric substrate. A first bandstop frequency selective unit is printed on the upper surface of the third dielectric substrate and a second bandstop frequency selective unit is printed on the upper surfaces of the fourth dielectric substrate, respectively. The FSS with out-of-band harmonic suppression characteristics proposed by the present invention utilizes cascaded suppression units, allowing the original ATFSS to suppress out-of-band higher harmonics while maintaining its original in-band transmission and out-of-band absorption characteristics, thereby greatly broadening the high-frequency stealth band.

Description

Technical Field

[0001] The present invention belongs to the technical field of metamaterials, and in particular relates to a wave-absorbing and wave-transmitting integrated frequency selective surface with out-of-band harmonic suppression characteristics. Background Art

[0002] The Absorptive Transmissive Frequency Selective Surface (ATFSS) is a composite structure combining an FSS and a circuit analog absorber (CAA). It not only ensures the proper transmission and transmission of signals within the operating frequency band, but also absorbs, rather than reflects, incident radar waves outside the band, reducing all-around electromagnetic scattering. In short, the ATFSS combines out-of-band absorption with in-band transmission, making it an excellent stealth electromagnetic window structure.

[0003] Frequency selective surfaces (FSS) are artificial electromagnetic periodic structures that can manipulate the transmission and reflection of incident electromagnetic waves. They are finding increasing application in antenna stealth technology. When enemy and friendly radars operate in different frequency bands, FSS radomes can be used to control the scattering of incident electromagnetic waves, reducing the aircraft's rearward RCS. Bandpass FSS-based frequency-selective radomes offer excellent wave transmission within the radar's operating frequency band, without affecting the antenna's normal operation. In out-of-band frequencies, FSS radomes resemble fully reflective metal hoods, their curved surface scattering incident electromagnetic waves in directions other than the primary threat. Using FSS hybrid radomes can effectively reduce the aircraft's nose cone RCS, with minimal changes to the original radome design and minimal impact on the radome's mechanical strength and the radar system's electrical characteristics. However, stealth and counter-stealth technologies are a mutually reinforcing and counteracting pair. FSS radomes that rely on external stealth are only effective against single-station radars, and this stealth often comes at the expense of increased RCS in other directions. With the development of "dual / multi-station" radar networking technology, its low detectability will lose most of its meaning.

[0004] Existing ATFSS designs primarily focus on expanding the bandwidth of the in-band transmission band, the out-of-band absorption band, and dynamically controlling the transmission window. Specifically, in 2019, the team led by Chen Qiang and Fu Yunqi from the National University of Defense Technology proposed a design and analysis method for a broadband wave-transmitting impedance surface based on a circular spiral resonant structure. They studied the design of a HT-ATFSS structure with broadband wave-transmitting characteristics, derived the equivalent impedance condition that the impedance surface must meet to achieve a broadband wave-transmitting design, and proposed an impedance surface design that meets this impedance condition by introducing a CSR structure within a hexagonal metal ring unit loaded with a lumped resistor. Regarding expanding the out-of-band absorption bandwidth, in 2020, the team led by Jiang Jianjun from Huazhong University of Science and Technology proposed a method for expanding the out-of-band absorption bandwidth using a double-layer impedance surface. The absorption bands of the two impedance surfaces are adjacent, but the two layers do not affect each other's absorption performance. At the same time, they share a common wave-transmitting band. Essentially, this is an ATFSS that transmits low frequencies and absorbs high frequencies, and an ATFSS that transmits mid-frequency waves and absorbs on both sides. In terms of dynamic control of the wave transmission window, in 2019, Ningbo University proposed a band-tunable ATFSS based on varactor diodes. The voltage loaded on both sides of the varactor diodes is adjusted through a voltage bias network to achieve different capacitance values. At the same time, the impact of the voltage bias network on the overall performance is also taken into account. The upper impedance surface and the lower band passband frequency selection share a set of bias networks to reduce the impact of the voltage bias network.

[0005] However, the bandpass FSS in the lower layers of the ATFSS generates high-frequency harmonics, significantly impacting the overall stealth performance of the ATFSS at higher frequencies within the ATFSS's absorption band. The high-order harmonics generated by the bandpass FSS exhibit high-frequency wave-transmission properties. Because the antennas within the carrier platform are strong scatterers, an enemy detection radar operating at a frequency harmonic of the ATFSS can easily detect the carrier combat platform.

[0006] Based on this, designing an ATFSS that can suppress the out-of-band harmonics in higher frequency bands while ensuring the in-band wave transmission and out-of-band wave absorption characteristics of the original ATFSS is particularly important for modern electromagnetic warfare. Summary of the Invention

[0007] In order to solve the above-mentioned problems existing in the prior art, the present invention provides a wave-absorbing and wave-transmitting integrated frequency selective surface with out-of-band harmonic suppression characteristics. The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0008] A wave-absorbing and wave-transmitting integrated frequency selective surface with out-of-band harmonic suppression characteristics comprises a plurality of periodically arranged resonant units having identical structures. The resonant units are a cascaded multilayer structure comprising a first dielectric substrate, a second dielectric substrate, a third dielectric substrate, and a fourth dielectric substrate arranged sequentially from top to bottom.

[0009] The first impedance surface is printed on the upper surface of the first dielectric substrate, the second impedance surface is printed on the lower surface of the first dielectric substrate, and the first impedance surface and the second impedance surface are arranged orthogonally;

[0010] A bandpass frequency selection unit is printed on the upper surface of the second dielectric substrate;

[0011] A first band-stop frequency selection unit is printed on the upper surface of the third dielectric substrate, and a second band-stop frequency selection unit is printed on the upper surface of the fourth dielectric substrate;

[0012] A first air layer is provided between the first dielectric substrate and the second dielectric substrate;

[0013] A second air layer is provided between the second dielectric substrate and the second dielectric substrate;

[0014] A third air layer is provided between the third dielectric substrate and the fourth dielectric substrate.

[0015] In one embodiment of the present invention, the first impedance surface and the second impedance surface have the same structure, both comprising a metal patch, a parallel resonant structure provided in the middle of the metal patch, and a patch resistor provided on each side of the parallel resonant structure.

[0016] In one embodiment of the present invention, the bandpass frequency selection unit includes four Jerusalem cross slot unit structures, each unit structure includes a Jerusalem cross slot and a Jerusalem cross placed inside the Jerusalem cross slot.

[0017] In one embodiment of the present invention, the internal Jerusalem cross includes an ordinary cross and a loading branch located at the end of the ordinary cross; wherein the length L3 of the ordinary cross is 6 mm and the width W3 is 0.4 mm; the length L32 of the loading branch is 2.6 mm and the width W32 is 0.5 mm.

[0018] In one embodiment of the present invention, the inner Jerusalem cross is spaced 0.15 mm from the Jerusalem cross gap.

[0019] In one embodiment of the present invention, the first band-stop frequency selection unit and the second band-stop frequency selection unit have the same structure, and both include four square metal rings.

[0020] In one embodiment of the present invention, the length L1 of the square metal ring is 7 mm and the width W1 is 1.2 mm.

[0021] In one embodiment of the present invention, the ratio of the periods of the first impedance surface, the second impedance surface, and the band-pass frequency selection unit, the first band-stop frequency selection unit, and the second band-stop frequency selection unit is 4:1.

[0022] In one embodiment of the present invention, the relative dielectric constant of the materials used for the first dielectric substrate, the second dielectric substrate, the third dielectric substrate, and the fourth dielectric substrate is 2.65, and the loss tangent is 0.002.

[0023] Beneficial effects of the present invention:

[0024] The integrated absorbing and transmitting frequency selective surface with out-of-band harmonic suppression characteristics proposed in the present invention uses cascaded suppression units to enable the original ATFSS to suppress out-of-band high-order harmonics while maintaining the original in-band transmission and out-of-band absorption characteristics, thereby greatly broadening the high-frequency stealth band; and in the lower frequency band, it has a wave-transmitting window and double-sided wave-absorbing windows, which can effectively deal with the detection of enemy dual-station radars; in the higher frequency band, a suppression unit is used to suppress high-order harmonics, making them exhibit reflection characteristics. At the same time, combined with the low-scattering design of the combat platform, it can effectively deal with the detection of enemy single-station radars, greatly reducing the probability of being detected by the enemy.

[0025] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic structural diagram of a resonant unit of an integrated wave-absorbing and wave-transmitting frequency selective surface with out-of-band harmonic suppression characteristics provided by an embodiment of the present invention;

[0027] Figure 2 is a schematic structural diagram of a first impedance surface provided by an embodiment of the present invention;

[0028] Figure 3 1 is a schematic structural diagram of a bandpass frequency selection unit provided by an embodiment of the present invention;

[0029] Figure 4 1 is a schematic structural diagram of a first band-stop frequency selection unit provided in an embodiment of the present invention;

[0030] Description of reference numerals:

[0031] 1-first dielectric substrate, 2-second dielectric substrate, 3-third dielectric substrate, 4-fourth dielectric substrate, 5-first impedance surface, 6-second impedance surface, 7-bandpass frequency selection unit, 8-first bandstop frequency selection unit, 9-second bandstop frequency selection unit, 10-first air interlayer, 11-second air interlayer, 12-third air interlayer. DETAILED DESCRIPTION

[0032] The present invention will be further described in detail below with reference to specific examples, but the embodiments of the present invention are not limited thereto.

[0033] Example 1

[0034] In order to make up for the defect of the integrated absorptive and transmissive frequency selective surface that affects the stealth performance due to the problem of high-order harmonics generated by the bandpass frequency selective surface below at high frequencies, this embodiment designs an ATFSS that has an absorptive window outside the band, a wave-transmitting window inside the band, and a full reflection characteristic in the high frequency band outside the band.

[0035] Specifically, the integrated wave-absorbing and wave-transmitting frequency selective surface with out-of-band harmonic suppression characteristics includes a plurality of periodically arranged resonant units with the same structure, each of which is a cascaded multi-layer structure. Figure 1 , Figure 1 Schematic diagram of a resonant unit of a wave-absorbing and wave-transmitting integrated frequency selective surface with out-of-band harmonic suppression characteristics provided by an embodiment of the present invention, comprising a first dielectric substrate 1, a second dielectric substrate 2, a third dielectric substrate 3, and a fourth dielectric substrate 4 arranged in order from top to bottom;

[0036] The upper surface of the first dielectric substrate 1 is printed with a first impedance surface 5, and the lower surface of the first dielectric substrate 1 is printed with a second impedance surface 6, and the first impedance surface 5 and the second impedance surface 6 are arranged orthogonally;

[0037] The upper surface of the second dielectric substrate 2 is printed with a bandpass frequency selection unit 7;

[0038] A first band-stop frequency selection unit 8 is printed on the upper surface of the third dielectric substrate 3 , and a second band-stop frequency selection unit 9 is printed on the upper surface of the fourth dielectric substrate 4 ;

[0039] A first air interlayer 10 is provided between the first dielectric substrate 1 and the second dielectric substrate 2;

[0040] A second air interlayer 11 is provided between the second dielectric substrate 2 and the second dielectric substrate 3;

[0041] A third air layer 12 is provided between the third dielectric substrate 3 and the fourth dielectric substrate 4 .

[0042] It can be understood that the first dielectric substrate 1, the second dielectric substrate 2, the third dielectric substrate 3, the fourth dielectric substrate 4, the first impedance surface 5, the second impedance surface 6, the band-pass frequency selection unit 7, the first band-stop frequency selection unit 8, the second band-stop frequency selection unit 9, the first air interlayer 10, the second air interlayer 11 and the third air interlayer 12 are all located at the geometric center of the unit structure.

[0043] Optionally, as an implementation manner, the sizes of the first dielectric substrate 1, the second dielectric substrate 2, the third dielectric substrate 3 and the fourth dielectric substrate 4 are all set to 18 mm×18 mm×0.5 mm, and the relative dielectric constant of the material used is 2.65 and the loss tangent is 0.002.

[0044] Accordingly, the sizes of the first air interlayer 10 , the second air interlayer 11 and the third air interlayer 12 can be designed to be 18 mm×18 mm×8.5 mm, 18 mm×18 mm×6 mm and 18 mm×18 mm×4.8 mm, respectively.

[0045] For further information, see Figure 2 , Figure 2 : is a schematic diagram of the structure of the first impedance surface provided by an embodiment of the present invention. In this embodiment, the first impedance surface 5 includes a metal patch, a parallel resonant structure is provided in the middle of the metal patch, and a patch resistor is provided on each side of the parallel resonant structure.

[0046] Specifically, a parallel resonant structure and two 0603 package chip resistors R are inserted into a metal patch with a length of L = 17.4 mm and a width of W = 1 mm. The parallel resonant structure in the middle adopts the form of PLC (parallel LC parallel LC structure), and its specific shape is as follows Figure 3 As shown, the parallel resonant structure has a larger capacitance, and the inductance and capacitance therein can be adjusted independently without affecting each other.

[0047] Alternatively, as an implementation, the dimensions of each component are as follows: Ll = 5 mm, Lc = 2 mm, Lc1 = 1 mm, Wl = 0.3 mm, W0 = 0.2 mm, g = 0.2 mm. The chip resistor R has a resistance of 175 ohms and is located at a distance a = 1 mm from the parallel resonant structure in the middle.

[0048] In this embodiment, the first impedance surface 5 is placed on the front surface of the first dielectric substrate 1, that is, the upper surface. The second impedance surface 6 has the same structure as the first impedance surface 5 and is placed orthogonally to the first impedance surface 5 on the back surface of the first dielectric substrate 1, that is, the lower surface.

[0049] In this embodiment, the ratio of the periods of the first impedance surface 5, the second impedance surface 6, and the band-pass frequency selection unit 7, the first band-stop frequency selection unit 8, and the second band-stop frequency selection unit 9 is 4:1.

[0050] See Figure 3 , Figure 3 3 is a structural diagram of a bandpass frequency selection unit provided by an embodiment of the present invention, which includes four Jerusalem cross slot unit structures, each unit structure including a Jerusalem cross slot and a Jerusalem cross placed inside the Jerusalem cross slot.

[0051] Specifically, the inner Jerusalem cross consists of a regular cross and a loading branch at the end of the regular cross. The regular cross has a length L3 of 6mm and a width W3 of 0.4mm; the loading branch has a length L32 of 2.6mm and a width W32 of 0.5mm. The gap between the inner Jerusalem cross and the Jerusalem cross gap is 0.15mm.

[0052] For further information, see Figure 4 , Figure 4 FIG2 is a schematic diagram of the structure of the first band-stop frequency selection unit provided by an embodiment of the present invention. The first band-stop frequency selection unit 8 includes four square metal rings. Specifically, the length L1 of the square metal rings is 7 mm and the width W1 is 1.2 mm.

[0053] In this embodiment, the second band-stop frequency selection unit 9 and the first band-stop frequency selection unit 8 have the same structure and size. The same band-stop frequency selection units can expand the out-of-band stopband width after being cascaded.

[0054] In this embodiment, the ATFSS based on the out-of-band suppression unit has the out-of-band total reflection characteristic in the high-frequency absorbing band, and adopts a double-layer cascaded band-stop frequency selective surface to suppress the out-of-band higher harmonics generated by the bandpass frequency selective surface at high frequencies, thereby ensuring that the wave transmission and wave absorption characteristics of the ATFSS in the lower frequency bands are not destroyed, while suppressing the high-frequency high-order harmonic transmission band, making it exhibit a total reflection characteristic.

[0055] It can be seen from the above embodiments that the beneficial effects of the present invention are:

[0056] The integrated absorbing and transmitting frequency selective surface with out-of-band harmonic suppression characteristics proposed in the present invention uses cascaded suppression units to enable the original ATFSS to suppress out-of-band high-order harmonics while maintaining the original in-band transmission and out-of-band absorption characteristics, thereby greatly broadening the high-frequency stealth band; and in the lower frequency band, it has a wave-transmitting window and double-sided wave-absorbing windows, which can effectively deal with the detection of enemy dual-station radars; in the higher frequency band, a suppression unit is used to suppress high-order harmonics, making them exhibit reflection characteristics. At the same time, combined with the low-scattering design of the combat platform, it can effectively deal with the detection of enemy single-station radars, greatly reducing the probability of being detected by the enemy.

[0057] In the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0058] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials, or characteristics described in conjunction 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 appropriate manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification.

[0059] Although the present application is described herein in conjunction with various embodiments, in the process of implementing the claimed application, those skilled in the art can understand and implement other variations of the disclosed embodiments by reviewing the drawings, the disclosure, and the appended claims.

[0060] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should be considered to fall within the scope of protection of the present invention.

Claims

1. A wave-absorbing and wave-transmitting integrated frequency selective surface with out-of-band harmonic suppression characteristics, characterized in that: The invention comprises a plurality of resonant units with the same structure and arranged periodically, wherein the resonant units are a cascaded multilayer structure, comprising a first dielectric substrate (1), a second dielectric substrate (2), a third dielectric substrate (3) and a fourth dielectric substrate (4) arranged in sequence from top to bottom; The first dielectric substrate (1) has a first impedance surface (5) printed on its upper surface, and a second impedance surface (6) printed on its lower surface, and the first impedance surface (5) and the second impedance surface (6) are arranged orthogonally; the first impedance surface (5) and the second impedance surface (6) have the same structure, both comprising a metal patch, a parallel resonant structure being provided in the middle of the metal patch, and a patch resistor being provided on each side of the parallel resonant structure; A bandpass frequency selection unit (7) is printed on the upper surface of the second dielectric substrate (2); the bandpass frequency selection unit (7) comprises four Jerusalem cross slot unit structures, each unit structure comprising a Jerusalem cross slot and a Jerusalem cross placed inside the Jerusalem cross slot; A first band-stop frequency selection unit (8) is printed on the upper surface of the third dielectric substrate (3), and a second band-stop frequency selection unit (9) is printed on the upper surface of the fourth dielectric substrate (4); the first band-stop frequency selection unit (8) and the second band-stop frequency selection unit (9) have the same structure, both comprising four square metal rings; A first air interlayer (10) is provided between the first dielectric substrate (1) and the second dielectric substrate (2); A second air interlayer (11) is provided between the second dielectric substrate (2) and the third dielectric substrate (3); A third air interlayer (12) is provided between the third dielectric substrate (3) and the fourth dielectric substrate (4).

2. The integrated wave-absorbing and wave-transmitting frequency selective surface with out-of-band harmonic suppression characteristics according to claim 1, characterized in that: The internal Jerusalem cross includes an ordinary cross and a loading branch located at the end of the ordinary cross; wherein the length L3 of the ordinary cross is 6 mm and the width W3 is 0.4 mm; the length L32 of the loading branch is 2.6 mm and the width W32 is 0.5 mm.

3. The integrated wave-absorbing and wave-transmitting frequency selective surface with out-of-band harmonic suppression characteristics according to claim 1, characterized in that: The inner Jerusalem cross is spaced 0.15 mm from the gap of the Jerusalem cross.

4. The integrated wave-absorbing and wave-transmitting frequency selective surface with out-of-band harmonic suppression characteristics according to claim 1, characterized in that: The length L1 of the square metal ring is 7 mm and the width W1 is 1.2 mm.

5. The integrated wave-absorbing and wave-transmitting frequency selective surface with out-of-band harmonic suppression characteristics according to claim 1, characterized in that: The ratio of the periods of the first impedance surface (5), the second impedance surface (6), the band-pass frequency selection unit (7), the first band-stop frequency selection unit (8), and the second band-stop frequency selection unit (9) is 4:

1.

6. The integrated wave-absorbing and wave-transmitting frequency selective surface with out-of-band harmonic suppression characteristics according to claim 1, characterized in that: The relative dielectric constant of the materials used for the first dielectric substrate (1), the second dielectric substrate (2), the third dielectric substrate (3) and the fourth dielectric substrate (4) is 2.65, and the loss tangent is 0.002.

Images