Radio wave reflector

Abstract

The purpose of the present embodiment is to provide a radio wave-reflecting plate in which permittivity changes stay within a certain range even if there are changes in the outside air temperature. The radio wave-reflecting plate of the present embodiment comprises: a first substrate having a first base material and a plurality of patch electrodes arranged in a matrix configuration at equal intervals along each of a first direction and a second direction; a second substrate having a second base material and a common electrode that faces the plurality of patch electrodes; a liquid crystal layer sandwiched between the first substrate and second substrate; a heat exchanger provided in contact with the second substrate; a temperature sensor that detects the temperature of the liquid crystal layer; and a temperature control unit that controls the heat exchanger on the basis of the temperature detected by the temperature sensor. Incident waves are incident on an incident surface of the first substrate, and the heat exchanger is provided on the surface on the reverse side from the incident surface.

Description

Technical Field

[0001] Embodiments of the present invention relate to a radio wave reflector.

Background Art

[0002] As a phase shifter used in a phased array antenna capable of electrically controlling directivity, a phase shifter using liquid crystal has been developed. In a phased array antenna, a plurality of antenna elements to which high-frequency signals are transmitted from corresponding phase shifters are arranged in one dimension (or two dimensions). In the phased array antenna as described above, it is necessary to adjust the dielectric constant of the liquid crystal so that the phase difference of the high-frequency signals input to adjacent antenna elements becomes constant.

[0003] In addition, studies have been made on a radio wave reflector that can control the reflection direction of radio waves using liquid crystal in the same manner as a phased array antenna. In this reflector, reflection control units having reflection electrodes are arranged in one dimension (or two dimensions). Also in the reflector, it is necessary to adjust the dielectric constant of the liquid crystal so that the phase difference of the radio waves to be reflected becomes constant between adjacent reflection control units.

[0004] The radio wave reflector is also assumed to be installed outdoors. However, the temperature of the liquid crystal changes due to temperature changes outdoors, and the dielectric constant may deviate from the desired value.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] This embodiment provides a radio wave reflector in which the change in dielectric constant remains within a certain range even when there is a change in the outside air temperature.

Means for Solving the Problems

[0007] A radio wave reflector according to one embodiment includes a first substrate having a first base material and a plurality of patch electrodes arranged in a matrix at equal intervals along the first direction and the second direction respectively, a second substrate having a second base material and a common electrode facing the plurality of patch electrodes, a liquid crystal layer sandwiched between the first substrate and the second substrate, a heat exchanger provided in contact with the second substrate, a temperature sensor for detecting the temperature of the liquid crystal layer, and a temperature control unit for controlling the heat exchanger based on the temperature detected by the temperature sensor. An incident wave is incident on the incident surface of the first substrate, and the heat exchanger is provided on the surface opposite to the incident surface.

Advantages of the Invention

[0008] According to this embodiment, it is possible to provide a radio wave reflector in which the change in dielectric constant remains within a certain range even when there is a change in the outside air temperature.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0010] Hereinafter, each embodiment of the present invention will be described with reference to the drawings. Note that the disclosure is merely an example, and for those that can be easily conceived by those skilled in the art with appropriate modifications while maintaining the gist of the invention, they are naturally included in the scope of the present invention. Also, for the purpose of making the description clearer, the drawings may schematically represent the width, thickness, shape, etc. of each part compared to the actual aspect, but this is merely an example and does not limit the interpretation of the present invention. Further, in this specification and each figure, elements similar to those described above with respect to the previously shown figures may be denoted by the same reference numerals, and detailed descriptions may be omitted as appropriate. Hereinafter, a radio wave reflector according to an embodiment will be described in detail with reference to the drawings.

[0011] In the present embodiment, the first direction X, the second direction Y, and the third direction Z are orthogonal to each other, but they may intersect at an angle other than 90 degrees. The direction toward the tip of the arrow of the third direction Z is defined as up or upward, and the direction opposite to the direction toward the tip of the arrow of the third direction Z is defined as down or downward.

[0012] Also, when referring to "the second member above the first member" and "the second member below the first member", the second member may be in contact with the first member or may be located away from the first member. In the latter case, a third member may be interposed between the first member and the second member. On the other hand, when referring to "the second member on the first member" and "the second member under the first member", the second member is in contact with the first member.

[0013] Also, assume that there is an observation position for observing the radio wave reflector on the tip side of the arrow in the third direction Z. Looking from this observation position toward the X-Y plane defined by the first direction X and the second direction Y is referred to as a plan view. Looking at the cross section of the radio wave reflector in the X-Z plane defined by the first direction X and the third direction Z, or in the Y-Z plane defined by the second direction Y and the third direction Z is referred to as a cross-sectional view.

[0014] FIG. 1 is a cross-sectional view showing the radio wave reflector of the present embodiment. The radio wave reflector RE can reflect radio waves and functions as a relay device for radio waves.

[0015] As shown in FIG. 1, the radio wave reflector RE includes a first substrate SUB1, a second substrate SUB2, and a liquid crystal layer LC. The first substrate SUB1 has an electrically insulating base material BA1, a plurality of patch electrodes PE, and an alignment film AL1. The base material BA1 is formed in a flat plate shape and extends along the X-Y plane including the first direction X and the second direction Y that are orthogonal to each other. The alignment film AL1 covers the plurality of patch electrodes PE.

[0016] The second substrate SUB2 is disposed to face the first substrate SUB1 with a predetermined gap therebetween. The second substrate SUB2 has an electrically insulating base material BA2, a common electrode CE, and an alignment film AL2. The base material BA2 is formed in a flat plate shape and extends along the X-Y plane. The common electrode CE faces the plurality of patch electrodes PE in a direction parallel to the third direction Z that is orthogonal to each of the first direction X and the second direction Y. The alignment film AL2 covers the common electrode CE. In the present embodiment, the alignment film AL1 and the alignment film AL2 are each a horizontal alignment film.

[0017] The first substrate SUB1 and the second substrate SUB2 are joined by a sealing material SE disposed at their respective peripheral portions. The liquid crystal layer LC is provided in a space surrounded by the first substrate SUB1, the second substrate SUB2, and the sealing material SE. The liquid crystal layer LC is held between the first substrate SUB1 and the second substrate SUB2. The liquid crystal layer LC faces the plurality of patch electrodes PE on one hand and the common electrode CE on the other hand.

[0018] Here, let the thickness (cell gap) of the liquid crystal layer LC be dl. The thickness dl is larger than the thickness of the liquid crystal layer of a normal liquid crystal display panel and is about 20 μm to 70 μm. In this embodiment, the thickness dl is 50 μm. However, if the reflection phase of the radio wave can be changed with a sufficient width, the thickness dl may be less than 50 μm. Or, in order to increase the reflection angle of the radio wave, the thickness dl may exceed 50 μm. The liquid crystal material used for the liquid crystal layer LC of the radio wave reflector RE is different from the liquid crystal material used for a normal liquid crystal display panel. Note that the reflection phase of the radio wave described above will be described later.

[0019] A common voltage is applied to the common electrode CE, and the potential of the common electrode CE is fixed. In this embodiment, the common voltage is the ground voltage, for example, 0V. A voltage is also applied to the patch electrode PE. In this embodiment, the patch electrode PE is driven by alternating current. The liquid crystal layer LC is driven by a so-called vertical electric field. When the voltage applied between the patch electrode PE and the common electrode CE acts on the liquid crystal layer LC, the dielectric constant of the liquid crystal layer LC changes.

[0020] When the dielectric constant of the liquid crystal layer LC changes, the propagation speed of the radio wave in the liquid crystal layer LC also changes. Therefore, by adjusting the voltage applied to the liquid crystal layer LC, the reflection phase of the radio wave can be adjusted. Thereby, the reflection direction of the radio wave can be adjusted.

[0021] In this embodiment, the absolute value of the voltage applied to the liquid crystal layer LC is 10V or less. This is because the dielectric constant of the liquid crystal layer LC reaches a saturated state at 10V. However, the absolute value of the voltage applied to the liquid crystal layer LC may exceed 10V. For example, when an improvement in the response speed of the liquid crystal is required, a voltage exceeding 10V may be applied to the liquid crystal layer LC at the initial stage of liquid crystal driving, and then a voltage of 10V or less may be applied to the liquid crystal layer LC.

[0022] The first substrate SUB1 has an incident surface Sa on the side opposite to the side facing the second substrate SUB2. In FIG. 1, the incident wave w1 is a radio wave incident on the radio wave reflector RE, and the reflected wave w2 is a radio wave reflected by the radio wave reflector RE.

[0023] FIG. 2 is a plan view showing the radio wave reflector shown in FIG. 1. In the radio wave reflector RE shown in FIG. 2, a plurality of patch electrodes PE are arranged in a matrix at intervals along each of the first direction X and the second direction Y. In the X-Y plane, the plurality of patch electrodes PE have the same shape and the same size.

[0024] The plurality of patch electrodes PE are arranged at equal intervals along the first direction X and are arranged at equal intervals along the second direction Y. The plurality of patch electrodes PE are included in a plurality of patch electrode groups GP extending along the second direction Y and arranged along the first direction X. In FIG. 2, the plurality of patch electrode groups GP have, for example, from the first patch electrode group GP1 to the eighth patch electrode group GP8.

[0025] The first patch electrode group GP1 has a plurality of first patch electrodes PE1, the second patch electrode group GP2 has a plurality of second patch electrodes PE2, the third patch electrode group GP3 has a plurality of third patch electrodes PE3, the fourth patch electrode group GP4 has a plurality of fourth patch electrodes PE4, the fifth patch electrode group GP5 has a plurality of fifth patch electrodes PE5, the sixth patch electrode group GP6 has a plurality of sixth patch electrodes PE6, the seventh patch electrode group GP7 has a plurality of seventh patch electrodes PE7, and the eighth patch electrode group GP8 has a plurality of eighth patch electrodes PE8. For example, the second patch electrode PE2 is located between the first patch electrode PE1 and the third patch electrode PE3 in the direction along the first direction X.

[0026] Each patch electrode group GP includes a plurality of patch electrodes PE arranged along the second direction Y and electrically connected to each other. In the present embodiment, the plurality of patch electrodes PE of each patch electrode group GP are electrically connected by connection wirings CL. The first substrate SUB1 has a plurality of connection wirings CL extending along the second direction Y and arranged along the first direction X. The connection wirings CL extend to a region of the first substrate SUB1 that does not face the second substrate SUB2. Note that, different from the present embodiment, the plurality of connection wirings CL may be connected to the plurality of patch electrodes PE in a one-to-one manner.

[0027] In the present embodiment, the plurality of patch electrodes PE arranged along the second direction Y and the connection wirings CL are integrally formed of the same conductor. Note that, the plurality of patch electrodes PE and the connection wirings CL may be formed of different conductors. The patch electrodes PE, the connection wirings CL, and the common electrode CE are formed of a metal or a conductor equivalent to a metal. For example, the patch electrodes PE, the connection wirings CL, and the common electrode CE may be formed of a transparent conductive material such as indium tin oxide (ITO). The connection wirings CL may be connected to pads of an outer lead bonding (OLB) (not shown).

[0028] The connection wirings CL are thin lines, and the width of the connection wirings CL is sufficiently smaller than a length Px described later. The width of the connection wirings CL is several μm to several tens of μm, which is on the order of μm. Note that, if the width of the connection wirings CL is too large, the patch electrode group GP behaves as a single rectangular electrode surface, and the sensitivity to the desired frequency components of the radio waves changes, which is not desirable.

[0029] The sealing material SE is disposed at the peripheral edge of the region where the first substrate SUB1 and the second substrate SUB2 face each other.

[0030] FIG. 2 shows an example in which eight patch electrodes PE are arranged in the direction along the first direction X and the direction along the second direction Y, but the present embodiment is not limited thereto. The number of patch electrodes PE can be variously deformed. For example, 100 patch electrodes PE may be arranged in the direction along the first direction X, and a plurality (for example, 100) may be arranged in the direction along the second direction Y. The length of the radio wave reflector RE (first substrate SUB1) in the direction along the first direction X is, for example, 40 cm or more and 80 cm or less.

[0031] FIG. 3 is an enlarged plan view showing the patch electrode. As shown in FIG. 3, the patch electrode PE has a square shape. The shape of the patch electrode PE is not particularly limited, but a square or a perfect circle is desirable. Paying attention to the outer shape of the patch electrode PE, a shape with an aspect ratio of 1:1 in the vertical and horizontal directions is desirable. This is because a 90° rotational symmetry structure is desirable in order to correspond to horizontal polarization waves and vertical polarization waves.

[0032] The patch electrode PE has a length Px in the direction along the first direction X and a length Py in the direction along the second direction Y. It is desirable to adjust the lengths Px and Py according to the frequency band of the incident wave w1. Next, the desirable relationship between the frequency band of the incident wave w1, the lengths Px and Py, will be exemplified.

[0033] 2.4 GHz: Px = Py = 35 mm 5.0 GHz: Px = Py = 16.8 mm 28 GHz: Px = Py = 3.0 mm

[0034] FIG. 4 is an enlarged cross-sectional view showing a part of the radio wave reflector. As shown in FIG. 4, the thickness dl (cell gap) of the liquid crystal layer LC is held by a plurality of spacers SS. In the present embodiment, the spacer SS is a columnar spacer, is formed on the second substrate SUB2, and protrudes toward the first substrate SUB1 side.

[0035] The width of the spacer SS is 10 μm or more and 20 μm or less. While the lengths Px and Py of the patch electrode PE are on the order of mm, the width of the spacer SS is on the order of μm. Therefore, it is necessary to have the spacer SS present in the region facing the patch electrode PE. Also, among the regions facing the patch electrode PE, the proportion of the region where a plurality of spacers SS are present is about 1%. Therefore, even if the spacer SS is present in the above region, the influence of the spacer SS on the reflected wave w2 is slight. Note that the spacer SS may be formed on the first substrate SUB1 and protrude toward the second substrate SUB2 side. Or, the spacer SS may be a spherical spacer.

[0036] The radio wave reflector RE includes a plurality of reflection control units RH. Each reflection control unit RH has one patch electrode PE among the plurality of patch electrodes PE, a portion of the common electrode CE that faces the one patch electrode PE, and a region of the liquid crystal layer LC that faces the one patch electrode PE. Each reflection control unit RH functions to adjust the phase of the radio wave (incident wave w1) incident from the incident surface Sa side according to the voltage applied to the patch electrode PE, and reflect the radio wave to the incident surface Sa side to obtain a reflected wave w2. In each reflection control unit RH, the reflected wave w2 is a combined wave of the radio wave reflected by the patch electrode PE and the radio wave reflected by the common electrode CE.

[0037] In the direction along the first direction X, the patch electrodes PE are arranged at equal intervals. Let the length (pitch) between adjacent patch electrodes PE be dk. The length dk corresponds to the distance from the geometric center of one patch electrode PE to the geometric center of the adjacent patch electrode PE. In the present embodiment, the reflected wave w2 will be described as being in-phase in the first reflection direction d1. In the X-Z plane of FIG. 4, the first reflection direction d1 is a direction that forms a first angle θ1 with the third direction Z. The first reflection direction d1 is parallel to the X-Z plane. θ1a in FIG. 4 is equal to θ1 (θ1 = θ1a).

[0038] In order for the radio waves reflected by the plurality of reflection control units RH to have the same phase in the first reflection direction d1, it is only necessary that the phases of the radio waves are the same on the straight two-dot chain line. For example, the phase of the reflected wave w2 at the point Q1b and the phase of the reflected wave w2 at the point Q2a only need to be the same. The physical straight-line distance from the point Q1a to the point Q1b of the first patch electrode PE1 is dk×sinθ1. Therefore, when paying attention to the first reflection control unit RH1 and the second reflection control unit RH2, the phase of the reflected wave w2 from the second reflection control unit RH2 may be delayed by a phase amount δ1 from the phase of the reflected wave w2 from the first reflection control unit RH1. Here, the phase amount δ1 is expressed by the following formula. δ1 = dk×sinθ1×2π / λ

[0039] FIG. 5 is a timing chart showing changes in the voltage applied to the patch electrodes for each period in the method of driving the radio wave reflector according to the present embodiment. In FIG. 5, the first period Pd1 to the fifth period Pd5 are shown during the driving period of the radio wave reflector RE.

[0040] As shown in FIGS. 4 and 5, when the driving of the radio wave reflector RE is started, in the first period Pd1, a voltage V is applied to the plurality of patch electrodes PE so that the radio waves reflected by the plurality of reflection control units RH are in the same phase in the first reflection direction d1. For example, a first voltage V1 is applied to the first patch electrode PE1, a second voltage V2 is applied to the second patch electrode PE2, and a third voltage V3 is applied to the third patch electrode PE3.

[0041] In the second period Pd2 following the first period Pd1, a voltage is applied to the plurality of patch electrodes PE so that the radio waves reflected by the plurality of reflection control units RH are kept in the same phase in the first reflection direction d1. For example, a second voltage V2 is applied to the first patch electrode PE1, a third voltage V3 is applied to the second patch electrode, and a fourth voltage V4 is applied to the third patch electrode PE3. In each period Pd, the same voltage is applied to the plurality of patch electrodes PE of each patch electrode group GP via the connection wiring CL.

[0042] In each of the first period Pd1 and the second period Pd2, when the potential of the common electrode CE is used as a reference, the polarity of the voltage applied to each patch electrode PE is periodically reversed. For example, the patch electrode PE is driven at a driving frequency of 60 Hz. Since the patch electrode PE is driven by alternating current, a fixed voltage is not applied to the liquid crystal layer LC for a long time. Since the occurrence of image sticking can be suppressed, the deviation of the direction of the reflected wave w2 with respect to the first reflection direction d1 can be suppressed.

[0043] Furthermore, in the present embodiment, in each patch electrode PE, the absolute value of the voltage applied in the second period Pd2 is different from the absolute value of the voltage applied in the first period Pd1. Since the occurrence of image sticking can be sufficiently suppressed, the deviation of the direction of the reflected wave w2 with respect to the first reflection direction d1 can be suppressed.

[0044] Even when the period Pd changes to another period Pd, the phase amount δ1 between the radio wave reflected in the first reflection direction d1 by one reflection control unit RH and the radio wave reflected in the first reflection direction d1 by the adjacent reflection control unit RH is maintained. In the present embodiment, the phase amount δ1 is 60°.

[0045] In the example shown in FIG. 5, the sixth voltage V6 is applied to the sixth patch electrode PE6 in the first period Pd1. A phase difference of 300° is provided between the radio wave reflected in the first reflection direction d1 by the first reflection control unit RH1 and the radio wave reflected in the first reflection direction d1 by the sixth reflection control unit having the sixth patch electrode PE6.

[0046] In order to provide a phase difference of 360° between the radio wave reflected in the first reflection direction d1 by the first reflection control unit RH1 and the radio wave reflected in the first reflection direction d1 by the seventh reflection control unit having the seventh patch electrode PE7, a seventh voltage may be applied to the seventh patch electrode PE7 in the first period Pd1. However, in the present embodiment, the first voltage V1 is applied to the seventh patch electrode PE7 in the first period Pd1. By the periodic voltage application pattern, a large number of patch electrodes PE can be driven while suppressing the types of the voltage V.

[0047] Consider the case where the above-described radio wave reflector RE is installed outdoors. The dielectric constant of the liquid crystal layer LC provided in the radio wave reflector RE depends on temperature. The dielectric constant of the liquid crystal depends on temperature even in a high frequency band, for example, the above-mentioned 28 GHz. The absolute value of the dielectric constant is important for the phase control of the radio wave reflector RE. Due to the change in the dielectric constant caused by temperature change, there is a possibility of generating an error in phase modulation.

[0048] The liquid crystal of the present embodiment has dielectric anisotropy, and the dielectric constant of the liquid crystal below the phase transition temperature is the dielectric constant ε⊥ in the direction perpendicular to the liquid crystal director and the dielectric constant ε / / in the parallel direction. Above the phase transition temperature, the liquid crystal exhibits isotropy and has only a single dielectric constant. Near the phase transition temperature, the change in the dielectric constant of the liquid crystal becomes steep. On the other hand, in the case of a temperature far from the phase transition temperature, the change in the dielectric constant of the liquid crystal is gentle.

[0049] As described above, for the phase control of the radio wave reflector RE, the absolute value ε (=|ε / / - ε⊥|) of the difference between the dielectric constants ε⊥ and ε / / is important. In the phase control of the radio wave reflector RE, it is more preferable that ε⊥, ε / / , and Δη are constant.

[0050] When the radio wave reflector RE is installed outdoors, due to the rise in the outside air temperature, there is a possibility that the phase transition temperature is exceeded and the liquid crystal transitions to isotropy. Also, even if the phase transition temperature is not exceeded, the change in the dielectric constant becomes steep near the phase transition temperature, and there is a possibility that the error in phase modulation increases. When the outside air temperature drops, as the temperature of the liquid crystal decreases, the viscosity of the liquid crystal increases, and there is also a possibility that the quality of the radio wave reflector RE deteriorates.

[0051] As described above, the liquid crystal has temperature dependence in dielectric anisotropy. The radio wave reflector of the present embodiment utilizes dielectric anisotropy and designs the dielectric constants ε⊥ and ε / / to be optimal values. However, if the dielectric constant deviates significantly from the optimal value due to the outside air temperature, there is a possibility that the radio wave reflector of the present embodiment cannot be driven optimally. Therefore, it is necessary to maintain the radio wave reflector of the present embodiment at an optimal temperature so that it does not deviate significantly from the dielectric anisotropy at the time of design.

[0052] Therefore, in this embodiment, a heat exchanger and a temperature sensor are provided on the radio wave reflector, and by preventing the temperature change of the radio wave reflector, the absolute value of the dielectric constant is controlled. Thereby, the error of the phase modulation in the radio wave reflector can be suppressed. In the radio wave reflector of this embodiment, it is possible to perform optimal driving based on the dielectric anisotropy at the time of design.

[0053] FIG. 6 is a perspective view of the radio wave reflector of this embodiment. The radio wave reflector REA shown in FIG. 6 includes the radio wave reflector RE described in FIGS. 1 to 5, a heat exchanger PT, and a temperature sensor SR. The heat exchanger PT is, for example, a Peltier element. The Peltier element is an element that can control one side surface to a heat generation state or a heat absorption state depending on the direction of the direct current flowing through it.

[0054] When the radio wave reflector RE becomes high temperature due to the outside air temperature, the radio wave reflector RE can be cooled by the Peltier element. Conversely, when the radio wave reflector RE becomes low temperature, the radio wave reflector RE can be heated by the Peltier element. However, the heat exchanger PT is not limited to the Peltier element, and other heat exchangers may be used. As another heat exchanger, for example, a heat exchanger having a cooling function and a heating function by air cooling or water cooling may be used. Although not shown in FIG. 6, a heat dissipation plate may be provided in contact with the heat exchanger PT.

[0055] The temperature sensor SR detects the temperature of the radio wave reflector RE, particularly the liquid crystal layer LC. Based on the detected temperature, the heat exchanger PT is controlled. In the radio wave reflector REA shown in FIG. 6, the temperature sensor SR is provided outside the radio wave reflector RE, but may be built in the radio wave reflector RE. The temperature sensor SR is preferably provided at a position closer to the liquid crystal layer LC. When the temperature sensor SR is provided outside the radio wave reflector RE, it may be provided in contact with the first substrate SUB1 or the second substrate SUB2.

[0056] FIG. 7 is a diagram for explaining the radio wave reflector of the present embodiment. The radio wave reflector REA shown in FIG. 7 includes a radio wave reflector RE, a temperature sensor SR, a heat exchanger PT, a temperature control unit TC, a drive circuit DRV, and a control unit CTL. The radio wave reflector RE has the same configuration as described above, but only a part of the components are shown in FIG. 7 for easy viewing of the drawing. The temperature sensor SR and the heat exchanger PT are the same as those in FIG. 6.

[0057] The temperature control unit TC controls the heat exchanger PT based on the temperature of the radio wave reflector RE detected by the temperature sensor SR. The drive circuit DRV drives the patch electrode PE and the common electrode CE. The control unit CTL controls the drive circuit DRV and the temperature control unit CT based on an external input.

[0058] When the outside air temperature rises in the environment where the radio wave reflector REA is placed, the temperature of the liquid crystal layer LC rises, and when the temperature sensor SR detects it, especially near the phase transition temperature, the temperature control unit CT outputs a control signal to the heat exchanger PT. The heat exchanger PT cools the radio wave reflector RE based on the control signal. By cooling the radio wave reflector RE, the liquid crystal layer LC can be maintained at a temperature below the phase transition.

[0059] Near the phase transition temperature, the dielectric constant of the liquid crystal layer LC changes steeply, so fine temperature control is desirable. When the temperature of the liquid crystal layer LC is away from the phase transition temperature, the dielectric constant of the liquid crystal layer LC changes gently, so finer temperature control is not necessary than in the above case.

[0060] When the temperature of the liquid crystal layer LC is away from the phase transition temperature (for example, 50 ° C or higher), for example, the temperature control of the heat exchanger PT may be performed so that the liquid crystal layer LC becomes about ± 30 ° C, preferably about ± 20 ° C. Also, the temperature control of the heat exchanger PT may be performed so that Δε, which is the change in the dielectric constant of the liquid crystal layer LC, is within ± 20%, preferably within ± 10%.

[0061] When the outside air temperature drops and the temperature of the liquid crystal layer LC drops in an environment where the radio wave reflector REA is placed, the temperature control unit CT outputs a control signal to the heat exchanger PT. Based on the control signal, the heat exchanger PT heats the radio wave reflector RE. Thereby, the temperature of the liquid crystal layer LC can be raised, and an increase in the viscosity of the liquid crystal can be prevented.

[0062] In FIGS. 6 and 7, the heat exchanger PT is provided on the surface of the radio wave reflector RE opposite to the incident surface Sa (also referred to as the reflection surface) of the incident wave w1. Thereby, the incidence of the incident wave w1 on the radio wave reflector RE and the reflection of the reflected wave w2 are not inhibited. Specifically, the heat exchanger PT is provided in contact with the base material BA2 of the second substrate SUB2. In this embodiment, the base materials BA1 and BA2 are also referred to as the first base material and the second base material, respectively.

[0063] The temperature sensor SR may be provided on the incident surface Sa or on the surface opposite to the incident surface Sa. Specifically, the heat exchanger PT may be provided in contact with the base material BA1 of the first substrate SUB1.

[0064] According to this embodiment, even when there is a change in the outside air temperature, it is possible to obtain a radio wave reflector in which the dielectric constant change is within a certain range.

[0065] <Configuration Example 1> FIG. 8 is a plan view showing another configuration example of the radio wave reflector in the embodiment. In the configuration example shown in FIG. 8, it is different from the configuration example shown in FIG. 2 in that the patch electrodes are driven by an active matrix.

[0066] FIG. 8 is a plan view of the radio wave reflector RE according to this configuration example. As shown in FIG. 8, the first substrate SUB1 has a plurality of signal lines SL, a plurality of control lines GL, a plurality of switching elements SW, a drive circuit DR, and a plurality of lead lines LE instead of the connection wiring CL.

[0067] The plurality of signal lines SL extend along the second direction Y and are arranged in the direction along the first direction X. The plurality of control lines GL extend along the first direction X and are arranged in the direction along the second direction Y. The plurality of control lines GL are connected to the driving circuit DR. The switching element SW is provided near the intersection of one signal line SL and one control line GL. The plurality of lead lines LE are connected to the driving circuit DR. The signal line SL and the lead line LE may each be connected to a pad of an outer lead bonding (OLB).

[0068] FIG. 9 is a partially enlarged cross-sectional view of the radio wave reflector. As shown in FIG. 9, the control line GL is provided on the base material BA1 of the radio wave reflector RE. The control line GL has a gate electrode GE. An insulating layer GI is formed on the base material BA1 and the control line GL. A semiconductor layer SMC is provided on the insulating layer GI. The semiconductor layer SMC overlaps the gate electrode GE and has a first region R1 and a second region R2. In the first region R1 and the second region R2, one is a source region and the other is a drain region.

[0069] The gate electrode GE, the semiconductor layer SMC, etc. constitute the switching element SW as a thin film transistor (TFT). The switching element SW may be a bottom gate type thin film transistor or a top gate type thin film transistor.

[0070] An insulating layer ILI1 is formed on the insulating layer GI and the semiconductor layer SMC. On the insulating layer ILI1, a connection electrode RY and a signal line SL are provided. Although not shown, the signal line SL is connected to the first region R1 of the semiconductor layer SMC. The connection electrode RY is connected to the second region R2 of the semiconductor layer SMC through a contact hole formed in the insulating layer ILI1.

[0071] An insulating layer ILI2 is formed over the insulating layer ILI1, the signal line SL, and the connection electrode RY. A patch electrode PE is formed over the insulating layer ILI2. The patch electrode PE is connected to the connection electrode RY through a contact hole formed in the insulating layer ILI2. An alignment film AL1 is formed over the insulating layer ILI2 and the patch electrode PE.

[0072] As shown in FIGS. 8 and 9, a plurality of patch electrodes PE can be individually driven by active matrix driving. Therefore, the plurality of patch electrodes PE can be driven independently. For example, the direction of the reflected wave w2 reflected by the radio wave reflector RE can be made parallel to the Y-Z plane. This configuration example has the same effects as those of the above-described embodiment.

[0073] Although the embodiments of the present invention have been described, the embodiments are presented as examples and are not intended to limit the scope of the invention. The novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. The embodiments and their modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and its equivalent scope.

Description of Reference Numerals

[0074] CE... Common electrode, CL... Connection wiring, CT... Temperature control unit, GP... Patch electrode group, LC... Liquid crystal layer, PE... Patch electrode, PT... Heat exchanger, RE... Radio wave reflector, REA... Radio wave reflector, SS... Spacer, SUB1... First substrate, SUB2... Second substrate, Sa... Incident surface, TC... Temperature control unit, w1... Incident wave, w2... Reflected wave.

Claims

1. A first substrate having a first base material and a plurality of patch electrodes arranged in a matrix at equal intervals along the first direction and the second direction respectively; A second substrate having a second base material and a common electrode facing the plurality of patch electrodes; A liquid crystal layer sandwiched between the first substrate and the second substrate; A heat exchanger provided in contact with the second substrate; A temperature sensor for detecting the temperature of the liquid crystal layer; A temperature control unit for controlling the heat exchanger based on the temperature detected by the temperature sensor; Comprising; The incident wave is incident on the incident surface of the first substrate, The heat exchanger is a radio wave reflector provided on the surface opposite to the incident surface.

2. The radio wave reflector according to claim 1, wherein the heat exchanger is a Peltier element.

3. Further comprising a plurality of connection wirings arranged along the first direction and extending along the second direction, The plurality of patch electrodes extend along the second direction and form a plurality of patch electrode groups arranged along the first direction, The plurality of patch electrodes in each patch electrode group are electrically connected by the connection wirings. The radio wave reflector according to claim 1.

4. The radio wave reflector according to claim 1, wherein each of the plurality of patch electrodes is connected to a switching element.

5. The radio wave reflector according to claim 1, wherein the temperature sensor is provided in contact with the first substrate or the second substrate.

6. The radio wave reflector according to claim 1, wherein the temperature sensor is built into the radio wave reflector.

7. The radio wave reflector according to claim 1, wherein the temperature control unit controls the heat exchanger so that the temperature of the liquid crystal layer becomes ±30°C.

8. The radio wave reflector according to claim 1, wherein the temperature control unit controls the heat exchanger so that the temperature of the liquid crystal layer becomes ±20°C.

9. The radio wave reflector according to claim 1, wherein the temperature control unit controls the heat exchanger so that the change in the dielectric constant of the liquid crystal layer is within ±20%.

10. The radio wave reflector according to claim 1, wherein the temperature control unit controls the heat exchanger so that the change in the dielectric constant of the liquid crystal layer is within ±10%.

11. The radio wave reflector according to claim 1, wherein the temperature control unit controls the heat exchanger so as to maintain the liquid crystal layer at a temperature below the phase transition.

Images