Liquid crystal-based reflective metasurface

Abstract

This liquid crystal-based reflective metasurface comprises: a first layer comprising a first substrate, a first metal layer formed on a first surface of the first substrate, and a second metal layer formed on a second surface of the first substrate; a second layer comprising a second substrate, bias lines formed on a first surface of the second substrate, and a third metal layer formed on a second surface of the second substrate; a third layer comprising a liquid crystal and a third substrate providing a space, in the central portion of a unit cell, in which the liquid crystal can be filled; and a fourth layer comprising a fourth substrate and a fourth metal layer formed on a first surface of the fourth substrate.

Description

Liquid crystal-based reflective metasurfaces

[0001] The present disclosure relates to a liquid crystal-based reflective metasurface, and more particularly, to a liquid crystal-based reflective metasurface implemented in a multilayer substrate package.

[0002] With the rapid development of 5th and 6th generation mobile communications, communication module design technology to support ultra-high-speed, high-capacity communications is rapidly evolving. In 6G communications, coverage expansion methods are being researched to expand the communication area due to the short radio wave range.

[0003] Reconfigurable Intelligent Surfaces (RIS) can expand communication coverage at a lower cost than repeater installations. Consequently, RIS is being actively developed by domestic and international telecommunications companies. However, the limited availability of phase-variable elements for use in high-frequency bands presents challenges in development and deployment.

[0004] Meanwhile, phased array antennas can adjust beam steering direction by electronically controlling the phase of radio waves on a per-element basis. This element-by-element phase control is typically implemented in phase shifters at the radio frequency (RF) level. These phase shifters increase the weight, size, and cost of the phased array antenna.

[0005] Liquid crystals (LCDs) have the property of variable dielectric properties that vary depending on the applied voltage. Therefore, research is currently underway on using liquid crystals as phase-variable elements for 6G beamforming.

[0006] Meanwhile, RIS modules utilizing phase-variable elements utilizing liquid crystals can be implemented using reflective metasurfaces. However, reflective metasurfaces, which operate as reflectors within a specific frequency band, suffer from the drawback of narrow-band reflection characteristics.

[0007] The present invention aims to improve the reflection performance over a wide frequency band in a liquid crystal-based reflective metasurface.

[0008] The present invention aims to improve phase tunability performance over a wide frequency band in liquid crystal-based reflective metasurfaces.

[0009] The purpose of this specification is to provide a multilayer substrate package having a liquid crystal-based reflective metasurface that can be manufactured in a display process using liquid crystals.

[0010] The present invention aims to improve the state transition speed for phase tunability in liquid crystal-based reflective metasurfaces.

[0011] A liquid crystal-based reflective metasurface according to the present invention comprises a first layer including a first substrate, a first metal layer formed on a first surface of the first substrate, and a second metal layer formed on a second surface of the first substrate; a second layer including a second substrate, bias lines formed on the first surface of the second substrate, and a third metal layer formed on the second surface of the second substrate; a third layer including a third substrate that provides a space in which the liquid crystal can be filled in a central portion of a unit cell; and a fourth layer including a fourth substrate and a fourth metal layer formed on the first surface of the fourth substrate.

[0012] According to an embodiment, in a structure in which the third metal layer covers the upper portion of the liquid crystal and the fourth metal layer covers the lower portion of the liquid crystal, the first substrate to the fourth substrate may be configured to have an input impedance of 2650 ohm or more.

[0013] According to an embodiment, the first metal layer may include a plurality of first patch elements spaced apart by a first interval in the first and second axis directions and having first unit cells of a first size. A radio signal incident on the first metal layer may be reflected with different phases by a permittivity that varies depending on a DC voltage applied to the first metal layer and the liquid crystal.

[0014] According to an embodiment, the second metal layer may be composed of a second unit cell including a plurality of second patch elements having second unit cells of a second size spaced apart from each other by a second interval in the first and second axis directions. Each of the second unit cells of the second size may include a plurality of square grid patterns. The plurality of square grid patterns may be arranged to correspond to an area in which any one of the plurality of first patch elements is arranged.

[0015] According to an embodiment, the third metal layer may include a plurality of third patch elements spaced apart by a third interval in the first and second axis directions and having a third unit cell of a third size. The third size may be formed to be the same as the first size. The third interval may be formed to be the same as the first interval. The plurality of third patch elements may be stacked with the plurality of first patch elements in the third axis direction and arranged to overlap on the first and second axes.

[0016] According to an embodiment of the present disclosure, a liquid crystal-based reflective metasurface implemented in a multilayer substrate package can improve reflection performance over a wide frequency band.

[0017] According to an embodiment of the present disclosure, a phase-tunable performance of 135 degrees or more can be obtained by changing the permittivity of the liquid crystal in a wideband frequency range in a liquid crystal-based reflective metasurface implemented as a multilayer substrate package.

[0018] According to an embodiment of the present disclosure, a structure of a double patch or more without a via structure is formed to form multiple resonant modes and can operate as a reflector throughout the entire operating frequency band.

[0019] According to an embodiment of the present disclosure, it is possible to manufacture a display process using a liquid crystal through a unit cell having a plurality of metal layers that do not include a via structure.

[0020] According to an embodiment of the present disclosure, a reflective metasurface capable of wideband operation can be provided while improving the switching speed by making the thickness of the liquid crystal thin.

[0021] According to an embodiment of the present disclosure, a triple-patch structured reflective metasurface can be provided that improves reflection coefficient performance and phase-variable characteristics in a wide band while improving switching speed by making the thickness of the liquid crystal thinner.

[0022] Further scope of the applicability of this specification will become apparent from the detailed description below. However, since various changes and modifications within the spirit and scope of this specification will be apparent to those skilled in the art, it should be understood that the detailed description and specific examples, such as preferred embodiments, are given by way of example only.

[0023] FIG. 1 illustrates the structure of an array antenna module including a plurality of elements according to the present specification.

[0024] Figure 2 shows a structure implemented with a reflective RIS and a transparent RIS according to the present specification.

[0025] Figure 3 shows structures in which the dielectric constant changes depending on the bias voltage applied to the liquid crystal layer.

[0026] Figures 4a and 4b illustrate cross-sectional and perspective views of a liquid crystal-based reflective metasurface comprising multiple layers comprising liquid crystals.

[0027] Figure 5a shows the reflection coefficient characteristics as the dielectric constant changes when the liquid crystal thicknesses are 150 μm and 250 μm. Figure 5b shows the phase characteristics of the reflection signal as the dielectric constant changes when the liquid crystal thicknesses are 150 μm and 250 μm.

[0028] Figure 6 shows the reflection coefficient characteristics according to changes in the thickness of the first substrate.

[0029] FIGS. 7a and 7b illustrate cross-sectional and perspective views of a liquid crystal-based reflective metasurface having improved phase-tunable velocity and reflection coefficient performance according to the present disclosure.

[0030] Figure 8a shows the reflection coefficient characteristics according to the change in permittivity in the liquid crystal-based reflective metasurface of Figures 7a and 7b.

[0031] Figure 8b shows the phase characteristics of the reflection signal according to the change in permittivity in the liquid crystal-based reflective metasurface of Figures 7a and 7b.

[0032] Figures 9a and 9b show a perspective view and an equivalent circuit model of the liquid crystal-based reflective metasurface of Figures 7a and 7b.

[0033] Figure 10 shows a front view of the first to fourth layers and an enlarged view of the second layer formed with a square grid structure.

[0034] Figure 11a shows an exploded perspective view of a reflective metasurface of a second structure in which the second metal layer is formed as a single patch element.

[0035] Figure 11b shows an exploded perspective view of a reflective metasurface of a third structure without a second metal layer.

[0036] Figure 12 shows the reflection coefficient characteristics when the permittivity of the liquid crystal is changed on the reflective metasurface of the second structure of Figure 11a.

[0037] Figure 13a shows the input impedance when the permittivity changes in the reflective metasurfaces of Figures 9 and 11a.

[0038] Figure 13b shows the input impedance when the permittivity changes in the reflective metasurfaces of Figures 9 and 11b.

[0039] Figures 14a and 14b show a front view and an exploded perspective view of a reflective metasurface having a 4x4 array structure.

[0040] Figure 15 shows a front view and a partially enlarged view of each layer of a reflective metasurface having a 4x4 array structure.

[0041] Hereinafter, specific embodiments of the present invention will be described in detail with drawings.

[0042] Hereinafter, embodiments related to this specification will be described in more detail with reference to the drawings. The suffixes "module" and "part" used in the following description for components are assigned or used interchangeably solely for the convenience of writing the specification, and do not have a distinct meaning or role in themselves.

[0043] Hereinafter, an array antenna module having phase-variable characteristics in relation to the present specification will be described.

[0044] In this regard, a module including a plurality of elements according to the present specification may be referred to as a phase delay array antenna module. The antenna module may be configured to include a plurality of radiators and a phase delay element capable of implementing phase delay. The phase delay element may be implemented as a feed structure of a specific structure without separate electronic components such as a phase shifter.

[0045] The array antenna module can be configured to support 6G wireless communication services. In this regard, the array antenna module can be configured to operate in the millimeter wave band or the 10 GHz band. The array antenna module can be applied to mobile communication antennas, vehicle antennas, or satellite communication antennas.

[0046] 6G wireless communication services aren't limited to electronic devices like mobile terminals or video display devices. They can also be applied to fully autonomous vehicles, artificial intelligence (AI) robots, and electronic devices supporting the augmented and virtual reality (AR / VR)-based metaverse.

[0047] FIG. 1 illustrates the structure of an array antenna module, which is a module including a plurality of elements according to the present specification. Referring to FIG. 1, the array antenna module (1000) may be configured as an array antenna including a plurality of elements (1100-1 to 1100-8). The number of the plurality of elements is not limited to eight and may vary depending on the application.

[0048] The antenna module (1000) may be configured as a one-dimensional array antenna in which a plurality of elements are arranged in one axial direction. As another example, the antenna module (1000) may be configured as a two-dimensional array antenna in which a plurality of elements are arranged in one axial direction and another axial direction perpendicular thereto.

[0049] The spacing (G1) between the plurality of elements (1100-1 to 1100-8) can be implemented as a numerical value related to a wavelength corresponding to an operating frequency. Each of the plurality of elements (1100-1 to 1100-8) can be operably coupled to a phase delay element (1150-1 to 1150-8). The phase delay elements (1150-1 to 1150-8) can be formed as a feed structure having a phase delay. The phase delay elements (1150-1 to 1150-8) can be formed as a feed structure connecting adjacent antenna elements.

[0050] A transmission line (1200) connected to a plurality of elements (1100-1 to 1100-8) may be implemented as a waveguide, a microstrip line, a strip line, or a substrate integrated waveguide (SIW). Each of the plurality of elements (1100-1 to 1100-8) may be independently controlled to be turned on / off. Each of the plurality of elements (1100-1 to 1100-8) may be independently controlled to be turned on / off to adjust the beam forming direction of the antenna module (1000).

[0051] As the plurality of elements (1100-1 to 1100-8) are independently turned on / off, the phase of the signal applied to the plurality of elements (1100-1 to 1100-8) can be varied as illustrated in the transmission line (1200) of FIG. 1. As the interval between the on / off operations among the plurality of elements (1100-1 to 1100-8) decreases, the phase difference between adjacent elements increases. Accordingly, as the interval between the on / off operations among the plurality of elements (1100-1 to 1100-8) decreases, the beamforming angle increases.

[0052] Meanwhile, an antenna module comprising a plurality of antenna elements according to the present specification may be capable of phase adjustment when combined with a reconfigurable intelligent surface (RIS). In this regard, FIG. 2 illustrates a structure implemented with a reflective RIS and a transmissive RIS according to the present specification.

[0053] Referring to FIG. 2(a), the antenna module (1000) may be configured to include a reflective RIS (1000a) and at least one external antenna (1300). A wireless signal radiated from the external antenna (1300) may be configured to be reflected by the reflective RIS (1000a). The beamforming angle of the wireless signal may be varied by independently varying the on / off state of each element constituting the reflective RIS (1000a).

[0054] Referring to FIG. 2(b), the antenna module (1000) may be configured to include a transitive RIS (1000a) and at least one external antenna (1300). A wireless signal radiated from the external antenna (1300) may be configured to pass through the transitive RIS (1000b). The beamforming angle of the wireless signal may be varied by independently varying the on / off state of each element constituting the transitive RIS (1000b).

[0055] Hereinafter, a liquid-based reflection meta surface implemented as a multilayer substrate package according to the present specification is described.

[0056] In this regard, Fig. 3 shows structures in which the dielectric constant changes depending on the bias voltage applied to the liquid crystal layer.

[0057] In Fig. 3(a), when the voltage (Vb) applied to the liquid crystal layer is 0 V, the alignment direction of the molecules within the liquid crystal layer is horizontal. When the voltage (Vb) is 0 V, the permittivity of the liquid crystal layer is the first permittivity (e.g., 2.5), which is a low permittivity. In Figs. 3(b) to 3(e), when the voltage (Vb) is applied to the liquid crystal layer, the electric field direction within the liquid crystal layer is formed in the vertical direction.

[0058] In Fig. 3(b), if the voltage (Vb) > Vth, molecules in the liquid crystal layer are formed at a first tilt angle, and the permittivity of the liquid crystal layer increases. In Fig. 3(c), if the voltage (Vb) > V2, molecules in the liquid crystal layer are formed at a second tilt angle greater than the first tilt angle, and the permittivity of the liquid crystal layer is a second permittivity (e.g., 3.0), which is an intermediate permittivity. In Fig. 3(d), if the voltage (Vb) > V3, molecules in the liquid crystal layer are formed at a third tilt angle greater than the second tilt angle, and the permittivity of the liquid crystal layer increases. In Fig. 3(e), if the voltage (Vb) > Vsat, molecules in the liquid crystal layer are arranged vertically. The permittivity of the liquid crystal layer is a third permittivity (e.g., 3.5), which is a high permittivity.

[0059] Meanwhile, as the voltage (Vb) applied to the liquid crystal layer increases from 0 to the maximum bias voltage (Vsat), the first reaction time (t) at which molecules within the liquid crystal layer are vertically aligned r ) is proportional to the thickness (d) of the liquid crystal layer as in mathematical equation 1. In addition, the second reaction time (t) at which molecules in the liquid crystal layer are horizontally aligned as the voltage (Vb) applied to the liquid crystal layer decreases from the maximum bias voltage (Vsat) to 0 d ) is the first reaction time (t r ) is proportional to the second reaction time (t d ) is also proportional to the thickness (d) of the liquid crystal layer.

[0060]

[0061] Therefore, to implement rapid phase switching characteristics, it is necessary to shorten the response time for dielectric constant changes within the liquid crystal layer. Accordingly, to implement rapid phase switching characteristics, it is necessary to reduce the thickness (d) of the liquid crystal layer.

[0062] Meanwhile, the liquid crystal-based reflective metasurface according to the present specification may be configured to include a plurality of layers. In this regard, FIGS. 4A and 4B illustrate cross-sectional and perspective views of a liquid crystal-based reflective metasurface including a plurality of layers including liquid crystals. The liquid crystal-based reflective metasurface may include a first layer (La1), a second layer (La2), and a third layer (La3). The first layer (La1) may include a first substrate (1010), a first metal layer (1110) formed on a first surface of the first substrate (1010), and a second metal layer (1120) formed on a second surface of the first substrate (1010). In this regard, the second metal layer (1120) may also be formed on the first surface of the second substrate (1020).

[0063] The second layer (La2) may include a second substrate (1020) that provides a space in which the liquid crystal (1020a) can be filled in the central portion of the unit cell and a liquid crystal (1020a). The thickness (d) of the liquid crystal (1020a) may be implemented in a range of 150 μm to 250 μm. The dielectric constant of the liquid crystal (1020a) may vary depending on the bias voltage applied to the second metal layer (1120). For example, as the bias voltage applied to the second metal layer (1120) varies from 0 V to 10 V to 20 V, the dielectric constant of the liquid crystal (1020a) may change to 2.5, 3.0, and 3.5. A ground layer (Lg) may be disposed on the second surface of the second layer (La2).

[0064] The third layer (La3) may include a third substrate (1030) and a third metal layer (1130) formed on a first surface of the third substrate (1030). In this regard, the third metal layer (1130) may also be formed on a second surface of the second substrate (1020).

[0065] Meanwhile, Fig. 5a shows the reflection coefficient characteristics as the dielectric constant changes when the liquid crystal thickness is 150 μm and 250 μm. Fig. 5b shows the phase characteristics of the reflection signal as the dielectric constant changes when the liquid crystal thickness is 150 μm and 250 μm.

[0066] Referring to FIGS. 4A to 5A, as the thickness (d) of the liquid crystal (1020a) decreases from 250 μm to 150 μm, the reflection coefficient may increase from within -5 dB to -8.8 dB when the dielectric constant is varied. In particular, when the thickness (d) of the liquid crystal (1020a) decreases to 150 μm as the dielectric constant (Dk) increases from 2.5, 3.0, and 3.5, the reflection performance may deteriorate.

[0067] Referring to FIGS. 4a, 4b, and 5b, even when the thickness (d) of the liquid crystal (1020a) is reduced from 250 μm to 150 μm, the change in the phase characteristics of the reflection signal when the dielectric constant is varied is not significant. In this regard, even when the thickness (d) of the liquid crystal (1020a) is reduced to 150 μm, the phase difference between the reflection signals when the dielectric constant is varied is maintained within a predetermined range based on a certain level, for example, 135 degrees. Therefore, it is necessary to design a liquid crystal-based reflective metasurface so that the reflection coefficient is -5 dB or less while reducing the thickness (d) of the liquid crystal (1020a) to increase the phase variation speed.

[0068] In this regard, it is examined whether the reflection coefficient performance is improved by increasing the thickness (t1) of the first substrate (1010) between the first and second metal layers (1110, 1120). Fig. 6 shows the reflection coefficient characteristics according to the change in the thickness of the first substrate.

[0069] Referring to FIGS. 4a, 4b, and 6, the reflection coefficient performance is shown by increasing the thickness (t1) of the first substrate (1010), which is the upper substrate of the liquid crystal-based reflective metasurface. In this regard, the dielectric constant of the liquid crystal (1020a) was set to 3.

[0070] When the thickness (t1) of the first substrate (1010) increases from 800 um to 1000 um, the reflection coefficient performance is somewhat improved. However, when the thickness (t1) of the first substrate (1010) increases from 1200 um to 1400 um, the reflection coefficient performance is rather deteriorated. Therefore, in order to improve the reflection coefficient performance while reducing the thickness (d) of the liquid crystal (1020a) to 150 um, a design with a different structure is required rather than increasing the thickness (t1) of the first substrate (1010).

[0071] A structure for improving both the phase-tunable velocity and reflection coefficient performance of a liquid crystal-based reflective metasurface according to the present disclosure is described. In this regard, FIGS. 7A and 7B illustrate cross-sectional and perspective views of a liquid crystal-based reflective metasurface according to the present disclosure with improved phase-tunable velocity and reflection coefficient performance.

[0072] The purpose of the present disclosure is to provide a liquid crystal-based reflective metasurface that improves the reflective performance over a wide frequency band in a liquid crystal-based reflective metasurface. The purpose of the present disclosure is to provide a liquid crystal-based reflective metasurface that improves the phase tunability over a wide frequency band in a liquid crystal-based reflective metasurface. The purpose of the present disclosure is to provide a multilayer substrate package having a liquid crystal-based reflective metasurface that can be manufactured in a display process using liquid crystals. The purpose of the present disclosure is to improve the state transition speed for phase tunability in a liquid crystal-based reflective metasurface.

[0073] A liquid crystal-based reflective metasurface according to the present disclosure will be described with reference to FIGS. 7A and 7B . Referring to FIGS. 7A and 7B , the liquid crystal-based reflective metasurface (1000) can be configured to include a first layer (La1), a second layer (La2), a third layer (La3), and a fourth layer (La4).

[0074] The first layer (La1) may include a first substrate (1010), a first metal layer (1110) formed on a first surface of the first substrate (1010), and a second metal layer (1120) formed on a second surface of the first substrate (1010). In this regard, the second metal layer (1120) may also be formed on the first surface of the second substrate (1020).

[0075] The second layer (La2) may include a second substrate (1020) and a third metal layer (1130) formed on a second surface of the second substrate (1020). The third metal layer (1130) may also be formed on a first surface of the third substrate (1030).

[0076] The third layer (La3) may include a third substrate (1030) that provides a space in which the liquid crystal (1030a) can be filled in the central portion of the unit cell. The fourth layer (La4) may include a fourth substrate (1040) and a fourth metal layer (1140) formed on a first surface of the fourth substrate (1040). A ground layer (Lg) may also be formed on the first surface of the fourth substrate (1040).

[0077] In a structure in which a third metal layer (1130) covers the upper portion of the liquid crystal (1030a) and a fourth metal layer (1140) covers the lower portion of the liquid crystal (1030a), the reflective metasurfaces of the first substrate (1010) to the fourth substrate (1040) have an input impedance greater than or equal to a critical value. For example, the reflective metasurfaces of the first substrate (1010) to the fourth substrate (1040) may be configured to have an input impedance greater than or equal to 2650 ohm.

[0078] Meanwhile, the reflection coefficient and phase characteristics of the reflection signal according to the change in permittivity in the liquid crystal-based reflective metasurface of FIGS. 7a and 7b are described. FIG. 8a shows the reflection coefficient characteristics according to the change in permittivity in the liquid crystal-based reflective metasurface of FIGS. 7a and 7b. FIG. 8b shows the phase characteristics of the reflection signal according to the change in permittivity in the liquid crystal-based reflective metasurface of FIGS. 7a and 7b.

[0079] Referring to FIGS. 7A to 8A, when the dielectric constant of the liquid crystal (1030a) is changed to 2.5, 3.0, and 3.5, the reflection coefficient has a value of -5 dB or less within a bandwidth (BW) of 1.7 GHz. Therefore, the reflection coefficient characteristics can be improved even when the thickness (d) of the liquid crystal (1030a) is formed as thin as 150 μm.

[0080] Meanwhile, the operating frequency bandwidth of the RIS module implemented with a reflective metasurface can be defined as the frequency range that simultaneously satisfies the performances of a reflection coefficient of -5 dB or less and a phase shift of 135 degrees or more. The average reflection coefficient within the operating frequency band is within -2.5 dB, and it has a high reflection performance that can reflect more than 55% of the electromagnetic signal applied to the RIS surface.

[0081] Therefore, the liquid crystal-based reflective metasurface according to the present specification has high reflection performance that can reflect more than 55% of the electromagnetic wave signal applied to the RIS surface at a level of less than 2.5 dB. In addition, the square lattice patterns formed by the second metal layer (1120) can improve the input impedance of the RIS surface by more than twice compared to the input impedance of a single patch structure. Accordingly, the liquid crystal-based reflective metasurface according to the present specification can be designed as a triple patch structure including the second metal layer (1120) implemented with square lattice patterns. Since the triple patch structure including the second metal layer (1120) implemented with square lattice patterns has high impedance characteristics, a high reflection RIS design is possible even when using a thin liquid crystal.

[0082] Referring to FIGS. 7a, 7b, and 8b, the phase tunable characteristic has a phase difference of 135 degrees or more within a bandwidth (BW) of 1.7 GHz in the first to third states according to changes in the dielectric constant of the liquid crystal (1030a) to 2.5, 3.0, and 3.5. Accordingly, the liquid crystal-based reflective metasurface (1000) including the first to fourth metal layers (1110 to 1140) satisfies a reflection coefficient of -5 dB or less and a phase tunable characteristic of 135 degrees or more within a bandwidth (BW) of 1.7 GHz.

[0083] Meanwhile, the liquid crystal-based reflective metasurface according to the present specification can be formed with a coupling structure of the first and second metal layers. In this regard, FIGS. 9A and 9B show a perspective view and an equivalent circuit model of the liquid crystal-based reflective metasurface of FIGS. 7A and 7B. FIG. 9A shows a perspective view of the liquid crystal-based reflective metasurface of FIGS. 7A and 7B. FIG. 9B shows an equivalent circuit model of the liquid crystal-based reflective metasurface of FIGS. 7A and 7B. Meanwhile, FIG. 10 shows a front view of the first to fourth layers and an enlarged view of the second layer formed with a square lattice structure.

[0084] Referring to FIGS. 7a, 7b, 9a, and 10, the first metal layer (1110) may be formed with first patch elements having a first size (L1p) in the first and second axis directions. The second metal layer (1120) may be formed with a plurality of second patch elements having a second size (L2p) in the first and second axis directions. In this regard, the first and second axis directions may correspond to the X and Y axes on the XY plane. The second size (L2p) of the second metal layer (1120) may be formed to be larger than the first size (L1p) of the first metal layer (1110). The plurality of second patch elements of the second metal layer (1120) may be arranged to correspond to the region where the first patch elements of the first metal layer (1110) are arranged.

[0085] The third metal layer (1130) may be formed as a third patch element having a third size (L3p). The second size (L3p) of the third metal layer (1130) may be formed to be the same size as the first size (L3p) of the first metal layer (1110), but is not limited thereto and may be changed depending on the application. As described above, a DC voltage may be applied to the third metal layer (1130) to vary the permittivity of the liquid crystal (1030a). The wireless signal incident on the first metal layer (1120) may be reflected with different phases due to the permittivity that varies depending on the DC voltage applied to the first metal layer (1120) and the liquid crystal (1030a).

[0086] The fourth metal layer (1140) may be formed as a fourth patch element having a fourth size (L4p) in the first and second axis directions. The fourth size (L4p) of the fourth metal layer (1130) may be formed to be larger than the first size (L1p) of the first metal layer (1110). The fourth size (L4p) of the fourth metal layer (1130) may be formed to be larger than the second size (L2p) of the second metal layer (1120).

[0087] The fourth metal layer (1140) may be electrically connected to the ground layer (Lg). In this regard, the fourth layer (La4) may include the fourth metal layer (1140) formed on the first surface of the fourth substrate (1040) and the ground layer (Lg) formed on the second surface of the fourth substrate (1030).

[0088] Meanwhile, in the liquid crystal-based reflective metasurface according to the present specification, the first to third metal layers may be formed in a floating structure without being interconnected and separated from the other metal layers. In this regard, the first patch element of the first metal layer (1110) disposed on the first surface of the first substrate (1010) may be configured not to be connected to the ground layer (Lg) and not to be connected to the second patch elements of the second metal layer (1120).

[0089] The third patch element disposed on the first surface of the third substrate (1030) may be configured so as not to be connected to the ground layer (Lg), not to be connected to the first patch element of the first metal layer (1110), and not to be connected to the second patch elements of the second metal layer (1120).

[0090] Meanwhile, in the liquid crystal-based reflective metasurface according to the present specification, the thicknesses of the first substrate (1010), the second substrate (1020), the third substrate (1030), and the fourth substrate (1040) can be designed to optimize the reflective performance. In this regard, the second thickness (t2) of the second substrate (1020) can be formed thicker than the thickness (t1) of the first substrate (1010). The third thickness (t3) of the third substrate (1030) can be formed thinner than the thickness (t1) of the first substrate (1010). Therefore, the thickness (d) of the liquid crystal (1030a) can be reduced to improve the phase switching speed. The fourth thickness (t4) of the fourth substrate (1040) can be formed thicker than the thickness (t1) of the first substrate (1010) and thinner than the second thickness (t2) of the second substrate (1020).

[0091] For example, the thickness (t1) of the first substrate (1010) may be formed within a predetermined range based on 200 um. The second thickness (t2) of the second substrate (1020) may be formed within a predetermined range based on 600 um. The third thickness (t3) of the third substrate (1030) may be formed within a predetermined range based on 150 um. The fourth thickness (t4) of the fourth substrate (1040) may be formed within a predetermined range based on 400 um.

[0092] Referring to FIGS. 9a and 9b, the unit cell of the RIS module can be equivalently expressed as an input impedance (Zin) based on the incident surface to which the radio wave is applied, with the metal patterns of the metal layers constituting the RIS module and the dielectric substrate as the reference. In this regard, the RIS module includes the first metal layer (1110) to the fourth metal layer (1140), and the metal patterns of each metal layer can be equivalentized to a parallel configuration of an equivalent circuit having a resistance component and a capacitance component. Using 377 ohms, which is the characteristic impedance (Z0) of air, as the reference for the input impedance (Zin) of the RIS module, the reflection coefficient can be derived as in Equation 2. Re{Zin} represents the real part of the input impedance (Zin).

[0093]

[0094] Meanwhile, in this specification, the reflection coefficient performance of the RIS module is improved by optimizing the impedance component formed by the square-structured lattice patterns of the second patch elements constituting the second metal layer.

[0095] In this regard, the first patch element of the first metal layer (1110) of the first layer (La1) of the liquid crystal-based reflective metasurface (1000) can be equivalent to a first resistor (R1) and a first capacitor (C1). The second patch elements of the second metal layer (1120) of the second layer (La2) of the liquid crystal-based reflective metasurface (1000) can be equivalent to a second resistor (R2) and a second capacitor (C2). The third patch element of the third layer (La3) of the liquid crystal-based reflective metasurface (1000) can be equivalent to a third resistor (R3) and a third capacitor (C3). The second resistor (R2) and the second capacitor (C2) can be optimized by controlling the respective sizes and spacings of the second patch elements of the second metal layer (1120) formed by a square lattice structure. Therefore, the size and spacing of each of the second patch elements of the second metal layer (1120) can be adjusted to improve the reflection coefficient of the RIS module.

[0096] The first substrate (1010) between the first metal layer (1110) and the second metal layer (1120) can be equivalentized to a first inductor (L1). One end of the first inductor (L1) can be equivalentized to be connected to the first capacitor (C1) and the other end can be equivalentized to be connected to the second capacitor (C2). The second substrate (1020) between the second metal layer (1120) and the third metal layer (1130) can be equivalentized to a second inductor (L2). One end of the second inductor (L2) can be equivalentized to be connected to the second capacitor (C2) and the other end can be equivalentized to be connected to the third capacitor (C3). The liquid crystal (1030a) of the third substrate (1030) can be equivalentized to a fourth resistor (R4) and a third inductor (L3). The fourth metal layer (1140) of the fourth layer (La4) can act as a ground (GND).

[0097] Meanwhile, in the liquid crystal-based reflective metasurface according to the present specification, the electrical characteristics may change depending on the arrangement and structure of the second metal layer under the first metal layer. In this regard, Fig. 11a shows an exploded perspective view of a reflective metasurface of a second structure in which the second metal layer is formed as a single patch element. Fig. 11b shows an exploded perspective view of a reflective metasurface of a third structure in which the second metal layer is not arranged.

[0098] Referring to FIG. 11a, a reflective metasurface (1000b) of a second structure may include a first metal layer (1110), a second metal layer (1120), a third metal layer (1130), and a fourth metal layer (1140). The first metal layer (1120) may be a first patch element having a first size in the first and second axis directions. The second metal layer (1120) may be a second patch element having a second size in the first and second axis directions.

[0099] Referring to FIG. 11b, a reflective metasurface (1000c) of a third structure may include a first metal layer (1110), a third metal layer (1130), and a fourth metal layer (1140). The first metal layer (1120) may be a first patch element having a first size in the first and second axis directions. No patch elements made of a metal material are disposed on the second surface of the first substrate (1010) and the first surface of the second substrate (1020).

[0100] Figure 12 shows the reflection coefficient characteristics when the permittivity of the liquid crystal is changed in the reflective metasurface of the second structure of Figure 11a. Referring to Figures 11a and 12, the permittivity (Dk) of the liquid crystal (1030a) in the reflective metasurface (1000a) of the second structure can be changed to 2.5, 3.0, and 3.5.

[0101] Referring to FIGS. 7A and 8A, when the structure of the second metal layer (1120) is designed with a square grid pattern, the reflection coefficient has a subcritical value of -2.5 dB or less. Referring to FIGS. 11A and 12, when a single patch element is applied to the second metal layer (1120), the reflection coefficient performance deteriorates as the permittivity (Dk) increases to 2.5, 3.0, and 3.5. For example, when the permittivity (Dk) is 3.5, the reflection coefficient deteriorates to -8 dB. In this regard, the impedance component by the second metal layer (1120) designed with a square grid pattern of FIGS. 7A and 7B can lower the reflection coefficient in the operating band.

[0102] Hereinafter, the electrical characteristics in terms of input impedance are compared according to the arrangement and structure of the second metal layer in the reflective metasurface according to the present specification. In this regard, Fig. 13a shows the input impedance when the permittivity is changed in the reflective metasurface of Figs. 9 and 11a. Fig. 13b shows the input impedance when the permittivity is changed in the reflective metasurface of Figs. 9 and 11b.

[0103] Referring to FIG. 9 and FIG. 13a, even when the dielectric constant (Dk) of the reflective metasurface (1000) is changed to 2.5, 3.0, and 3.5, the input impedance of the reflective metasurface (1000) has a value of 2650 ohm or more. The input impedance of the reflective metasurface (1000) can be designed to have a high input impedance of 3000 to 5000 ohm.

[0104] Referring to FIGS. 11A and 13A, the reflective metasurface (1000b) of the second structure is formed with a triple patch structure including a second metal layer (1120) implemented as a single patch element. The input impedance of the reflective metasurface (1000b) of the second structure having a permittivity (Dk) of 2.5 and 3.0 has a value of 1000 to 2000 ohm. The input impedance of the reflective metasurface (1000b) of the second structure having a permittivity (Dk) of 3.5 has a value of 2500 ohm or more, but is still lower than the reference value of 2650 ohm. Therefore, if a single patch structure rather than a square lattice pattern is used for the second metal layer (1120), the input impedance value is lower than the reference value, and the reflection coefficient is not improved.

[0105] In this regard, as the thickness of the liquid crystal (1030a) becomes thinner, it is not easy to design an RIS having an input impedance of 2650 ohm or more using only a single patch structure. Therefore, the triple-patch structure reflective metasurface (1000) using a square lattice structure proposed in this specification can be designed as a high reflection RIS.

[0106] Referring to FIGS. 11b and 13b, the reflective metasurface (1000c) of the third structure is formed as a double patch structure without a second metal layer. The input impedance of the reflective metasurface (1000b) of the second structure having a dielectric constant (Dk) of 2.5, 3.0, and 3.5 has a value of 1000 to 2000 ohm.

[0107] In this regard, as the thickness of the liquid crystal (1030a) becomes thinner, it becomes difficult to design an RIS having an input impedance of 2000 ohms or more. Therefore, the triple-patch structured reflective metasurface (1000) using the square lattice structure proposed in this specification can be designed as a high reflection RIS.

[0108] Meanwhile, the first metal layer of the liquid crystal-based reflective metasurface according to the present specification may be formed in an array structure composed of a plurality of patch elements. In this regard, FIGS. 14a and 14b illustrate a front view and an exploded perspective view of a reflective metasurface having a 4x4 array structure. Meanwhile, FIG. 15 illustrates a front view and a partially enlarged view of each layer of the reflective metasurface having a 4x4 array structure.

[0109] Referring to FIGS. 7A, 7B, 9A, 14A to 15, a liquid crystal-based reflective metasurface having an array structure according to the present specification will be described. In this regard, the liquid crystal-based reflective metasurface (1000) may form a two-dimensional array structure by arranging a plurality of unit cell structures in the first and second axis directions. For example, the liquid crystal-based reflective metasurface (1000) may be formed in a 4×4 array structure and implemented in a direct addressing manner in which each bias line is connected to 16 unit cells.

[0110] In this regard, the liquid crystal-based reflective metasurface (1000) may be formed in a spherical shape with five metal layers, including the first metal layer (1110) to the fourth metal layer (1140) and a metal layer on which a bias line is formed. The first and second metal layers (1110, 1120) of a floating structure may be formed on the first and second surfaces of the first substrate (1010), which is the uppermost substrate of the liquid crystal-based reflective metasurface (1000). The RIS module implemented with the liquid crystal-based reflective metasurface (1000) is not limited to a 4x4 array structure. The RIS module implemented with the liquid crystal-based reflective metasurface (1000) can be expanded to 8x8, 10x10, 12x12, 16x16, 20x20, 30x30, etc. Therefore, the RIS module implemented with a liquid crystal-based reflective metasurface (1000) can be expanded and used as a large scale array using more than 1000 unit cells depending on the usage environment.

[0111] A liquid crystal-based reflective metasurface (1000) may be configured to include a first layer (La1), a second layer (La2), a third layer (La3), and a fourth layer (La4). The liquid crystal-based reflective metasurface (1000) may include a metal layer region (1100R) in which metal layers are arranged and a pad region (PDR) in which pads are arranged.

[0112] The first layer (La1) may include a first substrate (1010), a first metal layer (1110) formed on a first surface of the first substrate (1010), and a second metal layer (1120) formed on a second surface of the first substrate (1010). In this regard, the second metal layer (1120) may also be formed on the first surface of the second substrate (1020).

[0113] The second layer (La2) may include a second substrate (1020), bias lines (BL11 to BL44) formed on a first surface of the second substrate (1020), and a third metal layer (1130) formed on a second surface of the second substrate (1020). The third metal layer (1130) may also be formed on the first surface of the third substrate (1030).

[0114] The third layer (La3) may include a third substrate (1030) that provides a space in which the liquid crystal (1030a) can be filled in the central portion of the unit cell. The fourth layer (La4) may include a fourth substrate (1040) and a fourth metal layer (1140) formed on a first surface of the fourth substrate (1040). A ground layer (Lg) may also be formed on the first surface of the fourth substrate (1040).

[0115] In a structure in which a third metal layer (1130) covers the upper portion of the liquid crystal (1030a) and a fourth metal layer (1140) covers the lower portion of the liquid crystal (1030a), the reflective metasurfaces of the first substrate (1010) to the fourth substrate (1040) have an input impedance greater than or equal to a critical value. For example, the reflective metasurfaces of the first substrate (1010) to the fourth substrate (1040) may be configured to have an input impedance greater than or equal to 2650 ohm.

[0116] The first metal layer (1110) may include a plurality of first patch elements (Pa11 to Pa44) spaced apart by a first interval (Ga1) in the first and second axis directions and having a first unit cell of a first size (L1p). The first metal layer (1110) and the liquid crystal (1030a) may reflect wireless signals incident on the first metal layer (1110) with different phases due to a dielectric constant that varies depending on a DC voltage applied to the first metal layer (1110).

[0117] The second metal layer (1120) may be formed of square grid patterns. The second metal layer (1120) may include a plurality of second patch elements (Pb11 to Pb14) having second unit cells of a second size (L2p) spaced apart from each other by a second spacing (Gb2) in the first and second axis directions. Each of the second unit cells of the second size (L2p) may include a plurality of square grid patterns. The plurality of square grid patterns may be arranged to correspond to an area where any one of the plurality of first patch elements (Pa11 to Pa44) is arranged. The second spacing (Gb2) of the second unit cells of the second metal layer (1120) may be formed to be the same as the first spacing (Ga1) of the first unit cells of the first metal layer (1110). Each of the second unit cells of the second metal layer (1120) can be positioned corresponding to each of the first unit cells of the first metal layer (1110).

[0118] The square grid patterns of the second patch elements can form a 6x6 grid structure in an area where one patch element of the first unit cell of the first size (L1p) is arranged. The second unit cells of the 6x6 grid structure can be composed of the second patch elements (Pb11 to Pb14) to form a 4x4 array structure.

[0119] The third metal layer (1130) may include a plurality of third patch elements (Pc11 to Pc44) spaced apart by a third gap (Gc3) in the first and second axis directions and having third unit cells of a third size (L3p). The third size (L3p) of the third patch elements (Pc11 to Pc44) may be formed to be the same as the first size (L1p) of the first patch elements (Pa11 to Pa44). The third gap (Gc3) of the third patch elements (Pc11 to Pc44) may be formed to be the same as the first gap (Ga1) of the first patch elements (Pa11 to Pa44). The second gap (Gc3) of the third unit cells of the third metal layer (1130) may be formed to be the same as the first gap (Ga1) of the first unit cells of the first metal layer (1110). Each of the third unit cells of the third metal layer (1130) can be arranged at a position corresponding to each of the first unit cells of the first metal layer (1110).

[0120] A plurality of third patch elements (Pc11 to Pc44) can be stacked with a plurality of first patch elements (Pa11 to Pa44) in the third axis (Z-axis) direction. A plurality of third patch elements (Pc11 to Pc44) can be arranged to overlap with a plurality of first patch elements (Pa11 to Pa44) on the first and second axes on the XY plane.

[0121] A plurality of first patch elements (Pa11 to Pa44) may be arranged in groups of four in the first and second axis directions to form a 4x4 array structure. A plurality of third patch elements (Pc11 to Pc44) may be arranged in groups of four in the first and second axis directions to form a 4x4 array structure.

[0122] Meanwhile, the fourth layer (La4), which is the lowest layer of the liquid crystal-based reflective metasurface (1000), may further include a ground layer (Lg) formed on the second surface of the fourth substrate (1040). A DC voltage may be applied between the third patch elements (Pc11 to Pc44) of the third metal layer (1130) of the third layer (La3) and the fourth metal layer (1140) connected to the ground layer (Lg). The permittivity of the space filled with the liquid crystal (1030a) may be varied by the DC voltage applied between the third metal layer (1130) and the fourth metal layer (1140).

[0123] In this regard, the DC voltage applied to each of the third patch elements (Pc11 to Pc44) of the third metal layer (1130) may be applied with the same voltage value or different voltage values. The same voltage value may be applied to each of the third patch elements (Pc11 to Pc44) of the third metal layer (1130) to maintain the phase variable characteristic constant. Meanwhile, different voltage values ​​may be applied to each of the third patch elements (Pc11 to Pc44) of the third metal layer (1130) to configure the phase variable characteristic differently. In this regard, a combination of DC voltages may be applied to form a first phase difference in the first axis direction and a second phase difference in the second axis direction. In addition, a combination of different DC voltages may be applied in consideration of the incident angle of the wireless signal applied to the reflective metasurface.

[0124] Hereinafter, the connection structure of the bias lines of the two-dimensional array RIS structure will be described. Each end of the bias lines (BL11 to BL44) can be formed as pads (PD11 to PD44). A DC voltage can be applied to the pads (PD11 to PD44). The pads (PD11 to PD44) can be formed on the same plane as the bias lines (BL11 to BL44).

[0125] The pads (PD11 to PD44) may be formed on a first surface of a second substrate (1020) that is coplanar with the bias lines (BL11 to BL44). The bias lines (BL11 to BL44) may be arranged between the second metal layer (1120) and the third metal layer (1130). The bias lines (BL11 to BL44) may be configured to be spaced apart from the second metal layer (1120) on the Z-axis. The other ends of each of the bias lines (BL11 to BL44) may be connected to each of the plurality of third patch elements (Pc11 to Pc33). A DC voltage applied to each of the bias lines (BL11 to BL44) may be applied to each of the plurality of third patch elements (Pc11 to Pc33).

[0126] The bias lines (BL11 to BL44) can be arranged so that four bias lines are adjacent to each other in the second axis direction. The four bias lines in the second axis direction are spaced apart from each other by the distance between the centers of the third patch elements (Pc11 to Pc44) in the first axis direction. Accordingly, among the bias lines (BL11 to BL44), four bias lines in the second axis direction can be arranged in the first axis direction, four each, to form 16 bias lines.

[0127] The pads (PD11 to PD44) may be arranged as 16 pads in a symmetrical configuration in a lower region of the XY plane of the second substrate (1020). The 16 pads (PD11 to PD44) may be arranged at equal intervals parallel to the first axis in a lower region of the XY plane of the second substrate (1020). The other ends of each of the bias lines (BL11 to BL44) may be connected to the centers of the third patch elements (Pc11 to Pc44) to provide a DC voltage to the third patch elements (Pc11 to Pc44).

[0128] Meanwhile, the first and second metal layers of the liquid crystal-based reflective metasurface (1000) according to the present specification may be formed in a floating structure. The first patch elements (Pa11 to Pa44) of the first metal layer (1110) may be arranged on the first surface of the first substrate (1010) so as not to be connected to the bias lines (BL11 to BL44). The second patch elements (Pb11 to Pb44) of the second metal layer (1120) may be arranged on the first surface of the second substrate (1020) so as not to be connected to the bias lines (BL11 to BL44).

[0129] Meanwhile, the liquid crystal-based reflective metasurface (1000) according to the present specification can change the permittivity of the liquid crystals (LC11 to LC44) as the DC voltage applied to the pads (PD11 to PD44) changes. In this regard, the DC voltage is applied to the pads (PD11 to PD44) corresponding to one end of the bias lines (BL11 to BL44). The other ends of the bias lines (BL11 to BL44) can be connected to each of a plurality of third patch elements (Pc11 to Pc44) to form signal vias. The permittivity value of the liquid crystals (LC11 to LC44) can be changed in a range of 2.5 to 3.5 depending on the DC voltage applied to one end of the bias lines (BL11 to BL44).

[0130] Meanwhile, each unit cell of the liquid crystal-based reflective metasurface (1000) according to the present specification may be configured to separate RF signals and DC signals. In this regard, the bias lines (BL11 to BL44) of the liquid crystal-based reflective metasurface (1000) may include radial stubs (RS11 to RS44) formed at points spaced apart from the signal vias, which are the other ends, by a predetermined distance. The radial stubs (RS11 to RS44) may be formed in a predetermined shape so that wireless signals are not introduced into the pads (PD11 to PD44). The radial stubs (RS11 to RS44) may be formed in a fan-shaped shape having a first radius and a first angle at the spaced apart points.

[0131] Meanwhile, each metal layer of the unit cell of the liquid crystal-based reflective metasurface (1000) according to the present specification may be formed to have a predetermined size. The first size (L1p) of the first patch elements of the first metal layer (1110) may be formed within a predetermined range based on 8 mm. The third size (L3p) of the third patch elements of the third metal layer (1130) may be formed to be the same as the first size (L1p) within a predetermined range based on 8 mm.

[0132] Meanwhile, the second metal layer (1120) between the first and third metal layers (1110, 1130) may be formed in a lattice structure. The second size (L2p) of the second patch elements of the second metal layer (1120) may be formed to be larger than the first size (L1p) of the first patch elements of the first metal layer (1110). The second size (L2p) of the second patch elements of the second metal layer (1120) may be formed to be larger than the third size (L3p) of the third patch elements of the third metal layer (1130).

[0133] The size (L2s) of each of the plurality of grid patterns of the second patch elements of the second metal layer (1120) can be formed within a predetermined range based on 1.4 mm. The spacing (Gs) of each of the plurality of grid patterns of the second patch elements of the second metal layer (1120) can be formed within a predetermined range based on 0.2 mm.

[0134] The above describes a liquid crystal-based reflective metasurface. The technical effects of the liquid crystal-based reflective metasurface according to the present specification are as follows.

[0135] According to an embodiment of the present disclosure, a liquid crystal-based reflective metasurface implemented in a multilayer substrate package can improve reflection performance over a wide frequency band.

[0136] According to an embodiment of the present disclosure, a phase-tunable performance of 135 degrees or more can be obtained by changing the permittivity of the liquid crystal in a wideband frequency range in a liquid crystal-based reflective metasurface implemented as a multilayer substrate package.

[0137] According to an embodiment of the present disclosure, a structure of a double patch or more without a via structure is formed to form multiple resonant modes and can operate as a reflector throughout the entire operating frequency band.

[0138] According to an embodiment of the present disclosure, it is possible to manufacture a display process using a liquid crystal through a unit cell having a plurality of metal layers that do not include a via structure.

[0139] According to an embodiment of the present disclosure, a reflective metasurface capable of wideband operation can be provided while improving the switching speed by making the thickness of the liquid crystal thin.

[0140] According to an embodiment of the present disclosure, a triple-patch structured reflective metasurface capable of improving reflection coefficient performance and phase-tunable characteristics in a wide band while increasing switching speed by thinning the thickness of the liquid crystal can be provided. Further scope of the applicability of the present disclosure will become apparent from the detailed description below. However, since various changes and modifications within the spirit and scope of the present disclosure will be apparent to those skilled in the art, it should be understood that the detailed description and specific embodiments, such as the preferred embodiments of the present disclosure, are given by way of example only. The detailed description should not be construed as limiting in all respects but rather as illustrative. The scope of the present disclosure should be determined by a reasonable interpretation of the appended claims, and all changes coming within the equivalent range of the present disclosure are intended to be embraced therein.

Claims

1. In liquid crystal-based reflective metasurfaces, A first layer comprising a first substrate, a first metal layer formed on a first surface of the first substrate, and a second metal layer formed on a second surface of the first substrate; A second layer including a second substrate, bias lines formed on a first surface of the second substrate, and a third metal layer formed on a second surface of the second substrate; A third layer comprising a third substrate that provides a space in which the liquid crystal can be filled in the central portion of the liquid crystal and unit cell; and A fourth substrate, comprising a fourth layer including a fourth metal layer formed on the first surface of the fourth substrate, A liquid crystal-based reflective metasurface, wherein the first substrate to the fourth substrate have an input impedance of 2650 ohm or more, in a structure in which the third metal layer covers the upper portion of the liquid crystal and the fourth metal layer covers the lower portion of the liquid crystal.

2. In paragraph 1, The first metal layer includes a plurality of first patch elements spaced apart by a first interval in the first and second axis directions and having a first unit cell of a first size, A liquid crystal-based reflective metasurface that reflects a wireless signal incident on the first metal layer with different phases by varying the permittivity depending on the DC voltage applied to the first metal layer and the liquid crystal.

3. In paragraph 2, The second metal layer is composed of a second unit cell including a plurality of second patch elements having second unit cells of a second size spaced apart from each other by a second interval in the first and second axis directions, Each of the second unit cells of the second size includes a plurality of square grid patterns, A liquid crystal-based reflective metasurface, wherein the plurality of square grid patterns are arranged correspondingly to an area where any one of the plurality of first patch elements is arranged.

4. In paragraph 3, The square grid patterns of the second patch elements form a 6x6 grid structure in the area where one patch element of the first unit cell is arranged, A liquid crystal-based reflective metasurface, wherein the second unit cells of the 6x6 lattice structure form a 4x4 array structure.

5. In paragraph 2 The third metal layer includes a plurality of third patch elements spaced apart by a third interval in the first and second axis directions and having a third unit cell of a third size, The third size is formed identically to the first size, The third interval is formed identically to the first interval, A liquid crystal-based reflective metasurface, wherein the plurality of third patch elements are stacked in the third axis direction with the plurality of first patch elements and are arranged to overlap on the first and second axes.

6. In paragraph 5, The plurality of first patch elements are arranged in groups of four in the first and second axis directions to form a 4x4 array structure, A liquid crystal-based reflective metasurface, wherein the plurality of third patch elements are arranged in groups of four in the first and second axis directions to form a 4x4 array structure.

7. In paragraph 6, The fourth layer further includes a ground layer formed on the second surface of the fourth substrate, A liquid crystal-based reflective metasurface, wherein the dielectric constant of the space filled with the liquid crystal is varied by a DC voltage applied between the third patch elements and the fourth metal layer connected to the ground layer.

8. In paragraph 7, Each end of the above bias lines is formed as pads, and a DC voltage is applied to the pads, A liquid crystal-based reflective metasurface, wherein each of the other ends of the above bias lines is connected to each of the plurality of third patch elements.

9. In paragraph 7 The above bias lines are, Four bias lines are arranged adjacently in the second axis direction, A liquid crystal-based reflective metasurface, wherein the four bias lines are arranged in groups of four and spaced apart from each other by the distance between the centers of the third patch elements in the first axis direction, thereby forming 16 bias lines.

10. In paragraph 8, The above pads are arranged in 16 pads in a symmetrical structure in the lower area of ​​the XY plane of the second substrate, A liquid crystal-based reflective metasurface, wherein the other ends of each of the above bias lines are connected to the centers of the third patch elements.

11. In paragraph 8, The first patch elements are arranged on the first surface of the first substrate so as not to be connected to the bias lines, A liquid crystal-based reflective metasurface, wherein the second patch elements are arranged on the first surface of the second substrate so as not to be connected to the bias lines.

12. In paragraph 8, A DC voltage is applied to the above-described terminals, and the other terminals are connected to each of the plurality of third patch elements to form signal vias. A liquid crystal-based reflective metasurface, wherein the liquid crystal changes its dielectric constant value in the range of 2.5 to 3.5 depending on the DC voltage applied to the above-described terminals.

13. In paragraph 8, The above bias lines further include radial stubs formed at points spaced a predetermined distance from each of the other ends to prevent the wireless signal from entering the pad, A liquid crystal-based reflective metasurface, wherein the radial stubs are formed in a fan shape having a first radius and a first angle at the spaced points.

14. In paragraph 5, The first size of the first patch elements is formed within a predetermined range based on 8 mm, A liquid crystal-based reflective metasurface, wherein the third size of the third patch elements is formed to be identical to the first size within a predetermined range based on 8 mm.

15. In paragraph 14, The second size of the second patch elements is formed to be larger than the first size and the third size, The size of each of the plurality of grid patterns of the second patch elements is formed within a predetermined range based on 1.4 mm, A liquid crystal-based reflective metasurface, wherein the spacing between the plurality of grid patterns is formed within a predetermined range based on 0.2 mm.

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