Millimeter wave reflector

Abstract

To provide a millimetric wave reflection board capable of reflecting an entered millimetric wave to a plurality of directions.SOLUTION: A millimetric wave reflection board 1 comprises: a surface-like dielectric body 20; two or more kinds of metal patterns 11, 12, and 13 which are provided onto a first surface of a dielectric body and have a different dimension or shape; and a metal layer provided onto a first surface and a second surface on the side opposite to the surface in the dielectric body. An arrangement mode of each metal pattern is that a super cell 10 having a plurality of metal patterns containing the metal patterns 11, 12, and 13 is arranged at a position corresponded to a basic arrangement in which their direction is aligned without a gap, and the metal pattern of 80% or less is removed from the basic arrangement.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a millimeter-wave reflector that reflects millimeter-wave radio waves.

Background Art

[0002] When various wireless devices corresponding to millimeter waves are put into practical use, the generation of radio wave dead zones has become a problem. Millimeter-wave radio waves are significantly more likely to attenuate and have high straightness compared to the widely used VHF waves and UHF waves. Therefore, it is difficult for millimeter-wave radio waves to penetrate behind obstacles due to diffraction.

[0003] As a means to eliminate the dead zone of millimeter-wave radio waves, a reflector that reflects millimeter-wave radio waves (hereinafter referred to as a "millimeter-wave reflector") has been proposed.

[0004] The multi-beam reflect array described in Patent Document 1 can function as the above millimeter-wave reflector. This multi-beam reflect array has a large number of reflection units that reflect millimeter waves at a predetermined angle on one surface of a planar dielectric, and a metal layer that functions as a ground on the other surface. Each reflection unit is composed of a plurality of metal patterns with different shapes.

[0005] Millimeter waves incident on the surface on which the reflection units are provided are reflected by both each metal pattern and the metal layer. By the interference of these reflected waves, the millimeter waves are reflected with a phase different from that at the time of incidence. Furthermore, interference waves based on different metal patterns have different phases, resulting in secondary interference. Therefore, by appropriately setting the shapes of the plurality of metal patterns constituting the reflection unit, the reflection direction of the incident millimeter waves can be set in a desired direction.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

[0007] The multi-beam reflect array described in Patent Document 1 has the characteristic of strongly reflecting radio waves in a specific direction. Therefore, it has the problem that it has limited effectiveness when it is desired to propagate radio waves over a wide area, as it can eliminate dead zones.

[0008] Based on the above circumstances, the present invention aims to provide a millimeter-wave reflector capable of reflecting incident millimeter waves in multiple directions. [Means for solving the problem]

[0009] The present invention is a millimeter-wave reflector comprising a planar dielectric, two or more metal patterns of different dimensions or shapes provided on the first surface of the dielectric, and a metal layer provided on the second surface of the dielectric opposite to the first surface. The arrangement of the metal patterns is such that supercells having multiple metal patterns, including a metal pattern provided on the second surface, are arranged in positions corresponding to a basic arrangement where they are aligned and arranged without gaps, and less than 80% of the number of metal patterns are removed from the basic arrangement. [Effects of the Invention]

[0010] The millimeter-wave reflector according to the present invention can reflect incident millimeter waves in multiple directions, contributing to the effective elimination of dead zones. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic partial cross-sectional view of a millimeter-wave reflector according to one embodiment of the present invention. [Figure 2] This is a perspective view of the millimeter-wave reflector. [Figure 3] This is a perspective view of a typical millimeter-wave reflector, showing the basic configuration of a supercell. [Figure 4] This figure shows the reflection characteristics of the millimeter-wave reflector. [Figure 5]This is a schematic diagram showing an example of a metal pattern arrangement. [Figure 6] This figure shows the reflection characteristics of the example shown in Figure 5. [Figure 7] (a), (b), and (c) are schematic partial plan views of a millimeter-wave reflector according to a modified example of the present invention. [Modes for carrying out the invention]

[0012] One embodiment of the present invention will be described with reference to Figures 1 to 5. Figure 1 is a schematic partial cross-sectional view showing a millimeter-wave reflector 1 according to this embodiment. As shown in Figure 1, the millimeter-wave reflector 1 comprises a planar dielectric 20, a supercell 10 and a metal layer 30 provided on the dielectric 20.

[0013] Figure 2 shows a perspective view of the millimeter-wave reflector 1. Multiple supercells 10 are provided on the first surface 20a of the dielectric 20 and have multiple metal patterns of different shapes. In this embodiment, the supercell 10 has three metal patterns 11, 12, and 13, which are cross-shaped metal patterns of different sizes, and the metal patterns 11, 12, and 13 are arranged in a line in one direction. The shape, number, and arrangement of the metal patterns are not limited to the configuration shown in Figure 2 and can be set as appropriate, and may be annular or a three-dimensional shape such as the mushroom structure described in Patent Document 1.

[0014] The material of the dielectric 20 is not particularly limited as long as it is a dielectric. Suitable examples of the dielectric 20 include glass cloth impregnated with synthetic resin, and films made of various synthetic resins. Among these, dielectrics having low-loss electrical properties are more preferred, and examples include high-purity glass (quartz glass), fluororesins, liquid crystal polymers, polyphenylene ethers, polyether ketones, and polyolefins. These may be used individually, or multiple types may be mixed or laminated.

[0015] The metal layer 30 is provided on the second surface 20b of the dielectric 20 opposite to the first surface 20a, and covers substantially the entire second surface 20b. The dielectric 20, the supercell 10, and the metal layer 30 can be manufactured, for example, by using a material in which metal foils are joined to both surfaces of the dielectric, and patterning the metal foils by etching or the like to form a plurality of supercells.

[0016] In the present embodiment, the supercell 10 and the metal layer 30 are made of copper, but the material is not limited to copper, and gold, silver, aluminum, etc. can also be used. Further, the metal layer in the present embodiment only needs to have a metal as the main component, and may contain substances other than metal within a range that maintains conductivity of about 10 -6 Ω·m or less. For example, conductive metal oxides such as silver-mixed paste, copper-mixed paste, and ITO can also be applied according to the application.

[0017] When millimeter waves are incident on the supercell 10, a part of them is reflected by the metal patterns 11, 12, 13, and another part passes through the dielectric 20 and is reflected by the metal layer 30. Due to the phase difference between these reflected waves and the mode of the metal pattern in the supercell 10, the incident millimeter waves are emitted from the millimeter wave reflector 1 as reflected waves according to the set reflection characteristics. Therefore, by arranging a plurality of supercells 10 with their orientations aligned, the millimeter wave reflector can reflect millimeter waves according to the reflection characteristics set for the supercell 10 as the entire first surface 20a. In the present embodiment, the outer dimensions of the rectangular supercell are determined within a generally constant range according to the parameters of the millimeter waves to be reflected. Based on the above, in a normal millimeter wave reflector, as shown in FIG. 3, a plurality of supercells 10 are arranged on the reflection surface with their orientations aligned and without gaps. In the following description, the arrangement of the supercells as shown in FIG. 3 will be referred to as the "basic arrangement".

[0018] In the process of conducting various studies on the reflection characteristics of the millimeter-wave reflector, the inventors discovered that in a millimeter-wave reflector in which some of the multiple metal patterns arranged according to the above basic arrangement are removed or omitted, reflection occurs that is different from the reflection characteristics based on the reflection characteristics of the supercell 10, and as a result, diffuse reflectivity can be imparted to the millimeter-wave reflector.

[0019] For example, in the example partially shown in Figure 2, the supercells 10 are arranged continuously without gaps in the direction of their short side, but in the direction of their long side, multiple supercells are arranged with a gap of the length of one supercell between them. In other words, the example shown in Figure 2 can be described as an arrangement in which the metal pattern corresponding to all rows of supercells has been removed from the basic arrangement by one column at a time. As will be shown in more detail in the experimental examples later, in the arrangement of the metal pattern shown in Figure 2, millimeter-wave reflection peaks occur at angles that would not occur in the basic arrangement, and the millimeter-wave reflector acquires diffuse reflection characteristics.

[0020] While some aspects of the mechanism by which a millimeter-wave reflector acquires diffuse reflectivity by removing or omitting parts of the metal pattern remain unclear, it is generally thought to be due to the following actions. Millimeter waves incident on areas without a metal pattern pass through the dielectric 20 and are reflected by the metal layer 30. However, since no interference occurs with the metal pattern, only specular reflection occurs in the metal layer 30. It is thought that further interference between this reflected wave and the reflected wave based on the reflection characteristics of the supercell 10 results in a reflection peak that is different from both the specular reflection and the reflection angle based on the reflection characteristics.

[0021] The diffuse reflection phenomenon described above will be explained using experimental examples. (Experimental Example 1) A 60.6mm x 60.6mm copper-clad laminate was prepared, with copper foil on both sides of the dielectric. The dielectric was fluororesin-impregnated glass cloth (800μm thick), and the thickness of the copper foil was 35μm on both sides, for a total thickness of 870μm. An example of a commercially available copper-clad laminate with this configuration is CGP-500 manufactured by Chuko Kasei Kogyo Co., Ltd.

[0022] Multiple supercells were formed by etching one side of a copper-clad laminate, creating a two-dimensional matrix arrangement. Each supercell consists of three cross-shaped metal patterns. The small pattern is 1.1 mm wide and 1.4 mm in length and width. The medium pattern is 1.4 mm wide and 3.0 mm in length and width. The large pattern is 1.4 mm wide and 3.8 mm in length and width. The three patterns were arranged in equal pitch in the order of small, medium, and large within a 5.05 mm × 15.15 mm area, forming the unit of the supercell. This supercell is designed to reflect 28 GHz millimeter waves incident perpendicularly, tilted at 45° from the small pattern towards the large pattern.

[0023] A supercell with the above configuration was formed in a 12x4 two-dimensional matrix. The other side was used as a metal layer without etching. Based on the above, a millimeter-wave reflector according to Experimental Example 1 was fabricated. The appearance of the millimeter-wave reflector 100 according to Experimental Example 1 is shown in Figure 3. The millimeter-wave reflector 100 has supercells arranged without gaps in the same orientation across its entire surface, which is the "basic arrangement" described above.

[0024] (Experimental Example 2) Two rows of supercells, arranged without gaps in the short-side direction, were formed in the long-side direction with a gap of one supercell between them. The millimeter-wave reflector for Experimental Example 2 was fabricated using the same procedure as in Experimental Example 1 in all other respects. The appearance of the millimeter-wave reflector for Experimental Example 2 is almost the same as that shown in Figure 2. The millimeter-wave reflector for Experimental Example 2 has 50% of the metal patterns compared to the "basic arrangement," and there are equal numbers of small, medium, and large metal patterns.

[0025] The millimeter-wave reflection characteristics of the millimeter-wave reflectors related to Experimental Examples 1 and 2 were evaluated using the following procedure. (Reflection characteristics evaluation) The millimeter-wave reflector for each example was mounted on a wooden beam so that the supercell side had a convex curved surface, and fixed in an anechoic chamber environment. The transmitted wave from the horn antenna was reflected by a curved reflector to generate a 28 GHz plane wave, which was then shone perpendicularly onto the millimeter-wave reflector. The reflected waves from the millimeter-wave reflector were measured using a receiving antenna positioned at a far-field location relative to the reflector. This receiving antenna was mounted on a robot and configured to orbit the reflector while maintaining a constant far-field distance, allowing for measurement of reflected waves over a wide angular range. The far-field distance can be calculated using 2D^2 / λ. The robot-mounted receiving antenna orbited the reflector for 180° to the right, then for 180° to the left. This allowed for measurement of the intensity of reflected waves from the reflector in a 358° range, excluding the 2° directly in front of the reflector.

[0026] Next, the measurement results for each example were analyzed using the finite element method analysis software "High-Frequency 3D Electromagnetic Field Analysis Software HFSS (FEM Solver)". The conditions were as follows: Setting of incident radio waves Incident angle: 0° Polarization: TE wave Frequency: 28GHz Incident position: 15 mm away from the supercell-side surface of the millimeter-wave reflector in the normal direction. Setting up the analysis model Dimensions of each part of the millimeter-wave reflector: As shown above. Conductor: Copper, conductivity 5.8 × 10 7 Dielectric material: Dielectric constant 2.6, dielectric loss tangent 0.0025

[0027] Figure 4 shows the analysis results. In Experimental Example 1, with the front as 0°, major reflection peaks were observed only at 45° and -45°. However, in Experimental Example 2, which lacked some of the metallic patterns, the reflection intensity at 45° and -45° decreased slightly, while new reflection peaks of sufficient size were generated at 0°, 22.5°, and -22.5°. From the above, it has been shown that by removing or omitting some of the multiple metal patterns arranged according to the basic configuration, millimeter waves can be diffusely reflected in multiple directions other than the reflection angles based on the specular reflection and supercell setting specifications.

[0028] Further investigation by the inventors revealed that the methods for removing or omitting the metal pattern that produces diffuse reflection are not limited to those described above.

[0029] First, it was found that the metal pattern does not necessarily have to be removed or omitted on a supercell basis, and that a portion of the metal pattern constituting the supercell may be removed or omitted. For example, in the example shown in Figure 5, the arrangement is created by repeatedly removing five columns of metal patterns while leaving two columns of metal patterns in the basic arrangement. As a result, there are no supercells in which all metal patterns are present, and the pairs of metal patterns in the remaining two columns do not match; on the left side, it is a pair of metal pattern 11 and metal pattern 12, while on the right side, it is a pair of metal pattern 12 and metal pattern 13. In the metal pattern arrangement shown in Figure 5, no perfect supercells exist, but all remaining metal patterns are located in positions corresponding to the basic arrangement. Even with this configuration of metal patterns, simulations using the above analysis software revealed new reflection peaks of sufficient size at 22.5° and -22.5°, as shown in Figure 6, indicating suitable diffuse reflectivity.

[0030] In the inventors' studies, diffuse reflection was no longer observed when the number of rows left empty after retaining two rows became nine. After various tests with different numbers of rows to retain and the number of rows left empty, it was determined that the proportion of metal patterns to be removed or omitted should preferably be 80% or less of the basic arrangement. On the other hand, if too few metal patterns are removed or omitted, different reflection peaks may not be generated, or if they are generated, they may be insufficient, making it highly likely that diffuse reflectivity will not be exhibited. In the inventors' above studies, it was considered preferable that the amount be approximately 20% or more of the basic arrangement, but this is not essential, and it may be less than 20% of the basic arrangement if diffuse reflectivity is actually exhibited. In this invention, "no diffuse reflection" is defined as a state in which no peaks with a difference of 10 dBsm (decibels square meters) or less from the largest reflection peak are in a phase different from either specular reflection or the reflection angle based on the reflection characteristics.

[0031] Furthermore, when the metal patterns were removed or omitted, and only one type of metal pattern remained, diffuse reflection ceased, even if the proportion of removed or omitted metal patterns was within the above range. Therefore, it was found that at least two types of metal patterns are necessary. The inventors' studies have shown that when there are two types of metal patterns, if the number of the smaller metal pattern is 40% or more of the larger metal pattern, good diffuse reflectivity is likely to be observed. Even if a supercell consists of three or more types of metal patterns, diffuse reflectivity can be imparted to the millimeter-wave reflector by removing or omitting some of the metal patterns so that at least two of them remain. In this case, there are no particular restrictions on the combination of metal patterns to be retained, and they can be selected as appropriate. In this case, if the above ratio is satisfied with the two patterns with the smallest difference among the three or more types, good diffuse reflectivity is likely to be observed. The two metal patterns do not necessarily have to be placed side by side; they may be placed spaced apart.

[0032] As described above, the millimeter-wave reflector according to this embodiment can reflect incident millimeter waves at multiple angles other than those based on the reflection characteristics of the supercell, and can effectively fill the space in which it is installed with millimeter waves.

[0033] Furthermore, in this invention, it is a fundamental premise that all remaining metal patterns are arranged in a manner consistent with a common basic arrangement, and it is believed that this maintains millimeter-wave reflection based on the reflection characteristics of the supercell. Therefore, it is important to note that the multiple types of metal patterns constituting the supercell cannot be freely arranged without any constraints.

[0034] A typical arrangement of the metal pattern according to the present invention is one in which a series of rows of rectangular supercells, arranged without gaps in the direction in which one of the long or short sides of the rectangle extends, are arranged in the direction of the other side, with spacing between them being an integer multiple of the other side. Specific examples of such typical arrangements include the example shown in Figure 2, where the spacing is the width of two supercells, and the arrangement in which a series of rows of supercells, arranged without gaps in the direction of the long side, are arranged in the direction of the short side with spacing between them being three times the length of the short side of the supercells. Even in this case, the size of the empty spaces does not need to be the same; for example, there may be a mix of spaces with two supercell-sized gaps and spaces with one supercell-sized gaps.

[0035] Although the present invention has been described above using embodiments and examples, the specific configuration is not limited to these embodiments, and modifications and combinations of the configuration that do not depart from the spirit of the present invention are also included.

[0036] For example, areas where the metal pattern has been removed or omitted do not necessarily have to be continuous in the long or short direction of the supercell. In the modified millimeter-wave reflector 1A shown in Figure 7(a) and the modified millimeter-wave reflector 1B shown in Figure 7(b), the areas where the metal pattern has been removed or omitted are continuous in an oblique direction and do not extend far in either the long or short direction of the supercell. However, in both millimeter-wave reflectors 1A and 1B, all types of the multiple metal patterns constituting the supercell are present, and the proportion of the removed or omitted metal patterns is 75%, thus exhibiting suitable diffuse reflectivity. In the modified millimeter-wave reflector 1C shown in Figure 7(c), the areas where the metal pattern has been removed or omitted are scattered in a checkerboard pattern, with each area corresponding to one metal pattern, and are not continuous in any direction. However, since all types of the multiple metal patterns that constitute the supercell are present, and the proportion of the removed or omitted metal patterns is 50%, it still exhibits suitable diffuse reflectivity.

[0037] Furthermore, multiple arrangements of metal patterns may be combined, for example, by using the configuration shown in Figure 7 in one region of the millimeter-wave reflector and the configuration shown in Figure 2 in other regions. This further diversifies the interference of reflected waves and enables three-dimensional diffuse reflection of the reflected waves.

[0038] In the present invention, the arrangement of the metal patterns may be such that the removed or omitted parts are distributed irregularly without any discernible pattern, as long as the number of types of metal patterns and the proportion of removal or omission described above are satisfied.

[0039] In the millimeter-wave reflector according to the present invention, the metal layer does not necessarily have to be provided without gaps on the second surface. For example, it may be in the form of a mesh with small openings, or it may have linear defects corresponding to the compartments of a supercell. However, in areas without a metal layer, incident millimeter waves are transmitted without being reflected, so if there are too many areas without a metal layer, it may affect the reflection performance. From this viewpoint, it is preferable that the maximum continuous length of the area without a metal layer be less than 1 / 4λ of the frequency to be reflected. In the case of a mesh, it is possible to transmit radio waves of a predetermined wavelength without reflection by adjusting the dimensions of the openings. [Explanation of symbols]

[0040] 1, 1A, 1B, 1C Millimeter-wave reflectors 10 Supercells 11, 12, 13 Metal Patterns 20 Dielectrics 20a Front page 20b Second side 30 metal layer

Claims

1. Planar dielectric and Two or more metal patterns of different dimensions or shapes are provided on the first surface of the dielectric, In the dielectric, a metal layer is provided on the second surface opposite to the first surface, Equipped with, The arrangement of the metal patterns is such that a supercell having multiple metal patterns including the metal pattern is placed in a position corresponding to a basic arrangement in which multiple metal patterns are arranged in the same orientation and without gaps, and in a state in which 80% or less of the metal patterns are removed from the basic arrangement. Millimeter wave reflector.

2. The aforementioned arrangement configuration is a state in which 20% or more of the metal patterns have been removed from the basic arrangement. The millimeter-wave reflector according to claim 1.

3. The supercell has a rectangular shape in plan view. The arrangement of the metal pattern is such that rows of the supercells, which are arranged without gaps in the direction of the shorter side of the rectangle, are arranged in the direction of the longer side of the rectangle at intervals that are integer multiples of the length of the longer side. The millimeter-wave reflector according to claim 1.

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