Energy selective surface with low RCS in broadband

Abstract

The invention discloses an energy selection surface with low RCS in a broadband. The energy selection surface comprises four centrosymmetric selection surface parts, each selective surface part comprises a plurality of periodically distributed selective surface units; each selective surface unit comprises a polarization conversion layer, a first dielectric layer, a first frequency selection layer, a second dielectric layer, an optional 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 formed by connecting a diode and a lumped inductor in parallel; by utilizing the impedance switching characteristic of cut-off and conduction of a diode, a wide passband with low insertion loss is generated under the incidence of low-power electromagnetic waves, and a wide scattering band covering a passband frequency and a high-frequency part is generated under the incidence of high-power electromagnetic waves. In addition, the structure also has the characteristic of polarization insensitivity, and also has a certain wave absorbing effect due to the characteristics of the diode.

Description

Technical Field

[0001] The invention belongs to the technical field of electromagnetic pulse protection, and in particular relates to an energy selective surface with low RCS (radar cross section) in a broadband band. Background Art

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

[0003] Due to the strong coupling effect of electromagnetic structures such as antennas on electromagnetic waves in space, strong electromagnetic pulses can be coupled into the circuit through the antenna array and sensor at the "front door" or through the metal gaps and cables at the "back door", causing irreversible breakdown and burning of circuit components, making electrical equipment unusable, and further causing damage to electronic equipment and communication paralysis. This has a huge impact on people's production and life, and the transmission of information. Therefore, how to ensure the reliable operation of electronic systems in complex electromagnetic environments has become a problem that needs to be solved urgently.

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

[0005] In recent years, the design of energy selective surfaces has tended to be multifunctional, including energy selective surfaces that absorb waves outside the passband and energy selective surfaces that have scattering characteristics outside the passband. These designs ignore the RCS characteristics within the passband, which deteriorates the RCS characteristics of the antenna under high-power electromagnetic waves. At the same time, the high-power electromagnetic energy is not guided secondary, making it easier for other electromagnetic devices to receive secondary damage. Summary of the invention

[0006] The purpose of the present invention is to address the deficiencies of the prior art and provide a broadband in-band low RCS energy selective surface. The structure is formed by a polarization conversion layer that is adaptively switched by high-power electromagnetic waves, and is cascaded with a first frequency selective layer, an energy selective layer, and a second frequency selective layer. Under the irradiation of low-power electromagnetic waves, broadband low insertion loss is achieved; and under the irradiation of high-power electromagnetic waves, it can adaptively switch to the effects of in-band scattering and out-of-band reflection. In addition, the structure is also polarization-insensitive, and due to the characteristics of the diode, it also has a certain wave absorbing effect. The overall structural design of the present invention is simple, easy to process, low cost, clear principle, and has broad application prospects.

[0007] The present invention discloses a broadband low RCS energy selective surface, comprising four centrosymmetric selective surface parts;

[0008] Each selective surface part includes a plurality of periodically distributed selective surface units; each selective surface unit is a vertically arranged structure, and includes, from top to bottom, a polarization conversion layer, a first dielectric layer, a first frequency selective layer, a second dielectric layer, an energy selective layer, a third dielectric layer, and a second frequency selective layer.

[0009] The polarization conversion layer includes four polarization conversion units distributed in a 2×2 matrix, each polarization conversion unit includes a first dielectric substrate and a polarization conversion metal patch located on the top layer of the first dielectric substrate; there is a distance between adjacent polarization conversion metal patches;

[0010] Preferably, each polarization conversion metal patch is located on the diagonal of the first dielectric substrate, and adopts a dumbbell-shaped structure; more preferably, the polarization conversion metal patch includes 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 RF 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 are also provided with a length of l near the first RF switch. 1 , a connecting segment with a width of s, used 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 selected surface unit, and the thickness t d1 Satisfy 0.005λ L ~0.011λ L ,λ L The wavelength corresponding to the passband center frequency of the energy selective surface structure;

[0013] The thickness of the first dielectric layer is ta1 Satisfy 0.01λ L ~0.02λ L ,λ L is the wavelength corresponding to the passband center frequency of the structure;

[0014] The first frequency selection layer includes nine first frequency selection units distributed in a 3×3 matrix, each first frequency selection unit includes a second dielectric substrate and a first frequency selection metal patch located 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 of the second dielectric substrate is one third of the length and width of the selected surface unit, and the thickness t d2 Satisfy 0.005λ L ~0.006λ L ,λ L The wavelength corresponding to the passband center frequency of the energy selective surface structure;

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

[0017] The energy selectable layer includes nine energy selectable units distributed in a 3×3 matrix, each energy selectable unit includes a third dielectric substrate, and a first energy selectable sublayer and a second energy selectable sublayer respectively located at the top and bottom layers of the third dielectric layer;

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

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

[0020] The thickness of the third dielectric layer is t a3 Satisfy 0.055λ L ~0.065λ L ,λ L is the wavelength corresponding to the center frequency of the structure's passband and t a2 Stay consistent;

[0021] The second frequency selection layer includes nine second frequency selection units distributed in a 3×3 matrix, each second frequency selection unit includes a fourth dielectric substrate and a second frequency selection metal patch located at the bottom layer of the fourth dielectric substrate, and there is a distance between the second frequency selection metal patches in adjacent second frequency selection units;

[0022] The length and width of the fourth dielectric substrate is one third of the length and width of the selected surface unit, and the thickness t d4 Satisfy 0.005λ L ~0.006λ L ,λ L is the wavelength corresponding to the center frequency of the structure's passband.

[0023] Preferably, the medium used in the first medium layer, the second medium layer and the third medium layer is air.

[0024] The first RF switch and the second RF switch have the same structure, both of which adopt a diode and a lumped inductor parallel structure;

[0025] The adjacent diodes located in the polarization conversion layer and along the length and width directions of the first dielectric substrate are placed in the same direction with positive and negative electrodes; the adjacent diodes located in the first energy selection sublayer and along the length and width directions of the first dielectric substrate are placed in a staggered manner with positive and negative electrodes; the adjacent diodes located in the second energy selection sublayer and along the length and width directions of the first dielectric substrate are placed in a staggered manner with positive and negative electrodes, so as to produce a better shielding effect under high power conditions.

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

[0027] Preferably, the first frequency selective layer is impedance matched with the second dielectric layer, the energy selective layer, and the second frequency selective layer, thereby achieving a third-order low insertion loss passband at low power; higher shielding effectiveness at high power, and at the same time providing a ground plane for the polarization conversion layer to achieve in-band scattering performance at 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 low-power electromagnetic waves are incident, the diodes of the polarization conversion layer and the energy selection layer are both in the cut-off state, and the diodes at this time can be equivalent to a series connection of a capacitor and an inductor. The polarization conversion layer is in a high-resistance state at this time, allowing electromagnetic waves to pass through the layer with low insertion loss. At the same time, the first energy selection sublayer, the second energy selection sublayer, and the third dielectric substrate form two transmission poles Q1 and Q2. In addition, the first frequency selection layer, the second dielectric layer, the third dielectric layer, and the second frequency selection layer jointly perform impedance matching on the transmission poles Q1 and Q2 to form the third transmission pole Q3, thereby forming a wide passband with an insertion loss of less than 1dB.

[0031] When a high-power electromagnetic wave is incident, the diodes of the polarization conversion layer are almost turned on at the same time as all the diodes of the first energy selection sublayer and all the diodes of the second energy selection sublayer. At this time, the diode can be equivalent to a small resistor and an inductor in series, and the impedance of the first energy selection sublayer and the second energy selection sublayer changes from high resistance to low resistance to reflect electromagnetic waves, providing a reflection surface for the upper polarization conversion layer, achieving the performance of in-band scattering under high power conditions, and at the same time, due to the second dielectric substrate with a high dielectric constant and the first frequency selection layer, the cross-section between the polarization conversion layer and the first energy selection sublayer can be reduced, so that the overall cross-section of the structure is reduced 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 multilayer structure, and an energy selective surface with in-band RCS reduction efficiency is provided through appropriate array arrangement under high power conditions. The polarization conversion metal unit structure design of the polarization conversion layer uses a symmetrical structure similar to a dumbbell, and the middle load adopts a first RF switch arranged in parallel with a diode and a lumped inductor. The impedance switching characteristics of the diode cutoff and conduction are utilized to adaptively generate a wide passband with low insertion loss under low power conditions, and a wide scattering band covering the passband frequency and high frequency part 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 protection.

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

[0035] Figure 1Schematic diagram of a three-dimensional structural unit of a broadband low RCS energy selective surface provided by an embodiment of the present invention;

[0036] Figure 2 is a schematic diagram of the three-dimensional structure of an energy selection surface unit provided in an embodiment of the present invention;

[0037] Figure 3 is a longitudinal cross-sectional view of an energy selection surface unit provided by an embodiment of the present invention;

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

[0039] Figure 5 is a schematic diagram of the structure of a polarization conversion layer provided by an embodiment of the present invention;

[0040] Figure 6 is a schematic diagram of the structure of the first frequency selection layer provided in an embodiment of the present invention;

[0041] Figure 7 is a schematic diagram of an energy-selective layer structure provided by an embodiment of the present invention;

[0042] Figure 8 is a schematic diagram of the structure of the second frequency selection layer provided by an embodiment of the present invention;

[0043] Fig. 9 Schematic diagram of an equivalent circuit of a broadband, low RCS energy selective surface provided by an embodiment of the present invention;

[0044] Fig.10 It is a comparison diagram of full-wave simulation and circuit simulation of a broadband low RCS energy selective surface provided by an embodiment of the present invention under irradiation of high and low power incident electromagnetic waves;

[0045] Fig.11 A comparison diagram of a single-station RCS of a broadband low-RCS energy selective surface provided by an embodiment of the present invention under high-power electromagnetic wave incidence and low-power electromagnetic wave incidence and an equal-sized metal surface;

[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 selective layer; 31. Second dielectric substrate; 32. First frequency selective 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 selective layer; 71. Fourth dielectric substrate; 72. Second frequency selective metal patch. Detailed implementation mode

[0047] The present invention will be further analyzed below 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 (i.e., the x and y axis directions) of the energy selection surface; adjacent selection surface units are seamlessly connected;

[0050] See Figure 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 selective layer 3, a second dielectric layer 4, an energy selection layer 5, a third dielectric layer 6, and a second frequency selective 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] In one implementation mode, see Figure 5, each polarization conversion metal patch is located on the diagonal line of the first dielectric substrate 11, and adopts a dumbbell-shaped structure, which 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 parallel structure, and the diode adopts SKYWORKS SMP1345; the first metal structure 121 has the same structure as the fourth metal structure 125, and adopts a metal wire; the second metal structure 122 has the same structure as the third metal structure 124, and adopts 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 RF 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 near the first RF switch 123 are also provided with a length of l 1 , a connecting segment 126 with a width s, used for connecting the first RF switch 123;

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

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

[0056] See also Figure 6 The first frequency selection layer 3 includes nine first frequency selection units distributed in a 3×3 matrix, which are arranged seamlessly in a "nine-square grid". 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. There is a distance between the first frequency selection metal patches 32 of adjacent frequency selection units; the first frequency selection metal patch 32 is a square structure, and its center 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 selected surface unit, and the thickness t d2 Satisfy 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 adopts Rogers 4350b, and the relative dielectric constant is 3.66;

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

[0059] See also Figure 7 The energy selection layer 5 includes nine energy selection units distributed in a 3×3 matrix, which are seamlessly arranged in a "nine-square grid". Each energy selection unit includes a third dielectric substrate 51, and a first energy selection sublayer 52 and a second energy selection 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 selected surface unit, and the thickness t d3 Satisfy 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, with a relative dielectric constant of 3.66;

[0061] The first selectable sublayer 52 and the second selectable sublayer 53 have the same structure, and both include a fifth metal structure 521, a sixth metal structure 522, and a second RF switch 523; the fifth metal structure 521 is in a square ring shape, the sixth metal structure 522 is in a square shape and is located inside the ring of the fifth metal structure 521, and is connected through four second RF switches 523; the second RF switch 523 adopts a parallel structure of a diode and a lumped inductor, and the diodes are all SKYWORKS SMP1330;

[0062] The third dielectric layer 6 is made of air and has a thickness of t a3 Satisfy 0.055λ L ~0.065λ L ,λ L is the wavelength corresponding to the center frequency of the structure's passband and t a2 Stay consistent;

[0063] See also Figure 8 , the second frequency selection layer 7 includes nine second frequency selection units distributed in a 3×3 matrix, arranged seamlessly in a "nine-square grid". Each second frequency selection unit includes a fourth dielectric substrate 71, and a second frequency selection metal patch 72 located at the bottom layer of the fourth dielectric substrate 71. There is a distance between the second frequency selection metal patches 72 in adjacent second frequency selection units; the second frequency selection metal patch 72 is a square, and its geometric center 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 in the same straight line;

[0064] The length and width of the fourth dielectric substrate 71 is one third of the length and width of the selected surface unit, and the thickness t d4 Satisfy 0.005λ L ~0.006λ L ,λ L is the wavelength corresponding to the passband center frequency of the structure. The fourth dielectric substrate is Rogers 4350b, with a relative dielectric constant of 3.66.

[0065] The adjacent diodes located in the polarization conversion layer 1 along the length and width directions of the first dielectric substrate 11 are placed in a manner in which the positive and negative poles are in the same direction; the adjacent diodes located in the first energy selection sublayer 52 along the length and width directions of the first dielectric substrate 11 are placed in a manner in which the positive and negative poles are staggered; the adjacent diodes located in the second energy selection sublayer 53 along the length and width directions of the first dielectric substrate 11 are placed in a manner in which the positive and negative poles are staggered, so as to produce a better shielding effect under high power conditions.

[0066] The above-mentioned design structure of the present invention is based on Figure 2 Designed for the smallest unit, when low-power electromagnetic waves are incident, the unit structure can produce a passband; when high-power electromagnetic waves are incident, the unit structure can produce a broadband polarization conversion effect, and the converted frequency band can cover the passband when low-power electromagnetic waves are incident. A new polarization conversion unit is constructed by rotating the polarization conversion unit 90°, and the original polarization conversion unit "0" and the new polarization conversion unit "1" are used to form a "chessboard" array (such as Figure 1 ), you can have the function of "broadband in-band RCS reduction" when high-power electromagnetic waves are incident.

[0067] Figure 2 The surface unit shown in the figure is selected as the smallest divisible unit of infinite period. Specifically, the polarization conversion layer 1 is composed of four polarization conversion units of equal size (a single polarization conversion unit is as follows Figure 5As shown), 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 polarization conversion. By placing a radio frequency switch at the center of the structure, the structure is transparent to the in-band electromagnetic waves under low power conditions. Under high power conditions, the radio frequency switch is adaptively turned on, so that the polarization conversion layer 1 produces an in-band polarization conversion effect. At the same time, the radio frequency switch of the energy selection layer 5 is also adaptively turned on due to high power, so that the energy selection layer 5 is converted from a broadband bandpass under low power conditions to a reflecting electromagnetic wave state, providing the polarization conversion layer 1 with an effect similar to the 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 is the length and width of the polarization conversion layer in each selected surface unit in the x and y axis directions, and is also the length and width of the first dielectric substrate. l is the length of the first metal structure and the fourth metal structure, s is the width of the first metal structure, a is the bottom length of the second metal structure and the third metal structure, and b is the hypotenuse length of the second metal structure and the third metal structure. d l1 , d w1 are respectively the length and width of the first RF switch; 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. 1 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; p 2 is the length and width of the second frequency selected 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 Fig. 9 As shown, the energy selective surface provided in this 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 to be equivalent to an inductor L2 The second metal structure and the third metal structure can be combined to be equivalent to the inductor L 1 , the diode in the first RF switch can be equivalent to a diode D 1 , the lumped inductance in the first RF switch can be equivalent to the inductance L p1 , the gap between the second metal structure and the third metal structure can be equivalent to a capacitor C 1 , the gap between the second metal structure and the adjacent polarization conversion metal patch can be equivalent to a capacitor C 2 , the gap between the first metal structure and the adjacent polarization conversion metal patch can be equivalent to a capacitor C 3 , the first dielectric substrate can be equivalent to a characteristic impedance of Z d1 The lossy transmission line, where β d1 and t d1 is the propagation constant and thickness of the first dielectric substrate; the first dielectric layer can be equivalent to a characteristic impedance of Z a1 lossless transmission line, where β a1 and t a1 is 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 C 4 , the second dielectric substrate can be equivalent to a characteristic impedance of Z d2 The lossy transmission line, where β d2 and t d2 is the propagation constant and thickness of the second dielectric substrate; the second dielectric layer can be equivalent to a characteristic impedance of Z a2 lossless transmission line, where β a2 and t a2 is the propagation constant and thickness of the second dielectric layer; the vertical portion of the fifth metal structure in the first energy-selective sublayer can be equivalent to an inductor L 3 , where the diodes in two adjacent second RF switches can be combined to form a diode D 2 , and the lumped inductors in the other two adjacent second RF switches can be combined to be equivalent to the inductor Lp 2 , the gap between the horizontal portion of the fifth metal structure and the sixth metal structure can be equivalent to a capacitor C 5 , the sixth metal structure can be equivalent to an inductor L 4 , the horizontal portion of the fifth metal structure can be equivalent to an inductor L 5 ; The third dielectric substrate can be equivalent to Z d3 The lossy transmission line, where β d3 and t d3 is 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 C 7 , the fourth dielectric substrate can be equivalent to a characteristic impedance of Z d4 The lossy transmission line, where βd4 and t d4 is the propagation constant and thickness of the fourth dielectric substrate; the third dielectric layer is consistent with the second dielectric layer; the second selectable sublayer is consistent with the first selectable sublayer;

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

[0072]

[0073] A 1 B 1 C 1 D 1 The transfer matrix describes the polarization conversion layer, where Z L1 is the combined equivalent impedance of the second metal structure and the third metal structure, Z L2 is the equivalent impedance of the first metal structure and the fourth metal structure combined, Z C1 is the equivalent capacitance C of the gap between the second metal structure and the third metal structure 1 The impedance, Z C2 is the coupling band content C between the second metal structure and the adjacent polarization conversion metal patch 2 The impedance, 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 RF switch, Z Lp1 is the impedance of the lumped inductor in the first RF switch; Z d1 , β d1 and t d1 are the characteristic impedance, propagation constant and thickness of the first dielectric substrate.

[0074]

[0075] A 2 B 2 C 2 D 2 The transmission matrix describes the first dielectric layer, where β a1 and t a1 is the propagation constant and thickness of the first dielectric layer, the characteristic impedance Z of the first dielectric layer (preferably air) a1 It is 377Ω.

[0076]

[0077] A 3 B 3 C 3 D 3 The transmission matrix describes the first frequency-selective layer, where ZC4 is the impedance of the first frequency selected metal patch; Z d2 , β d2 and t d2 are the characteristic impedance, propagation constant and thickness of the second dielectric substrate.

[0078]

[0079] A 4 B 4 C 4 D 4 The transmission matrix describes the second dielectric layer, where β a2 and t a2 is the propagation constant and thickness of the second dielectric layer, the characteristic impedance Z of the second dielectric layer (preferably air) a2 It is 377Ω.

[0080]

[0081] A 5 B 5 C 5 D 5 The transmission matrix describes the first selectable sublayer and the second selectable sublayer, where Z L3 is the impedance of the vertical portion of the fifth metal structure, Z C5 is the equivalent capacitance 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 RF switch, Z LP2 is the impedance of the lumped inductor in parallel with the diode in the second RF switch, Z L4 is the impedance of the sixth metal structure, Z L5 is the impedance of the horizontal portion of the fifth metal structure; the second selectable sublayer is consistent with 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] A 6 B 6 C 6 D 6 The transmission matrix describes the third dielectric layer, where β a2 and t a2 is the propagation constant and thickness of the third dielectric layer, and the characteristic impedance Z of the third dielectric layer (preferably air) a2 It is 377Ω.

[0084]

[0085] A 7 B 7 C 7 D 7 The transmission matrix describes the second frequency-selective layer, where Z C7 is the impedance of the metal patch for the second frequency selection; Z d4 , β d4 and t d4 are the characteristic impedance, propagation constant and thickness of the fourth dielectric substrate.

[0086]

[0087] The ABCD transmission matrix describes the energy selective surface provided by this embodiment. According to the matrix, the formulas of reflection coefficient and transmission coefficient can be obtained:

[0088]

[0089] Under ideal conditions, Z0 is air with an impedance of 377Ω. With the incidence of electromagnetic waves of different powers, the diode will present different equivalent impedances, that is, when low-power electromagnetic waves are incident, the diode is cut off and equivalent to a capacitor; when high-power electromagnetic waves are incident, the diode is equivalent to a small resistor. Through the impedance change of the equivalent circuit, two different states can be obtained, namely the working state and the protection scattering state.

[0090] like Fig.10 As shown, it can be seen that the comparison curves of full-wave simulation (IL) and circuit simulation (ADS_IL) under the condition of normal incidence of low-power electromagnetic waves are basically consistent in curve fitting. The low-frequency resonance point offset is because the circuit fitting of the polarization conversion layer is actually slightly deviated. This is due to the influence of the 45° characteristic of the structure itself and the polarization, which is also one of the defects of the equivalent circuit. The present invention has a third-order passband at 4.5-7.5GHz, an insertion loss of less than 1dB, and a relative bandwidth of 50%. The comparison curves of full-wave simulation (SE) and circuit simulation (ADS_SE) under the condition of normal incidence of high-power electromagnetic waves are shown. The shielding effectiveness generated by the circuit simulation curve is higher because the electric field excitation cannot make the diode fully conductive during full-wave simulation, while the conduction state of the diode under circuit simulation is ideal. In addition, the influence of some parasitic parameters is ignored during circuit simulation, which ultimately results in slightly different curves. It can be seen that the shielding effectiveness of the present invention 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 at different powers, which will cause the structure to exhibit different responses and can achieve power adaptive protection capabilities.

[0091] like Fig.11As shown, it can be seen that by arranging the structural units in a chessboard pattern (three units are arranged in the x and y directions of each chessboard), the RCS of the present invention is reduced by 5dB at 4.4-8.1GHz compared with the metal surface of the same size under normal incidence of low-power electromagnetic waves, and the average reduction reaches 13.68dB. Under normal incidence of high-power electromagnetic waves, the RCS of the present invention 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 a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the present invention, by replacing the material type / properties of the polarization conversion layer, the first to the second frequency selective layer, the first to the second energy selective layer and the first to the third dielectric layer, the first to the fourth dielectric substrate, or changing the structural form, size, and other improvements and modifications, these improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An energy selective surface with low RCS in a broadband band, characterized in that: It includes four centrosymmetric selected surface parts; Each selective surface portion comprises a plurality of periodically distributed selective surface units; each selective surface unit comprises, from top to bottom, a polarization conversion layer (1), a first dielectric layer (2), a first frequency selective layer (3), a second dielectric layer (4), an energy selective layer (5), a third dielectric layer (6), and a second frequency selective layer (7); The polarization conversion layer (1) is loaded with a first radio frequency switch (123), wherein the first radio frequency switch (123) is a diode and a lumped inductor arranged in parallel; utilizing the impedance switching characteristics of the diode when it is cut off and turned on, a wide passband with low insertion loss is generated under the incidence of low-power electromagnetic waves, and a wide scattering band covering the passband frequency and the high-frequency part is generated under the incidence of high-power electromagnetic waves.

2. The energy selective surface according to claim 1, characterized in that: The polarization conversion layer (1) comprises four polarization conversion units distributed in a 2×2 matrix, each polarization conversion unit comprising 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; The first frequency selection layer (3) comprises nine first frequency selection units distributed in a 3×3 matrix, each first frequency selection unit comprises 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 energy selectable layer (5) comprises nine energy selectable units distributed in a 3×3 matrix, each energy selectable unit comprising a third dielectric substrate (51), and a first energy selectable sublayer (52) and a second energy selectable sublayer (53) respectively located on the top and bottom layers of the third dielectric layer (6); The second frequency selection layer (7) comprises nine second frequency selection units distributed in a 3×3 matrix, each second frequency selection unit comprising a fourth dielectric substrate (71) and a second frequency selection metal patch (72) located at the bottom layer of the fourth dielectric substrate (71), and a distance exists between the second frequency selection metal patches (72) in adjacent second frequency selection units.

3. The energy selective surface according to claim 2, characterized in that: In the polarization conversion layer (1), each polarization conversion metal patch is located on a diagonal line of the first dielectric substrate (11) and has a dumbbell-like structure.

4. The energy selective surface according to claim 2, characterized in that: The first selectable sublayer (52) and the second selectable sublayer (53) have the same structure, both comprising a fifth metal structure (521), a sixth metal structure (522), and a second radio frequency switch (523); the fifth metal structure (521) is annular, the sixth metal structure (522) is located inside the annular structure of the fifth metal structure (521), and is connected via two second radio frequency switches (523) in the horizontal and vertical directions; the second radio frequency switch (523) is a diode and a lumped inductor arranged in parallel.

5. The energy selective surface according to claim 2, characterized in that: The length and width of the first dielectric substrate (11) are half of the length and width of the selected surface unit, and the thickness t d1 Satisfy 0.005λ L ~0.011λ L ,λ L The wavelength corresponding to the passband center frequency of the energy selective surface structure; The length and width of the second dielectric substrate (31) is one third of the length and width of the selected surface unit, and the thickness t d2 Satisfy 0.005λ L ~0.006λ L ; The length and width of the third dielectric substrate (51) is one third of the length and width of the selected surface unit, and the thickness is t d3 Satisfy 0.036λ L ~0.041λ L ; The length and width of the fourth dielectric substrate (71) is one third of the length and width of the selected surface unit, and the thickness is t d4 Satisfy 0.005λ L ~0.006λ L .

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

7. The energy selective surface according to claim 2, characterized in that: The medium used in the first medium layer (2), the second medium layer (4) and the third medium layer (6) is air.

8. The energy selective surface according to claim 2, characterized in that: Adjacent diodes located in the polarization conversion layer (1) along the length and width directions of the first dielectric substrate (11) are placed in a manner with positive and negative poles in the same direction; adjacent diodes located in the first energy selection sublayer (52) along the length and width directions of the first dielectric substrate (11) are placed in a manner with positive and negative poles staggered; and adjacent diodes located in the second energy selection sublayer (53) along the length and width directions of the first dielectric substrate (11) are placed in a manner with positive and negative poles staggered.

9. The energy selective surface according to claim 2, characterized in that: 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 according to claim 2, characterized in that: When a low-power electromagnetic wave is incident, the diodes of the polarization conversion layer (1) and the energy selection layer (5) are both in a cut-off state, and the diodes are equivalent to a series connection of a capacitor and an inductor; the polarization conversion layer (1) is in a high-resistance state, so that the electromagnetic wave can pass through the layer with low insertion loss. At the same time, the first energy selection sublayer (52), the second energy selection sublayer (53), and the third dielectric substrate (51) form two transmission poles Q1 and Q2, and the first frequency selection layer (3), the second dielectric layer (4), the third dielectric layer (6), and the second frequency selection layer (7) jointly perform impedance matching on the transmission poles Q1 and Q2 to form a third transmission pole Q3, thereby forming a wide passband and having an insertion loss of less than 1 dB; When a high-power electromagnetic wave is incident, the diodes of the polarization conversion layer (1) are almost turned on simultaneously with all the diodes of the first energy selection sublayer (52) and all the diodes of the second energy selection sublayer (53); at this time, the diodes can be equivalent to a small resistor and an inductor connected in series, and the impedance of the first energy selection sublayer (52) and the second energy selection sublayer (53) changes from high resistance to low resistance, showing an effect of reflecting electromagnetic waves, providing a reflection surface for the upper polarization conversion layer (1), achieving the performance of in-band scattering characteristics under high power conditions, and at the same time, due to the high-dielectric constant second dielectric substrate (31) and the first frequency selection layer (3), the cross-section between the polarization conversion layer (1) and the first energy selection layer (5) can be reduced, so that the overall cross-section of the structure is reduced.

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