JP7797850B2 - reflector - Google Patents

Description

This disclosure relates to a reflector that reflects electromagnetic waves in a specific frequency band in a direction other than the specular reflection direction.

In mobile communication systems, reflectarray technology is being considered to improve the propagation environment and coverage area (for example, Patent Documents 1 and 2, Non-Patent Document 1). In particular, the high frequencies used in fifth-generation communication systems (5G) have a strong tendency to propagate in a straight line, making it important to eliminate coverage holes (areas where radio waves cannot reach).

It is desirable for a reflectarray to be able to reflect electromagnetic waves of a specific frequency incident from a base station in a specified direction in a desired direction. Such a reflectarray, for example, has an array of multiple reflecting elements, and by changing the dimensions and shape of the reflecting elements, the resonant frequency of each reflecting element can be changed, controlling the reflection phase of the electromagnetic waves, and thereby controlling the incident and reflection directions of the electromagnetic waves.

In the above-mentioned reflect array, it is known that the pattern of the reflective elements is formed, for example, by etching a metal layer using photolithography technology.

To obtain a reflectarray with reflection characteristics at the desired reflection angle, it is necessary to precisely control the reflection phase within the reflectarray surface. However, because photomasks are used in photolithographic processing of the metal layer, manufacturing costs tend to rise as miniaturization and precision increase. Furthermore, there are limits to the processing precision that can be achieved in photolithographic processing of the metal layer, making it difficult to precisely control the reflection phase at high frequencies, which have short wavelengths and require high processing precision.

Furthermore, in the above-mentioned reflectarray, for example, the reflection angle can be increased by narrowing the pitch of the reflective elements, but in a planar array of reflective elements, there is a limit to how narrow the pitch of the reflective elements can be, making it difficult to increase the reflection angle.

Patent No. 5371633 Patent No. 5162677 International Publication No. 2016/002832

Mayumi Yoshino et al., "Improvement of received power in non-line-of-sight environments in L-shaped corridors using a face reflector," IEICE Technical Report A・P2020-5 (April 2020)

This disclosure was made in light of the above situation, and its main objective is to provide a reflector that can reduce manufacturing costs.

One embodiment of the present disclosure provides a reflector that reflects electromagnetic waves in a specific frequency band in a direction different from the specular reflection direction, having a concave-convex structure in which a plurality of unit structures having a thickness distribution in which the thickness increases in a predetermined direction are arranged, the unit structures having a plurality of cell regions of different thicknesses, the unit structures including at least a first unit structure having two or more cell regions of different thicknesses, a conductive layer on the surface facing the concave-convex structure, and adjacent cell regions being electrically conductive to each other.

In the present disclosure, it is preferable that the conductive layer is also disposed on the side surfaces of each of the cell regions.

Furthermore, in the present disclosure, when the wavelength of the electromagnetic waves is λ, m is an integer, and a is a real number greater than or equal to 0, it is preferable that the thickness of the maximum thickness cell region having the maximum thickness in the unit structure be expressed as (λ/2) × m + a.

Furthermore, in the present disclosure, when the wavelength of the electromagnetic waves is λ and n is an integer, it is preferable that the difference in thickness between adjacent cell regions in the unit structure be expressed as (λ/2)/n.

Furthermore, in the present disclosure, it is preferable that the difference in thickness between adjacent cell regions in the unit structure is equal.

Furthermore, in the present disclosure, it is preferable that in the above unit structure, the difference in thickness between the minimum thickness cell region having the minimum thickness and the maximum thickness cell region having the maximum thickness is less than 1/2 the wavelength λ of the above electromagnetic wave.

Furthermore, it is preferable that the reflector of the present disclosure has a periodic structure in which the above-mentioned unit structures are repeatedly arranged.

Furthermore, the reflector of the present disclosure may have, as the unit structure, a second unit structure different from the first unit structure.

The reflector disclosed herein has the advantage of being able to reduce manufacturing costs.

1A to 1C are a schematic plan view and a cross-sectional view illustrating a reflector of the present disclosure, and a schematic diagram for explaining the relative reflection phase of an electromagnetic wave in each cell region of a unit structure in the reflector of the present disclosure. 1A and 1B are schematic diagrams illustrating the reflection characteristics of a reflector according to the present disclosure. 1 is a schematic perspective view illustrating an example of a unit structure in a reflector according to the present disclosure. 1 is a schematic plan view illustrating a unit structure of a reflector according to the present disclosure. 1 is a schematic cross-sectional view illustrating a reflector according to the present disclosure. 1 is a schematic cross-sectional view illustrating a reflector according to the present disclosure. 1 is a schematic cross-sectional view illustrating a reflector according to the present disclosure. 1A and 1B are schematic diagrams illustrating the reflection characteristics of a reflector according to the present disclosure. 1 is a schematic plan view illustrating a reflector according to the present disclosure. 1A and 1B are a schematic cross-sectional view illustrating a reflector according to the present disclosure, and a schematic diagram for explaining the relative reflection phase of an electromagnetic wave in each cell region of a unit structure in the reflector according to the present disclosure. 1A and 1B are schematic diagrams illustrating the configuration of a unit structure in a reflector according to the present disclosure. 1A and 1B are a schematic perspective view showing a simulation model of Example 1 and a graph showing simulation results.

Embodiments of the present disclosure are described below with reference to the drawings. However, the present disclosure can be implemented in many different forms, and should not be construed as being limited to the description of the embodiments exemplified below. Furthermore, to clarify the explanation, the drawings may show the width, thickness, shape, etc. of each part schematically compared to the actual form, but these are merely examples and do not limit the interpretation of the present disclosure. Furthermore, in this specification and each figure, elements similar to those previously described with reference to the previous figures are designated by the same reference numerals, and detailed descriptions may be omitted as appropriate.

In this specification, when describing the arrangement of another component on a component, the terms "above" or "below" are used, unless otherwise specified, to include both the case where another component is placed directly above or below the component, so as to be in contact with the component, and the case where another component is placed above or below the component, with another component interposed between them. When describing the arrangement of another component above a component, the terms "above" or "below" are used, unless otherwise specified, to include both the case where another component is placed directly above or below the component, so as to be in contact with the component, the case where another component is placed above or below the component, with another component interposed between them, and the case where another component is placed above or below the component, with another component interposed between them. Furthermore, in this specification, when describing the arrangement of another component on the surface of a component, the terms "on the surface" are used, unless otherwise specified, to include both the case where another component is placed directly above or below the component, so as to be in contact with the component, and the case where another component is placed above or below the component, with another component interposed between them.

The reflector disclosed herein is described in detail below.

The reflector disclosed herein is a reflector that reflects electromagnetic waves in a specific frequency band in a direction different from the specular reflection direction, and has a concave-convex structure in which multiple unit structures are arranged, each having a thickness distribution in which the thickness increases in a predetermined direction. The unit structures have multiple cell regions of different thicknesses, and the unit structures include at least a first unit structure having two or more cell regions of different thicknesses. A conductive layer is provided on the surface facing the concave-convex structure, and adjacent cell regions are electrically connected to each other.

The reflector of the present disclosure will be described with reference to the drawings. FIGS. 1(a) and 1(b) are a schematic plan view and a cross-sectional view showing an example of the reflector of the present disclosure, and FIG. 1(b) is a cross-sectional view taken along line A-A in FIG. 1(a). As shown in FIGS. 1(a) and 1(b), the reflector 1 is a reflector that reflects electromagnetic waves in a specific frequency band and has a concavo-convex structure in which multiple unit structures 10 are arranged, each having a thickness distribution in which thicknesses t1 to t6 increase in a predetermined direction D1. Each unit structure 10 also has multiple cell regions 11a to 11f with different thicknesses t1 to t6. For example, in FIG. 1(b), the unit structure 10 has a staircase shape in which the thicknesses t1 to t6 increase stepwise in the predetermined direction D1. The staircase shape has six steps, and the unit structure 10 has six cell regions 11a to 11f. In addition, the reflector 1 has a conductive layer 3 on the surface with the concave-convex structure, and the conductive layer 3 can also be placed on the side surfaces of the cell regions 11a to 11f, providing electrical continuity between adjacent cell regions.

In Figure 1(b), the reflector 1 has a base layer 4 with an irregular surface on one side and a conductive layer 3 disposed on the irregular surface of the base layer 4, but the configuration of the reflector is not limited to this.

In the reflector 1, the thicknesses t1 to t6 of each cell region 11a to 11f of the unit structure 10 are different, so the round-trip optical path length when the electromagnetic wave is reflected from the surface of the reflector 1 on the uneven structure side and emitted to the electromagnetic wave incident side is different, and these differences in the round-trip optical path length of the electromagnetic wave create differences in the reflection phase.

The term "optical path length" is used in this specification because the wavelengths of the frequency bands covered in this disclosure are closer to those of light and have a higher degree of directivity compared to conventional pre-LTE frequency bands, making it easier to explain the behavior of the wave as being similar to that of light. In practice, this term refers to the effective distance that electromagnetic waves travel through air.

In the reflector 1, in the unit structure 10, the ends E1 to E6 of each cell region 11a to 11f are aligned on the same line in a cross section of the unit structure 10 in the thickness direction in the predetermined direction D1.

For example, if the length of each cell region 11a-11f in the specified direction D1 is the same and the difference in thickness between adjacent cell regions is the same, then in the cross section of the unit structure 10 in the thickness direction in the specified direction D1, the ends E1-E6 of each cell region 11a-11f will be aligned on the same straight line (the dashed dotted line in the figure).

Specifically, in a unit structure 10 having six cell regions 11a-11f, when the wavelength of the electromagnetic wave is λ, the difference in thickness between adjacent cell regions can be designed to be λ/2 divided by 6, or λ/12. In this case, if the wavelength of the electromagnetic wave is λ, m is an integer, a is a real number greater than or equal to 0, and the thickness t6 of the thickest cell region 11f having the maximum thickness t6 is (λ/2) × m + a, the thicknesses t1-t6 of each cell region 11a-11f can be designed as follows:

t1: {(λ/2)×m}-{(λ/12)×5}+a
t2: {(λ/2)×m}-{(λ/12)×4}+a
t3: {(λ/2)×m}-{(λ/12)×3}+a
t4: {(λ/2)×m}-{(λ/12)×2}+a
t5: {(λ/2)×m}-{(λ/12)×1}+a
t6: {(λ/2)×m}+a

For example, when m = 1 and a = 0, the thicknesses t1 to t6 of each cell region 11a to 11f are as follows:

t1: 1λ/12
t2: 2λ/12
t3: 3λ/12
t4: 4λ/12
t5: 5λ/12
t6: 6λ/12

In such a case, the delay in the reflection phase of the electromagnetic wave increases in the order of cell regions 11a, 11b, 11c, 11d, 11e, and 11f, with cell region 11f having the smallest reflection phase. If the reflection phase in cell region 11f, which has the smallest reflection phase, is used as a reference, the relative reflection phases in each of cell regions 11a to 11f are as shown in Figure 1(c), for example. In Figure 1(c), the relative reflection phases of the electromagnetic wave in each of cell regions 11a to 11f of unit structure 10 are -300 degrees, -240 degrees, -180 degrees, -120 degrees, -60 degrees, and 0 degrees, respectively, and the absolute value of the difference in the relative reflection phase of the electromagnetic wave between adjacent cell regions is 60 degrees.

As described above, in each cell region 11a to 11f of the unit structure 10, the thicknesses t1 to t6 change, changing the round-trip optical path length of the electromagnetic wave and changing the reflection phase of the electromagnetic wave. As a result, as shown in the example in Figure 2, the incident electromagnetic wave W1 can be reflected in a direction different from the regular reflection (specular reflection) direction. In this case, the incident angle θ1 of the incident electromagnetic wave W1 is different from the reflection angle θ2 of the reflected electromagnetic wave W2.

Therefore, in the reflector disclosed herein, by varying the thickness of each cell region of the unit structure, the round-trip optical path length of the electromagnetic wave can be varied for each cell region, thereby controlling the reflection phase of the electromagnetic wave. This makes it possible to control the reflection direction of the electromagnetic wave relative to a specified incident direction to any direction.

In this specification, "reflection phase" refers to the amount of change in the phase of a reflected wave relative to the phase of an incident wave incident on a surface.

In addition, in this specification, "relative reflection phase" refers to the reflection phase delay in a cell region relative to the reference reflection phase, expressed as a negative sign, using the reflection phase in the cell region with the smallest reflection phase delay in one unit structure as a reference. For example, if the reflection phase in the cell region with the smallest reflection phase delay in one unit structure is -10 degrees, the relative reflection phase in a cell region with a reflection phase of -40 degrees will be -30 degrees.

Unless otherwise specified, the reflection phase is in the range of more than -360 degrees and less than 360 degrees, with -360 degrees and +360 degrees returning to 0 degrees. Unless otherwise specified, the relative reflection phase is in the range of more than -360 degrees and less than 0 degrees, with -360 degrees returning to 0 degrees.

In addition, in this specification, the term "cell region" refers to a region in a unit structure that has the same thickness, i.e., a region in which the reflection phase of electromagnetic waves is the same.

In a conventional reflectarray in which multiple reflecting elements are arranged, the reflection phase can be delayed or advanced by adjusting the dimensions and shape of the reflecting elements, for example. In the reflector of the present disclosure, the reflection phase in the cell region with the smallest thickness is used as the reference, and by increasing the thickness of each cell region of the unit structure, the reflection phase can be advanced, allowing the direction of the reflected wave to be controlled. Furthermore, in the reflector of the present disclosure, the reflection phase in the cell region with the largest thickness is used as the reference, and the reflection phase delays as the thickness of each cell region of the unit structure decreases, allowing the direction of the reflected wave to be controlled by utilizing this.

In the present disclosure, there is no need to arrange multiple reflective elements as in conventional methods, thereby reducing manufacturing costs. Furthermore, the concave-convex structure in the present disclosure can be formed by various methods, such as cutting, laser processing, molding using a mold, 3D printing, and joining small pieces. Therefore, unlike conventional reflectarrays, which require photolithography to process the metal layer, a photomask is not required. Therefore, when designing the thickness of each cell region of a unit structure to achieve the desired reflection characteristics with the desired angle of incidence and reflection, the desired reflector can be manufactured relatively inexpensively and in a short period of time. Furthermore, since the thickness and size of the unit structures, which affect the control of reflection characteristics, can be manipulated over a relatively wide range, it is possible to increase the incidence and reflection angles of electromagnetic waves, for example, thereby widening the control range of reflection characteristics. Furthermore, since the thickness of the unit structures and the pitch of the cell regions of the unit structures have a relatively wide margin of dimensional processing accuracy to achieve the desired reflection phase, the desired reflection characteristics can be easily obtained and the effects of dimensional variation can be reduced. Therefore, the reflection characteristics of the reflector can be easily customized.

The following describes each configuration of the reflector disclosed herein.

1. Uneven Structure The reflector of the present disclosure has an uneven structure in which a plurality of unit structures having a thickness distribution in which the thickness increases in a predetermined direction are arranged.

The unit structure has multiple cell regions of different thicknesses.

Furthermore, if both the incident wave and the reflected wave can be considered as plane waves, then in each unit structure, the ends of each cell region will be on the same straight line in a cross section of the unit structure's thickness direction in a specified direction.

On the other hand, for example, when the incident wave is a spherical wave or when the reflected beam profile is controlled by a reflector, the cross section of the unit structure in the thickness direction in a specified direction will have a periodic step shape with a certain thickness as its upper limit, specifically, a step shape in which the thickness periodically increases and decreases with a certain thickness as its upper limit.

Note that the term "end of a cell region" refers to the end of a cell region that is adjacent to the cell region in a direction of increasing thickness in the cross section of a unit structure, and that is located on the side of the other cell region that is thinner than the first cell region. For example, in Figure 1(b), the end of cell region 11b refers to the end of cell region 11a, which is adjacent to cell region 11b in a specific direction D1 and that is thinner than cell region 11b, and is indicated by E2. Similarly, the ends of cell regions 11c to 11f are indicated by E3 to E6, respectively. Note that, in the cross section of a unit structure, if there are no other cell regions that are adjacent to the first cell region in a direction of increasing thickness, and that are thinner than the first cell region, the end of the first cell region refers to the end located on the opposite side of the other cell region that is thicker than the first cell region. For example, in Figure 1(b), the end of cell region 11a refers to the end located on the opposite side to cell region 11b, which is thicker than cell region 11a, and is indicated by E1.

Furthermore, in a cross section of the unit structure in the thickness direction in a predetermined direction, the difference in thickness between the ends of each cell region is preferably within ±λ/2, more preferably within ±λ/4, and even more preferably within ±λ/6.

The unit structure has a thickness distribution in which the thickness increases in a predetermined direction. For example, the unit structure may have a thickness distribution in which the thickness increases in only one direction, or may have a thickness distribution in which the thickness increases in two directions: a first direction and a second direction perpendicular to the first direction. For example, Figure 3(a) is an example of a unit structure 10 having a thickness distribution in which the thickness increases only in the first direction D1, while Figures 3(c), (e), and 4(a) are examples of unit structures 10 having a thickness distribution in which the thickness increases in both the first direction D1 and the second direction D2.

As described above, in each unit structure, if the ends of each cell region are on the same line in a cross section of the unit structure's thickness direction in a specified direction, and the unit structure has a thickness distribution in which the thickness increases in only one direction, the ends of each cell region will be on the same line in a cross section of the unit structure's thickness direction in that one direction. Furthermore, in the above case, if the unit structure has a thickness distribution in which the thickness increases in two mutually perpendicular directions, the ends of each cell region will be on the same line in a cross section of the unit structure's thickness direction in each of those two directions.

On the other hand, as described above, when the cross section of a unit structure in a specified direction in the thickness direction has a periodic step shape with a constant thickness as its upper limit, specifically, a step shape in which the thickness periodically increases and decreases with a constant thickness as its upper limit, and when the unit structure has a thickness distribution in which the thickness increases in only one direction, the cross section of the unit structure in the thickness direction in that one direction will have a periodic step shape with a constant thickness as its upper limit. Furthermore, in the above case, when the unit structure has a thickness distribution in which the thickness increases in two mutually perpendicular directions, the cross section of the unit structure in the thickness direction in each of those two directions will have a periodic step shape with a constant thickness as its upper limit.

In one unit structure, the thickness of the maximum thickness cell region having the maximum thickness is preferably expressed as (λ/2) × m + a, where λ is the wavelength of the electromagnetic wave, m is an integer, and a is a real number greater than or equal to 0. a is a real number greater than or equal to 0 and is also the thickness of the base of the reflector. It is set appropriately taking into consideration overall strength, ease of formation, and other factors. a can be, for example, approximately 0 mm or greater and 3 mm or less. Note that the thickness of the base a is a different concept from the thickness of the minimum thickness cell region having the minimum thickness. m is an integer, and can be, for example, an integer greater than or equal to 1, preferably an integer greater than or equal to 1 and less than or equal to 3. As m increases, the thickness of the entire reflector increases, which may make installation of the reflector more difficult. For example, in Figure 1(b), the thickness t6 of the maximum thickness cell region 11f having the maximum thickness t6 is preferably (λ/2) × m + a.

In one unit structure, the difference in thickness between adjacent cell regions is preferably expressed as (λ/2)/n, where λ is the wavelength of the electromagnetic wave and n is an integer. n is an integer, and when, for example, the cross-sectional shape of the unit structure is stepped and the difference in thickness between adjacent cell regions is equal, n corresponds to the number of steps in the stepped shape, i.e., the number of cell regions.

For example, Figure 1(b) shows an example in which the cross-sectional shape of the unit structure 10 is stepped, the number of steps in the stepped shape is six, and the difference in thickness between adjacent cell regions is equal. In this case, it is preferable that the difference in thickness between adjacent cell regions is (λ/2)/6 = λ/12.

Furthermore, for example, Figure 5 shows an example in which the cross-sectional shape of the unit structure 10 is stepped, the number of steps of the stepped shape is four, and the difference in thickness between adjacent cell regions is different. In this case, the difference in thickness between adjacent cell regions is preferably (λ/2)/n. Specifically, the thicknesses t1 to t4 of each cell region 11a to 11d of the unit structure 10 can be 1λ/12, 3λ/12, 4λ/12, and 6λ/12, respectively, and the difference in thickness between adjacent cell regions 11a and 11b can be 2λ/12, the difference in thickness between adjacent cell regions 11b and 11c can be λ/12, and the difference in thickness between adjacent cell regions 11c and 11d can be 2λ/12. In this case, the differences in thickness between adjacent cell regions are 2λ/12 = λ/6 = (λ/2)/3 and λ/12 = (λ/2)/6, respectively.

Furthermore, within one unit structure, the difference in thickness between adjacent cell regions may be equal or different, but it is preferable that the difference is equal. For example, Figure 1(b) shows an example in which the difference in thickness between adjacent cell regions is equal, while Figure 5 shows an example in which the difference in thickness between adjacent cell regions is different.

Furthermore, in one unit structure, it is preferable that the difference in thickness between the minimum thickness cell region having the minimum thickness and the maximum thickness cell region having the maximum thickness be less than 1/2 of the wavelength λ of the electromagnetic wave. Furthermore, in one unit structure, it is preferable that the difference in thickness between the minimum thickness cell region having the minimum thickness and the maximum thickness cell region having the maximum thickness be more than 1/6 of the wavelength λ of the electromagnetic wave. For example, as shown in Figure 1(b), if unit structure 10 has six cell regions, it is preferable that the difference in thickness t1 between minimum thickness cell region 11a having the minimum thickness t1 and maximum thickness cell region 11f having the maximum thickness t6 be less than λ/2 in one unit structure 10. Specifically, in one unit structure 10, the thickness t1 of the minimum thickness cell region 11a having the minimum thickness t1 can be set to λ/12, the thickness t6 of the maximum thickness cell region 11f having the maximum thickness t6 can be set to 6λ/12, and the difference between the thickness t1 of the minimum thickness cell region 11a having the minimum thickness t1 and the thickness t6 of the maximum thickness cell region 11f having the maximum thickness t6 can be set to 5λ/12.

The size of the unit structure, specifically the length of the unit structure in a specified direction in which the thickness increases, is set appropriately according to the desired reflection characteristics. The length of the unit structure in a specified direction in which the thickness increases results in a shift of one wavelength (phase difference: 360 degrees), making it possible to adjust the reflection angle. For example, by shortening the length of the unit structure in a specified direction in which the thickness increases, the difference between the reflection angle and the specular reflection angle can be increased; conversely, by increasing the length of the unit structure in a specified direction in which the thickness increases, the difference between the reflection angle and the specular reflection angle can be reduced.

Note that the length of a unit structure in a predetermined direction in which the thickness increases refers to the length of the unit structure in that predetermined direction when the unit structure has a thickness distribution in which the thickness increases in that predetermined direction. For example, in Figure 5, the thickness of unit structure 10 increases in predetermined direction D1, and the length of unit structure 10 in this predetermined direction D1 is L.

The cross-sectional shape of the unit structure may be, for example, a stepped shape in which the thickness increases stepwise in a predetermined direction, or a tapered shape in which the thickness increases gradually in a predetermined direction. For example, Figures 1(b) and 5 show examples in which the unit structure 10 has a stepped shape, and Figure 6 shows an example in which the unit structure 10 has a tapered shape.

Note that a unit structure has multiple cell regions of different thicknesses, but if the cross-sectional shape of the unit structure is tapered, the number of cell regions in the unit structure can be considered to be infinitely large. Even in this case, the thickness distribution of the unit structure is designed so that the thickness of each cell region is set as described above.

Furthermore, since the reflector is made up of an arrangement of multiple unit structures with thickness distribution, the pattern shape of the unit structures in a planar view can be any shape that allows them to be arranged without gaps, such as a rectangle or a regular hexagon. For example, Figures 3(a) to (f) and Figure 4(a) show examples in which the pattern shape of the unit structures 10 in a planar view is rectangular.

In the unit structure, the thickness of each cell region is designed to be as described above. The thickness of each cell region is set appropriately depending on the wavelength of the electromagnetic wave and the desired reflection characteristics. For example, if the frequency of the electromagnetic wave is 30 GHz, i.e., the wavelength of the electromagnetic wave is 10 mm, it is preferable that the thickness of each cell region be approximately 0.1 mm or more and 5.1 mm or less.

In the unit structure, the pitch and width of the cell area are set appropriately.

Furthermore, regarding the size of the cell region, for example, if the pattern shape of the cell region in a planar view is striped, the width of the cell region can be λ/p or more, where λ is the wavelength of the electromagnetic wave and p is an integer. In other words, the unit structure can be configured with cell regions each with a width of λ/p or less laid out closely together. p can be approximately 2 or more and 10 or less. Meanwhile, in the above case, the length of the cell region only needs to be equal to or less than the length of one side of the reflector. Furthermore, the number of cell regions laid out in one unit structure will vary depending on the direction and angle of the incident wave and reflected wave, but will be 2 or more.

Furthermore, it is preferable that the pitch of the cell regions in one unit structure is uniform.

Note that the pitch of a cell area refers to the distance from the center of one cell area to the center of an adjacent cell area.

Furthermore, in one unit structure, the width of the cell region in a given direction in which the thickness increases may be equal or different, but it is preferable that it be equal.

In the unit structure, the pattern shape of the cell region in a planar view can be, for example, a stripe shape, a shape obtained by dividing a concentric square into four equal parts by lines parallel to the sides and perpendicular to each other, a microarray shape, a concentric quadrant shape, which is a shape obtained by dividing a concentric circle into four equal parts by perpendicular diameters, or a curved staircase shape. For example, Figure 3(b) is an example of a stripe shape, Figure 3(d) is an example of a shape obtained by dividing a concentric square into four equal parts by lines parallel to the sides and perpendicular to each other, Figures 3(f) and 4(a) are examples of a microarray shape, Figure 4(b) is an example of a concentric quadrant shape, and Figure 4(c) is an example of a curved staircase shape. Note that Figure 3(b) is a top view of Figure 3(a), Figure 3(d) is a top view of Figure 3(c), and Figure 3(f) is a top view of Figure 3(e). Furthermore, when these exemplified unit structures are arranged without gaps, there are no particular restrictions on the arrangement direction; for example, rectangular unit structures can be arranged over the entire surface while rotated 30 degrees clockwise in a plan view; the unit structures can be arranged at an appropriate angle and in an appropriate arrangement direction depending on the required reflection characteristic design.

A unit structure has multiple cell regions. The number of cell regions in one unit structure is, for example, three or more, and preferably six or more. The greater the number of cell regions in one unit structure, the smaller the difference in thickness between adjacent cell regions, which in turn reduces the difference in the reflection phase of electromagnetic waves between adjacent cell regions, resulting in a smoother wavefront of the reflected wave. Furthermore, the greater the number of cell regions in one unit structure, the more preferable it is, with no particular upper limit. Note that if the cross-sectional shape of the unit structure is stepped, the number of cell regions corresponds to the number of steps in the stepped shape. Furthermore, if the cross-sectional shape of the unit structure is tapered, as described above, the tapered shape can be considered to have an infinitely large number of cell regions.

The reflector has at least a first unit structure having two or more cell regions of different thicknesses as a unit structure.

Furthermore, the reflector may have only a first unit structure as its unit structure, or may further have a second unit structure that is different from the first unit structure. In other words, the reflector may have only the same unit structure as its unit structure, or may have unit structures that are different from each other. If the reflector is made up of multiple unit structures that are different from each other, this can affect the overall reflection characteristics of the reflector. Specific examples include adjusting the polarization characteristics and affecting the beam profile (high directivity, diffusion, multi-beam, etc.).

The first unit structure and the second unit structure can have different reflection characteristics, for example, different lengths of the unit structures in the direction of increasing thickness, thickness distribution, number of cell regions, width, pitch, pattern shapes of the unit structures in a planar view, and pattern shapes of the cell regions in a planar view.

Furthermore, if the reflector has unit structures that are different from each other, there is no particular limit to the number of types of unit structures.

In a reflector, the thickness distribution is appropriately selected and multiple unit structures are arranged so that the normal vector of the same phase plane of the reflected wave relative to the incident wave incident at a predetermined incident angle is aligned in the desired reflection direction. For example, when reflecting an incident wave in a single direction, i.e., as a plane wave, it is preferable for the reflector to have multiple identical unit structures arranged therein. It is more preferable that the length of the unit structures in the predetermined direction of thickness increase be the same, and that the pattern shape of the cell region in a planar view be striped. For example, Figures 1(a) and 1(b) show an example in which the reflector 1 has multiple identical unit structures, the lengths of the unit structures 10a and 10b in the predetermined direction D1 are the same, and the pattern shape of the cell regions 11a-11f in a planar view is striped. In this case, as illustrated in Figure 2, an incident wave W1 incident at a predetermined incident angle θ1 can be reflected at a single reflection angle θ2, and the reflected wave W2 can be a plane wave without spreading. Furthermore, while Figure 1(a) shows an arrangement in which the longitudinal direction of the stripes in the cell region is parallel to the lateral direction of the reflector, this is not limited to this, and in an actual reflector, the longitudinal and lateral directions of the stripes in the cell region can be set arbitrarily depending on the design of the reflection characteristics.

Furthermore, for example, when diffusing electromagnetic waves, i.e., reflecting them as cylindrical waves, it is preferable that the reflector be an arrangement of multiple different unit structures, with the unit structures having different lengths in a predetermined direction of thickness increase, and the cell region having a striped pattern in a planar view. For example, in Figure 7, reflector 1 has three different types of unit structures 10a and 10b, and 10c and 10d, and these unit structures 10a and 10b, and 10c and 10d have different lengths L1, L2, and L3 of the unit structures in a predetermined direction D1. Furthermore, cell regions 11a, 12a, and 13a have the same thickness, and similarly, cell regions 11b, 12b, and 13b have the same thickness, cell regions 11c, 12c, and 13c have the same thickness, cell regions 11d, 12d, and 13d have the same thickness, cell regions 11e, 12e, and 13e have the same thickness, cell regions 11f, 12f, and 13f have the same thickness, and cell regions 11g, 12g, and 13g have the same thickness. As a result, the slopes of the lines passing through the ends of each of cell regions 11a to 11g of unit structure 10a, the lines passing through the ends of each of cell regions 12a to 12g of unit structures 10b and 10c, and the lines passing through each of cell regions 13a to 13g of unit structure 10d are different from one another, and the reflection characteristics of the three types of unit structures 10a and 10b, and 10c and 10d are different from one another. Although not shown, the pattern shape of cell regions 11a-11g, 12a-12g, and 13a-13g in a planar view is striped. In this case, as shown in the example of Figure 8, an incident wave W1 incident at a predetermined incident angle θ1 can be reflected at reflection angles θ2, θ2', and θ2" depending on the unit structure, resulting in a broadened reflection and a broadened wavefront of the reflected wave W2.

Furthermore, when the reflector has unit structures that are different from one another, it is possible to use multiple types of unit structures with different reflection characteristics, arrange multiple unit structures of each type, and arrange regions where multiple unit structures of the same type are arranged in a plane. For example, in Figure 9, two types of unit structures 10a, 10b with different reflection characteristics are used, and the reflector 1 is formed by arranging a first region 5a where multiple unit structures 10a of one type are arranged in a plane, and a second region 5b where multiple unit structures 10b of the other type are arranged in a plane. In this manner, it is possible to accommodate multiple coverage holes.

Furthermore, if the reflector has unit structures that are different from each other, the thickness of each cell region of the N unit structures may be set so that, for example, the N unit structures are shifted by N wavelengths (phase difference: N x 360 degrees). N is an integer of 2 or greater.

For example, Figures 10(a) and 10(b) show an example in which the reflector 1 has two different types of unit structures 10a and 10b, and the thicknesses of the cell regions 11a-11b and 12a-12c of the two unit structures 10a and 10b are set so that the two unit structures 10a and 10b are shifted by two wavelengths (phase difference: 720 degrees).

For example, if the length of each cell region 11a-11b, 12a-12c in the specified direction D1 is the same and the difference in thickness between adjacent cell regions is the same, then in the cross section of the thickness direction of unit structures 10a and 10b in the specified direction D1, the slope of a line passing through ends E1-E2 of each cell region 11a-11b of unit structure 10a will be the same as the slope of a line passing through ends E3-E5 of each cell region 12a-12c of unit structure 10b.

Specifically, in two unit structures 10a and 10b each having a total of five cell regions 11a-11b and 12a-12c, where λ is the wavelength of the electromagnetic wave, the difference in thickness between adjacent cell regions can be designed to be λ divided by 5, or λ/5. In this case, if λ is the wavelength of the electromagnetic wave, a is a real number greater than or equal to 0, and the thickness t5 of the thickest cell region 12c having the maximum thickness t5 is (λ/2) + a, then the thicknesses t1-t4 of each cell region 11a-11b and 12a-12c can be designed as follows:

t1:λ-{(λ/5)×4}+a
t2: λ-{(λ/5)×3}+a
t3: (λ/2)-{(λ/5)×2}+a
t4: (λ/2)-{(λ/5)×1}+a
t5: (λ/2)+a

For example, when a = 0, the thicknesses t1 to t4 of each cell region 11a-11b and 12a-12c are as follows:

t1: 2λ/10
t2: 4λ/10
t3: 1λ/10
t4: 3λ/10
t5: 5λ/10

In such a case, if the reflection phase in cell region 12c, which has the smallest reflection phase, is used as the reference, the relative reflection phase in each cell region 11a-11b, 12a-12c will be as shown, for example, in Figures 10(b) and 10(c). Note that Figure 10(b) is a graph in which the range of the relative reflection phase of the electromagnetic wave is greater than -360 degrees and less than 0 degrees, while Figure 10(c) is a graph in which the range of the relative reflection phase of the electromagnetic wave is greater than -720 degrees and less than 0 degrees, and the points where the relative reflection phase is substantially in phase, shifted by 360 degrees, are complemented. These unit structures 10a and 10b have different lengths in the specified direction D1, and different numbers of cell regions 11a-11b, 12a-12c.

Furthermore, when the incident wave and reflected wave are plane waves, the reflector has a periodic structure in which unit structures are repeatedly arranged. A "periodic structure" refers to a structure in which unit structures are periodically and repeatedly arranged. Unit structures in a periodic structure that have the same reflection characteristics can have the same length in the thickness direction, thickness distribution, number of cell regions, width, pitch, pattern shape of the unit structure in a planar view, and pattern shape of the cell regions in a planar view. Even when a reflector has a periodic structure, as described above, unit structures with different reflection characteristics can be combined. In this case, the reflection characteristics of the combined unit structures are appropriately designed according to the desired reflection characteristics. Specifically, the length in the thickness direction, thickness distribution, number of cell regions, width, pitch, pattern shape of the unit structure in a planar view, and pattern shape of the cell regions in a planar view of the combined unit structures are appropriately set according to the desired reflection characteristics.

Generally, in designing reflection characteristics that reflect a plane wave as a plane wave in a direction different from the specular reflection direction, the design can be achieved by, for example, decomposing the reflection characteristics into the in-plane x-direction and in-plane y-direction of the reflector, converting them into reflection phase distributions in the x- and y-directions, and incorporating them as the thickness distribution of the unit structures. For example, as shown in Figure 11, a portion of a reflector in which 10 x 10 (i = 10, j = 10) cell regions of the same size, each with an individually adjustable reflection phase, are arranged will be described as an example. It should be noted that the size of the 10 x 10 cell regions does not necessarily correspond to the size of the unit structures. When a plane wave incident from an incident angle (θ _in , φ _in ) is reflected as a plane wave in a reflection angle (θ _out , φ _out ), the reflection phase δ _i,j required for the cell region at position (i, j) is given by the following equation:

δ _i,j =2π{p×i×(sinθ _out ×cosφ _out −sinθ _in ×cosφ _in )+
p×j×(sinθ _out ×sinφ _out −sinθ _in ×sinφ _in )}/λ
Here, in the above formula,
δ _i,j : Reflection phase of the cell area at the (i,j) position relative to the phase center (0,0) λ: Wavelength of the reflected wave [m]
p: Size of cell area [m]
θ _in : θ gradient of incident wave φ _in : φ gradient of incident wave θ _out : θ gradient of reflected wave φ _out : φ gradient of reflected wave.

Here, assuming that t is the thickness of the cell region, t _min is the thickness of the minimum thickness cell region, Δt is the thickness increase from the minimum thickness, λ is the wavelength of the electromagnetic wave, and the reflection phase when Δt = 0 is the reference (0), the reflection phase δ is roughly expressed by the following formula.
δ[rad]=4×π×(Δt/λ)
From the above equation, Δt is expressed as follows:
Δt=(δ×λ)/(4×π)
Therefore, it is sufficient to arrange the cell regions having a thickness t that matches the reflection phase δ _i,j according to the following formula.
t=t _min +Δt=t _min +((δ×λ)/(4×π))

Furthermore, in the above equation, when Δt = λ/2, δ = 2π [rad], and any reflection phase can be created below that thickness. Similarly, in the above equation, when the reflection phase δ _i,j exceeds 2π [rad], the remainder of the reflection phase δ _i,j modulo 2π can be regarded as the reflection phase δ _i,j .

Furthermore, the thickness t of the cell region does not need to be exactly the thickness calculated from the above formula, but may be rounded to a thickness increment equivalent to, for example, 2π/n [rad] (n is a real number greater than 1, preferably 2 or greater).

2. Layer Structure The reflector of the present disclosure has a conductive layer on the surface on the concave-convex structure side, and adjacent cell regions are electrically connected to each other.

The reflector must have at least a conductive layer. For example, it may have a substrate layer and a conductive layer disposed on the surface of the substrate layer, or it may have only a conductive layer.

The following describes a first embodiment in which the reflector has a substrate layer and a conductive layer, and a second embodiment in which the reflector has only a conductive layer.

(1) First Aspect The reflector of this aspect has a substrate layer and a conductive layer disposed on the surface of the substrate layer.

(a) Conductive Layer In this specification, the term "conductive layer" refers to a layer having a sheet resistance of 100 Ω/□ or less. The sheet resistance of the conductive layer is preferably 1 Ω/□ or less, and more preferably 0.01 Ω/□ or less. The lower limit of the sheet resistance of the conductive layer is not particularly limited, but can be, for example, 0.001 Ω/□ or more.

The sheet resistance of the conductive layer can be measured using the four-terminal method.

The conductive layer may be placed on the surface of the reflector facing the concave-convex structure, but it is preferable that it also be placed on the side of the cell region to provide electrical conductivity between adjacent cell regions.

The conductive layer is not particularly limited as long as it is capable of reflecting electromagnetic waves in a specified frequency band and satisfies the above-mentioned sheet resistance. Examples include metal films; metal oxide films such as ITO, IZO, AZO, GZO, and ATO; carbon films; and metal mesh.

The thickness of the conductive layer is not particularly limited as long as it is capable of reflecting electromagnetic waves in a specified frequency band and satisfies the above-mentioned sheet resistance. For example, it is preferably 100 nm or more and 100 μm or less, more preferably 100 nm or more and 10 μm or less, and even more preferably 1 μm or more and 10 μm or less.

The method for forming the conductive layer is not particularly limited as long as it can be formed on the substrate layer described below, and examples include PVD methods such as vacuum deposition and sputtering; CVD methods; and plating methods.

(b) Substrate Layer The substrate layer is a member that supports the conductive layer.

The material for the substrate layer is not particularly limited, and examples include resin, glass, quartz, and ceramics. Of these, resin is preferred, considering the ease with which the uneven structure can be formed.

Furthermore, when the base layer contains a resin, it may further contain conductive particles. In this case, even if the above-mentioned conductive layer is not disposed on the side surfaces of the cell regions, adjacent cell regions can be made conductive to each other.

Furthermore, when the substrate layer contains a resin, it may contain additives as needed.

The substrate layer may be, for example, a single layer or multiple layers. The substrate layer may also have a base substrate portion and an uneven portion disposed on the base substrate portion.

Furthermore, the base layer may be, for example, a single member in which all cell regions are integrally formed, or may be a layer in which each cell region is formed separately and arranged in a block-like fashion.

The method for forming the base layer is not particularly limited as long as it is capable of forming the desired uneven structure, and examples include cutting a resin sheet, laser processing, molding using a mold or vacuum casting, modeling using a 3D printer, and joining small parts. Forming methods that do not use molds, such as cutting, laser processing, and 3D printing, are easy to customize according to the desired reflection angle, and are therefore suitable for special installation situations or for tuning the design when designing and developing large-scale reflectors that are difficult to simulate.

(2) Second Aspect The reflector of this aspect has only a conductive layer.

The definition of the conductive layer is the same as in the first aspect above.

The conductive layer is not particularly limited as long as it is capable of reflecting electromagnetic waves in a specified frequency band and satisfies the above-mentioned sheet resistance. Examples include metal films; metal oxide films such as ITO, IZO, AZO, GZO, and ATO; and carbon films.

The method for forming the conductive layer is not particularly limited as long as it is capable of forming a conductive layer with the specified uneven structure. Examples include cutting a metal sheet, shaping using a mold, laser processing, modeling using a metal 3D printer, and joining small parts.

Furthermore, the conductive layer may be, for example, a single member in which all cell regions are integrally formed, or may be a block-shaped arrangement in which each cell region is formed separately.

3. Control of the Reflection Direction of Electromagnetic Waves In the reflector of the present disclosure, by changing the thickness of each cell region of the unit structure, the round-trip optical path length of the electromagnetic wave can be changed for each cell region, thereby controlling the reflection phase of the electromagnetic wave. As a result, by adjusting the size and planar view pattern of the unit structure, as well as the number and thickness of the cell regions of the unit structure, it is possible to control the reflection direction of electromagnetic waves incident from a predetermined direction.

Furthermore, as described above, the reflection characteristics of the unit structure can be controlled by adjusting the length of the unit structure in a predetermined direction in which the thickness increases. For example, by shortening the length of the unit structure in a predetermined direction in which the thickness increases, the reflection angle of the electromagnetic wave can be increased, while by increasing the length of the unit structure in a predetermined direction in which the thickness increases, the reflection angle of the electromagnetic wave can be decreased.

Furthermore, if t is the thickness of the cell region, b is the minimum thickness of the cell region due to processing, λ is the wavelength of the electromagnetic wave, and the reflection phase when t = b is taken as the reference (0), the reflection phase δ can be roughly expressed as follows:
δ[rad]=4×π×{(t-b)/λ)}
From the above equation, the thickness t of the cell region is expressed as follows:
t={(δ×λ)/(4×π)}+b
Therefore, the thickness t of the cell region expressed by the above formula is arranged so as to become the reflection phase δ _i,j of the cell region at the above-mentioned (i, j) position.

4. Other Configurations The reflector of the present disclosure may have other configurations as needed.

(1) Ground Layer When the reflector of the present disclosure has the above-described base layer and conductive layer, it may have a ground layer on the surface of the base layer opposite the conductive layer. The ground layer can block interference with objects present on the back surface of the reflector and suppress noise generation. For example, a general conductive film such as a metal film, a metal mesh, a carbon film, or an ITO film can be used as the ground layer.

(2) Fixing Member When the reflector of the present disclosure is used by attaching it to, for example, a wall, a fixing member having a mechanism for attaching the reflector may be disposed on the surface of the reflector opposite the concave-convex structure. Furthermore, to suppress interference between the fixing member and the reflector, a metal layer may be disposed between the fixing member and the reflector, or the fixing member may also serve as the metal layer. Furthermore, when attaching the reflector of the present disclosure to a wall, the fixing member may have a mechanism for varying the angle of the normal direction of the reflector so that deviations between the designed incident direction and reflection direction of the electromagnetic wave and the actual incident direction and reflection direction of the electromagnetic wave can be corrected.

5. Characteristics of the Reflector The reflector of the present disclosure reflects electromagnetic waves of a specific frequency band in a direction different from the direction of specular reflection. The frequency band of the electromagnetic waves is preferably 24 GHz or higher, and more preferably 24 GHz or higher and 300 GHz or lower. If the frequency band of the electromagnetic waves is within the above range, the reflector of the present disclosure can be used in fifth-generation mobile communication systems, also known as 5G.

The reflector of the present disclosure can be used, for example, as a reflector for communications, and is particularly suitable as a reflector for mobile communications.

Note that this disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical concept described in the claims of this disclosure and that provides similar effects is encompassed within the technical scope of this disclosure.

The following examples will explain this disclosure in more detail.

[Example 1]
A simulation of the reflection characteristics of a reflector was performed. In the simulation, the unit structure of the reflector had a thickness distribution in which the thickness increased in two directions, as shown in Figure 12(a), and had a total of 36 cell regions of eight different thicknesses, and a model was used that had a periodic structure in which the unit structures were repeatedly arranged in both directions. In addition, the following parameters were used for the reflector in the simulation.

Incident wave frequency: 28 GHz
Incident angle of incident wave: (θ, φ) = (20°, 90°)
Desired reflection angle of reflected wave: (θ, φ) = (45°, 0°)
Thickness of each cell area: 0.1 mm to 5.6 mm
Thickness difference between adjacent cell areas: 1.1 mm

The simulation results are shown in Figures 12(b)-(d). Figure 12(b) is a 3D display of the bistatic radar cross section of the reflector for electromagnetic waves arriving from the (θ, φ) = (20°, 90°) direction. The axis extending to the lower left and front is the x-axis, the axis extending to the lower right and front is the y-axis, and the axis extending vertically is the z-axis, which are the right-handed Cartesian coordinate axes. The polar coordinates (θ, φ) are determined accordingly, as shown in Figure 11 above. Note that the RCS (radar cross section) that appears to be reflected straight ahead from the page is the reflected wave from the present design. Meanwhile, the RCS (radar cross section) of the incident wave that passed around the reflector appears larger in the lower left and front. However, this is because the surrounding air gap was wider than the reflector in the simulation model, and is unrelated to the essence of the present design. Figure 12(c) is a diagram of the bistatic radar cross section in the XZ plane swept with θ. Also, Figure 12(d) shows the bistatic radar cross section at θ = 45° swept with φ.

REFERENCE SIGNS LIST 1 ... reflector 3 ... conductive layer 4 ... base material layer 10, 10a, 10b ... unit structure 11a to 11g, 12a to 12f, 13a to 13e ... cell region D1 ... predetermined direction L ... length of unit structure in a predetermined direction in which thickness increases t1, t2, t3, t4, t5, t6 ... thickness of cell region

Claims (14)

A reflector that reflects electromagnetic waves in a specific frequency band in a direction different from the specular reflection direction,
a concave-convex structure in which a plurality of unit structures having a thickness distribution in which the thickness increases in a predetermined direction are arranged;
The unit structure has a plurality of cell regions with different thicknesses,
The unit structure includes at least a first unit structure having two or more cell regions with different thicknesses,
a conductive layer is provided on the surface of the concave-convex structure side, and adjacent cell regions are electrically connected to each other;
A reflector , wherein the conductive layer is also disposed on a side surface of each of the cell regions . 2. The reflector according to claim 1, wherein, when the wavelength of the electromagnetic wave is λ, m is an integer, and a is a real number greater than or equal to 0, the thickness of the maximum thickness cell region having the maximum thickness in the unit structure is expressed as (λ/ 2 ) × m + a. 3. The reflector according to claim 1, wherein, in the unit structure, a difference in thickness between adjacent cell regions is expressed as (λ/2)/n, where λ is the wavelength of the electromagnetic wave and n is an integer. 4. The reflector according to claim 1 , wherein the difference in thickness between adjacent cell regions in the unit structure is equal. 5. The reflector according to claim 1, wherein in the unit structure, a difference between the thickness of a minimum thickness cell region having a minimum thickness and the thickness of a maximum thickness cell region having a maximum thickness is less than 1/2 of the wavelength λ of the electromagnetic wave. The reflector according to claim 1 , which has a periodic structure in which the unit structures are repeatedly arranged. 7. The reflector according to claim 1, wherein the unit structure comprises a second unit structure different from the first unit structure. 8. The reflector according to claim 1, wherein a difference in thickness between the ends of the cell regions is within ±λ/2. The reflector according to claim 1 , wherein the unit structures have a staircase shape. 10. The reflector according to claim 1, wherein the number of the cell regions in one unit structure is three or more. The reflector of claim 10, wherein the edges of each of the cell regions are collinear. 12. The reflector according to claim 1, comprising a substrate layer having an irregularity on one surface thereof, and the conductive layer disposed on the irregular surface of the substrate layer. The reflector according to claim 12 , further comprising a ground layer on the surface of the base layer opposite to the conductive layer. The reflector according to claim 1 , further comprising a fixing member disposed on a surface of the reflector opposite to the concave-convex structure.