Frequency selective surface with polarization reconfigurable properties

Abstract

The present invention discloses a frequency selective surface with polarization reconfigurable characteristics, including first, second and third dielectric layers arranged in sequence from top to bottom, and two adjacent dielectric layers are separated by an air gap layer; each dielectric layer is a square structure with the same side length, and the upper and lower surfaces of each dielectric layer are respectively provided with metal layers. When the diode in the middle layer is turned on, the capacitor-inductor-capacitor resonance generated by the multilayer structure is utilized to realize the second-order filtering function. When the diode in the middle layer is disconnected, the middle layer and the other two layers form an FP cavity to realize the broadband polarization conversion function. The connection directions of the diodes on the upper and lower surfaces of the top layer and the bottom layer are orthogonal to each other, which can well control the polarization characteristics of the incident wave and the outgoing wave to realize independent polarization control. The present invention realizes co-polarization transmission, transmission-type linear polarization to cross polarization, transmission-type linear polarization to circular polarization, reflection-type linear polarization to cross polarization, and switchable total reflection function.

Description

Technical Field

[0001] The invention relates to a frequency selective surface with polarization reconfigurable characteristics, belonging to the technical field of electromagnetic materials. Background Art

[0002] Frequency Selective Surface (FSS) is a special electromagnetic material that is usually used to pass, reflect or absorb electromagnetic waves within a specific frequency band, while presenting a higher impedance to other frequency bands. Frequency selective surfaces have a variety of applications, including antenna technology, microwave equipment, wireless communications, radar systems, and electromagnetic shielding. At present, frequency selective surfaces with various characteristics have been studied, but the functions of most FSS are fixed and cannot change with changes in the environment. Therefore, reconfigurable frequency selective surfaces with multiple functions have attracted widespread attention. By controlling the voltage-controlled elements in the structure, electromagnetic waves can be flexibly controlled to adapt to complex communication environments. Despite this, the current reconfigurable frequency selective surfaces still have some defects, so this type of design is still one of the development trends of FSS devices in the future.

[0003] Polarization is one of the basic properties of electromagnetic waves. Common polarization states include linear polarization and circular polarization. These different polarization properties play an important role in the propagation and application of electromagnetic waves. By controlling the polarization properties of electromagnetic waves, functions such as signal modulation, optimization of communication systems, and identification of radar targets can be achieved. Therefore, regulating the polarization properties of electromagnetic waves is of great significance to fields such as electromagnetism and communication engineering.

[0004] However, for most reconfigurable FSSs, most of them only focus on the switchability of the transmission and shielding functions of the same polarization electromagnetic waves, ignoring the regulation of the polarization characteristics of the transmitted waves within the passband, which greatly limits the application of filtering metasurfaces in the field of modern communications. For example, Lin et al. designed a polarization conversion surface with frequency selective characteristics using a three-layer aperture-coupled patch periodic structure (B. Lin, W. Huang, L. Lv, et al. Second-OrderPolarization Rotating Frequency-Selective Surface[J]. IEEE Transactions onAntennas and Propagation, 2021, 69(11): 7976-7981), which has the characteristics of broadband and low loss; however, this structure can only realize the polarization conversion function, and cannot realize the same polarization filtering characteristics. Zhao et al. designed a three-layer second-order bandpass filtering surface (Zhao Y, Fu J, Wang Z, et al. Design of a broadband switchable active frequency selective surfaces based on modified diode model[J]. IEEE Antennas and Wireless Propagation Letters, 2022, 21(7): 1378-1382), and realized the switchability of electromagnetic wave transmission and shielding modes by loading PIN diodes on the top and bottom layers; however, it can only realize the switchability of transmission and shielding, and cannot realize the polarization conversion function. Wang et al. proposed a transmission-type polarization conversion metasurface (Wang X, Cao H, Yan Y, et al. Design of broadband dual-polarised reconfigurable frequency selective surface based on dual-branch parallelcircuit model[J]. IET Microwaves, Antennas&Propagation, 2023, 17(5): 403–413), whose function can dynamically switch between linear to circular and linear to linear polarization conversion, but does not have the functions of co-polarization transmission and reflection-type polarization conversion.

[0005] In view of the fact that most current passive FSS devices have unchangeable filtering characteristics for electromagnetic waves, some switchable FSS designs cannot achieve separate control of TE and TM polarizations, most switchable FSS designs cannot achieve polarization conversion functions, and most transmission-type polarization converters cannot achieve reflected polarization conversion functions. It is necessary to design a reconfigurable FSS with multiple polarization control functions to meet the needs of specific polarization signals when the antenna transmits or receives signals. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a frequency selective surface with polarization reconfigurable characteristics, which can realize single-polarization second-order filtering, dual-polarization second-order filtering, transmission-type line-to-line polarization conversion, transmission-type line-to-circular polarization conversion, reflection-type line-to-line polarization conversion and full shielding function.

[0007] The present invention adopts the following technical solutions to solve the above technical problems:

[0008] A frequency selective surface with polarization reconfigurable characteristics, the frequency selective surface comprising: first, second and third dielectric layers arranged in sequence from top to bottom, two adjacent dielectric layers separated by an air gap layer; each dielectric layer is a square structure with the same side length, the upper and lower surfaces of the first dielectric layer are respectively provided with a first metal layer and a second metal layer, the upper and lower surfaces of the second dielectric layer are respectively provided with a third metal layer and a fourth metal layer, and the upper and lower surfaces of the third dielectric layer are respectively provided with a fifth metal layer and a sixth metal layer;

[0009] The first metal layer includes four metal units of the same size, each of which is formed by overlapping two isosceles right triangles of the same size, and the hypotenuses of the two isosceles right triangles are on a straight line; the four metal units correspond to the four sides of the first dielectric layer respectively, and the hypotenuses of the two isosceles right triangles of each metal unit coincide with the corresponding sides of the first dielectric layer; the length of the side where the metal unit overlaps with the first dielectric layer is less than the side length of the first dielectric layer; the middle hollow part surrounded by the four metal units is a hollow square, the center of the hollow square coincides with the center of the first dielectric layer, and the diagonal of the hollow square coincides with the perpendicular bisector of the first dielectric layer; the space between two adjacent metal units is hollowed out, and the structure surrounded by the four metal units is a centrally symmetrical and axially symmetrical figure; the two metal units corresponding to the two perpendicular sides of the first dielectric layer are connected through a first PIN diode, and the remaining two sides are connected through a second PIN diode, and the conduction directions of the first PIN diode and the second PIN diode are consistent;

[0010] The structures of the first, second, fifth and sixth metal layers are the same, the diagonal where the two PIN diodes of the second metal layer are located is orthogonal to the diagonal where the two PIN diodes of the first metal layer are located; the diagonal where the two PIN diodes of the sixth metal layer are located is orthogonal to the diagonal where the two PIN diodes of the fifth metal layer are located, and the positions of the two PIN diodes of the fifth metal layer are the same as the positions of the two PIN diodes of the first metal layer;

[0011] The third metal layer includes four L-shaped metal structures of the same size, wherein the L-shaped metal structures are formed by a thick side and a thin side being perpendicular to each other, and the structure formed by the four L-shaped metal structures is an axially symmetrical figure with the perpendicular midline of the second dielectric layer as the axis, wherein the thin sides of two L-shaped metal structures coincide with the side A of the upper surface of the second dielectric layer, and the thick sides are connected through the third PIN diode; the thin sides of the other two L-shaped metal structures coincide with the side B of the upper surface of the second dielectric layer, and the side A is parallel to the side B;

[0012] The fourth metal layer includes two rectangular metal strips of the same size. The length of the metal strips is equal to the side length of the second dielectric layer. The two metal strips coincide with the side C and the side D of the lower surface of the second dielectric layer respectively. The side C is parallel to the side D, and the side C is perpendicular to the side A.

[0013] As a preferred solution of the present invention, the first, second and third dielectric layers are all made of Rogers board with model RO5880.

[0014] As a preferred solution of the present invention, when the third PIN diode on the third metal layer is turned on, the two PIN diodes on the first metal layer are turned on, the two PIN diodes on the second metal layer are turned off, the two PIN diodes on the fifth metal layer are turned on, and the two PIN diodes on the sixth metal layer are turned off, the upper and lower surface metal layers of the second dielectric layer are equivalent to metal grids, and CLC resonance is generated with the metal layers on the upper and lower surfaces of the first and third dielectric layers, forming a second-order filter passband, realizing TE wave transmission and TM wave shielding;

[0015] When the third PIN diode on the third metal layer is turned on, the two PIN diodes on the first metal layer are turned off, the two PIN diodes on the second metal layer are turned on, the two PIN diodes on the fifth metal layer are turned off, and the two PIN diodes on the sixth metal layer are turned on, the upper and lower surface metal layers of the second dielectric layer are equivalent to metal grids, which generate CLC resonance with the metal layers on the upper and lower surfaces of the first and third dielectric layers, forming a second-order filtering passband, realizing TM wave transmission and TE wave shielding;

[0016] When the third PIN diode on the third metal layer is turned on, the two PIN diodes on the first metal layer are turned off, the two PIN diodes on the second metal layer are turned off, the two PIN diodes on the fifth metal layer are turned off, and the two PIN diodes on the sixth metal layer are turned off, the upper and lower surface metal layers of the second dielectric layer are equivalent to metal grids, which generate CLC resonance with the metal layers on the upper and lower surfaces of the first and third dielectric layers, forming a second-order filtering passband, and realizing TE wave transmission and TM wave transmission.

[0017] As a preferred solution of the present invention, when the third PIN diode on the third metal layer is disconnected, the two PIN diodes on the first metal layer are turned on, the two PIN diodes on the second metal layer are disconnected, the two PIN diodes on the fifth metal layer are disconnected, and the two PIN diodes on the sixth metal layer are turned on, the upper and lower surface metal layers of the first dielectric layer are regarded as a first whole, the upper and lower surface metal layers of the third dielectric layer are regarded as a second whole, the first whole and the second whole form a mutually perpendicular grating structure, the upper and lower surface metal layers of the second dielectric layer are equivalent to a polarization conversion structure, and the entire frequency selective surface structure forms an FP cavity, realizing TE linear polarization conversion to TM linear polarization and TM wave shielding;

[0018] When the third PIN diode on the third metal layer is disconnected, the two PIN diodes on the first metal layer are disconnected, the two PIN diodes on the second metal layer are turned on, the two PIN diodes on the fifth metal layer are turned on, and the two PIN diodes on the sixth metal layer are disconnected, the upper and lower surface metal layers of the first dielectric layer are regarded as a first whole, the upper and lower surface metal layers of the third dielectric layer are regarded as a second whole, the first whole and the second whole form a mutually perpendicular grating structure, the upper and lower surface metal layers of the second dielectric layer are equivalent to a polarization conversion structure, and the entire frequency selective surface structure forms an FP cavity, realizing the conversion of TM linear polarization to TE linear polarization and TE wave shielding.

[0019] As a preferred solution of the present invention, when the third PIN diode on the third metal layer is disconnected, the two PIN diodes on the first metal layer are turned on, the two PIN diodes on the second metal layer are disconnected, the two PIN diodes on the fifth metal layer are disconnected, and the two PIN diodes on the sixth metal layer are disconnected, the fourth metal layer is equivalent to an inductor, and the third metal layer is equivalent to a capacitor. By controlling the equivalent values ​​of the capacitors and inductors in two mutually perpendicular directions, a phase difference is generated between the two perpendicular components of the incident TE linear polarization wave, thereby realizing the conversion of TE linear polarization to circular polarization and TM wave shielding;

[0020] When the third PIN diode on the third metal layer is disconnected, the two PIN diodes on the first metal layer are disconnected, the two PIN diodes on the second metal layer are turned on, the two PIN diodes on the fifth metal layer are disconnected, and the two PIN diodes on the sixth metal layer are disconnected, the fourth metal layer is equivalent to an inductor, and the third metal layer is equivalent to a capacitor. By controlling the equivalent values ​​of the capacitors and inductors in two mutually perpendicular directions, a phase difference is generated between the two perpendicular components of the incident TM linear polarization wave, thereby realizing the conversion of TM linear polarization into circular polarization and TE wave shielding.

[0021] As a preferred solution of the present invention, when the third PIN diode on the third metal layer is disconnected, the two PIN diodes on the first metal layer are disconnected, the two PIN diodes on the second metal layer are disconnected, the two PIN diodes on the fifth metal layer are turned on, and the two PIN diodes on the sixth metal layer are turned on, the metal layer structure on the upper and lower surfaces of the third dielectric layer is equivalent to a metal plate, and the incident polarized wave passes through the upper and lower surfaces of the first dielectric layer, undergoes polarization conversion after passing through the metal layers on the upper and lower surfaces of the second dielectric layer, and is reflected by the metal plate when passing through the metal layers on the upper and lower surfaces of the third dielectric layer, thereby achieving reflected polarization conversion.

[0022] As a preferred solution of the present invention, when the third PIN diode on the third metal layer is disconnected, the two PIN diodes on the first metal layer are turned on, the two PIN diodes on the second metal layer are turned on, the two PIN diodes on the fifth metal layer are disconnected, and the two PIN diodes on the sixth metal layer are disconnected, the metal layer structure on the upper and lower surfaces of the first dielectric layer is equivalent to a metal plate, and all incident polarized waves are reflected by the metal plate to achieve full shielding.

[0023] As a preferred solution of the present invention, the first dielectric layer, the second dielectric layer and the third dielectric layer have side lengths of 10 mm and thicknesses of 0.5 mm; the thickness of the air gap layer is 5 mm, the side length of the hollow square is 5 mm, and the spacing between two adjacent metal units is 1.5 mm; the width of the thick side of the L-shaped metal structure is 1 mm, the width of the thin side is 0.3 mm, the length of the thick side is 3.7 mm, and the length of the thin side is 4.5 mm; the spacing between the thick sides of the two L-shaped metal structures overlapping with the side A on the upper surface of the second dielectric layer is 1 mm; the width of the rectangular metal strip is 0.6 mm.

[0024] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

[0025] 1. The frequency selective surface with polarization reconfigurable characteristics of the present invention realizes multiple adjustments to the polarization characteristics of electromagnetic waves, and can realize co-polarization transmission, transmission-type linear polarization to cross-polarization, transmission-type linear polarization to circular polarization, reflection-type linear polarization to cross-polarization, and switchable total reflection function.

[0026] 2. The frequency selective surface of the present invention has polarization reconfigurable characteristics, which realizes independent polarization control and can independently control the transmission or shielding of TE or TM polarized waves, while traditional devices generally do not distinguish between polarization forms.

[0027] 3. The frequency selective surface of the present invention has polarization reconfigurable characteristics, which realizes the switchability of filtering function and polarization rotation function by changing the polarization characteristics of the transmitted wave within its passband. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic structural diagram of a frequency selective surface with polarization reconfigurable characteristics of the present invention;

[0029] Figure 2 is a front view of a frequency selective surface with polarization reconfigurable characteristics of the present invention;

[0030] Figure 3 is a structural diagram of the first, second, fifth and sixth metal layers;

[0031] Figure 4 It is a structural diagram of the third metal layer;

[0032] Figure 5 is a structural diagram of the fourth metal layer;

[0033] Figure 6 is the equivalent circuit model diagram in mode A, where (a) is the second-order filtering function equivalent circuit, and (b) is the diode equivalent circuit;

[0034] Figure 7 It is the equivalent circuit simulation diagram under mode A, where (a) is TE wave transmission and (b) is TM wave shielding;

[0035] Figure 8 are the scattering parameters in A and B modes, where (a) is TE wave transmission in A mode, (b) is TM wave shielding in A mode, (c) is TM wave transmission in B mode, and (d) is TE wave shielding in B mode;

[0036] Fig. 9 is the scattering parameter in C mode, where (a) is TE wave transmission and (b) is TM wave transmission;

[0037] Fig.10 are the scattering parameters in the D and E modes, where (a) is the conversion of the incident TE wave into TM wave in the D mode, (b) is the shielding of the incident TM wave in the D mode, (c) is the conversion of the incident TM wave into TE wave in the E mode, and (b) is the shielding of the incident TM wave in the E mode;

[0038] Fig.11 This is the FP cavity resonance model diagram in D mode;

[0039] Fig.12 are the scattering parameters in F and G modes, where (a) is the conversion of TE wave incident in F mode into circularly polarized wave, (b) is the shielding of TM wave incident in F mode, (c) is the conversion of TM wave incident in G mode into circularly polarized wave, and (d) is the shielding of TM wave incident in G mode;

[0040] Fig.13 is the axial ratio of circularly polarized waves in F and G modes, where (a) is F mode and (b) is G mode;

[0041] Fig.14 are the scattering parameters and polarization conversion rate in H mode, where (a) is the incident TE wave converted into TM wave; (b) is the incident TM wave converted into TE wave; (c) is the polarization conversion rate of TE wave converted into TM wave; (d) is the polarization conversion rate of TM wave converted into TE wave;

[0042] Fig.15 is the scattering parameter under I mode, where (a) is full shielding of TE waves and (b) is full shielding of TM waves. DETAILED DESCRIPTION

[0043] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be interpreted as limiting the present invention.

[0044] like Figure 1-Figure 5 As shown, the present invention proposes a reconfigurable FSS with nine working modes, which is composed of a six-layer metal layer structure and a three-layer Rogers RO5880 dielectric layer. When the diode in the middle layer is turned on, the capacitor-inductor-capacitor resonance generated by the multilayer structure is used to achieve the second-order filtering function. When the diode in the middle layer is disconnected, the middle layer and the other two layers form an FP cavity, which can realize the broadband polarization conversion function. The connection directions of the diodes on the upper and lower surfaces of the top and bottom layers are orthogonal to each other, which can well control the polarization characteristics of the incident wave and the outgoing wave to achieve polarization independent control.

[0045] In order to achieve the desired purpose of independent polarization control, the top and bottom metal layer structures are connected by diodes in orthogonal directions. The control of the conduction of the PIN diode can form gratings in different directions. It is well known that when the electric field is parallel to the grating, the electric dipole will be excited and the electromagnetic wave will be completely reflected. When the electric field is perpendicular to the grating, the electromagnetic wave can directly pass through the structure. The top and bottom metal layers adopt an orthogonal structure, which can transmit or reflect a polarization wave respectively to achieve separate control of TE polarization and TM polarization. When the PIN diode in the middle layer is turned on, the metal layer in the middle layer can be equivalent to a metal grid, generating CLC resonance with the first and third layers to form a second-order filter passband, achieving the effect of co-polarization transmission, corresponding to the three modes A, B, and C in Table 1. When the PIN diode in the middle layer is closed, when the conduction directions of the diodes on the upper and lower surfaces of the first and third layers are orthogonal to each other, the three-layer structure can form an FP cavity, thereby realizing the function of polarization conversion, corresponding to the D and E modes in Table 1. When the PIN diodes in the middle layer are disconnected, only one of the upper and lower diodes in the first layer is turned on, and the diodes in the third layer are all disconnected, by controlling the equivalent values ​​of the capacitance and inductance in the two mutually perpendicular directions of the middle layer, the two perpendicular components of the incident polarized wave produce a phase difference, thereby achieving the effect of linear polarization to circular polarization, corresponding to the F and G modes in Table 1. When the PIN diodes in the first and middle layers are all disconnected, and the diodes in the third layer are all turned on, the metal layer structure of the first layer has no effect on the electromagnetic wave, and the third layer is equivalent to a metal plate, producing a reflected polarization conversion effect, corresponding to the H mode in Table 1. When the diodes in the first layer are all turned on, all polarized waves are reflected, corresponding to the I mode in Table 1. The multi-mode switchable function is achieved by combining different bias states of the diodes on the three layers.

[0046] Table 1 Nine operating modes of reconfigurable frequency selective surface

[0047]

[0048] In order to analyze the working mechanism of the proposed metasurface in the second-order filtering function (A, B, C modes), an equivalent circuit model corresponding to the unit structure is established for analysis. Because the structure is symmetrical, only one polarization case needs to be established for circuit analysis. For example, the A mode is used. Figure 6 As shown in (a).

[0049] Parameters of components in the equivalent circuit: , , , , , PIN diode built-in capacitor , , When the diode is turned on, it is equivalent to a series connection of resistor and inductor. When the diode is closed, it is equivalent to a series connection of resistor and capacitor. Figure 6 as shown in (b).

[0050] Based on the above design ideas, the simulation software ADS is used to Figure 6 The equivalent circuit is simulated, and the results are as follows Figure 7 (a)- Figure 7 As shown in (b), Txx represents the incident TE wave and the outgoing TE wave, Rx represents the incident TE wave and the reflected TE wave, Tyy represents the incident TM wave and the outgoing TM wave, Ryy Represents the incident TM wave reflected TM wave. For TE polarized incident wave, the three-layer structure produces CLC resonance, and the equivalent circuit forms a second-order transmission window at 1.7-3.4 GHz, while the incident TM polarized wave is totally reflected.

[0051] Figure 8 (a)- Figure 8 (d) shows the transmission of polarized waves in A and B working modes. In A mode, the top diodes of the first and third layers are turned on, the bottom diodes of the first and third layers are turned off, and the diodes of the middle layer are turned on. TE waves penetrate the structure within the working frequency band, while TM waves are totally reflected. In B mode, the top diodes of the first and third layers are turned off, the bottom diodes of the first and third layers are turned on, and the diodes of the middle layer are turned on. TM waves penetrate the structure within the working frequency band, while TE waves are totally reflected. Independent control of polarized waves is achieved by controlling the conduction state of the PIN diodes of the first and second layers.

[0052] Fig. 9 (a)- Fig. 9 (b) is the C working mode, in which all diodes in the first and third layers are disconnected and the diodes in the middle layer are turned on. Within the working frequency band, both polarized waves can pass through the structure, achieving the full-pass function.

[0053] Fig.10 (a)- Fig.10 (d) is the scattering parameter (Sparameter) in D and E working modes, Tyx represents the incident TE wave and the outgoing TM wave, TxRepresents the incident TM wave and the outgoing TE wave. It can be seen that one incident polarization wave is converted into a polarization wave in an orthogonal direction and transmitted out, while the incident wave in the other polarization direction is shielded. In D mode. The upper surface diode of the first layer is turned on, the lower surface diode is turned off, the upper surface diode of the third layer is turned off, and the lower surface diode is turned on, and the first and third layers form a mutually orthogonal grating structure. Therefore, the polarization directions of the electromagnetic waves that can pass through the first layer and the third layer must be perpendicular to each other. At this time, the diode in the middle layer is disconnected, forming an FP cavity with the other two layers, achieving the effect of broadband polarization conversion.

[0054] In order to better analyze the working principle of the structure of the present invention in the polarization rotation state, Fig.11 The FP resonance model in D mode is given. When the electric field is parallel to the grating, the electric dipole will be excited, resulting in complete reflection of the electromagnetic wave. When working in C mode and D mode, the top grating and the bottom grating are arranged perpendicular to each other, and the polarization waves that can pass through the top and bottom layers are orthogonal. If the structure consists of only the top and bottom layers, the transmission of electromagnetic waves cannot be achieved, so the conversion layer in the middle is crucial. The transmission process is explained as follows:

[0055] When the metasurface works in D mode, the grating and the intermediate conversion layer form a FP cavity, and the propagation of the incident wave is as follows: Fig.11 As shown in Figure 1, the polarized wave will be reflected multiple times in the space between the middle layer and the bottom layer. When the incident electromagnetic wave passes through the first layer, only the incident wave x Polarization Component Can penetrate the top layer, y Polarization Component Reflected. Incident x The polarized wave interacts with the middle layer. Due to the electric and magnetic resonances generated by the middle conversion layer and the bottom grating, part of x The polarized wave is converted into y The polarized wave is then transmitted and reflected. Therefore, the converted component The remaining component is transmitted through the bottom grating The polarization direction of the electromagnetic wave passing through the metasurface is determined by the underlying layer. By repeating multiple reflections in the FP cavity, the incident TE polarized wave can be converted into a TM polarized wave.

[0056] Fig.12 (a)- Fig.12 (d) is the S parameter in F and G working modes, Pxx represents the phase of the incident TE wave and the outgoing TE wave, Pyx represents the phase of the incident TE wave and the outgoing TM wave, Px represents the phase of the incident TM wave and the outgoing TE wave, Pyy Represents the phase of the incident TM wave and the outgoing TM wave. Around 3GHz ( Fig.12 (a) and Fig.12 In the shaded part of (c), the two transmitted polarized waves have similar amplitudes and phase differences. Around. In the F mode, it can be seen that one of the incident polarized waves is converted into a circularly polarized wave and transmitted out, while the incident wave in the other polarization direction is shielded. In the F mode, the upper surface diodes of the first layer are turned on, the lower surface diodes are turned off, the upper and lower surface diodes of the third layer are both turned off, and the middle layer diodes are turned off. In the G mode, the upper surface diodes of the first layer are turned off, the lower surface diodes are turned on, the upper and lower surface diodes of the third layer are both turned off, and the middle layer diodes are turned off. Since the top layer diodes are turned on in one direction, only polarized waves in one direction can be incident. The transmitted polarized wave can be decomposed into two mutually perpendicular components, and the middle layer can produce a phase delay for one of the components, so a phase difference will be generated between the two components, and ultimately the effect of circular polarization will be achieved.

[0057] Fig.13 (a)- Fig.13 (b) is the axial ratio (AR) of circularly polarized waves in F and G modes. Near 3 GHz, the axial ratios are all below 3 dB, which well demonstrates the circular polarization performance.

[0058] Fig.14 (a)- Fig.14 (b) shows the polarization wave reflection in the H working mode. In the H mode, the first layer diodes are all disconnected, the third layer diodes are all turned on, and the middle layer diodes are disconnected. At this time, the first layer FSS structure has no effect on electromagnetic waves, and all polarization waves can pass through, while the third layer FSS structure can be equivalent to a metal plate, reflecting both polarization waves. The three-layer structure can be equivalent to a reflective polarization conversion surface. Fig.14 (c)- Fig.14 It can be seen from (d) that within the working frequency band, the polarization conversion rate (PCR) of the metasurface for polarized waves is above 90%.

[0059] Fig.15 (a)- Fig.15 (b) shows the polarized wave reflection in the I working mode, where both TE and TM polarized waves are reflected. In the I mode, all diodes in the first layer are turned on, all diodes in the third layer are turned off, and the diodes in the middle layer are turned off. At this time, the FSS structure of the first layer is equivalent to a metal plate that fully reflects electromagnetic waves, and all polarized waves are shielded.

[0060] The above embodiments are only for illustrating the technical idea of ​​the present invention, and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. A frequency selective surface with polarization reconfigurable characteristics, characterized in that: The frequency selective surface comprises: first, second and third dielectric layers arranged in sequence from top to bottom, with an air gap layer separating two adjacent dielectric layers; each dielectric layer is a square structure with the same side length, the first dielectric layer is provided with a first metal layer and a second metal layer on the upper and lower surfaces respectively, the second dielectric layer is provided with a third metal layer and a fourth metal layer on the upper and lower surfaces respectively, and the third dielectric layer is provided with a fifth metal layer and a sixth metal layer on the upper and lower surfaces respectively; The first metal layer includes four metal units of the same size, each of which is formed by overlapping two isosceles right triangles of the same size, and the hypotenuses of the two isosceles right triangles are on a straight line; the four metal units correspond to the four sides of the first dielectric layer respectively, and the hypotenuses of the two isosceles right triangles of each metal unit coincide with the corresponding sides of the first dielectric layer; the length of the side where the metal unit overlaps with the first dielectric layer is less than the side length of the first dielectric layer; the middle hollow part surrounded by the four metal units is a hollow square, the center of the hollow square coincides with the center of the first dielectric layer, and the diagonal of the hollow square coincides with the perpendicular bisector of the first dielectric layer; the space between two adjacent metal units is hollowed out, and the structure surrounded by the four metal units is a centrally symmetrical and axially symmetrical figure; the two metal units corresponding to the two perpendicular sides of the first dielectric layer are connected through a first PIN diode, and the remaining two sides are connected through a second PIN diode, and the conduction directions of the first PIN diode and the second PIN diode are consistent; The structures of the first, second, fifth and sixth metal layers are the same, the diagonal where the two PIN diodes of the second metal layer are located is orthogonal to the diagonal where the two PIN diodes of the first metal layer are located; the diagonal where the two PIN diodes of the sixth metal layer are located is orthogonal to the diagonal where the two PIN diodes of the fifth metal layer are located, and the positions of the two PIN diodes of the fifth metal layer are the same as the positions of the two PIN diodes of the first metal layer; The third metal layer includes four L-shaped metal structures of the same size, wherein the L-shaped metal structures are formed by a thick side and a thin side being perpendicular to each other, and the structure formed by the four L-shaped metal structures is an axially symmetrical figure with the perpendicular midline of the second dielectric layer as the axis, wherein the thin sides of two L-shaped metal structures coincide with the side A of the upper surface of the second dielectric layer, and the thick sides are connected through the third PIN diode; the thin sides of the other two L-shaped metal structures coincide with the side B of the upper surface of the second dielectric layer, and the side A is parallel to the side B; The fourth metal layer includes two rectangular metal strips of the same size. The length of the metal strips is equal to the side length of the second dielectric layer. The two metal strips coincide with the side C and the side D of the lower surface of the second dielectric layer respectively. The side C is parallel to the side D, and the side C is perpendicular to the side A.

2. The frequency selective surface with polarization reconfigurable characteristics according to claim 1, characterized in that: The first, second and third dielectric layers are all made of Rogers plates of model RO5880.

3. The frequency selective surface with polarization reconfigurable characteristics according to claim 1, characterized in that: When the third PIN diode on the third metal layer is turned on, the two PIN diodes on the first metal layer are turned on, the two PIN diodes on the second metal layer are turned off, the two PIN diodes on the fifth metal layer are turned on, and the two PIN diodes on the sixth metal layer are turned off, the upper and lower surface metal layers of the second dielectric layer are equivalent to metal grids, which generate CLC resonance with the metal layers on the upper and lower surfaces of the first and third dielectric layers, forming a second-order filter passband, realizing TE wave transmission and TM wave shielding; When the third PIN diode on the third metal layer is turned on, the two PIN diodes on the first metal layer are turned off, the two PIN diodes on the second metal layer are turned on, the two PIN diodes on the fifth metal layer are turned off, and the two PIN diodes on the sixth metal layer are turned on, the upper and lower surface metal layers of the second dielectric layer are equivalent to metal grids, which generate CLC resonance with the metal layers on the upper and lower surfaces of the first and third dielectric layers, forming a second-order filtering passband, realizing TM wave transmission and TE wave shielding; When the third PIN diode on the third metal layer is turned on, the two PIN diodes on the first metal layer are turned off, the two PIN diodes on the second metal layer are turned off, the two PIN diodes on the fifth metal layer are turned off, and the two PIN diodes on the sixth metal layer are turned off, the upper and lower surface metal layers of the second dielectric layer are equivalent to metal grids, which generate CLC resonance with the metal layers on the upper and lower surfaces of the first and third dielectric layers, forming a second-order filtering passband, and realizing TE wave transmission and TM wave transmission.

4. The frequency selective surface with polarization reconfigurable characteristics according to claim 1, characterized in that: When the third PIN diode on the third metal layer is disconnected, the two PIN diodes on the first metal layer are turned on, the two PIN diodes on the second metal layer are disconnected, the two PIN diodes on the fifth metal layer are disconnected, and the two PIN diodes on the sixth metal layer are turned on, the upper and lower surface metal layers of the first dielectric layer are regarded as a first whole, the upper and lower surface metal layers of the third dielectric layer are regarded as a second whole, the first whole and the second whole form a mutually perpendicular grating structure, the upper and lower surface metal layers of the second dielectric layer are equivalent to a polarization conversion structure, and the entire frequency selective surface structure forms an FP cavity, realizing the conversion of TE linear polarization to TM linear polarization and TM wave shielding; When the third PIN diode on the third metal layer is disconnected, the two PIN diodes on the first metal layer are disconnected, the two PIN diodes on the second metal layer are turned on, the two PIN diodes on the fifth metal layer are turned on, and the two PIN diodes on the sixth metal layer are disconnected, the upper and lower surface metal layers of the first dielectric layer are regarded as a first whole, the upper and lower surface metal layers of the third dielectric layer are regarded as a second whole, the first whole and the second whole form a mutually perpendicular grating structure, the upper and lower surface metal layers of the second dielectric layer are equivalent to a polarization conversion structure, and the entire frequency selective surface structure forms an FP cavity, realizing the conversion of TM linear polarization to TE linear polarization and TE wave shielding.

5. The frequency selective surface with polarization reconfigurable characteristics according to claim 1, characterized in that: When the third PIN diode on the third metal layer is disconnected, the two PIN diodes on the first metal layer are turned on, the two PIN diodes on the second metal layer are disconnected, the two PIN diodes on the fifth metal layer are disconnected, and the two PIN diodes on the sixth metal layer are disconnected, the fourth metal layer is equivalent to an inductor, and the third metal layer is equivalent to a capacitor. By controlling the equivalent values ​​of the capacitors and inductors in two mutually perpendicular directions, a phase difference is generated between the two perpendicular components of the incident TE linear polarization wave, thereby realizing the conversion of TE linear polarization to circular polarization and TM wave shielding. When the third PIN diode on the third metal layer is disconnected, the two PIN diodes on the first metal layer are disconnected, the two PIN diodes on the second metal layer are turned on, the two PIN diodes on the fifth metal layer are disconnected, and the two PIN diodes on the sixth metal layer are disconnected, the fourth metal layer is equivalent to an inductor, and the third metal layer is equivalent to a capacitor. By controlling the equivalent values ​​of the capacitors and inductors in two mutually perpendicular directions, a phase difference is generated between the two perpendicular components of the incident TM linear polarization wave, thereby realizing the conversion of TM linear polarization into circular polarization and TE wave shielding.

6. The frequency selective surface with polarization reconfigurable characteristics according to claim 1, characterized in that: When the third PIN diode on the third metal layer is disconnected, the two PIN diodes on the first metal layer are disconnected, the two PIN diodes on the second metal layer are disconnected, the two PIN diodes on the fifth metal layer are turned on, and the two PIN diodes on the sixth metal layer are turned on, the metal layer structure on the upper and lower surfaces of the third dielectric layer is equivalent to a metal plate, and the incident polarized wave passes through the upper and lower surfaces of the first dielectric layer, undergoes polarization conversion after passing through the metal layers on the upper and lower surfaces of the second dielectric layer, and is reflected by the metal plate when passing through the metal layers on the upper and lower surfaces of the third dielectric layer, thereby achieving reflected polarization conversion.

7. The frequency selective surface with polarization reconfigurable characteristics according to claim 1, characterized in that: When the third PIN diode on the third metal layer is disconnected, the two PIN diodes on the first metal layer are turned on, the two PIN diodes on the second metal layer are turned on, the two PIN diodes on the fifth metal layer are disconnected, and the two PIN diodes on the sixth metal layer are disconnected, the metal layer structures on the upper and lower surfaces of the first dielectric layer are equivalent to metal plates, and all incident polarized waves are reflected by the metal plates to achieve full shielding.

8. The frequency selective surface with polarization reconfigurable characteristics according to claim 1, characterized in that: The side lengths of the first dielectric layer, the second dielectric layer and the third dielectric layer are all 10 mm, and the thicknesses are all 0.5 mm; the thickness of the air gap layer is 5 mm, the side length of the hollow square is 5 mm, and the spacing between two adjacent metal units is 1.5 mm; the width of the thick side of the L-shaped metal structure is 1 mm, the width of the thin side is 0.3 mm, the length of the thick side is 3.7 mm, and the length of the thin side is 4.5 mm; the spacing between the thick sides of the two L-shaped metal structures overlapping with the side A on the upper surface of the second dielectric layer is 1 mm; the width of the rectangular metal strip is 0.6 mm.

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