Transmissive window covering c-band absorption-transmission integrated tunable metasurface and design method thereof

Abstract

The application provides a transmissive window covering C-band absorption and transmission integrated adjustable super surface and a design method thereof, which comprises a plurality of periodically arranged adjustable super surface units, the adjustable super surface unit is a two-layer structure and is composed of a top layer unit and a bottom layer unit; the bottom layer unit is composed of a first upper surface composed of a "cross" metal wire, a first intermediate layer and a first bottom surface which is a transmissive frequency selection surface; the top layer unit is composed of a second upper surface for transmissive frequency selection, a second intermediate layer and a second bottom surface composed of a "cross" metal wire; the adjustable super surface is an absorption and transmission integrated adjustable super surface design capable of covering the whole C-band (4GHz-8GHz) of the transmissive window, and can be completely completed by a mature PCB (printed circuit board) process.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of antennas, and particularly relates to a transmissive window covering C-band absorbing and transmissive integrated tunable metasurface device and a design method thereof. BACKGROUND

[0002] In the microwave frequency band, it is a relatively mature technology to use metamaterials to construct an absorbing structure to absorb electromagnetic waves incident on the structure to achieve invisibility. On this basis, the reflected signal obtained by reflecting the electromagnetic wave emitted by us also needs to be detected by us again, which requires the design of a wideband low-reflection structure with a transmissive window function. In addition, it is also hoped that the frequency of this transmissive window can be adjusted to obtain information of different frequency bands. The combination of tunable lumped elements and metamaterial design provides a solution to this demand.

[0003] The current related design mainly uses a variable capacitance diode, i.e. a lumped element whose capacitance value can be controlled by an external DC voltage, and different metal pattern structure arrangements to change the frequency of the transmissive window by an external DC voltage, while the absorption band remains unchanged. For example, in the paper entitled Broadband Frequency-Selective Rasorber With Varactor-Tunable Interabsorption Band Transmission Window published in IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, Vol. 67, 2019 by Lijie Wu, Shuomin Zhong, etc., an absorbing and transmissive integrated transmissive window tunable metasurface device based on a variable capacitance diode is proposed, which is composed of a double-layer structure of a complex metal pattern on the top layer, a variable capacitance diode, a metal via, and a metal ring structure on the bottom layer, and a variable capacitance diode, which realizes the transmissive window tunable function of 2.2GHz-3.3GHz and wideband absorption of 1.9GHz-5.4GHz. The metal via of this design needs to be completed in air as long as 13.5mm, which increases the difficulty of the experiment.

[0004] In the existing design, there is no absorbing and transmissive integrated tunable metasurface design with a transmissive window covering the entire C-band (4GHz-8GHz), and it is hoped that the experimental processing can be completely completed by the mature PCB (printed circuit board) process. SUMMARY

[0005] To solve the problems in the prior art, the application provides an absorbing and transmissive integrated tunable metasurface with a transmissive window covering the C-band and a design method thereof.

[0006] The technical scheme adopted by the application to solve the technical problems is as follows:

[0007] According to a first aspect of the present application, the present application provides a transmissive window covering C-band absorption and transmission integrated tunable metasurface, comprising a plurality of periodically arranged tunable metasurface units, the tunable metasurface unit is a two-layer structure, composed of a top layer unit and a bottom layer unit, separated by air between the top layer unit and the bottom layer unit;

[0008] The bottom layer unit is composed of a first upper surface, a first intermediate layer and a first bottom surface, wherein the first upper surface is composed of a "cross" metal line to provide a bias circuit; the first intermediate layer is a substrate; and the first bottom surface is a transmissive frequency selective surface; the center of the first upper surface and the first bottom surface is connected by a metal via penetrating the substrate;

[0009] The top layer unit is composed of a second upper surface, a second intermediate layer and a second bottom surface, a transmissive frequency selection structure is arranged at the center of the second upper surface, the transmissive frequency selection structure comprises a square metal sheet at the center, a square metal frame surrounding the square metal sheet and having the same gap width between the square metal sheet and the square metal frame, and four varactor diodes uniformly distributed in the gap for connecting the square metal sheet and the square metal frame; each side of the square metal frame is connected to a metal connecting arm; the transmissive frequency selection structures on the second upper surfaces of adjacent tunable metasurface units are connected by the respective metal connecting arms; a capacitor and a resistor are connected in series on each metal connecting arm; the second intermediate layer is a substrate; the second bottom surface is composed of a "cross" metal line to provide a bias circuit; and the center of the second upper surface and the second bottom surface is connected by a metal via penetrating the substrate.

[0010] According to a second aspect of the present application, the present application provides a design method of the transmissive window covering C-band absorption and transmission integrated tunable metasurface, comprising the following steps:

[0011] Step 1), according to the parameters of the selectable varactor diode, the structural parameters of the first bottom surface of the bottom layer unit are designed to make the transmissive frequency selective surface realize transmission at the target frequency and reflection of electromagnetic waves at other frequencies;

[0012] Step 2), for the transmission line theory of two-layer infinitely thin planes in air, the ABCD matrix is:

[0013]

[0014] Wherein Y1 represents the equivalent admittance of the top layer unit, Y2 represents the equivalent admittance of the bottom layer unit, Y0 represents the admittance of air, Z0 represents the impedance of air, and θ0 represents the change amount of phase when the electromagnetic wave is transmitted in the air between the top layer unit and the bottom layer unit; the S parameter is:

[0015]

[0016] Wherein, S11 represents the reflection coefficient, S21 represents the transmission coefficient, M=Z1Z2, N=Z1+Z2, P=2Z0, Z1 represents the equivalent impedance of the top layer, Z2 represents the equivalent impedance of the bottom layer; since the value of Y2 with the frequency change has been obtained, the ideal value of Y1 can be deduced reversely; it is obtained from the expression of S parameter that the top layer unit and the bottom layer unit need to be open at the same frequency point, so that the electromagnetic wave can pass through the structure to obtain a transmission window; and the frequency point of the transmission window is determined by the varactor diode; therefore, the equivalent circuit of the top layer unit should be a series structure, and the open frequency point of the series structure is determined by the parallel circuit composed of the varactor diode and the inductance equivalent to the metal line; the second upper surface structure is designed.

[0017] Step 3), since the capacitance of the varactor diode needs to be changed by an external bias circuit, that is, all the positive poles of the varactor diodes of the top layer unit and the bottom layer unit are connected in parallel, and all the negative poles are also connected in parallel, so that when the external DC source voltage changes, the capacitance of all the varactor diodes also changes;

[0018] Step 4), the designed adjustable metasurface unit is arranged periodically, the first upper surface of the adjacent adjustable metasurface unit is connected to each other through the metal line, and the first bottom surface is connected to each other through the square metal frame; the second upper surface of the adjacent adjustable metasurface unit is connected to each other through the metal connecting arm, and the second bottom surface is connected to each other through the metal line, so that the transmission window covering the C band is obtained.

[0019] Compared with the prior art, the present application has the beneficial effects including:

[0020] 1) The present application adopts the technical means of double-layer metasurface combined with varactor diode, resistance, capacitance and other lumped elements, realizes wideband impedance matching, and obtains a reflection coefficient of less than -10dB in the C band;

[0021] 2) The transmission frequency points of the transmission frequency selective surface of the bottom layer and the top layer are adjusted to be consistent to obtain the transmission window effect; 3) the adjustable characteristic of the varactor diode with an external DC voltage is utilized to realize the transmission window covering the C band. In summary, the present application proposes an absorption and transmission integrated adjustable metasurface with a transmission window covering the C band and a design method thereof. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 It is a structure schematic view of the present application of the absorption and transmission integrated adjustable metasurface unit with a transmission window covering the C band.

[0023] Figure 2 It is a structure schematic view of the bottom surface unit.

[0024] Figure 3is a schematic diagram of the metal lines on the first upper surface.

[0025] Figure 4 is a schematic diagram of the structure of the first bottom surface.

[0026] Figure 5 is a graph of the simulation results of the S parameters of the bottom layer unit transmissive frequency selective surface.

[0027] Figure 6 is a schematic diagram of the structure of the second upper surface.

[0028] Figure 7 is a schematic diagram of the structure of the second bottom surface.

[0029] Figure 8 is a graph of the simulation results of the S parameters of the tunable metasurface unit changing with the parameters of the varactor diode. DETAILED DESCRIPTION

[0030] The present application will be further described and illustrated in conjunction with the specific embodiments. The embodiments are only exemplary and do not define the scope of the disclosure. The technical features of the various embodiments of the present application can be combined accordingly without conflict.

[0031] Referring to Figure 1 , the present embodiment provides a specific structural schematic diagram of a transmissive window covering C-band absorption-transmissive integrated tunable metasurface unit. A plurality of the illustrated tunable metasurface units are arranged periodically, i.e., to constitute a transmissive window covering C-band absorption-transmissive integrated tunable metasurface.

[0032] As Figure 1 illustrated, the tunable metasurface unit is a two-layer structure, composed of a top layer unit and a bottom layer unit, separated by air between the top layer unit and the bottom layer unit. In the present embodiment, the top layer unit and the bottom layer unit are both square, with a side length p of 24 mm; the distance h between the top layer unit and the bottom layer unit is 12.5 mm.

[0033] Referring to Figures 2-4 , the bottom layer unit is composed of a first upper surface, a first intermediate layer, and a first bottom surface, wherein the first upper surface is composed of a "cross" type metal line to provide a bias circuit; the first intermediate layer is a substrate; the first bottom surface is a transmissive frequency selective surface; the center of the first upper surface and the first bottom surface is connected by a metal via hole penetrating the substrate. The intermediate layer is a f4B substrate with a dielectric constant of 2.65.

[0034] wherein the width of each metal line of the "cross" type metal line is 0.1-1 mm; in Figure 3In the specific schematic diagram shown, the width w3 of the two metal lines is 0.5 mm; the metal lines on the first upper surface of adjacent metasurface units are connected to each other (vertical lines connect metasurface units on the column, and horizontal lines connect metasurface units on the row); the preferred material for the metal lines is copper.

[0035] like Figure 4 As shown, the first bottom surface includes a square metal sheet at the center, a square metal frame surrounding the square metal sheet and having a gap of the same width between them, and four varactor diodes evenly distributed within the gaps to connect the square metal sheet and the square metal frame; the square metal frames on the first bottom surfaces of adjacent adjustable metasurface units are interconnected as a whole. The first bottom surfaces of adjacent adjustable metasurface units are interconnected via square metal frames. Both the square metal sheet and the square metal frame are square and made of copper. The side length w1 of the square metal sheet is 9mm; the variable length w2 of the square window inside the square metal frame is 10mm. The four varactor diodes are located at the center of the four straight gaps. When an external DC voltage is applied, the capacitance of the varactor diodes changes, and the transmission frequency changes accordingly, such as... Figure 5 The simulation results show how the S-parameters of the bottom transmission frequency selection surface change with the capacitance of the varactor diode. It can be concluded that as the capacitance of the varactor diode changes, the frequency of the transmission window also shifts and covers the entire C-band.

[0036] like Figure 6 and 7 As shown, the top-level unit consists of a second upper surface, a second intermediate layer, and a second bottom surface. A transmission frequency selection structure is located at the center of the second upper surface. This structure includes a centrally located square metal sheet, a square metal frame surrounding the square metal sheet with a gap of the same width between them, and four varactor diodes evenly distributed within the gap to connect the square metal sheet and the square metal frame. Each side of the square metal frame is connected to a metal connecting arm. The transmission frequency selection structures on the second upper surfaces of adjacent adjustable metasurface units are connected via their respective metal connecting arms. Each metal connecting arm has a capacitor and a resistor connected in series. The second intermediate layer is a substrate. The second bottom surface consists of cross-shaped metal lines to provide a bias circuit. The centers of the second upper surface and the second bottom surface are connected through metal vias penetrating the substrate. The intermediate layer is an f4B substrate with a dielectric constant of 2.65.

[0037] Among them, the width of each metal line of the "+" shaped metal line of the top unit is 0.1-1mm; the width w3 of the two metal lines is 0.5mm; the metal lines of the first upper surface of adjacent metasurface units are connected to each other (vertical lines connect metasurface units on the column, and horizontal lines connect metasurface units on the row); the preferred material of the metal lines is copper.

[0038] As Figure 8 The simulation results of the S parameters of the overall structure changing with the capacitance of the varactor diode are shown in the figure, and it can be concluded that the frequency of the transmission window moves with the change of the capacitance of the varactor diode, and covers the entire C band, and the reflection coefficient in the C band is lower than -10dB, that is, the transmission window covering the C band is realized. The design of the absorption and transmission integrated adjustable metasurface.

[0039] The design method of the absorption and transmission integrated adjustable metasurface with the transmission window covering the C band includes the following steps:

[0040] Step 1), according to the parameters of the alternative varactor diode, the structural parameters of the first bottom surface of the bottom unit are designed, so that the transmission frequency selective surface realizes transmission at the target frequency and reflection of electromagnetic waves at other frequencies;

[0041] The design principle can be analyzed by equivalent circuit, in which the external square metal frame is equivalent to inductance L, and the varactor diode is equivalent to capacitance C. For the transmission frequency selective surface, the transmission frequency is analyzed by the parallel circuit of inductance L and capacitance C, and the transmission frequency is:

[0042]

[0043] Since the capacitance value of the varactor diode is known, by designing the width of the square metal sheet and the square metal frame, the inductance L can be changed, thereby changing the transmission frequency, and then realizing transmission at the target frequency and reflection of electromagnetic waves at other frequencies;

[0044] Step 2), for the transmission line theory of two-layer infinite thin planes in air, the ABCD matrix is:

[0045]

[0046] Where Y1 represents the equivalent admittance of the top layer unit, Y2 represents the equivalent admittance of the bottom layer unit, Y0 represents the admittance of air, Z0 represents the impedance of air, and θ0 represents the change of phase when the electromagnetic wave is transmitted in the air between the top layer unit and the bottom layer unit. ; Its S parameter is:

[0047]

[0048] Wherein, M=Z1Z2, N=Z1+Z2, P=2Z0, Z1 represents the equivalent impedance of the top layer, Z2 represents the equivalent impedance of the bottom layer; since the value of Y2 with frequency change has been obtained, the ideal value of Y1 can be deduced; from the expression of S parameter: the top layer unit and the bottom layer unit need to be open at the same frequency point, so that the electromagnetic wave can pass through the structure to obtain a transmission window; and the frequency point of the transmission window is determined by the varactor diode; therefore, the equivalent circuit of the top layer unit should be a series structure, and the open frequency point is determined by the parallel circuit composed of the varactor diode and the inductance equivalent to the metal line; thus the structure of the second upper surface is designed. The second upper surface selects the combination of metal short line and "back" type structure, and matches the lumped element (capacitor, resistor, varactor diode), which realizes the adjustable transmission window in C band under the premise of ensuring that the reflection coefficient is less than -10dB in a wide frequency band as much as possible.

[0049] Step (3), since changing the capacitance of the varactor diode needs an external bias circuit, that is, all the anodes of the varactor diodes in the top layer and the bottom layer are connected in parallel, and all the cathodes are also connected in parallel, so that when the external DC source voltage changes, the capacitance of all the varactor diodes also changes. Specifically, the square metal inside the "back" type structure of each super surface unit is connected to the "cross" type metal line on the other side of the substrate (material f4B) through a metal via, so that the anodes of the varactor diodes connected to the metal inside the "back" type structure are all connected together through the "cross" type metal line, and the cathodes of the varactor diodes connected to the metal outside the "back" type structure are originally connected together. Therefore, by connecting the "cross" type metal line and the metal outside the "back" type structure to the two poles of the power supply respectively, the synchronous control of all the varactor diodes can be realized.

[0050] Step 4), the designed adjustable super surface unit is arranged periodically, the first upper surface of adjacent adjustable super surface units is connected to each other through metal lines, and the first bottom surface is connected to each other through square metal frames; the second upper surface of adjacent adjustable super surface units is connected to each other through metal connecting arms, and the second bottom surface is connected to each other through metal lines, so that the absorption and transmission integrated adjustable super surface covering the C band transmission window is obtained.

[0051] Further, the circuit needs to be isolated from DC and AC, the purpose is to isolate the DC to avoid the influence of the alternating current generated by the incident electromagnetic wave on the direct current generated by the external DC source. The specific implementation method is to place an inductor with a self-resonant frequency lower than the working frequency of the super surface in the circuit (here, an inductor with a self-resonant frequency of 1.5GHz is used).

[0052] For the applied circuit of applying direct current voltage, we only need to adopt the simplest power supply which can provide voltage range of 0-20V adjustable. The positive pole of the power supply is connected to the "cross" metal wire of the top layer and the bottom layer respectively, and the negative pole of the power supply is connected to the metal connecting arm of the top layer and the metal frame of the bottom layer respectively, so as to realize the synchronous control of all varactor diodes. In addition, in order to make the direct current signal generated by the direct current source not interact with the alternating current signal generated in the structure by the interaction of the super surface and the electromagnetic wave, a series inductance with self-resonant frequency lower than the working frequency of the super surface (here, it is 4GHz) needs to be introduced at the connection between the power supply and the super surface, so as to realize the effect of isolating alternating current and passing direct current.

[0053] The above-mentioned embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it cannot be understood as the limitation of the patent scope of the present application. For ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present application, which belongs to the protection scope of the present application.

Claims

1. A transmissive integrated tunable metasurface with a transmission window covering the C-band, comprising a plurality of periodically arranged tunable metasurface units, characterized in that, The adjustable metasurface unit has a two-layer structure, consisting of a top layer unit and a bottom layer unit, with air separating the top layer unit and the bottom layer unit; The bottom unit consists of a first upper surface, a first intermediate layer, and a first bottom surface. The first upper surface is composed of cross-shaped metal lines to provide a bias circuit. The first intermediate layer is a substrate. The first bottom surface is a transmission frequency selection surface. The centers of the first upper surface and the first bottom surface are connected by a metal via penetrating the substrate. The top-level unit consists of a second upper surface, a second intermediate layer, and a second bottom surface. A transmission frequency selection structure is located at the center of the second upper surface. This structure includes a square metal sheet at the center, a square metal frame surrounding the square metal sheet with a gap of the same width between them, and four varactor diodes evenly distributed within the gap to connect the square metal sheet and the square metal frame. Each side of the square metal frame is connected to a metal connecting arm. The transmission frequency selection structures on the second upper surfaces of adjacent adjustable metasurface units are connected via their respective metal connecting arms. Each metal connecting arm has a capacitor and a resistor connected in series. The second intermediate layer is a substrate. The second bottom surface consists of cross-shaped metal lines to provide a bias circuit, and each cross-shaped metal line on the second bottom surface has an inductor connected in series. The centers of the second upper surface and the second bottom surface are connected through metal vias penetrating the substrate. The first bottom surface includes a square metal sheet at the center, a square metal frame surrounding the square metal sheet and having a gap of the same width between them, and four varactor diodes evenly distributed in the gap for connecting the square metal sheet and the square metal frame; the square metal frames on the first bottom surface of adjacent adjustable metasurface units are connected to each other as a whole.

2. The tunable metasurface with a transmission window covering the C-band as described in claim 1, characterized in that, The width of each of the cross-shaped metal wires that make up the bottom and top units is 0.1-1mm.

3. The tunable metasurface with a transmission window covering the C-band as described in claim 1, characterized in that... Both the first and second intermediate layers are f4B substrates with a dielectric constant of 2.65.

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