KR20240043418A - Liquid crystal-based reconfigurable intelligent surface (ris) device and ris unit cell structure thereof - Google Patents

Abstract

The present disclosure relates to a liquid crystal (LC)-based transmissive RIS device in a wireless communication system and a liquid crystal-based RIS unit cell structure therefor. A liquid crystal-based transmissive reconfigurable intelligent surface (RIS) device in a wireless communication system according to an embodiment of the present disclosure. is a control voltage application line, a plurality of liquid crystal-based transmissive RIS unit cells to which a control voltage is applied through the control voltage application lines, and the control voltage is applied to the plurality of liquid crystal-based transmissive RIS units through the control voltage application lines. and a RIS controller that controls resonators in the plurality of liquid crystal-based transmissive RIS unit cells to operate at a resonant frequency by supplying the same to the cells, wherein each of the plurality of liquid crystal-based transmissive RIS unit cells includes a first metal element that operates as a first resonator. It includes a pattern and a second metal pattern operating as a second resonator, and at least a portion of the first metal pattern and the second metal pattern are physically spaced apart.

Description

Liquid crystal-based transmissive reconfigurable intelligent surface (RIS) device and RIS unit cell structure therefor {LIQUID CRYSTAL-BASED RECONFIGURABLE INTELLIGENT SURFACE (RIS) DEVICE AND RIS UNIT CELL STRUCTURE THEREOF}

This disclosure relates to antenna technology in a wireless communication system, and to a liquid crystal-based transmissive reconfigurable intelligent surface (RIS) device that can improve communication quality by attaching/installing on glass of buildings, vehicles, etc.

5G mobile communication technology defines a wide frequency band to enable fast transmission speeds and new services, and includes sub-6 GHz ('Sub 6GHz') bands such as 3.5 gigahertz (3.5 GHz) as well as millimeter wave (mm) bands such as 28 GHz and 39 GHz. It is also possible to implement it in the ultra-high frequency band ('Above 6GHz') called Wave. In addition, in the case of 6G mobile communication technology, which is called the system of Beyond 5G, Terra is working to achieve a transmission speed that is 50 times faster than 5G mobile communication technology and an ultra-low delay time that is reduced to one-tenth. Implementation in Terahertz bands (e.g., 95 GHz to 3 THz) is being considered.

In the early days of 5G mobile communication technology, there were concerns about ultra-wideband services (enhanced Mobile BroadBand, eMBB), ultra-reliable low-latency communications (URLLC), and massive machine-type communications (mMTC). With the goal of satisfying service support and performance requirements, efficient use of ultra-high frequency resources, including beamforming and massive array multiple input/output (Massive MIMO) to alleviate radio wave path loss in ultra-high frequency bands and increase radio transmission distance. Various numerology support (multiple subcarrier interval operation, etc.) and dynamic operation of slot format, initial access technology to support multi-beam transmission and broadband, definition and operation of BWP (Band-Width Part), large capacity New channel coding methods such as LDPC (Low Density Parity Check) codes for data transmission and Polar Code for highly reliable transmission of control information, L2 pre-processing, and dedicated services specialized for specific services. Standardization of network slicing, etc., which provides networks, has been carried out.

Currently, discussions are underway to improve and enhance the initial 5G mobile communication technology, considering the services that 5G mobile communication technology was intended to support, based on the vehicle's own location and status information. V2X (Vehicle-to-Everything) to help autonomous vehicles make driving decisions and increase user convenience, and NR-U (New Radio Unlicensed), which aims to operate a system that meets various regulatory requirements in unlicensed bands. ), NR terminal low power consumption technology (UE Power Saving), Non-Terrestrial Network (NTN), which is direct terminal-satellite communication to secure coverage in areas where communication with the terrestrial network is impossible, positioning, etc. Physical layer standardization for technology is in progress.

In addition, IAB (IAB) provides a node for expanding the network service area by integrating intelligent factories (Industrial Internet of Things, IIoT) to support new services through linkage and convergence with other industries, and wireless backhaul links and access links. Integrated Access and Backhaul, Mobility Enhancement including Conditional Handover and DAPS (Dual Active Protocol Stack) handover, and 2-step Random Access (2-step RACH for simplification of random access procedures) Standardization in the field of wireless interface architecture/protocol for technologies such as NR) is also in progress, and a 5G baseline for incorporating Network Functions Virtualization (NFV) and Software-Defined Networking (SDN) technology Standardization in the field of system architecture/services for architecture (e.g., Service based Architecture, Service based Interface) and Mobile Edge Computing (MEC), which provides services based on the location of the terminal, is also in progress.

When this 5G mobile communication system is commercialized, an explosive increase in connected devices will be connected to the communication network. Accordingly, it is expected that strengthening the functions and performance of the 5G mobile communication system and integrated operation of connected devices will be necessary. To this end, eXtended Reality (XR) and Artificial Intelligence are designed to efficiently support Augmented Reality (AR), Virtual Reality (VR), and Mixed Reality (MR). , AI) and machine learning (ML), new research will be conducted on 5G performance improvement and complexity reduction, AI service support, metaverse service support, and drone communication.

In addition, the development of these 5G mobile communication systems includes new waveforms, full dimensional MIMO (FD-MIMO), and array antennas to ensure coverage in the terahertz band of 6G mobile communication technology. , multi-antenna transmission technology such as Large Scale Antenna, metamaterial-based lens and antenna to improve coverage of terahertz band signals, high-dimensional spatial multiplexing technology using OAM (Orbital Angular Momentum), RIS ( In addition to Reconfigurable Intelligent Surface technology, Full Duplex technology, Satellite, and AI (Artificial Intelligence) to improve the frequency efficiency of 6G mobile communication technology and system network are utilized from the design operation, and end-to-end. -to-End) Development of AI-based communication technology that realizes system optimization by internalizing AI support functions, and next-generation distributed computing technology that realizes services of complexity beyond the limits of terminal computing capabilities by utilizing ultra-high-performance communication and computing resources. It could be the basis for .

Additionally, RIS technology is being researched as one of the next-generation communication technologies. The RIS forms a reflection pattern by combining the phases and/or amplitudes of each RE (reflecting element) included in the RIS, and can reflect the base station's transmission beam incident on the RIS in a desired direction according to the reflection pattern. Using the RIS, the transmission beam incident on the RIS can be reflected to a terminal located in a shaded area where the transmission beam cannot reach from the base station and delivered to the terminal in the shaded area.

Another example of the RIS technology is transmissive RIS. Transmissive RIS is installed/attached to glass walls and windows of buildings, vehicles, etc. to improve the gain of the transmitted beam of an incident base station or to improve signal attenuation or coverage of the transmitted beam by steering the direction of the incident transmitted beam. You can.

Figure 1 is a diagram for explaining an example in which a transmissive RIS device is used in a wireless communication system.

Figure 1 (a) shows an example in which the transmission beam (or source beam) 110 radiated from the base station is propagated when the RIS device is not installed. The transmission beam 110 is transmitted through glass located indoors, such as a building. As it passes through walls, windows, etc., signal strength may be reduced or coverage may be limited. Figure 1(b) shows an example in which the transmission beam 110 radiated from the base station propagates when a transmissive RIS device is installed on a glass wall or window located indoors in a building. Referring to (b) of FIG. 1, the radio wave of the transmission beam 110 is transmitted (or reflected) through the transmissive RIS device 130 attached/installed in a shaded area or on a glass wall or window of a building, vehicle, etc., and is transmitted through the RIS. The device 130 may perform beam gain improvement and beam steering adjustment on the incident transmission beam 110. The transmissive RIS device 130 can be used to improve indoor communication performance and coverage in an outdoor-to-indoor (O2I) environment. Using the transmission-type RIS device 130, the gain of the transmission beam 110 is improved and beam steering control is performed when the radio wave of the transmission beam 110 penetrates the exterior wall of a building, etc., or a glass wall, a glass window, etc. 120, As a result, signal attenuation of the transmitted beam 140 may be minimized or coverage limitations may be improved.

The present disclosure provides a liquid crystal (LC)-based transmissive RIS device in a wireless communication system and a liquid crystal-based RIS unit cell structure therefor.

This disclosure proposes an LC-based RIS unit cell structure that can improve performance without increasing the thickness of the LC layer.

In a wireless communication system according to an embodiment of the present disclosure, a liquid crystal-based transmissive reconfigurable intelligent surface (RIS) device includes control voltage application lines and a plurality of liquid crystal-based transmissive RIS units to which a control voltage is applied through the control voltage application lines. cells, and a RIS controller that applies the control voltage to the plurality of liquid crystal-based transmissive RIS unit cells through the control voltage application lines to control resonators in the plurality of liquid crystal-based transmissive RIS unit cells to operate at a resonance frequency; , each of the plurality of liquid crystal-based transmissive RIS unit cells includes a first metal pattern operating as a first resonator and a second metal pattern operating as a second resonator, and the first metal pattern and the second metal pattern At least some are physically separated.

In addition, the liquid crystal-based transmissive reconfigurable intelligent surface (RIS) unit cell according to an embodiment of the present disclosure includes a first substrate and a first resonator disposed on the lower surface of the first substrate and to which a control voltage is applied through the first substrate. A first electrode formed with a first metal pattern that operates as a resonator, a second electrode disposed on the upper surface of the second substrate and formed with a second metal pattern that operates as a second resonator, and between the first electrode and the second electrode. It includes a liquid crystal layer disposed in, wherein at least a portion of the first metal pattern and the second metal pattern are physically spaced apart, and the first metal pattern and the second metal pattern generate resonance at a resonance frequency.

1 is a diagram illustrating an example in which a transmissive RIS device is used in a wireless communication system;
Figure 2 is a diagram to explain the molecular arrangement of the LC layer reorganized according to the applied voltage in the LC-based RIS unit cell;
Figure 3 is a diagram to explain the change in dielectric constant of the LC layer reconfigured according to the applied voltage in the LC-based RIS unit cell;
Figure 4 is a diagram showing an example configuration of an LC-based RIS unit cell;
FIG. 5 is a diagram showing an example of the surface current distribution and magnetic field (H-field) of the first and second resonators in the LC-based RIS unit cell having the structure of FIG. 4;
FIG. 6 is a diagram for explaining the equivalent circuit and resonance frequency of the first resonator and the second resonator in the LC-based RIS unit cell having the structure of FIG. 4;
FIG. 7 is a diagram illustrating performance degradation due to mutual inductance in an LC-based RIS unit cell having the structure of FIG. 4;
8 is a diagram showing an example configuration of an LC-based RIS unit cell according to an embodiment of the present disclosure;
FIG. 9 is a diagram illustrating a structure for reducing inductive coupling by spaced apart metal patterns in an LC-based RIS unit cell according to an embodiment of the present disclosure;
FIG. 10 is a diagram showing various structures of spaced apart metal patterns in an LC-based RIS unit cell according to an embodiment of the present disclosure;
FIG. 11 is a diagram showing improved performance by reducing mutual inductance (mutual coupling) in an LC-based RIS unit cell according to an embodiment of the present disclosure;
FIG. 12 is a diagram showing the structure of metal patterns in which bar structures forming the main current source are spaced apart in an LC-based RIS unit cell according to an embodiment of the present disclosure, and
FIG. 13 is a diagram illustrating the performance of improving passband characteristics by controlling mutual inductance in an LC-based RIS unit cell to which the example of FIG. 12 is applied according to an embodiment of the present disclosure; and
FIG. 14 is a diagram illustrating an example configuration of a transmissive RIS device including a plurality of LC-based RIS unit cells according to an embodiment of the present disclosure.

Hereinafter, the operating principle of the present disclosure will be described in detail with reference to the attached drawings. In the following description of the present disclosure, if a detailed description of a related known function or configuration is determined to unnecessarily obscure the gist of the present disclosure, the detailed description will be omitted. In addition, the terms described below are terms defined in consideration of the functions in the present disclosure, and may vary depending on the intention or custom of the user or operator. Therefore, the definition should be made based on the contents throughout this specification.

The advantages and features of the present disclosure and methods for achieving them will become clear by referring to the embodiments described in detail below along with the accompanying drawings. However, the present disclosure is not limited to the embodiments disclosed below and may be implemented in various different forms, and the present embodiments are merely intended to ensure that the disclosure is complete and are within the scope of common knowledge in the technical field to which the present disclosure pertains. It is provided to fully inform those who have the scope of the invention, and the present disclosure is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

At this time, it will be understood that each block of the processing flow diagrams and combinations of the flow diagram diagrams can be performed by computer program instructions.

Additionally, each block may represent a module, segment, or portion of code that includes one or more executable instructions for executing specified logical function(s). Additionally, it should be noted that in some alternative execution examples it is possible for the functions mentioned in the blocks to occur out of order. For example, it is possible for two blocks shown in succession to be performed substantially at the same time, or it is possible for the blocks to be performed in reverse order depending on the corresponding function.

At this time, the term '~unit' used in this embodiment refers to software or hardware components such as FPGA (Field Programmable Gate Array) or ASIC (Application Specific Integrated Circuit), and '~unit' performs certain roles. do. However, '~part' is not limited to software or hardware. The '~ part' may be configured to reside in an addressable storage medium and may be configured to reproduce on one or more processors. Therefore, as an example, '~ part' refers to components such as software components, object-oriented software components, class components, and task components, processes, functions, properties, and procedures. , subroutines, segments of program code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays, and variables. The functions provided within the components and 'parts' may be combined into a smaller number of components and 'parts' or may be further separated into additional components and 'parts'. Additionally, components and 'parts' may be implemented to regenerate one or more CPUs within a device or a secure multimedia card. Also, in an embodiment, '~ part' may include one or more processors.

In the present disclosure, “A or B”, “at least one of A and B”, “at least one of A or B”, “A, B or C”, “at least one of A, B and C” and “A, Each of phrases such as “at least one of B, or C” may include any one of the items listed together in the corresponding phrase, or any possible combination thereof. Terms such as "first", "second", or "first" or "second" may be used simply to distinguish one component from another, and may refer to that component in other respects, such as importance or order) is not limited.

Terms used in the following description to identify a connection node, a term referring to network entities, a term referring to messages, a term referring to an interface between network objects, and a term referring to various types of identification information. The following are examples for convenience of explanation. Accordingly, the present disclosure is not limited to the terms described below, and other terms referring to objects having equivalent technical meaning may be used.

In the present disclosure, a base station (BS) is a network entity that performs resource allocation for a terminal and can communicate with the terminal through a wireless network, including eNode B, Node B, gNB, RAN (Radio Access Network), and AN. It may be at least one of (Access Network), RAN node, Integrated Access/Backhaul (IAB) node, radio access unit, base station controller, node on the network, or TRP (transmission reception point). A terminal (user equipment: UE) may be at least one of a terminal, MS (Mobile Station), cellular phone, smartphone, computer, or multimedia system capable of performing communication functions.

For convenience of description below, this disclosure uses terms and names defined in the 5GS and NR standards, which are the most recent standards defined by the 3rd Generation Partnership Project (3GPP) organization among currently existing communication standards. However, the present disclosure is not limited by the above terms and names, and may be equally applied to wireless communication networks complying with other standards. In particular, the present disclosure can be applied to 5G systems as well as systems beyond 5G systems (for example, 6G systems).

A RIS device may be configured to include a plurality of RIS unit cells, and the RIS unit cell may be implemented using various active elements and/or variable materials to change phase distribution. Examples of various active devices include PIN diodes, varactors, and MEMS (Micro Electro Mechanical Systems) switches. In addition, the transmissive RIS unit cell may include liquid crystal (LC), and the dielectric constant is controlled according to the applied voltage applied to the liquid crystal (LC) in the transmissive RIS unit cell (hereinafter referred to as LC-based RIS unit cell) using liquid crystal, thereby controlling the LC-based RIS. The characteristics of the unit cell can be changed, and compared to other active devices, liquid crystal (LC) can be used in a wide frequency band (for example, GHz to THz band).

Figure 2 is a diagram to explain the molecular arrangement of the LC layer reorganized according to the applied voltage in the LC-based RIS unit cell.

To design an LC-based RIS unit cell, the property that the dielectric constant of the liquid crystal (LC) layer varies depending on the applied voltage is utilized. Referring to FIG. 2, the LC layer 201 is disposed between the top electrode 202 and the bottom electrode 203. The area shown in an oval shape in FIG. 2 represents the molecular arrangement 204 of the LC layer 201. When voltage is applied to the top electrode 202 and the bottom electrode 203 on which the metal pattern is formed, an electric field (E-field) 205 is created between the top electrode 202 and the bottom electrode 203. The molecular arrangement 204 of the LC layer 201 can be reconfigured depending on the intensity of the E-field 205.

As sequentially illustrated in (a), (b), and (c) of Figure 2, as the E-field 205 increases, the molecules of the LC layer 201 move in the direction of the E-field 205 due to polarization. are rearranged to be parallel to For the molecular arrangement of these LC layers, see "Wittek, Michael, Carsten Fritzsch, and Dieter Schroth. "Employing Liquid CrystalBased Smart Antennas for Satellite and Terrestrial Communication." Information Display 37.1 (2021): 17-22." there is.

Figure 3 is a diagram to explain the change in dielectric constant of the LC layer reconfigured according to the applied voltage in the LC-based RIS unit cell.

In an LC-based RIS unit cell, it is possible to variably control the effective dielectric constant depending on the applied voltage. As in the example of FIG. 3, when the applied voltage is below the threshold value (301), a constant effective dielectric constant value is maintained, as indicated by reference number 302, and when a voltage above the threshold (>Vth) is applied, the effective dielectric constant is increased, as indicated by reference number 303. This is starting to change. Therefore, as the applied voltage increases in the LC-based RIS unit cell, the effective dielectric constant value gradually increases. This change in dielectric constant of the LC layer is J. "Kim and J. Oh, "Liquid-Crystal-Embedded Aperture-Coupled Microstrip Antenna for 5G Applications," in IEEE Antennas and Wireless Propagation Letters, vol. 19, no. 11, pp. 1958-1962, Nov. 2020, doi: 10.1109/LAWP.2020.3014715."

Referring to the examples of FIGS. 2 and 3 above, the relationship between the applied voltage and the effective dielectric constant change varies depending on the thickness of the LC layer 201 in the LC-based RIS unit cell. As the LC layer 201 becomes thicker, the LC The distance between the top electrode 202 and the bottom electrode 203 of the base RIS unit cell increases. Therefore, in proportion to the thickness of the LC layer 201, a stronger E-field 205 is required to reorganize the molecular arrangement of the LC layer 201, and Vth, which is the threshold value 301 of the applied voltage, also increases. Additionally, the control range of the applied voltage to obtain the variable range of the effective dielectric constant of the LC layer 201 in a desired range becomes larger. As a result, Vmax, which is the maximum value of the applied voltage of the LC-based RIS unit cell, also increases. For example, if a high voltage of hundreds of volts (V) is used, a major stability problem occurs. Therefore, in order for the LC-based RIS unit cell to operate within a substantially controllable voltage range, the thickness of the LC layer 201 must be limited.

Figure 4 is a diagram showing an example configuration of an LC-based RIS unit cell.

In the example of FIG. 4, the LC-based RIS unit cell 400 includes a first electrode 402 disposed on the lower surface of the first substrate 401 and a second electrode 404 disposed on the upper surface of the second substrate 405. and an LC layer 403 disposed between the first electrode 402 and the second electrode 404. The first electrode 402 is used as the top electrode of the LC layer 403, and the second electrode 404 is used as the bottom electrode of the LC layer 403. A first metal pattern and a second metal pattern are formed on the first electrode 402 and the second electrode 404, respectively, to generate resonance at the resonance frequency. The first metal pattern formed/included in the first electrode 402 operates as a first resonator, and the second metal pattern formed in/included in the second electrode 404 operates as a second resonator. Here, the first metal pattern and the second metal pattern may have the same pattern. When the LC-based RIS unit cell 400 having this structure is used in a transmissive RIS device, the transmissive RIS device can obtain transmission characteristics and phase variable characteristics at the resonant frequency.

Assuming that the desired variable range of the effective dielectric constant of the LC layer 403 is 2.5 to 3.5, and considering the voltage range (0 to 20 V) of the controllable applied voltage in the LC-based RIS unit cell 400, the LC layer 403 The thickness 406 may be limited to 200 μm or less. However, as described above, as the thickness 406 of the LC layer 403 becomes thicker, the desired variable range of effective dielectric constant is not obtained or the controllable applied voltage range is exceeded.

FIG. 5 shows an example of the surface current distribution and magnetic field (H-field) of the first and second resonators in the LC-based RIS unit cell having the structure of FIG. 4.

Referring to Figure 5, it shows the surface current distribution 501 of the first resonator and the second resonator formed/included in the first electrode 402 and the second electrode 404, respectively. It can be seen that a strong H-field (502) is generated due to the current. The H-field generated from the first metal pattern of the first resonator and the H-field generated from the second metal pattern of the second resonator may overlap to generate mutual inductance.

FIG. 6 is a diagram for explaining the equivalent circuit and resonance frequency of the first and second resonators in the LC-based RIS unit cell having the structure of FIG. 4.

In FIG. 6, reference symbols L and C represent inductance and capacitance by the first and second metal patterns of the first and second resonators, respectively, and reference symbol L _m represents the first and second metal patterns of the first and second resonators, respectively. This shows the mutual inductance caused by the metal pattern. I ₁ and I ₂ represent the current, and V ₁ and V ₂ represent the voltage between T ₁ -T' ₁ and T ₂ -T' ₂ , respectively. In the equivalent circuit of FIG. 6, as the mutual inductance L _m increases, the difference between the resonance frequency f _e and f _m values gradually increases.

FIG. 7 is a diagram to explain performance degradation due to mutual inductance in an LC-based RIS unit cell having the structure of FIG. 4.

Referring to FIG. 7, due to the mutual inductance (L _m ) generated in the first and second metal patterns of the first and second resonators in the LC-based RIS unit cell having the structure of FIG. 4, (a) of FIG. 7 Performance deterioration occurs as the passband loss increases (701) and the phase variable range decreases (702) as shown in (b) of FIG. 7. This degrades the performance of the LC-based RIS unit cell.

Figure 8 is a diagram showing an example configuration of an LC-based RIS unit cell according to an embodiment of the present disclosure.

In the example of FIG. 8, the LC-based RIS unit cell 800 includes a first electrode 802 disposed on the lower surface of the first substrate 801 and a second electrode 804 disposed on the upper surface of the second substrate 805. and an LC layer 803 disposed between the first electrode 802 and the second electrode 804. The first electrode 802 is used as the top electrode of the LC layer 803, and the second electrode 804 is used as the bottom electrode of the LC layer 403. The first substrate 801 and the second substrate 805 may include a dielectric. A first metal pattern and a second metal pattern are formed on the first electrode 802 and the second electrode 804, respectively, to generate resonance at the resonance frequency. The first metal pattern formed/included in the first electrode 802 operates as a first resonator, and the second metal pattern formed in/included in the second electrode 804 operates as a second resonator. Here, the first metal pattern and the second metal pattern have patterns spaced apart from the center according to an embodiment of the present disclosure. The passband loss, phase variable range within the passband, and phase linearity of the LC-based RIS unit cell can be improved by adjusting at least one of the direction and distance in which the first and second metal patterns are separated from the center. Additionally, the first metal pattern and the second metal pattern may have the same pattern or different patterns. In addition, in another embodiment, instead of using an LC-based RIS unit cell, only the rod structures forming the main current source in the first and second metal patterns are spaced apart to improve passband loss, phase variable range within the passband, and phase linearity. You may.

When the LC-based RIS unit cell 800 having the above-described structure is used in a transmissive RIS device, the interaction generated in the first and second metal patterns of the first and second resonators is reduced without increasing the thickness of the LC layer 803. Inductance (L _m ) (mutual coupling) can be reduced, and better transmission characteristics and phase variable characteristics can be obtained at the resonant frequency. The LC-based RIS unit cell 800 assumes a variable range of the desired effective dielectric constant of the LC layer 803 of 2.5 to 3.5 and a controllable voltage range of the applied voltage (0 to 20V). The thickness 806 may be limited to, for example, a critical thickness of 200 μm or less. In an embodiment of the present disclosure, the variable range of the effective dielectric constant, the voltage range of the applied voltage, and the range of the thickness 806 of the LC layer 803 are examples, and the present disclosure is not limited to these ranges.

In the embodiment of FIG. 8, the LC-based RIS unit cell 800 is illustrated in a square shape, but this is only an example, and the LC-based RIS unit cell 800 may be implemented in various shapes such as polygonal, circular, or oval. You can. Likewise, the first and second metal patterns that operate as resonators may also be designed into various types of patterns including a rod structure that forms a main current source.

FIG. 9 is a diagram illustrating a structure for reducing inductive coupling by spaced apart metal patterns in an LC-based RIS unit cell according to an embodiment of the present disclosure. The embodiment of FIG. 9 will be described with reference to FIG. 8 .

In Figure 9(a), the first metal pattern 901 of the first electrode 802 operates as a first resonator, and in Figure 9(b), the second metal pattern 903 of the second electrode 804 operates as a first resonator. operates as a second resonator. Referring to the surface current distribution of the resonator described in the example of FIG. 5, the current of the resonator flows most strongly in the rod structure at the center of the metal pattern. Therefore, the surface current of the first resonator flows most strongly in the rod structure 902 at the center of the first metal pattern 901, and the surface current of the first resonator flows most strongly in the rod structure 904 at the center of the second metal pattern 903. flows most strongly in Therefore, in the first resonator, the H-field is formed in a direction (z-axis) perpendicular to the longitudinal direction (y-axis) of the rod structure 902 and forms inductive coupling with the rod structure 904 of the adjacent second resonator. . The embodiment of FIG. 9 maintains the thickness of the LC layer 803 and maintains the physical distance between the bar structures 902 and 904 of the first metal pattern 901 and the second metal pattern 903 to achieve inductive coupling. (For example, a structure that reduces mutual inductance (Lm)) is proposed. The distance between the first metal pattern 901 and the second metal pattern 903 is, for example, the thickness of the metal line located at the edge of the first metal pattern 901 and the second metal pattern 903 ( d) can be determined by considering (905).

Figure 10 is a diagram showing various structures of metal patterns spaced apart in an LC-based RIS unit cell according to an embodiment of the present disclosure. The embodiment of FIG. 10 will be described with reference to FIG. 8 .

Figure 10(a) shows the first metal pattern of the first electrode 802 and the second metal pattern of the second electrode 804 based on the dotted line 1001 indicating the direction of vertical polarization (V-pol) in the antenna. 2 shows an example of a structure that physically separates the metal pattern from the center, and Figure 10(b) shows the first electrode 802 based on the dotted line 1002 indicating the direction of horizontal polarization (H-pol) in the antenna. ) shows an example of a structure that physically separates the first metal pattern of the second electrode 804 from the center. In the examples of Figures 10 (a) and (b), the degree of separation may vary in the range of tens of μm to thousands of μm depending on the operating frequency of the resonator. In addition, as the first metal pattern of the first electrode 802 and the second metal pattern of the second electrode 804 are spaced apart from each other, the thickness ( d) Since (905) may violate the PCB minimum process requirements, the maximum value of the separation degree may be determined according to the process possible range.

In the example of Figures 10 (a) and (b), the direction of separation from the center of the first and second metal patterns that operate as the first and second resonators to reduce the mutual inductance (Lm) is the first and second metal patterns. is correlated with the direction of the surface current. The intensity and direction of the surface current can be determined depending on the polarization of the antenna and the structure of the resonator, and as an example in Figures 10 (a) and (b), the first and second resonators for V-pol and H-pol Mutual inductance (L _m ) (mutual coupling) can be reduced by separating the centers of the first and second metal patterns in such a way that the direction of the surface current is away from each other.

FIG. 11 is a diagram showing improved performance by reducing mutual inductance (L _m ) (mutual coupling) in an LC-based RIS unit cell according to an embodiment of the present disclosure. The simulation results in Figures 7 and 11 were obtained under the condition that the thickness of the LC layer was the same in the LC-based RIS unit cell.

Referring to FIG. 11, in the LC-based RIS unit cell having the structure of FIG. 8, the first and second metal patterns operating as first and second resonators are spaced apart to reduce mutual inductance (L _m ) (mutual coupling). The passband loss is improved (1101) as shown in (a) of FIG. 11, and the phase linearity is improved (702) as shown in (b) of FIG. 11, improving the performance of the LC-based RIS unit cell. will improve.

According to the embodiments of the present disclosure described above, the mutual inductance (mutual inductance) is increased by increasing the physical distance between the main current sources in the first and second metal patterns without increasing the thickness of the LC layer in the LC-based RIS unit cell. By reducing _Lm ), mutual coupling that causes performance degradation can be reduced. This can improve passband loss, phase tunable range and phase linearity within the passband in LC-based RIS unit cells.

FIG. 12 is a diagram showing the structure of metal patterns in which bar structures forming a main current source are spaced apart in an LC-based RIS unit cell according to an embodiment of the present disclosure. The embodiment of FIG. 10 will be described with reference to FIG. 8 .

Referring to FIG. 12, a first metal pattern and a second metal pattern are formed on the first electrode 802 and the second electrode 804, respectively, to generate resonance at the resonance frequency. The first metal pattern formed/included in the first electrode 802 operates as a first resonator, and the second metal pattern formed in/included in the second electrode 804 operates as a second resonator. Here, the first metal pattern and the second metal pattern are not spaced apart from the entire resonator pattern, but are arranged in a direction in which the bar structures 1202 and 1204 forming the main current source are physically separated from the first metal pattern and the second metal pattern, respectively. It has a spaced structure. Depending on the degree to which the bar structures 1202 and 1204 are spaced apart, the L and C parameters of the equivalent circuit described in FIG. 6 may change and the resonance frequency may change. However, compared to the structure of FIG. 9, the change in resonance frequency is minimal. Substantially the same performance improvement effect can be provided in the LC-based RIS unit cell simply by spacing the rod structures 1202 and 1204 within an acceptable range.

FIG. 13 is a diagram illustrating the performance of improving passband characteristics by controlling mutual inductance (L _m ) in an LC-based RIS unit cell to which the example of FIG. 12 is applied according to an embodiment of the present disclosure.

In FIG. 13, reference number 1301 indicates improved passband characteristics, and the rod structures 1202 and 1204 that form main current sources in the first and second metal patterns, respectively, rather than separating the entire resonator pattern, are ) can be spaced apart to provide substantially the same performance improvement effect.

In the LC-based RIS unit cell structure of FIG. 8 described above, the degree to which the resonator patterns (i.e., first and second metal patterns) are spaced apart according to the embodiment of FIG. 9 or the embodiment of FIG. 12 is determined by the LC-based RIS unit cell 800. are different depending on the physical properties of the first substrate 801, which is the upper substrate, and the second substrate 805, which is the lower substrate, and the physical properties of the internal LC layer 803. When the dielectric constant of the first substrate 801 and the second substrate 805 increases, the guided-wavelength inside the LC-based RIS unit cell decreases, thereby increasing the electrical length for the same physical separation distance.

Accordingly, the dielectric constant of the first substrate 801 and the degree to which the first metal pattern formed/included in the first electrode 802 are separated (separation distance) are inversely proportional. According to the same principle, the dielectric constant of the LC layer 803 in close contact with the first metal pattern is inversely proportional to the degree to which the first metal pattern is spaced apart. The second substrate 805 is in close contact with the second metal pattern formed/included in the second electrode 804, and the degree to which the second metal pattern is separated is inversely proportional to the dielectric constant of the second substrate 805. Likewise, since the second metal pattern is in close contact with the LC layer 803, the degree of separation of the second metal pattern is inversely proportional to the dielectric constant of the LC layer 803. That is, the separation distance between the first metal pattern and the second metal pattern is inversely proportional to the dielectric constants of the first and second substrates.

The degree of separation between the first metal pattern and the second metal pattern is also affected by the resonance frequency. As the resonant frequency increases, the electrical length decreases and the physical size of the LC-based RIS unit cell and the first and second metal patterns also decreases, so the degree of separation between the first and second metal patterns decreases. . Therefore, the resonance frequency and the degree of separation between the first and second metal patterns are inversely proportional.

FIG. 14 is a diagram illustrating an example configuration of a transmissive RIS device including a plurality of LC-based RIS unit cells according to an embodiment of the present disclosure.

The transmissive RIS device 1400 of FIG. 14 includes control voltage application lines 1401, a first substrate layer 1402, a first electrode layer 1403, a liquid crystal (LC) layer 1404, and a second electrode layer 1405. ), a second substrate layer 1406, and a RIS controller 1407. A third substrate layer 1404a for fixing the liquid crystal layer 140 may be disposed between the liquid crystal (LC) layer 1404 and the second electrode layer 1405. The first substrate layer 1402, the second substrate layer 1406, and the third substrate layer 1404a may include a dielectric. The third substrate layer 1404a may be optionally included.

The RIS controller 1407 applies a control voltage for controlling the liquid crystal (LC) layer 1404 to the first electrode layer 1403 through control voltage application lines 1401. The second electrode layer 1405 is electrically grounded. The transmissive RIS device 1400 includes a plurality of LC-based RIS unit cells 800, and the plurality of LC-based RIS unit cells 800 may be arranged in an array. For example, a plurality of squares in the first electrode layer 1403 and the second electrode layer 1405 shown in FIG. 14 respectively operate as a first resonator and a second resonator in the structure of the LC-based RIS unit cell 800. Corresponds to the first electrode 802 and the second electrode 804 on which the first metal pattern and the second metal pattern are formed, and a plurality of first and second metal patterns are formed on the first and second electrode layers 1403 and 1405. It can be placed in an array form. In the LC-based RIS unit cell 800 of FIG. 8, the first substrate 801 and the second substrate 805 correspond to parts of the first substrate layer 1402 and the second electrode layer 1405, respectively.

Each of the control voltage application lines 1401 may be positioned independently without being electrically conductive, and each LC-based RIS unit cell ( 800) is electrically connected to Control voltage application lines 1401 are disposed on the top of the first substrate layer 1402, and a first electrode layer 1403 is disposed on the bottom of the first substrate layer 1402 to provide the control voltage application lines 1401 and , supports the plurality of first metal patterns formed in an array on the first electrode layer 1403 to be fixed, and prevents liquid crystal from leaking out of the liquid crystal (LC) layer 1404. A second electrode layer 1403 is disposed on the top of the second substrate layer 1406, supports and secures a plurality of second metal patterns formed in an array on the second electrode layer 1403, and a liquid crystal (LC) layer ( 1404) Prevent my liquid crystal from leaking. The plurality of second metal patterns are electrically conductive and have a direct current ground (DC GND) potential with respect to the control voltage. A space large enough to place the liquid crystal (LC) layer 1404 is formed between the first electrode layer 1403 and the second electrode layer 1403.

In the specific embodiments of the present disclosure described above, components included in the invention are expressed in singular or plural numbers depending on the specific embodiment presented. However, singular or plural expressions are selected to suit the presented situation for convenience of explanation, and the present disclosure is not limited to singular or plural components, and even components expressed in plural may be composed of singular or singular. Even expressed components may be composed of plural elements.

Meanwhile, in the detailed description of the present disclosure, specific embodiments have been described, but of course, various modifications are possible without departing from the scope of the present disclosure. Therefore, the scope of the present disclosure should not be limited to the described embodiments, but should be determined not only by the scope of the patent claims described later, but also by the scope of this patent claim and equivalents.

Claims (15)

In a liquid crystal-based transmissive reconfigurable intelligent surface (RIS) device in a wireless communication system,
Control voltage application lines;
A plurality of liquid crystal-based transmissive RIS unit cells to which a control voltage is applied through the control voltage application lines; and
And a RIS controller that applies the control voltage to the plurality of liquid crystal-based transmissive RIS unit cells through the control voltage application lines to control resonators in the plurality of liquid crystal-based transmissive RIS unit cells to operate at a resonance frequency,
Each of the plurality of liquid crystal-based transmissive RIS unit cells includes a first metal pattern operating as a first resonator and a second metal pattern operating as a second resonator, and at least one of the first metal pattern and the second metal pattern Liquid crystal-based transmissive RIS devices, some of which are physically spaced apart.
According to claim 1,
Each of the plurality of liquid crystal-based transmissive RIS unit cells includes a liquid crystal layer,
The thickness of the liquid crystal layer is limited to a critical thickness or less based on the effective dielectric constant of the liquid crystal layer and the control voltage,
A liquid crystal-based transmissive RIS device, wherein at least one of the separation direction and distance between the first metal pattern and the second metal pattern is determined to reduce mutual inductance by the first metal pattern and the second metal pattern.
According to claim 1,
A liquid crystal-based transmissive RIS device in which the entire first metal pattern and the second metal pattern are spaced apart in each liquid crystal-based transmissive RIS unit cell.
According to claim 1,
A liquid crystal-based transmissive RIS device in which rod structures forming main current sources in the first metal pattern and the second metal pattern are spaced apart in each liquid crystal-based transmissive RIS unit cell.
According to claim 1,
A liquid crystal-based transmissive RIS device in which the separation distance between the first metal pattern and the second metal pattern is determined based on the thickness of the metal line located at the edges of the first metal pattern and the second metal pattern.
According to claim 1,
Each of the plurality of liquid crystal-based transmissive RIS unit cells,
A first substrate on which vias, which are metal wires, are formed;
a first electrode disposed on a lower surface of the first substrate and to which the control voltage is applied through the via;
a second electrode disposed on the upper surface of the second substrate; and
It includes a liquid crystal layer disposed between the first electrode and the second electrode,
The first metal pattern operating as the first resonator and the second metal pattern operating as the second resonator are formed on the first electrode and the second electrode, respectively, to generate resonance at the resonance frequency. RIS device.
According to claim 1,
A liquid crystal-based transmissive RIS device in which the separation distance between the first metal pattern and the second metal pattern is inversely proportional to the dielectric constants of the first and second substrates.
According to claim 1,
A liquid crystal-based transmissive RIS device in which the separation distance between the first metal pattern and the second metal pattern is inversely proportional to the resonance frequency.
In a liquid crystal-based transmissive reconfigurable intelligent surface (RIS) unit cell,
first substrate;
a first electrode disposed on a lower surface of the first substrate and formed with a first metal pattern operating as a first resonator to which a control voltage is applied through the first substrate;
a second electrode disposed on the upper surface of the second substrate and formed with a second metal pattern operating as a second resonator; and
It includes a liquid crystal layer disposed between the first electrode and the second electrode,
A liquid crystal-based transmissive RIS unit cell wherein at least a portion of the first metal pattern and the second metal pattern are physically spaced apart, and the first metal pattern and the second metal pattern generate resonance at a resonance frequency.
According to clause 9,
The thickness of the liquid crystal layer is limited to a critical thickness or less based on the effective dielectric constant of the liquid crystal layer and the control voltage,
A liquid crystal-based transmissive RIS unit cell wherein at least one of the separation direction and distance between the first metal pattern and the second metal pattern is determined to reduce mutual inductance by the first metal pattern and the second metal pattern. .
According to clause 9,
A liquid crystal-based transmissive RIS unit cell in which the entire first metal pattern and the second metal pattern are spaced apart.
According to clause 9,
A liquid crystal-based transmissive RIS unit cell in which rod structures forming main current sources are spaced apart from each other in the first metal pattern and the second metal pattern.
According to clause 9,
A liquid crystal-based transmissive RIS unit cell in which the separation distance between the first metal pattern and the second metal pattern is determined based on the thickness of the metal line located at the edge of the first metal pattern and the second metal pattern.
According to clause 9,
A liquid crystal-based transmissive RIS unit cell in which the separation distance between the first metal pattern and the second metal pattern is inversely proportional to the dielectric constants of the first and second substrates.
According to clause 9,
A liquid crystal-based transmissive RIS unit cell in which the separation distance between the first metal pattern and the second metal pattern is inversely proportional to the resonance frequency.

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