Radar reflection cross section switching device and radar reflection cross section switching method

Abstract

To realize switching between an abnormal / retroreflective state and a non-retroreflective state with a simple configuration.SOLUTION: A radar reflection cross section switching device includes a plane conductor formed in a planar shape. The radar reflection cross section switching device includes a dielectric disposed in contact with the plane conductor. The radar reflection cross section switching device includes a first resonant conductor pair. The first resonant conductor pair consists of two first resonant conductors of different shapes, each elongated and parallel to each other, arranged on the opposite side of the plane conductor with the dielectric sandwiched between them, and spaced apart to form a gap in a direction perpendicular to the longitudinal direction. The radar reflection cross section switching device includes a first electrical switching unit disposed in electrical connection with the first resonant conductors and switchable between a connected state and a disconnected state. The radar reflection cross section switching device includes a control unit that switches the first electrical switching unit between a connected state and a disconnected state.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present disclosure relates to switching detectability by radar devices. [Background technology]

[0002] A radar device generates a radar image by transmitting microwaves and receiving reflected waves from surrounding targets. The surrounding targets are, for example, moving objects. There are known devices that are configured to reflect the microwaves in a manner that does not follow the laws of natural reflection. Hereinafter, such reflections may be referred to as anomalous reflections.

[0003] Retroreflection is the reflection of radio waves coming from a transmitting source back in the direction of their arrival within a certain range of illumination angle. Retroreflection is a type of anomalous reflection. Devices that generate retroreflection are sometimes applied to moving objects, for example, to make them easier to detect by radar.

[0004] Two methods have been proposed to achieve microwave retroreflection: one is to use a well-known reflector such as a corner reflector or a Luneberg lens reflector, and the other is to use multiple antenna elements to re-radiate the received microwave with a desired phase difference. A radio wave retroreflector using the latter method is disclosed in, for example, Patent Document 1.

[0005] The radio wave retroreflector of Patent Document 1 has a plurality of antenna elements that are regularly arranged to form an antenna array. The radio wave retroreflector has a plurality of transmission lines that connect each of a plurality of pairs of antenna elements selected from the plurality of antenna elements. The pair of antenna elements is arranged in positions that are point-symmetrical with respect to the center of the antenna array. The transmission lines connect the pair of antenna elements with equal electrical lengths.

[0006] With this configuration, radio waves incident on a pair of antenna elements are radiated from the other antenna element of the pair. Because the pair of antenna elements are arranged point-symmetrically, the timing of the incident radio waves is delayed before they are radiated. This allows for retroreflection in the direction from which the radio waves arrived. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2017-204681 Summary of the Invention [Problem to be solved by the invention]

[0008] Whether or not it is necessary to make a moving object easier to detect by radar may differ depending on the timing and situation. In this regard, the retroreflector shown in Patent Document 1 cannot switch the reflection mode.

[0009] The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a radar reflection switching device that can electrically switch the reflection mode. [Means for solving the problem]

[0010] The problem to be solved by the present disclosure is as described above. Next, the means for solving this problem and the effects thereof will be described.

[0011] According to a first aspect of the present disclosure, there is provided a radar cross section switching device to be provided on a moving object, having the following configuration. Specifically, the radar cross section switching device includes a plane conductor, a dielectric, a first resonant conductor pair, a first electrical switching unit, and a control unit. The plane conductor is formed in a planar shape. The dielectric is arranged in contact with the plane conductor. The first resonant conductor pair is composed of two first resonant conductors. The two first resonant conductors are elongated and parallel to each other. Each of the first resonant conductors is arranged on the opposite side of the plane conductor with the dielectric sandwiched between them. The two first resonant conductors are spaced apart from each other and spaced apart in a direction perpendicular to their longitudinal directions. The two first resonant conductors have different shapes. The first electrical switching unit is arranged electrically connected to the first resonant conductors and is switchable between a connected state and a disconnected state. The control unit switches the first electrical switching unit between the connected state and the disconnected state.

[0012] According to a second aspect of the present disclosure, there is provided a radar cross section switching method using a radar cross section switching device provided on a mobile object, as follows. That is, the radar cross section switching device includes a plain conductor, a dielectric, a first resonant conductor pair, a first electrical switching unit, a connecting conductor, and a control unit. The plain conductor is formed in a planar shape. The dielectric is arranged in contact with the plain conductor. The first resonant conductor pair is made of two first resonant conductors. The two first resonant conductors are each formed elongated and parallel to each other. Each of the first resonant conductors is arranged on the opposite side of the plane conductor with the dielectric sandwiched between them. The two first resonant conductors are arranged apart from each other so as to form a gap therebetween in a direction perpendicular to their longitudinal direction. The two first resonant conductors have different shapes. The first electrical switching unit is arranged in electrical connection with the first resonant conductors. The first electrical switching unit is switchable between a connected state and a disconnected state. The connecting conductor is arranged on the opposite side of the plane conductor with the dielectric interposed therebetween. The control unit switches the first electrical switching unit between the connected state and the disconnected state. The first electrical switching unit is arranged at both longitudinal ends of each of the first resonant conductors. The ends of the first resonant conductors are connected to the connecting conductors via the first switching unit. In the radar cross section switching method, the control unit switches the first electrical switching unit to the connected state, thereby electrically connecting the first resonant conductors and the connecting conductors and increasing the proportion of specular reflection of radar. The control unit switches the first electrical switching unit to the disconnected state, thereby electrically disconnecting the first resonant conductors and the connecting conductors and decreasing the proportion of specular reflection of radar.

[0013] According to a third aspect of the present disclosure, there is provided a radar cross section switching method using a radar cross section switching device provided on a mobile object. Specifically, the radar cross section switching device includes a plain conductor, a dielectric, a first resonant conductor pair, a first electrical switching unit, and a control unit. The plain conductor is formed in a planar shape. The dielectric is arranged in contact with the plain conductor. The first resonant conductor pair includes two first resonant conductors. The two first resonant conductors are elongated and parallel to each other. Each of the first resonant conductors is arranged on the opposite side of the plane conductor with the dielectric sandwiched between them. The two first resonant conductors are spaced apart from each other in a direction perpendicular to their longitudinal directions. The two first resonant conductors have different shapes. The first electrical switching unit is arranged electrically connected to the first resonant conductors and is switchable between a connected state and a disconnected state. The control unit switches the first electrical switching unit between the connected state and the disconnected state. Each of the first resonant conductors is composed of a first element and a second element arranged to divide the longitudinal length of the first resonant conductor. The first electrical switching unit is arranged to connect the first element and the second element. In the radar cross section switching method, the control unit switches the first electrical switching unit to the connected state, thereby electrically connecting the first element and the second element and reducing the proportion of specular reflection of radar. The control unit switches the first electrical switching unit to the disconnected state, thereby electrically disconnecting the first element and the second element and increasing the proportion of specular reflection of radar.

[0014] This allows the radar wave to be freely switched between a state in which it is reflected retrogradely or abnormally and a state in which it is not. The plane conductor, the dielectric, and the first resonant conductor pair can be easily formed into a plate or sheet shape as a whole. Therefore, when the radar cross section switching device is installed on a mobile body, it can be easily configured so that it does not protrude from the outer surface. As a result, air resistance when the mobile body moves can be reduced. [Effects of the Invention]

[0015] According to the present disclosure, it is possible to realize a radar cross section switching device that can electrically switch the reflection mode and is applicable to various shapes. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a side view showing an example in which a radar cross section switching device according to an embodiment of the present disclosure is applied to an automobile. [Figure 2] A perspective view showing the basic structure of a retroreflective metasurface reflector. [Figure 3] FIG. 10 is a perspective view showing in detail structural units that are repeatedly arranged in the basic structure. [Figure 4] FIG. 10 is a schematic diagram illustrating the repeated arrangement of structural units in the antenna arrangement direction. [Figure 5] FIG. 1 is a perspective view for schematically explaining specular reflection and extraordinary reflection. [Figure 6] 1 is a graph showing the distribution of propagating diffraction orders corresponding to the angle of incidence and the angle of reflection. [Figure 7] 10 is a graph showing the relationship between the shape of the resonant conductor and the amplitude coefficient. [Figure 8] FIG. 1 is a perspective view showing the retroreflective metasurface reflector of the first embodiment in detail. [Figure 9] 6 is a graph illustrating switching of RCS characteristics. [Figure 10] FIG. 10 is a perspective view showing the retroreflective metasurface reflector of the second embodiment in detail. [Figure 11] FIG. 10 is a schematic diagram illustrating the repeated arrangement of structural units in the antenna arrangement direction in the first modified example. [Figure 12] 6 is a graph illustrating switching of RCS characteristics. [Figure 13] FIG. 10 is a schematic diagram illustrating the repeated arrangement of structural units in the antenna arrangement direction in the second modified example. [Figure 14] 10A and 10B are diagrams conceptually illustrating the arrangement of first resonant conductor pairs in the third and fourth embodiments. [Figure 15] FIG. 11 is a perspective view showing the retroreflective metasurface reflector of the third embodiment in detail. [Figure 16]FIG. 10 is a perspective view showing the retroreflective metasurface reflector of the fourth embodiment in detail. DETAILED DESCRIPTION OF THE INVENTION

[0017] 1 is a side view showing an example in which a radar reflection switching device 110 according to an embodiment of the present disclosure is applied to an automobile 100. As shown in FIG.

[0018] First, an example will be described in which the radar reflection switching device 110 of this embodiment is used. The radar reflection switching device 110 is a type of radar cross section switching device.

[0019] The radar reflection switching device 110 can be applied to various types of moving bodies, such as an automobile 100. For example, when the automobile 100 is traveling on a highway, it is advantageous in terms of safety if the automobile 100 is easily detected by the radar device 150 mounted on the automobile traveling behind it. On the other hand, when the automobile 100 is traveling in an urban area, if the automobile 100 is more easily detected than necessary, there is a possibility that the radar device 150 of the automobile traveling behind may erroneously detect the distance between the automobiles during traffic congestion, which is undesirable.

[0020] RCS is an index that indicates the ease of detection by the radar device 150. RCS is an abbreviation for radar cross section. Unless otherwise specified, in this specification, RCS refers to the RCS of a monostatic radar device in which the transmitting antenna and the receiving antenna are installed in the same location. Vehicle detection is an example in which the radar reflection switching device 110 is applied, and the wavelength of the radar wave is not particularly limited.

[0021] The automobile 100 is equipped with a radar reflection switching device 110. The radar reflection switching device 110 includes a radar reflector 40 and a control unit 80. When the control unit 80 detects a user operation, it changes the RCS of the radar reflector 40. The user is, for example, the driver of the automobile.

[0022] Next, the radar reflector 40 of this embodiment will be described in detail. In this embodiment, the radar reflector 40 includes a base member 41 and a retroreflective metasurface reflector 42A. The base member 41 is designed to have a predetermined mechanical strength. The base member 41 is formed in a flat or gently curved shape that conforms to the surface of the automobile 100. However, the shape and material of the base member 41 are arbitrary. The material of the base member may be, for example, a metal such as aluminum or copper, or a good conductor such as a composite material containing carbon fiber. The retroreflective metasurface reflector 42A is fixed to the surface of the base member 41. Because the retroreflective metasurface reflector 42A is shaped to be substantially integrated with the surface of the automobile 100, air resistance during travel of the automobile 100 can be reduced.

[0023] The retroreflective metasurface reflector 42A of this embodiment essentially corresponds to a partially modified version of the retroreflective metasurface reflector 42p with the basic structure shown in Figure 2. The same is true for the retroreflective metasurface reflector 42B of the second embodiment described below. Therefore, the retroreflective metasurface reflector 42p with the basic structure will be described first.

[0024] 2, the retroreflective metasurface reflector 42p of the basic structure includes a ground plane 31, a dielectric 32, and a conductor pattern 33. The ground plane 31 corresponds to a plane conductor.

[0025] The ground plane 31 is disposed on one surface in the thickness direction of the dielectric 32. Any material can be used for the ground plane 31. The material for the ground plane 31 is, for example, a material that is generally called a good conductor and through which an electric current flows easily, such as aluminum or copper, or a composite material containing carbon fiber.

[0026] The dielectric 32 is formed in the shape of a plate with a uniform thickness. The material of the dielectric 32 can be any material as long as it has electrical insulation properties, but it can be GFRP, for example. GFRP is an abbreviation for Glass Fiber Reinforced Plastic. To reduce dielectric loss, fluorine-based, aramid-based, polyimide-based, or other materials may be used for the dielectric 32. A flexible material can be used for the dielectric 32. In this case, even if the surface of the base member 41 is curved, the retroreflective metasurface reflector 42p can be installed so that its shape conforms to the curved surface, which is preferable.

[0027] The conductor pattern 33 is disposed on one surface in the thickness direction of the dielectric 32. The conductor pattern 33 is disposed so as to sandwich the dielectric 32 between the conductor pattern 33 and the ground plane 31. The material of the conductor pattern 33 is arbitrary. For example, the material of the conductor pattern 33 is a material that is generally called a good conductor and allows current to flow easily, and can be a metal such as aluminum or copper. The material of the conductor pattern 33 may be the same as or different from the material of the ground plane 31.

[0028] The conductor pattern 33 includes a large number of first resonant conductor pairs 1 periodically arranged on the surface of the dielectric 32 .

[0029] Each first resonant conductor pair 1 consists of two first resonant conductors 1a and 1b. Each of the two first resonant conductors 1a and 1b is formed to be elongated. The longitudinal directions of the first resonant conductors 1a and 1b are parallel to each other. Among the multiple first resonant conductor pairs 1, the longitudinal directions of the first resonant conductors 1a and 1b are parallel to each other.

[0030] The lengths of the two first resonant conductors 1a and 1b are different from each other. Instead of or in addition to the lengths, the widths may be different. The difference in shape between the first resonant conductors 1a and 1b is determined so that the reflection phase difference is substantially 180° for radar waves incident at a predetermined specific incident angle. In the retroreflective metasurface reflector 42p with a basic structure, a first resonant conductor pair 1 consisting of two such first resonant conductors 1a and 1b is periodically arranged.

[0031] In the retroreflective metasurface reflector 42p having a basic structure, a section including one first resonant conductor 1a constitutes one unit cell C1, and a section including one first resonant conductor 1b also constitutes one unit cell C1. In this specification, the unit cell C1 refers to a virtual small section in the retroreflective metasurface reflector 42p. FIG. 2 shows a case where the unit cell C1 is square. The size of each unit cell C1 is sufficiently smaller than the wavelength of the target radar wave. A combination of two unit cells C1, one of adjacent first resonant conductors 1a and one of adjacent first resonant conductors 1b, constitutes a structural unit U1. A metasurface structure is obtained by arranging these structural units U1 periodically in a two-dimensional manner. Each unit cell C1 functions as a resonator. The structural unit U1 is a structural unit in which the phase difference between the reflected wave reflected from one unit cell C1 including the first resonant conductor 1a and the reflected wave reflected from one unit cell C1 including the first resonant conductor 1b is 180°.

[0032] In this specification, a metasurface refers to a surface that is constructed by periodically arranging artificial structures smaller than the wavelength of the target radio waves, so that the refractive index of the radio waves becomes macroscopically negative. The metasurface structure shown in Figure 2 is a type of what is called a Huygens metasurface. By making the refractive index that governs the reflection of radio waves negative, retroreflection of radio waves can be achieved.

[0033] 3, focusing on one structural unit U1, the configuration of the first resonant conductors 1a and 1b is illustrated in detail. As shown in FIG. 3, a ground plane 31, a dielectric 32, and a conductor pattern 33 form an MIM structure. MIM is an abbreviation for Metal-Insulator-Metal. In FIG. 3, the dielectric 32 is drawn perspectively with a dashed line to clearly show the structural unit U1.

[0034] In the MIM structure, each of the first resonant conductors 1a and 1b functions as an antenna. Taking this into consideration, hereinafter, the longitudinal direction of each of the first resonant conductors 1a and 1b is sometimes referred to as the antenna longitudinal direction D1, and the direction in which the two first resonant conductors 1a and 1b included in the structural unit U1 are aligned is sometimes referred to as the antenna alignment direction D2. Considering the shapes of the first resonant conductors 1a and 1b, the antenna longitudinal direction D1 can also be referred to as the conductor length direction, and the antenna alignment direction D2 can also be referred to as the conductor width direction. The pair of first resonant conductors 1a and 1b included in the structural unit U1 is sometimes referred to as the first resonant conductor pair 1.

[0035] The repeated arrangement of the structural unit U1 will now be explained. Figure 4 is a schematic diagram of a retroreflective metasurface reflector 42p with a basic structure, viewed from the thickness direction. In Figure 4, only one row of structural units U1 is drawn aligned in the antenna alignment direction D2, but in reality, many such rows are arranged in the antenna longitudinal direction D1. The dimension of the structural unit U1 in the antenna alignment direction D2 is equivalent to two unit cells C1. The structural units U1 are repeatedly arranged in the antenna alignment direction D2 at a pitch RP1 equal to this dimension.

[0036] Each of the two first resonant conductors 1a and 1b is disposed at the center of the unit cell C1 to which it belongs. Therefore, the separation pitch DP1 between the first resonant conductors 1a and 1b belonging to one structural unit U1 is equal to the size of one unit cell C1.

[0037] The MIM structure will be explained below in relation to the principle of retroreflection.

[0038] Surface impedance is one of the boundary conditions that determine the reflection characteristics of waves that reach a boundary and are reflected. A retroreflector can be realized by implementing a surface impedance on the boundary surface that satisfies the boundary condition for the desired anomalous reflected waves. By periodically arranging the unit cells C1 described above, such impedance conditions can be satisfied macroscopically.

[0039] In general, it is desirable that the spatial discretization by the unit cell C1 be performed with a sufficiently fine granularity to simulate continuous impedance characteristics.

[0040] Consider the case where radio waves are incident on a metasurface as shown in Figure 5. The number of propagation diffraction orders required to reflect an incident wave at an arbitrary incident angle to the intended reflection angle is defined as N, and the period required for that propagation diffraction is defined as λ. g , wave number k g Then, N, λ g , k g are defined by equations (1) and (2), respectively. The propagation diffraction order N represents the number of reflection lobes generated by reflection or diffraction. The period λ g represents the size of one structural unit U1.

number

number

[0041] Figure 6 shows the incident angle θ i and reflection angle θ rThe distribution of the propagation diffraction orders N corresponding to the incident angle θ is calculated according to the above formula (1). i and the horizontal axis is the reflection angle θ r Retroreflection is the reflection of radio waves coming from the source of the radio waves back in the direction of their arrival, so θ r =-θ i As is clear from the graph in Figure 6, for example, (θ r ,θ i The point where N=(−60, 60) is included in the region where N=2. In this embodiment, in consideration of simplifying the structure, the minimum propagation analysis order N required to achieve the intended anomalous or retroreflection is set to 2.

[0042] θ r =-θ i Even if the condition of θ is not satisfied, r If θ<0, it can be said that the radio wave is reflected to the same side as the radio wave transmission source, i.e., the radar device 150. r The area where <0 is sometimes called the retroreflective area.

[0043] From the above, a retroreflector using extraordinary reflection of the smallest propagation diffraction order can be obtained as follows. [a]θ r =-θ i Under the condition that (N=2), the sizes of two unit cells C1 are selected in the region where N=2. Then, the length L and width W of the first resonant conductors 1a and 1b are selected from the configuration of the two unit cells C1. The length L and width W of the first resonant conductors 1a and 1b are selected so that the amplitude reflection coefficient, which is the amplitude of the reflection coefficient, is as close to 1 as possible, and the absolute value of the phase difference between the reflected waves indicated by the reflection coefficient is π, i.e., 180°. The size of each of the two unit cells C1 is determined by dividing the period obtained by the above equation (2) by λ g Then, λ g If the phases of the reflected waves for the two unit cells C1 are φ1 and φ2, respectively, then, according to the above condition, |φ1-φ2|=π. [b] The two selected unit cells C1 are arranged in the same order with the period λ gArrange them alternately according to the order.

[0044] FIG. 3 shows an MIM structure corresponding to one structural unit U1. In FIG. 3, the unit cell corresponding to the first resonant conductor 1a is labeled C1a, and the unit cell corresponding to the first resonant conductor 1b is labeled C1b. The MIM structure shown in FIG. 3 is one of the structures that realizes unit cells C1a and C1b that can ensure an amplitude reflection coefficient close to 1 and a phase difference of 180° or more. When radar waves are incident on this MIM structure, loop currents flow in each of the first resonant conductors 1a and 1b. In the loop current in the first resonant conductor 1a, the direction of the current flowing through the first resonant conductor 1a is opposite to the direction of the current flowing through the ground plane 31. In the loop current in the first resonant conductor 1b, the direction of the current flowing through the first resonant conductor 1b is opposite to the direction of the current flowing through the ground plane 31. These loop currents are shown as out-of-phase currents in FIG. 3. These loop currents cause magnetic resonance between the two unit cells C1a and C1b. This magnetic resonance affects the phase of the reflected wave. By changing the length or width of the first resonant conductors 1a and 1b, it is possible to easily achieve a phase difference over the entire range required for phase control based on magnetic resonance. The entire range required for phase control is the range from -π to +π.

[0045] The ground plane 31 of the MIM structure has a wide-area shielding effect. Therefore, complete reflection can be easily achieved regardless of whether a resonance state exists or not. Complete reflection refers to reflection with an amplitude reflection coefficient close to 1. The lengths of the first resonant conductors 1a and 1b of the MIM structure are both approximately 1 / 4 of the resonant frequency. Therefore, the unit cells C1a and C1b required for the reflector can be configured to be sufficiently smaller than the wavelength of the target wave.

[0046] When radio waves are reflected at a location far enough away from the transmitting source, the incident wave can be considered locally as a plane wave near the reflection point. Plane waves are generally known to be divided into TE-polarized and TM-polarized waves. To achieve retroreflection in the retroreflective metasurface reflector 42p shown in Figure 2, the incident wave must be TE-polarized and the incident plane PL1 must be perpendicular or nearly perpendicular to the longitudinal direction of the first resonant conductors 1a and 1b. Here, the incident plane PL1 refers to the plane that includes the normal V1 of the interface 35 and the direction of the incident wave. The interface 35 is the surface of the retroreflective metasurface reflector 42p.

[0047] 2 also shows the magnetic field vector H and electric field vector E of the incident wave. The incident wave must be TE polarized and the incident plane PL1 must be perpendicular to the longitudinal direction of the first resonant conductors 1a and 1b because magnetic resonance does not occur in the above-mentioned MIM structure unless the incident wave has a magnetic field component in the incident plane PL1.

[0048] In summary, a metasurface reflector composed of unit cells C1 can be designed by the following steps: [P] The wavelength λ0 is calculated from the frequency of the target radar wave. This wavelength λ0 and the desired anomalous or retroreflection angle are substituted into the above equation (2) to obtain the period λ g The desired angle of extraordinary or retroreflection is the angle of incidence θ i and reflection angle θ r The period λ g λ is half the value of g Let / 2 be the length of one side of the square of unit cell C1. [Q] Unit cells C1 are arranged two-dimensionally and a resonant conductor is placed on each surface. At least one of the length L and width W of the resonant conductor is varied as a parameter, and the target radar wave is measured at an incident angle θ i The reflection coefficient is obtained when light is incident on the boundary surface at . The reflection coefficient is expressed as a complex number and contains two pieces of information: amplitude and phase. This calculation can be realized, for example, by a known simulation calculation. [R] Two sets of parameters (L, W) are selected such that the phase difference between the reflection coefficients is 180°. One of the two sets of parameters (L, W) is applied to the length La and width Wa of one of the first resonant conductors 1a, and the other set of parameters (L, W) is applied to the length Lb and width Wb of the other first resonant conductor 1b. The repetition pitch RP1 of the structural unit U1 in the antenna arrangement direction D2 is set equal to the above-mentioned period λ g It is defined as equal to.

[0049] Regarding the above [Q], Fig. 7 shows an example of the change in the reflection coefficient when the width W of the resonant conductor is kept constant at 0.5 mm and the length L is changed from 0.5 mm to 3.5 mm. The horizontal axis of Fig. 7 is the length of the resonant conductor, the left vertical axis is the reflection coefficient related to amplitude, and the right vertical axis is the reflection coefficient related to phase. In this example, assuming application to millimeter-wave radar, the design frequency is set to 24 GHz. The desired retroreflection is determined by the angle of incidence θ i 60°, reflection angle θ r The dielectric constant etc. of the dielectric material is set to be the same as that of the base material of a commonly used GFRP printed circuit board.

[0050] The dashed line in the graph in Figure 7 indicates the amplitude reflection coefficient. The amplitude reflection coefficient drops slightly from 1 near L = 2.5 mm, which corresponds to the resonant frequency. This is due to dielectric loss. The solid line in the graph indicates the relative phase of the reflected wave with respect to the incident wave. As the length L changes from 0.5 mm to 3.5 mm, the phase changes from 0° to approximately -300°. Therefore, there is ample room to select a combination of lengths L that produces a phase difference of 180°. For example, as shown by the two circles in Figure 7, if the length La of one first resonant conductor 1a is set to 2.7 mm and the length Lb of the other first resonant conductor 1b is set to 1.7 mm, a phase difference of approximately 180° can be achieved.

[0051] Next, a configuration for switching the RCS depending on the situation will be described.

[0052] In the retroreflective metasurface reflector 42p with the basic structure illustrated in Fig. 2, the retroreflective characteristics are fixed at the time of manufacture and cannot be changed thereafter. In contrast, the retroreflective metasurface reflector 42A of the first embodiment shown in Fig. 8 has the following features that allow the reflection characteristics to be electrically switched.

[0053] 8 illustrates only two structural units U1 of the retroreflective metasurface reflector 42A of the first embodiment. Similar to the retroreflective metasurface reflector 42p of the basic structure, the retroreflective metasurface reflector 42A includes a ground plane 31, a dielectric 32, and a conductor pattern 33. The conductor pattern 33 includes a number of first resonant conductor pairs 1 periodically arranged on the surface of the dielectric 32. The length L and width W of the first resonant conductor pairs 1 are designed according to the design procedures [P] to [R] described above.

[0054] A large number of structural units U1 are repeatedly arranged in both the antenna longitudinal direction D1 and the antenna arrangement direction D2. For convenience of explaining the connecting conductors 6a and 6b, FIG. 8 shows two structural units U1 adjacent to each other in the antenna longitudinal direction D1. Each of the two structural units U1 has a first resonant conductor 1a having a longer length and a first resonant conductor 1b having a shorter length. Between the two structural units U1, the first resonant conductors 1a, 1a having a longer length are arranged to face each other in the antenna longitudinal direction D1. Between the two structural units U1, the first resonant conductors 1b, 1b having a shorter length are arranged to face each other in the antenna longitudinal direction D1.

[0055] In this embodiment, structural units U1 are repeatedly arranged in the antenna longitudinal direction D1 so that two first resonant conductors having the same shape are aligned in a straight line in the antenna longitudinal direction D1. A connecting conductor 6a is arranged on the surface of the dielectric 32 between the long first resonant conductors 1a, 1a. A connecting conductor 6b is arranged on the surface of the dielectric 32 between the short first resonant conductors 1b, 1b. The connecting conductors 6a, 6b are included in the conductor pattern 33 and can be formed in the same manner as the first resonant conductors 1a, 1b.

[0056] The connecting conductor 6a is formed in an elongated linear shape in the antenna longitudinal direction D1. The connecting conductor 6a may be made of any material. For example, the connecting conductor 6a may be made of a material that is generally called a good conductor and allows current to flow easily, such as metal such as aluminum or copper. One longitudinal end of the connecting conductor 6a is connected to the first resonant conductor 1a on one side via a diode 7. The diode 7 corresponds to a first electrical switching unit. The other longitudinal end of the connecting conductor 6a is connected to the first resonant conductor 1a on the other side via the diode 7.

[0057] The connecting conductor 6b is formed in a long, thin, linear shape in the antenna longitudinal direction D1. The connecting conductor 6b may be made of any material. For example, the connecting conductor 6b may be made of a material that is generally called a good conductor and allows current to flow easily, such as a metal such as aluminum or copper. One longitudinal end of the connecting conductor 6b is connected to the first resonant conductor 1b on one side via a diode 7. The other longitudinal end of the connecting conductor 6b is connected to the first resonant conductor 1b on the other side via a diode 7.

[0058] In this embodiment, the multiple diodes 7 are all configured as known PIN diodes. A PIN diode has a layer structure in which P-type, I-type, and N-type layers are arranged in this order, and is characterized by a high resistance value of the I-type semiconductor. It is known that a PIN diode is equivalent to an LR series circuit when a forward voltage is applied, and is equivalent to an LC series circuit when a reverse voltage is applied.

[0059] Each of the connection conductors 6a, 6b is electrically connected to the ground plane 31 via a plane connection via 8 formed in the dielectric 32. The plane connection via 8 is formed to extend in the thickness direction of the ground plane 31. The material of the plane connection via 8 is arbitrary. For example, the material of the plane connection via 8 is a material that is generally called a good conductor and allows current to flow easily, and can be metal such as aluminum or copper. In this embodiment, two plane connection vias 8 are provided for one connection conductor 6a, but the number may be one or three or more. Two plane connection vias 8 are provided for one connection conductor 6b, but the number may be one or three or more.

[0060] Each diode 7 is arranged so that the first resonance conductors 1a and 1b are connected to the P layer and the connecting conductors 6a and 6b are connected to the N layer. In Fig. 8, the P layer side of each diode 7 is indicated by an *.

[0061] A bias conductor 9 formed long and narrow along the antenna alignment direction D2 is disposed in the middle of the dielectric 32 in the thickness direction. The bias conductor 9 may be made of any material. For example, the bias conductor 9 may be made of a material that is generally known as a good conductor and allows current to flow easily, such as aluminum or copper. In FIG. 8, each bias conductor 9 is illustrated with a cut-out portion corresponding to one structural unit U1, but in reality, one bias conductor 9 is provided in common for a row of structural units U1 that are aligned in the antenna alignment direction D2.

[0062] When viewed from the thickness direction of the retroreflective metasurface reflector 42A, the bias conductor 9 is arranged so as to intersect with the longitudinal center of each of the first resonant conductors 1a and 1b. Each of the first resonant conductors 1a and 1b is connected to the bias conductor 9 via a bias via 10 formed inside the dielectric 32. The bias via 10 is formed so as to extend in the thickness direction of the dielectric 32. The bias via 10 may be made of any material. For example, the bias via 10 may be made of a material that is generally called a good conductor and allows current to flow easily, such as a metal such as aluminum or copper.

[0063] The bias conductor 9 is disposed inside the dielectric 32. When viewed in the thickness direction of the ground plane 31, the bias conductor 9 is disposed so as to perpendicularly intersect with each of the first resonant conductors 1a and 1b. This makes it possible to prevent the current flowing through the bias conductor 9 from affecting the magnetic resonance of the first resonant conductors 1a and 1b.

[0064] The ground plane 31 is connected to ground by an appropriate method. A voltage source 11 is disposed between the ground plane 31 and the plurality of bias conductors 9. The voltage source 11 can apply a DC voltage between each bias conductor 9 and the ground plane 31. The voltage source 11 is connected to a control unit 80, which is an appropriate computer. The control unit 80 outputs a voltage control signal to the voltage source 11 in response to an operator operating a pointer member. The pointer member is, for example, a switch. The voltage source 11 can switch the voltage it applies between positive and negative in response to a command from the control unit 80.

[0065] Consider the case where the voltage source 11 applies a positive voltage between the bias conductor 9 and the ground plane 31 in this configuration. Because the potential of the first resonant conductors 1a and 1b becomes higher than the potential of the connecting conductors 6a and 6b, a forward bias voltage is applied to each of the diodes 7. Therefore, each of the diodes 7 electrically connects the first resonant conductors 1a and 1b to the corresponding connecting conductors 6a and 6b. The state in which the first resonant conductors 1a and 1b are electrically connected to the corresponding connecting conductors 6a and 6b is also referred to as a connected state. As a result, both longitudinal ends of each of the first resonant conductors 1a and 1b are short-circuited to the ground plane 31 via the connecting conductors 6a and 6b and the plane connecting vias 8. In this state, the first resonant conductors 1a and 1b do not substantially resonate even when radio waves are incident, so no retroreflection occurs, and only specular reflection occurs.

[0066] Conversely, consider the case where the voltage source 11 applies a negative voltage between the bias conductor 9 and the ground plane 31. Because the potential of the first resonant conductors 1a and 1b becomes lower than the potential of the connecting conductors 6a and 6b, a reverse bias voltage is applied to each of the diodes 7. Therefore, each of the diodes 7 electrically isolates the first resonant conductors 1a and 1b from the corresponding connecting conductors 6a and 6b. The state in which the first resonant conductors 1a and 1b are electrically isolated from the corresponding connecting conductors 6a and 6b is also referred to as an isolation state. Therefore, the length L and width W of the first resonant conductors 1a and 1b become equal to the predetermined length and width designed to cause retroreflection of incident radar waves, and the first resonant conductors 1a and 1b are in a resonant state, thereby allowing retroreflection of incident radar waves.

[0067] As described above, the presence or absence of retroreflection can be easily switched by switching the positive and negative voltages applied to the bias conductor 9, thereby changing the RCS of the retroreflective metasurface reflector 42A. In other words, the presence or absence of retroreflection can be said to be the proportion of specular reflection among the reflections of radar waves.

[0068] Figure 9 shows the RCS characteristics of a retroreflective metasurface reflector 42p with a basic structure manufactured under the same assumptions as in Figure 7, and a simple metal plate. The RCS characteristics of the retroreflective metasurface reflector 42p are shown by a solid line, and the RCS characteristics of the simple metal plate are shown by a dashed line. The horizontal axis represents the incident angle θ i The vertical axis represents the magnitude of the RCS. The RCS of the retroreflective metasurface reflector 42p is i When the angle is near 60°, the RCS characteristic is increased by approximately 30 dBsm compared to a metal plate. This corresponds to an increase in radar detection range of approximately six times. The retroreflective metasurface reflector 42A of this embodiment can switch between the two RCS characteristics shown in FIG. 9 depending on the situation.

[0069] In this embodiment, the conductors are alternately arranged in the antenna longitudinal direction D1, such as the first resonant conductor 1a, the connecting conductor 6a, the first resonant conductor 1a, the connecting conductor 6a, and so on. The same applies to the relationship between the first resonant conductor 1b and the connecting conductor 6b. Of the numerous diodes 7 arranged at the boundaries of the arranged conductors, any two adjacent diodes 7 in the antenna longitudinal direction D1 have opposite polarities. The connecting conductors 6a and 6b are electrically connected to the ground plane 31 via the plane connecting vias 8, and the first resonant conductors 1a and 1b are connected to the bias conductor 9 via the bias vias 10. This allows a forward or reverse bias voltage to be applied to all the diodes 7 via the common ground plane 31 arranged across the numerous structural units U1. This allows for a simplified configuration of the bias conductor 9.

[0070] As described above, the radar reflection switching device 110 is provided in, for example, the automobile 100. The radar reflection switching device 110 includes a ground plane 31, a dielectric 32, a first resonant conductor pair 1, a diode 7, and a control unit 80. The ground plane 31 is formed in a planar shape. The dielectric 32 is disposed in contact with the ground plane 31. The first resonant conductor pair 1 includes two first resonant conductors 1a and 1b. The two first resonant conductors 1a and 1b are elongated and parallel to each other. The first resonant conductors 1a and 1b are disposed on opposite sides of the ground plane 31 with the dielectric 32 interposed therebetween. The two first resonant conductors 1a and 1b are disposed apart from each other in the antenna arrangement direction D2, which is perpendicular to the longitudinal direction of the first resonant conductors 1a and 1b. The shapes of the two first resonant conductors 1a and 1b are different from each other. The diode 7 is disposed in electrical connection with the first resonant conductor 1a and is switchable between a connected state and a disconnected state. The control unit 80 switches the diode 7 between a connected state and a cut-off state.

[0071] This allows the radar reflection switching device 110 to be freely switched between a state in which the radar wave is reflected retrogradely or abnormally and a state in which it is not. The ground plane 31, the dielectric 32, and the first resonant conductor pair 1 can be easily formed into a plate or sheet shape as a whole. Therefore, when the radar reflection switching device 110 is installed in the automobile 100, it does not protrude from the outer surface, thereby reducing air resistance.

[0072] The radar reflection switching device 110 of this embodiment applies a voltage to the diode 7 and includes a voltage source 11 that can switch the applied voltage between positive and negative. The diode 7 switches between a connected state and a disconnected state by reversing the direction in which the voltage is applied to the diode 7.

[0073] This allows the radar wave to be switched between a retroreflected / abnormally reflected state and a non-retroreflected state with simple voltage control.

[0074] The radar reflection switching device 110 of this embodiment includes connecting conductors 6a and 6b arranged on the opposite side of the ground plane 31 with a dielectric 32 sandwiched therebetween. Diodes 7 are arranged at both longitudinal ends of each of the first resonant conductors 1a and 1b. An end of the first resonant conductor 1a is connected to the connecting conductor 6a via the diode 7. An end of the first resonant conductor 1b is connected to the connecting conductor 6b via the diode 7.

[0075] This makes it possible to switch between a state in which radar waves are reflected / abnormally and a state in which they are not, using a simple configuration in which the diode 7 switches between electrical conduction and non-conduction between the first resonant conductors 1a, 1b and the connecting conductors 6a, 6b.

[0076] The radar reflection switching device 110 of this embodiment includes a voltage source 11 and a bias conductor 9. The voltage source 11 applies a voltage to the diode 7 and is capable of switching the applied voltage between positive and negative. The bias conductor 9 electrically connects the voltage source 11 to the first resonant conductors 1a and 1b. The diode 7 switches between a connected state and a disconnected state by reversing the direction in which the voltage is applied to the diode 7. The control unit 80 switches the applied voltage of the voltage source 11 between positive and negative.

[0077] This allows switching between a state in which a forward bias voltage is applied to the diode 7 and a state in which a reverse bias voltage is applied to the diode 7 by simple voltage control.

[0078] In the radar reflection switching device 110 of this embodiment, a bias via 10 and a plane connection via 8 are formed in the dielectric 32. The bias via 10 extends in the thickness direction of the ground plane 31 and connects the first resonant conductors 1a and 1b to the bias conductor 9. The plane connection via 8 extends in the thickness direction of the ground plane 31 and connects the connection conductors 6a and 6b to the ground plane 31.

[0079] This simplifies the configuration for electrically switching between a state in which radar waves are retroreflected / abnormally reflected and a state in which they are not.

[0080] In the radar reflection switching device 110 of this embodiment, the bias conductor 9 is formed to be elongated in a direction intersecting the longitudinal direction of the first resonant conductors 1a and 1b. At least a portion of the bias conductor 9 is disposed inside the dielectric 32. A bias via 10 is formed in the dielectric 32. The bias via 10 extends in the thickness direction of the ground plane 31 and connects the bias conductor 9 to the first resonant conductors 1a and 1b.

[0081] This makes it possible to switch between a state in which a forward bias voltage is applied to the diode 7 and a state in which a reverse bias voltage is applied to the diode 7 with a simple circuit configuration.

[0082] In the radar reflection switching device 110 of this embodiment, the bias conductor 9 is electrically connected to a voltage source 11. At least a portion of the bias conductor 9 is disposed inside a dielectric 32. The diodes 7, which are disposed at both longitudinal ends of each of the first resonant conductors 1a and 1b, are connected to the first resonant conductor 1a with their polarities reversed. The voltage source 11 applies a voltage between the bias conductor 9 and a ground plane 31. The two first resonant conductors 1a and 1b constituting the first resonant conductor pair 1 are electrically connected to a common bias conductor 9. The connecting conductors 6a and 6b are electrically connected to the ground plane 31.

[0083] As a result, by using the ground plane 31, it is possible to simplify the circuitry that electrically switches between a state in which a forward bias voltage is applied to the diode 7 and a state in which a reverse bias voltage is applied.

[0084] In the radar reflection switching device 110 of this embodiment, the first resonant conductor pair 1 is repeatedly arranged so that the repetition pitch RP1 in the antenna arrangement direction D2 is constant. i The angle of reflection that does not follow the law of reflection is θ r When the repetition pitch RP1 of the first resonant conductor pair 1 in the antenna arrangement direction D2 is λ g =λ0 / |sinθ r -sinθi The period λ calculated by the formula | g The width W and length L of each of the two first resonant conductors 1a and 1b constituting the first resonant conductor pair 1 are equal to the period λ g , wavelength λ0, incident angle θ i , and the reflection angle θ r Based on this, the phase difference between the radar reflected waves at the two first resonant conductors 1a and 1b is set to be 180°.

[0085] This allows for proper detection of abnormal or retroreflected radar waves.

[0086] Next, a retroreflective metasurface reflector 42B according to a second embodiment will be described. In the following description of this embodiment, the same or similar components as those in the previous embodiment will be denoted by the same reference numerals in the drawings, and their description may be omitted.

[0087] The retroreflective metasurface reflector 42B of the second embodiment shown in FIG. 10 is also capable of electrically switching the reflection characteristics, similar to the first embodiment.

[0088] 10, only one structural unit U1 is shown extracted from the retroreflective metasurface reflector 42B of the second embodiment. Many structural units U1 are repeatedly arranged in both the antenna longitudinal direction D1 and the antenna arrangement direction D2.

[0089] In this embodiment, the first resonant conductor 1a is divided into two in the length direction, constituting a first element 1a1 and a second element 1a2. The first element 1a1 and the second element 1a2 are connected via a diode 7. The diode 7 is a PIN diode, similar to the diode 7 in the retroreflective metasurface reflector 42A of the first embodiment. The diode 7 is arranged so that the second element 1a2 side is connected to the P layer and the first element 1a1 side is connected to the N layer.

[0090] The first element 1a1 constituting the first resonant conductor 1a is connected to the ground plane 31 through a plane connecting via 8. The second element 1a2 is connected to the bias conductor 9 through a bias via .

[0091] Like the first resonant conductor 1a, the first resonant conductor 1b is also divided into two in the length direction to form a first element 1b1 and a second element 1b2. The first element 1b1 and the second element 1b2 are connected via a diode 7. The diode 7 is arranged so that the second element 1b2 side is connected to the P layer and the first element 1b1 side is connected to the N layer.

[0092] The first element 1b1 constituting the first resonant conductor 1b is connected to the ground plane 31 through a plane connecting via 8. The second element 1b2 is connected to the bias conductor 9 through a bias via .

[0093] In this embodiment, each of the first resonant conductors 1a is divided at the center in the longitudinal direction so as to divide its length into approximately two equal parts, and the same is true for the first resonant conductors 1b.

[0094] In this embodiment, consider the case where the voltage source 11 applies a positive voltage between the bias conductor 9 and the ground plane 31. Because the potentials of the second elements 1a2 and 1b2 are higher than the potentials of the first elements 1a1 and 1b1, a forward bias voltage is applied to each of the diodes 7. Therefore, the diode 7 provides electrical continuity between the second element 1a2 and the first element 1a1, and the diode 7 provides electrical continuity between the second element 1b2 and the first element 1b1. The state in which the diode 7 provides electrical continuity between the second element 1b2 and the first element 1b1 is referred to as a connected state. As a result, the effective length L connecting the first resonant conductor 1a, the diode 7, and the first resonant conductor 1b becomes equal to a predetermined length designed to cause retroreflection of incident radar waves, thereby enabling resonance and enabling retroreflection of incident radio waves.

[0095] Conversely, consider the case where the voltage source 11 applies a negative voltage between the bias conductor 9 and the ground plane 31. Because the potentials of the second elements 1a2 and 1b2 become higher than the potentials of the first elements 1a1 and 1b1, a reverse bias voltage is applied to each of the diodes 7. Therefore, the diodes 7 create a non-conductive connection between the second element 1a2 and the first element 1a1, and a non-conductive connection between the second element 1b2 and the first element 1b1. The state in which the diodes 7 create a non-conductive connection between the second element 1b2 and the first element 1b1 is referred to as the interrupted state. As a result, the effective lengths of the first resonant conductors 1a and 1b are halved. In this state, the first resonant conductors 1a and 1b do not substantially resonate when radio waves are incident, so no retroreflection occurs, and only specular reflection occurs.

[0096] In this embodiment as well, by switching the positive and negative sides of the voltage applied to the bias conductor 9, it is possible to easily switch between the presence and absence of retroreflection and change the RCS of the retroreflective metasurface reflector 42B.

[0097] As described above, in the retroreflective metasurface reflector 42B of this embodiment, the first resonant conductor 1a is composed of the first element 1a1 and the second element 1a2. The first element 1a1 and the second element 1a2 are arranged to divide the longitudinal length of the first resonant conductor 1a. The first resonant conductor 1b is composed of the first element 1b1 and the second element 1b2. The first element 1b1 and the second element 1b2 are arranged to divide the longitudinal length of the first resonant conductor 1b. In the first resonant conductor 1a, the diode 7 is arranged to connect the first element 1a1 and the second element 1b2. In the first resonant conductor 1b, the diode 7 is arranged to connect the first element 1b1 and the second element 1b2.

[0098] This makes it possible to switch between a state in which radar waves are reflected / abnormally and a state in which they are not, using a simple configuration in which the diode 7 switches between electrical conduction and non-conduction between the elements that make up the first resonant conductors 1a and 1b.

[0099] In this embodiment, voltage source 11 applies a voltage between first element 1a1 and second element 1a2 and between first element 1b1 and second element 1b2, and is capable of switching the applied voltage between positive and negative. Diode 7 switches between a connected state and a disconnected state by reversing the direction in which voltage is applied to diode 7. Control unit 80 switches the applied voltage of voltage source 11 between positive and negative.

[0100] This allows switching between a state in which a forward bias voltage is applied to the diode 7 and a state in which a reverse bias voltage is applied to the diode 7 by simple voltage control.

[0101] In this embodiment, a plane connection via 8 is formed in the dielectric 32. The plane connection via 8 extends in the thickness direction of the ground plane 31 and connects the ground plane 31 to the first elements 1a1 and 1b1.

[0102] As a result, by using the ground plane 31, it is possible to simplify the circuit that switches between a state in which a forward bias voltage is applied to the diode 7 and a state in which a reverse bias voltage is applied.

[0103] In this embodiment, the retroreflective metasurface reflector 42B includes a bias conductor 9 connected to a voltage source 11 and at least a portion of which is disposed inside the dielectric 32. A bias via 10 is formed in the dielectric 32. The bias via 10 extends in the thickness direction of the ground plane 31 and connects the bias conductor 9 to the second elements 1a2 and 1b2.

[0104] This makes it possible to switch between a state in which a forward bias voltage is applied to the diode 7 and a state in which a reverse bias voltage is applied to the diode 7 with a simple circuit configuration.

[0105] Next, a first modification of the above embodiment will be described.

[0106] The retroreflective metasurface reflectors 42A and 42B can be made retroreflective to achieve anomalous or retroreflection at a specific incident angle, as shown in Figure 9, thereby increasing the RCS. However, if radio waves are incident at an angle that deviates somewhat from the designed incident angle, the RCS decreases.

[0107] If the retroreflection condition (1) above can be satisfied for multiple incident angles, it is believed that extraordinary / retroreflection can be achieved over a wide range of angles. However, it is difficult to realize a structure that can resonate with multiple incident angles in a single structural unit U1.

[0108] Taking this into consideration, in the first modified example shown in Figure 11, multiple structural units U1 and U2 that can resonate at different incident angles are arranged alternately in the antenna alignment direction D2. Figure 11 is a schematic diagram of a modified retroreflective metasurface reflector viewed from the thickness direction. In Figure 11, only one row of structural units U1 and U2 is drawn aligned in the antenna alignment direction D2, but in reality, many such rows are aligned in the antenna longitudinal direction D1.

[0109] The two structural units U1 and U2 have the same configuration except for the different dimensions of the paired resonant conductors. Hereinafter, the resonant conductor pair in the structural unit U2 will be referred to as the second resonant conductor pair 2, and the resonant conductors included in the second resonant conductor pair 2 will be referred to as the second resonant conductors 2a and 2b. Similar to the first resonant conductors 1a and 1b shown in Figures 8 and 10, diodes are electrically connected to the second resonant conductors 2a and 2b. The diodes connected to the second resonant conductors 2a and 2b correspond to second electrical switching units.

[0110] For example, in the structural unit U1, the combination of dimensions indicated by the circles in the graph of FIG. 7 can be applied to the first resonant conductors 1a and 1b, and in the structural unit U2, the combination of dimensions indicated by the triangles can be applied to the second resonant conductors 2a and 2b. Although not specifically shown in the graph of FIG. 7, a phase difference of approximately 180° can also be achieved by the combination of dimensions indicated by the triangles. In the example of the graph of FIG. 7, the length of one second resonant conductor 2a is 2.0 mm, and the length of the other second resonant conductor 2b is 2.8 mm. Since the two structural units U1 and U2 are repeatedly arranged in the antenna arrangement direction D2, the repetition pitch RP1 of the first resonant conductor pair 1 and the repetition pitch RP1 of the second resonant conductor pair 2 both have the period λ obtained by the above-mentioned formula (2). g It is twice as much.

[0111] A common bias conductor 9 is disposed so as to penetrate the structural units U1 and U2 in the antenna arrangement direction D2. In response to a command from the control unit 80, the voltage source 11 simultaneously switches between positive and negative bias voltages applied to both the diodes 7 of the first resonant conductors 1a and 1b and the diodes of the second resonant conductors 2a and 2b.

[0112] The principle will be explained below. When retroreflection occurs in the metasurface reflector of FIG. 4 in which only the first resonant conductor pair 1 is repeatedly arranged, θ i =-θ r Therefore, the following equation (3) holds true.

number

[0113] The period λ g If we introduce a periodicity that is n times larger than the normal, then we will have additional angles of extraordinary or retroreflection that satisfy equation (4) below.

number

[0114] In Figure 12, θ i= 60°, N=2, θ r1 11. The RCS characteristics of the configuration corresponding to FIG. 11 are shown when the length L and width W of the first resonant conductors 1a and 1b and the second resonant conductors 2a and 2b are set as follows: θ = -60°, n = 2, a = 1. The RCS characteristics of the configuration corresponding to FIG. 11 are shown by a solid line, and the RCS characteristics of a simple metal plate are shown by a dashed line. The horizontal axis represents the incident angle θ i The vertical axis represents the magnitude of RCS. In this graph, the incident angle θ i In addition to when the angle is near 60°, retroreflection occurs and the RCS increases when the angle is near 26°. i can be made wider-angle.

[0115] The arrangement of the structural units U1 and U2 described in this modification can be applied to all four embodiments described in this specification, as well as to the second modification described below.

[0116] As described above, the retroreflective metasurface reflector according to the first modification of FIG. 11 includes a second resonant conductor pair 2 and a diode. The second resonant conductor pair 2 includes two second resonant conductors 2a and 2b. The two second resonant conductors 2a and 2b are elongated and parallel to each other. The second resonant conductors 2a and 2b are disposed on opposite sides of the ground plane 31 across the dielectric 32. The two second resonant conductors 2a and 2b are spaced apart from each other in the antenna alignment direction D2. The shapes of the two second resonant conductors 2a and 2b are different from each other. The diode is electrically connected to the second resonant conductors 2a and 2b and is switchable between a connected state and a disconnected state. The control unit 80 switches the diode connected to the second resonant conductors 2a and 2b between a connected state and a disconnected state. The longitudinal direction of each of the second resonant conductors 2a and 2b is parallel to the longitudinal direction of the first resonant conductors 1a and 1b. The combination of lengths L of the two second resonant conductors 2a, 2b constituting the second resonant conductor pair 2 is different from the combination of lengths L of the two first resonant conductors 1b constituting the first resonant conductor pair 1. Units including the first resonant conductor pair 1 and the second resonant conductor pair 2 are repeatedly arranged at a constant pitch RP1 in the antenna arranging direction D2. The unit including the first resonant conductor pair 1 and the second resonant conductor pair 2 is a unit consisting of a combination of two structural units U1, U2.

[0117] This makes it possible to achieve retroreflection at a plurality of angles of incidence with a simple configuration.

[0118] Next, a second modified example will be described.

[0119] In the second modified example shown in Fig. 13, three mutually different structural units U1, U2, and U3 are repeatedly arranged in the antenna arranging direction D2. The configuration of the structural unit U3 is the same as that of the structural unit U1, except that the dimensions of the paired resonant conductors are different, similar to the aforementioned structural unit U2. Hereinafter, the resonant conductor pair in the structural unit U3 will be referred to as the third resonant conductor pair 3, and the resonant conductors included in the third resonant conductor pair 3 will be referred to as the third resonant conductors 3a and 3b. Diodes are also electrically connected to these third resonant conductors 3a and 3b.

[0120] A unit including the first resonant conductor pair 1, the second resonant conductor pair 2, and the third resonant conductor pair 3 is repeatedly arranged at a constant pitch RP1 in the antenna arranging direction D2. The unit including the first resonant conductor pair 1, the second resonant conductor pair 2, and the third resonant conductor pair 3 is a unit consisting of a combination of three structural units U1, U2, and U3. In this way, the repetition pitch RP1 in the antenna arranging direction D2 at which the first resonant conductor pair 1, etc. are arranged is determined by the period λ obtained by Equation (2): g Four or more structural units may be repeatedly arranged.

[0121] Next, a common technical concept will be described for a third embodiment and a fourth embodiment, which will be described later, in which the first resonant conductor pairs 1 are arranged in three directions.

[0122] As mentioned above, to cause retroreflection at the boundary surface where the first resonant conductor pairs 1 are repeatedly arranged, the incident wave must be TE polarized and the incident plane PL1 must be perpendicular to the antenna longitudinal direction D1, which significantly reduces the degree of freedom of the incident wave that causes retroreflection.

[0123] To solve this problem, it is possible to introduce a rotational symmetry axis parallel to the normal line V1 of the boundary surface. Here, as shown in Figure 14, the resonator structure is periodically arranged using a hexagonal lattice. Therefore, in the configuration of Figure 14, the unit cell C1 is a regular hexagon. The reason for using a hexagonal lattice is that the maximum rotational order is 6, out of the possible rotational orders of 2, 3, 4, and 6 that can be taken by a crystal structure.

[0124] In the example of FIG. 14, the multiple first resonant conductor pairs 1 constituting the conductor pattern 33 can be divided into three groups. The antenna arrangement directions D2 of the respective groups differ by 60°. Similarly, the antenna longitudinal directions D1 of the respective groups differ by 60°. Each structural unit U1 includes two adjacent unit cells C1, but the direction in which the two unit cells C1 are adjacent differs depending on the group. The period λ applied to the first resonant conductor pairs 1 of each group is g are equal to each other.

[0125] The first resonant conductors 1a and 1b constituting each first resonant conductor pair 1 are arranged offset relative to each other in the antenna longitudinal direction D1. Due to the geometrical properties of the hexagonal lattice, the lattices are arranged substantially side by side in the antenna aligning direction D2 while partially overlapping in the antenna aligning direction D2. Therefore, the repetition pitch RP1 of the structural units U1 in the antenna aligning direction D2 is smaller than the dimension of the structural units U1 in the antenna aligning direction D2.

[0126] With this configuration, there are three incident surfaces that generate anomalous or retroreflection. Furthermore, the rotationally symmetric arrangement of the resonator structure applies rotational symmetry to the incident electromagnetic field components as well. Therefore, the degree of freedom for TE polarization or TM polarization of the incident wave can be increased at the same time. As a result, even with a resonator that has a structure that resonates only with TE polarization or TM polarization, the improved degree of freedom for polarization allows anomalous / retroreflection to occur for both polarizations. In other words, it is possible to widen the rotation angle of anomalous or retroreflection.

[0127] Next, a third embodiment and a fourth embodiment will be described.

[0128] The retroreflective metasurface reflector 42C of the third embodiment shown in FIG. 15 is a modified version of the retroreflective metasurface reflector 42A of the first embodiment shown in FIG. 8 , which employs the hexagonal lattice described in FIG. 14 . Each hexagonal lattice corresponds to a unit cell C1, and a combination of two adjacent unit cells C1 corresponds to one structural unit U1. Focusing on one hexagonal lattice, three first resonant conductors 1a or 1b are arranged to correspond to each side of an equilateral triangle connecting every other vertex. In this embodiment, the connecting conductors 6 extend radially from every other vertex of the hexagonal lattice and connect to the first resonant conductors 1a and 1b via diodes 7. The bias conductor 9 has a honeycomb structure to electrically connect all of the first resonant conductors 1a and 1b via bias vias 10. Voltage control by a single voltage source 11 switches between the connected and disconnected states of all of the diodes 7 belonging to the three groups.

[0129] The retroreflective metasurface reflector 42D of the fourth embodiment shown in Fig. 16 is a modification of the retroreflective metasurface reflector 42B of the second embodiment shown in Fig. 10, in which the hexagonal lattice described in Fig. 14 is applied. In this embodiment, as in the third embodiment, the bias conductor 9 generally has a honeycomb structure.

[0130] As described above, the retroreflective metasurface reflectors 42C and 42D of the third and fourth embodiments include three groups of resonant conductors. Each group includes a first resonant conductor pair 1. The longitudinal directions of the first resonant conductors 1a and 1b constituting the first resonant conductor pair 1 are different among the three groups. In other words, the longitudinal direction of the first resonant conductors 1a and 1b is the antenna longitudinal direction D1.

[0131] This relaxes the conditions for causing retroreflection or abnormal reflection, such as the orientation of the incident plane PL1 of the radar wave, making it easier to detect.

[0132] As described above, in the retroreflective metasurface reflectors 42C and 42D of the third and fourth embodiments, the antenna longitudinal direction D1 for each of the three groups differs by an angle of 60° from the antenna longitudinal direction D1 for either of the other two groups.

[0133] This allows for retroreflection or anomalous reflection of radar waves to occur in various orientations of the plane of incidence PL1.

[0134] The preferred embodiments and modifications of the present disclosure have been described above, but the above configurations can be modified, for example, as follows. A single modification may be made, or multiple modifications may be made in any combination.

[0135] In the above-described embodiment, the retroreflective metasurface reflectors 42A to 42D are fixed to the surface of the base member 41. Alternatively, if the retroreflective metasurface reflectors 42A to 42D have sufficient mechanical strength, the base member 41 need not be provided. In this case, the retroreflective metasurface reflectors 42A to 42D are provided directly on the surface of the moving object. If the material of the base member 41 is a metal such as aluminum or copper, or a good conductor such as a composite material containing carbon fiber, the base member 41 may also serve as the ground plane 31. In this case, the ground plane 31 is read as the base member 41.

[0136] Instead of the diode 7, for example, a mechanical switch, a shape memory alloy, or the like may be used as the electrical switching unit that switches between the connected state and the disconnected state.

[0137] In the above-described embodiment, the radar reflection switching device 110 is provided so as to be integrated into the surface of the automobile. Alternatively, for example, a special convex portion may be provided on the surface of the moving object, and various retroreflective metasurface reflectors may be provided on the surface of this convex portion.

[0138] Regarding retroreflection, all of the above examples assume that the propagation diffraction order N is 2. However, even when N is 3 or greater, extraordinary or retroreflection can be achieved by periodically arranging N unit cells with the required diffraction order, each of which has a phase difference of 2π per period. However, when N is 3 or greater, larger diffraction orders are generated than when N is 2. Therefore, in order to generate strong retroreflection, it is desirable to have more than two unit cells C1 constituting the structural unit U1.

[0139] The phase difference between the two unit cells C1 constituting the structural unit U1 is not limited to the MIM structure described above, but may be realized, for example, by a well-known mushroom structure. The phase difference between the two unit cells C1 is not limited to a method directly using the phase difference due to the difference in resonant frequency of the resonator structure, but may also be realized using a geometric phase resulting from the anisotropy of the resonant characteristics within the metasurface, or a phase difference due to the PB phase. The PB phase refers to the well-known Pancharatnam-Berry phase. When using a geometric phase, care should be taken because the reflected wave is subject to spin polarization.

[0140] The retroreflective metasurface reflectors 42A to 42D are not limited to a configuration in which all periodic structures are arranged on one plate. For example, a retroreflective metasurface reflector can be configured by arranging multiple reflector elements in a matrix.

[0141] In the above example, the resonant frequency of the resonator corresponding to the structural unit U1 is fixed by the structure. Alternatively, the resonant frequency can be made adjustable by using an active element such as a diode or an FET.

[0142] The above-described radar reflection switching device can also be mounted on moving objects other than automobiles, such as aircraft, ships, flying vehicles, and the like.

[0143] The functions of the elements disclosed herein can be performed using circuits or processing circuitry, including general-purpose processors, special-purpose processors, integrated circuits, ASICs (Application Specific Integrated Circuits), conventional circuits, and / or combinations thereof, configured or programmed to perform the disclosed functions. A processor is considered a processing circuit or circuitry because it includes transistors and other circuitry. In this disclosure, a circuit, unit, or means is hardware that performs the recited functions or hardware that is programmed to perform the recited functions. The hardware may be hardware disclosed herein or other known hardware that is programmed or configured to perform the recited functions. Where the hardware is a processor, which is considered a type of circuit, the circuit, means, or unit is a combination of hardware and software, and the software is used to configure the hardware and / or processor. [Explanation of symbols]

[0144] 1 First resonant conductor pair 1a, 1b First resonant conductor 1a1, 1a2 Elements of the first resonant conductor 1a 1b1, 1b2 Elements of the first resonant conductor 1b 6a, 6b Connecting conductor 7 Diode (first electrical switching unit, second electrical switching unit) 8 Plane Connection Vias 9 Bias conductor 10 Bias Vias 11 Voltage Source 31 Ground plane (plane conductor) 32 Dielectric 80 Control Unit 110 Radar reflection switching device (radar reflection cross section switching device) θ i angle of incidence θ r reflection angle RP1 Repeat Pitch

Claims

1. A radar cross section reflection switching device provided on a moving object, a plane conductor formed in a planar shape; a dielectric disposed in contact with the plane conductor; a first resonant conductor pair including two first resonant conductors having different shapes, each of which is formed elongated and parallel to each other, each of which is disposed on the opposite side of the plane conductor with the dielectric therebetween, and each of which is spaced apart in a direction perpendicular to the longitudinal direction of the first resonant conductor; a first electrical switching unit electrically connected to the first resonant conductor and switchable between a connected state and a disconnected state; a control unit that switches the first electrical switching unit between the connected state and the disconnected state; A radar cross section switching device comprising:

2. 2. The radar cross section switching device according to claim 1, a voltage source that applies a voltage to the first electrical switching unit and is capable of switching the applied voltage between positive and negative; the first electrical switching unit switches between the connected state and the disconnected state by reversing a direction in which a voltage is applied to the first electrical switching unit; The control unit switches the applied voltage of the voltage source between positive and negative.

3. 2. The radar cross section switching device according to claim 1, a connecting conductor disposed on the opposite side of the plane conductor with the dielectric interposed therebetween; the first electrical switching units are disposed at both longitudinal ends of the first resonant conductors, an end of the first resonant conductor and the connecting conductor are connected via the first electrical switching unit; and

4. 4. The radar cross section switching device according to claim 3, a voltage source that applies a voltage to the first electrical switching unit and is capable of switching the applied voltage between positive and negative; a bias conductor electrically connecting the voltage source and the first resonant conductor; Equipped with the first electrical switching unit switches between the connected state and the disconnected state by reversing a direction in which a voltage is applied to the first electrical switching unit; The control unit switches the applied voltage of the voltage source between positive and negative.

5. 5. The radar cross section switching device according to claim 4, a bias via and a plane connection via are formed in the dielectric; the bias via extends in a thickness direction of the plane conductor to connect the first resonant conductor and the bias conductor; The plane connection via extends in a thickness direction of the plane conductor to connect the connection conductor and the plane conductor.

6. 5. The radar cross section switching device according to claim 4, the bias conductor is formed to be elongated in a direction intersecting the longitudinal direction of the first resonant conductor, At least a portion of the bias conductor is disposed within the dielectric; a bias via is formed in the dielectric; The bias via extends in a thickness direction of the plane conductor and connects the bias conductor and the first resonant conductor.

7. 5. The radar cross section switching device according to claim 4, the bias conductor is electrically connected to the voltage source and is at least partially disposed within the dielectric; the first electrical switching units arranged at both longitudinal ends of each of the first resonant conductors are connected to the first resonant conductors with polarities opposite to each other; the voltage source applies a voltage between the bias conductor and the plane conductor; the two first resonant conductors constituting the first resonant conductor pair are electrically connected to a common bias conductor; The connecting conductor is electrically connected to the plane conductor.

8. 2. The radar cross section switching device according to claim 1, each of the first resonant conductors is composed of a first element and a second element that are arranged to divide the length of the first resonant conductor in the longitudinal direction; The radar cross section switching device, wherein the first electrical switching unit is arranged to be connected to the first element and the second element.

9. 9. The radar cross section switching device according to claim 8, a voltage source that applies a voltage between the first element and the second element and is capable of switching the applied voltage between positive and negative; the first electrical switching unit switches between the connected state and the disconnected state by reversing a direction in which a voltage is applied to the first electrical switching unit; The control unit switches the applied voltage of the voltage source between positive and negative.

10. 10. The radar cross section switching device according to claim 9, a plane connection via formed in the dielectric; The plane connection via extends in a thickness direction of the plane conductor to connect the plane conductor and the first element.

11. 10. The radar cross section switching device according to claim 9, a bias conductor connected to the voltage source and at least a portion of which is disposed within the dielectric; a bias via is formed in the dielectric; The bias via extends in a thickness direction of the plane conductor and connects the bias conductor and the second element.

12. 2. The radar cross section switching device according to claim 1, the first resonant conductor pairs are repeatedly arranged at a constant pitch in a conductor width direction, which is a direction perpendicular to the longitudinal direction of the first resonant conductors; The radar wavelength is λ 0 , the assumed radar incident angle is θ i The angle of reflection that does not follow the law of reflection is θ r When the repetition pitch of the first resonant conductor pair in the conductor width direction is λ g = λ 0 / |sinθ r -sinθ i The period λ calculated by the formula g is equal to or an integer multiple of The width and length of each of the two first resonant conductors constituting the first resonant conductor pair are set to the period λ g , the radar wavelength λ 0 , the incident angle θ i , and the reflection angle θ r The radar cross section switching device is configured so that the phase difference between the radar reflected waves at the two first resonant conductors is 180° based on the above.

13. 2. The radar cross section switching device according to claim 1, a second resonant conductor pair including two second resonant conductors having different shapes, each of which is formed elongated and parallel to each other, each of which is disposed on the opposite side of the plane conductor with the dielectric therebetween, and which is spaced apart in a direction perpendicular to the longitudinal direction; a second electrical switching unit electrically connected to the second resonant conductor and switchable between a connected state and a disconnected state; Equipped with the control unit switches the second electrical switching unit between the connected state and the disconnected state, a longitudinal direction of each of the second resonant conductors is parallel to a longitudinal direction of the first resonant conductor; the shapes of the two second resonant conductors constituting the second resonant conductor pair are different from the shapes of the two first resonant conductors constituting the first resonant conductor pair, a radar cross section switching device in which units including the first resonant conductor pair and the second resonant conductor pair are repeatedly arranged at a constant pitch in a conductor width direction, which is a direction perpendicular to the longitudinal direction of the first resonant conductors.

14. 14. The radar cross section switching device according to claim 13, The radar wavelength is λ 0 , the assumed radar incident angle is θ i The angle of reflection that does not follow the law of reflection is θ r When the repeat pitch of the unit in the conductor width direction is λ g = λ 0 / |sinθ r -sinθ i The period λ calculated by the formula g is an integer multiple of The period λ g , the radar wavelength λ 0 , the incident angle θ i , and the reflection angle θ r the width and length of each of the two first resonant conductors constituting the first resonant conductor pair are determined so that the phase difference between the radar reflected waves at the two first resonant conductors is 180°, and the width and length of each of the two second resonant conductors constituting the second resonant conductor pair are determined so that the phase difference between the radar reflected waves at the two second resonant conductors is 180°, a radar cross section switching device, wherein the widths and lengths of the first resonant conductors and the second resonant conductors are determined so that a combination of phases of radar reflected waves at the two first resonant conductors is different from a combination of phases of radar reflected waves at the two second resonant conductors.

15. 13. The radar cross section switching device according to claim 12, three groups of resonant conductors; each of the groups includes the first resonant conductor pair; a radar cross section switching device, wherein the longitudinal directions of the first resonant conductors constituting the first resonant conductor pairs are different among the three groups;

16. 16. The radar cross section switching device according to claim 15, A radar cross section switching device, wherein the longitudinal direction of the first resonant conductors belonging to each of the three groups differs by an angle of 60° from the longitudinal direction of the first resonant conductors belonging to either of the other two groups.

17. A radar cross section switching method using a radar cross section switching device provided on a moving object, comprising: The radar cross section switching device a plane conductor formed in a planar shape; a dielectric disposed in contact with the plane conductor; a first resonant conductor pair including two first resonant conductors having different shapes, each of which is formed elongated and parallel to each other, each of which is disposed on the opposite side of the plane conductor with the dielectric therebetween, and each of which is spaced apart in a direction perpendicular to the longitudinal direction of the first resonant conductor; a first electrical switching unit electrically connected to the first resonant conductor and switchable between a connected state and a disconnected state; a connecting conductor disposed on the opposite side of the plane conductor with the dielectric interposed therebetween; a control unit that switches the first electrical switching unit between the connected state and the disconnected state; Equipped with the first electrical switching units are disposed at both longitudinal ends of the first resonant conductors, an end of the first resonant conductor and the connecting conductor are connected via the first electrical switching unit; The radar cross section switching method includes: The control unit switches the first electrical switching unit to the connected state, thereby electrically conducting the first resonant conductor and the connecting conductor, thereby increasing the proportion of specular reflection of the radar; a radar cross section switching method, wherein the control unit switches the first electrical switching unit to the cut-off state, thereby electrically disconnecting the first resonant conductor and the connecting conductor and reducing the proportion of specular reflection of the radar.

18. A radar cross section switching method using a radar cross section switching device provided on a moving object, comprising: The radar cross section switching device a plane conductor formed in a planar shape; a dielectric disposed in contact with the plane conductor; a first resonant conductor pair including two first resonant conductors having different shapes, each of which is formed elongated and parallel to each other, each of which is disposed on the opposite side of the plane conductor with the dielectric therebetween, and each of which is spaced apart in a direction perpendicular to the longitudinal direction of the first resonant conductor; a first electrical switching unit electrically connected to the first resonant conductor and switchable between a connected state and a disconnected state; a control unit that switches the first electrical switching unit between the connected state and the disconnected state; Equipped with each of the first resonant conductors is composed of a first element and a second element that are arranged to divide the length of the first resonant conductor in the longitudinal direction; the first electrical switching unit is disposed in connection with the first element and the second element; The radar cross section switching method includes: The control unit switches the first electrical switching unit to the connected state, thereby electrically connecting the first element and the second element to reduce the proportion of specular reflection of the radar; a radar cross section switching method, wherein the control unit switches the first electrical switching unit to the cut-off state, thereby electrically disconnecting the first element and the second element and increasing the proportion of specular reflection of the radar.

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