An active frequency selective surface based on switches and varactor diodes

Abstract

An active frequency selective surface based on switches and varactor diodes, comprising a frequency selective surface, a feeding network and active devices. The frequency selective surface includes a top metal layer, an intermediate metal layer, a bottom metal layer and a dielectric substrate. The feeding network includes feed lines, loading inductors and metallized vias. The active devices include varactor diodes and switches. The active frequency selective surface of the present invention can change the resonant frequency within an ultra-wide range by changing the state of the loaded switches and the capacitance value of the loaded varactor diodes. The on-off of the switch structure is used to realize the switching of the transmission window of the active frequency selective surface between the higher frequency band and the lower frequency band, achieving a large-span adjustment. The small-span adjustment of the transmission window is realized by changing the capacitance value of the varactor diode, so as to realize a broadband low-loss transmission window within an ultra-wide adjustable range, and maintain the polarization stability and angular stability of the resonant frequency, which is suitable for complex electromagnetic environments.

Description

Technical Field

[0001] The present invention belongs to the field of electromagnetic fields and microwave technologies, and particularly relates to an active frequency selective surface based on switches and varactor diodes. Background Art

[0002] Active Frequency Selective Surfaces (AFSS) refer to the artificial control of the filtering characteristics of frequency selective surfaces by loading active devices (such as PIN diodes, varactor diodes, etc.). Generally speaking, an active frequency selective surface is made by loading a series of active devices in the unit structure of a traditional passive frequency selective surface and designing a corresponding feeding system. The functions that an active frequency selective surface can achieve include the switching control of the filtering characteristics of the frequency selective surface in a specified frequency band, the adjustment of the working frequency band of the frequency selective surface, the control of the strength of the filtering performance of the frequency selective surface, etc. This also provides a new solution for the research in fields such as microwave absorbing materials, tunable filters, active phased array radars, and tunable electromagnetic shielding materials, and has very important research value.

[0003] Currently, the transmission characteristics of the studied active frequency selective surfaces can be regulated. However, there are still problems such as a narrow tuning range, a narrow bandwidth of the transmission window, and high insertion loss within the transmission window, resulting in the need to improve the performance of the current active frequency selective surfaces. Summary of the Invention

[0004] In order to overcome the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide an active frequency selective surface based on switches and varactor diodes, in order to solve one or all of the problems such as the narrow tuning range, narrow bandwidth of the transmission window, and high insertion loss within the transmission window of the existing active frequency selective surfaces.

[0005] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0006] An active frequency selective surface based on switches and varactor diodes, comprising a frequency selective surface, a feeding network, and active devices;

[0007] The frequency selective surface includes a top metal layer, a first upper dielectric layer, a second upper dielectric layer, an intermediate metal layer, a first lower dielectric layer, a second lower dielectric layer, and a bottom metal layer from top to bottom;

[0008] The top metal layer and the bottom metal layer have the same shape, and are both composed of a grid structure, a cross-shaped patch, and four square patches; the grid structure is a closed square. Taking two adjacent sides of the closed square as the X direction and the Y direction respectively, and the vertical direction as the Z direction, the cross-shaped patch is arranged at the inner center of the grid structure, and its cross shape is along the X direction and the Y direction, dividing the interior of the grid structure into four regions. The four square patches are respectively located in one of the regions, and the sides of the square patches are in the X direction or the Y direction;

[0009] The middle metal layer is a cross-shaped structure composed of two rectangular patches perpendicular to each other along the X direction and the Y direction;

[0010] The feeding network feeds power to the cross-shaped patch and the square patch;

[0011] The active devices include an inner varactor diode, an outer varactor diode, and a loading switch; in each of the regions, the inner varactor diode connects the included angle of the cross-shaped patch and the vertex angle of the square patch close to the included angle, the outer varactor diode connects the vertex angle of the square patch far from the included angle and the vertex angle of the grid structure; the loading switch connects the end of the cross-shaped patch and the inner side of the frame of the grid structure.

[0012] In one embodiment, the first upper dielectric layer, the second upper dielectric layer, the first lower dielectric layer, and the second lower dielectric layer have the same relative dielectric constant, the same loss tangent, and the same dimensions in the X direction and the Y direction, and are distributed in the middle.

[0013] In one embodiment, the first upper dielectric layer and the second lower dielectric layer have the same thickness, and the second upper dielectric layer and the first lower dielectric layer have the same thickness.

[0014] In one embodiment, the feeding network includes an upper feeding network and a lower feeding network, which have the same shape and are symmetrically distributed along the plane formed by the middle metal layer in the vertical direction.

[0015] In one embodiment, both the upper feeding network and the lower feeding network are composed of a feeder structure, inductors, and metallized vias.

[0016] The feeder structure includes three metal lines with the same width in the Y direction, which are the first feeder structure, the second feeder structure, and the third feeder structure in sequence;

[0017] The inductors are loaded on the feeder structure; including a first inductor, a second inductor, and a third inductor loaded at both ends and the center of the first feeder structure; a fourth inductor and a fifth inductor loaded at both ends of the second feeder structure; and a sixth inductor, a seventh inductor, and an eighth inductor loaded at both ends and the center of the third feeder structure;

[0018] The metallized vias are respectively loaded inside the first upper dielectric layer and the second lower dielectric layer, and are used to connect each feeder structure to the feeding points on the top metal layer, and the feeding points on the top metal layer are located on the cross-shaped patch and the square patch.

[0019] In one embodiment, the first feeder structure, the second feeder structure and the third feeder structure are respectively located at three quarter lines of the dielectric substrate where they are located; one end of the metallized via is located at the center of each segment of each feeder structure; the feeding points on the cross-shaped patch are located at its center position, and the feeding points on each square patch are symmetrically distributed about the center.

[0020] In one embodiment, the inductance values of the first inductor, the second inductor, the fourth inductor, the fifth inductor, the sixth inductor and the seventh inductor are equal, and are 1 / 2 of the inductance values of the third inductor and the eighth inductor.

[0021] In one embodiment, a first isosceles right triangle patch is respectively arranged at four inner top corners of the grid structure, and a rectangular patch is respectively arranged at the inner midpoint positions of the four sides of the grid structure; a second isosceles right triangle patch is respectively arranged at four included angles of the cross-shaped patch; the square patch is a square, and an isosceles right triangle is respectively cut off from the top corners connected to the inner varactor diode and the outer varactor diode; the inner varactor diode is connected between the second isosceles right triangle patch and the top corner of the square patch where an isosceles right triangle is cut off; the outer varactor diode is connected between the first isosceles right triangle patch and the other top corner of the square patch where an isosceles right triangle is cut off; the loading switch is connected between the end of the cross-shaped patch and the rectangular patch of the grid structure.

[0022] In one embodiment, the capacitance value change range of the inner varactor diode is 0.05 pF - 0.2 pF; the capacitance value change range of the outer varactor diode is 0.05 pF - 0.3 pF.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] First, compared with a general active frequency selective surface, the present invention proposes an active frequency selective surface based on switches and varactor diodes. It realizes a large-scale change in the resonant frequency of the frequency selective surface by loading a switch structure, and realizes a small-scale change in the resonant frequency of the frequency selective surface by varactor diodes, thus realizing an active frequency selective surface with an ultra-wide tunable range.

[0025] Second, compared with general active frequency selective surfaces, the wave - transmitting window of the present invention has a relatively wide bandwidth, achieves low insertion loss within the wave - transmitting window, and has good polarization stability and angular stability.

[0026] Third, after loading a feeding network inside the dielectric plate, the present invention conducts an integrated simulation design on the overall structure. By loading inductors on the feeder lines, feeding is achieved for active devices without affecting the performance of the active frequency selective surface, and the structure of the feeding network does not increase the extra height for the active frequency selective surface. Description of the Drawings

[0027] Figure 1 is the exploded view of the overall structure of the active frequency selective surface of the present invention.

[0028] Figure 2 is the schematic diagram of the overall structure of the active frequency selective surface of the present invention.

[0029] Figure 3 is the structural diagram of the top - layer metal layer of the active frequency selective surface of the present invention. Among them, (a) is the schematic diagram of the structure, and (b) is a schematic diagram of one kind of dimension.

[0030] Figure 4 is the structural diagram of the middle - layer metal layer of the active frequency selective surface of the present invention.

[0031] Figure 5 is the structural diagram of the feeding network of the active frequency selective surface of the present invention. Among them, (a) is the schematic diagram of the structure, and (b) is a schematic diagram of one kind of dimension.

[0032] Figure 6 is the transmission coefficient curve when the incident wave is incident at an angle of 0° in the closed - switch state of Embodiment 1 of the present invention. Among them, (a) is the transmission coefficient curve under TE polarization, and (b) is the transmission coefficient curve under TM polarization.

[0033] Figure 7 is the transmission coefficient curve when the incident wave is incident at an angle of 0° in the open - switch state of Embodiment 1 of the present invention. Among them, (a) is the transmission coefficient curve under TE polarization, and (b) is the transmission coefficient curve under TM polarization.

[0034] Figure 8 is the transmission coefficient curve when the incident wave is incident at an angle of 30° in the closed - switch state of Embodiment 1 of the present invention. Among them, (a) is the transmission coefficient curve under TE polarization, and (b) is the transmission coefficient curve under TM polarization.

[0035] Figure 9In Embodiment 1 of the present invention, the transmission coefficient curve when the incident wave is incident at an angle of 30° in the off state of the switch, where (a) is the transmission coefficient curve under TE polarization and (b) is the transmission coefficient curve under TM polarization. Detailed implementation manners

[0036] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0037] As described above, there are still some problems with the tuning range, the bandwidth of the transmission window, and the insertion loss within the transmission window of the existing active frequency selective surface. For this reason, the present invention provides an active frequency selective surface, which mainly improves the performance based on switches and varactor diodes. By changing the state of the loaded switches and the capacitance value of the loaded varactor diodes, the resonant frequency can be changed within an ultra-wide range, and the polarization stability and angular stability of the resonant frequency are maintained, which is applicable to wireless communication systems in complex electromagnetic environments, such as radar, radome, aircraft stealth, etc.

[0038] Specifically, reference can be made to Figures 1 to 5 As shown, the active frequency selective surface of the present invention based on switches and varactor diodes mainly includes a frequency selective surface 1, a feeding network 2, and active devices.

[0039] Among them, with reference to Figure 2 , the frequency selective surface 1 includes a top metal layer 11, a first upper dielectric layer 12, a second upper dielectric layer 13, an intermediate metal layer 14, a first lower dielectric layer 15, a second lower dielectric layer 16, and a bottom metal layer 17 from top to bottom. Alternatively, it may also be composed only of the above-mentioned top metal layer 11, first upper dielectric layer 12, second upper dielectric layer 13, intermediate metal layer 14, first lower dielectric layer 15, second lower dielectric layer 16, and bottom metal layer 17.

[0040] Among them, the top metal layer 11 and the bottom metal layer 17 have the same shape and preferably the same size. Both are composed of a grid structure 111, a cross-shaped patch 112, and four square patches 113.

[0041] The grid structure 111 is in the shape of a closed square. In the present invention, for the convenience of description, the following XYZ directions are defined: taking two adjacent sides of the closed square as the X direction and the Y direction respectively, and the vertical direction as the Z direction, with the upper part of the vertical direction being the positive Z direction. With reference to Figure 3 as shown in (a) of

[0042] Reference Figure 4 The middle - layer metal layer 14 is in a cross - shape structure, which is composed of two rectangular patches perpendicular to each other along the X - direction and the Y - direction. Obviously, the center of the middle - layer metal layer 14 is preferably located on the vertical projection of the center of the cross - shaped patch 112.

[0043] Reference Figure 5 As shown in Fig. (a) of the reference, the active devices include a varactor diode and a loading switch 116. The varactor diode is used to connect the grid structure 111, a square patch 113, and the cross - shaped patch 112 in sequence, and the loading switch 116 is used to directly connect the cross - shaped patch 112 and the grid structure 111. In an embodiment of the present invention, the varactor diode is composed of four inner - ring varactor diodes 114 and four outer - ring varactor diodes 115, and there are also four loading switches 116.

[0044] In each of the foregoing regions, a specific connection method: an inner - ring varactor diode 114 connects the included angle (i.e., the intersection position) of the cross - shaped patch 112 and the vertex angle of the square patch 113 close to this included angle, and the outer - ring varactor diode 115 connects the vertex angle of the square patch 113 far from this included angle and the vertex angle of the grid structure 111. The four ends of the cross - shaped patch 112 are respectively connected to the inner side of the frame of the grid structure 111 through a loading switch 116.

[0045] The feeding network 2 is used to feed power to the cross - shaped patch 112 and the square patch 113. In an embodiment of the present invention, the feeding network 2 includes an upper - layer feeding network 21 and a lower - layer feeding network 22, which have the same shape and are symmetrically distributed along the plane formed by the middle - layer metal layer 14 in the vertical direction. Among them, the upper - layer feeding network 21 is located between the first upper - layer dielectric plate 12 and the second upper - layer dielectric plate 13, and can be printed on the lower surface of the first upper - layer dielectric plate 12 or on the upper surface of the second upper - layer dielectric plate 13. The lower - layer feeding network 22 is located between the first lower - layer dielectric plate 15 and the second lower - layer dielectric plate 16, and can be printed on the lower surface of the first lower - layer dielectric plate 15 or on the upper surface of the second lower - layer dielectric plate 16.

[0046] A form of the upper - layer feeding network 21 and the lower - layer feeding network 22 of the present invention is composed of a feeder structure, an inductor, and a metallized via.

[0047] Specifically, the feeder structure includes three metal lines with the same width in the Y - direction, namely the first feeder structure 2111, the second feeder structure 2121, and the third feeder structure 2131. For example, the widths of the first feeder structure 2111, the second feeder structure 2121, and the third feeder structure 2131 are all 0.2 mm, and they are respectively located at the three quarter - lines of the dielectric substrate where they are located, that is, the three are evenly distributed on the dielectric substrate.

[0048] The inductors are loaded on the feeder structure, specifically including the first inductor 2112, the second inductor 2114, and the third inductor 2113 loaded at both ends and the center of the first feeder structure 2111; the fourth inductor 2122 and the fifth inductor 2123 loaded at both ends of the second feeder structure 2121; and the sixth inductor 2132, the seventh inductor 2134, and the eighth inductor 2133 loaded at both ends and the center of the third feeder structure 2131. Among them, the inductors at both ends, namely the first inductor 2112, the second inductor 2114, the fourth inductor 2122, the fifth inductor 2123, the sixth inductor 2132, and the seventh inductor 2134, have equal inductance values, and the inductors in the middle, namely the third inductor 2113 and the eighth inductor 2133, have equal inductance values. And the inductance value of the inductors at both ends is 1 / 2 of the inductance value of the inductors in the middle. By way of example, the inductance value of the inductors at both ends is 1H, and the inductance value of the inductors in the middle is 2H.

[0049] The metallized vias 214 are respectively loaded inside the first upper dielectric layer 12 and the second lower dielectric layer 16 for connecting each feeder structure to the feeding points on the top metal layer 11, where the feeding points on the top metal layer 11 are located on the cross-shaped patch 112 and the square patch 113. Preferably, one end of the metallized via 214 is located at the center of each section of each feeder structure. The feeding point on the cross-shaped patch 112 is located at its center position, and the feeding points on each square patch 113 are symmetrically distributed about the center. By way of example, the diameter of the metallized via can be 0.1 mm.

[0050] An embodiment of the present invention provides more specific forms of the grid structure 111, the cross-shaped patch 112, and the square patch 113. A first equilateral right-angled triangle patch is respectively connected and arranged at the four inner top corners of the grid structure 111, and a rectangular patch is respectively arranged at the midpoint positions inside the four sides of the grid structure 111, that is, the first equilateral right-angled triangle patches are respectively embedded at the four top corners inside the square frame and connected to the frame, and the four rectangular patches are all located at the centers of the respective frames and connected to the square ring frame. Second equilateral right-angled triangle patches are respectively arranged at the four included angles of the cross-shaped patch 112, and the four second equilateral right-angled triangles are respectively embedded at the four included angles of the cross intersection and connected to the cross-shaped patch 112. The square patch 113 is square, and at a vertex close to the top corner of the grid structure 111, an equilateral right-angled triangle one is cut off, and at a vertex close to an included angle of the cross-shaped patch 112, an equilateral right-angled triangle two is cut off. The vertex of the cut-off equilateral right-angled triangle coincides with the vertex of the square patch, and the two sides of the cut-off equilateral right-angled triangle coincide with the sides of the square patch.

[0051] The inner varactor diode 114 is connected between the second isosceles right triangle patch and the vertex of the second isosceles right triangle cut off from the square patch 113. The outer varactor diode 115 is connected between the first isosceles right triangle patch and the vertex of the first isosceles right triangle cut off from the square patch 113. The widths of the inner varactor diode 114 and the outer varactor diode 115 are preferably equal and equal to the hypotenuse length of the first isosceles right triangle or the second isosceles right triangle. The loading switch 116 is connected between the end of the cross-shaped patch 112 and the rectangular patch of the grid structure 111. Exemplarily, the capacitance value of the inner varactor diode 114 varies in the range of 0.05 pF - 0.2 pF; the capacitance value of the outer varactor diode 115 varies in the range of 0.05 pF - 0.3 pF.

[0052] In an embodiment of the present invention, the horizontal planes of the first upper dielectric layer 12, the second upper dielectric layer 13, the first lower dielectric layer 15, and the second lower dielectric layer 16 have the same shape, that is, their dimensions in the X and Y directions are the same and are centered, while they have different thicknesses in the vertical direction, so as to facilitate the processing and production of the thickness of the dielectric layer while maintaining the high performance of the active frequency selective surface.

[0053] Exemplarily, the thicknesses of the first upper dielectric layer 12 and the second lower dielectric layer 16 are equal, h1 = 0.45 mm, and the thicknesses of the second upper dielectric layer 13 and the first lower dielectric layer 15 are equal, h2 = 1.2 mm.

[0054] Reference Figure 1 and Figure 2 , an active frequency selective surface based on switches and varactor diodes, characterized in that it includes a frequency selective surface (1), a feeding network (2), and active devices;

[0055] The frequency selective surface (1) includes a top metal layer (11), a first upper dielectric layer (12), a second upper dielectric layer (13), an intermediate metal layer (14), a first lower dielectric layer (15), a second lower dielectric layer (16), and a bottom metal layer (17) from top to bottom. Among them, the top metal layer (11) contains an equivalent inductance structure and an equivalent capacitance structure, and the external resonant ring can link each frequency selective surface unit and is attached to the outside of the first upper dielectric layer (12); the intermediate metal layer (14) is an equivalent inductance structure, which couples with the top metal layer (11) and the bottom metal layer (17) to produce a spatial filtering effect and is attached between the second upper dielectric layer (13) and the first lower dielectric layer (15); the bottom metal layer (17) has the same structure as the top metal layer (11) to produce better angular stability and polarization stability;

[0056] In the feeder network (2) to which it belongs, both the upper-layer feeder network and the lower-layer feeder network are composed of a feeder structure, an inductor, and a metallized via hole. Among them, the feeder structure is used to transfer the external voltage; the inductor is used to choke the current on the feeder structure, thereby avoiding the generation of additional resonance; the metallized via hole is used to load the voltage on the feeder structure onto the corresponding metal patch;

[0057] The active devices include an inner-ring varactor diode, an outer-ring varactor diode, and a loading switch. The inner-ring varactor diode and the outer-ring varactor diode are used to change the capacitance value to achieve a small-span adjustment of the wave-transmitting window; the switch structure is used to change the on-off state to achieve a large-span adjustment of the wave-transmitting window.

[0058] In an embodiment 1 of the present invention, the first upper-layer dielectric plate 12, the second upper-layer dielectric plate 13, the first lower-layer dielectric plate 15, and the second lower-layer dielectric plate 16 are all rectangular structures, and the relative dielectric constants of the materials used are all 2.2, and the loss tangent values are all 0.0009. Refer to Figure 2 As shown, the height h2 + h of the first upper-layer dielectric plate 12 p is 1.35 mm, the length p x is 8.2 mm, the width p y is 8.2 mm, the thickness h1 is 0.45 mm; the height of the second upper-layer dielectric plate 13 is 0 mm, the length p x is 8.2 mm, the width p y is 8.2 mm, the thickness h2 is 1.2 mm; the height -h1 of the first lower-layer dielectric plate 15 is -0.45 mm, the length p x is 8.2 mm, the width p y is 8.2 mm, the thickness h1 is 0.45 mm; the height -h1 - h2 - h of the second lower-layer dielectric plate 16 p is -1.8 mm, the length p x is 8.2 mm, the width p y is 8.2 mm, the thickness h1 is 0.45 mm.

[0059] The width s1 of the square ring structure of the grid structure 111 is 0.1 mm, the external length p of the square ring x is 8.2 mm, the width p y is 8.2 mm, the side length a of the equilateral right triangle at the four corners of the square ring is 0.7 mm, the width s0 of the rectangular patch 113 at the center of each side of the square ring is 1.4 mm, and the length s3 is 0.4 mm; the length l0 of the two rectangular patches of the cross-shaped patch 112 is 6.6 mm, the width s0 is 1.4 mm, and the side length a1 of the equilateral right triangle at the intersection of the rectangular patches is 0.5 mm; the side length l of the square patch forming the square patch 113 is 2.4 mm, and the side length a0 of the cut-off equilateral right triangle is 0.4 mm.

[0060] The length p of the two rectangular patches that make up the intermediate metal layer 14 x is 8.2 mm for both, and the width w is 0.8 mm for both.

[0061] Reference Figure 5 As shown in (b) of the reference, the first feeder structure 2111 is located at the quarter line on the left side of the dielectric substrate, and the width d x is 0.2 mm, and the length p y is 8.2 mm; the second feeder structure 2121 is located at the quarter line in the middle of the dielectric substrate, and the width d x is 0.2 mm, and the length p y is 8.2 mm; the third feeder structure 2131 is located at the quarter line on the right side of the dielectric substrate, and the width d x is 0.2 mm, and the length p y is 8.2 mm; the first inductor 2112 is loaded on the top of the first feeder structure 2111, and the width d x is 0.2 mm, and the length d y0 / 2 is 1 mm; the third inductor 2113 is loaded in the middle of the first feeder structure 2111, and the width d x is 0.2 mm, and the length d y0 is 2 mm; the second inductor 2114 is loaded on the bottom of the first feeder structure 2111, and the width d x is 0.2 mm, and the length d y0 / 2 is 1 mm; the fourth inductor 2122 is loaded on the top of the second feeder structure 2121, and the width d x is 0.2 mm, and the length d y0 / 2 is 1 mm; the fifth inductor 2123 is loaded on the bottom of the second feeder structure 2121, and the width d x is 0.2 mm, and the length d y0 / 2 is 1 mm; the sixth inductor 2132 is loaded on the top of the third feeder structure 2131, and the width d x is 0.2 mm, and the length d y0 / 2 is 1 mm; the eighth inductor 2133 is loaded in the middle of the third feeder structure 2131, and the width d x is 0.2 mm, and the length d y0 is 2 mm; the seventh inductor 2134 is loaded on the bottom of the third feeder structure 2131, and the width d x is 0.2 mm, and the length d y0 / 2 is 1 mm; the upper metallized via is loaded inside the upper dielectric substrate 12 and is located at the central part of each section of each feeder structure (i.e., the sections separated by inductors), and the diameter d kAll are 0.1 mm; the lower metallized vias are loaded inside the lower dielectric substrate 16 and are located at the central parts of the symmetric structures of the feeder structures 2111, 2121, and 2131, with a diameter d k All are 0.1 mm.

[0062] The widths of the inner varactor diodes 114 are all 0.57 mm, the lengths are all 0.64 mm, and the capacitance value varies in the range of 0.05 pF - 0.2 pF; the widths of the outer varactor diodes 115 are all 0.57 mm, the lengths are all 0.5 mm, and the capacitance value varies in the range of 0.05 pF - 0.3 pF; the loaded switches 116 have widths of all 0.57 mm, lengths of all 0.4 mm, and have two states of closed and open.

[0063] The effects of the present invention can be further illustrated by the following simulations:

[0064] I. Simulation software:

[0065] Commercial Ansoft HFSS 19.0 software.

[0066] II. Simulation content:

[0067] Simulation 1, the transmission coefficient curve when the incident wave is incident at an angle of 0° in the closed state of the switch in Embodiment 1 of the present invention. The simulation results under TE polarization are as shown in Figure 6 (a) in, and the simulation results under TM polarization are as shown in Figure 6 (b) in. It can be seen from Figure 6 that Embodiment 1 realizes continuously adjustable passbands in the range of 11.36 - 13.785 GHz, while maintaining good passband consistency. As the capacitance values of the varactor diode 114 and the varactor diode 115 increase, the in-band dips are not obvious, the in-band insertion loss remains below 0.5 dB, and the absolute bandwidth of each passband is between 1.12 GHz and 1.5 GHz, having a relatively wide bandwidth;

[0068] Simulation 2, the transmission coefficient curve when the incident wave is incident at an angle of 0° in the open state of the switch in Embodiment 1 of the present invention. The simulation results under TE polarization are as shown in Figure 7 (a) in, and the simulation results under TM polarization are as shown in Figure 7 (b) in. It can be seen from Figure 7 that Embodiment 1 realizes continuously adjustable passbands in the range of 7.71 - 10.46 GHz, while maintaining good passband consistency. As the capacitance values of the varactor diode 114 and the varactor diode 115 increase, the in-band dips are not obvious, the in-band insertion loss remains below 0.5 dB, and the absolute bandwidth of each passband is between 1.3 GHz and 1.58 GHz, having a relatively wide bandwidth;

[0069] Simulation 3. In the closed-switch state of Embodiment 1 of the present invention, the transmission coefficient curve when the incident wave is incident at an incident angle of 30°. The simulation results under TE polarization are as shown in Figure 8 (a) therein, and the simulation results under TM polarization are as shown in Figure 8 (b) therein. As can be seen from Figure 8 , Embodiment 1 achieves that the transmission curve at oblique incidence is basically the same as that at normal incidence, with only a small frequency offset, and has good angle stability;

[0070] Simulation 4. In the open-switch state of Embodiment 1 of the present invention, the transmission coefficient curve when the incident wave is incident at an incident angle of 30°. The simulation results under TE polarization are as shown in Figure 9 (a) therein, and the simulation results under TM polarization are as shown in Figure 9 (b) therein. As can be seen from Figure 9 , Embodiment 1 achieves that the transmission curve at oblique incidence is basically the same as that at normal incidence. Only some frequencies resonate, but it does not affect the transmission rate within the transmission window, and has good angle stability.

[0071] It can be seen that by turning the switch on and off, the present invention can achieve a large-span adjustment of the transmission window, so that the resonant frequency point of the active frequency selective surface can be switched between a higher frequency band and a lower frequency band. Referring to Figure 6 (a) therein and Figure 7 (a) therein, when the capacitance value of the inner varactor diode (114) is 0.1 pF and the capacitance value of the outer varactor diode (115) is 0.15 pF, the center frequency point of the passband in the closed-switch state is 12.765 GHz, while the center frequency point of the passband in the open-switch state is 8.98 GHz. A large-span adjustment of 3.785 GHz of the center frequency point of the passband is achieved by turning the switch on and off. By changing the capacitance value of the varactor diode, a small-span adjustment of the transmission window can be achieved. Referring to Figure 6 (a) therein, when the capacitance value of the inner varactor diode (114) is 0.1 pF and the capacitance value of the outer varactor diode (115) is 0.1 pF, the center frequency point of the passband in the closed-switch state is 13.785 GHz, while when the capacitance value of the inner varactor diode (114) is 0.1 pF and the capacitance value of the outer varactor diode (115) is 0.15 pF, the center frequency point of the passband in the closed-switch state is 12.765 GHz. A small-span adjustment of 1.02 GHz of the center frequency point of the passband is achieved by changing the capacitance value of the varactor diode. In summary, the active frequency selective surface of the present invention can achieve a broadband low-loss transmission window within an ultra-wide adjustable range. Referring to Figure 6 and Figure 7, it realizes continuously adjustable passbands in the range of 7.71 - 13.785 GHz, has a wide frequency domain tuning range of approximately 1.79 octaves, the in-band insertion loss is maintained below 0.5 dB, and the absolute bandwidth of each passband is between 1.12 GHz and 1.58 GHz, having a relatively wide bandwidth.

[0072] The above description is only one embodiment of the present invention and does not constitute any limitation to the present invention. Obviously, for professionals in the field, after understanding the content and principle of the present invention, various corrections and changes in form and details may be made without departing from the principle and structure of the present invention. However, these corrections and changes based on the idea of the present invention are still within the scope of the claims and protection of the present invention.

Claims

1. An active frequency selective surface based on switches and varactor diodes, characterized in that It includes a frequency selective surface (1), a feeding network (2) and an active device; The frequency selective surface (1) includes, from top to bottom, a top metal layer (11), a first upper dielectric plate (12), a second upper dielectric plate (13), an intermediate metal layer (14), a first lower dielectric plate (15), a second lower dielectric plate (16) and a bottom metal layer (17); The top metal layer (11) and the bottom metal layer (17) have the same shape, and are both composed of a grid structure (111), a cross-shaped patch (112) and four square patches (113); the grid structure (111) is a closed square. Taking two adjacent sides of the closed square as the X-direction and the Y-direction respectively, and the vertical direction as the Z-direction, the cross-shaped patch (112) is arranged at the inner center of the grid structure (111), and its cross shape is along the X-direction and the Y-direction, dividing the inside of the grid structure (111) into four regions. The four square patches (113) are respectively located in one of the regions, and the sides of the square patches (113) are in the X-direction or the Y-direction; The intermediate metal layer (14) is a cross-shaped structure composed of two rectangular patches vertically and crosswise along the X-direction and the Y-direction; The feeding network (2) feeds the cross-shaped patch (112) and the square patches (113); the feeding network (2) includes an upper feeding network (21) and a lower feeding network (22), which have the same shape and are symmetrically distributed along the plane formed by the intermediate metal layer (14) in the vertical direction; Both the upper feeding network (21) and the lower feeding network (22) are composed of a feeder structure, an inductor and a metallized via hole (214); The feeder structure includes three metal lines with the same width in the Y-direction, which are successively a first feeder structure (2111), a second feeder structure (2121) and a third feeder structure (2131); The inductor is loaded on the feeder structure; it includes a first inductor (2112), a second inductor (2114) and a third inductor (2113) loaded at both ends and the center of the first feeder structure (2111); a fourth inductor (2122) and a fifth inductor (2123) loaded at both ends of the second feeder structure (2121); and a sixth inductor (2132), a seventh inductor (2134) and an eighth inductor (2133) loaded at both ends and the center of the third feeder structure (2131); The metallized via holes (214) are respectively loaded inside the first upper dielectric plate (12) and the second lower dielectric plate (16) for connecting each feeder structure to the feeding points on the top metal layer (11), and the feeding points on the top metal layer (11) are located on the cross-shaped patch (112) and the square patches (113); The active device includes an inner varactor diode (114), an outer varactor diode (115), and a loading switch (116); within each of the regions, the inner varactor diode (114) is connected to the included angle of the cross-shaped patch (112) and the vertex angle of the square patch (113) close to the included angle, the outer varactor diode (115) is connected to the vertex angle of the square patch (113) far from the included angle and the vertex angle of the grid structure (111); the loading switch (116) is connected to the end of the cross-shaped patch (112) and the inner side of the border of the grid structure (111).

2. The active frequency selective surface based on switches and varactor diodes according to claim 1, characterized in that, The first upper dielectric layer (12), the second upper dielectric layer (13), the first lower dielectric layer (15), and the second lower dielectric layer (16) have the same relative dielectric constant, the same loss tangent, and the same dimensions in the X and Y directions, and are centrally distributed.

3. The active frequency selective surface based on switches and varactor diodes according to claim 1 or 2, characterized in that, The first upper dielectric layer (12) and the second lower dielectric layer (16) have the same thickness, and the second upper dielectric layer (13) and the first lower dielectric layer (15) have the same thickness.

4. The active frequency selective surface based on switches and varactor diodes according to claim 1, wherein The first feeder structure (2111), the second feeder structure (2121), and the third feeder structure (2131) are respectively located at the three quarter lines of their respective dielectric substrates; one end of the metallized via (214) is located at the center of each segment of each feeder structure; the feeding point on the cross-shaped patch (112) is located at its center position, and the feeding points on each of the square patches (113) are symmetrically distributed about the center.

5. The active frequency selective surface based on switches and varactor diodes according to claim 1, wherein The inductance values of the first inductor (2112), the second inductor (2114), the fourth inductor (2122), the fifth inductor (2123), the sixth inductor (2132), and the seventh inductor (2134) are equal, and are 1 / 2 of the inductance values of the third inductor (2113) and the eighth inductor (2133).

6. The active frequency selective surface based on switches and varactor diodes according to claim 1, characterized in that A first isosceles right triangle patch is respectively arranged at the four internal vertex angles of the grid structure (111), and a rectangular patch is respectively arranged at the internal midpoint positions of the four sides of the grid structure (111); a second isosceles right triangle patch is respectively arranged at the four included angles of the cross-shaped patch (112); the square patch (113) is a square, and an isosceles right triangle is cut off from each of the vertex angles connected to the inner varactor diode (114) and the outer varactor diode (115); the inner varactor diode (114) is connected between the second isosceles right triangle patch and the vertex angle of the square patch (113) where an isosceles right triangle is cut off; the outer varactor diode (115) is connected between the first isosceles right triangle patch and the other vertex angle of the square patch (113) where an isosceles right triangle is cut off; the loading switch (116) is connected between the end of the cross-shaped patch (112) and the rectangular patch of the grid structure (111).

7. The active frequency selective surface based on switches and varactor diodes according to claim 1, characterized in that, The capacitance value of the inner varactor diode (114) varies in the range of 0.05 pF - 0.2 pF; the capacitance value of the outer varactor diode (115) varies in the range of 0.05 pF - 0.3 pF.

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