reflector

Abstract

To provide a reflection board which can reduce a manufacturing cost.SOLUTION: A reflection board 1 that reflects an electromagnetic wave of a specified frequency band to a direction different from a specular direction, includes an uneven structure in which a plurality of unit structures 10 including a thickness distribution where a thickness is increased to a predetermined direction is arranged. The unit structure 10 includes a plurality of cell regions 11a to 11f each having a different thickness, at least includes a first unit structure having two or more cell regions each having a different thickness as a unit structure, and includes a conductive layer 3 on a surface on each uneven structure side. Both of the adjacent cell regions are conducted.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a reflector that reflects electromagnetic waves in a specific frequency band in a direction different from the specular reflection direction. [Background technology]

[0002] In mobile communication systems, reflectarray technology is being studied to improve the propagation environment and coverage area (for example, Patent Documents 1 and 2, Non-Patent Document 1). In particular, high frequencies used in fifth-generation communication systems (5G) have a strong tendency to propagate in a straight line, so eliminating coverage holes (areas where radio waves cannot reach) is an important issue.

[0003] A reflectarray is desired to be able to reflect electromagnetic waves of a specific frequency incident from a base station in a desired direction. Such a reflectarray, for example, has an array of multiple reflecting elements, and a technology has been developed that changes the dimensions and shape of the reflecting elements to change the resonant frequency of each reflecting element and control the reflection phase of the electromagnetic wave, thereby controlling the incident direction and reflection direction of the electromagnetic wave.

[0004] In the reflectarray, it is known that the pattern of the reflective elements is formed by etching a metal layer using, for example, photolithography technology.

[0005] To obtain a reflectarray with reflection characteristics with the desired reflection angle, it is necessary to precisely control the reflection phase within the reflectarray surface. However, because photomasks are used in photolithography processing of the metal layer, manufacturing costs tend to rise as miniaturization and precision increase. Furthermore, since there are limits to the processing precision in photolithography processing of the metal layer, it is difficult to precisely control the reflection phase at high frequencies, which have short wavelengths and require high processing precision.

[0006] Furthermore, in the above-mentioned reflect array, for example, the reflection angle can be increased by narrowing the pitch of the reflecting elements, but in a planar arrangement of reflecting elements, there is a limit to how narrow the pitch of the reflecting elements can be, making it difficult to increase the reflection angle. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 5371633 [Patent Document 2] Patent No. 5162677 [Patent Document 3] International Publication No. 2016 / 002832 [Non-patent literature]

[0008] [Non-Patent Document 1] Mayumi Yoshino et al., "Improvement of received power in non-line-of-sight environments using a face reflector in an L-shaped corridor," IEICE Technical Report A·P2020-5 (April 2020) Summary of the Invention [Problem to be solved by the invention]

[0009] The present disclosure has been made in view of the above circumstances, and has as its main object to provide a reflector that can reduce manufacturing costs. [Means for solving the problem]

[0010] One embodiment of the present disclosure provides a reflector that reflects electromagnetic waves of a specific frequency band in a direction different from the direct reflection direction, the reflector 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 having 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 conductive to each other.

[0011] In the present disclosure, it is preferable that the conductive layer is also disposed on the side surfaces of each of the cell regions.

[0012] Furthermore, in the present disclosure, 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, it is preferable that in the unit structure, the thickness of the maximum thickness cell region having the maximum thickness is expressed as (λ / 2)×m+a.

[0013] Furthermore, in the present disclosure, when the wavelength of the electromagnetic wave is λ and n is an integer, the difference in thickness between adjacent cell regions in the unit structure is preferably expressed as (λ / 2) / n.

[0014] In the present disclosure, it is also preferable that the difference in thickness between adjacent cell regions in the unit structure is equal.

[0015] In addition, in the present disclosure, it is preferable that in the unit structure, the difference between the thickness of the minimum thickness cell region having the minimum thickness and the thickness of the maximum thickness cell region having the maximum thickness is less than 1 / 2 of the wavelength λ of the electromagnetic wave.

[0016] Furthermore, the reflector of the present disclosure preferably has a periodic structure in which the above-described unit structures are repeatedly arranged.

[0017] The reflector of the present disclosure may have, as the unit structure, a second unit structure different from the first unit structure. [Effects of the Invention]

[0018] The reflector of the present disclosure has the effect of reducing manufacturing costs. [Brief explanation of the drawings]

[0019] [Figure 1] 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. [Figure 2] 1A and 1B are schematic diagrams illustrating the reflection characteristics of a reflector according to the present disclosure. [Figure 3] 1 is a schematic perspective view illustrating an example of a unit structure in a reflector according to the present disclosure. [Figure 4] 1 is a schematic plan view illustrating a unit structure of a reflector according to the present disclosure. [Figure 5] 1 is a schematic cross-sectional view illustrating a reflector according to the present disclosure. [Figure 6] 1 is a schematic cross-sectional view illustrating a reflector according to the present disclosure. [Figure 7] 1 is a schematic cross-sectional view illustrating a reflector according to the present disclosure. [Figure 8] 1A and 1B are schematic diagrams illustrating the reflection characteristics of a reflector according to the present disclosure. [Figure 9] 1 is a schematic plan view illustrating a reflector according to the present disclosure. [Figure 10] 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. [Figure 11] 1A and 1B are schematic diagrams illustrating the configuration of a unit structure in a reflector according to the present disclosure. [Figure 12] 1 is a schematic perspective view showing a simulation model of Example 1 and a graph showing the simulation results. DETAILED DESCRIPTION OF THE INVENTION

[0020] Embodiments of the present disclosure will be described below with reference to the drawings and the like. 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 schematically depict the width, thickness, shape, etc. of each part compared to the actual form, but these are merely examples and are not intended to limit the interpretation of the present disclosure. Furthermore, in this specification and each drawing, elements similar to those previously described with reference to the preceding drawings will be designated by the same reference numerals, and detailed descriptions may be omitted as appropriate.

[0021] In this specification, when describing a mode in which another component is disposed on a certain component, the term "above" or "below" is used to include both cases in which another component is disposed directly above or below the component so as to be in contact with the component, and cases in which another component is disposed above or below the component through another component, unless otherwise specified. When describing a mode in which another component is disposed above a certain component, the term "above" or "below" is used to include both cases in which another component is disposed directly above or below the component so as to be in contact with the component, cases in which another component is disposed above or below the component through another component, and cases in which another component is disposed above or below the component through a space, unless otherwise specified. Furthermore, in this specification, when describing a mode in which another component is disposed on the surface of a certain component, the term "on the surface" is used to include both cases in which another component is disposed directly above or below the component so as to be in contact with the component, and cases in which another component is disposed above or below the component through another component, unless otherwise specified.

[0022] The reflector of the present disclosure will be described in detail below.

[0023] The reflector of the present disclosure is a reflector that reflects electromagnetic waves of a specific frequency band in a direction different from the direct reflection direction, and has 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, and the unit structures have a plurality of 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, and has a conductive layer on the surface facing the concave-convex structure, so that adjacent cell regions are conductive to each other.

[0024] 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 AA 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 a plurality of 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 has a plurality of 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 each unit structure 10 has six cell regions 11a to 11f. The reflector 1 has a conductive layer 3 on the surface facing the concavo-convex structure. The conductive layer 3 can also be arranged on the side surfaces of the cell regions 11a to 11f, providing electrical continuity between adjacent cell regions.

[0025] In FIG. 1(b), the reflector 1 has a base layer 4 having an uneven surface on one side and a conductive layer 3 arranged on the uneven surface of the base layer 4, but the configuration of the reflector is not limited to this.

[0026] In the reflector 1, the thicknesses t1 to t6 of the cell regions 11a to 11f of the unit structure 10 are different, and therefore the round-trip optical path lengths when the electromagnetic waves are reflected from the surface on the uneven structure side of the reflector 1 and emitted to the electromagnetic wave incident side are different, and these differences in the round-trip optical path lengths of the electromagnetic waves result in differences in the reflection phases.

[0027] Here, the reason why the term "optical path length" is used in this specification is that the wavelengths of the frequency bands targeted in this disclosure are closer to those of light and have a higher degree of directivity compared to conventional pre-LTE frequency bands, and therefore it is easier to explain it as behaving similarly to light, and in fact it means the effective distance that electromagnetic waves travel when they pass through air.

[0028] In the reflector 1, in the unit structure 10, the ends E1 to E6 of the cell regions 11a to 11f are on the same straight line in a cross section of the unit structure 10 in the thickness direction in the predetermined direction D1.

[0029] For example, if the length of each cell region 11a to 11f in a predetermined direction D1 is the same and the difference in thickness between adjacent cell regions is the same, in the unit structure 10, the ends E1 to E6 of each cell region 11a to 11f will be aligned on the same straight line (the dotted line in the figure) in a cross section of the unit structure 10 in the thickness direction in the predetermined direction D1.

[0030] 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, that is, λ / 12. In this case, when 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 the cell regions 11a-11f can be designed as follows:

[0031] 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

[0032] For example, when m=1 and a=0, the thicknesses t1 to t6 of the cell regions 11a to 11f are as follows:

[0033] t1:1λ / 12 t2:2λ / 12 t3:3λ / 12 t4:4λ / 12 t5:5λ / 12 t6:6λ / 12

[0034] In this 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. When 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.

[0035] As described above, in each of the cell regions 11a to 11f of the unit structure 10, thicknesses t1 to t6 change, which changes the round-trip optical path length of the electromagnetic wave and the reflection phase of the electromagnetic wave, so that the incident electromagnetic wave W1 can be reflected in a direction different from the regular reflection (specular reflection) direction, as illustrated in Fig. 2. 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.

[0036] Therefore, in the reflector of the present disclosure, by changing the thickness of each cell region of the unit structure, it is possible to change the round-trip optical path length of the electromagnetic wave for each cell region and control the reflection phase of the electromagnetic wave, thereby controlling the reflection direction of the electromagnetic wave relative to a predetermined incident direction to any direction.

[0037] In this specification, the term "reflected 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.

[0038] In addition, in this specification, the "relative reflection phase" refers to the reflection phase delay in a cell region of one unit structure relative to the reflection phase delay in the cell region with the smallest reflection phase delay as a reference, and is expressed as a negative sign. 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.

[0039] Unless otherwise specified, the reflection phase is in the range of more than -360 degrees and less than 360 degrees, and -360 degrees and +360 degrees return to 0 degrees. Furthermore, unless otherwise specified, the relative reflection phase is in the range of more than -360 degrees and 0 degrees or less, and -360 degrees returns to 0 degrees.

[0040] In this specification, the term "cell region" refers to a region in a unit structure that has the same thickness, that is, a region in which the reflection phase of electromagnetic waves is the same.

[0041] In a conventional reflectarray in which multiple reflecting elements are arranged, for example, the reflection phase can be delayed or advanced by adjusting the dimensions and shape of the reflecting elements. In the reflector of the present disclosure, the reflection phase can be advanced by using the reflection phase in the cell region with the smallest thickness as a reference and increasing the thickness of each cell region of the unit structure, thereby controlling the direction of the reflected wave. Furthermore, in the reflector of the present disclosure, the reflection phase in the cell region with the largest thickness as a reference can be used to control the direction of the reflected wave by utilizing the fact that the reflection phase delays as the thickness of each cell region of the unit structure decreases.

[0042] In the present disclosure, there is no need to arrange multiple reflective elements as in the past, 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 manufacturing a reflector by 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 angle, a 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, desired reflection characteristics can be easily obtained and the effects of dimensional variation can be reduced. Therefore, it is easy to customize the reflection characteristics of the reflector.

[0043] Hereinafter, each configuration of the reflector of the present disclosure will be described.

[0044] 1.Uneven structure The reflector of the present disclosure has a concavo-convex structure in which a plurality of unit structures having a thickness distribution in which the thickness increases in a predetermined direction are arranged.

[0045] The unit structure has a plurality of cell regions with different thicknesses.

[0046] Furthermore, when both the incident wave and the reflected wave can be regarded as plane waves, in each unit structure, the ends of each cell region are on the same straight line in a cross section of the unit structure in the thickness direction in a predetermined direction.

[0047] 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.

[0048] The end of a cell region refers to the end of a cell region that is thinner than the first cell region among the other cell regions adjacent to the first cell region in a direction of increasing thickness in the cross section of a unit structure. For example, in FIG. 1(b), the end of cell region 11b refers to the end of cell region 11a, which is thinner than cell region 11b among the other cell regions 11a and 11c adjacent to cell region 11b in a predetermined direction D1, 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 adjacent to the first cell region in a direction of increasing thickness, the end of the first cell region refers to the end opposite the other cell region that is thicker than the first cell region. For example, in FIG. 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.

[0049] Furthermore, in a cross section of the thickness direction of the unit structure in a predetermined direction, the difference in thickness direction between the ends of each cell region is preferably within ±λ / 2, more preferably within ±λ / 4, and even more preferably within ±λ / 6.

[0050] The unit structures have a thickness distribution in which the thickness increases in a predetermined direction. For example, the unit structures may have a thickness distribution in which the thickness increases only in 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, FIG. 3(a) shows an example of a unit structure 10 having a thickness distribution in which the thickness increases only in a first direction D1, while FIGS. 3(c), 3(e), and 4(a) show examples of a unit structure 10 having a thickness distribution in which the thickness increases in both the first direction D1 and a second direction D2.

[0051] As described above, in each unit structure, when the ends of each cell region are on the same line in the cross section of the unit structure in the thickness direction in a predetermined direction, and when the unit structure has a thickness distribution in which the thickness increases in only one direction, the ends of each cell region are on the same line in the cross section of the unit structure in the thickness direction in that one direction. Also, in the above case, when the unit structure has a thickness distribution in which the thickness increases in two mutually perpendicular directions, the ends of each cell region are on the same line in the cross section of the unit structure in the thickness direction in each of those two directions.

[0052] On the other hand, as described above, when the cross section of a unit structure in a predetermined 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 directions perpendicular to each other, the cross sections of the unit structure in the thickness direction in each of the two directions will have a periodic step shape with a constant thickness as its upper limit.

[0053] 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, and is set appropriately taking into account overall strength, ease of formation, and the like. a can be, for example, approximately 0 mm or greater and 3 mm or less. 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, for example, greater than or equal to 1, preferably greater than or equal to 3. As m increases, the overall thickness of the reflector increases, which may make installation of the reflector more difficult. For example, in FIG. 1(b), the thickness t6 of the maximum thickness cell region 11f having the maximum thickness t6 is preferably (λ / 2) × m + a.

[0054] 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 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.

[0055] 1(b) shows an example in which the cross-sectional shape of the unit structure 10 is a staircase shape with six steps, and the difference in thickness between adjacent cell regions is equal. In this case, the difference in thickness between adjacent cell regions is preferably (λ / 2) / 6=λ / 12.

[0056] 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 the cell regions 11a to 11d of the unit structure 10 can be set to 1λ / 12, 3λ / 12, 4λ / 12, and 6λ / 12, respectively, and the difference in thickness between adjacent cell regions 11a and 11b can be set to 2λ / 12, the difference in thickness between adjacent cell regions 11b and 11c can be set to λ / 12, and the difference in thickness between adjacent cell regions 11c and 11d can be set to 2λ / 12. In this case, the difference in thickness between adjacent cell regions is 2λ / 12 = λ / 6 = (λ / 2) / 3 and λ / 12 = (λ / 2) / 6, respectively.

[0057] In addition, the difference in thickness between adjacent cell regions in one unit structure may be equal or different, but is preferably equal. For example, Fig. 1(b) shows an example in which the difference in thickness between adjacent cell regions is equal, and Fig. 5 shows an example in which the difference in thickness between adjacent cell regions is different.

[0058] Furthermore, in one 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 preferably less than 1 / 2 the wavelength λ of the electromagnetic wave. Furthermore, in one 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 preferably more than 1 / 6 the wavelength λ of the electromagnetic wave. For example, as shown in FIG. 1(b), if a unit structure 10 has six cell regions, the difference in thickness t1 between the minimum thickness cell region 11a having the minimum thickness t1 and the maximum thickness cell region 11f having the maximum thickness t6 in one unit structure 10 is preferably less than λ / 2. Specifically, in one unit structure 10, the thickness t1 of the minimum thickness cell region 11a having the minimum thickness t1 can be λ / 12, the thickness t6 of the maximum thickness cell region 11f having the maximum thickness t6 can be 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 5λ / 12.

[0059] The size of the unit structure, specifically the length of the unit structure in a predetermined direction in which the thickness increases, is appropriately set according to the desired reflection characteristics. The length of the unit structure in the predetermined 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 the predetermined direction in which the thickness increases, the difference between the reflection angle and the specular reflection angle can be increased, while by increasing the length of the unit structure in the predetermined direction in which the thickness increases, the difference between the reflection angle and the specular reflection angle can be reduced.

[0060] In addition, the length of a unit feature in a predetermined direction in which the thickness increases refers to the length of the unit feature in the predetermined direction when the unit feature has a thickness distribution in which the thickness increases in the predetermined direction. For example, in Figure 5, the thickness of unit feature 10 increases in predetermined direction D1, and the length of unit feature 10 in this predetermined direction D1 is L.

[0061] The cross-sectional shape of the unit feature may be, for example, a step 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 of unit features 10 having a step shape, and Figure 6 shows an example of unit features 10 having a tapered shape.

[0062] Although the unit structure has multiple cell regions with different thicknesses, if the cross-sectional shape of the unit structure is tapered, the unit structure can be considered to have an infinite number of cell regions. 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.

[0063] Furthermore, since the reflector is an arrangement of a plurality of unit structures having thickness distribution, the pattern shape of the unit structures in plan view may be any shape that allows for gap-free arrangement, such as a rectangle, a regular hexagon, etc. For example, Figures 3(a) to (f) and Figure 4(a) show examples in which the pattern shape of the unit structures 10 in plan view is rectangular.

[0064] In the unit structure, the thickness of each cell region is designed to be set as described above. The thickness of each cell region is appropriately set depending on the wavelength of the electromagnetic wave and the desired reflection characteristics. For example, when the frequency of the electromagnetic wave is 30 GHz, that is, when the wavelength of the electromagnetic wave is 10 mm, the thickness of each cell region is preferably approximately 0.1 mm or more and 5.1 mm or less.

[0065] In the unit structure, the pitch and width of the cell region are set appropriately.

[0066] Furthermore, as for 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. That is, the unit structure can be configured with cell regions each having a width of λ / p or less, arranged 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 less than the length of one side of the reflector. Furthermore, the number of cell regions arranged closely together in one unit structure is 2 or more, although this varies depending on the direction and angle of the incident wave and reflected wave.

[0067] In addition, it is preferable that the pitch of the cell regions in one unit structure is uniform.

[0068] The pitch of the cell regions refers to the distance from the center of one cell region to the center of an adjacent cell region.

[0069] Furthermore, in one unit structure, the widths of the cell regions in a predetermined direction in which the thickness increases may be equal or different, but are preferably equal.

[0070] 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 obtained by dividing a concentric circle into four equal parts by perpendicular diameters, a curved staircase shape, etc. For example, Figure 3(b) shows an example of a stripe shape, Figure 3(d) shows 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) show examples of a microarray shape, Figure 4(b) shows an example of a concentric quadrant shape, and Figure 4(c) shows 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 planar view; the unit structures can be arranged at an appropriate angle and in an appropriate arrangement direction depending on the required reflection characteristic design.

[0071] Each unit structure has multiple cell regions. The number of cell regions in one unit structure is, for example, 3 or more, and preferably 6 or more. The greater the number of cell regions in one unit structure, the smaller the difference in thickness between adjacent cell regions, the smaller the difference in the reflection phase of electromagnetic waves between adjacent cell regions, and the smoother the wavefront of the reflected wave. Furthermore, the greater the number of cell regions in one unit structure, the more preferable it is, and there is no particular upper limit. Note that, when the cross-sectional shape of the unit structure is a stepped shape, the number of cell regions corresponds to the number of steps in the stepped shape. Furthermore, when the cross-sectional shape of the unit structure is a tapered shape, as described above, the tapered shape can be considered to have an infinitely large number of cell regions.

[0072] The reflector has, as a unit structure, at least a first unit structure having two or more cell regions with different thicknesses.

[0073] Furthermore, the reflector may have only a first unit structure as a unit structure, or may further have a second unit structure different from the first unit structure. That is, the reflector may have only the same unit structure as a unit structure, or may have unit structures that are different from each other. When the reflector is an arrangement of a plurality of unit structures that are different from each other, it can affect the overall reflection characteristics of the reflector. Specifically, examples of such effects include adjustment of polarization characteristics and effects on beam profiles (high directivity, diffusion, multi-beam, etc.).

[0074] The first unit structure and the second unit structure can have different reflection characteristics, and for example, at least one of the length of the unit structure in the direction in which the thickness increases, the thickness distribution, the number of cell regions, the width, the pitch, the pattern shape of the unit structure in a planar view, and the pattern shape of the cell regions in a planar view can be made different.

[0075] Furthermore, when the reflector has unit structures that are different from one another, the number of types of unit structures is not particularly limited.

[0076] In a reflector, a 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 so-called plane wave, the reflector preferably has multiple identical unit structures arranged therein, and more preferably, the unit structures have the same length in the predetermined thickness direction and a striped pattern in the planar view of the cell region. For example, Figures 1(a) and 1(b) show an example in which the reflector 1 has multiple identical unit structures, the unit structures 10a and 10b have the same length in the predetermined direction D1, and the cell regions 11a to 11f have a striped pattern in the planar view. 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, Figure 1(a) shows an arrangement in which the longitudinal direction of the stripes in the cell region is parallel to the short-side direction of the reflector, but this is not limited to this, and in an actual reflector, the longitudinal and short-side directions of the stripes in the cell region can be set arbitrarily depending on the design of the reflection characteristics.

[0077] Furthermore, for example, when diffusing electromagnetic waves, i.e., reflecting them as cylindrical waves, it is preferable that the reflector be an arrangement of a plurality of different unit structures, in which the lengths of the unit structures in a predetermined direction of thickness increase are different, and the pattern shape of the cell region in a planar view is striped. For example, in Fig. 7, the 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 structure 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 the cell regions 11a to 11g, 12a to 12g, and 13a to 13g in a plan view is striped. In this case, as shown in FIG. 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, and the reflected wave W2 can be reflected with a wide wavefront.

[0078] Furthermore, when the reflector has different unit structures as unit structures, multiple types of unit structures with different reflection characteristics may be used, and multiple unit structures of each type may be arranged in a plane, with regions where multiple unit structures of the same type are arranged. For example, in Fig. 9, two types of unit structures 10a and 10b with different reflection characteristics are used, with a first region 5a where multiple unit structures 10a of one type are arranged and a second region 5b where multiple unit structures 10b of the other type are arranged in a plane, to form a reflector 1. In this embodiment, multiple coverage holes can be accommodated.

[0079] Furthermore, when the reflector has unit structures that are different from one another, the thickness of each cell region of the N unit structures may be set so that the N unit structures are shifted by N wavelengths (phase difference: N × 360 degrees), where N is an integer of 2 or more.

[0080] 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).

[0081] For example, if the length of each cell region 11a-11b, 12a-12c in a specified direction D1 is the same and the difference in thickness between adjacent cell regions is the same, in a cross section of the thickness direction of unit structures 10a, 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.

[0082] Specifically, in two unit structures 10a and 10b each having a total of five cell regions 11a-11b and 12a-12c, when the wavelength of the electromagnetic wave is λ, the difference in thickness between adjacent cell regions can be designed to be the value obtained by dividing λ by 5, that is, λ / 5. In this case, when the wavelength of the electromagnetic wave is λ, 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, the thicknesses t1 to t4 of each of the cell regions 11a-11b and 12a-12c can be designed as follows:

[0083] 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

[0084] For example, when a=0, the thicknesses t1 to t4 of the cell regions 11a to 11b and 12a to 12c are as follows:

[0085] t1:2λ / 10 t2:4λ / 10 t3:1λ / 10 t4:3λ / 10 t5:5λ / 10

[0086] In such a case, when the reflection phase in cell region 12c, which has the smallest reflection phase, is used as a reference, the relative reflection phases in each of cell regions 11a-11b and 12a-12c are as shown in Figures 10(b) and 10(c), for example. Figure 10(b) is a graph in which the range of the relative reflection phase of the electromagnetic wave is expressed as more 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 expressed as more 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 predetermined direction D1, and the numbers of cell regions 11a-11b and 12a-12c are different.

[0087] Furthermore, when the incident wave and the reflected wave are plane waves, the reflector has a periodic structure in which unit structures are repeatedly arranged. The term "periodic structure" refers to a structure in which unit structures are periodically and repeatedly arranged. Among unit structures in a periodic structure, unit structures with the same reflection characteristics can be made identical in terms of the length of the unit structure in the direction of increasing thickness, the thickness distribution, the number, width, and pitch of cell regions, the pattern shape of the unit structure in a planar view, and the pattern shape of the cell region 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 of the unit structure in the direction of increasing thickness, the thickness distribution, the number, width, and pitch of cell regions, the pattern shape of the unit structure in a planar view, and the pattern shape of the cell region in a planar view, etc., of the combined unit structures are appropriately set according to the desired reflection characteristics.

[0088] Generally, in designing reflection characteristics that reflect a plane wave as a plane wave in a direction different from the specular reflection direction, it is possible to design 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 structure. For example, as shown in Figure 11, we will explain a portion of a reflector in which 10 x 10 (i = 10, j = 10) cell areas of the same size, which can individually adjust the reflection phase, are arranged. At this time, it is important to note that the size of the 10 x 10 cell areas is not necessarily the size of the unit structure. The angle of incidence (θ in , φ in ) is reflected from the direction of the reflected wave (θ out , φ out ) the reflection phase δ required for the cell area at position (i, j) when a plane wave is reflected in the direction i,j is given by the following equation:

[0089] 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 position (i,j) relative to the phase center (0,0) λ: Wavelength of reflected wave [m] p: Cell area size [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 Shows.

[0090] where t is the thickness of the cell area, t min is the thickness of the minimum thickness cell region, Δt is the increase in thickness from the minimum thickness, λ is the wavelength of the electromagnetic wave, and the reflection phase when Δt = 0 is taken as the reference (0), the reflection phase δ is roughly expressed as follows: δ[rad]=4×π×(Δt / λ) From the above equation, Δt can be expressed as follows: Δt=(δ×λ) / (4×π) Therefore, the reflection phase δ is calculated by the following formula: i,j The cell region may be arranged to have a thickness t that matches the thickness t of the cell. t=t min +Δt=t min +((δ×λ) / (4×π))

[0091] In addition, in the above formula, when Δt=λ / 2, δ=2π [rad], and any reflection phase can be created with a thickness less than that. Similarly, in the above formula, the reflection phase δ i,j If exceeds 2π [rad], the reflection phase δ i,j The remainder of 2π is the reflection phase δ i,j It is okay to consider it as such.

[0092] Furthermore, the thickness t of the cell region does not need to be exactly the thickness calculated from the above formula, and 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).

[0093] 2.Layer composition 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.

[0094] The reflector must have at least a conductive layer, and may, for example, have a base layer and a conductive layer disposed on the surface of the base layer, or may have only a conductive layer.

[0095] Hereinafter, 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 will be described separately.

[0096] (1) First aspect The reflector of this embodiment has a substrate layer and a conductive layer disposed on the surface of the substrate layer.

[0097] (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.

[0098] The sheet resistance of the conductive layer can be measured by a four-terminal method.

[0099] The conductive layer may be disposed on the surface of the reflector facing the concave-convex structure, but it is preferable that the conductive layer also be disposed on the side surfaces of the cell regions to provide electrical continuity between adjacent cell regions.

[0100] The conductive layer is not particularly limited as long as it can reflect electromagnetic waves in a predetermined frequency band and satisfies the above-mentioned sheet resistance, and examples thereof include metal films; metal oxide films such as ITO, IZO, AZO, GZO, and ATO; carbon films; and metal meshes.

[0101] The thickness of the conductive layer is not particularly limited as long as it can reflect electromagnetic waves in a predetermined frequency band and satisfies the above-mentioned sheet resistance, and is, for example, 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.

[0102] 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 thereof include PVD methods such as vacuum deposition and sputtering; CVD methods; and plating methods.

[0103] (b) Base material layer The substrate layer is a member that supports the conductive layer.

[0104] The material of the base layer is not particularly limited, and may be, for example, resin, glass, quartz, ceramics, etc. Among these, resin is preferable in view of the ease of forming the concave-convex structure.

[0105] Furthermore, when the base layer contains a resin, it may further contain conductive particles, in which case adjacent cell regions can be electrically connected to each other even if the conductive layer is not disposed on the side surfaces of the cell regions.

[0106] When the substrate layer contains a resin, it may contain an additive, if necessary.

[0107] The substrate layer may be, for example, a single layer or multiple layers. The substrate layer may have a substrate portion that serves as a base and an uneven portion disposed on the substrate portion.

[0108] Furthermore, the base material layer may be, for example, a single member in which all cell regions are integrally formed, or may be a layer in which the individual cell regions are formed separately and the cell regions are arranged in a block shape.

[0109] The method for forming the base layer is not particularly limited as long as it is a method capable of forming a predetermined uneven structure, and examples thereof include cutting a resin sheet, laser processing, molding using a mold or vacuum casting, modeling using a 3D printer, joining small pieces, etc. Formation methods that do not use a mold, such as cutting, laser processing, or 3D printers, can be easily customized according to the desired reflection angle, and can therefore be suitably used for tuning the design when designing and developing special installation situations or large-scale reflectors that are difficult to simulate.

[0110] (2) Second mode The reflector of this embodiment has only a conductive layer.

[0111] The definition of the conductive layer is the same as in the first embodiment.

[0112] The conductive layer is not particularly limited as long as it can reflect electromagnetic waves in a predetermined frequency band and satisfies the above-mentioned sheet resistance, and examples thereof include metal films; metal oxide films such as ITO, IZO, AZO, GZO, and ATO; and carbon films.

[0113] The method for forming the conductive layer is not particularly limited as long as it is a method that can form a conductive layer having a predetermined uneven structure, and examples include cutting a metal sheet, shaping using a mold, laser processing, modeling using a metal 3D printer, and joining small parts.

[0114] Furthermore, the conductive layer may be, for example, a single member in which all the cell regions are integrally formed, or may be a layer in which the individual cell regions are formed separately and the cell regions are arranged in a block shape.

[0115] 3. Controlling the direction of electromagnetic wave reflection 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, and the reflection phase of the electromagnetic wave can be controlled. 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, the reflection direction of the electromagnetic wave incident from a predetermined direction can be controlled.

[0116] Furthermore, as described above, the reflection characteristics of the unit structures can be controlled by adjusting the length of the unit structures in a predetermined direction in which the thickness increases. For example, by shortening the length of the unit structures in the predetermined direction in which the thickness increases, the reflection angle of the electromagnetic wave can be increased, while by lengthening the length of the unit structures in the predetermined direction in which the thickness increases, the reflection angle of the electromagnetic wave can be decreased.

[0117] Furthermore, if t is the thickness of the cell area, b is the minimum thickness of the cell area 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×{(tb) / 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 the reflection phase δ of the cell region at the above-mentioned (i, j) position. i,j The components are arranged so that:

[0118] 4. Other configurations The reflector of the present disclosure may have other configurations as needed.

[0119] (1) Ground layer When the reflector of the present disclosure has the above-described substrate layer and conductive layer, it may have a ground layer on the surface of the substrate layer opposite the conductive layer. The ground layer can block interference with objects present on the back side of the reflector and suppress noise generation. For example, a common conductive film such as a metal film, a metal mesh, a carbon film, or an ITO film can be used as the ground layer.

[0120] (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 to 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 and reflection directions of electromagnetic waves and the actual incident and reflection directions of electromagnetic waves can be corrected.

[0121] 5. Characteristics of reflectors The reflector of the present disclosure reflects electromagnetic waves of a specific frequency band in a direction different from the specular reflection direction. The frequency band of the electromagnetic waves is preferably, for example, 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 a fifth-generation mobile communication system, known as 5G.

[0122] 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.

[0123] The present 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 idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure. [Example]

[0124] The present disclosure will be specifically described below with reference to examples.

[0125] [Example 1] A simulation was performed to determine the reflection characteristics of the reflector. 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 contained a total of 36 cell regions with eight different thicknesses, and the unit structures were used as a model with a periodic structure in which they were repeatedly arranged in both directions. In addition, the following parameters were used for the reflector in the simulation:

[0126] Incident wave frequency: 28GHz Incident angle of incident wave: (θ, φ)=(20°, 90°) Desired reflection angle of reflected wave: (θ, φ) = (45°, 0°) Thickness of each cell area: 0.1mm~5.6mm Thickness difference between adjacent cell areas: 1.1 mm

[0127] 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. The polar coordinates (θ, φ) are defined accordingly, as shown in Figure 11 above. Note that the RCS (radar cross section) that appears to be reflected from the paper to the front 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 larger 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. FIG. 12(d) shows the bistatic radar cross section at θ=45° swept with φ. [Explanation of symbols]

[0128] 1 … Reflector 3...Conductive layer 4 … Base material layer 10, 10a, 10b... unit structure 11a~11g, 12a~12f, 13a~13e ... Cell area D1: Predetermined direction L: length of the unit structure in a given direction of thickness increase t1, t2, t3, t4, t5, t6 … Thickness of the cell area

Claims

1. 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. 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. 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. 4. The reflector according to claim 1, wherein the difference in thickness between adjacent cell regions in the unit structure is equal.

5. 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.

6. 6. The reflector according to claim 1, which has a periodic structure in which the unit structures are repeatedly arranged.

7. 7. The reflector according to claim 1, wherein the unit structure comprises a second unit structure different from the first unit structure.

8. A reflector described in any one of claims 1 to 7, wherein the difference in thickness between the ends of each cell region is within ±λ / 2.

9. A reflector described in any one of claims 1 to 8, wherein the unit structure has a stepped shape.

10. A reflector described in any one of claims 1 to 9, wherein the number of cell regions in one unit structure is three or more.

11. A reflector as described in claim 10, wherein the ends of each cell region are on the same straight line.

12. A reflector described in any one of claims 1 to 11, having a substrate layer having an uneven surface on one side and the conductive layer arranged on the uneven surface of the substrate layer.

13. A reflector as described in claim 12, having a ground layer on the side of the base material layer opposite the conductive layer.

14. A reflector described in any one of claims 1 to 13, wherein a fixing member is arranged on the surface of the reflector opposite to the uneven structure.

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