Radio wave reflector

Abstract

Provided is a radio wave reflector which can be disposed without crossing transmission lines and has good reflection characteristics.　The radio wave reflector comprises: two first antenna elements provided along a first direction; a first transmission line connecting the two first antenna elements; two second antenna elements disposed at positions that are at equal distances from a center point between the two first antenna elements in the first direction and sandwich the two first antenna elements along the first direction; and a second transmission line connecting the two second antenna elements. When the electrical length of the wavelength of radio waves transmitted and received by the two first antenna elements and the two second antenna elements is λe and an arbitrary natural number is N, the difference in length between the first transmission line and the second transmission line is λe × N.

Description

Radio wave reflector

[0001] The present disclosure relates to a radio wave reflector.

[0002] Conventionally, there has been a radio wave retroreflector that retroreflects transmitted radio waves, and that includes a plurality of antenna elements arranged in a matrix to form an antenna array, and a plurality of transmission lines that connect pairs of antenna elements selected from the plurality of antenna elements, where the pair of antenna elements are arranged in positions that are point-symmetric with respect to the center of the antenna array, and the transmission lines connect the pair of antenna elements with equal electrical lengths. Two antenna elements that are point-symmetric with respect to the center form a pair (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2017-204681

[0004] In conventional radio wave retroreflectors (radio wave reflectors), two antenna elements located point-symmetrically with respect to the center of the matrix are connected to every antenna element by transmission lines of equal electrical length. As a result, multiple transmission lines intersect on the surfaces of the multiple antenna elements, and there is a risk that the desired reflection characteristics of the radio wave reflector cannot be obtained due to interference between the transmission lines or impedance mismatch.

[0005] Therefore, an object of the present invention is to provide a radio wave reflector that can be arranged without crossing transmission lines and has good reflection characteristics.

[0006] A radio wave reflector according to an embodiment of the present disclosure includes two first antenna elements arranged along a first direction, a first transmission line connecting the two first antenna elements, two second antenna elements positioned equidistant from a center point between the two first antenna elements in the first direction and sandwiching the two first antenna elements along the first direction, and a second transmission line connecting the two second antenna elements, wherein the transmission line wavelength (electrical length) of radio waves transmitted and received by the two first antenna elements and the two second antenna elements is λe and N is an arbitrary natural number, the difference in electrical length between the first transmission line and the second transmission line is λe × N.

[0007] It is possible to provide a radio wave reflector that can be arranged without crossing transmission lines and has good reflection characteristics.

[0008] 1 is a diagram illustrating an example of the configuration of a radio wave reflector of embodiment 1. FIG. 2 is a diagram illustrating the lengths of three transmission lines of the radio wave reflector of embodiment 1. FIG. 3 is a diagram illustrating an example of the configuration of a radio wave reflector of a first modified example of embodiment 1. FIG. 4 is a diagram illustrating an example of the configuration of a radio wave reflector of a second modified example of embodiment 1. FIG. 5 is a diagram illustrating an example of the configuration of a radio wave reflector of a third modified example of embodiment 1. FIG. 6 is a diagram illustrating an example of an actual measurement value of the angular characteristic of the radar cross section of the radio wave reflector of the third modified example of embodiment 1. FIG. 7 is a diagram illustrating an example of a simulation result of the angular characteristic of the radar cross section of a simulation model of the radio wave reflector of the third modified example of embodiment 1. FIG. 8 is a diagram illustrating an example of the configuration of a radio wave reflector of a fourth modified example of embodiment 1. FIG. 9 is a diagram illustrating an example of the configuration of a radio wave reflector of the fourth modified example of embodiment 1. FIG. 10 is a diagram illustrating an example of the configuration of a radio wave reflector of a fifth modified example of embodiment 1. FIG. 11 is a diagram illustrating an example of the configuration of a radio wave reflector of the fifth modified example of embodiment 1. FIG. 12 is a diagram illustrating an example of the configuration of a radio wave reflector of the fifth modified example of embodiment 1. FIG. 13 is a diagram illustrating an example of the configuration of a radio wave reflector of the sixth modified example of embodiment 1. FIG. 14 is a diagram illustrating an example of the configuration of a radio wave reflector of the sixth modified example of embodiment 1. FIG. 15 is a diagram illustrating an example of the configuration of a radio wave reflector of the sixth modified example of embodiment 1. Fig. 10 is a diagram showing an example of the configuration of a radio wave reflector according to a sixth modified example of embodiment 1. Fig. 11 is a diagram showing an example of the configuration of a radio wave reflector according to a seventh modified example of embodiment 1. Fig. 12 is a diagram showing an example of the configuration of a radio wave reflector according to a seventh modified example of embodiment 1. Fig. 13 is a diagram showing an example of the configuration of a radio wave reflector according to embodiment 2. Fig. 14 is a diagram showing an example of the configuration of a radio wave reflector according to embodiment 2.

[0009] Hereinafter, embodiments to which the radio wave reflector of the present disclosure is applied will be described. In the following, the same elements will be given the same reference numerals, and duplicated explanations may be omitted.

[0010] In the following description, the XYZ coordinate system is defined. The direction parallel to the X axis (X direction), the direction parallel to the Y axis (Y direction), and the direction parallel to the Z axis (Z direction) are perpendicular to each other. The XYZ coordinate system is an example of a Cartesian coordinate system. Viewing the XY plane is referred to as planar view. In the following, the X direction may be referred to as left and right, the +Z direction as up, and the −Z direction as down, but these do not represent the universal left and right directions and up and down directions. In the following, the length, width, thickness, etc. of each part may be exaggerated to make the configuration easier to understand. Furthermore, terms such as parallel, right angle, orthogonal, horizontal, vertical, up and down, etc., are intended to allow for deviations to the extent that they do not impair the effects of the embodiments.

[0011] 1 is a diagram showing an example of the configuration of a radio wave reflector 100 according to embodiment 1. The radio wave reflector 100 includes a substrate 101, two antenna elements 110A, two antenna elements 110B, two antenna elements 110C, transmission lines 115A, 115B, and 115C, and a ground layer 120. Here, the description will be given assuming that there is a virtual symmetry plane parallel to the YZ plane at the center of the radio wave reflector 100 in the X direction.

[0012] <Substrate 101> The substrate 101 is parallel to the XY plane, and the two antenna elements 110A, the two antenna elements 110B, and the two antenna elements 110C are arranged along the X direction. The X direction is an example of a first direction, and the Y direction is an example of a second direction.

[0013] The substrate 101 may be any type of wiring substrate on which a conductive layer can be mounted. As an example, two antenna elements 110A, two antenna elements 110B, two antenna elements 110C, and transmission lines 115A, 115B, and 115C are provided on the surface of the substrate 101 on the +Z direction side, and a ground layer 120 is provided on the surface of the substrate 101 on the −Z direction side. The two antenna elements 110A, two antenna elements 110B, two antenna elements 110C, the transmission lines 115A, 115B, and 115C, and the ground layer 120 are realized by conductive layers provided on both sides of the substrate 101, so that a printed circuit board with a simple configuration without an inner layer can be used. The conductive layer is made of copper, for example, but may also be made of a metal other than copper, such as aluminum.

[0014] Furthermore, the substrate 101 may be a flexible substrate. As a flexible substrate, for example, a substrate made of polyimide resin or the like can be used. When the substrate 101 is flexible, the radio wave reflector 100 can be attached to a curved surface of an object, such as a curved surface. The substrate 101 may be a multilayer substrate having an inner layer.

[0015] <Antenna elements 110A, 110B, 110C> Two of each of the antenna elements 110A, 110B, and 110C are provided on the surface on the +Z direction side of the substrate 101. The two antenna elements 110A, the two antenna elements 110B, and the two antenna elements 110C are arranged symmetrically with respect to a virtual symmetry plane in a plan view, and are provided in the order of antenna elements 110A, 110B, and 110C from the side closest to the virtual symmetry plane. As an example, the positions of the two antenna elements 110A, the two antenna elements 110B, and the two antenna elements 110C in the Y direction are equal.

[0016] As an example, the radio wave reflector 100 is a reflector that performs retroreflection, reflecting radio waves arriving from various directions in the +Z direction back toward the direction of arrival. Therefore, the antenna elements 110A, 110B, and 110C may be any antenna elements as long as they have directivity in the +Z direction. However, as an example, a configuration will be described in which the antenna elements 110A, 110B, and 110C are antenna elements for patch antennas. Each of the two antenna elements 110A, the two antenna elements 110B, and the two antenna elements 110C, together with the ground layer 120, constitutes a patch antenna. The patch antenna has directivity in the direction from the ground layer 120 toward the antenna elements 110A, 110B, and 110C (the +Z direction), and therefore provides good reflection characteristics.

[0017] Furthermore, as an example, when the radio wave reflector 100 is used as a reflector for an in-vehicle ultra-wideband radar, the frequency of the radio waves is, for example, 79 GHz. However, the use of the radio wave reflector 100 is not limited to such use.

[0018] Here, a form in which the shape of the antenna elements 110A, 110B, and 110C in a plan view is rectangular will be described as an example, but the shape is not limited to a rectangular shape and may be circular, elliptical, etc. As an example, the antenna elements 110A, 110B, and 110C can be fabricated by patterning a conductive layer formed on the surface of the substrate 101 on the +Z direction side by wet etching or the like.

[0019] The two antenna elements 110A are connected by a transmission line 115A. Similarly, the two antenna elements 110B are connected by a transmission line 115B, and the two antenna elements 110C are connected by a transmission line 115C.

[0020] As an example, the antenna elements 110A, 110B, and 110C each have two recesses recessed from the end on the -Y direction side toward the center in a plan view, and the transmission lines 115A, 115B, and 115C are, as an example, connected to a power supply portion between the two recesses from the -Y direction side. Therefore, as an example, the excitation direction of the antenna elements 110A, 110B, and 110C is the Y direction. As an example, when the radio wave reflector 100 is used in an upright position so that the +Y direction or the -Y direction faces vertically upward, the antenna elements 110A, 110B, and 110C transmit and receive vertically polarized radio waves. Note that the two recesses sandwiching the power supply portion are patterns for adjusting the input impedance of the antenna elements 110A, 110B, and 110C.

[0021] The two antenna elements 110A receive radio waves at the antenna element 110A on the -X direction side, the received radio wave signal propagates via the transmission line 115A to the antenna element 110A on the +X direction side, and the antenna element 110A on the +X direction side transmits the radio waves, thereby reflecting the radio waves. Also, the two antenna elements 110A receive radio waves at the antenna element 110A on the +X direction side, the received radio wave signal propagates via the transmission line 115A to the antenna element 110A on the -X direction side, and the antenna element 110A on the -X direction side transmits the radio waves, thereby reflecting the radio waves. In this way, the two antenna elements 110A perform retroreflection, reflecting incoming radio waves in the direction of arrival. The same is true for the two antenna elements 110B and 110C.

[0022] As an example, the shapes of the two antenna elements 110A in a plan view are symmetrical and the sizes in a plan view are the same. Similarly, the shapes of the two antenna elements 110B in a plan view are symmetrical and the sizes in a plan view are the same. Furthermore, the shapes of the two antenna elements 110C in a plan view are symmetrical and the sizes in a plan view are the same. Here, as an example, the shapes and sizes in a plan view of the two antenna elements 110A, the two antenna elements 110B, and the two antenna elements 110C are all the same.

[0023] The two antenna elements 110A are provided symmetrically with respect to a virtual plane of symmetry in a plan view. That is, the two antenna elements 110A are provided at positions equidistant from the virtual plane of symmetry. As an example, being equidistant from the virtual plane of symmetry means that the distance from the center of one antenna element 110A in a plan view to the virtual plane of symmetry is equal to the distance from the center of the other antenna element 110A in a plan view to the virtual plane of symmetry. Note that being equidistant may also mean that the distance from the center of gravity of one antenna element 110A in a plan view to the virtual plane of symmetry is equal to the distance from the center of gravity of the other antenna element 110A in a plan view to the virtual plane of symmetry.

[0024] The two antenna elements 110B are positioned equidistant from the center point between the two antenna elements 110A in the X direction, and are positioned on either side of the two antenna elements 110A along the X direction. That is, the two antenna elements 110B are provided outside the two antenna elements 110A in the X direction and equidistant from the imaginary symmetry plane. As an example, being equidistant from the imaginary symmetry plane means that the distance from the center of one antenna element 110B in a planar view to the imaginary symmetry plane is equal to the distance from the center of the other antenna element 110B in a planar view to the imaginary symmetry plane. Note that the distance between the antenna element 110B and the imaginary symmetry plane may be the distance from the center of gravity of the antenna element 110B in a planar view to the imaginary symmetry plane.

[0025] The two antenna elements 110C are positioned equidistant from the center point between the two antenna elements 110A in the X direction, and are positioned along the X direction to sandwich the two antenna elements 110A and the two antenna elements 110B. That is, the two antenna elements 110C are positioned outward of the two antenna elements 110B in the X direction and equidistant from the imaginary symmetry plane. "Equidistant from the imaginary symmetry plane" means, for example, that the distance from the center of one antenna element 110C in a plan view to the imaginary symmetry plane is equal to the distance from the center of the other antenna element 110C in a plan view to the imaginary symmetry plane. Note that the distance between the antenna element 110C and the imaginary symmetry plane may be the distance from the center of gravity of the antenna element 110C in a plan view to the imaginary symmetry plane.

[0026] Here, the two antenna elements 110A and the two antenna elements 110B have a relationship in which the two antenna elements 110A are an example of two first antenna elements, and the two antenna elements 110B are an example of two second antenna elements. In this case, the transmission line 115A connecting the two antenna elements 110A is an example of a first transmission line, and the transmission line 115B connecting the two antenna elements 110B is an example of a second transmission line.

[0027] Furthermore, the two antenna elements 110B and the two antenna elements 110C have a relationship in which the two antenna elements 110B are an example of two first antenna elements, and the two antenna elements 110C are an example of two second antenna elements. In this case, the transmission line 115B connecting the two antenna elements 110B is an example of a first transmission line, and the transmission line 115C connecting the two antenna elements 110C is an example of a second transmission line.

[0028] Furthermore, the two antenna elements 110A and the two antenna elements 110C have a relationship in which the two antenna elements 110A are an example of two first antenna elements, and the two antenna elements 110C are an example of two second antenna elements. In this case, the transmission line 115A connecting the two antenna elements 110A is an example of a first transmission line, and the transmission line 115C connecting the two antenna elements 110C is an example of a second transmission line.

[0029] That is, the two second antenna elements are positioned equidistant from the center point between the two first antenna elements in the X direction (first direction), and are positioned between the two first antenna elements along the X direction (first direction).

[0030] The pitch between the antenna element 110C on the -X direction side and the antenna element 110B on the -X direction side is defined as P1. The pitch is the distance between the center in the X direction of the antenna element 110C on the -X direction side and the center in the X direction of the antenna element 110B on the -X direction side. This also applies to the other antenna elements.

[0031] The pitch between antenna element 110B on the -X direction side and antenna element 110A on the -X direction side is P2, the pitch between antenna element 110A on the -X direction side and antenna element 110A on the +X direction side is P3, the pitch between antenna element 110A on the +X direction side and antenna element 110B on the +X direction side is P4, and the pitch between antenna element 110B on the +X direction side and antenna element 110C on the +X direction side is P5.

[0032] <Transmission Lines 115A, 115B, 115C> The transmission line 115A connects the two antenna elements 110A together. The transmission line 115B connects the two antenna elements 110B together, and the transmission line 115C connects the two antenna elements 110C together.

[0033] As an example, the transmission lines 115A, 115B, and 115C can be fabricated by patterning a conductive layer formed on the surface of the substrate 101 on the +Z direction side by wet etching or the like. The transmission lines 115A, 115B, and 115C extend without intersecting with each other in a planar view. Because the transmission lines 115A, 115B, and 115C are arranged without intersecting with each other, the reflection characteristics of the six antenna elements 110A, 110B, and 110C can be improved.

[0034] The transmission line 115A connects the two antenna elements 110A that are located innermost among the six antenna elements 110A, 110B, and 110C, and therefore extends within the region of the three transmission lines 115A, 115B, and 115C that is closest to the two antenna elements 110A in the Y direction.

[0035] The transmission line 115C connects the two outermost antenna elements 110C among the six antenna elements 110A, 110B, and 110C, and therefore extends within the region of the three transmission lines 115A, 115B, and 115C that is farthest from the two antenna elements 110A in the Y direction.

[0036] The transmission line 115B connects two antenna elements 110B located between the two innermost antenna elements 110A and the two outermost antenna elements 110C among the six antenna elements 110A, 110B, and 110C. Therefore, the transmission line 115B extends in a region between a region where the transmission line 115A extends and a region where the transmission line 115C extends among the three transmission lines 115A, 115B, and 115C in the Y direction.

[0037] The transmission line 115A has a characteristic impedance that matches the input impedance of the two antenna elements 110A. The transmission line 115B has a characteristic impedance that matches the input impedance of the two antenna elements 110B. The transmission line 115C has a characteristic impedance that matches the input impedance of the two antenna elements 110C.

[0038] Here, if the transmission path wavelength (electrical length) of the radio waves transmitted and received by the six antenna elements 110A, 110B, and 110C is λe and an arbitrary natural number is N, then the difference in electrical length (hereinafter abbreviated as "length") between the first transmission line and the second transmission line is λe × N. The transmission path wavelength (electrical length) is the electrical length of the radio waves in the first transmission line and the second transmission line. In other words, the difference in length between the transmission line 115A and the transmission line 115B is λe × N. In other words, if the electrical length of the transmission line 115A is L, then the difference in length between the transmission line 115A and the transmission line 115B is L + λe × N.

[0039] The difference in length between the transmission line 115B and the transmission line 115C is λe×N. In other words, if the length of the transmission line 115B is L, then the length of the transmission line 115C is L+λe×N. Also, the difference in length between the transmission line 115A and the transmission line 115C is λe×N. In other words, if the length of the transmission line 115A is L, then the electrical length of the transmission line 115C is L+λe×N. By setting the difference in length to this value, it is possible to align the reflection phases of the two antenna elements 110A and the two antenna elements 110B. It is also possible to align the reflection phases of the two antenna elements 110B and the two antenna elements 110C. Furthermore, the reflection phases of the two antenna elements 110A and the two antenna elements 110C can be aligned.

[0040] The lengths of the transmission lines 115A, 115B, and 115C will be described using FIG. 2 in addition to FIG. 1. FIG. 2 is a diagram illustrating the lengths of the transmission lines 115A, 115B, and 115C. In FIG. 2, the six antenna elements 110A, 110B, and 110C and the transmission lines 115A, 115B, and 115C are shown in a simplified form, with other components omitted. The lengths of the transmission lines 115A, 115B, and 115C are denoted by La, Lb, and Lc, respectively. The lengths La, Lb, and Lc are expressed in electrical length.

[0041] In FIG. 2 , radio waves arrive from the +X direction and the +Z direction as indicated by the solid arrows, and the radio wave reflector 100 reflects the radio waves in the direction indicated by the dashed arrows. The direction of arrival of the radio waves is the same as the direction of reflection of the radio waves. That is, the direction of arrival of the radio waves and the direction of reflection of the radio waves for the six antenna elements 110A, 110B, and 110C are the same. Also, in FIG. 2 , dashed lines indicate six representative equiphase planes of the radio waves arriving at and reflected from the six antenna elements 110A, 110B, and 110C. The six equiphase planes shown in FIG. 2 are equiphase planes of the radio waves when the six antenna elements 110A, 110B, and 110C receive and reflect the radio waves. The equiphase plane for the antenna element 110C on the +X direction side is designated as E1.

[0042] 2, the path differences of radio waves in the arrival direction and reflection direction for two adjacent antenna elements among the six antenna elements 110A, 110B, and 110C are denoted as d1, d2, d3, d4, and d5. For ease of explanation, the path differences d1, d2, d3, d4, and d5 are expressed in terms of electrical length.

[0043] Here, for the six antenna elements 110A, 110B, and 110C, the path length of the radio wave that arrives after passing through the equiphase surface E1 and is reflected before passing through the equiphase surface E1 is as follows.

[0044] The path length when receiving at the antenna element 110A on the −X direction side and radiating at the antenna element 110A on the +X direction side is as follows: d5+d4+d3+La+d4+d5=La+d3+2(d4+d5) (1)

[0045] The path length when receiving at the antenna element 110A on the +X direction side and radiating at the antenna element 110A on the −X direction side is as follows: d5+d4+La+d3+d4+d5=La+d3+2(d4+d5) (2)

[0046] The path length when receiving at the antenna element 110B on the −X direction side and radiating at the antenna element 110B on the +X direction side is as follows: d5+d4+d3+d2+Lb+d5=Lb+d3+d2+d4+2d5 (3)

[0047] The path length when receiving at antenna element 110B on the +X direction side and radiating at antenna element 110B on the −X direction side is as follows: d5+Lb+d2+d3+d4+d5=Lb+d3+d2+d4+2d5 (4)

[0048] The path length when receiving at the antenna element 110C on the −X direction side and radiating at the antenna element 110C on the +X direction side is as follows: d5+d4+d3+d2+d1+Lc (5)

[0049] The path length when receiving at the antenna element 110C on the +X side and radiating at the antenna element 110C on the −X side is as follows: Lc+d1+d2+d3+d4+d5 (6)

[0050] Since the path length when a signal is received by antenna element 110A on the −X side and radiated by antenna element 110A on the +X side is equal to the path length when a signal is received by antenna element 110B on the −X side and radiated by antenna element 110B on the +X side, the following relationship holds from equations (1) and (3): La+d3+2(d4+d5)=Lb+d3+d2+d4+2d5 (7)

[0051] Here, since the difference in length between the transmission line 115A and the transmission line 115B has a relationship of λe×N, if it is considered that La=Lb holds true for the phase, the following relationship can be obtained from equation (7): d2=d4 (8)

[0052] Similarly, the path length when a signal is received by antenna element 110B on the −X side and radiated by antenna element 110B on the +X side is equal to the path length when a signal is received by antenna element 110C on the −X side and radiated by antenna element 110C on the +X side, so the following relationship holds from equations (3) and (5): Lb+d3+d2+d4+2d5=d5+d4+d3+d2+d1+Lc (9)

[0053] Here, since the difference in length between the transmission line 115B and the transmission line 115C has a relationship of λe×N, if it is considered that Lb=Lc holds for the phase, the following relationship can be obtained from equation (9): d1=d5 (10)

[0054] From the above, for the six antenna elements 110A, 110B, and 110C that make up three pairs, the conditions for retroreflection are that the difference in length between the three transmission lines 115A, 115B, and 115C is λe×N, and that P2 = P4 and P1 = P5. Note that d2 = d4 corresponds to P2 = P4, and d1 = d5 corresponds to P1 = P5.

[0055] Furthermore, if the phase delay of a signal propagating through the transmission line 115A between the two antenna elements 110A is φ0, then the phase delay of the signal propagating through the transmission line 115B between the two antenna elements 110B is φ0 + λe × N. Similarly, the phase delay of the signal propagating through the transmission line 115C between the two antenna elements 110C is φ0 + λe × N. However, the value of N for the two antenna elements 110B is different from the value of N for the two antenna elements 110C.

[0056] As an example, if N for the phase delay of a signal when propagating through transmission line 115B is 1 and N for the phase delay of a signal when propagating through transmission line 115C is 2, and an antenna element is added outside antenna elements 110A to 110C, the length of the transmission line may be set so that the phase delay of the signal when propagating through the transmission line connecting the Kth antenna element from antenna element 110A is φ0 + λe × K.

[0057] <Ground layer 120> The ground layer 120 is formed over substantially the entire surface on the −Z direction side of the substrate 101. The ground layer 120 overlaps with the antenna elements 110A to 110C in plan view, and the outer edge of the ground layer 120 encompasses the antenna elements 110A to 110C in plan view. In other words, the outer edge of the ground layer 120 encompasses at least two first antenna elements and two second antenna elements.

[0058] Furthermore, if the wavelength in free space of the radio waves reflected by the radio wave reflector 100 is λ, the distance G between the outer edge of the antenna elements 110A to 110C and the outer edge of the ground layer 120 in the excitation direction (Y direction) of the antenna elements 110A to 110C is less than λ. In other words, G<λ.

[0059] When antenna elements 110A to 110C are excited, an electric field distribution is also generated on ground layer 120. When antenna elements 110A to 110C are excited in the Y direction, an electric field distribution that changes in the Y direction is generated on ground layer 120 due to secondary inductive radiation, and radio waves of opposite phase are radiated from ground layer 120. When radio waves of opposite phase to the radio waves radiated by antenna elements 110A to 110C are radiated from ground layer 120, the radio waves radiated by antenna elements 110A to 110C are canceled out, and the radiation intensity in the +Z direction is greatly reduced.

[0060] Therefore, in order to reduce radiation of radio waves from the ground layer 120 and maintain a high radiation intensity in the +Z direction of radio waves radiated by the antenna elements 110A to 110C, the distance G in the excitation direction (Y direction) of the antenna elements 110A to 110C between the outer edges of the antenna elements 110A to 110C and the outer edge of the ground layer 120 is set to less than λ. This is because by setting the distance G between the outer edges of the antenna elements 110A to 110C on the ±Y direction sides and the outer edge of the ground layer 120 to less than λ, the intensity of secondary induced radiation generated in the ground layer 120 can be reduced.

[0061] Furthermore, because secondary induced radiation occurring in the ground layer 120 also occurs in the X direction, it is preferable that the distance between the outer edge of the ground layer 120 and the outer edge of the −X direction side of the antenna element 110C on the −X direction side is also less than λ. Similarly, it is preferable that the distance between the outer edge of the ground layer 120 and the outer edge of the +X direction side of the antenna element 110C on the +X direction side is also less than λ.

[0062] <Effects> The radio wave reflector 100 includes two antenna elements 110A (two first antenna elements) provided along the X direction (first direction), a transmission line 115A (first transmission line) connecting the two antenna elements 110A, and two antenna elements 110B (two second antenna elements) that are positioned equidistant from the center point between the two antenna elements 110A in the X direction (first direction) and that are positioned on either side of the two antenna elements 110A along the X direction (first direction), and a transmission line 115B (second transmission line) connecting the two antenna elements 110B. When the transmission line wavelength (electrical length) of the radio waves transmitted and received by the two antenna elements 110A and the two antenna elements 110B is λe and N is an arbitrary natural number, the difference in electrical length between the transmission line 115A and the transmission line 115B is λe × N.

[0063] Therefore, the reflection phases of the two antenna elements 110A and the two antenna elements 110B can be aligned to perform retroreflection. Furthermore, since the difference in length between the transmission lines 115A and 115B is λe×N and the transmission line 115B is longer than the transmission line 115A, the transmission lines 115A and 115B can be arranged without crossing each other. Furthermore, since the transmission lines 115A and 115B can be arranged without crossing each other, interference between the transmission lines 115A and 115B and impedance mismatch can be suppressed, and good reflection characteristics can be obtained for the two antenna elements 110A and the two antenna elements 110B.

[0064] Therefore, it is possible to provide a radio wave reflector 100 that can be arranged without crossing the transmission lines 115A and 115B and has good reflection characteristics.

[0065] Here, the description is given for a case where the two antenna elements 110A are an example of two first antenna elements, the transmission line 115A is an example of a first transmission line, the two antenna elements 110B are an example of two second antenna elements, and the transmission line 115B is an example of a second transmission line. However, the same applies to a case where the two antenna elements 110B are an example of two first antenna elements, the transmission line 115B is an example of a first transmission line, the two antenna elements 110C are an example of two second antenna elements, and the transmission line 115C is an example of a second transmission line. The same also applies to a case where the two antenna elements 110A are an example of two first antenna elements, the transmission line 115A is an example of a first transmission line, the two antenna elements 110C are an example of two second antenna elements, and the transmission line 115C is an example of a second transmission line. The same also applies to the effects described below.

[0066] The radio wave reflector 100 may further include a substrate 101 (wiring substrate), and the two antenna elements 110A, the transmission line 115A, the two antenna elements 110B, and the transmission line 115B may be formed of a conductive layer provided on one surface of the substrate 101. There is no need to use a multilayer substrate, and a single-sided printed circuit board having the two antenna elements 110A, the transmission line 115A, the two antenna elements 110B, and the transmission line 115B formed on one surface can be used as the substrate 101. This makes it possible to provide a radio wave reflector 100 with a simple configuration and reduced manufacturing costs. Furthermore, using a single-sided printed circuit board as the substrate 101 allows the radio wave reflector 100 to be made thinner.

[0067] The substrate 101 may further include a ground layer 120 provided on the other surface thereof. There is no need to use a multilayer substrate, and a double-sided printed circuit board can be used as the substrate 101, in which two antenna elements 110A, a transmission line 115A, two antenna elements 110B, and a transmission line 115B are formed on one surface, and the ground layer 120 is formed on the other surface. This makes it possible to provide a radio wave reflector 100 with a simple configuration and reduced manufacturing costs. Furthermore, by using a double-sided printed circuit board as the substrate 101, the radio wave reflector 100 can be made thinner.

[0068] Furthermore, each of the two antenna elements 110A and the two antenna elements 110B and the ground layer 120 may form a patch antenna. By using a patch antenna having directivity in the direction from the ground layer 120 toward the two antenna elements 110A and the two antenna elements 110B, it is possible to provide a radio wave reflector 100 with good reflection characteristics.

[0069] Furthermore, the outer edge of the ground layer 120, in a plan view, contains at least two antenna elements 110A and two antenna elements 110B, and if the wavelength of the radio waves is λ, the distance between the outer edges of the two antenna elements 110A and two antenna elements 110B and the outer edge of the ground layer 120 in the excitation direction (Y direction) of the two antenna elements 110A and two antenna elements 110B may be less than λ. By reducing the anti-phase radio waves caused by secondary induced radiation generated in the ground layer 120, it is possible to prevent the radio waves radiated by the antenna elements 110A to 110C from being canceled out, and to suppress a decrease in radiation intensity in the +Z direction. This makes it possible to provide a radio wave reflector 100 with high radiation intensity in the +Z direction.

[0070] <First to Seventh Modifications of First Embodiment> Next, using Figures 3A to 8B, the radio wave reflectors of the first to seventh modifications of the first embodiment will be described, focusing on the differences from the radio wave reflector 100 of the first embodiment shown in Figure 1. The radio wave reflectors of the first to seventh modifications of the first embodiment achieve the same effects as the radio wave reflector 100 of the first embodiment shown in Figures 1 and 2.

[0071] <First Modification> Fig. 3A is a diagram showing an example of the configuration of a radio wave reflector 100A according to a first modification of embodiment 1. The radio wave reflector 100A includes a substrate 101, two antenna elements 110A, two antenna elements 110B, transmission lines 115A and 115B, and a ground layer 120. The radio wave reflector 100A differs from the radio wave reflector 100 shown in Fig. 1 in that it does not include the two antenna elements 110C and the transmission line 115C, and the substrate 101 and the ground layer 120 are small.

[0072] The two antenna elements 110A are an example of two first antenna elements, the two antenna elements 110B are an example of two second antenna elements, the transmission line 115A is an example of a first transmission line, and the transmission line 115B is an example of a second transmission line.

[0073] The distance in the excitation direction (Y direction) of the antenna elements 110A, 110B between the outer edges of the antenna elements 110A, 110B and the outer edge of the ground layer 120 is less than λ. It is also preferable that the distance between the outer edge of the ground layer 120 and the outer edge of the −X-direction side of the antenna element 110B on the −X-direction side, and the distance between the outer edge of the ground layer 120 and the outer edge of the +X-direction side of the antenna element 110B on the +X-direction side are also less than λ.

[0074] The radio wave reflector 100A of the first modified example has a configuration in which the two antenna elements 110C and the transmission line 115C are omitted from the radio wave reflector 100 shown in Figure 1, and therefore can operate in the same way as the four antenna elements 110A and 110B of the radio wave reflector 100 shown in Figure 1, and is capable of retroreflection.

[0075] <Second Modification> Fig. 3B is a diagram showing an example of the configuration of a radio wave reflector 100B of a second modification of embodiment 1. The radio wave reflector 100B is obtained by changing the configuration of the antenna elements 110A and 110B of the radio wave reflector 100A of the first modification shown in Fig. 3A.

[0076] As an example, the antenna elements 110A and 110B of the radio wave reflector 100B have a configuration in which three rectangular radiating elements 111 are arranged in the Y direction and connected by a line 112. Such antenna elements 110A and 110B, together with the ground layer 120, form a patch antenna.

[0077] The sizes of the substrate 101 and the ground layer 120 are larger than those of the substrate 101 and the ground layer 120 shown in Fig. 3A in order to match the sizes of the antenna elements 110A and 110B. The other configurations are the same as those of the radio wave reflector 100A shown in Fig. 3A. Even when the antenna elements 110A and 110B having the configuration shown in Fig. 3B are used, it is possible to operate in the same way as the radio wave reflector 100A of the first modified example shown in Fig. 3A, and retroreflection is possible.

[0078] 4A is a diagram showing an example of the configuration of a radio wave reflector 100C according to a third modified example of embodiment 1. The radio wave reflector 100C includes two antenna elements 110A, two antenna elements 110B, two antenna elements 110C, two transmission lines 115A, two transmission lines 115B, a substrate 101, and a ground layer 120.

[0079] The two antenna elements 110A, the two antenna elements 110B, the two antenna elements 110C, and the transmission lines 115A and 115B configure the antenna 105. The radio wave reflector 100C includes two antennas 105. The configurations of the two antenna elements 110A, the two antenna elements 110B, the two antenna elements 110C, and the transmission lines 115A and 115B in the two antennas 105 are similar to the configurations of the two antenna elements 110A, the two antenna elements 110B, the two antenna elements 110C, and the transmission lines 115A and 115B in the radio wave reflector 100 shown in FIG.

[0080] The two antennas 105 are arranged side by side in the Y direction. The arrangement of the two antenna elements 110A, two antenna elements 110B, two antenna elements 110C, and transmission lines 115A and 115B in the antenna 105 on the −Y direction side is similar to the arrangement of the two antenna elements 110A, two antenna elements 110B, two antenna elements 110C, and transmission lines 115A and 115B in the radio wave reflector 100 shown in FIG.

[0081] The two antenna elements 110A, two antenna elements 110B, and two antenna elements 110C and transmission lines 115A and 115B of the antenna 105 on the +Y direction side are arranged in mirror symmetry with respect to the line A that passes through the centers of the two antennas 105 in the Y direction and is parallel to the X axis, while the two antenna elements 110A, two antenna elements 110B, and two antenna elements 110C and transmission lines 115A and 115B of the antenna 105 on the −Y direction side are arranged in mirror symmetry with respect to the line A. Note that, as an example, the ground layer 120 is common to the two antennas 105.

[0082] For example, when the frequency of the radio waves transmitted and received by the radio wave reflector 100C is 79 GHz, the length of the substrate 101 in the X direction is 11.7 mm, the length in the Y direction is 6.3 mm, and the thickness of the radio wave reflector 100C in the Z direction is 0.282 mm. The substrate 101 is a flexible substrate made of polyimide.

[0083] In this way, the radio wave reflector 100C of the third modified example can be made very thin. If the substrate 101 is a flexible substrate, it can be easily attached to a curved surface or the like.

[0084] 4B is a diagram showing an example of measured values ​​of the angle characteristics of the radar cross section of the radio wave reflector 100C of the third modified example. In FIG. 4B, the horizontal axis represents the angle of the radio wave, and the vertical axis represents the radar cross section (RCS) of the reflected wave. The angle of the radio wave is the reflection angle of retroreflection in the XZ plane and is equal to the angle of arrival of the radio wave. The direction of 0 degrees is the +Z direction, and a positive angle greater than 0 degrees represents an angle tilted toward the +X direction from the +Z direction in the XZ plane, and a negative angle less than 0 degrees represents an angle tilted toward the -X direction from the +Z direction in the XZ plane.

[0085] 4B, the solid line indicates the measured value of the angular characteristic of the radar cross section of the radio wave reflector 100C of the third modified example, and the dashed line indicates the measured value of the angular characteristic of the radar cross section of a radio wave reflector for comparison. The radio wave reflector for comparison is a radio wave reflector made of a metal plate having the same area in a plan view as the radio wave reflector 100C.

[0086] 4C, the RCS of the radio wave reflector 100C exceeded −25 dBsm in the front direction where the angle is 0 degrees, and exceeded −30 dBsm within a range of ±25 degrees. With the comparative radio wave reflector, the RCS dropped significantly to −30 dBsm or less when the range of ±10 degrees was exceeded.

[0087] 4C is a diagram showing an example of a simulation result of the angular characteristics of the radar cross section of a simulation model of the radio wave reflector 100C of the third modified example. In FIG. 4C, the horizontal axis represents the angle of the radio wave, and the vertical axis represents the radar cross section (RCS) of the reflected wave. The angle of the radio wave is the reflection angle of retroreflection in the XZ plane and is equal to the arrival angle of the radio wave. The direction of 0 degrees is the +Z direction, and a positive angle greater than 0 degrees represents an angle tilted toward the +X direction from the +Z direction in the XZ plane, and a negative angle less than 0 degrees represents an angle tilted toward the -X direction from the +Z direction in the XZ plane.

[0088] As shown in Figure 4C, the RCS reached a maximum value of approximately -23.06 in the front direction, where the angle was 0 degrees, and within a range of approximately ±20 degrees, the RCS decreased by approximately 6.5 relative to the front direction. It was confirmed that a sufficiently practical level of retroreflection could be obtained within the ±20 degree range.

[0089] <Fourth Modification> Figures 5A and 5B are diagrams showing an example of the configuration of a radio wave reflector 100D according to a fourth modification of embodiment 1. As shown in Figure 5A, the radio wave reflector 100D includes 16 antennas 105. The 16 antennas 105 are arranged two in the X direction and eight in the Y direction. Since the configuration of each antenna 105 is as shown in Figure 4A, the reference numerals of the respective components are omitted in Figure 5A.

[0090] The radio wave reflector 100D of the fourth modified example includes 16 antennas 105 arranged in a matrix in the X and Y directions, and therefore, a radio wave reflector 100D with a large area can be realized.

[0091] 5B, a total of eight ground layers 120 are arranged, two in the X direction and four in the Y direction, and one ground layer 120 is provided for two antennas 105 arranged in mirror symmetry as shown in FIG. 4A. In other words, the ground layer 120 for the 16 antennas 105 is divided into eight. Dividing the ground layer 120 can reduce the influence of other surrounding antennas 105.

[0092] As an example, the radio wave reflector 100D shown in Fig. 5A has a length in the X direction of 23.2 mm, a length in the Y direction of 26.8 mm, and a thickness in the Z direction of 0.282 mm. The substrate 101 is, for example, a flexible substrate made of polyimide. The radio wave reflector 100D of the fourth modified example can be made very thin, even though it includes 16 antennas 105. If the substrate 101 is a flexible substrate, it can be easily attached to a curved surface, etc.

[0093] <Fifth Modification> FIG. 6A is a diagram showing an example of the configuration of a radio wave reflector 100E1 according to a fifth modification of the first embodiment.

[0094] 6A, the radio wave reflector 100E1 includes a substrate 101, two antenna elements 110A, two antenna elements 110B, two antenna elements 110C, transmission lines 115A, 115B, and 115C, and ground layers 120A, 120B, and 120C. In the radio wave reflector 100E1, the ground layer is divided into three ground layers 120A, 120B, and 120C.

[0095] Here, the two antenna elements 110A, the two antenna elements 110B, the two antenna elements 110C, the transmission lines 115A, 115B, and 115C, and the ground layers 120A, 120B, and 120C constitute an antenna 105E1.

[0096] For example, the positions of the two antenna elements 110A in the Y direction are equal, the positions of the two antenna elements 110B in the Y direction are equal, and the positions of the two antenna elements 110C in the Y direction are equal. The two antenna elements 110A are located furthest in the +Y direction, the two antenna elements 110C are located furthest in the -Y direction, and the two antenna elements 110B are located midway in the Y direction.

[0097] <Ground Layer 120A> The ground layer 120A overlaps with the two antenna elements 110A and the transmission line 115A in plan view. The outer edge of the ground layer 120A encompasses the two antenna elements 110A and the transmission line 115A in plan view. The ground layer 120A has a shape corresponding to the shape of the area in which the two antenna elements 110A and the transmission line 115A are arranged.

[0098] The ground layer 120A also has a slit 121A located between the two antenna elements 110A in a planar view. The slit 121A is recessed between the two antenna elements 110A, from the +Y direction to the −Y direction, so as to recess the outer edge of the ground layer 120A. The portion of the slit 121A located on the −Y direction side of the −Y direction end overlaps with the transmission line 115A, and is configured to connect the overlapping portions of the two antenna elements 110A in the X direction. The slit 121A is provided to reduce the mutual influence of secondary induced radiation from each of the two antenna elements 110A and improve reflection characteristics. Note that instead of the slit 121A, an open slot extending along the Y direction between the two antenna elements 110A may be provided. Even when a slot is provided, the influence of secondary induced radiation can be reduced and reflection characteristics can be improved, similar to when the slit 121A is provided.

[0099] Furthermore, the distance between the outer edge of the ground layer 120A and the outer edge of the antenna element 110A in the excitation direction (Y direction) of the antenna element 110A is set to be less than λ in order to reduce the intensity of secondary induced radiation generated in the ground layer 120A and increase the radiation intensity in the +Z direction of the radio wave reflector 100E1.

[0100] It is also preferable that the distance between the outer edge of the ground layer 120A on the −X direction side and the outer edge of the antenna element 110A on the −X direction side, and the distance between the outer edge of the ground layer 120A on the +X direction side and the outer edge of the antenna element 110A on the +X direction side are also less than λ.

[0101] It is also preferable that the distance in the X direction between the slit 121A and the two antenna elements 110A is less than λ.

[0102] <Ground layer 120B> The ground layer 120B overlaps with the two antenna elements 110B and the transmission line 115B in plan view. The outer edge of the ground layer 120B encompasses the two antenna elements 110B and the transmission line 115B in plan view. The ground layer 120B has a shape corresponding to the shape of the area in which the two antenna elements 110B and the transmission line 115B are arranged.

[0103] The ground layer 120B has a concave shape in plan view so as to avoid the outer edges of the ground layer 120A on the −X direction side, −Y direction side, and +X direction side. The ground layer 120B has a shape in which the outer edges of the two antenna elements 110B and the transmission line 115B, which are spaced apart in the X direction, are spread outward in plan view. In other words, the ground layer 120B has a shape in which two rectangular portions where the two antenna elements 110B, which are spaced apart in the X direction, are arranged are connected by a portion extending in the X direction where the transmission line 115B is arranged.

[0104] Furthermore, the distance between the outer edge of the ground layer 120B and the outer edge of the antenna element 110B in the excitation direction (Y direction) of the antenna element 110B is set to be less than λ in order to reduce the intensity of secondary induced radiation generated in the ground layer 120B and increase the radiation intensity in the +Z direction of the radio wave reflector 100E1.

[0105] It is also preferable that the distance between the outer edge of the ground layer 120B and the outer edge of the antenna element 110B on the −X direction side, and the distance between the outer edge of the ground layer 120B and the outer edge of the antenna element 110B on the +X direction side, are less than λ.

[0106] The ground layer 120B has two portions that overlap with the two antenna elements 110B, which are spaced apart in the X direction and connected by a thin, elongated portion that overlaps with the transmission line 115B, thereby reducing the mutual influence of the secondary induced radiation of the two antenna elements 110B and improving the reflection characteristics.

[0107] <Ground layer 120C> The ground layer 120C overlaps with the two antenna elements 110C and the transmission line 115C in plan view. The outer edge of the ground layer 120C encompasses the two antenna elements 110C and the transmission line 115C in plan view. The ground layer 120C has a shape corresponding to the shape of the area in which the two antenna elements 110C and the transmission line 115C are arranged.

[0108] The ground layer 120C has a concave shape in plan view so as to avoid the outer edges of the ground layer 120B on the −X, −Y, and +X directions. The ground layer 120C has a shape corresponding to the planar shapes of the two antenna elements 110C and the transmission line 115C, which are spaced apart in the X direction. In other words, the ground layer 120C has a shape such that the portion of the ground layer 120B that overlaps with the transmission line 115B is stretched in the X direction.

[0109] Furthermore, the distance between the outer edge of the ground layer 120C and the outer edge of the antenna element 110C in the excitation direction (Y direction) of the antenna element 110C is set to be less than λ in order to reduce the intensity of secondary induced radiation generated in the ground layer 120C and increase the radiation intensity of the radio wave reflector 100E1 in the +Z direction.

[0110] It is also preferable that the distance between the outer edge of the ground layer 120C and the outer edge of the antenna element 110C on the −X direction side, and the distance between the outer edge of the ground layer 120C and the outer edge of the antenna element 110C on the +X direction side, are less than λ.

[0111] The ground layer 120C has two portions that overlap with the two antenna elements 110C, which are spaced apart in the X direction and connected by a thin, elongated portion that overlaps with the transmission line 115C, thereby reducing the mutual influence of the secondary induced radiation of the two antenna elements 110C and improving the reflection characteristics.

[0112] The radio wave reflector 100E1 described above allows the transmission lines 115A, 115B, and 115C to be arranged without crossing each other. The radio wave reflector 100E1 also has ground layers 120A, 120B, and 120C that are divided corresponding to the two antenna elements 110A and the transmission line 115A, the two antenna elements 110B and the transmission line 115B, and the two antenna elements 110C and the transmission line 115C. The ground layer 120A that overlaps with the two antenna elements 110A located at the center in the X direction has a slit 121A that extends in the Y direction at the center in the X direction.

[0113] Therefore, it is possible to provide a radio wave reflector 100E1 that has good reflection characteristics and that allows the transmission lines 115A, 115B, and 115C to be arranged without crossing each other. Also, it is possible to reduce the influence of secondary induced radiation from the ground layers 120A, 120B, and 120C, thereby obtaining a radio wave reflector 100E1 that has good reflection characteristics.

[0114] Note that the radio wave reflector 100E1 may have a configuration in which two antennas 105E1 are provided. Fig. 6B is a diagram showing an example of the configuration of a radio wave reflector 100E2 according to a fifth modified example of the first embodiment.

[0115] The radio wave reflector 100E2 has a configuration including two antennas 105E1 shown in Fig. 6A. The radio wave reflector 100E2 includes the two antennas 105E1 and a substrate 101. The substrate 101 is common to the two antennas 105E1.

[0116] Each antenna 105E1 includes two antenna elements 110A, two antenna elements 110B, two antenna elements 110C, transmission lines 115A, 115B, and 115C, and ground planes 120A, 120B, and 120C.

[0117] The two antennas 105E1 have configurations that are mirror-symmetrical to each other with respect to a line A that passes through the centers of the two antennas 105E1 in the Y direction and is parallel to the X axis. The configuration of the antenna 105E1 on the -Y direction side is the same as the configuration of the antenna 105E1 included in the radio wave reflector 100E1 shown in Fig. 6A. The antenna 105E1 on the +Y direction side has a configuration that is mirror-symmetrical to the antenna 105E1 on the -Y direction side with respect to the line A.

[0118] The radio wave reflector 100E2 includes two antennas 105E1 with a mirror-symmetric configuration. Each antenna 105E1 can be arranged without crossing the transmission lines 115A, 115B, and 115C. This allows the radio wave reflector 100E2 to have good reflection characteristics. Furthermore, the influence of secondary induced radiation from the ground layers 120A, 120B, and 120C is reduced, resulting in a radio wave reflector 100E2 with good reflection characteristics.

[0119] 6C is a diagram showing an example of the configuration of a radio wave reflector 100E3 according to a fifth modified example of the first embodiment.

[0120] The radio wave reflector 100E3 includes two antenna elements 110A, two antenna elements 110B, two antenna elements 110C, two antenna elements 110D, two antenna elements 110E, two antenna elements 110F, transmission lines 115A, 115B, 115C, 115D, 115E, and 115F, and ground layers 120A, 120B, 120C, 120D, 120E, and 120F.

[0121] The radio wave reflector 100E3 has a configuration in which two antenna elements 110D, two antenna elements 110E, two antenna elements 110F, transmission lines 115D, 115E, and 115F, and ground layers 120D, 120E, and 120F are added to the radio wave reflector 100E1 shown in FIG. 6A.

[0122] The two antenna elements 110D, the transmission line 115D, and the ground layer 120D have a configuration in which the transmission line 115C of the two antenna elements 110C, the transmission line 115C, and the ground layer 120C, and a portion of the ground layer 120C that overlaps with the transmission line 115C, are stretched in the X direction. The two antenna elements 110E, the transmission line 115E, and the ground layer 120E have a configuration in which the transmission line 115D of the two antenna elements 110D, the transmission line 115D, and the ground layer 120D, and a portion of the ground layer 120D that overlaps with the transmission line 115D, are stretched in the X direction. The two antenna elements 110F, the transmission line 115F, and the ground layer 120F have a configuration in which the transmission line 115E of the two antenna elements 110E, the transmission line 115E, and the portion of the ground layer 120E that overlaps with the transmission line 115E are stretched in the X direction.

[0123] Even in a configuration like radio wave reflector 100E3, in which the number of antenna elements and ground layers is increased even more than in radio wave reflector 100E1 (see FIG. 6A), transmission lines 115A to 115F can be arranged without crossing each other, reducing the influence of secondary induced radiation from ground layers 120A to 120F, and radio wave reflector 100E3 with good reflection characteristics can be obtained.

[0124] The ground layer may be a single ground layer instead of being divided into six ground layers 120A, 120B, 120C, 120D, 120E, and 120F. Also, the ground layers 120A, 120B, 120C, 120D, 120E, and 120F may be grouped together.

[0125] <Sixth Modification> FIG. 7A is a diagram showing an example of the configuration of a radio wave reflector 100F1 according to a sixth modification of the first embodiment.

[0126] 7A, the radio wave reflector 100F1 includes a substrate 101, two antenna elements 110A, two antenna elements 110B, two antenna elements 110C, transmission lines 115A, 115B, and 115C, and ground layers 120A and 120C. In the radio wave reflector 100F1, the ground layer is divided into two ground layers 120A and 120C.

[0127] Here, the two antenna elements 110A, the two antenna elements 110B, the two antenna elements 110C, the transmission lines 115A, 115B, and 115C, and the ground layers 120A and 120C constitute an antenna 105F1.

[0128] The two antenna elements 110A are arranged in a state where the two antenna elements 110A of the radio wave reflector 100E1 of the fifth modified example are rotated 180 degrees in a plan view, and the two recesses of each antenna element 110A are recessed from the +Y direction side toward the center. The transmission line 115A extends in the X direction on the +Y direction side of the two antenna elements 110A and is connected to the two antenna elements 110A from the +Y direction side. Therefore, the two antenna elements 110A are excited in the Y direction. The operation of the two antenna elements 110A of the radio wave reflector 100F1 is the same as that of the two antenna elements 110A of the radio wave reflector 100E1 of the fifth modified example.

[0129] The arrangement of the two antenna elements 110B and the two antenna elements 110C is the same as that of the two antenna elements 110B and the two antenna elements 110C of the radio wave reflector 100E1 of the fifth modified example (see FIG. 6A ). Furthermore, the connection relationship between the two antenna elements 110B and the two antenna elements 110C and the transmission lines 115B and 115C is the same as that in the radio wave reflector 100E1 of the fifth modified example.

[0130] In the radio wave reflector 100F1, one ground layer 120A is provided for two antenna elements 110A, two antenna elements 110B, and transmission lines 115A and 115B.

[0131] The ground layer 120A overlaps with the two antenna elements 110A, the two antenna elements 110B, and the transmission lines 115A and 115B in a plan view. The outer edge of the ground layer 120A encompasses the two antenna elements 110A, the two antenna elements 110B, and the transmission lines 115A and 115B in a plan view. The ground layer 120A has a shape corresponding to the shape of the area in which the two antenna elements 110A, the two antenna elements 110B, and the transmission lines 115A and 115B are arranged.

[0132] The ground layer 120A has a slot 122A located between the two antenna elements 110A, and two slits 123A located between the two antenna elements 110A and the two antenna elements 110B.

[0133] Furthermore, the distance between the outer edge of the ground layer 120A and the outer edges of the antenna elements 110A and 110B in the excitation direction (Y direction) of the antenna elements 110A and 110B is set to be less than λ in order to reduce the intensity of secondary induced radiation generated in the ground layer 120A and increase the radiation intensity in the +Z direction of the radio wave reflector 100F1.

[0134] It is also preferable that the distance between the outer edge of the ground layer 120A and the outer edge of the antenna element 110B on the −X direction side, and the distance between the outer edge of the ground layer 120A and the outer edge of the antenna element 110B on the +X direction side, are less than λ.

[0135] It is also preferable that the X-direction spacing between the slot 122A and the two antenna elements 110A, and the X-direction spacing between the slit 123A and the two antenna elements 110A and the two antenna elements 110B be less than λ.

[0136] The radio wave reflector 100F1 described above allows the transmission lines 115A, 115B, and 115C to be arranged without crossing each other. The radio wave reflector 100F1 also has two antenna elements 110A, two antenna elements 110B, and ground layers 120A and 120C that are divided to correspond to the transmission lines 115A and 115B, and the two antenna elements 110C and the transmission line 115C. The ground layer 120A also has a slot 122A that extends in the Y direction at the center in the X direction, and two slits 123A.

[0137] Therefore, it is possible to provide a radio wave reflector 100F1 that has good reflection characteristics and that allows the transmission lines 115A, 115B, and 115C to be arranged without crossing each other. Also, it is possible to reduce the influence of secondary induced radiation from the ground layers 120A and 120C, thereby obtaining a radio wave reflector 100F1 that has good reflection characteristics.

[0138] Furthermore, since the portion of the ground layer 120A on the +Y direction side of the slot 122A overlaps with the transmission line 115A and the portion of the slot 122A on the −Y direction side overlaps with the transmission line 115B, it is possible to bring the positions of the two antenna elements 110A and the two antenna elements 110B closer together in the Y direction. Furthermore, with this configuration, it is possible to shorten the length of the substrate 101 in the Y direction, thereby improving the packaging density.

[0139] The radio wave reflector 100F1 may have two antennas 105F1, and the two antennas 105F1 may be configured to be mirror symmetrical.

[0140] Furthermore, the number of antenna elements and ground layers in the radio wave reflector 100F1 may be further increased.

[0141] FIG. 7B is a diagram showing an example of the configuration of a radio wave reflector 100F2 according to a sixth modified example of the first embodiment.

[0142] 7B , the radio wave reflector 100F2 includes a substrate 101, two antenna elements 110A, two antenna elements 110B, two antenna elements 110C, two antenna elements 110D, transmission lines 115A, 115B, 115C, and 115D, and ground layers 120A, 120C, and 120D. In the radio wave reflector 100F2, the ground layer is divided into three ground layers 120A, 120C, and 120D.

[0143] Here, the two antenna elements 110A, the two antenna elements 110B, the two antenna elements 110C, the two antenna elements 110D, the transmission lines 115A, 115B, 115C, and 115D, and the ground layers 120A, 120C, and 120D constitute an antenna 105F2.

[0144] The configuration of the two antenna elements 110A, two antenna elements 110B, transmission lines 115A, 115B, and ground layer 120A of the radio wave reflector 100F2 is the same as that of the radio wave reflector 100F1 (see FIG. 7A).

[0145] In the radio wave reflector 100F2, the two antenna elements 110C are rotated 180 degrees in a plan view so that the two recesses are located on the +Y direction side. The transmission line 115C extends in the X direction on the +Y direction side of the two antenna elements 110C, and the portion of the ground layer 120C that overlaps with the transmission line 115C extends in the X direction on the +Y direction side of the ground layer 120A.

[0146] The two antenna elements 110D, the transmission line 115D, and the ground layer 120D have a configuration in which the transmission line 115C of the two antenna elements 110C, the transmission line 115C, and the ground layer 120C of the radio wave reflector 100F1 shown in FIG. 7A and the portion of the ground layer 120C that overlaps with the transmission line 115C are stretched in the X direction.

[0147] In the radio wave reflector 100F2, the transmission lines 115A and 115C are located on the +Y direction side, and the transmission lines 115B and 115D are located on the -Y direction side, so the length of the board 101 in the Y direction can be shortened. In addition, the two antenna elements 110A, the two antenna elements 110B, the two antenna elements 110C, and the two antenna elements 110D can be positioned closer to each other in the Y direction, which also makes it possible to shorten the length of the board 101 in the Y direction. With this configuration, the radio wave reflector 100F2 can improve packaging density.

[0148] Furthermore, for the ground layers 120A, 120C, and 120D, the spacing corresponding to the spacing G in the radio wave reflector 100 shown in Fig. 1 is set to be less than λ in order to reduce the intensity of secondary induced radiation generated in the ground layers 120A, 120C, and 120D and increase the radiation intensity in the +Z direction of the radio wave reflector 100F2.

[0149] In addition, in the ground layers 120A, 120C, and 120D, it is preferable that the distance in the X direction between the antenna elements 110A to 110D and the outer edges of the ground layers 120A, 120C, and 120D is also less than λ.

[0150] The radio wave reflector 100F2 described above can be arranged so that the transmission lines 115A to 115D do not cross each other. The radio wave reflector 100F2 also has divided ground layers 120A, 120C, and 120D. The ground layer 120A also has a slot 122A that is centered in the X direction and extends in the Y direction, and two slits 123A.

[0151] Therefore, it is possible to provide a radio wave reflector 100F2 that has good reflection characteristics and that can be arranged without crossing the transmission lines 115A to 115D. Furthermore, it is possible to reduce the influence of secondary induced radiation from the ground layers 120A, 120C, and 120D, thereby obtaining a radio wave reflector 100F2 with good reflection characteristics.

[0152] The radio wave reflector 100F2 may have two antennas 105F2, and the two antennas 105F2 may be configured to be mirror symmetrical.

[0153] Furthermore, the number of antenna elements and ground layers in the radio wave reflector 100F2 may be further increased.

[0154] FIG. 7C is a diagram showing an example of the configuration of a radio wave reflector 100F3 according to a sixth modified example of the first embodiment.

[0155] 7C , the radio wave reflector 100F3 includes a substrate 101, two antenna elements 110A, two antenna elements 110B, two antenna elements 110C, two antenna elements 110D, transmission lines 115A, 115B, 115C, and 115D, and ground layers 120A, 120B, and 120D. In the radio wave reflector 100F3, the ground layer is divided into three ground layers 120A, 120B, and 120D.

[0156] Here, the two antenna elements 110A, the two antenna elements 110B, the two antenna elements 110C, the two antenna elements 110D, the transmission lines 115A, 115B, 115C, and 115D, and the ground layers 120A, 120B, and 120D constitute an antenna 105F3.

[0157] In the radio wave reflector 100F3, two antenna elements 110A, two antenna elements 110C, and transmission lines 115A and 115C are arranged overlapping on a common ground layer 120A. Furthermore, two antenna elements 110B and a transmission line 115B are arranged overlapping on a ground layer 120B, and two antenna elements 110D and a transmission line 115D are arranged overlapping on a ground layer 120D. The configurations of the two antenna elements 110D, the transmission line 115D, and the ground layer 120D are the same as those in the radio wave reflector 100F2.

[0158] In the radio wave reflector 100F3, the transmission lines 115A and 115B extend in the X direction on the +Y direction side, and the transmission lines 115C and 115D extend in the X direction on the −Y direction side.

[0159] The ground layer 120A has one rectangular portion where the two antenna elements 110A are arranged, two rectangular portions where the two antenna elements 110C are arranged, and a portion extending in the X direction where the transmission line 115C is arranged. The ground layer 120A also has a slot 122A extending in the Y direction at the center in the X direction of the one rectangular portion where the two antenna elements 110A are arranged.

[0160] The transmission line 115A extends in the X direction on the +Y side of the slot 122A, and the transmission line 115C extends in the X direction on the −Y side of the slot 122A.

[0161] The configurations of the two antenna elements 110C, the transmission line 115C, and the ground layer 120C, and the configurations of the two antenna elements 110D, the transmission line 115D, and the ground layer 120D are the same as the configuration of the radio wave reflector 100E3 of the fifth modified example of embodiment 1 (see Figure 6C).

[0162] In the radio wave reflector 100F3, the transmission lines 115A and 115B are located on the +Y direction side, and the transmission lines 115C and 115D are located on the -Y direction side, so the length of the substrate 101 in the Y direction can be shortened. In addition, the two antenna elements 110A, the two antenna elements 110B, the two antenna elements 110C, and the two antenna elements 110D can be positioned closer to each other in the Y direction, which also shortens the length of the substrate 101 in the Y direction. With this configuration, the radio wave reflector 100F3 can improve packaging density.

[0163] Furthermore, for the ground layers 120A, 120B, and 120D, the spacing corresponding to the spacing G in the radio wave reflector 100 shown in Fig. 1 is set to be less than λ. This is to reduce the intensity of secondary induced radiation generated in the ground layers 120A, 120B, and 120D and increase the radiation intensity in the +Z direction of the radio wave reflector 100F3.

[0164] In addition, in the ground layers 120A, 120B, and 120D, it is preferable that the distance in the X direction between the antenna elements 110A to 110D and the outer edges of the ground layers 120A, 120B, and 120D is also less than λ.

[0165] The radio wave reflector 100F3 described above can be arranged so that the transmission lines 115A to 115D do not cross each other. The radio wave reflector 100F3 also has divided ground layers 120A, 120B, and 120D. The ground layer 120A also has a slot 122A that extends in the Y direction at the center in the X direction.

[0166] Therefore, it is possible to provide a radio wave reflector 100F3 that has good reflection characteristics and that can be arranged without crossing the transmission lines 115A to 115D. Furthermore, it is possible to reduce the influence of secondary induced radiation from the ground layers 120A, 120B, and 120D, thereby obtaining a radio wave reflector 100F3 with good reflection characteristics.

[0167] The radio wave reflector 100F3 may have two antennas 105F3, and the two antennas 105F3 may be configured to be mirror symmetrical.

[0168] Furthermore, the number of antenna elements and ground layers in the radio wave reflector 100F3 may be further increased.

[0169] FIG. 7D is a diagram showing an example of the configuration of a radio wave reflector 100F4 according to a sixth modified example of the first embodiment.

[0170] 7D , the radio wave reflector 100F4 includes a substrate 101 and two antennas 105F4. Each antenna 105F4 includes two antenna elements 110A, two antenna elements 110B, two antenna elements 110C, two antenna elements 110D, and two antenna elements 110E, transmission lines 115A, 115B, 115C, 115D, and 115E, and ground layers 120A, 120C, 120D, and 120E. In the radio wave reflector 100F4, the ground layer is divided into four ground layers 120A, 120C, 120D, and 120E.

[0171] The configurations of the two antenna elements 110A, two antenna elements 110B, two antenna elements 110C, two antenna elements 110D, transmission lines 115A, 115B, 115C, and 115D, and ground layers 120A, 120C, and 120D in each antenna 105F4 are the same as the configurations of the antenna 105F2 of the radio wave reflector 100F2 shown in Figure 7B.

[0172] The antenna 105F4 has a configuration in which two antenna elements 110E, a transmission line 115E, and a ground layer 120E are added to the antenna 105F2 shown in Fig. 7B. The configurations of the two antenna elements 110E, the transmission line 115E, and the ground layer 120E are similar to the configurations of the radio wave reflector 100E3 (see Fig. 6C) of the fifth modified example of the first embodiment.

[0173] The two antennas 105F4 have configurations that are mirror-symmetrical to each other with respect to a line A that passes through the centers of the two antennas 105F4 in the Y direction and is parallel to the X axis.

[0174] The radio wave reflector 100F4 includes two antennas 105F4 with a mirror-symmetric configuration. Each antenna 105F4 can be arranged without crossing the transmission lines 115A to 115E. This makes it possible to provide a radio wave reflector 100F4 with good reflection characteristics. Furthermore, the influence of secondary induced radiation from the ground layers 120A, 120C, 120D, and 120E is reduced, resulting in a radio wave reflector 100F4 with good reflection characteristics.

[0175] FIG. 7E is a diagram showing an example of the configuration of a radio wave reflector 100F5 according to a sixth modified example of the first embodiment.

[0176] 7E , the radio wave reflector 100F5 includes a substrate 101, two antenna elements 110A, two antenna elements 110B, two antenna elements 110C, two antenna elements 110D, two antenna elements 110E1, and two antenna elements 110E2, transmission lines 115A, 115B, 115C, 115D, 115E1, and 115E2, and ground layers 120A, 120C, 120D, 120E1, and 120E2. In the radio wave reflector 100F5, the ground layer is divided into five ground layers 120A, 120C, 120D, 120E1, and 120E2.

[0177] Two antenna elements 110A, two antenna elements 110B, two antenna elements 110C, two antenna elements 110D, two antenna elements 110E1, two antenna elements 110E2, transmission lines 115A, 115B, 115C, 115D, 115E1, 115E2, and ground layers 120A, 120C, 120D, 120E1, 120E2 constitute an antenna 105F5.

[0178] The configurations of the two antenna elements 110A, two antenna elements 110B, two antenna elements 110C, two antenna elements 110D, transmission lines 115A, 115B, 115C, and 115D, and ground layers 120A, 120C, and 120D in the antenna 105F5 are the same as the configurations of the antenna 105F2 of the radio wave reflector 100F2 shown in Figure 7B.

[0179] The antenna 105F5 has a configuration in which two antenna elements 110E1, two antenna elements 110E2, transmission lines 115E1 and 115E2, and ground layers 120E1 and 120E2 are added to the antenna 105F2 shown in FIG. 7B.

[0180] The two antenna elements 110E1, the transmission line 115E1, and the ground layer 120E1 and the two antenna elements 110E2, the transmission line 115E2, and the ground layer 120E2 are configured to be mirror-symmetrical with respect to a line B that is parallel to the X direction and passes through the center of the Y direction length of the substrate 101. The two antenna elements 110E1, the transmission line 115E1, and the ground layer 120E1 are located on the −Y direction side of the line B, and the two antenna elements 110E2, the transmission line 115E2, and the ground layer 120E2 are located on the +Y direction side of the line B.

[0181] The two antenna elements 110E1, the transmission line 115E1, and the ground layer 120E1 have a configuration in which the transmission line 115D of the two antenna elements 110D, the transmission line 115D, and the portion of the ground layer 120D that overlaps with the transmission line 115D is stretched in the X direction.

[0182] The radio wave reflector 100F5 can be arranged without crossing the transmission lines 115A to 115E2 and has good reflection characteristics. Furthermore, the influence of secondary induced radiation from the ground layers 120A, 120C, 120D, 120E1, and 120E2 is reduced, resulting in a radio wave reflector 100F5 with good reflection characteristics.

[0183] <Seventh Modification> FIG. 8A is a diagram showing an example of the configuration of a radio wave reflector 100G1 according to a seventh modification of the first embodiment.

[0184] 8A , the radio wave reflector 100G1 includes a substrate 101, two antenna elements 110A, two antenna elements 110B, two antenna elements 110C, transmission lines 115A, 115B, and 115C, and a ground layer 120. In the radio wave reflector 100F1, the ground layer 120 is common to the two antenna elements 110A, two antenna elements 110B, two antenna elements 110C, and the transmission lines 115A, 115B, and 115C.

[0185] The radio wave reflector 100G1 has a configuration in which transmission lines 115A, 115B, and 115C are connected to the sides extending in the Y direction on the +X direction side of antenna element 110A, antenna element 110B, and antenna element 110C that are on the −X direction side of the imaginary symmetry plane, and transmission lines 115A, 115B, and 115C are connected to the sides extending in the Y direction on the −X direction side of antenna element 110A, antenna element 110B, and antenna element 110C that are on the +X direction side of the imaginary symmetry plane.

[0186] Here, two antenna elements 110A, two antenna elements 110B, two antenna elements 110C, and transmission lines 115A, 115B, and 115C constitute an antenna 105G1.

[0187] In such a radio wave reflector 100G1, the two antenna elements 110A, the two antenna elements 110B, and the two antenna elements 110C are excited in the X direction. As an example, if the radio wave reflector 100G1 is used in an upright position so that the +Y direction or the −Y direction faces vertically upward, the two antenna elements 110A, the two antenna elements 110B, and the two antenna elements 110C will transmit and receive horizontally polarized radio waves.

[0188] The radio wave reflector 100G1 as described above allows the transmission lines 115A, 115B, and 115C to be arranged without crossing each other. Furthermore, because the transmission lines 115A, 115B, and 115C can be arranged without crossing each other, interference and impedance mismatch between the transmission lines 115A, 115B, and 115C can be suppressed, and good reflection characteristics can be obtained for the two antenna elements 110A, two antenna elements 110B, and two antenna elements 110C.

[0189] Therefore, it is possible to provide a radio wave reflector 100G1 that can be arranged without crossing the transmission lines 115A, 115B, and 115C and has good reflection characteristics.

[0190] The radio wave reflector may include a plurality of antennas 105G1. Fig. 8B is a diagram showing an example of the configuration of a radio wave reflector 100G2 according to a seventh modified example of the first embodiment.

[0191] The radio wave reflector 100G2 includes a substrate 101, two antennas 105G1, and a ground layer 120. The substrate 101 and the ground layer 120 are common to the two antennas 105G1.

[0192] The two antennas 105G1 are arranged side by side in the Y direction. The arrangement of the two antenna elements 110A, two antenna elements 110B, two antenna elements 110C, and transmission lines 115A, 115B, and 115C in the antenna 105G1 on the −Y direction side is the same as the arrangement in the antenna 105G1 shown in FIG. 8A.

[0193] The arrangement of the two antenna elements 110A, two antenna elements 110B, two antenna elements 110C, and transmission lines 115A, 115B, and 115C of antenna 105G1 on the +Y direction side is such that the arrangement of the two antenna elements 110A, two antenna elements 110B, two antenna elements 110C, and transmission lines 115A, 115B, and 115C of antenna 105G1 on the -Y direction side is mirror symmetrical with respect to line A that passes through the centers of the two antennas 105G1 in the Y direction and is parallel to the X axis.

[0194] The radio wave reflector 100G2 as described above allows the transmission lines 115A, 115B, and 115C to be arranged without crossing each other in each of the two antennas 105G1. Furthermore, because the transmission lines 115A, 115B, and 115C can be arranged without crossing each other, interference and impedance mismatch between the transmission lines 115A, 115B, and 115C can be suppressed, and good reflection characteristics can be obtained for the two antenna elements 110A, two antenna elements 110B, and two antenna elements 110C in each of the two antennas 105G1.

[0195] Therefore, it is possible to provide a radio wave reflector 100G2 that can be arranged without crossing the transmission lines 115A, 115B, and 115C and has good reflection characteristics.

[0196] 9A is a diagram showing an example of the configuration of a radio wave reflector 200 according to embodiment 2. The radio wave reflector 200 includes a substrate 101, two antenna elements 110A, an antenna element 210, transmission lines 115A and 215, and a ground layer 120. Here, the description will be given assuming that there is a virtual plane of symmetry parallel to the YZ plane at the center of the radio wave reflector 200 in the X direction. The antenna element 210 is an example of a second antenna element, and the transmission line 215 is an example of a second transmission line.

[0197] The substrate 101 and the ground layer 120 have a different size from, but a similar configuration to, the substrate 101 and the ground layer 120 of the radio wave reflector 100 of embodiment 1. Furthermore, the two antenna elements 110A and the transmission line 115A are the same as the two antenna elements 110A and the transmission line 115A of the radio wave reflector 100 of embodiment 1.

[0198] The radio wave reflector 200 of the second embodiment includes an antenna element 210 and a transmission line 215, instead of the two antenna elements 110B, two antenna elements 110C, and transmission lines 115B and 115C of the radio wave reflector 100 of the first embodiment. As an example, the radio wave reflector 200 is a reflector that performs retroreflection, that is, reflecting radio waves arriving from various directions on the +Z direction side back in the direction of arrival.

[0199] <Antenna element 210> The antenna element 210 may be any antenna element as long as it has directivity in the +Z direction, but here, as an example, a form in which the antenna element is an antenna element for a patch antenna will be described. The antenna element 210 constitutes a patch antenna together with the ground layer 120. The patch antenna has directivity in the direction from the ground layer 120 toward the antenna element 210 (the +Z direction), and therefore good reflection characteristics can be obtained.

[0200] Furthermore, as an example, when the radio wave reflector 200 is used as a reflector for an in-vehicle ultra-wideband radar, the frequency of the radio waves is, for example, 79 GHz. However, the use of the radio wave reflector 200 is not limited to such use.

[0201] Here, a form in which the shape of the antenna element 210 in a plan view is rectangular will be described as an example, but it is not limited to a rectangular shape and may be circular, elliptical, or the like. The shape of the antenna element 210 in a plan view may be different from that of the two antenna elements 110A. As an example, the antenna element 210, together with the two antenna elements 110A, can be fabricated by patterning a conductive layer formed on the surface on the +Z direction side of the substrate 101 by wet etching or the like.

[0202] One end of a transmission line 215 is connected to the antenna element 210. The other end of the transmission line 215 is connected to the ground (reference potential point), for example. More specifically, the other end of the transmission line 215 is connected to the ground layer 120 via a via that penetrates the substrate 101 in the Z direction, for example. Note that the other end of the transmission line 215 may be an open end instead of being connected to the ground. The other end of the transmission line 215 is an example of an end of the transmission line 215.

[0203] For example, the antenna element 210 has the same shape as the antenna element 110A, and the transmission line 215 is connected from the -Y direction side, for example. Therefore, for example, the excitation direction of the antenna element 210 is the Y direction. For example, if the radio wave reflector 200 is used in an upright position so that the +Y direction or the -Y direction faces vertically upward, the antenna element 210, together with the antenna element 110A, transmits and receives vertically polarized radio waves.

[0204] When antenna element 210 receives radio waves, the received radio wave signal is transmitted through transmission line 215, reflected at the end, and returned to antenna element 210, which then transmits the radio waves, thereby reflecting the radio waves. In this way, antenna element 210, like two antenna elements 110A, performs retroreflection, reflecting incoming radio waves in the direction of arrival.

[0205] The antenna element 210 is provided on the surface on the +Z direction side of the substrate 101 so that its center in a planar view is located on a virtual symmetry plane. The antenna element 210 is provided at a central position between the two antenna elements 110A. As an example, the central position between the two antenna elements 110A is the central position between the centers of the two antenna elements 110A in a planar view (the midpoint on the line connecting the two centers). The antenna element 210 being provided at a central position between the two antenna elements 110A means that the center of the antenna element 210 in a planar view is located at the central position between the two antenna elements 110A. Note that instead of the centers of the antenna element 210 and the two antenna elements 110A in a planar view, the center of gravity in a planar view may be used.

[0206] <Transmission Line 215> The transmission line 215 has a characteristic impedance that matches the input impedance of the antenna element 210. Here, if the electrical length of the wavelength of the radio waves transmitted and received by the antenna element 210 is λe and an arbitrary natural number is N, then the difference in length between the transmission line 115A and the transmission line 215 is λe×N−λe / 2 when the transmission line 215 has an end connected to ground. The reason for subtracting λe / 2 is that when a signal is reflected at the end connected to ground, the phase of the signal shifts by 180 degrees. When the transmission line 215 has an end connected to ground, setting the difference in length to this value can align the reflection phases of the two antenna elements 110A and 210.

[0207] Furthermore, when the transmission line 215 has an open end, the phase of the signal does not shift at the open end, so the difference in length between the transmission line 115A and the transmission line 215 can be set to λe × N. When the transmission line 215 has an open end, setting such a difference in length makes it possible to align the reflection phases of the two antenna elements 110A and 210.

[0208] The radio wave reflector of the second embodiment may have the configuration shown in Fig. 9B. Fig. 9B is a diagram showing an example of the configuration of a radio wave reflector 200A of the second embodiment. The radio wave reflector 200 shown in Fig. 9B has two antenna elements 110A and 210 of the radio wave reflector 200 shown in Fig. 9A that have the same configuration as the antenna elements 110A and 110B of the radio wave reflector 100B shown in Fig. 3B, and has a configuration in which three rectangular radiating elements 111 arranged in the Y direction are connected by a line 112. Even when the antenna elements 110A and 210 having the configuration shown in Fig. 9B are used, they can operate in the same way as the radio wave reflector 200 shown in Fig. 9A and are capable of retroreflection.

[0209] <Effect> The radio wave reflector 200 includes two antenna elements 110A (two first antenna elements) provided along the X direction (first direction), a transmission line 115A (first transmission line) connecting the two antenna elements 110A, an antenna element 210 (second antenna element) arranged at a central position between the two antenna elements 110A in the X direction (first direction), and a transmission line 215 (second transmission line) connected to the antenna element 210 and having an end connected to ground or an open end. When the transmission line wavelength (electrical length) of radio waves transmitted and received by the two antenna elements 110A and the antenna element 210 is λe and an arbitrary natural number is N, the difference in electrical length between the transmission line 115A and the transmission line 215 is λe×N−λe / 2 when the transmission line 215 has an end connected to ground, and is λe×N when the transmission line 215 has an open end.

[0210] Therefore, retroreflection is possible by aligning the reflection phases of the two antenna elements 110A and 210. Furthermore, since the difference in length between the transmission lines 115A and 215 is λe×N and the transmission line 115A is longer than the transmission line 215, the transmission lines 115A and 215 can be arranged without crossing each other. Furthermore, since the transmission lines 115A and 215 can be arranged without crossing each other, interference between the transmission lines 115A and 215 and impedance mismatch can be suppressed, and good reflection characteristics of the two antenna elements 110A and 210 can be obtained.

[0211] Therefore, it is possible to provide a radio wave reflector 200 that can be arranged without crossing the transmission lines 115A and 215 and has good reflection characteristics.

[0212] The substrate 101 (wiring board) may further be included, and the two antenna elements 110A, the transmission line 115A, the antenna element 210, and the transmission line 215 may be formed of a conductive layer provided on one surface of the substrate 101. There is no need to use a multilayer board, and a single-sided printed circuit board having the two antenna elements 110A, the transmission line 115A, the antenna element 210, and the transmission line 215 formed on one surface can be used as the substrate 101. A radio wave reflector 200 can be provided with a simple configuration and reduced manufacturing costs. Furthermore, by using a single-sided printed circuit board as the substrate 101, the radio wave reflector 200 can be made thinner.

[0213] The substrate 101 may further include a ground layer 120 provided on the other surface thereof. There is no need to use a multilayer substrate, and a double-sided printed circuit board in which the two antenna elements 110A, the transmission line 115A, the antenna element 210, and the transmission line 215 are formed on one surface and the ground layer 120 is formed on the other surface can be used as the substrate 101. A radio wave reflector 200 can be provided with a simple configuration and reduced manufacturing costs. Furthermore, by using a double-sided printed circuit board as the substrate 101, the radio wave reflector 200 can be made thinner.

[0214] Furthermore, each of the two antenna elements 110A and 210 and the ground layer 120 may form a patch antenna. By using a patch antenna having directivity in the direction from the ground layer 120 toward the two antenna elements 110A and 210, it is possible to provide a radio wave reflector 200 with good reflection characteristics.

[0215] Furthermore, the outer edge of the ground layer 120 may contain at least two antenna elements 110A and 210 in a planar view, and if the wavelength of the radio waves is λ, the distance between the outer edges of the two antenna elements 110A and 210 and the outer edge of the ground layer 120 in the excitation direction (Y direction) of the two antenna elements 110A and 210 may be less than λ. By reducing the anti-phase radio waves caused by secondary induced radiation generated in the ground layer 120, it is possible to prevent the radio waves radiated by the two antenna elements 110A and 210 from being canceled out, and to suppress a decrease in radiation intensity in the +Z direction. This makes it possible to provide a radio wave reflector 200 with high radiation intensity in the +Z direction.

[0216] The contents of the first to seventh modified examples of the first embodiment can also be applied to the radio wave reflector 200 of the second embodiment.

[0217] The radio wave reflectors of exemplary embodiments of the present disclosure have been described above, but the present disclosure is not limited to the specifically disclosed embodiments, and various modifications and changes are possible without departing from the scope of the claims.

[0218] This international application claims priority based on Japanese Patent Application No. 2023-146951, filed on September 11, 2023, the entire contents of which are incorporated herein by reference.

[0219] 100, 100A, 100B, 100C, 100D, 100E1, 100E2, 100E3, 100F1, 100F2, 100F3, 100F4, 100F5, 100G1, 100G2 Radio wave reflector 101 Substrate 105, 105E1, 105G1, 105F1, 105F2, 105F3, 105F4, 105F5, 105G1 Antenna 110A, 110B, 110C, 110D, 110E, 110E1, 110E2, 110F Antenna element 115A, 115B, 115C, 115D, 115E, 115E1, 115E2, 115F Transmission line 120, 120A, 120B, 120C, 120D, 120E, 120E1, 120E2, 120F ground layers 121A, 123A slits 122A slots 200, 200A radio wave reflectors 210 antenna elements 215 transmission lines

Claims

1. A radio wave reflector comprising: two first antenna elements arranged along a first direction; a first transmission line connecting the two first antenna elements; two second antenna elements positioned equidistant from a center point between the two first antenna elements in the first direction and positioned to sandwich the two first antenna elements along the first direction; and a second transmission line connecting the two second antenna elements, wherein the transmission line wavelength (electrical length) of radio waves transmitted and received by the two first antenna elements and the two second antenna elements is λe and N is an arbitrary natural number, and the difference in electrical length between the first transmission line and the second transmission line is λe x N.

2. The radio wave reflector described in claim 1, further comprising a wiring board, wherein the two first antenna elements, the first transmission line, the two second antenna elements, and the second transmission line are formed from a conductive layer provided on one surface of the wiring board.

3. The radio wave reflector according to claim 2, further comprising a ground layer provided on the other surface of said wiring board.

4. The radio wave reflector according to claim 3, wherein each of the two first antenna elements and the two second antenna elements and the ground layer constitutes a patch antenna.

5. A radio wave reflector as described in claim 3, wherein the outer edge of the ground layer contains at least the two first antenna elements and the two second antenna elements in a planar view, and the distance between the outer edges of the two first antenna elements and the two second antenna elements and the outer edge of the ground layer in the excitation direction of the two first antenna elements and the two second antenna elements is less than λ, where λ is the wavelength of the radio waves.

6. A radio wave reflector as described in claim 3, wherein the ground layer has a slit or slot provided at a position between the two first antenna elements or between the first antenna element and the second antenna element in a planar view.

7. A radio wave reflector as described in claim 3, wherein the ground layer is divided into a portion overlapping the two first antenna elements and the first transmission line, and a portion overlapping the two second antenna elements and the second transmission line.

8. A radio wave reflector as described in any one of claims 1 to 7, comprising a plurality of antennas each composed of the two first antenna elements, the first transmission line, the two second antenna elements, and the second transmission line, the plurality of antennas being arranged in the first direction or a second direction perpendicular to the first direction in a planar view.

9. A radio wave reflector as described in any one of claims 1 to 7, comprising a plurality of antennas each composed of the two first antenna elements, the first transmission line, the two second antenna elements, and the second transmission line, the plurality of antennas being arranged in a matrix.

10. A radio wave reflector comprising: two first antenna elements arranged along a first direction; a first transmission line connecting the two first antenna elements; a second antenna element arranged at a central position between the two first antenna elements in the first direction; and a second transmission line connected to the second antenna element and having an end connected to ground or an open end, wherein, when the transmission line wavelength (electrical length) of radio waves transmitted and received by the two first antenna elements and the second antenna element is λe and N is an arbitrary natural number, the difference in electrical length between the first transmission line and the second transmission line is λe×N-λe / 2 when the second transmission line has an end connected to the ground, and is λe×N when the second transmission line has the open end.

11. The radio wave reflector described in claim 10, further comprising a wiring board, wherein the two first antenna elements, the first transmission line, the second antenna element, and the second transmission line are formed from a conductive layer provided on one surface of the wiring board.

12. The radio wave reflector according to claim 11, further comprising a ground layer provided on the other surface of said wiring board.

13. The radio wave reflector according to claim 12, wherein each of the two first antenna elements and the second antenna element and the ground layer constitutes a patch antenna.

14. A radio wave reflector as described in claim 12, wherein the outer edge of the ground layer, in a planar view, contains at least the two first antenna elements and the second antenna element, and the distance in the excitation direction of the two first antenna elements and the second antenna element between the outer edges of the ground layer and the outer edges of the two first antenna elements and the second antenna element is less than λ, where λ is the wavelength of the radio waves.

15. The radio wave reflector described in claim 12, wherein the ground layer has a slit or slot provided at a position between the two first antenna elements or between the first antenna element and the second antenna element in a planar view.

16. The radio wave reflector described in claim 12, wherein the ground layer is divided into a portion that overlaps with the two first antenna elements and the first transmission line, and a portion that overlaps with the second antenna element and the second transmission line.

17. A radio wave reflector as described in any one of claims 10 to 16, comprising a plurality of antennas each composed of the two first antenna elements, the first transmission line, the second antenna element, and the second transmission line, the plurality of antennas being arranged in the first direction or a second direction perpendicular to the first direction in a planar view.

18. A radio wave reflector as described in any one of claims 10 to 16, comprising a plurality of antennas each composed of the two first antenna elements, the first transmission line, the second antenna element, and the second transmission line, the plurality of antennas being arranged in a matrix.

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