A high-angle stable dual-frequency transparent window adjustable frequency selective surface

Abstract

The application discloses a high-angle stable dual-frequency wave-transparent window adjustable frequency selective surface, which comprises a metal resonant structure, a dielectric substrate and a bottom metal feeding structure; the top metal resonant structure comprises a cross-dipole with an arc-shaped branch, an arc-shaped metal ring with a bent branch and a square patch with an inner concave round corner; a first variable capacitance diode is welded between the arc-shaped branch and the bent branch, and a second variable capacitance diode is welded between the patch and the arc-shaped metal ring; the bottom metal feeding structure comprises a cross metal feeding line and a T-shaped metal feeding line, and a lumped resistor is loaded between the feeding lines to form a complete direct-current power supply network; the upper and lower surfaces of the dielectric substrate are communicated in the vertical direction by a metal via, so that the bottom feeding line can provide a reverse bias voltage for the two groups of variable capacitance diodes on the top layer to independently regulate and control the passband resonant frequency. The application has the advantages of few active devices, dual-frequency independence, continuous adjustability and high-angle stability.

Description

Technical Field

[0001] The invention belongs to the field of electromagnetic field and microwave technology, and in particular relates to a frequency selective surface with an adjustable dual-frequency wave-transmitting window and high-angle stability. Background Art

[0002] A frequency selective surface (FSS) is typically a two-dimensional periodic array structure that exhibits specific selectivity for electromagnetic wave operating frequency, polarization, and angle of incidence, effectively controlling the reflection and transmission of electromagnetic waves. Due to its unique spatial filtering properties, FSSs are widely used in radar stealth, electromagnetic compatibility, wireless communications, and electronic countermeasures.

[0003] To overcome the limitation of traditional passive frequency selective surfaces (FSSs), which retain their fixed resonant characteristics after fabrication, active devices (such as PIN diodes and varactors) are incorporated into FSS structures to adapt to complex and changing electromagnetic environments. Due to the advantages of varactors, such as short response time, wide tuning range, compact size, and low cost, tunable FSSs based on varactors have become a research hotspot in recent years. These tunable FSSs not only address the in-band stealth issue of radomes but also provide tuning solutions for absorbing materials, electromagnetic shielding materials, active phased array radars, and beam-steering antennas, offering broad application prospects.

[0004] Dual-band FSSs have a wide range of applications in areas such as MIMO antennas and multi-band communication systems, and have garnered significant attention in recent years. However, research on dual-band tunable FSSs is relatively limited. The bias network that provides the bias voltage for the varactors affects the electromagnetic properties of the tunable frequency selective surface, and the complexity of the feeder increases the design difficulty of independently tunable dual-passband FSSs. Furthermore, independent tuning of the dual-band wave-transmitting windows requires multiple varactor diodes. Active FSS structures proposed in the literature require 16 varactor diodes per periodic unit. Arraying these components results in a large number of active components, which increases manufacturing complexity and cost. Furthermore, the resonant frequency of the frequency selective surface shifts when electromagnetic waves are incident at large angles. Further research is needed to achieve stable wave-transmitting performance to meet the requirements of practical applications in engineering fields such as conformal radar radomes.

[0005] Purpose of the Invention

[0006] In response to the shortcomings of existing technologies and the current application requirements of broadband, ultra-wideband, multi-frequency and frequency conversion in military radar, modern communications and other fields, the present invention provides a high-angle stable dual-frequency wave-transmitting window with an adjustable frequency selective surface to achieve independent tuning of the two frequencies, thereby improving stability at large incident angles while reducing the number of active components.

[0007] In order to achieve the above tasks, the present invention adopts the following technical solutions:

[0008] A highly angle-stable dual-frequency wave-transmitting window continuously adjustable frequency selective surface comprises: a dielectric substrate on which frequency selective units of a square structure are distributed;

[0009] Each frequency selection unit includes a top metal resonant structure arranged on the upper surface of the dielectric substrate, a bottom metal feeding structure arranged on the lower surface of the dielectric substrate, an active device, and a first metal via and a second metal via connecting the upper and lower surfaces, wherein:

[0010] The top metal resonant structure is a centrosymmetrical structure, comprising: a cross dipole with an arcuate branch, an arcuate metal ring with a bent branch, and a square patch with concave rounded corners on all sides; the arcuate metal rings are distributed around the square patch, the ends of adjacent arcuate metal rings are connected, the bent branches are connected to the outside of the arcuate metal rings, and the cross dipoles are arranged on the outside of the bent branches; the arcuate metal rings of adjacent frequency selective units are connected to each other, and the cross dipoles of adjacent frequency selective units are connected to each other;

[0011] The bottom metal feeding structure includes: a cross metal feed line and a T-shaped metal feed line; the cross metal feed line is connected to the square patch on the upper surface of the dielectric substrate through a first metal via, and the first metal via is located in the center of the frequency selection unit; the T-shaped metal feed lines are distributed around the cross metal feed line and the ends are connected to each other; the T-shaped metal feed line is connected to the cross dipole on the upper surface of the dielectric substrate through a second metal via, and the second metal via is located at the four corners of the frequency selection unit; there is a first gap between each T-shaped metal feed line and the cross metal feed line, and a second gap is left near the two ends of each T-shaped metal feed line; the T-shaped metal feed lines of adjacent frequency selection units are connected to each other to form a cross-shaped structure; lumped resistors are provided in part of the first gap and the second gap;

[0012] The active device includes a first varactor diode and a second varactor diode; the positive electrode of the first varactor diode is connected to the arc-shaped branch of the top metal resonant structure, and the negative electrode is connected to the bent branch; the positive electrode of the second varactor diode is connected to the corner of the square patch, and the negative electrode is connected to the end connection of the adjacent arc-shaped metal ring.

[0013] Furthermore, the positive pole of the DC power supply is connected to the arc-shaped metal ring; the negative pole of the DC power supply is connected to the cross metal feed line in the center of the frequency selection unit, and a reverse bias voltage is provided to the square patch through the first metal via; the other negative pole of the DC power supply is connected to the T-shaped metal feed line, and another reverse bias voltage is provided to the cross dipole through the second metal via; by changing the bias voltage, the change of the variable capacitance value of the active device is controlled, thereby independently regulating the dual operating frequency bands of the adjustable frequency selection surface, realizing the broadband reconfigurable function of the wave-transparent window.

[0014] Furthermore, one side of the frequency selection unit is denoted as the X direction, and a lumped resistor is arranged in the first gap in the X direction between the cross metal feed line and the T-shaped metal feed line and in the second gap in the X direction on the T-shaped metal feed line, thereby connecting the cross metal feed line in the X direction with the T-shaped metal feed line.

[0015] Furthermore, the cross dipoles and the arc-shaped branches together form a T-shaped structure, the arc-shaped branch is a section of arc-shaped metal sheet; the cross dipoles are distributed at the four corners of the frequency selection unit.

[0016] Furthermore, the bent branch on the arc-shaped metal ring is a structure composed of the ends of multiple arc-shaped metal sheets with gradually decreasing arc lengths connected in sequence. These arc-shaped metal sheets and the arc-shaped metal ring have the same center of the circle, and the bent branch is located on the outside of the arc-shaped metal ring; the bent branch is connected to the middle part of the inner side of the arc-shaped metal ring through a metal sheet.

[0017] Furthermore, the square patch with rounded inner corners is a structure formed by cutting circular recesses on the four sides of a square metal sheet and processing the corners into rounded corners; there is an arc-shaped through groove between the arc-shaped metal ring and the square patch.

[0018] Furthermore, the T-shaped metal feeder is composed of a first feeder located on the outside and a second feeder arranged vertically in the middle of the inside of the first feeder. There is a first gap between the second feeder and the cross metal feeder, and a second gap is left near each end of the first feeder; the width of the first feeder is smaller than that of the second feeder, and after the first feeders in adjacent frequency selection units are spliced ​​together, the first feeder and the second feeders inside the two first feeders together form a cross structure.

[0019] Furthermore, the dielectric substrate is made of F4B material with a thickness of 0.5 mm, a dielectric constant of 2.55, and a loss tangent of 0.001.

[0020] Furthermore, the first varactor diode and the second varactor diode can provide a variable capacitance between 0.1-1 pF at a reverse bias voltage between 16V and 0V.

[0021] Compared with the prior art, the present invention has the following technical features:

[0022] 1. This invention utilizes a composite multi-resonant structure to achieve dual-band independent tuning performance within a single-layer frequency selective surface. By controlling the bias voltage of the corresponding varactor diodes, the passbands can be independently tuned within the 2.4-5.75 GHz and 5.7-9.63 GHz ranges, respectively, with insertion loss less than 1 dB. The operating frequency range covers 2.4-9.63 GHz, with a relative operating bandwidth of 120.2%.

[0023] 2. The present invention uses a bending structure and a compact array to miniaturize the design of a dual-frequency adjustable frequency selective surface, and exhibits a stable transmission response when the incident TE and TM dual-polarized electromagnetic waves changes from 0° to 75°.

[0024] 3. The present invention requires only 8 active devices in one period unit, which significantly reduces the number of active devices, reduces processing complexity, and saves costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a schematic diagram of the overall structure of an adjustable frequency selective surface in one embodiment of the present invention;

[0026] Figure 2 is a schematic diagram of a top-layer resonant structure in one embodiment of the present invention;

[0027] Figure 3 is a schematic diagram of the bottom feeding structure in one embodiment of the present invention;

[0028] Figure 4 is a schematic cross-sectional view of a dielectric substrate in one embodiment of the present invention;

[0029] Figure 5 1 is a simulation result diagram of independent regulation of varactor diodes in one embodiment of the present invention, wherein (a) is the transmission curve corresponding to the second varactor diode value C2 being maintained at 0.1pF and the first varactor diode value C1 being changed from 0.1pF to 0.8pF; (b) is the transmission curve corresponding to the first varactor diode value C1 being maintained at 0.8pF and the second varactor diode value C1 being changed from 0.1pF to 0.5pF.

[0030] Figure 6 These are simulation results of the adjustable frequency selective surface of an embodiment of the present invention under incident waves at different angles, where (a) is the oblique incidence transmission curve corresponding to the second varactor diode value C2 being maintained at 0.1pF and the first varactor diode value C1 being maintained at 0.4pF; (b) is the oblique incidence transmission curve corresponding to the first varactor diode value C1 being maintained at 0.8pF and the second varactor diode value C1 being maintained at 0.3pF.

[0031] Explanation of the numbers in the figure: 1 dielectric substrate, 2 top metal resonant structure, 21 cross dipole, 22 arc-shaped branch, 23 square patch, 24 bent branch, 25 arc-shaped metal ring, 3 bottom metal feeding structure, 31 cross metal feed line, 32 T-shaped metal feed line, 321 first feed line, 322 second feed line, 33 first gap, 34 second gap, 4 first varactor diode, 5 second varactor diode, 6 lumped resistor, 7 first metal via, 8 second metal via. DETAILED DESCRIPTION

[0032] The present invention provides a frequency selective surface with an adjustable dual-frequency wave-transmitting window and high-angle stability. The surface adopts miniaturization technology to achieve high-angle stability characteristics. The multi-band independent control technology is used to achieve independent adjustment of the dual-frequency wave-transmitting window while effectively reducing the number of active components, reducing processing complexity and saving costs. This structure has greater advantages in application fields such as frequency hopping communication, MIMO antennas, and collaboration between different standards and systems.

[0033] See also Figure 1 The present invention provides a high-angle stable dual-frequency wave-transmitting window continuously adjustable frequency selective surface, comprising: a dielectric substrate 1, on which frequency selective units of a square structure are distributed;

[0034] Each frequency selection unit includes a top metal resonant structure 2 arranged on the upper surface of the dielectric substrate 1, a bottom metal feeding structure 3 arranged on the lower surface of the dielectric substrate 1, an active device, and a first metal via 7 and a second metal via 8 connecting the upper and lower surfaces, wherein:

[0035] 1. Top metal resonant structure 2

[0036] The top metal resonant structure 2 is a centrosymmetrical structure, comprising: a cross dipole 21 with an arcuate branch 22, an arcuate metal ring 25 with a bent branch 24, and a square patch 23 with concave rounded corners on all sides; the arcuate metal rings 25 are distributed around the square patch 23, the ends of adjacent arcuate metal rings 25 are connected, and after rotating an arcuate metal ring 25 90° clockwise or counterclockwise, the bent branches 24 on it can overlap with the bent branches 24 on the adjacent arcuate metal ring 25; the bent branches 24 are connected to the outside of the arcuate metal ring 25, and the cross dipole 21 is arranged on the outside of the bent branch 24; the arcuate metal rings 25 of adjacent frequency selection units are connected to each other, and the cross dipoles 21 of adjacent frequency selection units are connected to each other.

[0037] See also Figure 1 and Figure 2 In this embodiment, the cross dipole 21 and the arc-shaped branch 22 together form a T-shaped structure, and the arc-shaped branch 22 is a section of arc-shaped metal sheet; the cross dipole 21 is distributed at the four corners of the frequency selection unit.

[0038] The bent branch 24 on the arc-shaped metal ring 25 is a structure composed of the ends of multiple arc-shaped metal sheets with gradually decreasing arc lengths connected in sequence. These arc-shaped metal sheets and the arc-shaped metal ring 25 have the same center of the circle, and the bent branch 24 is located on the outside of the arc-shaped metal ring 25; the bent branch 24 is connected to the middle part of the inner side of the arc-shaped metal ring 25 through a metal sheet.

[0039] The square patch 23 with rounded inner corners refers to a structure formed by cutting circular recesses on the four sides of a square metal sheet and processing the corners into rounded corners; there is an arc-shaped through groove between the arc-shaped metal ring 25 and the square patch 23.

[0040] See attached Figure 2 In this embodiment of the present invention, the side length p of the frequency selective unit is 6.75 mm, the spacing g between the side of the end connection of adjacent arc-shaped metal rings 25 and the edge of the frequency selective unit is 3.2 mm, the distance l1 from the end of the cross dipole 21 to the outside of the arc-shaped branch 22 is 1.25 mm, the diagonal spacing l2 of the square patch 23 is 3.55 mm, the width w1 of the second varactor diode 5 at the installation position is 0.3 mm, the width w2 of the end connection of adjacent arc-shaped metal rings 25 is 0.4 mm, the length d1 of the first varactor diode 4 at the installation position is 0.7 mm, the length d2 of the second varactor diode 5 at the installation position is 0.4 mm, the spacing d3 between the bent branch 24 and the arc-shaped metal ring 25 is 0.2 mm, the spacing d4 between adjacent arc-shaped metal sheets in the bent branch 24 is 0.25 mm, and the spacing d5 between the arc-shaped branch 22 and the edge of the frequency selective unit is 0.2 mm.

[0041] 2. Bottom metal feed structure 3

[0042] The bottom metal feeding structure 3 includes: a cross metal feed line 31 and a T-shaped metal feed line 32. The cross metal feed line 31 is connected to the square patch 23 on the top surface of the dielectric substrate 1 through a first metal via 7, which is located at the center of the frequency selective unit. The T-shaped metal feed lines 32 are distributed around the cross metal feed line 31 and connected at their ends, forming a square structure that matches the size of the frequency selective unit. The T-shaped metal feed lines 32 are connected to the cross dipoles 21 on the top surface of the dielectric substrate 1 through second metal vias 8, which are located at the four corners of the frequency selective unit. A first gap 33 is formed between each T-shaped metal feed line 32 and the cross metal feed line 31, and a second gap 34 is left near the ends of each T-shaped metal feed line 32. The T-shaped metal feed lines 32 of adjacent frequency selective units are connected to each other to form a cross-shaped structure.

[0043] See attached Figure 1 and Figure 3A cross metal feed line 31 is located at the center of the lower surface of the dielectric substrate 1 in each frequency selective unit, with four T-shaped metal feed lines 32 distributed around it. The T-shaped metal feed line 32 consists of a first feed line 321 located on the outside and a second feed line 322 arranged perpendicularly in the middle of the inside of the first feed line 321. A first gap 33 exists between the second feed line 322 and the cross metal feed line 31, and a second gap 34 is left near each end of the first feed line 321. The width of the first feed line 321 is smaller than that of the second feed line 322. When the first feed lines 321 in adjacent frequency selective units are spliced ​​together, their width is the same as that of the second feed lines 322. In other words, the spliced ​​first feed line 321 and the second feed lines 322 inside the two first feed lines 321 together form a cross structure.

[0044] exist Figure 3 In the given embodiment, the spacing between adjacent second gaps 34 on the T-shaped metal feed line 32 is l3 = 4.75 mm, the length l4 of each feed line in the cross metal feed line 31 is l4 = 1 mm, the width w of each feed line is w = 0.2 mm; the width d of the second gap 34 is 0.5 mm.

[0045] exist Figure 4 In the given embodiment, the dielectric substrate 1 is made of F4B material with a thickness of 0.5 mm, a dielectric constant of 2.55, a loss tangent of 0.001, and a diameter of the first metal via 7 of r=0.2 mm.

[0046] 3. Active devices

[0047] The active device includes a first varactor diode 4 and a second varactor diode 5; the first varactor diode 4 is welded between the arc branch 22 and the bent branch 24 of the top metal resonant structure 2, and its positive electrode is connected to the cross dipole 21 through the arc branch 22, and its negative electrode is connected to the bent branch 24; the second varactor diode 5 is welded between the end connection of the adjacent arc-shaped metal ring 25 and the corresponding square patch 23 corner, and its positive electrode is connected to the square patch 23, and its negative electrode is connected to the arc-shaped metal ring 25.

[0048] Let the two adjacent sides of the frequency selection unit be the X direction and the Y direction respectively, and the vertical direction be the Z direction. Then, a lumped resistor 6 is arranged in the first gap 33 in the X direction between the cross metal feed line 31 and the T-shaped metal feed line 32, and in the second gap 34 in the X direction on the T-shaped metal feed line 32, thereby connecting the cross metal feed line 31 and the T-shaped metal feed line 32 in the X direction. The resistance of the lumped resistor 6 is 10000Ω.

[0049] In this embodiment, the first varactor diode 4 and the second varactor diode 5 are both of model MA46H120, which can provide a variable capacitance between 0.1-1 pF at a reverse bias voltage between 16V and 0V.

[0050] Please refer to Figure 1 The top metal resonant structure 2 on the upper and lower surfaces of the dielectric substrate 1 corresponds to the center of the cross metal feed line 31 in the bottom metal feed structure 3, and is vertically connected by a first metal via 7. The top metal resonant structure 2 on the upper surface of the dielectric substrate 1 forms three different potentials: the positive electrode of the DC power supply is connected to the arc-shaped metal ring 25; the negative electrode of the DC power supply is connected to the cross metal feed line 31 in the center of the frequency selective unit, providing a reverse bias voltage to the square patch 23 through the first metal via 7; the other negative electrode of the DC power supply is connected to the T-shaped metal feed line 32, providing another reverse bias voltage to the cross dipole 21 through the second metal via 8. By changing the bias voltage, the variable capacitance value of the active device is controlled, thereby independently adjusting the dual operating frequency bands of the adjustable frequency selective surface, realizing the broadband reconfigurable function of the wave-transmitting window.

[0051] The following is a further explanation of the technical effects of the present invention in conjunction with simulation experiments:

[0052] In order to verify that the proposed adjustable frequency selective surface has the characteristics of broadband reconfigurable wave window, the transmission curves of the varactor diodes of the embodiment of the present invention are simulated independently. The results are as follows: Figure 5 shown.

[0053] See also Figure 5 Figure (a) shows the frequency response curves for TE-polarized waves with perpendicular incidence, while the second varactor value C2 remains at 0.1pF and the first varactor value varies. It can be seen that as the first varactor value C1 increases from 0.1pF to 0.8pF, the resonant frequency of the second passband remains constant at 9.63GHz, while the resonant frequency of the first passband can be continuously tuned over the range of 2.4-5.75GHz, achieving a relative bandwidth of 82.1% and an insertion loss consistently below 1dB.

[0054] See also Figure 5 Figure (b) shows the frequency response curves for different first varactor values, with the first varactor value C1 maintained at 0.8pF, for a TE-polarized wave with normal incidence. As can be seen, as the second varactor value C2 increases from 0.1pF to 0.4pF, the resonant frequency of the first passband remains constant at 2.4GHz, while the resonant frequency of the second passband can be continuously tuned over the range of 5.7-9.63GHz, achieving a relative bandwidth of 51.2% and an insertion loss consistently less than 1dB.

[0055] In order to verify that the proposed adjustable frequency selective surface has the characteristic of stable incident angle, the transmission curves of electromagnetic waves with different oblique incident angles of the embodiment of the present invention are simulated. The results are as follows: Figure 6 shown.

[0056] See also Figure 6 Figure (a) shows the frequency response curves for different incident angles of TE polarized waves, with the first varactor diode C1 maintained at 0.1pF and the second varactor diode C2 maintained at 0.4pF. As can be seen, as the angle of the oblique incident electromagnetic wave increases to 75°, the resonant frequency remains essentially the same as at normal incidence, and the in-band insertion loss remains below 3dB, demonstrating good angular stability.

[0057] See also Figure 6 Figure (b) shows the frequency response curves for different incident angles of TE polarized waves, with the first varactor diode C1 maintained at 0.8pF and the second varactor diode C2 maintained at 0.3pF. As can be seen, as the angle of the oblique incident electromagnetic wave increases to 75°, the resonant frequency remains essentially the same as at normal incidence, and the in-band insertion loss remains below 3dB, demonstrating good angular stability.

[0058] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present application, and should all be included in the scope of protection of the present application.

Claims

1. A highly angularly stable dual-frequency wave-transmitting window continuously adjustable frequency selective surface, characterized in that: include: A dielectric substrate (1), on which frequency selection units having a square structure are distributed; Each frequency selection unit comprises a top metal resonant structure (2) arranged on the upper surface of a dielectric substrate (1), a bottom metal feeding structure (3) arranged on the lower surface of the dielectric substrate (1), an active device, and a first metal via (7) and a second metal via (8) connecting the upper and lower surfaces, wherein: The top metal resonant structure (2) is a centrosymmetric structure, comprising: a cross dipole (21) with an arcuate branch (22), an arcuate metal ring (25) with a bent branch (24), and a square patch (23) with concave rounded corners on all sides; the arcuate metal rings (25) are distributed around the square patch (23), the ends of adjacent arcuate metal rings (25) are connected, the bent branch (24) is connected to the outside of the arcuate metal ring (25), and the cross dipole (21) is arranged on the outside of the bent branch (24); the arcuate metal rings (25) of adjacent frequency selection units are connected to each other, and the cross dipoles (21) of adjacent frequency selection units are connected to each other; The bottom metal feeding structure (3) comprises: a cross metal feed line (31) and a T-shaped metal feed line (32); the cross metal feed line (31) is connected to the square patch (23) on the upper surface of the dielectric substrate (1) through a first metal via (7), and the first metal via (7) is located at the center of the frequency selection unit; the T-shaped metal feed line (32) is distributed around the cross metal feed line (31) and the ends are connected to each other; the T-shaped metal feed line (32) is connected to the dielectric substrate through a second metal via (8). (1) A cross dipole (21) on the upper surface, and a second metal via (8) located at the four corners of the frequency selection unit; a first gap (33) exists between each T-shaped metal feed line (32) and the cross metal feed line (31); a second gap (34) is left near the two ends of each T-shaped metal feed line (32); a lumped resistor (6) is provided in part of the first gap (33) and the second gap (34); the T-shaped metal feed lines (32) of adjacent frequency selection units are connected to each other to form a cross-shaped structure; The active device comprises a first varactor diode (4) and a second varactor diode (5); the positive electrode of the first varactor diode (4) is connected to the arc-shaped branch (22) of the top metal resonant structure (2), and the negative electrode is connected to the bent branch (24); the positive electrode of the second varactor diode (5) is connected to the corner of the square patch (23), and the negative electrode is connected to the end connection of the adjacent arc-shaped metal ring (25).

2. The highly angle-stable dual-frequency wave-transmitting window continuously adjustable frequency selective surface according to claim 1, characterized in that: The positive electrode of a DC power supply is connected to an arc-shaped metal ring (25); the negative electrode of the DC power supply is connected to a cross metal feed line (31) at the center of a frequency selection unit, and a reverse bias voltage is provided to a square patch (23) through a first metal via (7); the other negative electrode of the DC power supply is connected to a T-shaped metal feed line (32), and another reverse bias voltage is provided to a cross dipole (21) through a second metal via (8); and the change of the variable capacitance value of the active device is controlled by changing the bias voltage, thereby independently regulating the dual working frequency bands of the adjustable frequency selection surface, and realizing the broadband reconfigurable function of the wave-transmitting window.

3. The highly angle-stable dual-frequency wave-transmitting window continuously adjustable frequency selective surface according to claim 1, characterized in that: Note that one side of the frequency selection unit is in the X direction, and a lumped resistor (6) is arranged in a first gap (33) in the X direction between the cross metal feed line (31) and the T-shaped metal feed line (32), and in a second gap (34) in the X direction on the T-shaped metal feed line (32), thereby connecting the cross metal feed line (31) in the X direction with the T-shaped metal feed line (32).

4. The highly angle-stable dual-frequency wave-transmitting window continuously adjustable frequency selective surface according to claim 1, characterized in that: The cross dipole (21) and the arc-shaped branch (22) together form a T-shaped structure, and the arc-shaped branch (22) is a section of arc-shaped metal sheet; the cross dipole (21) is distributed at the four corners of the frequency selection unit.

5. The highly angle-stable dual-frequency wave-transmitting window continuously adjustable frequency selective surface according to claim 1, characterized in that: The bent branch (24) on the arc-shaped metal ring (25) is a structure composed of the ends of multiple arc-shaped metal sheets with gradually decreasing arc lengths connected in sequence. These arc-shaped metal sheets and the arc-shaped metal ring (25) have the same center of a circle, and the bent branch (24) is located on the outside of the arc-shaped metal ring (25); the bent branch (24) is connected to the middle part of the inner side of the arc-shaped metal ring (25) through a metal sheet.

6. The highly angularly stable dual-frequency wave-transmitting window continuously adjustable frequency selective surface according to claim 1, characterized in that: The square patch (23) with concave rounded corners on all sides is a structure formed by cutting circular concave corners on all sides of a square metal sheet and processing the corners into rounded corners; an arc-shaped through groove exists between the arc-shaped metal ring (25) and the square patch (23).

7. The highly angle-stable dual-frequency wave-transmitting window continuously adjustable frequency selective surface according to claim 1, characterized in that: The T-shaped metal feed line (32) is composed of a first feed line (321) located on the outside and a second feed line (322) vertically arranged in the middle of the inside of the first feed line (321); a first gap (33) exists between the second feed line (322) and the cross metal feed line (31), and a second gap (34) is left near both ends of the first feed line (321); the width of the first feed line (321) is smaller than that of the second feed line (322); after the first feed lines (321) in adjacent frequency selection units are spliced ​​together, the first feed line (321) and the second feed lines (322) inside the two first feed lines (321) together form a cross structure.

8. The highly angle-stable dual-frequency wave-transmitting window continuously adjustable frequency selective surface according to claim 1, characterized in that: The dielectric substrate (1) is made of F4B material with a thickness of 0.5 mm, a dielectric constant of 2.55, and a loss tangent of 0.

001.

9. The highly angle-stable dual-frequency wave-transmitting window continuously adjustable frequency selective surface according to claim 1, characterized in that: The first varactor diode (4) and the second varactor diode (5) can provide a variable capacitance between 0.1 and 1 pF at a reverse bias voltage between 16 and 0 V.

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