Frequency selection wave absorber with in-band RCS reduction

Abstract

The invention discloses a frequency selective wave absorber with in-band RCS reduction. On the basis of the existing absorption type frequency selective surface technology, a metal reflecting surface below a lossy layer is replaced by the polarization rotation impedance layer, impedance matching is carried out on the polarization rotation impedance layer and the characteristic impedance of the isolation dielectric layer, so that a polarization rotation reflection band is constructed at the working frequency band of the antenna, and in-band RCS reduction is achieved. In a working frequency band, the wave absorber shows a unique polarization rotation characteristic, so that in-band RCS (radar cross section) reduction is realized, the normal radiation performance of an antenna is ensured, and the risk of radar detection is remarkably reduced.

Description

Technical Field

[0001] The present invention belongs to the field of microwave technology and relates to a frequency selective absorber with in-band RCS reduction, which can be applied to electromagnetic stealth and protection platforms such as electromagnetic compatibility, antenna stealth and protection systems. Background Art

[0002] In the current situation where the electromagnetic combat environment is becoming increasingly complex and radar technology is constantly innovating, the enemy radar's ability to detect targets has been significantly improved, and electromagnetic interference may also cause the combat system to fail. This requires accelerating the development of stealth technology to enhance the platform's survivability and anti-interference performance and maintain battlefield advantages in complex electromagnetic environments. In recent years, frequency-selective absorbers with broadband notch reflection capabilities have gradually become a research hotspot. Their advantage is that they can construct a wide reflection band within a specific frequency band and efficiently absorb out-of-band electromagnetic waves, thereby improving the stealth and communication effects of the overall system.

[0003] Faced with the ever-evolving enemy detection systems and increasingly complex electromagnetic environments, traditional frequency selective absorbers often fail to meet modern stealth requirements due to their lack of in-band RCS (radar cross section) reduction capabilities, especially out-of-band absorption and in-band RCS reduction. Summary of the invention

[0004] The object of the present invention is to provide a frequency selective absorber with in-band RCS reduction in view of the deficiencies of the prior art.

[0005] The present invention discloses a frequency selective absorber with in-band RCS reduction, comprising a plurality of frequency selective absorber units with periodic structural distribution, each of which comprises an absorbing frequency selective unit located at an upper layer and a polarization rotation unit located at a lower layer; an isolation medium layer is provided between the absorbing frequency selective unit and the polarization rotation unit.

[0006] The wave absorbing frequency selection unit comprises a first dielectric plate, a first metal surface printed on the upper side of the first dielectric plate, and a second metal surface printed on the lower side of the first dielectric plate, wherein the first metal surface and the second metal surface are connected through a first metallized via;

[0007] The polarization rotation unit includes a second dielectric plate, and a third metal surface and a fourth metal surface respectively printed on the upper side and the lower side of the second dielectric plate;

[0008] The third metal surface is a polygonal metal surface with an asymmetric structure;

[0009] The fourth metal surface is a metal back plate.

[0010] Preferably, the first metal surface includes a metal square loop, four interdigital capacitors, and eight first lumped resistors. The four interdigital capacitors are respectively located at the centers of the four sides of the metal square loop, and one first lumped resistor is serially connected to each side of the interdigital capacitor on the four sides of the metal square loop.

[0011] Preferably, the second metal surface includes four meandered line inductors; the four meandered line inductors are respectively located below the four interdigital capacitors; more preferably, both sides of each meandered line inductor are respectively connected to both sides of the interdigital capacitor above through a first metallized via.

[0012] Preferably, the isolation dielectric layer uses air as the dielectric.

[0013] Preferably, the third metal surface is a polygonal metal surface that is asymmetric with respect to both the electric field direction central axis and the magnetic field direction central axis.

[0014] Preferably, the third metal surface is a hexagon formed by cutting off two opposite corners of a square, where the length of the cut-off diagonal a1 - a2 is not equal to the remaining side length a2.

[0015] Preferably, the side length of the third metal surface satisfies 2a2 < a1 < 3a2, and the thickness of the second dielectric plate is between 1.5 mm and 3.05 mm, so that the polarization rotation band falls within the working frequency band to ensure out-of-band co-polarization reflection.

[0016] Preferably, a1 < the side length of the second dielectric plate in the third metal surface, and the side length of the fourth metal surface is equal to the side length of the second dielectric plate.

[0017] Preferably, the second metal surface is connected to the interdigital capacitor through a first metallized via, jointly forming a band-pass resonator; near the resonance frequency, the band-pass resonator generates strong resonance, enabling electromagnetic waves to pass through the surface smoothly; while electromagnetic waves far from the resonance frequency will be guided to the metal square loop and an induced current will be generated and absorbed at the first lumped resistor.

[0018] The polarization rotation unit relies on the synergistic effect of the third metal surface, the fourth metal surface, and the second dielectric plate to achieve phase flipping of electromagnetic waves in the target frequency band, resulting in a polarization rotation effect.

[0019] By making the resonance frequency of the polarization rotation unit coincide with the resonance frequency of the wave absorption frequency selection unit, the functions of polarization rotation and absorption are simultaneously achieved within the working frequency band.

[0020] The present invention has the following advantages:

[0021] (1) Within the working frequency band, the absorber of the present invention exhibits unique polarization rotation characteristics, thereby achieving in-band RCS reduction, which not only ensures the normal radiation performance of the antenna but also significantly reduces the risk of being detected by radar.

[0022] (2) The structural design of the present invention has excellent out-of-band electromagnetic wave absorption capability, effectively reduces RCS, further improves the security of the communication system and the stealth performance of the platform, and is particularly suitable for complex electromagnetic environments.

[0023] (3) The overall design of the present invention is simple and easy to implement, which not only reduces the design and manufacturing costs, but also improves the reliability and feasibility of engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the three-dimensional structure of the frequency selective absorber of the present invention, wherein t1 is the thickness of the first dielectric plate, t2 is the thickness of the second dielectric plate, and h1 is the thickness of the isolation dielectric layer.

[0025] Figure 2 1 is a top-level schematic diagram of the absorbing frequency selective unit of the present invention, wherein P is the period length of the frequency selective absorbing body unit in the x-axis and y-axis directions, w1 is the line length of the square metal ring, w2 is the line width of the square metal ring, s1 is the line width of the interdigital capacitor, s2 is the line length of the interdigital capacitor, s3 is the gap between the fingers of the interdigital capacitor, s4 is the line width of the interdigital capacitor, and R1 is the resistance value of the first lumped resistor.

[0026] Figure 3 It is a bottom layer schematic diagram of the wave absorbing frequency selection unit of the present invention, wherein l1 is the line width of the meander line inductor, l2 is the meander line spacing of the meander line inductor, l3 is the line length of the meander line inductor, and l4 is the width of the connection patch between the meander line inductor and the first metallized via.

[0027] Figure 4 : is a top-level schematic diagram of the frequency selection unit of the present invention, a1 is the effective height of the diamond-shaped metal patch, and a2 is the effective width of the diamond-shaped metal patch.

[0028] Figure 5 It is a bottom schematic diagram of the frequency selection unit of the present invention.

[0029] Figure 6 It is a frequency response characteristic curve diagram of the present invention.

[0030] Figure 7 is a diagram of the RCS reduction performance of the present invention.

[0031] Markings in the figure: 1. absorbing frequency selection unit; 11. first dielectric plate; 12. first metal surface; 13. second metal surface; 14. first metalized via; 121. metal square ring; 122. interdigital capacitor; 123. first lumped resistor; 2. polarization rotation unit; 21. second dielectric plate; 22. third metal surface; 23. fourth metal surface. DETAILED DESCRIPTION

[0032] The present invention is further analyzed below in conjunction with specific embodiments.

[0033] The present invention provides a frequency selective absorber with out-of-band absorption and in-band RCS reduction. Based on the existing absorption frequency selective surface technology, the metal reflection surface under the lossy layer is replaced with a polarization rotation impedance layer, and impedance matching is performed with the characteristic impedance of the isolation medium layer (such as air medium), so as to construct a polarization rotation reflection band at the antenna working frequency band, achieve in-band RCS reduction, and ensure RCS reduction performance for out-of-band electromagnetic waves. This new absorber not only maintains good absorption performance out of the band, but also significantly reduces the probability of target detection through in-band RCS reduction, and has a simple structure, clear principle, easy processing, and low design cost. It provides a solution for modern combat systems that takes into account the dual needs of communication and stealth, and has broad application prospects and great strategic significance.

[0034] The frequency selective absorber designed in the present invention adopts a vertically stacked periodic multilayer structure, and multiple frequency selective absorber units are arranged in a certain period to form an overall system. Figure 1 As shown in the figure, each frequency selective absorber unit is composed of two vertically stacked substructures, namely the absorbing frequency selective unit 1 and the polarization rotation unit 2, which are separated by an isolation medium layer. In practical applications, this multi-layer design has shown obvious advantages. For example, in military stealth technology, especially in key parts such as fighter fuselage or radar cover, this structure can adaptively adjust electromagnetic waves with different incident directions and frequencies, thereby optimizing the absorption and reflection characteristics, effectively reducing the probability of being detected by enemy radar, and significantly improving the stealth performance of equipment.

[0035] like Figure 2 and Figure 3 As shown, the tunable wave absorbing frequency selection unit 1 is composed of a first dielectric plate 11, and the upper and lower surfaces thereof are printed with a first metal surface 12 and a second metal surface 13, respectively. Among them, the first metal surface 12 integrates a metal square ring 121, an interdigital capacitor 122 and a first lumped resistor 123, and the interdigital capacitor 122 and the first lumped resistor are both connected to the metal square ring 121; the second metal surface 13 includes four meander line inductors; the four meander line inductors are respectively located below the four interdigital capacitors (122). The second metal surface 13 is connected to the interdigital capacitor 122 through a first metallized via 14, and together they form a bandpass resonator. Near the resonant frequency, the resonator can generate strong resonance, allowing electromagnetic waves to pass through the surface smoothly; while electromagnetic waves far from the resonant frequency will be guided to the metal square ring 121, and an induced current will be generated at the first lumped resistor 123 and absorbed.

[0036] like Figure 3 and Figure 4As shown in the figure, the polarization rotation unit 2 is composed of a second dielectric plate 21 and third and fourth metal surfaces 22 and 23 printed on its upper and lower sides. The thickness of the second dielectric plate 21 needs to be reasonably designed according to actual application requirements. Its thickness directly affects the characteristic impedance of the unit, and further determines the operating frequency and bandwidth of the polarization rotation band. Taking the incident direction of electromagnetic waves as the z-axis direction, the magnetic field direction and the electric field direction as the x-axis and y-axis directions respectively, the third metal surface 22 is designed as a polygonal structure that is asymmetrically arranged with respect to the y-axis and the x-axis. Through its asymmetric layout, phase conversion of electromagnetic waves in a specific frequency band is achieved, thereby generating a polarization rotation effect. At the same time, the fourth metal surface 23 serves as a metal reflector for reflecting the electromagnetic waves that pass through the absorbing frequency selection unit 1. Relying on the synergistic effect of the third metal surface 22, the fourth metal surface 23 and the second dielectric plate 21, the polarization rotation unit 2 realizes phase flipping of electromagnetic waves in the target frequency band, causing it to produce a polarization rotation effect. By making the resonance frequency of the polarization rotation unit 2 coincide with the resonance frequency of the absorbing frequency selection unit 1, the functions of polarization rotation and absorption can be simultaneously achieved within this frequency band. This cooperative working mechanism enables the absorber to adapt to complex and changing electromagnetic environments, effectively suppressing out-of-band interference signals, while ensuring the stealth effect and communication stability within the working frequency band.

[0037] Exemplarily, as Figure 3 shown, the third metal surface 22 is a hexagon formed by cutting off two diagonals of a square, where the length of the cut-off diagonal a1 - a2 is not equal to the remaining side length a2. The side length of the third metal surface 22 satisfies 2a2 < a1 < 3a2, and the thickness of the second dielectric plate 21 is between 1.5 mm and 3.05 mm, such that the polarization rotation band falls within the working frequency band, ensuring out-of-band co-polarization reflection. a1 < the side length of the second dielectric plate 21, and the side length of the fourth metal surface 23 is equal to the side length of the second dielectric plate 21.

[0038] Figure 6 is the frequency response characteristic curve graph of this embodiment. It can be seen that the proposed structure can achieve (|S 11 | ≤ -10 dB) within the range of 3.75 - 14.16 GHz, ensuring that the co-polarization reflection coefficient in this frequency band is very low, thereby producing the effect of RCS reduction and achieving the function of absorption and scattering integration within the range of 6.96 - 10.52 GHz. This fully demonstrates the advantages of the present invention in broadband absorption performance and in-band RCS reduction performance, laying a solid foundation for its wide application in fields such as electromagnetic compatibility and antenna reflector systems.

[0039] Figure 7 is the RCS reduction performance graph of this embodiment. It can be found that the structure achieves broadband RCS reduction performance within the range of 3.8 - 14.4 GHz, which fully illustrates the advantages of the broadband RCS reduction performance of this structure.

[0040] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A frequency selective absorber with in-band RCS reduction, comprising a plurality of frequency selective absorber units with periodic structure distribution, characterized in that Each frequency selective absorber unit includes an absorbing frequency selective unit (1) located in the upper layer and a polarization rotation unit (2) located in the lower layer; there is an isolation dielectric layer between the absorbing frequency selective unit (1) and the polarization rotation unit (2). The polarization rotation unit (2) includes a second dielectric plate (21), and a third metal surface (22) and a fourth metal surface (23) printed on the upper side and the lower side of the second dielectric plate (21), respectively. The third metal surface (22) is a polygonal metal surface with an asymmetric structure. The fourth metal surface (23) is a metal backplane.

2. The frequency selective absorber with in-band RCS reduction according to claim 1, characterized in that: The absorbing frequency selective unit (1) includes a first dielectric plate (11), a first metal surface (12) printed on the upper side of the first dielectric plate (11), and a second metal surface (13) printed on the lower side of the first dielectric plate (11), where the first metal surface (12) and the second metal surface (13) are connected through a first metallized via (14).

3. The frequency selective absorber with in-band RCS reduction according to claim 2, characterized in that: The first metal surface (12) includes a metal square loop (121), four interdigital capacitors (122), and eight first lumped resistors (123). The four interdigital capacitors (122) are respectively located at the centers of the four sides of the metal square loop (121), and a first lumped resistor (123) is serially connected on each side of the interdigital capacitor (122) on the four sides of the metal square loop (121).

4. The frequency selective absorber with in-band RCS reduction according to claim 3, characterized in that: The second metal surface (13) includes four meandered line inductors; the four meandered line inductors are respectively located below the four interdigital capacitors (122).

5. The frequency selective absorber with in-band RCS reduction according to claim 4, characterized in that: Both sides of each meandered line inductor are respectively connected to both sides of the interdigital capacitor (122) located above through a first metallized via (14).

6. The frequency selective absorber with in-band RCS reduction according to claim 1, characterized in that: The isolation dielectric layer uses air dielectric.

7. The frequency selective absorber with in-band RCS reduction according to claim 1, characterized in that: The third metal surface (22) is a polygonal metal surface with an asymmetric structure with respect to both the electric field direction central axis and the magnetic field direction central axis.

8. The frequency selective absorber with in-band RCS reduction according to claim 1, characterized in that: The third metal surface (22) is a hexagon formed by cutting off two diagonals of a square, where the length a1 - a2 of the cut-off diagonal is not equal to the remaining side length a2.

9. The frequency selective absorber with in-band RCS reduction according to claim 8, characterized in that: The side length of the third metal surface (22) satisfies 2a2 < a1 < 3a2, and the thickness of the second dielectric plate (21) is between 1.5 mm and 3.05 mm, so that the polarization rotation band falls within the working frequency band to ensure out-of-band co-polarization reflection.

10. The frequency selective absorber with in-band RCS reduction according to claim 3, characterized in that: The second metal surface (13) is connected to the interdigital capacitor (122) through a first metallized via (14), jointly forming a band-pass resonator; near the resonant frequency, the band-pass resonator generates strong resonance, enabling the electromagnetic wave to pass through the surface smoothly; while the electromagnetic wave far from the resonant frequency will be guided to the metal square loop (121) and an induced current will be generated and absorbed at the first lumped resistor (123). The polarization rotation unit (2) relies on the synergistic effect of the third metal surface (22), the fourth metal surface (23) and the second dielectric plate (21) to achieve phase flipping of the electromagnetic wave in the target frequency band, generating a polarization rotation effect. The resonant frequency of the polarization rotation unit (2) is made to coincide with the resonant frequency of the absorbing frequency selective unit (1) to simultaneously achieve the functions of polarization rotation and absorption within the working frequency band.

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