Pure-metal double-frequency double-rotation-direction-line circular polarization converter and design method thereof

Abstract

The invention discloses a pure metal double-frequency double-rotation-direction-line circular polarization converter and a design method thereof, and belongs to the technical field of antennas and electromagnetic metasurfaces. The atomic unit array is of a reflective structure and is composed of a plurality of atomic unit periodic arrays, and adjacent atomic units are tightly connected. The atomic unit comprises an upper-layer metal structure and a lower-layer metal structure which are separated by air. The upper-layer metal structure is a square pixel metal plate structure and is formed by performing material reduction slotting on a square slotting structure and a strip-shaped slotting structure on a pure metal plate; the lower layer metal structure is a pure metal plate structure. External incident electromagnetic waves are incident to the upper-layer metal structure along the normal direction, and are reflected and returned at the lower-layer metal structure to form target circularly polarized waves after combined action with air. According to the converter, under the condition of not depending on dielectric substrate printing, reflection circular polarization output of incident ray polarization waves in two different frequency bands is achieved through a manufacturable pure metal laminated structure, the output rotation directions of the two frequency bands are opposite, and the structure realizability and the design reproducibility are improved.

Description

Technical Field

[0001] This invention belongs to the field of antenna and electromagnetic metasurface technology, and relates to a pure metal dual-frequency dual-rotational linear circular polarization converter and its design method. Specifically, it is a pure metal dual-frequency dual-rotational linear circular polarization converter and its design method based on a multi-port network. Background Technology

[0002] Currently, metasurfaces are a class of artificial electromagnetic structures composed of subwavelength-scale periodic units. Their ability to manipulate the amplitude, phase, and polarization state of incident electromagnetic waves can typically be characterized by parameters such as equivalent impedance and equivalent polarizability, thereby enabling functions such as beamforming, frequency selection, and polarization conversion [F. Liu, D.-H. Kwon, and S. Tretyakov, “Reflectarrays and metasurface reflectors as diffraction gratings: A tutorial”, IEEE Antennas and Propagation Magazine, vol. 65, no. 3, pp. 21–32, doi: 10. 1109 / MAP. 2023. 3236278, 2023.], [M. Akbari, F. Samadi, A. - R. Sebak, and TA Denidni, “Superbroadband diffuse wave scattering based on coding metasurfaces: Polarization conversion metasurfaces”, IEEE Antennas andPropagation Magazine, vol. 61, no. 2, pp. 40–52, Apr. 2019, doi: 10.1109 / MAP.2019. 2896218, 2019.], [L. Nama, N. Bhattacharyya, and PK Jain, “Ametasurface-based, ultrathin, dual-band, "linear-to-circular, reflective polarization converter: Easing uplinking and downlinking for wireless communication", IEEE Antennas and Propagation Magazine, vol. 63, no. 4, pp.100–110, 2021, doi: 10. 1109 / MAP. 2020. 3043460, 2021.].

[0003] Linear-to-Circular Polarization Converters (LCPCs) typically operate based on the anisotropic response of metasurface units. After reflection or transmission, a linearly polarized incident wave can be decomposed into two orthogonal components. If the amplitudes of the two orthogonal components are approximately equal and their phase difference is close to ±90° within the target frequency band, a circularly polarized output can be achieved. To obtain dual-frequency characteristics, existing technologies typically introduce multi-scale geometry, multiple current paths, or multi-mode resonances to ensure that the structure satisfies the aforementioned circular polarization conditions in both frequency bands. Furthermore, to obtain dual-rotation output, the signs of the phase difference between the orthogonal components need to be reversed in the two frequency bands, thereby forming circularly polarized waves with opposite rotation directions in different frequency bands [J. Lundgren, O. Zetterstrom, F. Mesa, NJG Fonseca, and O. Quevedo-Teruel, “Fullymetallic dual-band linear-to-circular polarizer for K / Ka-band”, IEEE Antennas and Wireless Propagation Letters, vol. 20, no. 11, pp. 2191–2195, doi:10.1109 / LAWP. 2021. 3081655, 2021].

[0004] Existing metasurface-based LCPC solutions mostly employ dielectric substrate printing and multilayer stacking processes. While these processes are mature and easy to implement complex patterns, space applications such as satellite communications often require simultaneous low-loss and environmental adaptability. Dielectric loss can lead to efficiency degradation, and environmental factors such as outgassing, thermal cycling, and irradiation can impose higher constraints on material reliability and structural stability. Therefore, under the constraints of engineering manufacturability and environmental adaptability, there is still room for improvement in achieving a pure metal, dual-frequency, dual-rotation linear-to-circular polarization converter that satisfies the axial ratio and polarization conversion efficiency [B. Lin, L.Lv, J. Guo, Z. Liu, X. Ji, and J. Wu, “An ultra-wideband reflective linear-to-circular polarization converter based on anisotropic metasurface”, IEEEAccess, vol. 8, pp. 82732–82740, doi: 10.1109 / ACCESS. 2020. 2988058, 2020.].

[0005] The existing technical solution is as follows: (1) Reflective LCPC printed on dielectric substrate: This type of scheme typically prints anisotropic metal patterns on one side of the dielectric substrate and sets a metal ground plane on the other side of the dielectric substrate, which is a reflective structure. The pattern layer, dielectric layer and ground plane form an equivalent resonant structure. By controlling the amplitude and phase of the two orthogonal reflection components, they can meet the circular polarization condition in the target frequency band. In order to achieve dual frequency or dual frequency dual rotation, multi-scale patterns, parasitic branches or multi-layer stacking are often used to make the structure resonate in two frequency bands and achieve phase difference control. This type of scheme has relatively mature technology and is easy to realize complex patterns, but its electromagnetic performance is usually related to the dielectric material parameters, interlayer thickness and processing consistency. In addition, under high frequency or harsh environment conditions, dielectric loss may lead to a decrease in polarization conversion efficiency.

[0006] (2) Multilayer / Tunable LCPC: This type of solution achieves dual-frequency, controllable polarization conversion or bandwidth expansion by stacking multiple metasurfaces or introducing tunable materials. The characteristics of this type of solution are high design freedom, but the sensitivity of interlayer alignment and assembly is increased. At the same time, it may introduce additional bias, packaging or complex processing requirements, thereby increasing the difficulty of engineering implementation and reliability assessment.

[0007] (3) All-metal polarization converter: This type of scheme usually uses an all-metal frequency selective surface (FSS), slot structure, and metal component array to achieve dual-frequency linear circular polarization conversion, which has advantages in material reliability and loss control. In existing all-metal structures, the unit topology is mostly a fixed geometric pattern, such as a specific cross, slot, or ring structure, and the design process usually requires a lot of full-wave simulation and parameter adjustment. In dual-frequency, dual-rotational targets, the amplitude and phase conditions of the two frequency bands are easily coupled, increasing the number of design iterations and potentially extending the design cycle [X. Zhao, C. Yuan, L. Liu, and H. Zhou, “All-metal transmit-array for circular polarization design using rotated cross-slot elements for high-power microwave applications”, IEEE Transactions on Antennas and Propagation, vol. 65, no. 6, pp. 3253–3256, doi: 10. 1109 / TAP. 2017. 2691460, 2017.], [N. Liu, X. Sheng, C. Zhang, J. Fan, and D. Guo, “A design method for synthesizing wideband band-stop FSS via its equivalent circuit model”. IEEE Antennas and Wireless Propagation Letters, vol. 16, pp.2721–2725, doi: 10.1109 / LAWP. 2017. 2743114, 2017.].

[0008] The drawbacks of existing technologies are: (1) When realizing dual-frequency, dual-rotation linear-circular polarization conversion on space carriers such as satellites, the existing “antenna feed network / multiple feed sources” scheme usually requires a relatively complex feed network and debugging process, which can easily lead to problems such as complex structure, increased volume and mass, and increased difficulty in engineering implementation.

[0009] (2) Existing linear-to-circular polarization converters (LCPCs) mostly employ dielectric substrate printing and multilayer dielectric stacking processes. Under space environment conditions such as thermal cycling, venting, and irradiation, the consistency requirements of material systems and processes are high. At the same time, dielectric loss may lead to a decrease in efficiency, which is not conducive to low-loss application scenarios.

[0010] (3) Even with an all-metal approach, the continuous parameterization design of traditional fixed resonant units and fixed connection methods has limited freedom, making it difficult to achieve dual-frequency operation and dual-rotation output under pure metal constraints, while meeting comprehensive requirements such as axial ratio and polarization conversion efficiency. Summary of the Invention

[0011] To address the aforementioned problems, this invention proposes a pure metal dual-frequency dual-rotation linear circular polarization converter based on a multi-port network and its design method. The converter of this invention, without relying on dielectric substrate printing, achieves reflected circular polarization output of the incident linearly polarized wave in two different frequency bands through a manufacturable pure metal stacked structure, and makes the rotation directions of the two frequency band outputs opposite, while improving structural feasibility and design reproducibility.

[0012] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A pure metal dual-frequency dual-rotation linear circular polarization converter, specifically a pure metal dual-frequency dual-rotation linear circular polarization converter based on a multi-port network, is a reflective structure composed of a periodic array of multiple atomic units, with adjacent atomic units closely connected. The atomic unit includes an upper metal structure 1 and a lower metal structure 2. The upper metal structure 1 and the lower metal structure 2 are stacked sequentially from top to bottom, separated by air gaps, the thickness of which is... , The range is 1~10mm.

[0013] The upper metal structure 1 is a square pixel metal plate structure with the same length and width, and a thickness ranging from 0 to 1 mm. It includes an outer metal frame 3, a cross-shaped metal conductor 4, an edge metal conductor 5, and a shorting strip topology 6. It is formed by subtractive grooving of the square slotted structure 7 and the strip slotted structure 8 on a pure metal plate. The thickness of the outer metal frame 3, the cross-shaped metal conductor 4, the edge metal conductor 5, the shorting strip topology 6, the square slotted structure 7, and the strip slotted structure 8 are all the same as the thickness of the upper metal structure 1.

[0014] The outer metal frame 3 is a ring of metal around the upper metal structure 1, used for connecting adjacent atomic unit arrays. The metal frame has a certain width, ranging from 0.1 to 0.6 mm.

[0015] The cross-shaped metal conductor 4 consists of nine identical cross-shaped metals arranged in a 3x3 uniform array within an atomic unit. Each cross-shaped metal is formed by two identical metal strips perpendicularly overlapping. A certain gap exists between adjacent cross-shaped metals. The thickness is 0.1~0.5mm.

[0016] The edge metal conductors 5 are connected to the outer metal frame 3, and there are a total of 12 edge metal conductors 5. Each side of the outer metal frame 3 has three edge metal conductors 5, and the edge metal conductors 5 on each side are evenly spaced. A certain gap is maintained between them and the cross metal conductors. The range is 0.1~0.5mm.

[0017] The square slotted structure 7 consists of sixteen identical square slots arranged in a regular 4x4 array. The length and width of each square slot are the same, and there is a certain distance between adjacent square slots.

[0018] The strip-shaped slot 8 connects to the edge of the square slot structure 7 (the edge is the two adjacent sides of the adjacent square slots; the square slot edges of the array edge have no strip-shaped slots), and the strip-shaped slot 8 is long. The range is 0.5~0.6mm, and the width is... It is 0~0.1mm.

[0019] The shorting bar topology 6 consists of multiple shorting bar structures located between adjacent cross-shaped metal conductors 4 and between adjacent cross-shaped metal conductors 4 and edge metal conductors 5. The shorting bar topology 6 is used to form a controllable current path. The presence or absence of shorting bar structures between adjacent cross-shaped metal conductors 4 and between adjacent cross-shaped metal conductors 4 and edge metal conductors 5 corresponds to current conduction and current interruption (i.e., short circuit and open circuit), respectively, and is determined by the design method of the pure metal dual-frequency dual-rotation circular polarization converter described below (the presence or absence of shorting bar structures between adjacent cross-shaped metal conductors and between adjacent cross-shaped metal conductors 4 and edge metal conductors 5). Simultaneously, the positions of the shorting bar structures correspond to the internal port positions in the design method below.

[0020] The lower metal structure 2 is a pure metal plate structure, with the same length, width, and thickness as the upper metal structure 1. External incident electromagnetic waves are incident along the normal direction to the upper metal structure 1, and after being interacted with by the upper metal structure 1 and the air, they are reflected at the lower metal structure 2 and return, thus forming a target circularly polarized wave in the reflection direction.

[0021] Furthermore, the upper metal structure 1 and the lower metal structure 2 are made of stainless steel, or can be made of copper alloy, titanium alloy or other metal materials, and can be manufactured by laser cutting, waterjet cutting, CNC milling or stamping.

[0022] A design method for a pure metal dual-frequency dual-rotation linear circular polarization converter mainly involves determining the layout of the shorting strip topology 6 in the upper metal structure 1 and the air gap thickness parameters between the upper metal structure 1 and the lower metal structure 2. Specifically, the method includes the following steps: The first step is to construct the pixelated platform and internal port layout definition of the upper metal structure 1, specifically: Step 1.1: Construct the pixelated platform of the upper metal structure 1, define the structural parameters of the upper metal structure 1 in the atomic unit and the geometric parameters of the shorting strip structure, and determine the outer metal frame 3 as the reference conductor for connectivity determination.

[0023] Step 1.2: The positions in the shorting bar structure are set as discrete internal ports. The preset set of discrete internal port positions is {p=1}. 2 … },in The number of internal ports (24 in total) is fixed, and their spatial locations and numbers are also fixed. The topology 6 of the jumper bar in the upper metal structure 1 is represented only by changes in the terminal states of the internal ports. The locations and numbers of the discrete ports are shown in the appendix. Figure 4 As shown; The second step involves obtaining the candidate topology of the atomic units based on the internal port layout obtained in the first step, and the air gap thickness between the upper metal structure 1 and the lower metal structure 2. Specifically: Step 2.1, Establish discrete internal ports Define the internal port binary terminal state vector. , .in This indicates that the internal port is short-circuited, and the corresponding shorting bar structure is conductive. This indicates that the internal port is open, and no jumper bar structure should be placed there.

[0024] Step 2.2: Using the internal port binary terminal state vector (short-circuit topology 6) and the air gap thickness between the upper metal structure 1 and the lower metal structure 2 as candidate indices, candidate topologies for atomic units are formed. .

[0025] The third step is to obtain candidate topologies for atomic units based on the second step. Connectivity algorithms are used to determine feasible candidate topologies. Specifically: Step 3.1: Abstract the atomic units into undirected graphs. , where the vertex set Represents the individual metallic conductor regions under the platform abstraction, and the edge set. This indicates a connection capable of supporting current flow. For each internal port, if its state is short-circuited ( If an open circuit is formed, then an edge is added between the two corresponding conductors. If the edge is not added, then a symmetric connectivity matrix is ​​constructed from the above relationships. .

[0026] Step 3.2, using a connected matrix A breadth-first search (BFS) is performed to avoid floating metal and electrical discontinuities and to determine reachability. Starting from the outer metal border 8, all adjacent reachable metal conductors are visited sequentially (metal conductors include the cross-shaped metal conductor 4, the edge metal conductor 5, and the shorting strip topology 6). If all metal conductors within the set are visited, the connectivity flag for that layer is true, and the candidate topology is feasible; otherwise, it is false, not feasible, and the candidate topology is discarded. The final candidate topologies that satisfy feasibility are... It has been reserved.

[0027] The fourth step, based on the atomic units obtained in the first step, is to construct external ports and define external channels. Specifically: Step 4.1: Set periodic boundary conditions in the transverse direction of the atomic unit and set open / radiative boundaries in the incident direction to simulate a periodic array, that is, a pure metal dual-frequency dual-rotation linear circular polarization converter composed of multiple atomic unit arrays.

[0028] Step 4.2: Establish Floquet external ports on the top and bottom sides of the atomic unit, respectively, and excite and read the fundamental mode TE / TM channels. Define the TE and TM fundamental mode channels as the external port set e, which is used to describe the fundamental mode energy exchange of the reflection.

[0029] Fifth step: Based on the internal ports obtained in step two and the external ports constructed in step four, the multi-port scattering matrix of the upper metal structure 1 is obtained and divided into blocks, specifically: Step 5.1, for candidate topologies The multi-port scattering matrix, including both external and internal ports, is obtained by solving on the frequency sampling set. .

[0030] Step 5.2, by external port With internal port right Divide into blocks, .in It is the scattering matrix between external ports. It is the coupling scattering submatrix from the internal port to the external port. It is the coupling scattering submatrix from the external port to the internal port. It is the scattering matrix between internal ports.

[0031] Step 6: Based on the multi-port scattering matrix of the upper metal structure 1 obtained in step 5. Perform internal port binary termination and internal port elimination to obtain the external equivalent layer response, specifically: Step 6.1, construct the internal port terminal diagonal matrix ,in .

[0032] Step 6.2: Apply termination to the internal ports and perform elimination to obtain the external equivalent scattering matrix containing only the external ports of the upper metal structure 1. , .

[0033] Step 7: Based on the external equivalent scattering matrix of the upper metal structure 1 obtained in step 6. By constructing an interlayer air gap network and cascading the networks, the overall external scattering matrix is ​​obtained. Specifically: Step 7.1: Model the air gap between the upper metal structure 1 and the lower metal structure 2 as a propagation and phase delay network to obtain the air layer scattering matrix. .

[0034] Step 7.2: Concatenate the external equivalent network and the air gap network using Redheffer star product in a stacking order to obtain the overall external scattering matrix. , .

[0035] Step 8: Based on the overall external scattering matrix obtained in Step 7, the dual-frequency dual-rotation circular polarization index of the pure metal dual-frequency dual-rotation linear-circular converter is obtained, specifically: Step 8.1, from Extraction of co-polarized and cross-polarized reflection coefficients and Furthermore, the reflection components of RHCP / LHCP are obtained.

[0036] Step 8.2, calculate the right-hand / left-hand polarization conversion efficiency. , and shaft ratio .

[0037] Step 9: Based on the dual-frequency, dual-rotation circular polarization index obtained in Step 8, construct the objective function and perform iterative optimization using the NSGA-III non-dominated sorting genetic algorithm to obtain the optimal topology. Specifically: Step 9.1, Define the first target frequency band With the second target frequency band and order .exist The target rotation direction is specified as RHCP. The target spin direction is specified as LHCP. Further, the desired polarization conversion efficiency profile is defined. :when Time to take ,when Time to take .

[0038] Step 9.2: Construct a multi-objective function and evaluate candidate solutions. Construct the following two objective functions: in It is the axis ratio threshold. To minimize To optimize the target, the polarization conversion efficiency within the joint passband should be as close to 1 as possible while the axial ratio should not exceed a preset threshold.

[0039] Step 9.3: Use NSGA-III to evaluate candidate topologies. Selection, crossover, and mutation are performed to generate a new generation of population. New candidate topologies are then generated. Repeat steps 2 to 9 until the stopping condition is met, and output the optimal or Pareto optimal combination of atomic unit topologies, including the shorting strip topology 6 of the atomic unit of the upper metal structure 1, the air gap thickness between the upper metal structure 1 and the lower metal structure 2, and finally obtain a pure metal dual-frequency dual-rotation linear circular polarization converter that meets the design requirements.

[0040] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The pure metal dual-frequency dual-rotation linear circular polarization converter proposed in this invention adopts a reflective structure composed of pure metal pixels, air gaps and metal ground planes. Metal and air are the main media, reducing the dependence on the dielectric substrate material system. It can reduce the risk of material parameter drift and additional loss caused by environmental factors such as thermal cycling, gas release and irradiation to a certain extent, thereby helping to improve the structural stability under space application conditions.

[0041] (2) The pure metal dual-frequency dual-rotation linear-circular polarization converter proposed in this invention adopts a pure metal structure and combines a topology reconfigurable design with open or short-circuited internal ports, so that a single device can realize linear-circular polarization conversion of two frequency bands with opposite rotation directions, thereby reducing the dependence on complex power supply networks and improving the system integration.

[0042] (3) The pure metal dual-frequency dual-rotation linear circular polarization converter design method proposed in this invention adopts multi-port matrix elimination and network cascading to replace generational full-wave trial and error, and introduces connectivity constraints as gating, which can reduce the workload of invalid search and manual screening, make the optimization process easier to repeat and reduce the dependence on experience parameter tuning.

[0043] (4) Technical effects achievable by the present invention: The pure metal dual-frequency dual-rotation linear circular polarization converter proposed in this invention can achieve right-hand circular polarization (RHCP) output in the first operating frequency band and left-hand circular polarization (LHCP) output in the second operating frequency band, while meeting the preset index requirements for axial ratio and polarization conversion efficiency within the corresponding frequency bands. In a preferred embodiment, the present invention adopts a reflective configuration, wherein the circular polarization output is manifested as circular polarization reflection, achieving RHCP reflection output in the 6.5–7.5 GHz frequency band and LHCP reflection output in the 9–10 GHz frequency band. The results show that circular polarization output with dominant rotation is obtained in both operating frequency bands while maintaining a low axial ratio, and the dominant polarization conversion efficiency is approximately 90%–95%. Furthermore, the insertion loss within the operating frequency band is estimated to be approximately 0.5 dB by comparison with the reflection of a solid metal plate of the same size, thus verifying the low loss and feasibility of the present invention in dual-frequency dual-rotation linear circular polarization conversion. Furthermore, the present invention can also achieve linear-circular polarization conversion via transmission by adjusting the structure, while still meeting the requirements for axial ratio and polarization conversion efficiency. Attached Figure Description

[0044] Figure 1 This is a design flowchart of the present invention; Figure 2 This is a schematic diagram of the atomic unit structure of the pure metal dual-frequency dual-rotation linear circular polarization converter proposed in this invention; Figure 3 This is a schematic diagram of the upper metal structure 1 in the atomic unit of the pure metal dual-frequency dual-rotation linear circular polarization converter proposed in this invention. Figure 4 This is a schematic diagram of the structural parameters of the upper metal structure 1 in the atomic unit of the pure metal dual-frequency dual-rotation linear circular polarization converter proposed in this invention. Figure 5 This is a schematic diagram of the pixelation platform and the multi-port upper metal structure 1 in the atomic unit; Figure 3 (a) in the figure is an example diagram of applying excitation to an external Floquet port; Figure 3 (b) in the diagram is a schematic diagram of the internal ports of the upper metal structure 1; Figure 3 (c) is a schematic diagram of the upper metal structure 1 in the optimized atomic unit; Figure 6 The simulation results show the co-polarization and cross-polarization reflection coefficients of the synthesized reflective LCPC under TE incident conditions. The co-polarization component was obtained through full-wave simulation. With cross-polarization components The amplitude and phase; Figure 7 The figure shows the simulation results of polarization conversion efficiency versus axial ratio of the synthesized LCPC under TE incident conditions. In the diagram: 1. Upper metal structure; 2. Lower metal structure; 3. Outer metal frame; 4. Cross-shaped metal conductor; 5. Edge metal conductor; 6. Shorting strip topology; 7. Square slotted structure; 8. Long slotted structure. Detailed Implementation

[0045] The specific embodiments of the present invention will now be described in conjunction with the accompanying drawings and technical solutions.

[0046] A pure metal dual-frequency dual-rotational linear circular polarization converter, specifically a pure metal dual-frequency dual-rotational linear circular polarization converter based on a multi-port network, wherein the pure metal dual-frequency dual-rotational linear circular polarization converter has a reflective structure, consisting of a 5×5 array of 25 atomic units, with adjacent atomic units closely connected. (See attached diagram) Figure 2 As shown, the atomic unit comprises an upper metal structure 1 and a lower metal structure 2. The upper metal structure 1 and the lower metal structure 2 are stacked sequentially from top to bottom, separated by air gaps, the thickness of which is... It is 6.5mm.

[0047] Appendix Figure 3 This is a schematic diagram of the atomic unit structure of the pure metal dual-frequency dual-rotation linear circular polarization converter proposed in this invention. The upper metal structure 1 is a square pixel metal plate structure with a length and width L1 of 12mm and a thickness of 0.5mm. It includes an outer metal frame 3, a cross-shaped metal conductor 4, an edge metal conductor 5, and a shorting strip topology 6. It is formed by subtractive grooving of the square slotted structure 7 and the strip slotted structure 8 on the pure metal plate. The thickness of the outer metal frame 3, the cross-shaped metal conductor 4, the edge metal conductor 5, the shorting strip topology 6, the square slotted structure 7, and the strip slotted structure 8 are all the same as the thickness of the upper metal structure 1.

[0048] Appendix Figure 4 This is a schematic diagram of the structural parameters of the atomic unit of the pure metal dual-frequency dual-rotation linear circular polarization converter proposed in this invention. The outer metal frame 3 is a ring of metal around the upper metal structure 1, used for connecting adjacent atomic unit arrays. The width of the metal frame is 0.6 mm.

[0049] The cross-shaped metal conductor 4 consists of nine identical cross-shaped metals arranged in a 3x3 uniform array within an atomic unit. Each cross-shaped metal is composed of two long... 2.5mm wide It is formed by vertically overlapping metal strips, each 0.6mm thick. There are gaps between adjacent cross-shaped metal strips. It is 0.5mm.

[0050] The edge metal conductors 5 are connected to the outer metal frame 3, and there are a total of 12 edge metal conductors 5. The edge metal conductors 5 are long... It is 0.95mm wide. The thickness is 0.6mm. Each edge of the outer metal frame 3 has three edge metal conductors 5, and the edge metal conductors 5 on each side are evenly spaced. A certain gap is maintained between them and the cross metal conductors. It is 0.5mm.

[0051] The square slotted structure 7 consists of sixteen identical square slots arranged in a regular four-by-four array. The length and width of the square slots... The distance between adjacent square slots is 2.4mm. It is 0.6mm.

[0052] The strip-shaped slot 8 connects to the edge of the square slot structure 7 (the edge is the two adjacent sides of the adjacent square slots; the square slot edges of the array edge have no strip-shaped slots), and the strip-shaped slot 8 is long. It is 0.5mm wide. It is 0.05mm.

[0053] The shorting strip topology 6 consists of multiple shorting strip structures, which are located between adjacent cross-shaped metal conductors 4 and between adjacent cross-shaped metal conductors 4 and edge metal conductors 5. The dimension of the shorting strip structure is length. It is 0.5mm wide. The shorting bar topology 6, with a diameter of 0.5 mm, is used to form a controllable current path. The presence or absence of shorting bar structures between adjacent cross-shaped metal conductors 4 and between adjacent cross-shaped metal conductors 4 and the edge metal conductor 5 corresponds to current conduction and current interruption (i.e., short circuit and open circuit), respectively. The presence or absence of shorting bar topology 6 (between adjacent cross-shaped metal conductors and between adjacent cross-shaped metal conductors 4 and the edge metal conductor 5) is determined by the design method of the pure metal dual-frequency dual-rotation circular polarization converter described below. Simultaneously, the position of the shorting bar structure corresponds to the position of the internal port in the design method below.

[0054] The lower metal structure 2 is a pure metal plate structure, with the same length, width, and thickness as the upper metal structure 1. External incident electromagnetic waves are incident along the normal direction to the upper metal structure 1, and after being interacted with by the upper metal structure 1 and the air, they are reflected at the lower metal structure 2 and return, thus forming a target circularly polarized wave in the reflection direction.

[0055] Furthermore, the upper metal structure 1 and the lower metal structure 2 are made of stainless steel, or can be made of copper alloy, titanium alloy or other metal materials, and can be manufactured by laser cutting, waterjet cutting, CNC milling or stamping.

[0056] A design method for a pure metal dual-frequency dual-rotation linear circular polarization converter is presented. This method primarily determines the layout of the shorting strip topology 6 in the upper metal structure 1 and the air gap thickness parameters between the upper metal structure 1 and the lower metal structure 2. The design process is shown in the attached figure. Figure 1 As shown, the specific steps include: The first step is to construct the pixelated platform and internal port layout definition of the upper metal structure 1, specifically: Step 1.1: Construct the pixelated platform of the upper metal structure 1, define the structural parameters of the upper metal structure 1 in the atomic unit and the geometric parameters of the shorting strip structure, and determine the outer metal frame 3 as the reference conductor for connectivity determination.

[0057] Step 1.2: The positions in the shorting bar structure are set as discrete internal ports. The preset set of discrete internal port positions is {p=1}. 2 … },in The number of internal ports (24 in total) is fixed, and their spatial locations and numbers are also fixed. The topology 6 of the jumper bar in the upper metal structure 1 is represented only by changes in the terminal states of the internal ports. The locations and numbers of the discrete ports are shown in the appendix. Figure 5 (b) The second step involves obtaining the candidate topology of the atomic units based on the internal port layout obtained in the first step, and the air gap thickness between the upper metal structure 1 and the lower metal structure 2. Specifically: Step 2.1, Establish discrete internal ports Define the internal port binary terminal state vector. , .in This indicates that the internal port is short-circuited, and the corresponding shorting bar structure is conductive. This indicates that the internal port is open, and no jumper bar structure should be placed there.

[0058] Step 2.2: Using the internal port binary terminal state vector (short-circuit topology 6) and the air gap thickness between the upper metal structure 1 and the lower metal structure 2 as candidate indices, candidate topologies for atomic units are formed. .

[0059] The third step is to obtain candidate topologies for atomic units based on the second step. Connectivity algorithms are used to determine feasible candidate topologies. Specifically: Step 3.1: Abstract the atomic units into undirected graphs. , where the vertex set Represents the individual metallic conductor regions under the platform abstraction, and the edge set. This indicates a connection capable of supporting current flow. For each internal port, if its state is short-circuited ( If an open circuit is formed, then an edge is added between the two corresponding conductors. If the edge is not added, then a symmetric connectivity matrix is ​​constructed from the above relationships. .

[0060] Step 3.2, using a connected matrix A breadth-first search (BFS) is performed to avoid floating metal and electrical discontinuities and to determine reachability. Starting from the outer metal border 8, all adjacent reachable metal conductors are visited sequentially (metal conductors include the cross-shaped metal conductor 4, the edge metal conductor 5, and the shorting strip topology 6). If all metal conductors within the set are visited, the connectivity flag for that layer is true, and the candidate topology is feasible; otherwise, it is false, not feasible, and the candidate topology is discarded. The final candidate topologies that satisfy feasibility are... It has been reserved.

[0061] The fourth step, based on the atomic units obtained in the first step, is to construct external ports and define external channels. Specifically: Step 4.1: Set periodic boundary conditions in the transverse direction of the atomic unit and set open / radiative boundaries in the incident direction to simulate a periodic array, that is, a pure metal dual-frequency dual-rotation linear circular polarization converter composed of multiple atomic unit arrays.

[0062] Step 4.2, as attached Figure 5 As shown in (a), Floquet external ports are established on the upper and lower sides of the atomic unit to excite and read the fundamental mode TE / TM channels. The TE and TM fundamental mode channels are defined as the external port set e, which is used to describe the fundamental mode energy exchange of the reflection.

[0063] Fifth step: Based on the internal ports obtained in step two and the external ports constructed in step four, the multi-port scattering matrix of the upper metal structure 1 is obtained and divided into blocks, specifically: Step 5.1, for candidate topologies The multi-port scattering matrix, including both external and internal ports, is obtained by solving on the frequency sampling set. .

[0064] Step 5.2, by external port With internal port right Divide into blocks, .in It is the scattering matrix between external ports. It is the coupling scattering submatrix from the internal port to the external port. It is the coupling scattering submatrix from the external port to the internal port. It is the scattering matrix between internal ports.

[0065] Step 6: Based on the multi-port scattering matrix of the upper metal structure 1 obtained in step 5. Perform internal port binary termination and internal port elimination to obtain the external equivalent layer response, specifically: Step 6.1, construct the internal port terminal diagonal matrix ,in .

[0066] Step 6.2: Apply termination to the internal ports and perform elimination to obtain the external equivalent scattering matrix containing only the external ports of the upper metal structure 1. , .

[0067] Step 7: Based on the external equivalent scattering matrix of the upper metal structure 1 obtained in step 6. By constructing an interlayer air gap network and cascading the networks, the overall external scattering matrix is ​​obtained. Specifically: Step 7.1: Model the air gap between the upper metal structure 1 and the lower metal structure 2 as a propagation and phase delay network to obtain the air layer scattering matrix. .

[0068] Step 7.2: Concatenate the external equivalent network and the air gap network using Redheffer star product in a stacking order to obtain the overall external scattering matrix. , .

[0069] Step 8: Based on the overall external scattering matrix obtained in Step 7, the dual-frequency dual-rotation circular polarization index of the pure metal dual-frequency dual-rotation linear-circular converter is obtained, specifically: Step 8.1, from Extraction of co-polarized and cross-polarized reflection coefficients and Furthermore, the reflection components of RHCP / LHCP are obtained.

[0070] Step 8.2, calculate the right-hand / left-hand polarization conversion efficiency. , and shaft ratio .

[0071] Step 9: Based on the dual-frequency, dual-rotation circular polarization index obtained in Step 8, construct the objective function and perform iterative optimization using the NSGA-III non-dominated sorting genetic algorithm to obtain the optimal topology. Specifically: Step 9.1, Define the first target frequency band With the second target frequency band and order .exist The target rotation direction is specified as RHCP. The target spin direction is specified as LHCP. Further, the desired polarization conversion efficiency profile is defined. :when Time to take ,when Time to take .

[0072] Step 9.2: Construct a multi-objective function and evaluate candidate solutions. Construct the following two objective functions: in It is the axis ratio threshold. To minimize To optimize the target, the polarization conversion efficiency within the joint passband should be as close to 1 as possible while the axial ratio should not exceed a preset threshold.

[0073] Step 9.3: Use NSGA-III to evaluate candidate topologies. Selection, crossover, and mutation are performed to generate a new generation of population. New candidate topologies are then generated. Repeat steps 2 through 9 until the stopping condition is met, outputting the optimal or Pareto optimal combination of atomic unit topologies, including the shorting strip topology 6 of the upper metal structure 1, and the air gap thickness between the upper metal structure 1 and the lower metal structure 2. Finally, a pure metal dual-frequency dual-rotation linear circular polarization converter that meets the design requirements is obtained. The optimized topology of the upper metal structure 1 is shown in the attached figure. Figure 5 As shown in (c), the air gap thickness between the upper metal structure 1 and the lower metal structure 2 is 6.5 mm.

[0074] Through the above steps, this invention can perform a collaborative search within the topological space (internal port open / short) and the parameter space (air gap thickness, etc.), enabling the resulting structure to achieve highly efficient circularly polarized reflection with opposite rotation directions in two frequency bands. The final simulation results are shown in the attached figure. Figure 6 and attached Figure 7 As shown, the pure metal dual-frequency dual-rotation linear circular polarization converter of this invention achieves RHCP reflection output in the 6.5–7.5 GHz frequency band and LHCP reflection output in the 9–10 GHz frequency band. It obtains circularly polarized output with dominant rotation in both operating frequency bands while maintaining a low axial ratio, and the dominant polarization conversion efficiency is approximately 90%–95%, meeting the design requirements.

[0075] The above specific embodiments further illustrate the purpose, technical solution and beneficial effects of this application. It should be understood that the above are only specific embodiments of this application and are not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made on the basis of the technical solution of this application should be included within the scope of protection of this application.

Claims

1. A pure metal dual-frequency dual-rotation linear circular polarization converter, characterized in that, The pure metal dual-frequency dual-rotation linear circular polarization converter is a reflective structure composed of a periodic array of multiple atomic units, with adjacent atomic units closely connected. The atomic unit includes an upper metal structure (1) and a lower metal structure (2). The upper metal structure (1) and the lower metal structure (2) are stacked sequentially from top to bottom, separated by air gaps, with the air gap thickness being [missing information]. ; The upper metal structure (1) is a square pixel metal plate structure, including an outer metal frame (3), a cross metal conductor (4), an edge metal conductor (5), and a shorting strip topology (6), which is formed by subtractive grooving of the square slotted structure (7) and the strip slotted structure (8) on a pure metal plate. The lower metal structure (2) is a pure metal plate structure, and its length, width and thickness are the same as those of the upper metal structure (1). External incident electromagnetic waves are incident along the normal direction to the upper metal structure (1). After the interaction between the upper metal structure (1) and the air, they are reflected at the lower metal structure (2) and return, forming a target circularly polarized wave in the reflection direction.

2. The pure metal dual-frequency dual-rotation linear circular polarization converter according to claim 1, characterized in that, The The range is 1~10mm.

3. The pure metal dual-frequency dual-rotation linear circular polarization converter according to claim 1, characterized in that, The thickness of the upper metal structure (1) ranges from 0 to 1 mm, and the thicknesses of the outer metal frame (3), cross metal conductor (4), edge metal conductor (5), shorting strip topology (6), square slotted structure (7), and strip slotted structure (8) are all the same as the thickness of the upper metal structure (1); specifically: The outer metal frame (3) is a ring of metal frames around the outer side of the upper metal structure (1), used for connecting adjacent atomic unit arrays; The cross-shaped metal conductor (4) is composed of nine identical cross-shaped metals arrayed inside atomic units; Cross-shaped metal is formed by two identical metal strips that intersect and overlap perpendicularly. The edge metal conductor (5) is connected to the outer metal frame (3), and there are multiple edge metal conductors (5); each frame of the outer metal frame (3) has three edge metal conductors (5), and the edge metal conductors (5) on each side are spaced at the same interval, and a certain gap is maintained with the cross metal conductor; The square slotted structure (7) consists of sixteen identical square slots arranged in a four-by-four regular array; the length and width of the square slots are the same, and adjacent square slots do not contact each other. The strip-shaped slotted structure (8) is connected to the edge of the square slotted structure (7); The shorting bar topology (6) is used to form a controllable current channel, which consists of multiple shorting bar structures located between adjacent cross metal conductors (4) and between adjacent cross metal conductors (4) and edge metal conductors (5).

4. A pure metal dual-frequency dual-rotation linear circular polarization converter according to claim 3, characterized in that, In the upper metal structure (1): The width of the outer metal frame (3) ranges from 0.1 to 0.6 mm. The gap between adjacent cross metals in the cross metal conductor (4) is 0.1~0.5mm; The edge metal conductors (5) of each side are spaced at the same intervals, and the gap between the cross metal conductors is 0.1~0.5mm. The length of the strip groove 8 ranges from 0.5 to 0.6 mm, and the width ranges from 0 to 0.1 mm.

5. A pure metal dual-frequency dual-rotation linear circular polarization converter according to claim 4, characterized in that, The upper metal structure (1) and the lower metal structure (2) are made of stainless steel, copper alloy, or titanium alloy and are manufactured by laser cutting, waterjet cutting, CNC milling, or stamping technology.

6. A design method for a pure metal dual-frequency dual-rotation linear circular polarization converter according to any one of claims 1-5, characterized in that, The design method determines the layout of the shorting bar topology (6) in the upper metal structure (1) and the air gap thickness parameters between the upper metal structure (1) and the lower metal structure (2) in the pure metal dual-frequency dual-rotation linear circular polarization converter, including the following steps: The first step is to construct the pixelated platform and internal port layout definition of the upper metal structure (1); The second step involves obtaining the candidate topology of the atomic unit based on the internal port layout obtained in the first step, as well as the air gap thickness between the upper metal structure (1) and the lower metal structure (2). ; The third step is to obtain candidate topologies for atomic units based on the second step. Connectivity algorithms are used to determine feasible candidate topologies. ; The fourth step involves constructing external ports and defining external channels based on the atomic units obtained in the first step. Fifth step: Based on the internal ports obtained in the second step and the external ports constructed in the fourth step, the multi-port scattering matrix of the upper metal structure (1) is obtained and divided into blocks; Step 6: Based on the multi-port scattering matrix of the upper metal structure (1) obtained in step 5. Perform internal port binary termination and internal port elimination to obtain the external equivalent layer response; Step 7: Based on the external equivalent scattering matrix of the upper metal structure (1) obtained in step 6. By constructing an interlayer air gap network and cascading the networks, the overall external scattering matrix is ​​obtained; Step 8: Based on the overall external scattering matrix obtained in step 7, the dual-frequency dual-rotation circular polarization index of the pure metal dual-frequency dual-rotation linear-circular converter is obtained. In the ninth step, based on the dual-frequency dual-rotation circular polarization index obtained in the eighth step, an objective function is constructed and the NSGA-III non-dominated sorting genetic algorithm is executed for iterative optimization to obtain the optimal topology.

7. The design method of a pure metal dual-frequency dual-rotation linear circular polarization converter as described in claim 6, characterized in that, The specific steps are as follows: The first step is specific: Step 1.1: Construct the pixelation platform of the upper metal structure (1), define the structural parameters of the upper metal structure (1) in the atomic unit and the geometric parameters of the shorting strip structure, and determine the outer metal frame (3) as the reference conductor for connectivity determination. Step 1.2: The position in the shorting bar structure is set as a discrete internal port; the preset discrete internal port position set {p=1} 2 … },in The number of internal ports is fixed, and their spatial location and numbering are fixed. The shorting bar topology (6) of the upper metal structure (1) is represented only by the change of the internal port terminal state. The second step is specific: Step 2.1, Establish discrete internal ports Define the internal port binary terminal state vector. , ;in This indicates that the internal port is short-circuited, and the corresponding shorting bar structure is conductive. This indicates that the internal port is open, and no jumper bar structure should be placed accordingly; Step 2.2: Using the internal port binary terminal state vector, i.e. the air gap thickness between the shorting strip topology (6) and the upper metal structure (1) and the lower metal structure (2), as candidate indices, candidate topologies of atomic units are formed. ; The third step is specific: Step 3.1: Abstract the atomic units into undirected graphs. , where the vertex set Represents the individual metallic conductor regions under the platform abstraction, and the edge set. This indicates a connection capable of supporting current flow; for each internal port, if its state is short-circuited, i.e. Then, add an edge between the two corresponding conductors. If it is an open circuit ( If the edge is not added, then a symmetric connectivity matrix is ​​constructed from the above relationships. ; Step 3.2, using a connected matrix Perform a breadth-first search (BFS) to determine reachability; starting from the outer metal border 8, visit all adjacent reachable metal conductors in sequence. The metal conductors include the cross metal conductor (4), the edge metal conductor (5), and the short-connection strip topology (6); if all metal conductors in the set are required to be visited, the connectivity flag of this layer is true, and the candidate topology satisfies feasibility; otherwise, it is false, does not satisfy feasibility, and the candidate topology is eliminated; finally, the candidate topology that satisfies feasibility is determined. Reserved; The fourth step is detailed as follows: Step 4.1: Set periodic boundary conditions in the transverse direction of the atomic unit and set open / radiative boundaries in the incident direction to simulate a periodic array, i.e., a pure metal dual-frequency dual-rotation linear circular polarization converter composed of multiple atomic unit arrays. Step 4.2: Establish Floquet external ports on the upper and lower sides of the atomic unit respectively, excite and read the fundamental mode TE / TM channels; define the TE and TM fundamental mode channels as the external port set e, which is used to describe the fundamental mode energy exchange of the reflection; The fifth step is detailed as follows: Step 5.1, for candidate topologies The multi-port scattering matrix, including both external and internal ports, is obtained by solving on the frequency sampling set. ; Step 5.2, by external port With internal port right Divide into blocks, ;in It is the scattering matrix between external ports. It is the coupling scattering submatrix from the internal port to the external port. It is the coupling scattering submatrix from the external port to the internal port. It is the inter-port scattering matrix; The sixth step is detailed as follows: Step 6.1, construct the internal port terminal diagonal matrix ,in ; Step 6.2: Apply termination to the internal ports and perform elimination to obtain the external equivalent scattering matrix containing only the external ports of the upper metal structure (1). , ; The seventh step is detailed as follows: Step 7.1: Model the air gap between the upper metal structure (1) and the lower metal structure (2) as a propagation and phase delay network to obtain the air layer scattering matrix. ; Step 7.2: Concatenate the external equivalent network and the air gap network using Redheffer star product in a stacking order to obtain the overall external scattering matrix. , ; The eighth step is detailed as follows: Step 8.1, from Extraction of co-polarized and cross-polarized reflection coefficients and And obtain the reflection components of RHCP / LHCP; Step 8.2, calculate the right-hand / left-hand polarization conversion efficiency. , and shaft ratio ; The ninth step is detailed as follows: Step 9.1, Define the first target frequency band With the second target frequency band and order ;exist The target rotation direction is specified as RHCP. The target spin direction is specified as LHCP; the desired polarization conversion efficiency profile is defined. :when Time to take ,when Time to take ; Step 9.2, construct a multi-objective function and evaluate candidate solutions; construct the following two objective functions: in, It is the axis ratio threshold. To minimize To optimize the target, the polarization conversion efficiency within the joint passband should be as close to 1 as possible while the axial ratio should not exceed a preset threshold. Step 9.3: Use NSGA-III to evaluate candidate topologies. Selection, crossover, and mutation are performed to generate a new generation of population; the newly generated candidate topologies are then analyzed. Repeat steps 2 to 9 until the stopping condition is met, and output the optimal or Pareto optimal combination of atomic unit topologies, including the shorting strip topology (6) of the upper metal structure (1) atomic units, the air gap thickness between the upper metal structure (1) and the lower metal structure (2), and finally obtain a pure metal dual-frequency dual-rotation linear circular polarization converter that meets the design requirements.

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