Inflatable radar reflector and inflatable radar reflector assembly

Abstract

To provide an inflatable radar reflector that can achieve wide-area reflection and has excellent portability.SOLUTION: According to the present invention, there is provided an inflatable radar reflector including a radio-wave transmissive outer body, a deformable reflective material, and at least two flexible wires, the outer body being deformable between a folded state and a deployed state and having a first surface and a second surface facing each other in the deployed state, the reflective material when the outer body is in the deployed state being suspended inside the outer body by the wires to form a plurality of unit reflectors arranged in a direction orthogonal to the wires.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an inflatable radar reflector, and also to an inflatable radar reflector assembly formed by combining several of these radar reflectors. [Background technology]

[0002] One type of radar technology is imaging SAR (Synthetic Aperture Radar). While conventional radar allows for determining the direction and distance to a target, imaging SAR allows for the acquisition of high-resolution images of the target. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent No. 2,463,517 Summary of the Invention [Problem to be solved by the invention]

[0004] In order to estimate the identity of a target from the waves reflected from it, it is necessary to know in advance what kind of backscattering occurs in relation to the geometric properties of the target. In acquiring data relating to the correspondence between the geometric properties of the target and backscattering, it is not realistic to use actual objects such as passenger cars or aircraft, so it is useful to be able to use dummies.

[0005] A balloon with an internal corner reflector is known as a dummy that strongly reflects radar waves (see, for example, Patent Document 1). However, conventional reflectors such as those described in Patent Document 1 are only expected to function as point reflection sources, and no dummy that achieves widespread reflection is currently available. [Means for solving the problem]

[0006] According to the present invention, the following inventions are provided. [1] An inflatable radar reflector comprising a radio wave transparent exterior body, a deformable reflective material, and two or more flexible wires, wherein the exterior body is configured to be deformable between a folded state and an unfolded state, and has a first surface and a second surface that face each other in the unfolded state, and the reflective material is suspended inside the exterior body by the wires when the exterior body is in the unfolded state, thereby forming a plurality of unit reflectors lined up in a direction perpendicular to the wires. [2] A radar reflector according to [1], wherein one end and the other end of each wire are fixed to the first surface and the second surface of the outer casing, respectively. [3] A radar reflector according to [1] or 2, wherein the plurality of unit reflectors include a plurality of columnar reflectors arranged between the first surface and the second surface. [4] A radar reflector as described in any one of [1] to [3], wherein the wire and the reflecting material divide the interior of the exterior body into a plurality of cavities when the exterior body is in an expanded state, and the reflecting material equalizes the air pressure between the cavities by allowing gas to pass through. [5] A radar reflector according to [4], wherein the reflective material is (a) a cloth containing conductive fibers, or (b) a conductive sheet having one or more air holes. [6] A radar reflector according to any one of [1] to [5], wherein each wire extends along one side that defines the opening of the unit reflector between the first surface and the second surface when the outer casing is in an expanded state. [7] A radar reflector according to any one of [1] to [6], wherein the exterior body has a hexahedral shape in an unfolded state, the hexahedral shape has third and fourth surfaces that face each other and are perpendicular to the first and second surfaces, and the plurality of unit reflectors further include a unit reflector that is located between the third and fourth surfaces and opens to the first or second surface. [8] An inflatable radar reflector assembly comprising a first unit and a second unit, each of which is a radar reflector according to any one of [1] to [7], and the internal space of the outer casing of the second unit is in communication with the internal space of the outer casing of the first unit. [9] An inflatable radar reflector assembly comprising a first unit and a second unit, each of the first unit and the second unit having a radio wave transparent exterior body and a deformable reflective material, the exterior body being configured to be deformable between a folded state and an unfolded state and having airtightness, the reflective material covering at least a portion of the outer surface of the exterior body, and the internal space of the exterior body of the second unit being in communication with the internal space of the exterior body of the first unit.

[0007] According to at least one embodiment of the present invention, an inflatable radar reflector is provided that is capable of achieving widespread reflection and is highly portable. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic perspective view showing an exemplary appearance of an inflatable radar reflector according to an embodiment of the present invention. FIG. [Figure 2] 2 is a diagram showing a schematic view of the radar reflector 100A shown in FIG. 1, with the reflector 20A and flexible wires 30s and 30t taken out. [Figure 3]FIG. 10 is a schematic perspective view showing an exemplary appearance of an inflatable radar reflector according to another embodiment of the present invention. [Figure 4] FIG. 10 is a schematic perspective view showing an exemplary appearance of an inflatable radar reflector according to yet another embodiment of the present invention. [Figure 5] FIG. 10 is a schematic perspective view showing an exemplary appearance of an inflatable radar reflector according to yet another embodiment of the present invention. [Figure 6] FIG. 10 is a schematic perspective view showing an exemplary appearance of an inflatable radar reflector according to yet another embodiment of the present invention. [Figure 7] FIG. 10 is a schematic perspective view showing an inflatable radar reflector assembly according to yet another embodiment of the present invention. [Figure 8] FIG. 10 is a schematic perspective view showing an inflatable radar reflector assembly according to yet another embodiment of the present invention. [Figure 9] FIG. 1 is a schematic perspective view showing an example of a box-shaped reflector formed from a metal plate. [Figure 10] FIG. 10 is a diagram showing the measurement results of RCS for reflector A. [Figure 11] FIG. 10 is a diagram showing the measurement results of RCS for reflector B. [Figure 12] FIG. 10 is a diagram showing the measurement results of RCS for reflector C. DETAILED DESCRIPTION OF THE INVENTION

[0009] The following describes embodiments of the present invention. The various features shown in the following embodiments can be combined with each other. Furthermore, each feature can be an independent invention.

[0010] 1. Inflatable radar reflector FIG. 1 shows an exemplary appearance of an inflatable radar reflector according to an embodiment of the present invention. The radar reflector 100A shown in FIG. 1 includes an exterior body 10 having a generally rectangular parallelepiped shape. In a typical embodiment of the present invention, the exterior body 10 is made of a radio wave-transparent sheet and can be expanded from a folded state to a desired shape (e.g., a rectangular parallelepiped) by supplying gas (typically air) to the interior. In this sense, the exterior body 10 is inflatable, and may also be referred to as a balloon. Hereinafter, for simplicity, an "inflatable radar reflector" may be simply referred to as a "radar reflector." Of course, the radar reflector of the present invention is not limited to this example, and may have various external shapes (e.g., polyhedrons such as hexahedrons).

[0011] FIG. 1 shows a radar reflector 100A in a state in which the exterior body 10 is unfolded. In the configuration illustrated in FIG. 1, the unfolded exterior body 10 has a hexahedral shape including a first surface 11 to a sixth surface 16. Of the six surfaces, the first surface 11 to the sixth surface 16, the first surface 11 and the second surface 12 face each other, and the third surface 13 and the fourth surface 14 also face each other. The pair of the third surface 13 and the fourth surface 14 is generally perpendicular to the first surface 11 and the second surface 12. Similarly, the fifth surface 15 and the sixth surface 16 face each other. The pair of the fifth surface 15 and the sixth surface 16 is generally perpendicular to all of the first surface 11 to the fourth surface 14.

[0012] A typical example of the material for the exterior body 10 is a polymer sheet such as polyolefin or polyvinyl chloride. By combining six sheets, each having a predetermined shape, by stitching, welding, or the like, it is possible to obtain, for example, the above-mentioned hexahedral shape.

[0013] As shown schematically in Fig. 1, the radar reflector 100A further includes a reflector 20A and two or more flexible wires. In this example, the radar reflector 100A includes a plurality of flexible wires 30s and a plurality of flexible wires 30t. The reflector 20A, the flexible wires 30s, and the flexible wires 30t are all disposed inside an exterior body 10. For ease of explanation, Fig. 1 shows the internal structure of the exterior body 10 with a portion of the exterior body 10 cut away, but the material constituting the exterior body 10 may be transparent or opaque as long as it is radio wave permeable.

[0014] Fig. 2 shows a schematic diagram of the reflective material 20A and flexible wires 30s, 30t extracted from the radar reflector 100A shown in Fig. 1. As shown in the upper part of Fig. 2, the reflective material 20A has a folding screen-like shape when the exterior body 10 is inflated, that is, when it is unfolded into its intended shape. More specifically, at least one surface of the reflective material 20A has a plurality of folds, thereby forming a plurality of reflective surfaces 21, 22, ..., 27, ... inside the exterior body 10.

[0015] A radio wave reflective material may be used for the reflective material 20A. Typical examples of the reflective material 20A include cloth containing conductive fibers and a conductive sheet. The conductive sheet may be, for example, a sheet in which a conductive film is formed on the surface of a resin film. Cloth or paper coated with conductive paint may also be used as the material for the reflective material 20A. In other words, a flexible material that exhibits radio wave reflective properties and can deform in accordance with the deformation of the exterior body 10 is selected for the reflective material 20A. FIG. 2 shows an example in which a cloth containing conductive fibers is used as the reflective material 20A. As will be described later, when a conductive sheet is used as the reflective material, one or more through holes may be provided in the conductive sheet.

[0016] The reflective material 20A is supported by the flexible wire inside the exterior body 10, for example by being sewn to the flexible wire. Here, five flexible wires 30s and six flexible wires 30t are arranged inside the exterior body 10. In the configuration illustrated in Fig. 2, each of the five flexible wires 30s and each of the six flexible wires 30t extend along the folds of the reflective material 20A.

[0017] Flexible wire 30s includes flexible wires 31s, 32s, ..., 35s. One end and the other end of each flexible wire 31s, 32s, ..., 35s are fixed to first surface 11 and second surface 12 of exterior body 10, respectively (see FIG. 1), and extend under tension between first surface 11 and second surface 12 when exterior body 10 is in an inflated state. Flexible wires 31s, 32s, ..., 35s are arranged inside exterior body 10 at predetermined intervals from one another along a direction connecting fifth surface 15 and sixth surface 16. On the other hand, the flexible wire 30t includes flexible wires 31t, 32t, ..., 36t, and similarly to the above-described flexible wires 31s, 32s, ..., 35s, one end and the other end of each of the flexible wires 31t, 32t, ..., 36t are fixed to the first surface 11 and the second surface 12, respectively, of the exterior body 10. The number of flexible wires included in the radar reflector 100A may be determined appropriately depending on the sizes of the exterior body 10 and the reflector 20A.

[0018] Any wire, natural or artificial, may be used as the flexible wire 30s and the flexible wire 30t, as long as it has flexibility and the necessary strength. For example, a thread or string made of a synthetic fiber such as nylon may be used as the flexible wire 30s and the flexible wire 30t. The thickness of each of the flexible wires 30s and the flexible wire 30t may be determined appropriately taking into account flexibility and strength. The length of the flexible wire 30s and the flexible wire 30t may also be selected appropriately depending on the distance between the first surface 11 and the twelfth surface when the exterior body 10 is in the unfolded state.

[0019] 2, flexible wires 31s, 32s, ..., 35s extend along the folds of reflector 20A, and flexible wires 31t, 32t, ..., 36t also extend along the folds of reflector 20A. In other words, in this example, flexible wires 31s, 32s, ..., 35s and flexible wires 31t, 32t, ..., 36t each extend along one side of reflecting surface 21, 22, ..., 27, ... of reflector 20A. In other words, each of reflecting surfaces 21, 22, ..., 27, ... is stretched by flexible wires 31s, 32s, ..., 35s and flexible wires 31t, 32t, ..., 36t, and is generally flat when exterior body 10 is inflated.

[0020] Here, two adjacent ones of the reflecting surfaces 21, 22, ..., 27, ... form a V-groove shape, and each of these V-groove shapes can function as a triangular prism-shaped retroreflector. Such a unit structure formed from a portion of the reflecting material 20A and capable of functioning as a retroreflector can be called a "unit reflector." In this example, of the flexible wire 30s and flexible wire 30t described above, the flexible wire 30s is located at the opening of the triangular prism-shaped unit reflector, while the flexible wire 30t is located at the bottom of the V-groove shape formed by the two reflecting surfaces.

[0021] In the example shown in Fig. 2, the reflector 20A includes unit reflectors R1, R2, R3, ... arranged in a direction substantially perpendicular to the extension direction of the flexible wires 30s and 30t. Unit reflector R1 is composed of a pair of reflecting surfaces 21 and 22, and unit reflector R2 is similarly composed of a pair of reflecting surfaces 23 and 24. In the example shown in Fig. 2, the angle θ between the two reflecting surfaces forming the V-groove shape is substantially 90 degrees. Each of the unit reflectors formed from the V-groove shape opens toward the third surface 13 of the exterior body 10, as shown in Fig. 1.

[0022] In this way, when the exterior body 10 is in an unfolded state, the reflecting material 20A is suspended inside the exterior body 10 by the tension of the flexible wires 30s and 30t, thereby forming a plurality of unit reflectors inside the exterior body 10. These unit reflectors are aligned inside the exterior body 10 in a direction perpendicular to the flexible wires when the exterior body 10 is unfolded, as shown schematically in Figures 1 and 2. Note that the side Ed of the reflecting material 20A, which corresponds to the outer edge of the outermost unit reflector, can be joined to the inner surface of the exterior body 10 by sewing, welding, or the like.

[0023] As can be seen from the above description, the radar reflector 100A of this embodiment functions as a self-supporting reflector, maintaining its outer shape, such as a hexahedron, by supplying gas to the interior of the exterior body 10, for example. As is clear from the above description, the basic units constituting the radar reflector 100A, namely, the exterior body 10, the reflecting material 20A, and the flexible wires 30s and 30t, are all deformable. Therefore, the radar reflector 100A can be folded up into a small size by venting gas from inside the exterior body 10. In FIG. 2, the reflecting material 20A in an extended state due to the exterior body 10 being unfolded and the reflecting material 20A in a folded state are both shown in a single figure. Furthermore, since the reflective material 20A and the flexible wires 30s and 30t are all flexible, it is possible not only to close the unit reflectors R1, R2, R3, ... in a direction perpendicular to the flexible wires, but also to further fold the reflective material 20A in the direction in which the flexible wires 30s and 30t extend, as shown in the lower part of Figure 2.

[0024] Because the radar reflector 100A has these characteristics, the user of the radar reflector 100A can carry the radar reflector 100A in a compact, folded state. Furthermore, the user of the radar reflector 100A can inflate the exterior body 10 at the location where the radar reflector 100A is expected to be used, and easily install the radar reflector 100A, which has been expanded into a rectangular parallelepiped shape or the like, at the desired location.

[0025] According to an embodiment of the present invention, by unfolding the radar reflector 100A into a desired shape, such as a rectangular parallelepiped, it is possible to unfold, for example, a row of multiple unit reflectors inside the exterior housing 10. The radar reflector 100A has an array of unit reflectors, which allows it to achieve widespread reflection, unlike conventional reflectors that function as point reflection sources, such as those described in Patent Document 1. Thus, the radar reflector 100A has a first mode that is lightweight and portable, and a second mode that can achieve widespread reflection. Furthermore, because its shape is maintained by pressure, such as gas, the radar reflector 100A has the advantage of being extremely lightweight, even in the unfolded second mode, compared to conventional corner reflectors made of rigid plates.

[0026] The external shape of the deployed exterior body 10 is not limited to a highly symmetrical shape that can be described by a group of regular polyhedrons. The size of the deployed exterior body 10 is also arbitrary, and the distance between the first surface 11 and the second surface 12, the distance between the third surface 13 and the fourth surface 14, or the distance between the fifth surface 15 and the sixth surface 16 can be, for example, in the range of approximately 100 mm to 500 mm.

[0027] It should be noted that in the embodiments of the present invention, it is not essential that the exterior body 10 be airtight. For example, it may be connected to a blower, air compressor, or cylinder to maintain the internal pressure at or above atmospheric pressure. For example, if the intended deployed shape (here, a hexahedral shape) can be maintained by continuously supplying gas to the interior of the exterior body 10, some leakage of gas from the seams of the sheet, for example, may be acceptable.

[0028] In that sense, the exterior body 10 may have an inlet 60 for connection to a blower or the like, as shown in Fig. 1. By continuously supplying gas to the interior of the exterior body 10, it is possible to prevent the shape of the exterior body 10 from unintentionally changing due to changes in atmospheric pressure. Note that, since the internal pressure of the exterior body 10 can be made equal to or greater than atmospheric pressure when deployed in this manner, the first surface 11 to the sixth surface 16 may have a gentle curvature rather than being strictly flat.

[0029] The exterior body 10 may be airtight, in which case the exterior body 10 may further include a valve for preventing gas leakage from the injection port 60. The radar reflector 100A may further include an adjustment mechanism that detects changes in atmospheric pressure and / or outside temperature and offsets changes in pressure inside the exterior body 10.

[0030] The exterior body 10 may be waterproof. If the exterior body 10 is waterproof, it is advantageous because it can be used outdoors regardless of the weather. Even if the exterior body 10 is not completely airtight, as long as the pressure inside the exterior body 10 is maintained higher than atmospheric pressure, it is possible to prevent water droplets from entering through seams between the sheets that make up the exterior body 10.

[0031] 2. Other examples of inflatable radar reflectors Fig. 3 shows a radar reflector according to another embodiment of the present invention. In Fig. 3, the internal structure of the exterior body 10 is shown assuming that the material constituting the exterior body 10 is transparent. In the subsequent drawings, the interior of the exterior body 10 is similarly shown by solid lines.

[0032] Similar to the above-described radar reflector 100A, the radar reflector 100B shown in Fig. 3 has a plurality of unit reflectors, each of which has a triangular prism shape, inside the exterior body 10 when the exterior body 10 is unfolded. Compared to the radar reflector 100A described with reference to Fig. 1, the radar reflector 100B shown in Fig. 3 has a reflector 20B instead of the reflector 20A.

[0033] Fig. 3 shows an example in which a conductive sheet is applied to reflective material 20B. In the example shown in Fig. 3, the ridges of reflective material 20B, which is zigzag when package 10 is unfolded, are in contact with either the third surface 13 or the fourth surface 14 of package 10. Note that this example shows an example in which the bottom of a V-groove formed from the reflective surface of reflective material 20B is fixed to fourth surface 14 of package 10 by stitching or the like. With this configuration, it is possible to omit the placement of a flexible wire at the bottom of the V-groove.

[0034] 3, the space inside the exterior body 10 is divided into a plurality of spaces AC (compartments) by reflecting material 20B. Each of these spaces AC defines a structure that reflects radar waves, and each of these spaces AC may also be called a cavity.

[0035] 3, the conductive sheet serving as reflector 20B has through-holes 20p on each of its reflective surfaces. These through-holes 20p are provided in the conductive sheet so as to connect the multiple cavities partitioned by the conductive sheet. The through-holes 20p in the conductive sheet function as air holes that allow gas to pass through and equalize the air pressure between the cavities.

[0036] By equalizing the air pressure between the cavities, it is possible to prevent the reflector shape from collapsing due to the pressure difference between the cavities. The number and arrangement of the through holes 20p, as well as the shape of each through hole 20p, may be determined appropriately as long as the air pressure between the cavities is equalized. Note that, as in the example shown in FIG. 1, when a cloth containing conductive fibers is used as the reflector 20A, the cloth itself exhibits breathability, so air holes such as the through holes 20p may be omitted. By using a cloth containing conductive fibers or a conductive sheet with air holes as the reflector, it is possible to achieve ventilation between the cavities while maintaining radar reflectivity and flexibility.

[0037] <3. Other examples of reflector shapes> Fig. 4 shows a radar reflector according to yet another embodiment of the present invention. Like the radar reflector 100A and radar reflector 100B described above, the radar reflector 100C shown in Fig. 4 has multiple unit reflectors inside the exterior body 10 when the exterior body 10 is deployed. However, in this example, as schematically shown in Fig. 4, the shape of the reflector deployed inside the exterior body 10 is different from the shape of the reflector in the above-described examples.

[0038] As shown in Fig. 4, the radar reflector 100C has, inside the exterior housing 10, a plurality of unit reflectors S1, S2, S3, ... arranged in a direction substantially perpendicular to the flexible wire 30s. In the configuration illustrated in Fig. 4, focusing on the individual unit reflectors, in this example, a columnar reflector is formed from three of the reflecting surfaces 21, 22, 23, ... of the reflecting material 20C. For example, the unit reflector S1 includes the reflecting surfaces 21 and 23 as side surfaces of the reflector shape, and includes the reflecting surface 22 as the bottom surface of the reflector shape.

[0039] As in the previous example described with reference to FIGS. 1 to 3, in the configuration illustrated in FIG. 4, the flexible wires 30s extend between the first surface 11 and the second surface 12 of the exterior body 10. As shown in FIG. 4, each flexible wire 30s extends along one side that defines the opening of the columnar reflector. In this example, the radar reflector 100C further includes flexible wires 30t that each extend between the first surface 11 and the second surface 12 of the exterior body 10. Here, each flexible wire 30t is arranged along one side of the rectangular bottom surface (e.g., the reflecting surface 22) of the columnar reflector.

[0040] By placing flexible wires 30s at the position of one side defining the opening of the columnar reflector and supporting the reflector 20C, the size of the opening of the columnar reflector can be controlled by adjusting the spacing between the flexible wires 30s. The spacing between the flexible wires 30s (and between the flexible wires 30t) can be adjusted by adjusting the degree of expansion of the exterior body 10. In other words, by changing the spacing between the flexible wires through the degree of expansion of the exterior body 10, the size of the opening of each unit reflector can be adjusted. This means that the size of backscattering can be changed after the fact, and by arranging multiple such unit reflectors, the spread of the reflection can be adjusted after the fact. In other words, a single radar reflector can simulate a reflective surface of any size within a certain range.

[0041] Figure 5 shows a radar reflector according to yet another embodiment of the present invention. Compared to the radar reflector 100C described with reference to Figure 4, the radar reflector 100D shown in Figure 5 has a reflector 20D instead of the reflector 20C. Furthermore, the radar reflector 100D further has flexible wires 40s and 40t extending between the fifth and sixth surfaces 15 and 16 of the outer casing 10, in addition to flexible wires 30s and 30t, respectively, extending between the first and second surfaces 11 and 12 of the outer casing 10.

[0042] In this example, the reflector 20D is suspended by the flexible wires 30s and 40s, thereby forming box-shaped unit reflectors T1, T2, ... inside the exterior body 10. As shown schematically in FIG. 5 , the unit reflectors T1, T2, ... are arranged in a matrix, and each of these unit reflectors T1, T2, ... is open toward the third surface 13 of the exterior body 10.

[0043] Here, each flexible wire 30s and each flexible wire 40s is arranged along one side of the opening of the unit reflector T1, T2, .... This example is not limiting, and the reflector 20D may be suspended inside the exterior body 10 by a knotless or knotted net having a shape corresponding to the opening of the unit reflector T1, T2, .... Note that other flexible wires may be arranged not only at the positions of the openings of the unit reflectors T1, T2, ..., but also along the outer edge of the rectangular bottom surface that defines the shape of the box-shaped unit reflector. In this example, flexible wires 30t and flexible wires 40t are arranged in a grid pattern at the bottom of the group of unit reflectors. By further arranging flexible wires 30t and flexible wires 40t at the bottom surface that defines the reflector shape, the shape of each unit reflector T1, T2, ... can be made to more accurately resemble a box shape when the exterior body 10 is unfolded. Instead of the flexible wires 30t and 40t, a knotless net or knotted net may be disposed at the bottom surface position that defines the shape of the reflector.

[0044] According to this embodiment, it is possible to realize a broadened reflection not only in the direction perpendicular to the flexible wire 30s but also in the direction perpendicular to the flexible wire 40s. Thus, the radar reflector 100D can achieve a two-dimensionally broadened reflection. As will be explained later with reference to examples, the inventors have confirmed that a box-shaped reflector made of, for example, a cloth containing conductive fibers can also exhibit reflection characteristics similar to those of a box-shaped reflector made of a metal plate.

[0045] Fig. 6 shows a radar reflector according to yet another embodiment of the present invention. The radar reflector 100E shown in Fig. 6 has a second reflector 20Eb inside the exterior housing 10 in addition to the reflector 20Ea. The radar reflector 100E also has flexible wires 50s and 50t, each extending between the third surface 13 and the fourth surface 14 of the exterior housing 10. As shown schematically in Fig. 6, each of the flexible wires 50s and 50t extends between the third surface 13 and the fourth surface 14 through the reflector 20Ea.

[0046] Like the reflector 20A of the radar reflector 100A shown in FIG. 1, the reflector 20Ea of the radar reflector 100E is suspended inside the exterior body 10 by the flexible wires 30s and 30t when the exterior body 10 is unfolded, thereby forming multiple unit reflectors. In this example, the reflector 20Eb is also supported by the flexible wires 50s and 50t, thereby forming multiple unit reflectors inside the exterior body 10 that are aligned in the direction connecting the fifth surface 15 and the sixth surface 16 of the exterior body 10, in other words, in a direction generally perpendicular to the flexible wires 50s and 50t. Here, the shape of each unit reflector formed by the reflector 20Eb is a triangular prism, similar to the unit reflector formed by the reflector 20Ea. Of course, the shapes of unit reflectors aligned in different directions may differ.

[0047] One end and the other end of each flexible wire 50s are fixed to the third surface 13 and the fourth surface 14 of the exterior body 10, respectively. Similarly, one end and the other end of each flexible wire 50t are fixed to the third surface 13 and the fourth surface 14 of the exterior body 10, respectively. Here, each flexible wire 50s extends along one side that defines the opening of a triangular prism-shaped unit reflector formed from the reflecting material 20Eb, and each flexible wire 50t extends along the bottom of the triangular prism-shaped unit reflector. Each of these triangular prism-shaped unit reflectors is located between the third surface 13 and the fourth surface 14 of the exterior body 10, and opens in a surface (here, the first surface 11) that is perpendicular to these surfaces.

[0048] In actual operation of the radar reflector 100E, the radar reflector 100E can be installed so that the direction connecting the third surface 13 and the fourth surface 14 of the exterior body 10 is parallel to the vertical direction, for example. This makes it possible to obtain not only reflection characteristics that are broad in the direction connecting the fifth surface 15 and the sixth surface 16 with the third surface 13 of the exterior body 10 as the front, but also reflection characteristics that are broad in the direction connecting the fifth surface 15 and the sixth surface 16 with the first surface 11 as the front. In other words, the radar reflector 100E can simulate backscattering not only in the depth direction of a target but also in the height direction.

[0049] As described above, according to the embodiment of the present invention, it is also possible to achieve a combination of reflection that spreads in a first direction and reflection that spreads in a second direction different from the first direction. Using a similar technique, a third reflecting material may be disposed inside the exterior body 10 to form multiple unit reflectors, thereby obtaining further reflection that spreads in another third direction. In this case, flexible wires may be disposed inside the exterior body 10 in three mutually intersecting directions, and these flexible wires may support three reflecting materials with different front directions inside the exterior body 10. As described above, according to the embodiment of the present invention, it is also easy to dispose a third group of unit reflectors inside the exterior body 10.

[0050] Previously, when attempting to simulate the backscattering of a large object, such as a passenger car, it was necessary to prepare a model that replicated the actual size and shape, or to use methods such as placing multiple corner reflectors along the object's contours. However, these methods required transporting a bulky model or transporting heavy corner reflectors and installing them at the required locations. In particular, installing multiple corner reflectors in multiple locations requires the laborious assembly and placement of each individual corner reflector, and it is also difficult to install corner reflectors at high locations far from the ground. Furthermore, the influence of unwanted reflections from the supports on which the corner reflectors are attached cannot be ignored.

[0051] In contrast, according to an embodiment of the present invention, the elements constituting the radar reflector are deformable, allowing the entire radar reflector to be foldable, and these elements are not required to be self-supporting, resulting in a lightweight radar reflector. Furthermore, since the radar reflector can be deployed into a predetermined shape by supplying gas inside the exterior body 10, unlike conventional reflectors made of plate materials, assembly is not required, and the lightweight design makes it easy to install in high locations. Furthermore, the position of each radar reflector can be easily changed and installed radar reflectors can be easily removed. Note that the inflatable radar reflector disclosed in Patent Document 1 only requires a strong reflection as a point reflection source, and the idea of ​​reproducing a widespread reflection, as in the present invention, has not been seen in conventional inflatable radar reflectors.

[0052] According to a typical embodiment of the present invention, it is possible to achieve planar reflection, including in the height direction, which was difficult to achieve with a collection of conventional corner reflectors. The radar reflector 100E shown in Fig. 6 not only obtains broad reflection in the direction connecting the fifth surface 15 and the sixth surface 16 of the exterior body 10, but also makes it possible to simulate backscattering in the height direction of a target while eliminating the influence of unnecessary backscattering due to pillars and the like.

[0053] 4. Inflatable radar reflector assembly The above-described radar reflectors 100A to 100E may be used alone or in combination of two or more. Even if each radar reflector has a simple outer shape, by arbitrarily combining multiple radar reflectors, it becomes possible to simulate backscattering from an object with a relatively complex surface shape by using the entirety of these radar reflectors.

[0054] Fig. 7 shows an inflatable radar reflector assembly according to yet another embodiment of the present invention. The radar reflector assembly 200 shown in Fig. 7 has a configuration in which a radar reflector 101 as a first unit and a radar reflector 102 as a second unit are integrally connected.

[0055] Any of the radar reflectors 100A to 100E described above can be used for radar reflector 101, which is the first unit. Similarly, any of the radar reflectors 100A to 100E can be used for radar reflector 102, which is the second unit. The number of radar reflectors included in radar reflector assembly 200 is also arbitrary. For simplicity's sake, the following description will be given taking as an example a radar reflector assembly obtained by stacking two radar reflectors, each having a configuration similar to radar reflector 100A shown in FIG. 1, in two layers with their orientations changed.

[0056] In the configuration illustrated in Fig. 7, the reflecting material 20A of the radar reflector 101 is suspended inside the exterior body 10 by flexible wires 30s and 30t, thereby forming a plurality of triangular prism-shaped reflectors lined up in the left-right direction of the figure. As shown schematically in Fig. 7, these triangular prism-shaped reflectors open upward in the radar reflector assembly 200.

[0057] On the other hand, looking at the radar reflector 102, the reflective material 20A of the radar reflector 102 is also suspended inside the exterior body 10 by flexible wires 30s and 30t, thereby forming multiple triangular prism-shaped reflectors lined up in the left-right direction of the figure. However, as shown schematically in Figure 7, the group of triangular prism-shaped reflectors of the radar reflector 102 opens toward the front of the radar reflector assembly 200.

[0058] In the example shown in Fig. 7, radar reflector 101 is placed on top of radar reflector 102, and the second surface 12 of radar reflector 102 and the fourth surface 14 of radar reflector 101 are in contact with each other. In this example, these two surfaces are connected via a connector 62. Connector 62 has an internal flow path and is configured to allow gas to be exchanged between the exterior housings 10 of the two radar reflectors. That is, in radar reflector assembly 200 shown in Fig. 7, the internal space of the exterior housing 10 of one unit (e.g., radar reflector 102) communicates with the internal space of the exterior housing 10 of the other unit (e.g., radar reflector 101) via the connector 62.

[0059] In this way, in this embodiment, gas can be exchanged between the exterior housings 10 of two or more radar reflectors. The connector 62 may be, for example, a resin tube. If the connector 62 is made of a flexible material, this is advantageous as it can prevent damage to the internal reflecting material 20A when the exterior housing 10 is in a folded state. Instead of providing the connector 62, for example, a hole may be provided in the portion where the exterior housing 10 of the radar reflector 101 and the exterior housing 10 of the radar reflector 102 come into contact.

[0060] As shown in the example of Figure 7, by including multiple radar reflectors, the radar reflector assembly of this embodiment is highly portable and can be used as a target that can simulate the reflection characteristics of an actual vehicle, aircraft, etc. The radar reflectors used as elements for constructing such an assembly may be any combination of the inflatable radar reflectors described in the examples above, and there are no particular restrictions on the number of inflatable radar reflectors. Inflatable radar reflectors of any shape and number can be flexibly combined and used as a target.

[0061] Furthermore, in this example, the internal spaces of the two inflatable radar reflectors are connected by a connector 62. By interposing the connector 62, which allows gas to move between the exterior bodies 10, between the two inflatable radar reflectors, the air pressure inside the exterior body 10 can be equalized between the two inflatable radar reflectors. As described above, in a typical embodiment of the present invention, the reflective material (e.g., reflective material 20A) is configured to allow gas to pass through. Therefore, by allowing gas to move between the two radar reflectors, the air pressure can be equalized between all cavities in each radar reflector. As a result, deformation of some of the multiple radar reflectors can be avoided.

[0062] Furthermore, by allowing gas to move between multiple radar reflectors, there is an advantage that gas can be sent to all of the radar reflectors in the assembly by supplying gas to at least one radar reflector in the assembly. For example, it is not necessary to prepare the same number of blowers as the number of radar reflectors in the assembly. The connector 62 connecting the two radar reflectors may further be provided with a check valve, a cock valve to temporarily stop the movement of gas, etc.

[0063] <5. Other examples of radar reflector assemblies> Figure 8 shows an inflatable radar reflector assembly according to yet another embodiment of the present invention. Similar to the example described with reference to Figure 7, the radar reflector assembly 300 shown in Figure 8 has a configuration in which a radar reflector 110 as a first unit and a radar reflector 120 as a second unit are integrally connected.

[0064] Each of the radar reflector 110, which is the first unit, and the radar reflector 120, which is the second unit, has a rectangular parallelepiped exterior body 70. As with the above-mentioned examples, the external shape of the exterior body 70 is not limited to a rectangular parallelepiped shape. Also, as with the above-mentioned examples, the exterior body 70 is made of a radio wave permeable sheet. However, here, both the exterior body 70 of the radar reflector 110 and the exterior body 70 of the radar reflector 120 are airtight.

[0065] As in the example described with reference to Fig. 7, in the radar reflector assembly 300 shown in Fig. 8, the internal space of the exterior body 70 of the radar reflector 120 is in communication with the internal space of the exterior body 70 of the radar reflector 110. Because the exterior body 70 is airtight, once gas is fed into the exterior body 70 of one of these two radar reflectors and the exterior body 70 is placed in the deployed state, the external shapes of these two radar reflectors can be maintained in the intended shape.

[0066] Each of radar reflector 110 and radar reflector 120 further includes a reflective material 83 that is capable of accepting deformation. However, in this example, the reflective material 83 is disposed on the outer surface 73a of the exterior body 70, rather than inside the exterior body 70. For example, in the case of radar reflector 110, the reflective material 83 is disposed on the outer surface 73a of the exterior body 70 so as to cover a portion of the outer surface 73a. The reflective material 83 may cover a portion of the outer surface 73a of the exterior body 70, or it may cover the entire outer surface 73a.

[0067] As the reflective material 83, for example, a cloth, a sheet, or the like similar to the reflective material 20A can be used. However, unlike the above-described reflective material 20A, the reflective material 83 does not need to be self-supporting. This is because the outer surface 73a of the exterior body 70 supports the reflective material 83. In this sense, for example, a vapor-deposited film of metal or the like and a radio wave-reflective coating film can also be used as the reflective material 83. Alternatively, a metal foil or the like may be used as the reflective material 83.

[0068] In this embodiment, when the exterior bodies 70 of the radar reflectors 110 and 120 are unfolded, the surfaces of the reflective materials 83 that were folded together with the exterior bodies 70 are unfolded. The surfaces of the reflective materials 83 that are unfolded as the exterior bodies 70 are unfolded function as reflective surfaces for radar waves. Furthermore, by appropriately combining radar reflectors each having such reflective surfaces, dummy targets with widespread reflective properties can be installed in desired locations without requiring complicated procedures. [Example]

[0069] We used corner reflectors fabricated by combining metal plates to examine how the radar cross section (RCS) can change depending on the corner reflector's shape. Here, we fabricated corner reflectors using stainless steel plates, with four box-shaped reflectors arranged in a two-by-two matrix, as shown in Figure 9. Each of the four box-shaped reflectors has a square opening, with one side measuring 410 mm. In other words, the side length of the entire corner reflector (indicated by the double-headed arrow H in Figure 9) is 820 mm. For the RCS evaluation, we prepared three corner reflectors with different depths (indicated by the double-headed arrow D in Figure 9). The depths of each corner reflector are as follows: Reflector A: 100mm Reflector B: 150mm Reflector C: 200mm

[0070] Prior to actual measurements, we simulated the RCS when irradiating radar waves using high-frequency 3D electromagnetic field analysis software (ANSYS HFSS, manufactured by Cybernet Systems Co., Ltd.) assuming the shapes of each of Reflectors A to C. In the simulation, the normal direction (indicated by the single arrow N in Figure 9) of the surface on which the corner reflector aperture is provided (hereafter simply referred to as the "aperture surface" for simplicity) was set to 0 degrees, and the frequency of the irradiated radar waves was set to 9.5 GHz, corresponding to the X-band. The following results were obtained for the RCS in the front direction (azimuth angle φ = 0°). The unit "dBsm" attached to each calculated value obtained by the simulation stands for decibel squared meter. Reflector A: 37.0 dBsm Reflector B: 36.9dBsm Reflector C: 36.6dBsm

[0071] Next, we placed each of Reflectors A to C in an anechoic chamber, irradiated them with 9.5 GHz radar waves, and measured the intensity of the reflected waves to determine the RCS. We then examined how the RCS changed depending on the direction of arrival of the radar waves by tilting the aperture of the reflector.

[0072] The simulation results described above and the RCS measurement results based on actual measurements of reflection intensity are shown in Table 1 below. Of the RCS measurement results based on actual measurements, the values ​​related to reflection in the front direction of the reflector (i.e., when the reflector angle is 0 degrees) are expected to match the RCS values ​​obtained by simulation for all of Reflectors A to C, but the results shown in Table 1 show some discrepancies between these values. This is thought to be due to factors such as bending of the plate material that makes up the corner reflector.

[0073] [Table 1]

[0074] 10 to 12 show the measurement results for reflectors A to C, respectively. In each of Figs. 10 to 12, the vertical axis indicates the magnitude of RCS, and the horizontal axis indicates the range of azimuth angles φ from the front direction to approximately ±75 degrees. It can be seen that for all of reflectors A to C, a high reflection intensity can be obtained over a relatively wide angular range centered on 0 degrees (front direction). In other words, by adopting a box-shaped reflector shape as shown in Fig. 9, it can be expected to function not as a point reflection source, but as a reflection source that exhibits widespread reflection. Furthermore, from the results shown in Table 1, it can be seen that when compared at the same scattering direction, the deeper the reflector, the greater the RCS that can be obtained.

[0075] Thus, it was found that it is possible to achieve widespread reflection and adjust the RCS depending on the geometric properties of the reflector. With a configuration such as the inflatable radar reflector shown as an embodiment of the present invention, the degree of expansion of the reflective material can be changed, for example, by adjusting the supply of gas inside the exterior body. In other words, the size and / or depth of each opening of the unit reflector deployed inside the exterior body can be flexibly adjusted. The inflatable radar reflector according to the embodiment of the present invention can achieve backscattering characteristics closer to those of an actual vehicle or aircraft. [Explanation of symbols]

[0076] 10, 70 exterior body 11 First surface of exterior body 12 Second surface of exterior body 13 Third surface of exterior body 14 Fourth side of exterior body 15 Fifth surface of exterior body 16 Sixth surface of exterior body 20A~20D, 20Ea, 20Eb, 83 Reflective material 20p through hole 21~27 Reflective surface 30s~35s, 30t~36t, 40s, 40t, 50s, 50t flexible wire 60 Inlet 62 connectors 73a Outer surface of exterior body 100A~100E, 101, 102, 110, 120 Radar Reflectors 200, 300 radar reflector assemblies R1~R3, S1~S3, T1~T2 unit reflectors

Claims

1. 1. An inflatable radar reflector, comprising: a radio wave transparent exterior body; a deformable reflective material; two or more flexible wires; Equipped with the exterior body is configured to be deformable between a folded state and an unfolded state, and has a first surface and a second surface that face each other in the unfolded state; A radar reflector in which the reflective material is suspended inside the exterior body by the wire when the exterior body is in an expanded state, thereby forming a plurality of unit reflectors arranged in a direction perpendicular to the wire.

2. 2. A radar reflector according to claim 1, A radar reflector, wherein one end and the other end of each wire are fixed to the first surface and the second surface of the outer casing, respectively.

3. 3. A radar reflector according to claim 1 or claim 2, A radar reflector, wherein the plurality of unit reflectors include a plurality of columnar reflectors arranged between the first surface and the second surface.

4. 3. A radar reflector according to claim 1 or claim 2, the wire rod and the reflector divide the interior of the exterior body into a plurality of cavities when the exterior body is in an expanded state; A radar reflector, wherein the reflector allows gas to pass through, thereby equalizing the air pressure between the cavities.

5. 5. A radar reflector according to claim 4, The reflective material is (a) a fabric containing conductive fibers, or (b) A conductive sheet having one or more air holes. That is, a radar reflector.

6. 3. A radar reflector according to claim 1 or claim 2, A radar reflector, wherein each wire extends along one side that defines the opening of the unit reflector between the first surface and the second surface when the exterior body is in an expanded state.

7. 3. A radar reflector according to claim 1 or claim 2, The exterior body has a hexahedral shape in an unfolded state, the hexahedron shape has third and fourth surfaces that face each other and are perpendicular to the first and second surfaces, A radar reflector, wherein the plurality of unit reflectors further include a unit reflector located between the third surface and the fourth surface and opening at the first surface or the second surface.

8. 1. An inflatable radar reflector assembly, comprising: A first unit; The second unit and Equipped with each of the first unit and the second unit is a radar reflector according to claim 1 or 2; A radar reflector assembly, wherein the interior space of the exterior body of the second unit is in communication with the interior space of the exterior body of the first unit.

9. 1. An inflatable radar reflector assembly, comprising: A first unit; The second unit and Equipped with Each of the first unit and the second unit comprises: a radio wave transparent exterior body; a deformable reflective material; and the exterior body is configured to be deformable between a folded state and an unfolded state and is airtight; the reflector covers at least a portion of the outer surface of the exterior body, A radar reflector assembly, wherein the interior space of the exterior body of the second unit is in communication with the interior space of the exterior body of the first unit.

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