Frequency selective surface unit and reconfigurable frequency selective surface

Abstract

The invention belongs to the technical field of electromagnetic stealth, and discloses a frequency selective surface unit and a reconfigurable frequency selective surface. The frequency selection surface unit adopts a cascade unit structure of four metal layers and three dielectric layers, and a PIN diode, a feed connecting line, a square patch, a double-square-ring patch shaped like a Chinese character'hui ', a single-square-ring patch and the like are combined to form a filtering structure with good performance. According to the reconfigurable frequency selective surface, lower passband insertion loss, wider passband, better incident angle stability, narrower transition band, better out-of-band rejection and good polarization stability are achieved, and the problems that an existing reconfigurable frequency selective surface is insufficient in passband bandwidth, poor in out-of-band rejection and the like are solved. According to the reconfigurable frequency selective surface, the PIN diodes and the patch structures on all the units are connected through the metal feed connecting lines, so that after the array structure is formed, all the units can be fed only by feeding a certain unit, the design of an extra feed network layer is avoided, and the unit structure is simplified.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic stealth technology and relates to a frequency selective surface unit and a reconfigurable frequency selective surface. Background Technology

[0002] With the development of electronic and communication technologies, radar detection technology plays a vital role in the military field and has been widely applied. To evade detection by enemy radar, it is necessary to develop military equipment with better electromagnetic stealth capabilities. Such electromagnetic stealth military equipment generally possesses one or more electromagnetic stealth structures, and the materials used to create these structures can be broadly categorized into two types: coating-type stealth materials and structural stealth materials.

[0003] Coated stealth materials are primarily applied to the surface of a target to reduce radar reflections. These materials offer advantages such as simple manufacturing processes, low cost, good electromagnetic wave absorption performance, and independence from target shape limitations. However, their application faces increasing challenges due to drawbacks such as narrow electromagnetic wave absorption bandwidth, thick coating thickness, and poor environmental resistance.

[0004] Structural stealth materials are mainly used as part of the target's structural composition to achieve the purposes of reflecting, transmitting, and absorbing electromagnetic waves. They have advantages such as wide absorption bandwidth, good environmental resistance, a balance between load-bearing capacity and wave absorption capacity, and high designability. They can meet the current development requirements of "thin, light, wide, and strong" electromagnetic stealth materials, and can realize the integrated design of structure and function. Therefore, structural stealth materials are more widely used and have a broader development prospect than coating stealth materials.

[0005] Frequency Selective Surface (FSS), as a type of structural stealth material, allows electromagnetic waves to propagate within the passband when in operation, thus ensuring normal communication functions; outside the passband, it reflects electromagnetic waves to safe directions, thereby effectively reducing the out-of-band radar cross-section and avoiding detection by enemy radar.

[0006] However, once a traditional passive frequency selective surface (FSE) is designed, its reflection and transmission characteristics are fixed and cannot be changed. In this case, even if the FSE is not in operation, enemy radar can still detect the electromagnetic waves within its passband, significantly increasing the risk of exposure. Therefore, researching a novel FSE that can adapt to complex and variable electromagnetic environments and modify its transmission and reflection characteristics according to actual conditions is of great significance. Summary of the Invention

[0007] The object of the present invention is to provide a frequency selective surface unit, which can optimize the working performance of the frequency selective surface unit in different working states through the designed multi-level cascade structure, metal layer structure and the arrangement of PIN diodes.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions: A frequency selective surface unit includes four metal layers and three dielectric layers; Define the four metal layers, which are the first, second, third and fourth metal layers from top to bottom; define the three dielectric layers, which are the first, second and third dielectric layers from top to bottom; the first dielectric layer is located between the first and second metal layers, the second dielectric layer is located between the second and third metal layers, and the third dielectric layer is located between the third and fourth metal layers; The first metal layer includes a metal patch, four first metal feed connection lines of the same size and four first PIN diodes of the same size; the metal patch is a square structure, and a first PIN diode is respectively arranged at the midpoint of each side of the metal patch, and each first PIN diode is connected to a first metal feed connection line; The second metal layer includes a first metal square ring and a second metal square ring. The size of the first metal square ring is larger than that of the second metal square ring, and the first metal square ring and the second metal square ring form a "hui" - shaped structure with a common center point; The third metal layer consists of a third metal square ring; The fourth metal layer includes a fourth metal square ring, a fifth metal square ring, four second metal feed connection lines of the same size and four second PIN diodes of the same size; the size of the fourth metal square ring is larger than that of the fifth metal square ring; The fourth metal square ring is the same size as the first metal square ring, and the fifth metal square ring is the same size as the second metal square ring; The fourth metal square ring and the fifth metal square ring form a "hui" - shaped structure with a common center point; A second PIN diode is respectively arranged at the midpoint of each outer side of the fourth metal square ring, and each second PIN diode is connected to a second metal feed connection line; the second PIN diode has the same structure as the first PIN diode.

[0009] In addition, on the basis of the above structure of the frequency selective surface unit, the present invention further provides a frequency selective surface with an array - type structure composed of multiple frequency selective surface units, and its technical solution is as follows: A reconfigurable frequency selective surface is formed by arranging multiple frequency selective surface units into an array with N×N. The frequency selective surface unit adopts the frequency selective surface unit described in any one of claims 1 to 8 above; The main feeder lines are designed on the first metal layer and the fourth metal layer, respectively; the feeder line structures designed on the first metal layer and the fourth metal layer are the same, and the feeder line structures are as follows: N×N frequency-selective surface units are connected sequentially to form an array of metal layers; N is a natural number. First cell feed lines are drawn from each cell structure below and to the right of the arrayed metal layer, and two identical PIN diodes are loaded between the two cells to ensure that the voltage reaching the cell from below and to the right is the same after power feeding. The first positive feed line is formed by N first unit feed lines drawn from the N unit structures on the right side of the arrayed metal layer and 2 (N-1) PIN diodes. The second positive feed line is formed by N first unit feed lines drawn from the N unit structures below the arrayed metal layer and 2 (N-1) PIN diodes. The first positive feeder line and the second positive feeder line are connected to form the main positive feeder line, which is used to connect to the positive terminal of the power supply. A second unit feed line is drawn from each unit structure above and to the left of the arrayed metal layer, and two identical PIN diodes are loaded between the two units to ensure that the voltage reaching each unit structure after power feeding is the same; The first negative electrode feed line is formed by N second unit feed lines drawn from the N unit structures above the array metal layer and 2 (N-1) PIN diodes. The second negative electrode feed line is formed by N second unit feed lines drawn from the N unit structures on the left side of the array metal layer and 2 (N-1) PIN diodes. The first negative feeder wire and the second negative feeder wire are connected to form the main negative feeder wire, which is used to connect to the negative terminal of the power supply.

[0010] The present invention has the following advantages: As described above, the present invention relates to a frequency selective surface unit and a reconfigurable frequency selective surface. A single frequency selective surface unit of the present invention adopts a cascaded unit structure of four metal layers and three dielectric layers, and combines PIN diodes, feed connection lines, square patches, "return" shaped double-sided ring patches, single-sided ring patches, etc. to form a filtering structure with good performance, achieving lower passband insertion loss, wider passband, better incident angle stability, narrower transition band, better out-of-band rejection, and good polarization stability, overcoming the problems of insufficient passband bandwidth and poor out-of-band rejection of existing reconfigurable frequency selective surfaces. In addition, the present invention strictly follows the grating lobe condition and adopts a technical solution of electromagnetic field coupling design to achieve miniaturization of the unit structure. The unit size is only 33.3% of the minimum wavelength corresponding to the maximum frequency of the incident electromagnetic wave, optimizing the problems such as poor incident angle stability caused by the excessively large unit structure size of existing reconfigurable frequency selective surfaces. In addition, for the reconfigurable frequency selective surface proposed in the present invention, metal feed connection lines are used to connect the PIN diodes and patch structures on each unit. Therefore, after forming an array structure, only one unit needs to be fed to feed all units, avoiding the design of an additional feed network layer and simplifying the unit structure. When forming an array, the unit arrangement method adopted in the present invention ensures good structural symmetry, the array edge is regular, and is completely consistent with the above-simulated unit structure. The PIN diodes loaded on the positive and negative feed lines ensure that the voltages reaching the unit from below and from the right are the same and ensure the stability of feeding. And only by connecting the positive total feed line to the positive pole of the power supply and the negative total feed line to the negative pole of the power supply can feeding be achieved, simplifying the feeding operation and optimizing the problems such as complex design of the additional feed layer and complex array feeding of existing reconfigurable frequency selective surfaces. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 Schematic diagram of the structure of the frequency selective surface unit in Embodiment 1 of the present invention; Figure 2 Top view of the first metal layer and the first dielectric layer in Embodiment 1 of the present invention; Figure 3 Top view of the second metal layer and the second dielectric layer in Embodiment 1 of the present invention; Figure 4 Top view of the third metal layer and the third dielectric layer in Embodiment 1 of the present invention; Figure 5 Top view of the fourth metal layer in Embodiment 1 of the present invention; Figure 6 Top layer schematic diagram of the array structure of the reconfigurable frequency selective surface in Embodiment 2 of the present invention; Figure 7 Schematic diagram of the generation of grating lobes by plane wave incidence in Embodiment 3 of the present invention; Figure 8 In Embodiment 3 of the present invention, the multifunctional reconfigurable frequency selection surface is in the "00" operating state. Schematic diagram of transmission characteristics at incident point; Figure 8 (a) in the image represents a vertically polarized wave. Transmission characteristics at incidence Figure 8 (b) in the image represents a horizontally polarized wave. Transmission characteristics at incidence; Figure 9 In Embodiment 3 of the present invention, the multifunctional reconfigurable frequency selection surface is in the "01" operating state. A schematic diagram of the transmission characteristics at incidence; where Figure 9 (a) in the image represents a vertically polarized wave. Transmission characteristics at incidence; Figure 9 (b) in the image represents a horizontally polarized wave. Transmission characteristics at incidence; Figure 10 In Embodiment 3 of the present invention, the multifunctional reconfigurable frequency selection surface is in the "10" operating state. A schematic diagram of the transmission characteristics at incidence; where Figure 10 (a) in the image represents a vertically polarized wave. Transmission characteristics at incidence; Figure 10 (b) in the image represents a horizontally polarized wave. Transmission characteristics at incidence; Figure 11 In Embodiment 3 of the present invention, the multifunctional reconfigurable frequency selection surface is in the "11" operating state. A schematic diagram of the transmission characteristics at incidence; where Figure 11 (a) in the image represents a vertically polarized wave. Transmission characteristics at incidence; Figure 11 (b) in the image represents a horizontally polarized wave. Transmission characteristics at incidence; Wherein, 1-first metal layer, 2-first dielectric layer, 3-second metal layer, 4-second dielectric layer, 5-third metal layer, 6-third dielectric layer, 7-fourth metal layer, 8-metal patch, 9-first metal feed connection line; 10-first PIN diode; 11-First PIN diode pad, 12-First metal square ring, 13-Second metal square ring, 14-Third metal square ring, 15-Fourth metal square ring, 16-Fifth metal square ring, 17-Second metal feed connection line, 18-Second PIN diode; 19-Second PIN diode pad, 20-Array metal layer, 21-Array dielectric layer, 23-Third PIN diode, 24-First positive electrode feed line, 25-Second positive electrode feed line, 26-Positive electrode main feed line, 27-Second unit feed line; 28 - Fourth PIN diode, 29 - First negative electrode feed line, 30 - Second negative electrode feed line, 31 - Main negative electrode feed line. Detailed Implementation

[0012] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments: Example 1 This embodiment 1 describes a frequency selective surface unit. By loading a PIN diode onto the structure, the forward conduction and reverse cutoff of the PIN diode can control the reconfigurable frequency selective surface to freely switch between multiple operating states.

[0013] like Figure 1 As shown, in this embodiment 1, the frequency selective surface unit adopts a multi-layer cascaded structure, wherein the side length of the frequency selective surface unit structure is... It consists of four metal layers and three dielectric layers.

[0014] The four metal layers are defined from top to bottom as: first metal layer 1, second metal layer 3, third metal layer 5, and fourth metal layer 7. The three dielectric layers are defined from top to bottom as: first dielectric layer 2, second dielectric layer 4, and third dielectric layer 6.

[0015] The first dielectric layer 2 is located between the first metal layer 1 and the second metal layer 3, the second dielectric layer 4 is located between the second metal layer 3 and the third metal layer 5, and the third dielectric layer 6 is located between the third metal layer 5 and the fourth metal layer 7.

[0016] The first metal layer 1 and the second metal layer 3 are separated by a thickness of [missing information]. The first dielectric layer 2 is connected, and the second metal layer 3 and the third metal layer 5 are connected by a thickness of The second dielectric layer is connected to phase 4.

[0017] The third metal layer 5 and the fourth metal layer 7 are separated by a thickness of The third dielectric layer 6 is connected.

[0018] Figure 1 The blue portion represents the dielectric layer, the yellow portion represents the metal layer, the black portion represents the PIN diode pads, and the red portion represents the PIN diodes. The first dielectric layer 2, the second dielectric layer 4, and the third dielectric layer 6 all use F4BM220 dielectric layers.

[0019] Of course, in this embodiment, the dielectric layers are not limited to using the F4BM220 type dielectric substrate material. They can also be replaced with other types of dielectric substrate materials with the same relative permittivity and loss tangent.

[0020] like Figure 2 As shown, the first metal layer 1 includes a metal patch 8, a first metal feed connection line 9, and a first PIN diode 10, wherein the first metal feed connection line 9 consists of four identical metal patches.

[0021] Similarly, there are four first PIN diodes 10, and all four first PIN diodes 10 are the same size.

[0022] In this embodiment 1, the first metal layer has a symmetrical structure to ensure that the final overall frequency-selective surface unit structure has good polarization stability and angular stability. The metal patch 8 has a square structure.

[0023] The side length of the metal patch 8 This simple structure can exhibit low-pass transmission characteristics.

[0024] Each of the first metal feed connection lines 9 has the same length, and the length is... ,Width Each first PIN diode 10 has the same length and width, and the length is... ,Width .

[0025] A first PIN diode 10 is disposed at the midpoint of each of the four sides (top, bottom, left, and right) of the metal patch 8, and each first PIN diode 10 is connected to a first metal feed connection line 9, such as... Figure 2 As shown.

[0026] Specifically, each first PIN diode 10 is connected via two first PIN diode pads 11.

[0027] The first PIN diode 10 is soldered onto the first PIN diode pad 11 and connected to the metal patch 8 and the first metal feed line 9, respectively; all the first PIN diode pads 11 are the same size.

[0028] The length of each first PIN diode pad 11 ,Width .

[0029] After the array is formed, the first metal feed connection line 9 connects the various units. Only one unit structure needs to be turned on to turn on all subsequent unit structures, that is, the entire array can be turned on, and no additional feed network layer needs to be designed.

[0030] As Figure 3 shown, the second metal layer 3 consists of a first metal square ring 12 and a second metal square ring 13, and the size of the first metal square ring 12 is larger than that of the second metal square ring 13.

[0031] Moreover, the first metal square ring 12 and the second metal square ring 13 form a "hui" - shaped structure with a common center point. The second metal layer 3 is a symmetric structure to ensure that the final overall unit structure has good polarization stability and angular stability.

[0032] The outer side length of the first metal square ring , and the inner side length .

[0033] The outer side length of the second metal square ring , and the inner side length .

[0034] Using this simple "hui" - shaped structure can exhibit good double - pass - band transmission characteristics.

[0035] As Figure 4 shown, the third metal layer consists of a third metal square ring 14. The outer side length of the third metal square ring 14 , and the inner side length . Using this simple metal square ring structure can exhibit good band - stop characteristics.

[0036] As Figure 5 shown, the fourth metal layer includes a fourth metal square ring 15, a fifth metal square ring 16, four second - metal feed connection lines 17 of the same size, and four second - PIN diodes 18 of the same size.

[0037] The fourth metal layer is a symmetric structure to ensure that the unit structure has good polarization stability and angular stability.

[0038] e The size of the fourth metal square ring 15 is larger than that of the fifth metal square ring 16. Among them, the fourth metal square ring 15 is the same size as the first metal square ring 12, and the fifth metal square ring 16 is the same size as the second metal square ring 13.

[0039] The outer side length of the fourth metal square ring 15 , and the inner side length .

[0040] The outer side length of the fifth metal square ring 16 , and the inner side length . <000018o>The fourth metal square ring 15 and the fifth metal square ring 16 form a "hui" - shaped structure with a common center point.

[0042] A second PIN diode 18 is set at the midpoint of each of the four outer edges of the fourth metal square ring 15 (top, bottom, left, and right), and each second PIN diode 18 is connected to a second metal feed line 17.

[0043] The length of each second metal feed connection line 17 ,Width .

[0044] The length of each second PIN diode 18 ,Width .

[0045] Specifically, each second PIN diode 18 is connected via two second PIN diode pads 19.

[0046] The second PIN diode 18 is soldered onto the second PIN diode pad 19 and connected to the fourth metal square ring 15 and the second metal feed connection line 17, respectively. Figure 5 As shown.

[0047] Each of the second PIN diode pads 19 is the same size and is of the same length. ,Width .

[0048] The second PIN diode 18 has the same structure as the first PIN diode 10, and both use the same model.

[0049] After the array is formed, the second metal feed connection line 17 connects the various units. Only one unit structure needs to be turned on to turn on all subsequent unit structures, that is, the entire array can be turned on, and no additional feed network layer needs to be designed.

[0050] Define the four first PIN diodes 10 as PIN1 and the four second PIN diodes 18 as PIN2; define the forward conduction state of the diode as the ON state; define the reverse cutoff state of the diode as the OFF state.

[0051] The different operating states of the reconfigurable frequency selector surface are controlled according to the different bias states of PIN1 and PIN2; When both PIN1 and PIN2 are in the OFF operating state, the frequency selective surface unit exhibits low-frequency wideband characteristics; When PIN1 and PIN2 are in the OFF and ON working states respectively, the frequency selection surface unit exhibits full-band stopband characteristics; When PIN1 and PIN2 are in ON and OFF working states respectively, the frequency selective surface unit exhibits high-frequency narrowband characteristics; When both PIN1 and PIN2 are in the OFF state, the frequency selective surface unit exhibits high-frequency dual-pass narrowband characteristics.

[0052] In this embodiment, the second PIN diode 18 and the first PIN diode 10 are SMP1321-040LF type PIN diodes. Of course, they can be replaced with other types of PIN diodes with the same forward conduction resistance and reverse cutoff capacitance.

[0053] This invention reduces manufacturing costs by selecting cheaper dielectric substrate materials and PIN diode models.

[0054] Furthermore, to verify the effectiveness of the frequency-selective surface unit proposed in this invention, the following comparative experiments are presented. In these comparative experiments, five frequency-selective surfaces with contrasting structural designs are shown, and the sources of these structures are as follows: Comparison document 1: B. Jiang, H. Hu, J. Tian, ​​S. Lei, M. Chen and B. Chen, "APolarization-Insensitive Dual-Band FSS With High Selectivity and Independently Switchable Characteristics," in IEEE Antennas and WirelessPropagation Letters, vol. 22, no. 1, pp. 14-18, Jan. 2023.

[0055] Comparison document 2: Z. Wang, J. Huang, Q. Zeng, M. Song, TA Denidni and L.Ran, "Novel Dual-Polarization Multimode Artificial Frequency-SelectiveSurface With Independently Reconfigurable Windows for Different Frequencies," in IEEE Transactions on Electromagnetic Compatibility, vol. 67, no. 1, pp.92-98, Feb. 2025.

[0056] Comparison document 3: C. Fan et al., "Switchable Frequency-Selective Surface forMultistate Highly Selective Transmission in Ku Band," in IEEE Antennas andWireless Propagation Letters, vol. 24, no. 3, pp. 641-645, March 2025.

[0057] Comparison document 4: G. Shah, Q. Cao, ZU Abidin and Z. Rafique, "A 2 b Dual-Band Multifunction Frequency Selective Surface," in IEEE Antennas andWireless Propagation Letters, vol. 19, no. 6, pp. 954-958, June 2020.

[0058] Comparison document 5: G. Shah, Q. Cao, ZU Abidin, Y. Jing and M. Azeem, "A 4-Bit Multistate Frequency-Selective Surface With Dual-Band MultifunctionResponse," in IEEE Antennas and Wireless Propagation Letters, vol. 20, no.10, pp. 1844-1848, Oct. 2021.

[0059] Prior art document 1 proposes a multifunctional reconfigurable frequency selective surface with a rotationally symmetric transmit-receive unit configuration. A PIN diode is loaded on top, and an additional feed network layer is designed to power the PIN diode through vias, enabling switchable operation in four states. However, prior art document 1 requires the design of an additional feed network and has a complex unit structure, increasing design and fabrication difficulty. Furthermore, the array edges are irregular after the unit structure is formed. In terms of structural performance, the frequency range is low, and all three operating states involve narrowband transmission with low transmission efficiency.

[0060] Prior art document 2 proposes a multifunctional reconfigurable frequency selective surface that loads PIN diodes at the top and bottom and applies different bias voltages to achieve switchable transmission and shielding states with two polarization modes at different frequencies. In terms of structural performance, prior art document 2 has a lower frequency range, operates with narrowband transmission in all three states, and has low transmission efficiency.

[0061] Comparative documents 2 and 3 propose a reconfigurable frequency selective surface employing an aperture-coupled patch resonator structure. PIN diodes are loaded at the top and bottom, and different bias voltages are applied to achieve frequency reconfiguration in four states within a frequency range. However, the PIN diodes in document 3 are expensive, resulting in high manufacturing costs. In terms of structural performance, all four operating states exhibit narrowband transmission with low efficiency. Furthermore, the lack of a full-band stopband design means that it still suffers from the problems inherent in traditional frequency selective surfaces.

[0062] Comparative document 4 proposes a multifunctional active frequency selective surface with PIN diodes loaded at the top and bottom to achieve switchable operation in four states. Comparative document 5 further improves upon comparative document 4, offering even more operating states. In terms of structural performance, comparative documents 4 and 5 have a lower frequency range, operate in narrowband with low transmission efficiency in all four states, have excessively wide transition bands resulting in poor frequency selectivity, and lack a full-band stopband design, thus exhibiting the problems inherent in traditional frequency selective surfaces.

[0063] Table 1. Performance comparison of the designed multifunctional reconfigurable frequency selective surface with existing similar structures.

[0064] As shown in Table 1, the frequency selective surface unit designed in this invention has lower passband insertion loss, wider passband, better incident angle stability, larger profile, and narrower transition band compared with similar structures described above.

[0065] Passband insertion loss affects the transmission of signals through the frequency selector surface. Lower insertion loss ensures better signal transmission integrity. A wider passband translates to higher signal transmission efficiency.

[0066] Better incident angle stability means that the larger the maximum incident angle, the more signals can be received from different directions.

[0067] A larger cross-section means greater structural load-bearing capacity and pressure resistance.

[0068] A narrower transition band means better frequency selectivity.

[0069] In addition, the present invention has the advantages of simple structure, no bending or other operations, convenient processing, and low price. The selected dielectric material and PIN diode are relatively inexpensive, and the processing cost is lower.

[0070] The number of modes in this invention is the same as that in existing structures. The more modes there are, the more functions the surface has, and the better it can adapt to different environments.

[0071] Example 2 This embodiment 2 describes a reconfigurable frequency selective surface, which is formed by arranging multiple frequency selective surface units to form an array of N×N, where N is, for example, a natural number greater than 2.

[0072] For ease of explanation, in this embodiment, N is, for example, 10, forming a 10×10 array. The frequency selective surface unit is the frequency selective surface unit as described in Embodiment 1 above.

[0073] Since the PIN diodes in the unit structure are only loaded on the first metal layer 1 and the fourth metal layer 7, it is only necessary to design the total feed line on the first metal layer 1 and the fourth metal layer 7.

[0074] In addition, since the total feed lines on the first metal layer 1 and the fourth metal layer 7 have similar structures and the same design process after the design is completed, only the total feed line structure on the first metal layer 1 will be shown below.

[0075] like Figure 6 As shown, 10×10 units are connected around each other to form an array metal layer 20, which is arranged on an array dielectric layer 21. The size of the array dielectric layer 21 is larger than the total size of the dielectric layer 1 of 10×10 units, and is used to design the total feed line.

[0076] First unit feed lines 22 are drawn from each unit structure below and to the right of the arrayed metal layer 20, and two identical PIN diodes, such as third PIN diodes 23, are loaded between the two units.

[0077] The third PIN diode 23 is used to ensure that the voltage reaching the cell from below and the right is the same after power is supplied.

[0078] Ten first unit feed lines 22 and two (N-1) third PIN diodes 23, which are 18 in total, are drawn from the ten unit structures on the right side of the arrayed metal layer 20, together forming the first positive feed line 24.

[0079] Ten first-unit feed lines 22 and two (N-1) third PIN diodes 23, which are 18 in total, are drawn from the ten unit structures below the arrayed metal layer 20, together forming the second positive feed line 25.

[0080] The first positive feeder line and the second positive feeder line are connected to form the positive main feeder line 26, which is used to connect to the positive terminal of the power supply.

[0081] A second unit feed line 27 is drawn from each unit structure above and to the left of the arrayed metal layer 20, and two identical PIN diodes, such as a fourth PIN diode 28, are loaded between the two units.

[0082] The fourth PIN diode 28 is used to ensure that the voltage reaching each cell structure is the same after power is supplied.

[0083] The first negative electrode feed line 29 is composed of 10 second unit feed lines 27 led out from 10 unit structures above the array metal layer 20 and 2 (N-1) fourth PIN diodes, i.e., 18.

[0084] The second negative electrode feed line 30 is composed of 10 second unit feed lines 27 led out from 10 unit structures on the left side of the arrayed metal layer 20 and 2 (N-1) fourth PIN diodes, i.e., 18.

[0085] The first negative feeder wire and the second negative feeder wire are connected to form the main negative feeder wire 31, which is used to connect to the negative terminal of the power supply.

[0086] Assume the forward conduction voltage of the PIN diode is To make all diodes conduct, the unit in the upper left corner needs to... The voltage required on the two adjacent units The voltage required on the three units adjacent to these two adjacent units. The voltage, and so on, the unit in the lower right corner needs to be... The voltage.

[0087] In summary, to ensure all PIN diodes are conducting during power supply, the positive terminal of the power supply needs to be connected to the positive main power supply line and provide power. Right now The voltage is such that the negative terminal of the power supply needs to be connected to the negative main feeder line.

[0088] The frequency selective surface proposed in this invention is formed by arranging the proposed multi-layer cascaded structural units into an array in a certain manner. The array has good symmetry and regular array edges, thus optimizing the problem of irregular array structure edges.

[0089] Example 3 This embodiment 3 describes a design method for a multifunctional frequency selective surface. This method, specifically for the reconfigurable frequency selective surface as described in embodiment 2 above, includes the following steps: Step 1. Select the appropriate dielectric substrate material and PIN diode model based on the frequency range and budget.

[0090] The operating frequency range of this invention is 2 GHz to 10 GHz.

[0091] Based on this frequency range, the dielectric layers use F4BM220, with a relative permittivity of... Loss tangent Each metal layer uses copper with a thickness of 0.035 mm.

[0092] The PIN diode selected is the Skyworks Solutions Inc. SMP1321-040LF in an SOD882 package, with the following parameters: Standard on-resistance ; Standard cutoff capacitor ; Standard inductance is .

[0093] Step 2. Define the required functions, bandwidth range, and resonant performance.

[0094] The multifunctional reconfigurable frequency selective surface designed in this invention needs to have four functions, namely: Low-frequency broadband, high-frequency narrowband, high-frequency dual-pass narrowband, and full-frequency stopband.

[0095] The frequency range of 2 GHz to 10 GHz is divided into two parts: 2 GHz to 6 GHz is the low frequency range, and 6 GHz to 10 GHz is the high frequency range. To ensure good resonant performance, multiple transmission zeros and transmission poles need to be designed.

[0096] Step 3. Determine the maximum and minimum cell sizes based on the relationship between the electromagnetic wave wavelength and the cell size of the multifunctional reconfigurable frequency selection surface within the frequency range, and determine the appropriate cell size required.

[0097] The first thing to consider when determining the element size is the grating lobe condition, which will be described in detail below.

[0098] Raster lobes are caused by the periodic arrangement of array elements. When multiple array elements radiate simultaneously, they can produce radiation in unexpected directions at specific angles. Raster lobes can lead to signal overlap in multiple directions, interfering with the effective signal and causing negative effects such as blurred target position, signal aliasing, and reduced anti-interference capability. Figure 7 As shown, when a plane wave... Incident on the cell interval is When it occurs on a periodic structure, not only will reflection and transmission occur, but also angles of [missing information] may be generated. The grating lobes. The phase of each cell is relative to that of its neighboring cells. The delay, if this delay is exactly If the value is an integer multiple of , then all electromagnetic waves emanating from each unit will be in... In the same direction, that is, electromagnetic waves may be... It propagates in the direction of propagation. Therefore, the condition for the appearance of grating lobes is: (1) in, , The wavelength is the plane wave wavelength.

[0099] The frequency of grating lobes is: (2) in, At the speed of light, It is a positive integer.

[0100] From equation (2), it can be seen that when , At this time, the frequency of the grating lobe is the lowest, and the lowest frequency is: (3) From equation (3), we can see that the lowest frequency at which the grating lobe appears is... Only with the angle of incidence of the plane wave and unit spacing It is related to, but not to, any other parameters. When the lowest frequency at which grating lobes appear is greater than or equal to the maximum value of the operating frequency, grating lobes can be avoided within the operating frequency range. Therefore, when the element spacing... When the angle of incidence remains constant It should be as large as possible; when the angle of incidence... When unchanged, the cell spacing It should be as small as possible. When the angle of incidence reaches its maximum value... At this point, the maximum unit interval is: (4) in, For maximum operating frequency, This represents the wavelength corresponding to the maximum operating frequency. In summary, to avoid the appearance of grating lobes, the cell elements need to be miniaturized, and the cell spacing should be less than or equal to half a wavelength.

[0101] Step 4. Use Ansys HFSS to model and simulate the designed reconfigurable frequency selective surface element structure to obtain its transmission reflection coefficient. Below, Ansys HFSS is used to model and simulate the designed reconfigurable frequency selective surface element structure, with an operating frequency range of 2 GHz to 10 GHz. The specific operation steps are as follows: I. Build the model and set the material properties correctly.

[0102] II. Create an air box, and set the front and back, left and right sides of the air box as the master and slave boundaries respectively to simulate a periodic structure, and define the incident angle as a variable to facilitate the change of the incident angle of the electromagnetic wave.

[0103] III. Set the top and bottom opposite faces of the air box as Floquet ports, and set the mode number to 2, representing vertical polarization (TE) and horizontal polarization (TM) respectively.

[0104] IV. Set the solution frequency range to 2 GHz~10 GHz, the scan step to 0.01 GHz, and the scan mode to discrete frequency sweep to ensure the accuracy of the simulation results and prevent the sudden change between two frequencies from being ignored due to the excessively large scan step.

[0105] For ease of description, the four PIN diodes on the first metal layer will be referred to as PIN1, and the four PIN diodes on the fourth metal layer will be referred to as PIN2. The forward conduction state of a diode is called the ON state, also known as the "1" state; the reverse cutoff state of a diode is called the OFF state, also known as the "0" state.

[0106] As shown in Table 2, different bias states of PIN1 and PIN2 control different operating states of the reconfigurable frequency selectable surface.

[0107] Table 2. Multifunctional Reconfigurable Frequency Selective Surface Operating State Switching Table

[0108] like Figure 8 As shown in (a) and (b), under the "00" operating state, the vertically polarized wave With increasing incident angle, the 3 dB relative bandwidth shifted from 31.91% (3.95 GHz ~ 5.45 GHz) to 28.69% (4.09 GHz ~ 5.46 GHz), and the maximum passband insertion loss shifted from 0.79 dB to 2.75 dB. (Horizontally polarized wave) At incidence, as the incident angle increases, the 3 dB relative bandwidth shifts from 31% (3.98 GHz ~ 5.44 GHz) to 36.14% (4.08 GHz ~ 5.88 GHz), and the maximum passband insertion loss shifts from 0.75 dB to 0.21 dB. This demonstrates that the reconfigurable frequency selectable surface exhibits good low-frequency broadband performance in the "00" operating state.

[0109] like Figure 9 As shown in (a) and (b), in the "01" operating state, electromagnetic waves exhibit both vertical and horizontal polarization. At incidence, the transmission coefficients are almost all less than -10 dB. This demonstrates that the reconfigurable frequency selectable surface exhibits excellent full-band stopband characteristics in the "01" operating state.

[0110] like Figure 10 As shown in (a) and (b), under the "10" operating condition, the vertically polarized wave With increasing incident angle, the 3 dB relative bandwidth shifted from 2.39% (9.1 GHz ~ 9.32 GHz) to 1.51% (9.18 GHz ~ 9.32 GHz), and the minimum passband insertion loss shifted from 0.8 dB to 0.75 dB. (Horizontally polarized wave) With increasing incident angle, the 3 dB relative bandwidth shifted from 2.39% (9.1 GHz ~ 9.32 GHz) to 4.33% (9.04 GHz ~ 9.44 GHz), and the minimum passband insertion loss shifted from 0.82 dB to 0.7 dB. This demonstrates that the reconfigurable frequency selectable surface exhibits good high-frequency narrowband performance in the "10" operating state.

[0111] like Figure 11 As shown in (a) and (b), under the "11" operating state, the vertically polarized wave As the incident angle increases, the 3 dB relative bandwidth of the first passband shifts from 2.52% (7.05 GHz ~ 7.23 GHz) to 1.5% (7.3 GHz ~ 7.41 GHz), and the minimum passband insertion loss shifts from 1.58 dB to 1.47 dB; the 3 dB relative bandwidth of the second passband shifts from 3.49% (9.01 GHz ~ 9.33 GHz) to 2.27% (9.13 GHz ~ 9.34 GHz), and the minimum passband insertion loss shifts from 0.48 dB to 0.61 dB. (Horizontally polarized wave) With increasing incident angle, the 3 dB relative bandwidth of the first passband shifts from 2.39% (7.03 GHz ~ 7.2 GHz) to 4.65% (7.14 GHz ~ 7.48 GHz), and the minimum passband insertion loss shifts from 1.62 dB to 0.9 dB; the 3 dB relative bandwidth of the second passband shifts from 3.4% (8.95 GHz ~ 9.26 GHz) to 7.11% (8.82 GHz ~ 9.47 GHz), and the minimum passband insertion loss shifts from 0.49 dB to 0.25 dB. This demonstrates that the reconfigurable frequency selectable surface exhibits good high-frequency dual-pass narrowband performance in the "11" operating state.

[0112] The multifunctional reconfigurable frequency selective surface obtained by the design method of this invention can be controlled to freely switch between four operating states—low-frequency broadband, high-frequency narrowband, high-frequency dual-pass narrowband, and full-band stopband—by changing the bias state of the PIN diode. Furthermore, this multifunctional reconfigurable frequency selective surface features low insertion loss, narrow transition band, and good frequency selectivity, polarization stability, and other characteristics. It offers angular stability, a simple structure, easy processing, and low cost.

[0113] Step 5. Arrange the unit structures designed in Step 4 into an array of 10×10 units, with a specific size of 140 mm×140 mm×4.572 mm, and design the total feed line.

[0114] Of course, the above description is only a preferred embodiment of the present invention. The present invention is not limited to the above-described embodiments. It should be noted that any equivalent substitutions or obvious modifications made by those skilled in the art under the guidance of this specification fall within the scope of this specification and should be protected by the present invention.

Claims

1. A frequency-selective surface unit, characterized in that, It includes four metal layers and three dielectric layers; Four metal layers are defined, which are the first, second, third, and fourth metal layers from top to bottom in sequence; three dielectric layers are defined, which are the first, second, and third dielectric layers from top to bottom in sequence; the first dielectric layer is located between the first and second metal layers, the second dielectric layer is located between the second and third metal layers, and the third dielectric layer is located between the third and fourth metal layers; The first metal layer includes a metal patch, four first metal feeding connection lines of the same size, and four first PIN diodes of the same size; where the metal patch is a square structure, and a first PIN diode is respectively arranged at the midpoint of each side of the metal patch, and each first PIN diode is connected to a first metal feeding connection line; The second metal layer includes a first metal square ring and a second metal square ring. The size of the first metal square ring is larger than that of the second metal square ring, and the first metal square ring and the second metal square ring form a "return" - shaped structure with a common center point; The third metal layer consists of a third metal square ring; The fourth metal layer includes a fourth metal square ring, a fifth metal square ring, four second metal feeding connection lines of the same size, and four second PIN diodes of the same size; the size of the fourth metal square ring is larger than that of the fifth metal square ring; The fourth metal square ring is the same size as the first metal square ring, and the fifth metal square ring is the same size as the second metal square ring; The fourth metal square ring and the fifth metal square ring form a "return" - shaped structure with a common center point; A second PIN diode is respectively arranged at the midpoint of each outer side of the fourth metal square ring, and each second PIN diode is connected to a second metal feeding connection line; the second PIN diode has the same structure as the first PIN diode.

2. The frequency - selective surface unit according to claim 1, wherein The side length of the metal patch The length of each first metal feeder connection line ,Width The length of each first PIN diode ,Width .

3. The frequency - selective surface unit according to claim 2, wherein Each of the first PIN diodes is respectively connected through two first PIN diode pads; where the first PIN diode is welded on the first PIN diode pad and is respectively connected to the metal patch and the first metal feeding connection line; The pads of each first PIN diode are all the same size and are of the same length. ,Width . The outer side length of the first metal square ring inner side length ; The outer side length of the second metal square ring inner side length .

4. The frequency - selective surface unit according to claim 1, wherein The outer side length of the third metal square ring inner side length .

5. The frequency - selective surface unit according to claim 1, wherein The fourth metal square ring is the same size as the first metal square ring, and its outer side length is... inner side length ; The fifth metal square ring has the same outer side length as the second metal square ring. inner side length ; The length of each second metal feed connection line ,Width The length of each second PIN diode ,Width .

6. The frequency - selective surface unit according to claim 1, wherein 7. The frequency - selective surface unit according to claim 1, wherein The pads of each second PIN diode are all the same size and are of the same length. ,Width . Each of the second PIN diodes is respectively connected through two second PIN diode pads; the second PIN diode is welded on the second PIN diode pad and is respectively connected to the fourth metal square ring and the second metal feeding connection line; 8. The frequency - selective surface unit according to claim 1, wherein Four first PIN diodes are defined as PIN1, and four second PIN diodes are defined as PIN2; the forward - conducting state of the diode is defined as the ON state; the reverse - cut - off state of the diode is defined as the OFF state; The different operating states of the reconfigurable frequency selector surface are controlled according to the different bias states of PIN1 and PIN2; When both PIN1 and PIN2 are in the OFF operating state, the frequency selective surface unit exhibits low-frequency wideband characteristics; When PIN1 and PIN2 are in the OFF and ON working states respectively, the frequency selection surface unit exhibits full-band stopband characteristics; When PIN1 and PIN2 are in ON and OFF working states respectively, the frequency selective surface unit exhibits high-frequency narrowband characteristics; When both PIN1 and PIN2 are in the OFF state, the frequency selective surface unit exhibits high-frequency dual-pass narrowband characteristics.

9. A reconfigurable frequency selective surface, comprising an array of N×N frequency selective surface units arranged in a plurality of such arrays, wherein the frequency selective surface units are frequency selective surface units as described in any one of claims 1 to 8. Its features are, The main feeder lines are designed on the first metal layer and the fourth metal layer, respectively; the feeder line structures designed on the first metal layer and the fourth metal layer are the same, and the feeder line structures are as follows: N×N frequency-selective surface units are connected sequentially to form an array of metal layers; N is a natural number. First cell feed lines are drawn from each cell structure below and to the right of the arrayed metal layer, and two identical PIN diodes are loaded between the two cells to ensure that the voltage reaching the cell from below and to the right is the same after power feeding. The first positive feed line is formed by N first unit feed lines drawn from the N unit structures on the right side of the arrayed metal layer and 2 (N-1) PIN diodes. The second positive feed line is formed by N first unit feed lines drawn from the N unit structures below the arrayed metal layer and 2 (N-1) PIN diodes. The first positive feeder line and the second positive feeder line are connected to form the main positive feeder line, which is used to connect to the positive terminal of the power supply. A second unit feed line is drawn from each unit structure above and to the left of the arrayed metal layer, and two identical PIN diodes are loaded between the two units to ensure that the voltage reaching each unit structure after power feeding is the same; The first negative electrode feed line is formed by N second unit feed lines drawn from the N unit structures above the array metal layer and 2 (N-1) PIN diodes. The second negative electrode feed line is formed by N second unit feed lines drawn from the N unit structures on the left side of the array metal layer and 2 (N-1) PIN diodes. The first negative feeder wire and the second negative feeder wire are connected to form the main negative feeder wire, which is used to connect to the negative terminal of the power supply.

10. The reconfigurable frequency selective surface according to claim 1, characterized in that, Assume the forward conduction voltage of a single PIN diode is When power is supplied, the positive terminal of the power supply is connected to the positive main power supply line and provides power. The voltage is such that the negative terminal of the power supply is connected to the negative main feed line to ensure that all PIN diodes are turned on.

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