WO2025249467A1 - Reflectarray - Google Patents

Abstract

The purpose of the present invention is to provide a technology that makes stable communication and motion detection possible even when the incidence angle or reflection angle with respect to an incident or reflected beam of a reflectarray deviates from design. For this purpose, a reflectarray according to the present invention is characterized by having multiple types of reflection control regions in which a plane wave from a design incidence angle θi satisfying formula (1) is most strongly reflected at a design reflection angle θr satisfying formula (2), wherein, in downlink communication (radiation wave), the plane wave incident in an angular range of ±α degrees satisfying formula (3) around a design center incidence angle [θi0]d is reflected such that the average value of reflection intensity in an angular range of ±α degrees around a design center reflection angle [θr0]d is higher by 5 dB or more than the average value of reflection intensity in an angular range of -90 to 90 degrees excluding the angular range, and a variation coefficient C[θr]d of reflection intensity derived from formula (4) for an arbitrary reflection angle [θr]d within the angular range is 0.6 or less.

Description

Reflectarray

The present invention relates to a reflectarray.

With the advancement of digitalization in society, data communication speeds in wireless communications have increased dramatically, and the accompanying increase in the frequency of electromagnetic waves (hereinafter also referred to as "radio waves"). However, as the frequency of electromagnetic waves increases, they tend to travel in a more directional manner, which means that they cannot bend around buildings and other obstacles, often resulting in blind zones where communication is not possible.
For these reasons, it is necessary to increase the number of base stations in order to realize 5G and 6G communications over a wide area. However, increasing the number of base stations requires a large amount of cost, which makes it difficult to increase the number of base stations quickly.
Furthermore, millimeter-wave radar (sensors), which use high-frequency electromagnetic waves to measure distances and detect moving objects with high precision, are being used in a variety of fields, including mobility, robotics, security, and healthcare. For example, in mobility, millimeter-wave radar is used in onboard radars for advanced driver assistance systems and autonomous driving technology, accurately measuring the position, speed, and distance of other vehicles and pedestrians, enabling safe following distances and obstacle avoidance. In healthcare, millimeter-wave sensors are used in non-contact sensors for monitoring and medical monitoring, enabling them to detect human movement, falls, and subtle changes in heart rate and breathing, even in dark places and through obstacles. While improved performance of millimeter-wave radar (sensors) is required for these applications, challenges remain, including beam directionality, obstacles, and reduced detection accuracy due to multipath interference.
In recent years, reflectarrays have been proposed as a technology for controlling the direction of electromagnetic waves in order to solve these issues with 5G and 6G communications and millimeter-wave radar (sensors).
A reflectarray (electromagnetic wave reflector) is a component that reflects electromagnetic waves, and includes not only those that perform symmetrical reflection where the angle of incidence and the angle of reflection are equal, but also those that perform asymmetrical reflection where the angle of incidence and the angle of reflection are different, those that retroreflect electromagnetic waves in the direction of incidence, those that scatter electromagnetic waves in multiple directions, and those that concentrate electromagnetic waves at a specific location.

Patent Document 1 discloses a frequency-selective reflector (reflector array) that reflects electromagnetic waves of a specific frequency band in a direction different from the direction of specular reflection, and that can widen or narrow the reflected beam of a plane wave incident from a uniform incident direction by arranging a main region and multiple sub-regions with different reflection directions.
Patent Document 2 also discloses a reflectarray that enables communication at multiple incident and reflection angles without reducing directional gain by arranging multiple supercells, each of which has one first element and one second element arranged in a row.

International Publication No. 2023/027195 Japanese Patent Application Laid-Open No. 2023-22427

However, while conventional reflectarrays function to reflect electromagnetic waves of a specific frequency band incident at a designed angle of incidence in a direction different from the specular reflection direction, they often do not function properly for incident waves at angles other than the designed angle of incidence. Furthermore, as the size of a reflectarray increases, the reflected beam becomes sharper and the area illuminated by the reflected beam becomes narrower. Due to these characteristics of reflectarrays, 5G and 6G communications face issues where communication stability can be compromised if the angle of incidence or reflection of the reflectarray's incident or reflected beam deviates from the design, such as (a) a deviation in the installation position or angle of the reflectarray, (b) a deviation in the terminal position, or (c) the terminal being unable to obtain sufficient reception power if an obstacle such as a person or object temporarily exists in the incident or reflected beam. Millimeter-wave radar (sensors) also face issues where motion detection stability can be compromised for similar reasons.

Patent Document 1 discloses a function for adjusting the reflected beam profile of a frequency selective reflector to widen the beam width of a reflected wave for a plane wave incident from a predetermined design angle of incidence, but does not explain how a similar function can be provided for a plane wave incident from an angle other than the design angle of incidence. Patent Document 1 also discloses a function for widening the reflected beam of a spherical wave for a spherical wave incident, but this is done by correcting the difference in the incident direction vector of the spherical incident wave, which is uniquely determined for each divided region, and setting the reflection direction vector for each divided region to be different, and does not explain the effect of the incident from a direction deviated from the uniquely determined incident direction vector.
Although Patent Document 2 describes that communication is possible using a plurality of incident and reflection angles, it does not recognize the problem of ensuring communication stability when the incident angle or reflection angle of the incident or reflected beam deviates from the design.
Therefore, an object of the present invention is to provide a technology that enables stable communication and moving object detection even when the angle of incidence or angle of reflection of the incident or reflected beam of the reflectarray deviates from the design.

In order to solve the above problems, one representative reflectarray of the present invention has a plurality of types of reflection control regions that most strongly reflect a plane wave from an arbitrary design incident angle θi that satisfies Equation (1) to an arbitrary design reflection angle θr that satisfies Equation (2) for an electromagnetic wave in a specific frequency band,

In downstream communication (or radiation wave), a plane wave incident within an angle range of ±α degrees (hereinafter referred to as the "downstream incident angle range ±α") that satisfies formula ( ₃ ) around the design central incident angle [θi ₀ ]d is strongly reflected within the downstream reflection angle range ±α so that the average value of the reflection intensity (bistatic RCS) within the angle range of ±α degrees (hereinafter referred to as the "downstream reflection angle range ±α") around the design central reflection angle [θr 0 ]d is 5 dB or more higher than the average value of the reflection intensity within the angle range of -90 degrees to 90 degrees excluding the downstream reflection angle range ±α, and when the reflection intensity of the plane wave from the incident angle [θi]d to the reflection angle [θr]d is σ[θi]d[θr]d, the coefficient of variation C _{[θr]d of the reflection intensity derived from formula (4) for any reflection angle [θr]d} within the downstream reflection angle range ±α is 0.6 or less.

According to the present invention, stable communication and moving object detection can be achieved even if the angle of incidence or angle of reflection of the incident or reflected beam on the reflectarray deviates from the design.
Problems, configurations, and effects other than those described above will become apparent from the following description of the preferred embodiments.

FIG. 1 is a cross-sectional view showing an example of a layer structure of a reflect array. FIG. 2 is a diagram showing an example of an element pattern shape. FIG. 3 is an example of a schematic diagram showing an enlarged reflection control area portion. FIG. 4 is a schematic diagram illustrating characteristic 1 of a single reflectarray. FIG. 5 is a schematic diagram illustrating characteristic 2 of a single reflectarray. FIG. 6 is a schematic diagram illustrating characteristic 3 of a single reflectarray. FIG. 7 is a schematic diagram showing an example of a failure in radio wave relay using a single reflectarray. FIG. 8 is a schematic diagram illustrating the function realized by the reflect array according to this embodiment. FIG. 9A is a schematic diagram showing an overall image of incident and reflected downstream communication radio waves (or radiation waves) in the reflect array of the first embodiment. FIG. 9B is a schematic diagram showing an overall image of incident and reflected upstream communication radio waves (or received waves) in the reflect array of the second embodiment. FIG. 10 is a schematic diagram of an arrangement of reflection control regions (groups) in the reflect array of Example 1. FIG. 11 is a graph showing reflection patterns (bistatic RCS) of the reflectarrays of Example 1 and Comparative Examples 1 and 2. FIG. 12 is a graph showing the reflection patterns (bistatic RCS) of the reflectarrays of Example 2 and Comparative Example 3.

Below, an embodiment of the present invention will be described with reference to the drawings. Note that the present invention is not limited to this embodiment. In addition, in the drawings, identical parts are denoted by the same reference numerals.

In the following description, an xyz coordinate system is applied, and the reflectarray is formed on the xy plane. The positive direction of the z axis is sometimes referred to as upward, and the negative direction as downward. A view of the xy plane viewed from above the z axis (planar view) is called a plan view, and a view of a plane cut by a plane parallel to the z axis viewed from the perpendicular direction (cross-section view) is called a cross-sectional view.
The shape of the reflectarray in the xy plane is arbitrary, but in the following description, the reflectarray is assumed to be the simplest rectangle, and is formed so that each side of the reflectarray is parallel to the x-axis and y-axis, respectively.

In the following description, "surface" may refer not only to the surface of a plate-shaped member, but also to the interface of a layer contained in a plate-shaped member that is approximately parallel to the surface of the plate-shaped member. Furthermore, "upper surface" and "lower surface" refer to the surface shown at the top or bottom of a drawing of a plate-shaped member or a layer contained in a plate-shaped member.

In the following description, electromagnetic waves (radio waves) are assumed to be plane waves, but when referring to plane waves, this also includes electromagnetic waves whose wavefronts can be considered to be virtually flat at far-field distances. In this disclosure, electromagnetic waves (radio waves) are sometimes simply referred to as plane waves. Although the wavefront theoretically extends infinitely, in practice, the wavefront can be considered to be virtually flat at far-field distances. This property is used in various fields of physics and engineering, and its application is also possible within the scope of this disclosure.

<Reflectarray configuration>
First, the configuration of the reflectarray will be described. Fig. 1 is a cross-sectional view showing an example of the layer configuration of a reflectarray. As shown in Fig. 1, the reflectarrays 4 and 40 have a configuration in which at least an element pattern 1, a dielectric layer 2, and a ground layer 3 are layered in a direction from the +z-axis direction to the -z-axis direction. In the following description, the configuration consisting of the three layers of the element pattern 1, the dielectric layer 2, and the ground layer 3 will be referred to as the "basic configuration."

In practice, it is preferable that the reflectarray have one or more layers (additional function layers 5) having various functions laminated on the element pattern 1 side of the basic configuration, the ground layer 3 side, or both. The lamination method on the element pattern 1 side may be to completely fill the gaps between the elements, or to cover the upper surfaces of the elements while leaving the gaps between the elements. Examples of the additional function layers 5 include a design layer that takes the scenery into consideration, an installation layer that makes it easy to install the electromagnetic wave reflector on a wall, ceiling, support, etc., a protective layer that protects the basic configuration, and a functional layer that imparts various functions.
Furthermore, if necessary, an adhesion improving layer may be formed between the element pattern 1 and the dielectric layer 2, between the ground layer 3 and the dielectric layer 2, and between the dielectric layer 2 and the element pattern 1 and the additional function layer 5 in order to improve the adhesion between the elements. The adhesion improving layer is made of an adhesive. The adhesive may be a water-dispersion adhesive, a solution-based adhesive, a solventless adhesive, or a solid-based adhesive.
The aforementioned additional functional layer and adhesion improving layer are sometimes collectively referred to as functional layers.

(Element pattern)
The element pattern 1 is provided to asymmetrically reflect the incident electromagnetic wave in a direction different from that of the symmetric reflection. The thickness of the element pattern is, for example, 10 nm to 105 μm.
The element pattern 1 preferably has a surface resistance of 100 Ω/□ or less. The material used for the element pattern 1 may be, for example, a conductive material. The same material as that used for the ground layer 3 may be used. A film of a conductive inorganic or organic material may be formed on the dielectric layer. From the viewpoints of flexibility, film-forming properties, stability, sheet resistance, and low cost, it is preferable to use a film formed by vapor deposition, which is a formation method described below, as the element pattern 1.

The shape of the element pattern 1 can be, but is not limited to, a cross patch. Figure 2 is a diagram showing an example of the element pattern shape. As shown in Figure 2, a reflectarray may be formed using element patterns 1 of any shape that reflects radio waves, such as a continuous film, a mesh, or a punched shape. For example, instead of a cross patch (Figure 2(a)), a cubic patch (Figure 2(b)), a cylindrical patch (Figure 2(c)), a triangular prism patch (Figure 2(d)), a Jerusalem cross patch (Figure 2(e)), multiple parallel conductive patterns (Figure 2(f)), a ring-shaped conductive pattern (Figure 2(g)), or an element pattern that combines multiple of these (Figure 2(h)) may be used.

The following describes the case where element pattern 1 is a cross patch. A cross patch refers to a shape in the xy plane where two rectangular patches intersect at right angles. The length of the cross patch element pattern is called the element length, and the width of the cross patch element pattern is called the element width. The reflection phase of the unit cell is controlled by varying either the element length or the element width, or both. When the element length is fixed, it is desirable to set the element length value as large as possible within the unit cell. Setting it large makes it easier to obtain the desired reflection phase characteristics. When the element width is fixed, it is desirable to set the element width value as large as possible within the unit cell. Setting the element width value large makes the slope of the reflection phase gentler, thereby improving processing accuracy. Note that the element length is not limited to being set for cross patch element patterns, but can also be set for element patterns with other shapes. The element length can be set to a common length within the reflection control region, or it can be set to a different length for each element pattern included in the reflection control region.

The method of forming the element pattern 1 can be a method of forming a conductive material over the entire surface of the dielectric layer 2 to form a continuous film, and then forming the element pattern by processing, or a method of forming an element pattern layer directly on the dielectric layer.
As a method for forming a continuous film of a conductive material over the entire surface of the dielectric layer 2, for metals, dry coating such as sputtering or vapor deposition, plating or gravure coating using metallic ink, wet coating such as die coating, etc. can be selected. Alternatively, a rolled metal plate can be attached to the dielectric layer. Similarly, a continuous film can be formed by dry coating for inorganic oxide materials, or wet coating for organic materials. Painting or spraying methods can also be used.

The continuous film thus formed is subjected to removal processing such as dry etching, wet etching, or cutting to remove unnecessary portions, thereby forming an element pattern.
When etching is used for removal processing, the edges of the element patterns that make up the reflect array may become rounded (in other words, they may become rounded), pinholes may occur, the cross-sectional shape may become forward or reverse tapered, or undercut or over-etching may occur. While such shape changes are expected to occur during the etching process, as long as the direction of the main beam of the reflected electromagnetic waves in the basic configuration is within a range of about ±5° of the designed reflection angle, this is considered to be an acceptable reflection phase characteristic. Formation by cutting, printing, dry coating, plating, painting, or spraying is also acceptable.

Methods for directly forming an element pattern on a dielectric layer include printing using letterpress printing, lithographic printing, intaglio printing, stencil printing, transfer printing, etc., or masking the dielectric layer except for the element pattern area with masking tape or a masking agent, etc., and then forming the element pattern using dry coating, plating, painting, or spraying.
The cross-sectional shape of the element pattern is preferably a forward tapered shape that widens from the top to the bottom. The forward tapered shape increases the surface area of the element pattern, which increases the adhesion to the functional layer when the functional layer is laminated, as described below, and makes it possible to suppress the inclusion of air bubbles.

The material of the element pattern 1 may be the same as that of the ground layer 3, or a different material may be used. For example, at least one of the ground layer and element pattern layers may be made of Cu or Al. Cu has excellent conductivity, which reduces conductor loss. Al has a low density, is lightweight, and is inexpensive, making it possible to form a lightweight and inexpensive reflect array.

When the element pattern 1 is in a mesh shape, the line width of the mesh is preferably 5 μm or more and 30 μm or less, and more preferably 6 μm or more and 15 μm or less. The line spacing of the mesh is preferably 50 μm or more and 500 μm or less, and more preferably 100 μm or more and 300 μm or less. Furthermore, when the wavelength at the operating frequency is λ, the line spacing of the mesh is preferably 0.5 × λ or less, more preferably 0.1 × λ or less, and even more preferably 0.01 × λ or less. If the line spacing of the mesh is 0.5 × λ or less, performance can be ensured. Furthermore, the line spacing of the mesh may be 0.001 × λ or more. When a metal mesh or a transparent conductive material is used, the reflect array exhibits visible light transparency, making it possible to maintain the appearance after installation.
When the element pattern is mesh-shaped or when a transparent conductive material is used, the reflect array exhibits visible light transparency, making it possible to maintain the appearance after installation.

When the element pattern 1 is in the form of a thin film, adhesion with the additional functional layer and the adhesion improving layer is improved, and the flexibility of the reflect array can be improved, making it possible to use it on curved surfaces and to carry out a roll-to-roll production process.
When the element pattern is formed using a thin film, the thickness thereof is preferably greater than the skin depth calculated from the following equation (9): where d is the skin depth, ω is the angular frequency, μ is the magnetic permeability of the material, and σ is the electrical conductivity of the material.
In order to increase the reflection efficiency of radio waves, it is necessary to reduce radio wave loss caused by the element, and therefore it is preferable that the surface roughness of the element is small.

(Dielectric)
As the dielectric, in addition to a simple resin, composite materials such as paper, glass fiber, or carbon fiber impregnated with resin can be used.
Examples of simple resins include polyethylene (εr=2.2 to 2.4), polypropylene (εr=2.0 to 2.6), polystyrene (εr=2.4 to 2.6), polyvinyl chloride (εr=2.8 to 8.0), AS resin (εr=2.6 to 3.1), ABS resin (εr=2.4 to 4.1), polyethylene terephthalate (εr=2.9 to 3.0), acrylic resin (εr=2.7 to 4.5), urethane resin (εr=4.0 to 7.1), epoxy resin (εr=2.5 to 6.0), nylon (εr Examples of suitable dielectric materials include polyimide (εr = 2.4 to 2.7), fluororesin (εr = 2.0 to 2.6), polycarbonate (εr = 2.9 to 8.9), polyphenylene ether (εr = 2.8 to 8.2), polyphenylene sulfide (εr = 3.2 to 4.6), polyvinylidene fluoride (εr = 6.4 to 10.0), polyethylene naphthalate (εr = 2.9), phenolic resin (εr = 3.0 to 12.0), and cycloolefin polymer (εr = 2.3 to 2.5). Here, εr indicates the relative dielectric constant. In particular, polyethylene (PS), polyethylene terephthalate (PET), and cycloolefin polymer (COP) are preferred due to their low cost and versatility. The dielectric layer can be a single layer or multiple layers. The dielectric layer may also be made of foamed materials made from the above materials. As the foam, a foam with high flexibility is preferably used.

Examples of composite materials include composite materials of paper/phenol resin, paper/epoxy resin, glass/epoxy resin, and glass/fluororesin.
Another example is the use of a mixture containing resin components or a dielectric compound and a resin component, from the viewpoint of adjusting the dielectric constant. The relative dielectric constant of the mixture can be adjusted by selecting the dielectric compound and its content.
The dielectric constant of a mixture can be predicted, for example, by using the Maxwell-Garnett law. In a mixture of a dielectric A having a dielectric constant εa and a dielectric B having a dielectric constant εb, when the volume fraction of the dielectric A is δa, the dielectric constant εm of the mixture is expressed by the following relational expression (10):
Examples of the dielectric compound include barium titanate (εr=250 to 20,000), titanium oxide (εr=83 to 183), lead zirconate titanate, strontium tantalate bismuthate, and bismuth ferrite.
When a transparent dielectric is used, the reflectarray exhibits visible light transmittance, making it possible to maintain the appearance after installation.

The relative dielectric constant of the dielectric layer 2 is preferably in the range of 1 or more and 20 or less, more preferably in the range of 1 or more and 10 or less, and even more preferably in the range of 2 or more and 4 or less. If the relative dielectric constant is within the above range, it tends to be easier to obtain the desired reflection phase characteristics in the reflectarray. Furthermore, the dielectric loss tangent is preferably in the range of 0.00005 or more and 0.01 or less, and more preferably in the range of 0.00005 or more and 0.001 or less. If it is within the above range, a reflectarray with low dielectric loss can be produced.

The dielectric layer 2 can be formed using, for example, wet coating such as die coating, comma coating, or gravure coating; melt extrusion methods such as the T-die method or inflation method; calendar film formation; solution casting; or heat pressing. Co-extrusion, in which multiple resins are extruded in multiple layers to form a film, may also be used.

The thickness of the dielectric layer 2 is selected appropriately depending on the design frequency. When the design frequency is 28 GHz, it is preferably 40 μm or more and 250 μm or less, and more preferably 50 μm or more and 200 μm or less. If it is too thin, it becomes difficult to ensure the reflection phase, making the design of the reflectarray difficult. On the other hand, if it is too thick, it tends to become difficult to ensure the reflection phase, the flexibility will be lost, and the total thickness of the reflectarray will increase, making it difficult to save space. For this reason, the thickness of the dielectric layer is preferably 250 μm or less. When the design frequency is 60 GHz, the thickness of the dielectric layer is preferably 10 μm or more and 250 μm or less. When the design frequency is 100 GHz or more, a thickness of the dielectric layer of several μm or more and 100 μm or less will make it easier to design the reflectarray.

(Ground layer)
The ground layer 3 is provided to reflect electromagnetic waves that reach the reflect array 4. It is also used to support and protect the dielectric layer 2. The ground layer is made of a conductive material such as an inorganic oxide material, a metal material, or a conductive organic material. The thickness of the ground layer is, for example, 10 nm to 105 μm.

For example, inorganic oxide materials and metal materials include indium tin oxide (ITO), indium zinc oxide (IZO), zinc aluminum oxide (AZO), gallium zinc oxide (GZO), antimony tin oxide, Ag, Al, Au, Pt, Pd, Cu, Co, Cr, In, Ag—Cu, Cu—Au, and Ni. Nanoparticles or nanowires containing at least one of these materials may also be used. Conductive organic materials include polythiophene derivatives, polyacetylene derivatives, polyaniline derivatives, polypyrrole derivatives, carbon nanotubes, and graphene. Cu and Al are particularly preferred from the standpoints of material cost, conductivity, and film formation. Furthermore, to reflect electromagnetic waves, it is desirable for the surface resistance of the ground layer to be 100 Ω/□ or less. If this condition can be met, a transparent reflect array can also be fabricated using ITO or a mixture of polyethylenedioxythiophene (PEDOT) and polystyrene sulfonic acid (PSS) (PEDOT/PSS).
The above materials can be used in the form of a continuous film, a mesh, a punched shape, or a periodic structure.

Here, mesh refers to a state in which a conductor has a mesh-like opening (opening) on its plane. When the conductor is formed in a mesh shape, the mesh may be rectangular or diamond-shaped. When the mesh is formed in a rectangular shape, the mesh is preferably square. Square meshes provide good design. They may also be randomly shaped by a self-organizing method. Making the mesh randomly can prevent moire. When processing metal into a mesh shape, methods such as punching a metal plate or etching a metal plate can be used.
When the ground layer 3 is mesh-shaped or when a transparent conductive material is used, the reflect array exhibits visible light transparency, making it possible to maintain the appearance after installation.
When the ground layer 3 is mesh-shaped, the line width of the mesh is preferably 5 μm to 30 μm, more preferably 6 μm to 15 μm. The line spacing of the mesh is preferably 50 μm to 500 μm, more preferably 100 μm to 300 μm. Furthermore, when the wavelength at the operating frequency is λ, the line spacing of the mesh is preferably 0.5×λ or less, more preferably 0.1×λ or less, and even more preferably 0.01×λ or less. If the line spacing of the mesh is 0.5×λ or less, performance can be ensured. Furthermore, the line spacing of the mesh may be 0.001×λ or more.

When a metal material is used, the ground layer 3 can be formed by dry coating such as sputtering or vapor deposition, wet coating such as gravure coating or die coating by turning the metal material into ink, or surface treatment such as plating. Alternatively, a rolled metal plate can be used as the ground layer. When an inorganic oxide material is used, dry coating can be selected as the ground layer formation method. When an organic material is used, wet coating can be selected as the ground layer formation method. Alternatively, the ground layer can be formed by painting or spraying.
If the ground layer 3 is in the form of a thin film formed by plating or vapor deposition, the flexibility of the reflect array can be improved, making it possible to use it on curved surfaces or to implement a roll-to-roll production process.
When the ground layer 3 is in the form of a thin film, its thickness is preferably larger than the skin depth calculated from equation (9) in the same manner as the element pattern.
Furthermore, in order to increase the reflection efficiency of electromagnetic waves, it is also necessary to reduce loss due to the ground layer, so it is preferable that the surface roughness of the ground layer is small.

If the ground layer 3 has a periodic structure, it can exhibit the function of selectively reflecting or transmitting specific frequencies. For example, if a structure with periodically arranged patch-like conductive patterns is used as the ground layer, it will be possible to reflect only specific frequencies, thereby providing the ability to transmit frequencies other than the operating frequency. Furthermore, if a structure is used in which holes are periodically arranged where no conductive material is present, it will be possible to design a reflect array that asymmetrically reflects the operating frequency while transmitting only specific frequencies.

In this disclosure, surface resistance measurements are performed in accordance with JIS-K-7194. Surface resistance measurement methods can be selected appropriately, including the four-terminal method, two-terminal method, four-probe method, dielectric method, and eddy current method. The surface resistance of the ground layer can be measured, for example, using the Loresta GP MCP-T610 (product name, manufactured by Mitsubishi Chemical Analytech Co., Ltd.).

(additional functional layer)
The function of the additional functional layer 5 can be selected as needed. Examples of functions that can be added include deterioration prevention, design, protection/scratch resistance, waterproofing, gas/water vapor barrier properties, flame retardancy, non-combustibility, self-extinguishing, weather resistance, stain resistance, antibacterial/antiviral properties, chemical resistance, deodorizing properties, and adhesiveness/bonding properties. One of these functions may be added, or multiple functions may be combined. The thickness of the additional functional layer is, for example, 5 μm or more and 6 mm or less.
Methods for laminating a sheet-like additional functional layer include bonding using lamination, extrusion lamination, etc., and methods for applying a liquid additional functional layer include, but are not limited to, printing, coating, dry lamination, wet lamination, etc. Furthermore, if the additional functional layer does not have tackiness or adhesiveness, there is a method for adhering it to the reflectarray using an adhesion improving layer (adhesive).

[Weather resistance]
Possible causes of reflectarray deterioration include oxidation and water vapor absorption due to exposure to the atmosphere, and alteration due to light (ultraviolet rays) such as sunlight. To prevent deterioration due to oxygen and water vapor, it is possible to provide a layer with excellent gas barrier properties, such as a barrier film, on the surface of the reflectarray. Furthermore, to prevent deterioration due to oxygen in particular, it is preferable that the oxygen permeability of the functional layer be 500 cc/ ^m² ·atm·day or less. If this condition can be met, a film may be laminated, or an overcoat layer may be provided by dry coating or wet coating. These layers may be single layers, or multiple layers may be combined or laminated. Examples of barrier films include a single film such as an ethylene-vinyl alcohol copolymer resin, a coextruded multilayer nylon (Ny) film, and a wet-coated film coated with vinylidene chloride (PVDC) or polyvinyl alcohol (PVA).
Furthermore, to prevent deterioration of the dielectric layer, an antioxidant, anti-deterioration agent, or antioxidant material may be added when forming the dielectric layer. Similarly, to prevent deterioration due to water vapor, it is preferable to provide a layer with a water vapor permeability of 300 g/ ^m2 ·day or less. To protect against light from sunlight, etc., it is possible to provide a film with UV protection or a layer with light-blocking properties. Furthermore, an ultraviolet scattering agent, an ultraviolet absorber, or a light stabilizer may be added. Examples of UV-blocking films include vinyl chloride resins and polyolefin resins.

[Design]
When a reflectarray is installed on the exterior or interior of a building, for example, it is possible to impart a design to it so that it harmonizes with the space. Specifically, the design can be imparted by bonding a designed sheet-like material to the reflectarray using an adhesive, or by welding and attaching the sheet-like material to the reflectarray by applying heat and pressure. Examples of such decorative sheets include a decorative sheet in which a printed pattern and an embossed surface pattern are harmonized by laminating a base sheet, a base pattern layer, and a transparent thermoplastic resin layer in this order, and a decorative sheet in which a color similar to that of real wood or stone is achieved by laminating a pattern layer, a transparent resin layer, and a surface protection layer in this order.

[Protection/scratch resistance]
Protection and scratch resistance refers to the function of preventing scratches on the reflectarray and preventing deterioration of the reflectarray itself. Methods for imparting such functions include coating the reflectarray to increase its surface hardness or laminating a synthetic resin film. Protection and scratch resistance are evaluated by a pencil hardness test based on JIS K5600-5-4, and the hardness is preferably H or higher. Furthermore, when rubbed with steel wool (#0000) at a load of 1,000 gf/ ^cm2 , it is preferable that scratches do not occur until the number of reciprocating strokes exceeds 1,000. Examples of synthetic resins include polyethylene terephthalate, cycloolefin polymer, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polymethyl methacrylate, polyester, polyformaldehyde, polyamide, polyphenylene ether, vinylidene chloride, polyvinyl acetate, polyvinyl acetal, AS resin, ABS resin, acrylic resin, fluororesin, nylon resin, polyacetal resin, polycarbonate resin, polyamide resin, and polyurethane resin.

[Flame retardant, non-flammable, self-extinguishing]
A method of imparting flame retardancy or non-combustibility to a reflectarray is to layer non-combustible, quasi-non-combustible, or flame-retardant materials that have been certified as fireproof under the Building Standards Act. Examples include flame-retardant fibers, flame-retardant plastics, non-combustible paints, and flame-retardant paints. Flame-retardant fibers include halogen-based compounds, phosphorus-based compounds, vinylon fibers, polyetherimide fibers, aramid fibers, polyester fibers, and vinylon fibers. Flame-retardant plastics include plastic materials to which halogen-based, phosphorus-based, or inorganic flame retardants such as aluminum hydroxide and magnesium hydroxide have been added. Self-extinguishing materials include nylon, polycarbonate, and polyvinyl chloride.

[Anti-fouling, antibacterial, anti-viral]
One method of imparting antifouling properties to a reflectarray is to laminate or coat it with a hydrophilic or water-repellent substrate. Photocatalytic materials, silica-based materials, and the like can be used as hydrophilic materials. Fluorocarbon resin-based, silicone-based, and other materials can be used as water-repellent materials. Photocatalytic materials, chlorine-based materials, organic materials containing cationic polymers, and materials containing metals such as silver and zinc can be used as antibacterial and antiviral materials. These materials can be laminated as films or used in coating processes, or mixed when forming a dielectric layer, for example.

(Adhesion improving layer)
The adhesion improving layer is a layer that has adhesive strength to bond layers together. The adhesion improving layer may be composed of two or more layers or may be composed of a combination of multiple materials. In this embodiment, the adhesion improving layer bonds the ground layer and the dielectric layer, or the dielectric layer and the element pattern, or the dielectric layer, the element pattern, and the additional function layer, and is composed of an adhesive. The adhesive may be a water-dispersion adhesive, a solution-based adhesive, a solventless adhesive, or a solid-based adhesive. Examples of adhesives include epoxy resin-based adhesives, polyvinyl acetate-based adhesives, nitrile rubber-based adhesives, phenolic resin-based adhesives, vinyl acetate-based adhesives, chloroprene rubber-based adhesives, acrylic resin-based adhesives, polyvinyl alcohol resin-based adhesives, silicone rubber-based adhesives, styrene-butadiene rubber-based adhesives, and urethane-based adhesives. In addition to the adhesive, the adhesion improving layer may also contain any synthetic resin or other material or any other component. The thickness of the adhesion improving layer is, for example, 5 μm to 500 μm.
If the additional function layer does not have tackiness or adhesiveness, it can be attached to the reflectarray using an adhesion improving layer.
The functional layer is a general term including a single or multiple additional functional layer, a single or multiple adhesion improving layer, or a layer in which a single or multiple additional functional layer and an adhesion improving layer are stacked.

(installation layer)
The mounting layer is a layer used to fix the reflectarray to the support. For example, an adhesive layer, a sticky layer, or a magnet can be used if the support is made of metal. When a magnet is used, the position and angle of the reflectarray can be easily changed.

(Support)
The reflectarray is installed on a support. The support may be a newly installed panel or pole, or an existing signboard, wall, ceiling, etc. It is also possible to use such an existing support. The support preferably has a mechanism that can adjust the angle of the reflectarray in the vertical or horizontal direction, and more preferably has a mechanism that can move the position of the reflectarray up, down, left, and right. The reflectarray is installed on the support and used as a reflectarray device.

The reflectarray may also be attached to human skin, clothing, or wearable equipment using an installation layer.

<Reflectarray design>
Next, the design of the reflectarray will be explained.
(Reflection control area)
The reflection control area is the smallest area that can reflect electromagnetic waves incident on that area in a predetermined direction. The reflection control area includes not only a two-dimensional area parallel to the area where the electromagnetic waves are incident, but also a layer structure formed in a direction perpendicular to the area.

Furthermore, a unit cell refers to an area obtained by dividing a reflection control area. A unit cell contains one element pattern. Two or more unit cells exist within one reflection control area. The size of the side of only one unit cell in the x-axis direction is defined as Ux, and the size of the side in the y-axis direction is defined as Uy. Within one reflection control area, the size (length) of a side where multiple unit cells are lined up in the x-axis direction is defined as Sx.

Figure 3 is an example of a schematic diagram showing an enlarged portion of the reflection control region. Figure 3(a) is a perspective view of the reflection control region 6. Figure 3(b) is a cross-sectional view of the reflection control region 6 in the xz plane taken along the y direction Uy/2 (Figure 3(b-1)), and a schematic diagram showing the design angle of incidence θi and the design angle of reflection θr (Figure 3(b-2)). Figure 3(c) is a cross-sectional view of an arbitrary unit cell of the reflection control region 6 taken along the x direction Ux/2 in the yz plane. An element pattern 1 having an element side surface is formed on one xy plane of the dielectric layer 2, and a ground layer 3 is formed on the other xy plane. When the unit cells are obtained by dividing the reflection control region into n equal parts along a predetermined direction, Ux is Sx/n, where n is an integer greater than or equal to 2 (in the example of Figure 3, the reflection control region is made up of three rectangular unit cells whose long side in the x-axis direction is divided into thirds).

The reflection control area is designed according to the following procedure. First, the length Sx of the long side of the reflection control area is determined by the following formula (11). Here, Sx is the length of the long side of the reflection control area, λ is the wavelength of the electromagnetic wave applied to the reflectarray (hereinafter also referred to as the "wavelength at the operating (design) frequency"), θi is the angle of incidence, and θr is the angle of reflection. The angle of incidence θi and the angle of reflection θr are values measured in the xz plane. Here, the direction parallel to the z axis is defined as θi = θr = 0°, the angle of rotation in the positive direction of the x axis is defined as θi = θr = 0 to 90°, and the angle of rotation in the negative direction is defined as θi = θr = 0 to -90° (see FIG. 3(b-2)).
Next, the reflection phase required in each reflection control area is calculated using the following equation (12).
Here, Zs(x) is a function of the surface impedance in the x-direction in the xy plane of the reflection control area, and represents the case where lossless reflection is realized. Also, 120π is the impedance of the incident wave. The equation for the surface impedance is as follows:
Here, Φr(x) represents the reflection phase, which is the phase of the reflection coefficient, as shown in the following equation (14).
From each equation, the element shape is determined for each position of the unit cell so as to satisfy the reflection phase (deflection angle of R) shown in the following equation (15). In other words, by determining the angle of incidence θi, the angle of reflection θr, and the wavelength λ of the electromagnetic wave, it is possible to calculate the value of the reflection phase at the coordinate in the long side direction of the reflection control region.
After the reflection phase is calculated by the above method, the shape of the element pattern is changed so as to satisfy the reflection phase in each unit cell, and a simulation is performed to optimize the shape of the element pattern. When an electromagnetic wave is incident on the element pattern, the relationship between the shape of the element pattern and the reflection phase can be calculated by a simulation using, for example, an electromagnetic analysis tool (High Frequency Structure Simulator: HFSS) or the like.

(Reflection control area group)
A group of reflection control areas is called a reflection control area group. Reflection control area groups include those composed of a group of single reflection control areas (hereinafter also referred to as a "single reflection control area group", although this also includes a single reflection control area), and those composed of a combination of multiple types of single reflection control area groups (hereinafter also referred to as a "composite reflection control area group"). The reflectarray 40 that is the subject of this embodiment is composed of composite reflection control areas, and is distinguished from the reflectarray 4 composed of a single reflection control area group (hereinafter also referred to as a "single reflectarray").
When the reflect array 40 is composed of a composite reflection control region group, each of the single reflection control region groups constituting the composite reflection control region group is arranged parallel to at least one or both of the x-axis and y-axis.

<Characteristics of reflectarray>
The following describes the characteristics exhibited when an electromagnetic wave is incident on and reflected from a single reflectarray. As described above, the reflectarray is designed to have an incident angle θi and a reflection angle θr (such a single reflectarray is sometimes written as R(θi, θr)).
In the following description, the propagation direction of an electromagnetic wave incident on a reflectarray of R(θi, θr) at an incident angle θi and reflected at a reflection angle θr is referred to as the forward direction (downstream communication/radiated wave), and the propagation direction of an electromagnetic wave incident at an incident angle θr and reflected at a reflection angle θi is referred to as the reverse direction (upstream communication/received wave). That is, for downstream communication (radiated wave), the "incident angle = designed incident angle" and "reflection angle = designed reflection angle," and for upstream communication (received wave), the "incident angle = designed reflection angle" and "reflection angle = designed incident angle." When it is desired to clarify whether a certain design incident angle θi is the incident angle for downstream communication or the reflection angle for upstream communication, the subscripts d and u may be added to the former, such as [θi]d, and the latter, such as [θi]u. Similarly, when it is desired to clarify whether a design reflection angle θr is the reflection angle for downstream communication (radiated wave) or the incident angle for upstream communication (received wave), it may be expressed as [θr]d for the former and [θr]u for the latter.
In 5G and 6G communications, the forward direction (downstream communications) generally refers to radio waves propagating from the base station to the reflectarray to the terminal, while the reverse direction (upstream communications) generally refers to radio waves propagating from the terminal to the reflectarray to the base station. Furthermore, in millimeter-wave radar (sensors), the forward direction (radiated waves) generally refers to radio waves propagating from the radio wave transmitter to the reflectarray to the target, while the reverse direction (received waves) generally refers to radio waves propagating from the target to the reflectarray to the radio wave receiver. When a reflectarray with retroreflection properties is installed on a target to enhance the received waves, the "design incident angle = design reflection angle." In this disclosure, unless there is a need to distinguish between applications such as communications and sensors in radio wave propagation, the terms "downstream communications" (radiated waves), "upstream communications" (received waves), etc. will be used.

Figure 4 is a schematic diagram illustrating characteristic 1 of a single reflectarray. As shown in Figure 4(a), for a reflectarray 4 of R(θi, θr), radio waves incident at an incident angle [θi]d in downstream communications are reflected most strongly in the direction of reflection angle [θr]d, while as shown in Figure 4(b), radio waves incident at an incident angle [θr]u in upstream communications are reflected most strongly in the direction of reflection angle [θi]u (characteristic 1 of a reflectarray).

Figure 5 is a schematic diagram illustrating characteristic 2 of a single reflectarray. As shown in Figure 5(a), for a reflectarray 4 of R(θi, θr), radio waves incident at an incident angle [θi - α]d that is a few degrees (α degrees) off from θi in downstream communications are most strongly reflected in the direction of a reflection angle [θr + α]d that is a few degrees (α degrees) off from θr. Also, as shown in Figure 5(b), radio waves incident at an incident angle [θr + α]u that is a few degrees (α degrees) off from θr in upstream communications are strongly reflected in the direction of a reflection angle [θi - α]u that is a few degrees (α degrees) off from θi (characteristic 2 of a reflectarray).

Figure 6 is a schematic diagram illustrating characteristic 3 of a single reflectarray. Figure 6(a) shows how radio waves are incident on and reflected from a conventional reflectarray 4 measuring several tens of centimeters square. However, in the case of radio waves in the high frequency band used for 5G, as shown in Figure 6(b), reflectarrays 4 generally use sizes larger than the conventional size of several tens of centimeters square. In this case, the gain increases in principle, and the reflected beam from the reflectarray exhibits the characteristic of becoming sharper (reflectarray characteristic 3).

These characteristics of a single reflectarray cause problems when relaying radio waves. Figure 7 is a schematic diagram showing an example of a failure in radio wave relay using a single reflectarray in 5G/6G communications. Due to characteristics 2 and 3 of a single reflectarray, in downstream communications, the terminal cannot obtain sufficient reception power if (a) the installation position or installation angle of the reflectarray is shifted (see Figure 7(a)), (b) the terminal position is shifted (see Figure 7(b)), or (c) an obstacle such as a person or object temporarily exists on the incoming reflected beam (see Figure 7(c)).
Furthermore, due to the characteristic 1 of a single reflectarray, communication failure occurs in the upstream communication as well as the downstream communication, in that the base station is unable to obtain sufficient reception power.

<Function of Reflect Array According to Embodiment>
The reflectarray according to this embodiment has been developed in consideration of the above-described circumstances. FIG. 8 is a schematic diagram illustrating the functions realized by the reflectarray according to this embodiment. First, as shown in FIG. 8( a), the reflectarray 40 has a function of widening the allowable angle range (described below) of the incident beam for downstream communication (function 1). Second, as shown in FIG. 8( b), the reflectarray 40 has a function of widening the width of the reflected beam for downstream communication (function 2). Third, as shown in FIG. 8( c), the reflectarray 40 has a function of achieving functions 1 and 2 in both uplink and downlink communication (function 3). These functions 1 to 3 make it possible to provide terminal users with an extremely stable communication environment. Similarly, millimeter-wave radar (sensor) also makes it possible to provide sensor users with extremely stable moving object detection.

<Configuration of Reflect Array According to Embodiment>
Next, the configuration of the reflectarray 40 of this embodiment that realizes the above-mentioned functions will be described. The reflectarray 40 of this embodiment has a composite reflection control area group formed by combining multiple types of single reflection control area groups that most strongly reflect plane waves from an arbitrary design angle of incidence θi that satisfies formula (1) to an arbitrary design angle of reflection θr that satisfies formula (2) for electromagnetic waves in a specific frequency band. The composite reflection control area group is preferably formed by juxtaposing three or more single reflection control area groups with different design angles of incidence or design reflection angles in the x-axis direction, and the manner in which they are juxtaposed may be formed by arranging separate single reflectarrays or may be formed integrally on a common dielectric layer, and is not particularly limited.

[Embodiment 1]
9A is a schematic diagram showing an overall image of the incident and reflected downstream communication radio waves (radiated waves) in the reflectarray of embodiment 1. In the reflectarray 40, which is a composite reflection control region group, when the design incident and reflection angles of the centrally located single reflection control region group 4-0 are the design central incident angle θi ₀ and the design central reflection angle θr ₀ , it is preferable that the design incident and reflection angles of the surrounding single reflection control region groups are both shifted by the same amount from the design central incident and reflection angle. For example, as shown in FIG. 9A , the reflection control region group 4-0 of R(θi ₀ , θr ₀ ) is located at the center of the reflectarray 40, and the reflection control region group 4-1 of (θi ₀ -α, θr ₀ -α) and the reflection control region group 4-2 of R(θi +α, θr ₀ +α) are located on either side of it, respectively. The positions of the reflection control region group 4-1 and the reflection control region group 4-2 may be reversed.

In the reflectarray 40 of embodiment 1, in downstream communication (radiated wave), as shown in FIG. 9A , a plane wave incident at a design central incident angle [θi ₀ ]d is incident on all of the reflection control area groups (4-0, 4-1, 4-2) constituting the reflectarray 40 at the incident angle [θi ₀ ]d and is asymmetrically reflected by each reflection control area group. Then, at the far-field distance, the reflected waves from each reflection control area group are combined to form a plane wave having a beam width of ±β degrees centered on the design central reflection angle [θr ₀ ]d (described later). Similarly, other plane waves incident from an angle range of ±α degrees centered on the design central incident angle [θi ₀ ]d become plane waves having a beam width of ±β degrees centered on the design central reflection angle [θr ₀ ]d (described later).

(Embodiment 1-1)
The reflectarray 40 of embodiment 1-1 strongly reflects, in downstream communication (radiated waves), plane waves incident within an angle range of ± _α degrees ("downstream incident angle range ±α") that satisfies the following formula (3) around the design central incident angle [θi ₀ ]d, to the angle range of ±α degrees ("downstream reflection angle range ±α") around the design central reflection angle [θr 0 ]d. Here, "strong reflection" means that when radio waves incident within the downstream incident angle range ±α are reflected, the average value of the reflection intensity (bistatic RCS [sm]) within the downstream reflection angle range ±α is 5 dB or more higher than the average value of the reflection intensity within the angle range of -90 degrees to 90 degrees excluding the downstream reflection angle range ±α.
Furthermore, the reflectarray 40 of embodiment 1-1 is characterized in that, when the reflection intensity (RCS[sm]) of a plane wave from an incident angle [θi]d of downstream communication (radiated wave) to a reflection angle [θr]d is σ[θi]d[θr]d, the variation coefficient C _[θr]d of the reflection intensity at any reflection angle [θr]d within the downstream reflection angle range ±α, calculated from the following equation (4), is 0.6 or less. Here, the variation coefficient is an index indicating the relative variation in data, and is calculated as the value obtained by dividing the standard deviation of the reflection intensity at each reflection angle within the downstream reflection angle range ±α for an incident wave from the downstream incident angle range ±α by the average, thereby deriving the degree of variation in the reflection intensity at each reflection angle due to a shift in the incident angle. In equation (4), j is a variable corresponding to each analysis angle when the incident angle range of -α to α degrees is divided by 1 degree, and the number of analysis angles is 2α + 1. It is also possible to derive the variation coefficient by using j as a continuous variable and replacing equation (4) with an integral. The smaller the coefficient of variation, the smaller the degree of variation in reflection intensity due to differences in the angle of incidence.

In this way, in the reflectarray 40 of embodiment 1-1, plane wave radio waves incident within the downstream incident angle range ±α are strongly reflected within the downstream reflection angle range ±α, and the coefficient of variation, which indicates the degree of variation in the reflection intensity reflected within the downstream reflection angle range ±α for all radio waves incident within the downstream incident angle range ±α, is kept at 0.6 or less. The angle range ±α in this case is called the allowable incident angle range. Therefore, it can be said that the reflectarray 40 of embodiment 1-1 has the function of expanding the allowable incident angle range for downstream communication (radiated waves) to any value of α that satisfies equation (3) (see Function 1, Figure 8(a), etc.).

(Embodiment 1-2)
In addition to the functions of embodiment 1-1, the reflectarray 40 of embodiment 1-2 can reflect, in downstream communication (radiated waves), any plane wave incident at a downstream incident angle range ±α with a spread over an angle range of ± _β degrees (hereinafter referred to as the "downstream reflection angle range ±β") that satisfies the following equation (6) around the design central reflection angle [θr 0 ]d (see FIG. 9A ). Here, "reflecting with a spread" means that when a radio wave incident at any incident angle [θi _{]d within the downstream incident angle range ±α is reflected, the diffusivity d[θi]d of the reflection pattern (bistatic RCS[sm]) derived from the following equation (7) is 0.6 or more in the downstream reflection angle range ±β} .
Here, the uniformity of the reflection directional characteristics of radio waves in a metamaterial diffuse reflector is defined as the diffusion coefficient. Specifically, the autocorrelation coefficient of the RCS for each reflection direction for an incident wave from a certain direction is derived. k is a variable corresponding to each analysis angle when the reflection angle range of -β to β degrees is divided by 1 degree, and the number of analysis angles is 2β + 1. It is also possible to derive the diffusion coefficient by replacing equation (7) with an integral using k as a continuous variable. Generally, for perfect diffuse reflection that is uniform in all directions, dθ = 1, and for perfect specular reflection, dθ = 0.
Therefore, since a higher degree of diffusion means that the reflection intensity is spread evenly over a wider area, the reflect array 40 of embodiment 1-2 has the function of uniformly spreading the width of the reflected beam in downstream communication (radiated wave) within the downstream reflection angle range ±β (function 2, see Figure 8(b) etc.).

[Embodiment 2]
9B is a schematic diagram showing an overall image of the incident and reflected waves of upstream communication radio waves (received waves) in the reflectarray of embodiment 2. The reflectarray 40 is the same as the one used for downstream communication (radiated waves). In upstream communication (received waves), as shown in FIG. 9B, a plane wave incident at the design central reflection angle [θr ₀ ]u is incident on all of the reflection control area groups (4-0, 4-1, 4-2) constituting the reflectarray 40 at an incident angle [θr ₀ ]u and is asymmetrically reflected by each reflection control area group. At the far-field distance, the reflected waves from each reflection control area group are combined to form a plane wave with a beam width of ±β degrees centered around the design central incident angle [θi ₀ ]u. Similarly, any other plane wave incident from within the downstream reflection angle range ±α becomes a plane wave with a beam width of ±β degrees centered around the design central incident angle [θi ₀ ]u.

(Embodiment 2-1)
In addition to the functions of embodiment 1-1, the reflectarray 40 of embodiment 2-1 strongly reflects a plane wave incident within the downstream reflection angle range ±α to the downstream incident angle range ±α in upstream communication (received wave). Here, "strong reflection" means that, similar to downstream communication (radiated wave), when a radio wave incident within the downstream reflection angle range ±α is reflected, the average value of the reflection intensity (bistatic RCS) within the downstream incident angle range ±α is 5 dB or more higher than the average value of the reflection intensity within the angle range from -90 degrees to 90 degrees excluding the downstream incident angle range ±α.
Furthermore, the reflectarray 40 of embodiment 2-1 is characterized in that, when the reflection intensity (RCS[sm]) of a plane wave at a reflection angle [θi]u from an incident angle [θr]u of upstream communication (received wave) to a reflection angle [θi]u is σ[θr]u[θi]u, the variation coefficient C[θi]u of the reflection intensity, derived from the following equation (5), at any reflection angle _[θi]u within a downstream incident angle range ±α is 0.6 or less. The meaning of the variation coefficient is the same as in the case of downstream communication (radiated wave), so details will be omitted.
Similar to downstream communication (radiated waves), the reflect array 40 of embodiment 2-1 can be said to have the function of expanding the allowable incident angle range in upstream communication (received waves) to any value of α that satisfies equation (3) (function 3, see Figure 8 (c) etc.).

(Embodiment 2-2)
In addition to the functions of embodiment 1-1, the reflectarray 40 of embodiment 2-2 can reflect, in upstream communication (received waves), any plane wave incident within a downstream reflection angle range ±α with a spread over an angle range of ±β degrees (hereinafter referred to as the "upstream reflection angle range ±β") that satisfies equation ( ₆ ) around the design central incident angle [θi 0 ]u (see FIG. 9B ). Here, "reflecting with a spread" means that when a radio wave incident at any incident angle [θr]u within the downstream reflection angle range ±α is reflected, the diffusion degree d[θr]u of the reflection pattern (bistatic RCS) derived from the following equation (8) is 0.6 or greater within the upstream reflection angle range ±β. The meaning of the diffusion degree is the same as in the case of downstream communication (radiated waves), and therefore details will be omitted.

In this way, the reflect array 40 of embodiment 2-2 has the function of uniformly widening the width of the reflected beam in upstream communication (received wave) within the upstream reflection angle range ±β (function 3, see Figure 8 (c) etc.).

<Example>
An example (Example 1) and comparative examples (Comparative Example 1 and Comparative Example 2) relating to a reflectarray that causes asymmetric reflection in which the angle of incidence and the angle of reflection are different, and an example (Example 2) and comparative example (Comparative Example 3) relating to a reflectarray that retroreflects electromagnetic waves in the incident direction will be described. The results of the reflection characteristics described in the examples and comparative examples were analyzed using finite element analysis software (HFSS) made by Ansys.
Example 1
10 is a schematic diagram of the arrangement of reflection control region(s) in the reflectarray of Example 1. Reflectarray 40 in Example 1 has three types of reflection control region groups 4-0, 4-1, and 4-2 arranged parallel to the x-axis direction such that reflection control region groups 4-1 and 4-2 are arranged on both sides of reflection control region group 4-0, and each reflection control region group has a plurality of reflection control regions (6-0, 6-1, 6-2) arranged parallel to the x-axis and y-axis directions. Here, reflection control regions 6-0, 6-1, and 6-2 have different designed incident reflection angles, ( _θi0 , _θr0 ), R( _θi0 -α, _θr0 -α), and ( _θi0 +α, _θr0 +α), respectively, and therefore also have different long side lengths Sx of the reflection control regions. On the other hand, in order to prevent deviation of the element pattern in the y-axis direction, the lengths of the short sides of the reflection control regions 6-0, 6-1, and 6-2 (= the length of one side of the unit cell) are unified to the longest length Uy, which makes it easier to process the reflect array.

The reflect array was constructed using 0.018 mm (18 μm) thick copper for the element pattern and ground layer, and a 0.764 mm thick glass/fluororesin composite for the dielectric. The conductivity of the copper was 5.8 × 10 siemens/m, the real part of the dielectric constant of the dielectric was 2.6, and tan δ was 0.0025.
The operating frequency was set to 28 GHz, the design incident reflection angle was set for each reflection control area group, and the size Sx of the reflection control area in the x-axis direction was determined using equation (11). The number of divisions of the reflection control area was set to 3, and the size Uy (= Sx/3) of the reflection control area in the y-axis direction within the reflection control area groups 4-0, 4-1, and 4-2 was unified to the largest value.
The shape of the element was a cross patch in which two square patches intersected at right angles in the xy plane. Here, the element lengths of the element patterns in the reflection control region were the same and only the element widths were different.
Each of reflection control region groups 4-0, 4-1, 4-2 has four reflection control regions 6-0, 6-1, 6-2 arranged in the x-axis direction, and an optimum number arranged in the y-axis direction. Specific specifications are shown in Table 1.

The coefficients of variation for downstream communication (radiated wave) and upstream communication (received wave) in Example 1 are shown in Table 2. In downstream communication (radiated wave), for all plane waves incident at each analysis angle ( ₁₁ analysis angles) when the incident angle range (α = 5) of -5 to +5 degrees, centered on 0 degrees which is the design central incident angle [θi 0 ]d, is divided in 1 degree increments, were strongly reflected in the angle range of -5 to +5 degrees centered on 45 degrees which is the design central reflection angle [θr ₀ ]d. Furthermore, as shown in Table 2, the coefficient of variation Cθ of the reflection intensity (bistatic RCS) derived from equation (4) at each reflection angle when this angle range is divided in 1 degree increments was 0.6 or less at all analysis angles.
Similarly, for uplink communications (received waves), all plane waves incident at each analysis angle (11 analysis angles) when the incident angle range (α = 5) of -5 to +5 degrees, centered on the design central reflection angle [θr ₀ ]u of 45 degrees, is divided in 1-degree increments, were strongly reflected in the angle range of -5 to +5 degrees centered on 0 degrees, the design central incident angle [θi ₀ ]u. Furthermore, as shown in Table 2, the coefficient of variation Cθ of the reflection intensity (bistatic RCS) derived from equation (5) at each reflection angle when the angle range is divided in 1-degree increments was 0.6 or less at all analysis angles.

The diffusivity in downstream communication (radiated wave) and upstream communication (received wave) in Example 1 is shown in Table 3. As shown in Table 3, in downstream communication (radiated wave), for plane waves incident at each incident angle obtained by dividing the allowable angle range of -5 to +5 degrees in increments of 1 degree, with ₀ degrees being the design central incident angle [θi ₀ ]d as the center, the diffusivity dθ of the reflection pattern (bistatic RCS) derived from equation (7) using the analysis angle (analysis angle number 21) obtained by dividing the reflection angle range of -10 to +10 degrees (β = 10) in increments of 1 degree, with 45 degrees being the design central reflection angle [θr 0 ]d as the center, was 0.6 or more at all incident angles.
As shown in Table 3, for uplink communication (received wave), similarly, for plane waves incident at each incident angle obtained by dividing the allowable angle range of -5 to +5 degrees in increments of 1 degree, with the design central reflection angle [ _{θr 0} ]u being 45 degrees as the center, the divergence dθ of the reflection pattern (bistatic RCS) derived from equation (8) using the analysis angle (analysis angle number 21) when the reflection angle range of -10 to +10 degrees (β = 10) is divided in increments of 1 degree, with the design central incidence angle [θi 0 ]u being 0 degrees as the center, was 0.6 or more at all incident angles.

(Comparative Example 1)
The reflectarray of Comparative Example 1 consists of a single reflection control region group, and as in Example 1, the number of divisions of the reflection control region was set to 3, and the size of the reflection control region in the y-axis direction, Uy (= Sx/3), was determined. Furthermore, in Comparative Example 1, the reflectarray had 12 x 36 reflection control regions arranged in the x-axis and y-axis directions, for a total of 432 regions. Specific specifications are shown in Table 1.
The coefficient of variation Cθ of the reflection intensity (bistatic RCS) in uplink and downlink communication was derived using the same method as in Example 1, and as shown in Table 2, it was greater than 0.6 at all analysis angles for both uplink and downlink communication.
Furthermore, when the diffusivity dθ of the reflection pattern (bistatic RCS) in uplink and downlink communication was derived using the same method as in Example 1, it was found to be smaller than 0.6 at all incident angles for both uplink and downlink communication, as shown in Table 3.

(Comparative Example 2)
The reflectarray of Comparative Example 2 is made up of composite reflection control region groups, but the designed incident and reflection angles of each of the reflection control region groups 4-0, 4-1, and 4-2 are different from those of Example 1. However, as in Example 1, the number of divisions of the reflection control region is set to 3, and the size Uy (= Sx/3) of the reflection control region in the y-axis direction within the reflection control region groups 4-0, 4-1, and 4-2 is unified to the largest value. Specific specifications are shown in Table 1.
The coefficient of variation Cθ of the reflection intensity (bistatic RCS) in uplink and downlink communication was derived using the same method as in Example 1. As shown in Table 2, the coefficient of variation Cθ was greater than 0.6 at some analysis angles for both uplink and downlink communication.
Furthermore, when the diffusion degree dθ of the reflection pattern (bistatic RCS) in uplink and downlink communication was derived using the same method as in Example 1, it was found to be smaller than 0.6 at some incident angles in uplink communication (received waves) and at all incident angles in downlink communication (emitted waves), as shown in Table 3.

Table 1 shows the specifications of the reflect arrays in Example 1, Comparative Example 1, and Comparative Example 2.

Table 2 shows the coefficient of variation Cθ of the reflect arrays in Example 1, Comparative Example 1, and Comparative Example 2.

Table 3 shows the diffusivity dθ of the reflect arrays in Example 1, Comparative Example 1, and Comparative Example 2.

11 is a graph showing reflection patterns (bistatic RCS) in the reflectarrays of Example 1 and Comparative Examples 1 and 2. The graph on the right for downstream communication (radiated wave) is an enlarged view of the reflection pattern in the angular range of ±β (β=10) centered on the design central reflection angle [θr ₀ ]d (45 degrees), and the graph on the right for upstream communication (received wave) is an enlarged view of the reflection pattern in the angular range of ±β (β=10) centered on the design central incident angle [θi ₀ ]u (0 degrees).
11, in Example 1 and Comparative Examples 1 and 2, radio waves are asymmetrically reflected with directivity in the 45-degree direction in downstream communications (radiated waves), and the analysis results show that the reflection intensity in the ±5-degree range is 5 dB or more higher than the reflection intensity in other reflection directions. Similarly, in upstream communications (received waves), radio waves are asymmetrically reflected with directivity in the 0-degree direction, and the analysis results show that the reflection intensity in the ±5-degree range is 5 dB or more higher than the reflection intensity in other reflection directions.
It can also be seen that the width of the asymmetric reflected beam in Comparative Example 1 is narrow, and the reflection intensity clearly varies depending on the incident angle. It can also be seen that the width of the asymmetric reflected beam in Comparative Example 2 is relatively wide, but the reflection intensity clearly varies depending on the incident angle, as in Comparative Example 1. Furthermore, it can be seen that the spread width of the reflected beam is smaller in upstream communication (received wave) compared to downstream communication (emitted wave) in both Comparative Examples 1 and 2. In contrast, it can be seen that the width of the asymmetric reflected beam is wide in both uplink and downlink communication in Example 1, and the degree of variation in reflection intensity depending on the incident angle is also small.

Example 2
Similar to Example 1, reflectarray 40 of Example 2 has three types of reflection control region groups 4-0, 4-1, 4-2 arranged parallel to the x-axis direction with reflection control region groups 4-1, 4-2 arranged on either side of reflection control region group 4-0, as shown in the schematic diagram of the arrangement of reflection control region(s) in Figure 10, and each reflection control region group has a plurality of reflection control regions (6-0, 6-1, 6-2) arranged parallel to the x-axis direction and y-axis direction. Here, reflection control regions 6-0, 6-1, 6-2 have different designed incident reflection angles, ( _θi0 , _θr0 ), R( _θi0 -α, _θr0 -α), and ( _θi0 +α, _θr0 +α), respectively, and therefore also have different long side lengths Sx of the reflection control regions. On the other hand, in order to prevent deviation of the element pattern in the y-axis direction, the lengths of the short sides of the reflection control regions 6-0, 6-1, and 6-2 (= the length of one side of the unit cell) are unified to the longest length Uy, which makes it easier to process the reflect array.

The reflect array was constructed using 0.035 mm (35 μm) thick copper for the element pattern and ground layer, and 0.600 mm thick epoxy resin for the dielectric. The conductivity of the copper was 5.8 × 10 siemens/m, the real part of the dielectric constant of the dielectric was 4.175, and tan δ was 0.014.
The operating frequency was set to 24.15 GHz, the design incident reflection angle was set for each reflection control area group, and the size Sx of the reflection control area in the x-axis direction was determined using equation (11). The number of divisions of the reflection control area was set to 3, and the size Uy (= Sx/3) of the reflection control area in the y-axis direction within the reflection control area groups 4-0, 4-1, and 4-2 was unified to the largest value.
The shape of the element was a cross patch in which two square patches intersected at right angles in the xy plane. Here, the element lengths of the element patterns in the reflection control region were the same and only the element widths were different.
Each of reflection control region groups 4-0, 4-1, 4-2 has four reflection control regions 6-0, 6-1, 6-2 arranged in the x-axis direction, and an optimum number arranged in the y-axis direction. Specific specifications are shown in Table 4.

The coefficient of variation for Example 2 is shown in Table 5. In Example 2, the design central incident angle [θi ₀ ]d and the design central reflection angle [θr ₀ ]u are equal, and radio waves are retroreflected. For all plane waves incident at each analysis angle (analysis angle number 11) when the incident angle range (α = 5) of -5 to +5 degrees, centered on the design central incident angle [θi ₀ ]d of -45 degrees, is divided by 1 degree, the plane waves are strongly reflected in the angle range of -5 to +5 degrees centered on the design central reflection angle [θr ₀ ]d of -45 degrees. Furthermore, as shown in Table 5, the coefficient of variation Cθ of the reflection intensity (bistatic RCS) derived from Equation (4) at each reflection angle when the angle range is divided by 1 degree was 0.6 or less at all analysis angles.

The diffusivity of Example 2 is shown in Table 6. As shown in Table 6, for plane waves incident at each incident angle obtained by dividing the allowable angle range of -5 to +5 degrees in increments of 1 degree, with -45 degrees being the design central incident angle [θi ₀ ]d as the center, the diffusivity dθ of the reflection pattern (bistatic RCS) derived from equation (7) using the analysis angle (number of analysis angles: 21) when the reflection angle range of -10 to +10 degrees (β=10) is divided in increments of 1 degree, with -45 degrees being the design central reflection angle [θr0]d as the center. was 0.6 or more at all incident angles.

(Comparative Example 3)
The reflectarray of Comparative Example 3 consists of a single reflection control region group, and the size of the reflection control region in the y-axis direction, Uy (= Sx/3), was determined by dividing the reflection control region into three, as in Example 2. In Comparative Example 3, the reflectarray had 12 x 36 reflection control regions arranged in the x-axis and y-axis directions, for a total of 432 regions. Specific specifications are shown in Table 4.
The coefficient of variation Cθ of the reflection intensity (bistatic RCS) was calculated using the same method as in Example 2, and as shown in Table 5, it was greater than 0.6 at some analysis angles.
Furthermore, when the diffusivity dθ of the reflection pattern (bistatic RCS) was calculated using the same method as in Example 2, it was found to be smaller than 0.6 at all angles of incidence, as shown in Table 6.

Table 4 shows the specifications of the reflect arrays in Example 2 and Comparative Example 3.

Table 5 shows the coefficient of variation Cθ of the reflectarrays in Example 2 and Comparative Example 3.

Table 6 shows the diffusion degree dθ of the reflect arrays in Example 2 and Comparative Example 3.

12 is a graph showing the reflection patterns (bistatic RCS) of the reflectarrays of Example 2 and Comparative Example 3. The graph is an enlarged view of the reflection patterns in the angle range of ±β (β=10) centered on the design central reflection angle [θr ₀ ]d (−45 degrees).
As shown in Figure 12, Example 2 and Comparative Example 3 retroreflect radio waves with directionality in the -45 degree direction, and the analysis results show that the reflection intensity in the ±5 degree range is 5 dB or more higher than the reflection intensity in other reflection directions.
It can also be seen that the width of the asymmetric reflected beam in Comparative Example 3 is narrow, and the reflection intensity varies clearly depending on the angle of incidence. In contrast, it can be seen that the width of the retroreflected beam in Example 2 is wide, and the degree of variation in reflection intensity depending on the angle of incidence is also small.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present invention. It goes without saying that, for example, combinations of embodiments 1-1 to 2-2 are possible.

The following are examples of possible embodiments of the present invention, but the present invention is not limited to these.
(Aspect 1)
For electromagnetic waves in a specific frequency band, the reflector has a plurality of types of reflection control regions that most strongly reflect a plane wave from an arbitrary design incident angle θi that satisfies Equation (1) to an arbitrary design reflection angle θr that satisfies Equation (2),
In downstream communication (radiated waves),
A plane wave incident within an angle range of ±α degrees (hereinafter referred to as the "downward incident angle range ±α") that satisfies Equation (3) with the design central incident angle [θi ₀ ]d as the center is:
The beam is strongly reflected in the downward reflection angle range ± _α so that the average value of the reflection intensity (bistatic RCS) in the angle range of ±α degrees (hereinafter referred to as the "downward reflection angle range ±α") centered on the design central reflection angle [θr 0 ]d is 5 dB or more higher than the average value of the reflection intensity in the angle range from -90 degrees to 90 degrees excluding the downward reflection angle range ±α, and
When the reflection intensity of a plane wave from an incident angle [θi]d to a reflection angle [θr]d is σ[θi]d[θr]d, the coefficient of variation C[θr]d of reflection intensity derived from equation (4) for any reflection angle _[θr] d within the downward reflection angle range ±α is 0.6 or less. A reflectarray.
(Aspect 2)
In upstream communication (received waves),
The plane wave incident within the downward reflection angle range ±α is
The downlink incident angle range ±α is strongly reflected so that the average value of the reflection intensity (bistatic RCS) in the downlink incident angle range ±α is 5 dB or more higher than the average value of the reflection intensity in the angle range from −90 degrees to 90 degrees excluding the downlink incident angle range ±α, and
The reflectarray according to aspect 1, wherein when the reflection intensity of a plane wave from an incident angle [θr]u to a reflection angle [θi]u is σ[θr]u[θi]u, the coefficient of variation C _{[θi]u of the reflection intensity (bistatic RCS) derived from Equation (5) for any reflection angle [θi]u} within the downward incident angle range ±α is 0.6 or less.
(Aspect 3)
In downstream communication (radiated waves),
The reflectarray according to aspect 1 or 2, characterized in that a plane wave incident at an arbitrary incident angle [ _θi ]d within the downward incident angle range ±α is reflected with a spread such that the diffusivity d _[θi]d of the reflection pattern (bistatic RCS) derived from equation (7) is 0.6 or more within an angular range of ±β degrees centered on the design central reflection angle [θr 0 ]d that satisfies equation (6).
(Aspect 4)
In upstream communication (received waves),
The reflectarray according to any one of aspects 1 to 3, characterized in that a plane wave incident at an arbitrary incident angle [ _θr ]u within the downward reflection angle range ±α is reflected with a spread such that the diffusivity d[θr]u of the reflection pattern (bistatic RCS) derived from equation (8) is 0.6 or more within an angle range of ±β degrees centered on the design central incident angle [θi 0 ]u so as to satisfy equation (6).
(Aspect 5)
The reflect array according to any one of aspects 1 to 4, characterized in that it is constituted by a reflection control region group including at least three types of reflection control regions having different design angles of incidence θi and design reflection angles θr.
(Aspect 6)
Aspect 6. The reflectarray according to aspect ₅ , characterized in that it is configured by the reflection control region group including three types of reflection control regions, whose design angles of incidence and design reflection angles are the design central incident angle θi _{0 and} the design central reflection angle θr ₀ , the design incident angle θi ₀ -α degrees and the design reflection angle θr 0 -α, and the design incident angle θi ₀ +α degrees and the design reflection angle θr 0 +α degrees, respectively.
(Aspect 7)
It has a layer structure in which an element pattern, a dielectric layer, and a ground layer are laminated in this order,
The reflection control region has the same length of a short side Uy in each reflection control region group and has at least two unit cells,
The reflect array according to aspect 5 or 6, wherein one element pattern is arranged in the unit cell.
(Aspect 8)
A reflect array according to aspect 7, further comprising an adhesion improving layer.
(Aspect 9)
The reflect array according to aspect 7 or 8, further comprising a functional layer.
(Aspect 10)
The reflect array according to any one of aspects 7 to 9, wherein the element pattern has a cross patch shape.
(Aspect 11)
the shape of the element pattern includes a cross patch;
The reflectarray according to any one of aspects 7 to 9, wherein, in the reflection control region, the element width in the x-axis direction and/or the element width in the y-axis direction of the element pattern differs for each of the element patterns arranged in at least two unit cells.
(Aspect 12)
The reflect array according to any one of aspects 7 to 11, wherein the ground layer has a form of a continuous film, a mesh, a punching shape, or a periodic structure.
(Aspect 13)
13. The reflect array according to any one of aspects 7 to 12, wherein the dielectric layer has a relative dielectric constant of 1 or more and 20 or less.
(Aspect 14)
The reflectarray according to any one of Aspects 1 to 13, wherein the reflectarray is disposed on a support.
(Aspect 15)
The reflectarray according to any one of aspects 1 to 13, wherein the reflectarray is attached to human skin, clothing, or a wearing tool by an installation layer.

1...element pattern, 2...dielectric layer, 3...ground layer, 4, 40...reflect array, 5...additional function layer, 6...reflection control area

Claims (16)

For electromagnetic waves in a specific frequency band, the reflector has a plurality of types of reflection control regions that most strongly reflect a plane wave from an arbitrary design incident angle θi that satisfies Equation (1) to an arbitrary design reflection angle θr that satisfies Equation (2),
In downstream communication (radiated waves),
A plane wave incident within an angle range of ±α degrees (hereinafter referred to as the "downward incident angle range ±α") that satisfies Equation (3) with the design central incident angle [θi ₀ ]d as the center is:
The beam is strongly reflected in the downward reflection angle range ± _α so that the average value of the reflection intensity (bistatic RCS) in the angle range of ±α degrees (hereinafter referred to as the "downward reflection angle range ±α") centered on the design central reflection angle [θr 0 ]d is 5 dB or more higher than the average value of the reflection intensity in the angle range from -90 degrees to 90 degrees excluding the downward reflection angle range ±α, and
When the reflection intensity of a plane wave from an incident angle [θi]d to a reflection angle [θr]d is σ[θi]d[θr]d, the coefficient of variation C[θr]d of reflection intensity derived from equation (4) for any reflection angle _[θr] d within the downward reflection angle range ±α is 0.6 or less. A reflectarray.
In upstream communication (received waves),
The plane wave incident within the downward reflection angle range ±α is
The downlink incident angle range ±α is strongly reflected so that the average value of the reflection intensity (bistatic RCS) in the downlink incident angle range ±α is 5 dB or more higher than the average value of the reflection intensity in the angle range from −90 degrees to 90 degrees excluding the downlink incident angle range ±α, and
2. The reflectarray according to claim 1, wherein, when the reflection intensity of a plane wave from an incident angle [θr]u to a reflection angle [θi]u is σ[θr]u[θi]u, the coefficient of variation C _{[θi]u of the reflection intensity (bistatic RCS) derived from Equation (5) for any reflection angle [θi]u} within the downward incident angle range ±α is 0.6 or less.
In downstream communication (radiated waves),
2. The reflectarray according to claim 1, wherein a plane wave incident at an arbitrary incident angle [θi]d within the downward incident angle range ±α is reflected with a spread such that the diffusivity d[θi]d of the reflection pattern (bistatic RCS) derived from equation (7) is _0.6 or more within an angular range of ±β degrees centered on a design central reflection angle _{[θr 0 ]d} that satisfies equation (6).
In upstream communication (received waves),
2. The reflectarray according to claim 1, wherein a plane wave incident at an arbitrary incident angle [θr]u within the downward reflection angle range ±α is reflected with a spread such that the diffusivity d[θr]u of the reflection pattern (bistatic RCS) derived from equation (8) is _0.6 or more within an angular range of ±β degrees centered on a design central incident angle [θi 0 ]u that satisfies equation (6).
In downstream communication (radiated waves),
A plane wave incident at an arbitrary incident angle [θi]d within the downward incident angle range ±α is reflected with a spread such that the diffusivity d[θi] _{d of the reflection pattern (bistatic RCS) derived from equation (7) is 0.6 or more within an angle range of ±β degrees centered on the design central reflection angle [θr 0} ]d, which satisfies equation (6), and
In upstream communication (received waves),
3. The reflectarray according to claim 2, wherein a plane wave incident at an arbitrary incident angle [θr]u within the downward reflection angle range ±α is reflected with a spread such that the diffusivity d[θr]u of the reflection pattern (bistatic RCS) derived from equation (8) is _0.6 or more within an angular range of ±β degrees centered on a design central incident angle [θi 0 ]u that satisfies equation (6).
The reflectarray described in any one of claims 1 to 5, characterized in that it is composed of a reflection control region group including at least three types of reflection control regions with different design angles of incidence θi and design reflection angles θr. 7. The reflectarray according to claim 6, wherein the reflectarray is configured with the reflection control region group including _three types of reflection control regions _, whose design angles of incidence and design reflection angles are the design central incident angle θi ₀ and the design central reflection angle θr ₀ , the design incident angle θi ₀ −α degrees and the design reflection angle θr 0 −α, and the design incident angle θi ₀ +α degrees and the design reflection angle θr 0 +α degrees, respectively. It has a layer structure in which an element pattern, a dielectric layer, and a ground layer are laminated in this order,
The reflection control region has the same length of a short side Uy in each reflection control region group and has at least two unit cells,
The reflect array according to claim 6 , wherein one element pattern is arranged in the unit cell. The reflectarray according to claim 8, further comprising an adhesion improving layer. The reflectarray according to claim 8, further comprising a functional layer. The reflect array according to claim 8, characterized in that the shape of the element pattern is a cross patch. the shape of the element pattern includes a cross patch;
9. The reflectarray according to claim 8, wherein, in the reflection control region, an element width in the x-axis direction and/or an element width in the y-axis direction of the element pattern differs for each of the element patterns arranged in at least two unit cells. The reflect array of claim 8, wherein the ground layer is in the form of a continuous film, a mesh, a punched shape, or a periodic structure. The reflect array described in claim 8, characterized in that the dielectric layer has a relative dielectric constant of 1 or more and 20 or less. The reflectarray described in any one of claims 1 to 5, characterized in that the reflectarray is disposed on a support. The reflectarray described in any one of claims 1 to 5, characterized in that the reflectarray is attached to human skin, clothing, or a wearing device by an installation layer.