A broadband in-band low rcs energy selective surface

Abstract

The application discloses a broadband in-band low-RCS energy selection surface, which comprises four central symmetrical selection surface parts; each selection surface part comprises a plurality of periodically distributed selection surface units; each selection surface unit comprises a polarization conversion layer, a first dielectric layer, a first frequency selection layer, a second dielectric layer, a selection layer, a third dielectric layer and a second frequency selection layer; a first radio frequency switch is loaded in the polarization conversion layer, and the first radio frequency switch is arranged in parallel with a diode and a lumped inductor; the impedance switching characteristic of the diode cut-off and conduction is utilized to generate a low-insertion-loss wide passband under low-power electromagnetic wave incidence and generate a wide scattering band covering the passband frequency and a high-frequency part under high-power electromagnetic wave incidence. In addition, the structure also has the characteristic of polarization insensitivity, and due to the characteristics of the diode, the structure also has a certain wave absorption effect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of electromagnetic pulse protection, and particularly relates to a broadband in-band low RCS (radar cross section) energy selective surface. BACKGROUND

[0002] With the development of science and technology, more and more antenna devices and radio frequency communication devices are applied to all aspects of people's life.

[0003] Due to the strong coupling effect of electromagnetic structures such as antennas on space electromagnetic waves, high-power electromagnetic pulses can be coupled into circuits through the "front door" antenna array, sensors, or through the "back door" metal gap, cable, causing irreversible breakdown, burning and other effects on circuit components, making electrical equipment unusable, and further causing electronic equipment damage, communication paralysis and the like. It has a huge impact on people's production and life, information transmission. Therefore, how to ensure the reliable operation of electronic systems in complex electromagnetic environments has become a difficult problem to be solved.

[0004] There are three main protection methods for high-power electromagnetic wave irradiation: FSS (Frequency Selective Surface), PL (Plasma Limiter), and ESS (Energy Selective Surface). FSS has good protection effect outside the working frequency band, but its passband is not sensitive to energy, so it has no protection effect in the band. PL can protect wideband electromagnetic waves and has super high power reflection characteristics, but PL needs to rely on the formation of plasma, is greatly affected by gas pressure and temperature, and requires additional thermal management to produce continuous protection effect. ESS can switch the passband and reflection band according to the power of electromagnetic waves and has the characteristics of flexible design, and has certain advantages.

[0005] In recent years, the design of energy selective surfaces tends to be multifunctional, with energy selective surfaces outside the passband and energy selective surfaces with scattering characteristics outside the passband. These designs ignore the RCS characteristics in the passband, which deteriorates the RCS characteristics of the antenna under high-power electromagnetic wave irradiation, and also makes the high-power electromagnetic energy not be redirected, thereby making other electromagnetic devices more susceptible to secondary damage. SUMMARY

[0006] The present application aims at the deficiencies of the prior art, and provides a broadband in-band low-RCS energy selection surface, which is formed by cascading a polarization conversion layer, a first frequency selection layer, an energy selection layer and a second frequency selection layer through adaptive switching of high-power electromagnetic waves.

[0007] The present application is a broadband in-band low-RCS energy selection surface, which comprises four center-symmetric selection surface parts.

[0008] Each selection surface part comprises a plurality of periodically distributed selection surface units, each of which is a vertical arrangement structure and comprises, from top to bottom, a polarization conversion layer, a first dielectric layer, a first frequency selection layer, a second dielectric layer, an energy selection layer, a third dielectric layer and a second frequency selection layer.

[0009] The polarization conversion layer comprises four 2x2 matrix distributed polarization conversion units, each of which comprises a first dielectric substrate and a polarization conversion metal patch located on the top layer of the first dielectric substrate; adjacent polarization conversion metal patches have a distance therebetween.

[0010] As a preferred embodiment, each polarization conversion metal patch is located on the diagonal line of the first dielectric substrate and adopts a dumbbell-like structure; more preferably, the polarization conversion metal patch comprises a first metal structure, a second metal structure, a first radio frequency switch, a third metal structure and a fourth metal structure connected in sequence.

[0011] One end of the first metal structure is directly connected to one end of the second metal structure, the other end of the second metal structure is connected to one end of the third metal structure through the first radio frequency switch, and the other end of the third metal structure is directly connected to one end of the fourth metal structure; the second metal structure and the third metal structure further comprise a connecting section with a length of l1 and a width of s near the first radio frequency switch, for connecting the first radio frequency switch.

[0012] The length and width of the first dielectric substrate are half of the length and width of the selection surface unit, and the thickness t d1 satisfies 0.005λ L ~0.011λ L , λ L is the wavelength corresponding to the center frequency of the passband of the energy selection surface structure.

[0013] The thickness t a10.01λ L ~0.02λ L , λ L is the wavelength corresponding to the center frequency of the passband of the structure;

[0014] The first frequency selection layer includes nine 3x3 matrix distributed first frequency selection units, each first frequency selection unit includes a second dielectric substrate, and a first frequency selection metal patch on the top layer of the second dielectric substrate, and there is a distance between the first frequency selection metal patches of adjacent frequency selection units;

[0015] The length and width dimensions of the second dielectric substrate are one third of the length and width dimensions of the selection surface unit, and the thickness t d2 0.005λ L ~0.006λ L , λ L is the wavelength corresponding to the center frequency of the passband of the energy selection surface structure;

[0016] The thickness t a2 0.055λ L ~0.065λ L , λ L is the wavelength corresponding to the center frequency of the passband of the structure;

[0017] The selection layer includes nine 3x3 matrix distributed selection units, each selection unit includes a third dielectric substrate, and a first selection sublayer and a second selection sublayer respectively located on the top layer and the bottom layer of the third dielectric layer;

[0018] The first selection sublayer and the second selection sublayer have the same structure and each include a fifth metal structure, a sixth metal structure, and a second radio frequency switch; the fifth metal structure is annular, and the sixth metal structure is located inside the annular fifth metal structure and is connected by two second radio frequency switches in the horizontal and vertical directions;

[0019] The length and width dimensions of the third dielectric substrate are one third of the length and width dimensions of the selection surface unit, and the thickness t d3 0.036λ L ~0.041λ L , λ L is the wavelength corresponding to the center frequency of the passband of the structure;

[0020] The thickness t a3 0.055λ L ~0.065λ L , λ L is the wavelength corresponding to the center frequency of the passband of the structure and t a2 is consistent;

[0021] The second frequency selection layer includes nine 3*3 matrix distributed second frequency selection units, each of which includes a fourth dielectric substrate and a second frequency selection metal patch on the bottom of the fourth dielectric substrate, and the second frequency selection metal patches in adjacent second frequency selection units are spaced apart;

[0022] The length and width dimensions of the fourth dielectric substrate are one third of the length and width dimensions of the surface unit, and the thickness t d4 0.005λ L ~0.006λ L , λ L is the wavelength corresponding to the center frequency of the passband of the structure.

[0023] Preferably, the first dielectric layer, the second dielectric layer, and the third dielectric layer use air as the dielectric.

[0024] The first radio frequency switch and the second radio frequency switch have the same structure, both of which use a diode and a lumped inductor in parallel.

[0025] The adjacent diodes along the length and width directions of the first dielectric substrate are placed in the same direction in the polarization conversion layer; the adjacent diodes along the length and width directions of the first dielectric substrate are placed in an alternating manner in the first frequency selection sub-layer; and the adjacent diodes along the length and width directions of the first dielectric substrate are placed in an alternating manner in the second frequency selection sub-layer, so as to achieve better shielding effect under high power.

[0026] Preferably, the first dielectric layer realizes a low insertion passband under low power by loading the first radio frequency switch.

[0027] Preferably, the first frequency selection layer, the second dielectric layer, the frequency selection layer, and the second frequency selection layer are impedance matched, realizing a low insertion passband of one third under low power, a higher shielding effect under high power, and providing a ground plane for the polarization conversion layer to achieve scattering performance in the passband under high power.

[0028] Preferably, the relative dielectric constant of the second dielectric substrate is greater than the dielectric constant of the first dielectric substrate.

[0029] Specific working principle:

[0030] When a low-power electromagnetic wave is incident, the diodes in both the polarization conversion layer and the energy-selective layer are in the off state. At this point, the diodes are equivalent to a series connection of a capacitor and an inductor. The polarization conversion layer is in a high-resistance state, allowing electromagnetic waves to pass through it with low insertion loss. The first energy-selective sublayer, the second energy-selective sublayer, and the third dielectric substrate form two transmission poles, Q1 and Q2. The first frequency-selective layer, the second dielectric layer, the third dielectric layer, and the second frequency-selective layer jointly impedance-match the transmission poles Q1 and Q2, forming a third transmission pole, Q3. This results in a wide passband with an insertion loss of less than 1dB.

[0031] When a high-power electromagnetic wave is incident, the diodes in the polarization-conversion layer conduct simultaneously, along with almost all the diodes in the first and second energy-selective sublayers. At this point, the diodes are equivalent to a small resistor and an inductor in series. The impedance of the first and second energy-selective sublayers changes from high resistance to low resistance, reflecting electromagnetic waves and providing a reflective surface for the upper polarization-conversion layer, achieving in-band scattering performance at high power. Furthermore, the high-dielectric-constant second dielectric substrate and the first frequency-selective layer reduce the cross-section between the polarization-conversion layer and the first energy-selective sublayer, thus reducing the overall cross-section of the structure to a certain extent.

[0032] Compared with the prior art, the broadband low RCS energy selective surface of the present invention has the following advantages:

[0033] (1) The present invention designs a wide passband with third-order low insertion loss under low power conditions based on a multi-layer structure. Under high power conditions, the array is provided with an energy selective surface with in-band RCS reduction efficiency through appropriate array arrangement. The polarization conversion metal unit structure design of the polarization conversion layer uses a symmetrical structure similar to a dumbbell, with a first RF switch in parallel with a diode and a lumped inductor loaded in the middle. By utilizing the impedance switching characteristics of the diode cutoff and conduction, a wide passband with low insertion loss is generated in a power-adaptive manner under low power conditions, and a wide scattering band covering the passband frequency and high frequency part is generated under high power conditions, which greatly reduces the RCS of the surface under high power, so that the subsequent antenna can obtain dual protection of electromagnetic stealth and electromagnetic shielding.

[0034] (2) The broadband energy selective surface provided by the present invention with reduced RCS within the band under high-power electromagnetic irradiation adopts a simple unit structure and uses a small number of diodes. By utilizing the state of the diodes under electromagnetic waves of different powers, good wave transmission and scattering effects are achieved. The design principle is clear, the structural design is simple, and the cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1A three-dimensional structure unit schematic diagram of a broadband in-band low RCS energy selection surface provided by the embodiment of the present application;

[0036] Figure 2 A three-dimensional structure unit schematic diagram of an energy selection surface provided by the embodiment of the present application;

[0037] Figure 3 A longitudinal sectional view of an energy selection surface unit provided by the embodiment of the present application;

[0038] Figure 4 A front perspective view of an energy selection surface unit provided by the embodiment of the present application;

[0039] Figure 5 A polarization conversion layer structure schematic diagram provided by the embodiment of the present application;

[0040] Figure 6 A first frequency selection layer structure schematic diagram provided by the embodiment of the present application;

[0041] Figure 7 An energy selection layer structure schematic diagram provided by the embodiment of the present application;

[0042] Figure 8 A second frequency selection layer structure schematic diagram provided by the embodiment of the present application;

[0043] Figure 9 An equivalent circuit schematic diagram of a broadband in-band low RCS energy selection surface provided by the embodiment of the present application;

[0044] Figure 10 A full-wave simulation and circuit simulation comparison diagram of a broadband in-band low RCS energy selection surface provided by the embodiment of the present application under high and low power incident electromagnetic wave irradiation;

[0045] Figure 11 A single station RCS and equal-sized metal surface comparison diagram of a broadband in-band low RCS energy selection surface provided by the embodiment of the present application under high power electromagnetic wave incidence and low power electromagnetic wave incidence;

[0046] Markings in the figure: 1. Polarization conversion layer; 11. First dielectric substrate; 12. Polarization conversion metal unit; 121. First metal structure; 122. Second metal structure; 123. First RF switch; 124. Third metal structure; 125. Fourth metal structure; 126. Connection segment; 2. First dielectric layer; 3. First frequency selection layer; 31. Second dielectric substrate; 32. First frequency selection metal patch; 4. Second dielectric layer; 5. Energy selection layer; 51. Third dielectric substrate; 52. First energy selection sub-layer; 521. Fifth metal structure; 522. Sixth metal structure; 523. Second RF switch; 53. Second energy selection sub-layer; 6. Third dielectric layer; 7. Second frequency selection layer; 71. Fourth dielectric substrate; 72. Second frequency selection metal patch. Detailed implementation mode

[0047] The following further analyzes the present invention in combination with specific implementation examples.

[0048] See Figure 1 , this embodiment provides an energy selection surface with low RCS in the broadband band, which includes four rotationally symmetric and seamlessly connected selection surface parts;

[0049] Each selection surface part includes a plurality of selection surface units periodically distributed along the length and width directions of the energy selection surface (i.e., the x and y axis directions); adjacent selection surface units are seamlessly connected;

[0050] See Figures 2-3 , each selection surface unit is a vertically arranged structure, and sequentially includes a polarization conversion layer 1, a first dielectric layer 2, a first frequency selection layer 3, a second dielectric layer 4, an energy selection layer 5, a third dielectric layer 6, and a second frequency selection layer 7 from top to bottom.

[0051] See Figure 4 , the polarization conversion layer 1 includes four polarization conversion units distributed in a 2×2 matrix, arranged seamlessly in a "field" shape. Each polarization conversion unit includes a first dielectric substrate 11 and a polarization conversion metal patch located on the top layer of the first dielectric substrate 11; there is a distance between the polarization conversion metal patches of adjacent polarization conversion units;

[0052] One implementation mode, see Figure 5Each polarization conversion metal patch is located on the diagonal of the first dielectric substrate 11, adopts a dumbbell-like structure, and is an axisymmetric structure; more specifically, the polarization conversion metal patch includes a first metal structure 121, a second metal structure 122, a first radio frequency switch 123, a third metal structure 124, and a fourth metal structure 125 connected in sequence; the first radio frequency switch 123 adopts a diode and a lumped inductor in parallel structure, and the diode adopts SMP1345 of SKYWORKS; the first metal structure 121 and the fourth metal structure 125 have the same structure and adopt metal wires; the second metal structure 122 and the third metal structure 124 have the same structure and adopt a triangular structure;

[0053] One end of the first metal structure 121 is directly connected to one end of the second metal structure 122, the other end of the second metal structure 122 is connected to one end of the third metal structure 124 through the first radio frequency switch 123, and the other end of the third metal structure 124 is directly connected to one end of the fourth metal structure 125; the second metal structure 122 and the third metal structure 124 are further provided with a connecting section 126 with a length of l1 and a width of s near the first radio frequency switch 123, for connecting the first radio frequency switch 123;

[0054] The length and width dimensions of the first dielectric substrate 11 are half of the length and width dimensions of the surface unit, and the thickness t d1 satisfies 0.005λ L ~0.011λ L , λ L is the wavelength corresponding to the passband center frequency of the energy selection surface structure; the dielectric of the first dielectric substrate is Rogers 5880 with a dielectric constant of 2.2.

[0055] The first dielectric layer 2 adopts air medium, and the thickness t a1 satisfies 0.01λ L ~0.02λ L , λ L is the wavelength corresponding to the passband center frequency of the structure;

[0056] Referring to Figure 6 , the first frequency selection layer 3 includes nine first frequency selection units distributed in a 3x3 matrix, and is arranged seamlessly in a "nine-square" pattern. Each first frequency selection unit includes a second dielectric substrate 31 and a first frequency selection metal patch 32 located on the top layer of the second dielectric substrate 31, and there is a distance between the first frequency selection metal patches 32 of adjacent frequency selection units; the first frequency selection metal patch 32 has a square structure, and the center thereof coincides with the geometric center of the second dielectric substrate 31;

[0057] The length and width of the second dielectric substrate 31 is one third of the length and width of the energy selective surface unit, and the thickness t d2 0.005λ L ~ 0.006λ L , λ L is the wavelength corresponding to the passband center frequency of the energy selective surface structure; the second dielectric substrate is Rogers 4350b, and the relative dielectric constant is 3.66;

[0058] The second dielectric layer 4 is air medium, and the thickness t a2 0.055λ L ~ 0.065λ L , λ L is the wavelength corresponding to the passband center frequency of the structure;

[0059] Referring to Figure 7 , the energy selective layer 5 includes nine 3x3 matrix distributed energy selective units, which are arranged in a seamless "nine-square" pattern. Each energy selective unit includes a third dielectric substrate 51, and a first energy selective sublayer 52 and a second energy selective sublayer 53 located at the top and bottom of the third dielectric layer 6 respectively;

[0060] The length and width of the third dielectric substrate 51 is one third of the length and width of the energy selective surface unit, and the thickness t d3 0.036λ L ~ 0.041λ L , λ L is the wavelength corresponding to the passband center frequency of the energy selective surface structure; the third dielectric substrate is Rogers 4350b, and the relative dielectric constant is 3.66;

[0061] The first energy selective sublayer 52 and the second energy selective sublayer 53 have the same structure, and each includes a fifth metal structure 521, a sixth metal structure 522, and a second radio frequency switch 523; the fifth metal structure 521 is a square ring, the sixth metal structure 522 is a square and located inside the ring of the fifth metal structure 521, and connected through four second radio frequency switches 523; the second radio frequency switch 523 adopts a diode and a lumped inductance parallel structure, and the diodes all adopt SMP1330 of SKYWORKS;

[0062] The third dielectric layer 6 is air medium, and the thickness t a3 0.055λ L ~ 0.065λ L , λ L is the wavelength corresponding to the passband center frequency of the structure, and t a2 is consistent;

[0063] Referring toFigure 8 The second frequency selective layer 7 includes nine 3*3 matrix distributed second frequency selective units, which are arranged in a seamless "nine-square" pattern. Each second frequency selective unit includes a fourth dielectric substrate 71 and a second frequency selective metal patch 72 located on the bottom layer of the fourth dielectric substrate 71. The second frequency selective metal patches 72 in adjacent second frequency selective units are spaced apart; the second frequency selective metal patch 72 is a square, and the geometric center of the second frequency selective metal patch 72 coincides with the geometric center of the fourth dielectric substrate 71; the geometric centers of the second dielectric substrate 31, the third dielectric substrate 51 and the fourth dielectric substrate 71 are located on the same straight line.

[0064] The length and width dimensions of the fourth dielectric substrate 71 are one-third of the length and width dimensions of the selection surface unit, and the thickness t d4 satisfies 0.005lambda L ~0.006lambda L , lambda L is the wavelength corresponding to the center frequency of the passband of the structure. The fourth dielectric substrate adopts Rogers4350b, and the relative dielectric constant is 3.66.

[0065] The adjacent diodes along the length and width directions of the first dielectric substrate 11 are placed in the same direction of the positive and negative electrodes in the polarization conversion layer 1; the adjacent diodes along the length and width directions of the first dielectric substrate 11 are placed in the staggered mode of the positive and negative electrodes in the first frequency selective sub-layer 52; the adjacent diodes along the length and width directions of the first dielectric substrate 11 are placed in the staggered mode of the positive and negative electrodes in the second frequency selective sub-layer 53, so as to generate a better shielding effect under high power conditions.

[0066] The above design structure of the present application is designed with Figure 2 as the minimum unit. When low-power electromagnetic waves are incident, the unit structure can generate a passband; and when high-power electromagnetic waves are incident, the unit structure can generate a broadband polarization conversion effect, and the converted frequency band can cover the passband under the low-power electromagnetic wave incidence. By rotating the polarization conversion unit by 90° to construct a new polarization conversion unit, and using the original polarization conversion unit "0" and the new polarization conversion unit "1" to form a "checkerboard" arranged array (such as Figure 1 ), the function of "wideband in-band RCS reduction" under high-power electromagnetic wave incidence can be achieved.

[0067] Figure 2 The selection surface unit shown in the above formula is taken as the minimum distinguishable unit of the infinite period. Specifically, the polarization conversion layer 1 is composed of four equal polarization conversion units (a single polarization conversion unit is shown in Figure 5As shown in the figure, specifically, a "dumbbell"-shaped structure inclined at 45° is used to produce a small Q value and multiple resonance points to achieve the effect of broadband bandpass / broadband intra-polarization conversion. By placing an RF switch at the center of the structure, the structure is transparent to intra-band electromagnetic waves under low power conditions. Under high power conditions, the RF switch is adaptively turned on, so that the polarization conversion layer 1 produces an intra-band polarization conversion effect. At the same time, the RF switch of the energy selection layer 5 is also adaptively turned on due to the high power, so that the energy selection layer 5 is converted from a broadband bandpass under low power conditions to a state of reflecting electromagnetic waves, providing the polarization conversion layer 1 with an effect similar to that of a ground plane. The two work together to produce a broadband polarization conversion effect.

[0068] The specific structural parameters of the energy selective surface provided in this embodiment are described as follows:

[0069] where p c d is the length and width of the polarization conversion layer in the x and y directions of each selected surface unit, which is also the length and width of the first dielectric substrate. l is the length of the first and fourth metal structures, s is the width of the first metal structure, a is the bottom length of the second and third metal structures, and b is the hypotenuse length of the second and third metal structures. l1 , d w1 are the length and width of the first RF switch respectively; p e is the length and width of the second dielectric substrate and the first dielectric layer, the second dielectric layer, the third dielectric layer, the third dielectric substrate, and the fourth dielectric substrate in the x and y axis directions. p1 is the length and width of the first frequency-selective metal patch in the x and y axis directions; w is the width of the fifth metal structure, and its outer length is p e , g is the width of the gap between the fifth metal structure and the sixth metal structure, d w2 is the width of the second RF switch, and its length is the same as the width of the gap, which is g; p2 is the length and width of the second frequency-selective metal patch in the x and y axis directions. d1 is the thickness of the first dielectric substrate 1, t a1 is the thickness of the first dielectric layer, t d2 is the thickness of the second dielectric substrate 3, t a2 is the thickness of the second dielectric layer, t d3 is the thickness of the third dielectric substrate, t a3 is the thickness of the third dielectric layer, t d4 is the thickness of the fourth dielectric substrate.

[0070] like Figure 9As shown, the energy selective surface provided by the embodiment can be equivalent to a specific circuit model. The first metal structure and the fourth metal structure of each polarization conversion metal patch in the polarization conversion layer can be combined and equivalent to an inductor L2, the second metal structure and the third metal structure can be combined and equivalent to an inductor L1, the diode in the first radio frequency switch can be equivalent to a diode D1, the lumped inductor in the first radio frequency switch can be equivalent to an inductor L p1 The gap between the second metal structure and the third metal structure can be equivalent to a capacitor C1, the gap between the second metal structure and the adjacent polarization conversion metal patch can be equivalent to a capacitor C2, the gap between the first metal structure and the adjacent polarization conversion metal patch can be equivalent to a capacitor C3, the first dielectric substrate can be equivalent to a lossy transmission line with a characteristic impedance of Z d1 , where β d1 and t d1 are the propagation constant and thickness of the first dielectric substrate; the first dielectric layer can be equivalent to a lossless transmission line with a characteristic impedance of Z a1 , where β a1 and t a1 are the propagation constant and thickness of the first dielectric layer; the first frequency selective metal patch of the first frequency selective layer can be equivalent to a capacitor C4, the second dielectric substrate can be equivalent to a lossy transmission line with a characteristic impedance of Z d2 , where β d2 and t d2 are the propagation constant and thickness of the second dielectric substrate; the second dielectric layer can be equivalent to a lossless transmission line with a characteristic impedance of Z a2 , where β a2 and t a2 are the propagation constant and thickness of the second dielectric layer; the fifth metal structure vertical part in the first energy selective sub-layer can be equivalent to an inductor L3, where two adjacent diodes in the second radio frequency switch can be combined and equivalent to a diode D2, and the lumped inductors in the other two adjacent second radio frequency switches can be combined and equivalent to an inductor Lp2, the gap between the horizontal part of the fifth metal structure and the sixth metal structure can be equivalent to a capacitor C5, the sixth metal structure can be equivalent to an inductor L4, and the horizontal part of the fifth metal structure can be equivalent to an inductor L5; the third dielectric substrate can be equivalent to a lossy transmission line with a characteristic impedance of Z d3 , where β d3 and t d3 are the propagation constant and thickness of the third dielectric substrate; the second frequency selective metal patch in the second frequency selective layer can be equivalent to a capacitor C7, the fourth dielectric substrate can be equivalent to a lossy transmission line with a characteristic impedance of Z d4 , where β d4 and t d4 are the propagation constant and thickness of the fourth dielectric substrate; the third dielectric layer is consistent with the second dielectric layer; the second energy selective sub-layer is consistent with the first energy selective sub-layer;

[0071] According to the equivalent circuit model, the ABCD transmission matrix of the polarization conversion layer, the first frequency selection layer, the first energy selection sub-layer, the second energy selection sub-layer, and the second frequency selection layer can be obtained respectively:

[0072]

[0073] The A1B1C1D1 transmission matrix describes the polarization conversion layer, wherein Z L1 is the combined equivalent impedance of the second metal structure and the third metal structure, Z L2 is the combined equivalent impedance of the first metal structure and the fourth metal structure, Z C1 is the impedance of the equivalent capacitance C1 between the second metal structure and the third metal structure, Z C2 is the impedance of the coupling band content C2 between the second metal structure and the adjacent polarization conversion metal patch, Z C3 is the impedance of the coupling capacitance between the first metal structure and the adjacent polarization conversion metal patch, Z D1 is the impedance of the diode in the first radio frequency switch, Z Lp1 is the impedance of the lumped inductance in the first radio frequency switch; Z d1 , β d1 and t d1 are the characteristic impedance, propagation constant and thickness of the first dielectric substrate.

[0074]

[0075] The A2B2C2D2 transmission matrix describes the first dielectric layer, wherein β a1 and t a1 are the propagation constant and thickness of the first dielectric layer, and the characteristic impedance Z a1 of the first dielectric layer (the medium is preferably air) is 377 Ω.

[0076]

[0077] The A3B3C3D3 transmission matrix describes the first frequency selection layer, wherein Z C4 is the impedance of the first frequency selection metal patch; Z d2 , β d2 and t d2 are the characteristic impedance, propagation constant and thickness of the second dielectric substrate.

[0078]

[0079] The A4B4C4D4 transmission matrix describes the second dielectric layer, wherein β a2 and t a2 are the propagation constant and thickness of the second dielectric layer, and the characteristic impedance Z a2 of the second dielectric layer (the medium is preferably air) is 377 Ω.

[0080]

[0081] A5B5C5D5transmission matrix describes the first selectable sublayer and the second selectable sublayer, wherein Z L3 is the impedance of the vertical part of the fifth metal structure, Z C5 is the equivalent capacitive impedance of the gap between the fifth metal structure and the sixth metal structure, Z D2 is the equivalent impedance of the diode in the second radio frequency switch, Z LP2 is the impedance of the lumped inductance in parallel with the diode in the second radio frequency switch, Z L4 is the impedance of the sixth metal structure, Z L5 is the impedance of the horizontal part of the fifth metal structure; the second selectable sublayer is identical to the first selectable sublayer; Z d3 , β d3 and t d3 are the characteristic impedance, propagation constant and thickness of the third dielectric substrate.

[0082]

[0083] A6B6C6D6transmission matrix describes the third dielectric layer, wherein β a2 and t a2 are the propagation constant and thickness of the third dielectric layer, the characteristic impedance of the third dielectric layer (the dielectric is preferably air) Z a2 is 377 Ω.

[0084]

[0085] A7B7C7D7transmission matrix describes the second frequency-selective layer, wherein Z C7 is the impedance of the second frequency-selective metal patch; Z d4 , β d4 and t d4 are the characteristic impedance, propagation constant and thickness of the fourth dielectric substrate.

[0086]

[0087] ABCDtransmission matrix describes the energy-selective surface provided by the embodiment, and according to the matrix, the formula of the reflection coefficient and the transmission coefficient can be obtained:

[0088]

[0089] Under ideal conditions, Z0 is air with an impedance of 377Ω. Under the incidence of electromagnetic waves with different powers, the diode will exhibit different equivalent impedances, that is, under the incidence of low-power electromagnetic waves, the diode is equivalent to a capacitor in the off state; under the incidence of high-power electromagnetic waves, the diode is equivalent to a small resistance. Two different states can be obtained through the impedance change of the equivalent circuit, which are the working state and the protection scattering state.

[0090] As shown in Figure 10 , it can be seen that the comparison curves of full-wave simulation (IL) and circuit simulation (ADS_IL) under the incidence of low-power electromagnetic waves are basically consistent, and the low-frequency resonance point deviation is due to the slight deviation of the circuit fitting of the polarization conversion layer, which is caused by the 45° characteristic of the structure itself and polarization. This is one of the defects of the equivalent circuit. The present application has a three-order passband at 4.5-7.5GHz, and the insertion loss is below 1dB, and the relative bandwidth is 50%. The comparison curves of full-wave simulation (SE) and circuit simulation (ADS_SE) under the incidence of high-power electromagnetic waves, and the shielding effectiveness of the circuit simulation curve is higher because the excitation of the electric field cannot make the state of the diode completely conductive in the full-wave simulation, while the conduction of the diode in the circuit simulation is ideal. In addition, some parasitic parameters are ignored in the circuit simulation, which finally causes the slight difference in the curves. It can be seen that the shielding effectiveness of the present application is greater than 30dB in the range of 1-11GHz. Through the analysis of the equivalent circuit simulation above, it can be seen that the diode has different impedances under different powers, so the structure will exhibit different responses, and the power adaptive protection capability can be realized.

[0091] As shown in Figure 11 , it can be seen that by arranging the structure units in a chessboard pattern (three units are arranged in the x and y directions of each chessboard), under the incidence of low-power electromagnetic waves, the RCS of the present application is reduced by 5dB compared with the same size metal surface at 4.4-8.1GHz, and the average reduction reaches 13.68dB. Under the incidence of high-power electromagnetic waves, the RCS of the present application is reduced by more than 7.5dB in the range of 4.6-9.5GHz, and the average reduction reaches 15.76dB.

[0092] The above is only the preferred embodiment of the present application, and it should be pointed out that for those skilled in the art, without departing from the principles of the present application, by replacing the polarization conversion layer, the first to second frequency selective layers, the first to second energy selective layers, and the first to third dielectric layer, the first to fourth dielectric substrate material types / attributes, or changing the structure form, size, and other several improvements and decorations, these improvements and decorations should also be considered as the protection scope of the present application.

Claims

1. A broadband in-band low-RCS energy-selective surface, characterized by, The four central symmetrical selection surface parts include a plurality of periodically distributed selection surface units. Each selection surface unit includes, from top to bottom, a polarization conversion layer (1), a first dielectric layer (2), a first frequency selection layer (3), a second dielectric layer (4), an energy selection layer (5), a third dielectric layer (6), and a second frequency selection layer (7). The polarization conversion layer (1) includes four 2x2 matrix distributed polarization conversion units, each of which includes a first dielectric substrate (11) and a polarization conversion metal patch on the top layer of the first dielectric substrate (11).

2. The energy selective surface of claim 1, wherein, The first frequency selection layer (3) includes nine 3x3 matrix distributed first frequency selection units, each of which includes a second dielectric substrate (31) and a first frequency selection metal patch (32) on the top layer of the second dielectric substrate (31). The energy selection layer (5) includes nine 3x3 matrix distributed energy selection units, each of which includes a third dielectric substrate (51) and a first energy selection sublayer (52) and a second energy selection sublayer (53) on the top and bottom layers of the third dielectric layer (6), respectively. The second frequency selection layer (7) includes nine 3x3 matrix distributed second frequency selection units, each of which includes a fourth dielectric substrate (71) and a second frequency selection metal patch (72) on the bottom layer of the fourth dielectric substrate (71). In the polarization conversion layer (1), each polarization conversion metal patch is located on the diagonal of the first dielectric substrate (11) and adopts a dumbbell-like structure.

3. The energy selective surface of claim 2, wherein, The first energy selection sublayer (52) and the second energy selection sublayer (53) have the same structure and each includes a fifth metal structure (521), a sixth metal structure (522), and a second radio frequency switch (523). The fifth metal structure (521) is ring-shaped, the sixth metal structure (522) is located inside the ring-shaped fifth metal structure (521) and is connected by two second radio frequency switches (523) in the horizontal and vertical directions, and the second radio frequency switch (523) is arranged in parallel with a diode and a lumped inductor.

4. The energy selective surface of claim 2, wherein, The first dielectric layer (2), the second dielectric layer (4), and the third dielectric layer (6) use air as the dielectric.

5. The energy selective surface of claim 2, wherein, The length-width dimension of the first dielectric substrate (11) is half of the length-width dimension of the surface unit, and the thickness t d1 satisfies 0.005λ L ~ 0.011λ L , λ L is the wavelength corresponding to the passband center frequency of the energy-selective surface structure; The length and width dimensions of the second dielectric substrate (31) are one third of the length and width dimensions of the surface unit, and the thickness t d2 0.005λ L ~ 0.006λ L ; The length and width dimensions of the third dielectric substrate (51) are one third of the length and width dimensions of the surface unit, and the thickness t d3 0.036λ L ~ 0.041λ L ; The fourth dielectric substrate (71) has a length-width dimension of one third of the length-width dimension of the surface unit and a thickness t d4 0.005λ L ~ 0.006λ L .

6. The energy selective surface of claim 2, wherein, The first dielectric layer (2) has a thickness t a1 satisfies 0.01λ L ~ 0.02λ L , λ L is the wavelength corresponding to the center frequency of the passband of the structure; The second dielectric layer (4) has a thickness t a2 satisfies 0.055λ L ~0.065λ L ; The third dielectric layer (6) has a thickness t a3 = t a2 .

7. The energy selective surface of claim 2, wherein, ​ 8. The energy selective surface of claim 2, wherein, The diodes in the polarization conversion layer (1) are placed in the same direction of the positive and negative poles along the length and width directions of the first dielectric substrate (11) respectively; the diodes in the first selectable sub-layer (52) are placed in the staggered direction of the positive and negative poles along the length and width directions of the first dielectric substrate (11) respectively; the diodes in the second selectable sub-layer (53) are placed in the staggered direction of the positive and negative poles along the length and width directions of the first dielectric substrate (11) respectively.

9. The energy selective surface of claim 2, wherein, The relative dielectric constant of the second dielectric substrate (31) is greater than that of the first dielectric substrate (11).

10. The energy selective surface of claim 2, wherein, When low-power electromagnetic waves are incident, the diodes of the polarization conversion layer (1) and the selectable layer (5) are in the off state, at this time, the diodes are equivalent to a series of capacitors and inductors; the polarization conversion layer (1) is in a high resistance state at this time, so that the electromagnetic waves can pass through the layer with low insertion loss, and the first selectable sub-layer (52), the second selectable sub-layer (53), and the third dielectric substrate (51) form two transmission poles Q1 and Q2, and the first frequency selective layer (3), the second dielectric layer (4), the third dielectric layer (6), and the second frequency selective layer (7) together match the impedance of the transmission poles Q1 and Q2 to form a third transmission pole Q3, thereby forming a wide passband with an insertion loss of less than 1 dB; When high-power electromagnetic waves are incident, the diodes of the polarization conversion layer (1) are almost simultaneously turned on with all the diodes of the first selectable sub-layer (52) and the second selectable sub-layer (53); at this time, the diodes can be equivalent to a small resistor and an inductor in series, and the impedance of the first selectable sub-layer (52) and the second selectable sub-layer (53) changes from high resistance to low resistance, which presents a reflected electromagnetic wave effect, providing a reflection surface for the polarization conversion layer (1) above, realizing the performance of in-band scattering characteristics under high power, and at the same time, due to the high dielectric constant of the second dielectric substrate (31) and the first frequency selective layer (3), the profile between the polarization conversion layer (1) and the first selectable layer (5) is reduced, so that the overall profile of the structure is reduced.

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