Driving method for radio wave reflecting device

Abstract

Provided is a driving method for a radio wave reflecting device that includes a first liquid crystal reflector plate and a second liquid crystal reflector plate and that reflects radio waves incident on the first liquid crystal reflector plate toward the second liquid crystal reflector plate, the driving method including driving the first liquid crystal reflector plate to change the phase of the incident radio waves such that the radio waves reflected by the first liquid crystal reflector plate are focused on the second liquid crystal reflector plate.

Description

Method for driving a radio wave reflector

[0001] The present invention relates to a method for driving a radio wave reflector that reflects radio waves.

[0002] In the telecommunications field, the introduction of the fifth-generation communication standard, known as 5G, is progressing. 5G utilizes radio waves in the millimeter-wave band, from 26 GHz to 29 GHz. 5G communication enables transmission over a wide bandwidth, achieving extremely high throughput.

[0003] Because radio waves in the millimeter-wave frequency band have high directivity, they do not easily reach areas such as the back of buildings. For this reason, in areas where radio waves do not easily reach, liquid crystal reflectors, such as those described in Patent Document 1, are installed to change the direction of radio wave transmission.

[0004] Special table 2019-530387 publication

[0005] However, compared to a metal plate that can reflect incident radio waves (hereinafter sometimes referred to as "incident radio waves") across its entire surface, liquid crystal reflectors may result in lower intensity of reflected radio waves (hereinafter sometimes referred to as "reflected radio waves"). In areas where multiple liquid crystal reflectors need to be installed, such as inside tunnels or curved corridors, the radio waves are reflected multiple times, resulting in a significant decrease in the intensity of reflected radio waves.

[0006] Therefore, one of the objectives of the present invention is to suppress the decrease in the intensity of reflected radio waves in a driving method for a radio wave reflecting device that includes multiple liquid crystal reflectors. The liquid crystal reflectors can be referred to as "IRS" (Intelligent Reflecting Surface), and the radio wave reflecting device can be referred to as "a device including an IRS."

[0007] A method for driving a radio wave reflector according to one embodiment of the present invention includes a first liquid crystal reflector and a second liquid crystal reflector, and is a method for driving a radio wave reflector that reflects radio waves incident on the first liquid crystal reflector toward the second liquid crystal reflector, comprising changing the phase of the incident radio waves and driving the first liquid crystal reflector so that the radio waves reflected by the first liquid crystal reflector are focused by the second liquid crystal reflector.

[0008] This is a schematic diagram showing the installation of a radio wave reflector according to one embodiment of the present invention. This is a plan view of a liquid crystal reflector according to one embodiment of the present invention. This is a cross-sectional view of the liquid crystal reflector between A and B shown in Figure 2. This is a plan view of a unit cell constituting the liquid crystal reflector. This is a cross-sectional view of the unit cell between C and D shown in Figure 4. This is a schematic diagram showing how the propagation direction of scattered waves changes due to the liquid crystal reflector. This is a schematic diagram showing the characteristics of reflected radio waves relative to incident radio waves at the liquid crystal reflector. This is a schematic diagram showing the relationship between incident and reflected radio waves at the first liquid crystal reflector. This is a diagram showing the relationship between the position of the unit cell at the first liquid crystal reflector and the phase that the unit cell imparts to the incident radio wave. This is a schematic diagram showing the relationship between the first liquid crystal reflector, the wave source, and the position where the reflected radio waves converge.

[0009] Embodiments of the present invention will be described below with reference to the drawings. While the drawings may schematically represent the width, thickness, shape, etc., of parts in order to clarify the explanation, they are merely examples and do not limit the interpretation of the present invention. In this specification and in the drawings, elements similar to those described above in previous drawings are denoted by the same reference numerals, and detailed explanations may be omitted as appropriate.

[0010] <Radio Wave Reflector> Figure 1 is a schematic diagram showing a radio wave reflector 10 according to one embodiment of the present invention installed in an area such as a corridor. As shown in Figure 1, the radio wave reflector 10 includes a first liquid crystal reflector 100-1 and a second liquid crystal reflector 100-2. Although not shown in Figure 1, the radio wave reflector 100 also includes a drive unit that drives the first liquid crystal reflector 100-1 and the second liquid crystal reflector 100-2.

[0011] The first liquid crystal reflector 100-1 and the second liquid crystal reflector 100-2 are installed at a predetermined distance apart so that radio waves emitted from a wave source Tx, such as an antenna, are transmitted to a desired receiving area Rx while avoiding obstacles such as walls. In Figure 1, the radio wave reflector 10 includes two liquid crystal reflectors 100, but it may include three or more liquid crystal reflectors 100 depending on the obstacles.

[0012] The first liquid crystal reflector 100-1 is driven by a drive unit to change the phase of the radio waves incident on it, so as to reflect the incident radio waves toward the second liquid crystal reflector 100-2. The first liquid crystal reflector 100-1 is also driven by a drive unit to change the phase of the incident radio waves so as to focus the incident radio waves toward the second liquid crystal reflector 100-2. Because the reflected radio waves are focused, their intensity can be improved compared to radio waves that are reflected uniformly. Furthermore, because the reflected radio waves are focused by the second liquid crystal reflector 100-2, the size of the second liquid crystal reflector 100-2 can be made smaller than the size of the first liquid crystal reflector 100-1. This reduces the power required to drive the radio wave reflector 10.

[0013] <Liquid Crystal Reflector> Figure 2 is a plan view of the liquid crystal reflector 100. Figure 3 is a cross-sectional view corresponding to the section A-B shown in Figure 2. As shown in Figures 2 and 3, the liquid crystal reflector 100 is plate-shaped and formed to be square in plan view. The shape of the liquid crystal reflector 100 is not limited to this, and for example, it may be a rectangular or circular plate in plan view. When the shape of the liquid crystal reflector 100 is a square plate in plan view, the size of the liquid crystal reflector 100 is set, for example, to have sides of 50 mm or more and 1000 mm or less, and a thickness of 1 mm or more and 10 mm or less.

[0014] As shown in Figures 2 and 3, the liquid crystal reflector 100 includes a counter electrode 102, at least one patch electrode 104, and a liquid crystal layer 106 disposed between these electrodes. As shown in Figure 2, the counter electrode 102 is formed to be planar in the XY plane, and the patch electrodes 104 are arranged in a matrix in the X-axis and Y-axis directions so as to face the counter electrode 102. The X-axis and Y-axis directions are used for explanatory purposes and specifically refer to the directions shown in Figure 2. The X-axis and Y-axis directions can also be interpreted as directions that intersect one direction and one direction.

[0015] The counter electrode 102 is formed to be planar in the XY plane. In contrast, the patch electrodes 104 are arranged with gaps between adjacent ones, and are physically separated. The counter electrode 102 is provided on the first substrate 132, and the patch electrodes 104 are provided on the second substrate 134. The liquid crystal reflector 100 is a device that scatters radio waves incident on the incident surface in a predetermined direction, with the second substrate 134 on the incident surface side and the first substrate 132 on the back side of the incident surface. That is, the patch electrode 104 is placed on the incident surface, and the counter electrode 102 is placed behind the patch electrode 104 with the liquid crystal layer 106 in between.

[0016] The liquid crystal reflector 100 has a structure in which the counter electrode 102, liquid crystal layer 106, and patch electrode 104 are arranged to overlap in a plan view. Furthermore, the liquid crystal reflector 100 is arranged so that the surface of the first substrate 132 on which the counter electrode 102 is provided and the surface of the second substrate 134 on which the patch electrode 104 is provided face each other, with the liquid crystal layer 106 arranged between them. The basic unit of the liquid crystal reflector 100 is a stacked structure of a set of counter electrode 102, liquid crystal layer 106, and patch electrode 104 (which may also include the first substrate 132 and the second substrate 134). Hereafter, this basic unit will be referred to as a unit cell 1000.

[0017] The second substrate 134 is provided with a selection signal line 110 extending in the X direction, a bias signal line 112 extending in the Y direction, and a switching element 116. The switching element 116 is provided in a one-to-one correspondence with the patch electrodes 104. The switching operation (on / off state) of the switching element 116 is controlled by the selection signal of the selection signal line 110, and a bias signal (bias voltage) is input from the bias signal line 112. The patch electrodes 104 are individually input with bias signals by the switching element 116. In other words, the patch electrodes 104, which are arranged in a matrix, are individually input with bias signals by the switching element 116.

[0018] A first alignment film 114A is provided on the first substrate 132 side, and a second alignment film 114B is provided on the second substrate 134. The first alignment film 114A is provided so as to cover the counter electrode 102, and the second alignment film 114B is provided so as to cover the patch electrode 104. The first alignment film 114A and the second alignment film 114B are provided to control the alignment state of the liquid crystal layer 106. The liquid crystal layer 106 contains elongated rod-shaped liquid crystal molecules. The initial alignment state (the alignment state when no electric field is acting) of the liquid crystal molecules is controlled by the first alignment film 114A and the second alignment film 114B.

[0019] The first alignment film 114A and the second alignment film 114B can have any configuration as long as they have the function of aligning liquid crystal molecules, and can be organic or inorganic materials, but for example, polyimide can be used. The orientation direction can also be horizontal, vertical, or tilt, but this embodiment shows the case where the film is horizontally aligned.

[0020] The orientation of the liquid crystal molecules in the liquid crystal layer 106 is controlled by the patch electrode 104. Since the bias voltage applied to the patch electrode 104 can be controlled for each unit cell 1000, the orientation of the liquid crystal molecules in the liquid crystal layer 106 can also be controlled for each unit cell 1000. The dielectric constant of the liquid crystal layer 106 changes depending on the orientation of the liquid crystal molecules. The scattered waves (sometimes referred to as "reflected waves") from the liquid crystal reflector 100 change in phase depending on the dielectric constant of the liquid crystal layer 106. Therefore, by changing the dielectric constant of the liquid crystal layer 106 for each unit cell 1000, it is possible to create a phase difference within the plane of the liquid crystal reflector 100 and control the direction of propagation of the scattered waves.

[0021] The liquid crystal reflector 100 scatters incident waves that come into contact with the surface on which the counter electrodes 102 are arranged; therefore, the counter electrodes 102 are also called scatterers.

[0022] Although not shown in Figures 2 and 3, the second substrate 134 may be provided with a drive circuit that outputs a selection signal to the selection signal line 110 and a drive circuit that outputs a bias signal to the bias signal line 112. Furthermore, input terminals may be provided for inputting signals and drive power to drive these drive circuits.

[0023] Figures 4 and 5 show details of the unit cell 1000 that constitutes the liquid crystal reflector 100. Figure 4 is a plan view of the unit cell 1000, and Figure 5 is a cross-sectional view between C and D shown in Figure 4. As shown in Figures 4 and 5, the unit cell 1000 is arranged so that the opposing electrode 102, the liquid crystal layer 106, and the patch electrode 104 are superimposed in a plan view.

[0024] The patch electrode 104 used in this embodiment has a shape that is symmetrical with respect to the vertical and horizontal polarization of the incident radio wave. Figure 4 shows an example in which the patch electrode 104 is square. The size (length and width) of the patch electrode 104 is set appropriately according to the frequency of the target radio wave. Note that the shape of the patch electrode 104 is not limited to a square, but may be rectangular or have other geometric shapes.

[0025] The counter electrode 102 is connected to a power supply circuit (not shown). Alternatively, the counter electrode 102 is grounded or connected to grounded wiring.

[0026] The patch electrode 104 is connected to the bias signal line 112 via the switching element 116. Figures 4 and 5 show an example in which the switching element 116 is formed by a transistor. The transistor has a structure in which a semiconductor layer 120, a gate insulating layer 122, and a gate electrode 124 are stacked. An interlayer insulating layer 126 is provided below the gate electrode 124, and the bias signal line 112 is provided below that. The switching element 116 and the bias signal line 112 are covered with a planarization layer 128. The patch electrode 104 is provided below the planarization layer 128. The patch electrode 104 is connected to the input / output terminal (drain) of the switching element (transistor) 116 via a contact hole. In addition, the gate electrode 124 of the switching element (transistor) 116 is connected to the selection signal line 110, and the input / output terminal (source) not connected to the patch electrode 104 is connected to the bias signal line 112.

[0027] The orientation of liquid crystal molecules in the liquid crystal layer 106 is controlled by the patch electrode 104. That is, the orientation of liquid crystal molecules in the liquid crystal layer 106 is controlled by a bias signal applied to the patch electrode 104. The bias signal is a DC voltage signal or a polarity-reversing DC voltage signal in which positive DC voltage and negative DC voltage alternately invert.

[0028] The liquid crystal layer 106 is formed from a liquid crystal material having dielectric anisotropy. For example, the liquid crystal material forming the liquid crystal layer 106 can be any material that exhibits liquid crystalline properties and dielectric anisotropy, and nematic liquid crystals are particularly preferred. The effect in this embodiment does not change whether the dielectric anisotropy of the liquid crystal material is positive or negative. Hereafter, this embodiment will be described using a liquid crystal layer 106 having positive dielectric anisotropy.

[0029] The dielectric constant of the liquid crystal layer 106 changes depending on the orientation of the liquid crystal molecules. The orientation of the liquid crystal molecules is controlled by the patch electrode 104. When the incident wave is scattered by the unit cell 1000, the phase of the scattered wave changes according to the dielectric constant of the liquid crystal layer.

[0030] The frequency bands to which the liquid crystal reflector 100 is applicable are the very high frequency (VHF), ultra-high frequency (UHF), super high frequency (SHF), submillimeter wave (THF), extra high frequency (EHF), and terahertz wave bands. The orientation of the liquid crystal molecules in the liquid crystal layer 106 changes depending on the bias voltage applied to the patch electrode 104, but it hardly follows the frequency of the radio waves incident on the patch electrode 104. Due to this characteristic of the liquid crystal molecules, the dielectric constant of the liquid crystal layer 106 can be changed by the patch electrode 104, while the radio waves are scattered by the counter electrode 102, and the phase of the scattered radio waves can be controlled.

[0031] The first substrate 132 and the second substrate 134 sandwich the liquid crystal layer 106 and are provided for forming wirings and the like, and are formed of a material having flatness such as glass, resin, or a metal plate. At this time, transparency is not a concern. Further, each layer provided on the first substrate 132 and the second substrate 134 is formed using the following materials. The semiconductor layer 120 is provided for forming the switching element 116, and is formed of an oxide semiconductor including a silicon semiconductor such as amorphous silicon or polycrystalline silicon, or a metal oxide such as indium oxide, zinc oxide, or gallium oxide. The gate insulating layer 122 and the interlayer insulating layer 126 are provided for insulating each wiring layer, and thus any material having insulating properties may be used. For example, they may be formed of a silicon oxide film, a silicon nitride film, or a stacked structure thereof. The selection signal line 110 and the gate electrode 124 are provided for transmitting an electrical signal, and a material having conductivity is preferable, and a metal film or the like may be used. For example, it may be composed of molybdenum (Mo), tungsten (W), or an alloy thereof. The bias signal line 112 is provided for transmitting an electrical signal, and a material having conductivity is preferable, and a metal film or the like may be used. For example, it may be composed of a stacked structure of titanium (Ti) / aluminum (Al) / titanium (Ti), or a stacked structure of molybdenum (Mo) / aluminum (Al) / molybdenum (Mo). The planarization layer 128 is formed for planarizing irregularities formed by the switching element or the like. Any material having flatness and insulating properties may be used. For example, an organic material is desirable, and an acrylic resin, an epoxy resin, a polyimide material, or the like may be used. The counter electrode 102 and the patch electrode 104 have a function of conducting a signal for driving the liquid crystal and a function of scattering the input radio wave. Both only need to have conductivity, and a metal film or the like may be used. In particular, a material having a low conductivity is desirable. For example, aluminum, copper, gold, or an alloy using them may be used. Further, in order to reduce the resistance, it is desirable to increase the film thickness compared to the bias signal line and the selection signal line.

[0032] Also, although not shown in FIG. 5, the first substrate 132 and the second substrate 134 are arranged to have a gap therebetween and are bonded together by a sealing material. The sealing material only needs to have a function of bonding the first substrate 132 and the second substrate 134, and is formed of an organic material such as an acrylic resin or an epoxy resin, for example. The liquid crystal layer 106 is enclosed within a region surrounded by the first substrate 132, the second substrate 134, and the sealing material. The gap between the first substrate 132 and the second substrate 134 is approximately 20 μm to 100 μm, and has, for example, a spacing of 40 μm. Although not shown, spacers for maintaining a constant spacing may be provided between the first substrate 132 and the second substrate 134.

[0033] As shown in FIG. 4, the patch electrode 104 is connected to the bias signal line 112 via the switching element 116 so that the potential can be controlled individually, thereby enabling the dielectric constant of the liquid crystal layer 106 to be changed for each unit cell 1000. Thereby, the phase of the scattered wave can be controlled for each unit cell 1000.

[0034] FIG. 6 schematically shows a mode in which the traveling direction of the reflected wave is changed by the first unit cell 1000-1 and the second unit cell 1000-2. A bias signal V1 is applied from the bias signal line 112A to the patch electrode 104A of the first unit cell 1000-1, and a bias signal V2 is applied from the bias signal line 112B to the patch electrode 104B of the second unit cell 1000-2. Here, the voltage levels of the bias signal V1 and the bias signal V2 are different (V1≠V2). The counter electrodes 102 of the first unit cell 1000-1 and the second unit cell 1000-2 are at the same potential, and are set to a common potential, for example.

[0035] Figure 6 schematically illustrates that when radio waves are incident on the first unit cell 1000-1 and the second unit cell 1000-2 with the same phase, different bias signals (V1 ≠ V2) are applied to the first unit cell 1000-1 and the second unit cell 1000-2, resulting in a larger phase change in the scattered wave due to the second unit cell 1000-2 compared to the first unit cell 1000-1. As a result, the phase of the scattered wave R1 scattered by the first unit cell 1000-1 is different from the phase of the scattered wave R2 scattered by the second unit cell 1000-2 (in Figure 6, the phase of scattered wave R2 is ahead of the phase of scattered wave R1), and the apparent direction of propagation of the scattered wave changes obliquely.

[0036] As shown in Figure 6, the liquid crystal reflector 100 can make the phase of the scattered wave different between the first unit cell 1000-1 and the second unit cell 1000-2 relative to the incident wave. Although Figure 6 schematically shows two unit cells 1000, in reality, by individually controlling the unit cells 1000 arranged in a matrix, the direction of propagation of the scattered wave can be controlled to any direction without changing the direction of the liquid crystal reflector 100.

[0037] Figure 7 is a schematic diagram showing the characteristics of reflected radio waves in the liquid crystal reflector 100 in response to incident radio waves. As shown in Figure 7, by changing the dielectric constant of the liquid crystal layer 106 for each unit cell 1000, it is possible to select from three types of reflected radio waves: normal reflection (Figure 7(a)) which uniformly reflects the incident radio waves in a certain direction, focused reflection (Figure 7(b)) which reflects the incident radio waves in a way that focuses them, and divergent reflection (Figure 7(c)) which reflects the incident radio waves in a way that causes them to diverge.

[0038] In Figure 1, the first liquid crystal reflector 100-1, which reflects radio waves toward the second liquid crystal reflector 100-2, may be controlled to allow selection of not only focused reflection, but also normal reflection and focused reflection. Furthermore, the second liquid crystal reflector 100-2, which reflects radio waves toward a desired reception area Rx, may be controlled to allow selection of normal reflection, focused reflection, and divergent reflection according to the requirements of the reception area Rx.

[0039] <Method for Driving the First Liquid Crystal Reflector> The method for driving the first liquid crystal reflector 100-1, which performs focused reflection, will now be described. Figure 8 is a schematic diagram showing the relationship between incident and reflected radio waves in the first liquid crystal reflector 100-1. The first liquid crystal reflector 100-1 is comprised of k (k≧2) unit cells 1000 in order from one end (the left end in Figure 8). The number of unit cells 1000 is set appropriately according to the size of the liquid crystal reflector 100. As shown in Figure 8, when the position FP where the reflected radio waves converge is to the right of the center of the first liquid crystal reflector 100-1, the left side of the first liquid crystal reflector 100-1 is further away from the position FP than the right side, and therefore the reflection angle θ of the reflected radio waves on the left side of the first liquid crystal reflector 100-1 １ This is the reflection angle θ of the reflected radio wave on the right side of the first liquid crystal reflector 100-1. ２ Compared to that, it can be seen that it becomes larger. Conversely, if the position FP where the reflected radio waves converge is to the left of the first liquid crystal reflector 100-1, the reflection angle θ １ The reflection angle θ ２ It becomes smaller compared to [the other one].

[0040] Figure 9 shows the relationship between the position n of the unit cell 1000 (where n is any integer from 1 to k) and the phase P(n) that the unit cell 1000 imparts to the incident radio wave, in the case of Figure 8. As shown in Figure 9, in order to reflect the incident radio wave, as the position of the unit cell 1000 moves away from the left edge, P(n) is increased by a constant rate R1 until it reaches 2π. When P(n) reaches 2π, P(n) returns to 0 (in Figure 9, n=4), and as the unit cell 1000 moves further away from the left edge, P(n) is increased by a constant rate R2 that is less than R1 until it reaches 2π. The same process is then carried out for all unit cells 1000. By decreasing the rate R of increase in the phase P(n) imparted to the incident radio wave by unit cell 1000 in response to an increase in the position n of unit cell 1000 (distance from the left edge of unit cell 1000), every 2π period of P(n), focused reflection can be performed at the first liquid crystal reflector 100-1. Conversely, if the position FP where the reflected radio waves are focused is to the left of the first liquid crystal reflector 100-1, the rate R of increase in the phase P(n) imparted to the incident radio wave by unit cell 1000 in response to an increase in the position n of unit cell 1000 is increased every 2π period of P(n). If the maximum phase change due to the liquid crystal is less than or equal to 2π, an approximate value may be used. For example, suppose the maximum phase modulation amount of the liquid crystal is 6 / 4π. If it is necessary to set 7 / 4π, but this is not possible with liquid crystal phase modulation, it may be set to 6 / 4π or 0.

[0041] The method for determining the phase P(n) imparted to the incident radio wave by the unit cell 1000 will be explained. Figure 10 is a schematic diagram showing the relationship between the first liquid crystal reflector 100-1, the wave source Tx, and the position FP where the reflected radio waves converge. As shown in Figure 10, the first liquid crystal reflector 100-1 has k (k≧2) unit cells 1000 that reflect the incident radio waves, starting from one end (the left end in Figure 10). The second liquid crystal reflector 100-2 can be positioned closer to the first liquid crystal reflector 100-1 than the position FP where the reflected radio waves converge.

[0042] Let the wavelength of the radio wave transmitted from the wave source Tx be λ, and the distance from the wave source Tx to the center of the n-th (n is an arbitrary integer from 1 to k) unit cell 1000 from the left end be l ｉ (n), and the distance from the center of the unit cell 1000 to the position FP where the reflected radio wave converges be l ｒ (n). When the phase given to the incident radio wave in the n-th unit cell 1000 from one end (the left end in FIG. 10) is P(n), the control unit drives the unit cell 1000 so that P(n) satisfies the following formula (1). Thereby, the first liquid crystal reflector 100-1 can perform convergent reflection. In formula (1), λ, l ｉ (n) and l ｒ (n) can use, for example, millimeters as the unit. 2π / λ(l ｉ (m) + l ｒ (m)) + P(m) = 2π / λ(l ｉ (n) + l ｒ (n)) + P(n) ··· (1) In formula (1), m is an integer among 1 to k, and P(m) is a value among 0 to 2π

[0043] For example, in formula (1), in the first unit cell 1000 from the left (m = 1), when a phase of π / 4 is given to the incident radio wave, for example, P(2) in the second unit cell 1000 from the left is 2π / λ(l ｉ (1) + l ｒ (1)) + π / 4 = 2π / λ(l ｉ (2) + l ｒ (2)) + P(2), and for example, P(3) in the third unit cell 1000 from the left is 2π / λ(l ｉ (1) + l ｒ (1)) + π / 4 = 2π / λ(l ｉ (3) + l ｒ (3)) + P(3), and thereafter, P(n) can be obtained similarly for all unit cells 1000

[0044] In the liquid crystal reflector 100, in order to make the incident radio waves (reflected radio waves) uniform, if the length of one side of the liquid crystal reflector 100 is D, then the distance R from the wave source Tx to the liquid crystal reflector 100 (the distance R from the liquid crystal reflector 100 to the receiving area Rx) must satisfy the far-field condition (R ≥ 2D). ２ The condition ( / λ) must be satisfied. Note that, in the far-field conditions, millimeters can be used as the units for R, D, and λ.

[0045] In this embodiment, since the first liquid crystal reflector 100-1 does not need to satisfy the far-field condition, the first liquid crystal reflector 100-1 is in all unit cells 1000, l ｉ (n) satisfies the following equation (2), l ｒ (n) can be arranged such that it satisfies the following equation (3): l ｉ (n) < 2D ２ / λ...(2) l ｒ (n) < 2D ２ / λ...(3)

[0046] Any other effects and advantages brought about by the embodiments described herein that are obvious from this specification or that can be appropriately conceived by those skilled in the art are naturally considered to be brought about by the present invention.

[0047] 10 Radio wave reflector 100 Liquid crystal reflector 1000 Unit cell Tx Wave source Rx Receiving area FP Position where reflected radio waves converge

Claims

1. A method for driving a radio wave reflecting device, which includes a first liquid crystal reflector and a second liquid crystal reflector, for reflecting radio waves incident on the first liquid crystal reflector toward the second liquid crystal reflector, comprising driving the first liquid crystal reflector so that the phase of the incident radio waves is changed so that the radio waves reflected by the first liquid crystal reflector are focused by the second liquid crystal reflector.

2. The first liquid crystal reflector has k unit cells that reflect the incident radio waves in order from one end, and the first liquid crystal reflector is driven by the wavelength of the radio waves being λ and the distance from the wave source emitting the radio waves to the center of the nth unit cell from the one end being l ｉ (n) l is the distance from the center of the unit cell to the position where the radio waves reflected by the first liquid crystal reflector converge. ｒ (n) When the phase given to the radio wave incident on the unit cell is P(n), the unit cell is driven such that P(n) satisfies the following equation (1), the method for driving a radio wave reflector according to claim 1. 2π / λ(l ｉ (m) + l ｒ (m))+P(m)=2π / λ(l ｉ (n) + l ｒ (n) + P(n) ... (1) In equation (1), m is an integer between 1 and k, and P(m) is a value between 0 and 2π.

3. When the length of one side of the first liquid crystal reflector is D, l ｉ (n) satisfies the following formula (2), and l ｒ (n) satisfies the following formula (3), and the first liquid crystal reflector is arranged so that, the driving method of the radio wave reflection device according to claim 2. l ｉ (n) < 2D ２ / λ... (2) l ｒ (n) < 2D ２ / λ... (3) 4. The method for driving a radio wave reflector according to claim 3, wherein the size of the second liquid crystal reflector is smaller than the size of the first liquid crystal reflector.

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