Radio wave lens, radio wave lens device, and radar apparatus

Abstract

Provided are: a radio wave lens that is less susceptible to adhesion of dust on one surface and makes it possible to sufficiently reduce reflection; a radio wave lens device; and a radar apparatus.　This radio wave lens has a first surface, a second surface, and an optical axis penetrating through the first surface and the second surface. The radio wave lens has, on the first surface, recessed portions or protruding portions provided concentrically or provided symmetrically about the optical axis in plan view, the depths of the recessed portions or the heights of the protruding portions being set according to the distances from the optical axis.

Description

Radio wave lens, radio wave lens device, and radar device

[0001] The present disclosure relates to a radio wave lens, a radio wave lens device, and a radar device.

[0002] A conventional dielectric lens has a dielectric body and a matching layer formed on the surface of the dielectric body. The matching layer has a groove of a predetermined depth formed in a spiral shape on the surface of the dielectric body. The groove is filled with a filler having a refractive index of approximately 1, and the depth of the groove is set to λ / 4 where λ is the wavelength of the target radio wave (see, for example, Patent Document 1).

[0003] Japanese Patent Application Publication No. 11-355035

[0004] In conventional dielectric lenses (radio lenses), the grooves are filled with the filler, which prevents dust and other particles from accumulating in the grooves. However, in radio lenses, the provision of uniform λ / 4-depth grooves on both sides of the lens and the filling of the grooves with the filler increase the manufacturing difficulty and lead to increased costs.

[0005] Therefore, an object of the present invention is to provide a radio wave lens, a radio wave lens device, and a radar device that are resistant to dust adhesion on one surface and can sufficiently reduce reflection.

[0006] A radio wave lens according to an embodiment of the present disclosure is a radio wave lens having a first surface, a second surface, and an optical axis penetrating the first surface and the second surface, and has recesses or protrusions on the first surface that are arranged concentrically or symmetrically around the optical axis in a plan view, and the depth of the recesses or the height of the protrusions are set according to the distance from the optical axis.

[0007] It is possible to provide a radio wave lens, a radio wave lens device, and a radar device that are resistant to dust adhesion on one surface and can sufficiently reduce reflection.

[0008] 1 is a diagram illustrating an example of the configuration of a radar device according to an embodiment. FIG. 1 is a diagram illustrating an example of the configuration of a radar device according to an embodiment. FIG. 2 is a diagram illustrating a cut surface obtained by cutting a radio wave lens in a YZ plane including the optical axis of the radio wave lens of the radar device according to an embodiment. FIG. 3 is a diagram illustrating an example of a reason why multiple reflections occur in a comparative radio wave lens. FIG. 4 is a diagram illustrating an example of a reason why multiple reflections occur in a comparative radio wave lens. FIG. 5 is a diagram illustrating an example of a reason why multiple reflections occur in a comparative radio wave lens. FIG. 6 is a diagram illustrating an example of a principle for reducing multiple reflections in a radio wave lens according to an embodiment. FIG. 7 is a diagram illustrating an example of a principle for reducing multiple reflections in a radio wave lens according to an embodiment. FIG. 8 is a diagram illustrating an example of a principle for reducing multiple reflections in a radio wave lens according to an embodiment. FIG. 9 is a diagram illustrating a thickness t etc. of a radio wave lens according to an embodiment. FIG. 10 is a diagram illustrating an example of the output strength of a radar detection signal relative to the distance between the radar device according to an embodiment and a measurement object. FIG. 11 is a diagram illustrating an example of the output strength of a radar detection signal relative to the distance between the comparative radar device and a measurement object. FIG. 12 is a diagram illustrating an example of the output strength of a radar detection signal relative to the distance between the radar device according to an embodiment and a measurement object. Fig. 1 is a diagram showing an example of the output strength of a radar detection signal with respect to the distance between a radar device for comparison and a measurement object. Fig. 2 is a diagram showing an example of a simulation result of the gain of a transmitting and receiving antenna of a radar device of an embodiment. Fig. 3 is a diagram showing an example of a simulation result of the gain of a transmitting and receiving antenna of a radar device for comparison. Fig. 4 is a diagram showing an example of the configuration of a radio wave lens of a modified example of an embodiment. Fig. 5 is a diagram showing an example of the configuration of a radio wave lens of a modified example of an embodiment.

[0009] Hereinafter, embodiments to which the radio wave lens, radio wave lens device, and radar device of the present disclosure are applied will be described.

[0010] 1A, 1B, and 1C are diagrams showing a radar device 100 according to an embodiment. Fig. 1A is a perspective view, Fig. 1B is a diagram showing a cross section taken along the line A-A in Fig. 1A, and Fig. 1C is a front view. Fig. 1D is a diagram showing a cross section obtained by cutting the radio wave lens 130 of the radar device 100 along a YZ plane including the optical axis of the radio wave lens 130.

[0011] In the following, the XYZ coordinate system will be defined and explained. For convenience of explanation, the -Z direction side will be referred to as the lower side or bottom, and the +Z direction side will be referred to as the upper side or top, but this does not represent a universal up-down relationship. Also, viewing from the XZ plane will be referred to as a planar view. Also, viewing an opening from the XZ plane will be referred to as an opening plane view.

[0012] The radar device 100 includes a substrate 101, a waveguide 110, a transmitting / receiving unit 120, and a radio wave lens 130. The radar device 100 excluding the substrate 101 and the transmitting / receiving unit 120 constitutes a radio wave lens device 100A of the embodiment. The radio wave lens device 100A includes the waveguide 110 and the radio wave lens 130.

[0013] The radar device 100 is a device that transmits and receives radio waves, and narrows the radiation pattern of the transmitted waves using a radio wave lens 130, while focusing the received radio waves using a lens. The radar device 100 also includes a radio wave lens 130 that is designed to reduce multiple reflected waves generated inside the radar device 100 due to multiple reflections.

[0014] As an example, such a radar device 100 can be used as a radar device that receives a reflected wave from a target object after transmitting a transmitted wave and measures the distance to the target object. The distance to the target object can be measured based on the round-trip time between transmitting a radio wave as a transmitted wave and receiving the reflected wave. Generally, in a radar device that measures the distance to a target object, the closer the target object is, the lower the detection accuracy becomes due to the effects of multiple reflections. This is because the closer the target object is, the shorter the round-trip time becomes, making it difficult to distinguish between received waves that are not multiple reflections and multiple reflected waves. When detection accuracy decreases, the shortest detectable distance (shortest detection distance) becomes longer. The radar device 100 of this embodiment solves this problem.

[0015] A multiple-reflected wave is a radio wave that is reflected two or more times within the space surrounded by the substrate 101, the waveguide 110, the transmitting / receiving unit 120, and the radio wave lens 130. For radio waves transmitted in the +Y direction from the transmitting / receiving unit 120, multiple-reflected waves may occur, for example, by being reflected by the surface on the -Y direction side of the radio wave lens 130 without passing through the radio wave lens 130. For radio waves that have passed through the radio wave lens 130 in the -Y direction, multiple-reflected waves may occur, for example, by being reflected by the inner wall surface 110A of the waveguide 110 without directly reaching the transmitting / receiving unit 120.

[0016] The radio waves transmitted and received by the radar device 100 are, for example, radio waves in the millimeter wave band. Millimeter waves are radio waves in the frequency band of 30 GHz to 300 GHz, and behave almost identically to light. However, the radio waves transmitted and received by the radar device 100 may be radio waves with frequencies belonging to a band other than the millimeter wave band.

[0017] <Configuration of substrate 101> The substrate 101 is a substrate on which the transceiver unit 120 is mounted, and may be, for example, a wiring substrate conforming to the FR-4 (Flame Retardant type 4) standard. The substrate 101 is fixed to the −Y direction side of the waveguide 110.

[0018] <Configuration of Waveguide 110> The waveguide 110 is, for example, a cylindrical, hollow circular waveguide. The waveguide 110 has an opening 111, an opening 111A, an opening 112, an opening 112A, an inner wall surface 110A, and an attachment portion 115. The interior of the waveguide 110 is a waveguide through which radio waves propagate. The inner wall surface 110A is an example of a first inner wall surface, the opening 111 is an example of a first opening, and the opening 112 is an example of a second opening. The opening 111A is located closer to the opening 112 than the opening 111, and the opening 112A is located closer to the opening 111 than the opening 112. The centers of the openings 111, 111A, 112, and 112A are aligned when viewed from the opening plane. The +Y direction is an example of the radiation direction of the transmitting antenna 120Tx of the transceiver unit 120.

[0019] 1A, 1B, 1C, and 2A, the origin of the XYZ coordinates coincides with the center of the opening 111, and the central axis C of the waveguide 110 coincides with the Y axis. The central axis C also coincides with the optical axis of the radio wave lens 130. In the figures, the central axis C and the Y axis are shown shifted from each other to make them easier to see.

[0020] Inner wall surface 110A is the inner wall surface of cylindrical hollow waveguide 110. As an example, inner wall surface 110A has a generally truncated cone shape that widens toward the +Y direction between openings 111A and 112A. Inner wall surface 110A has a larger diameter on the opening 111 side than opening 111A, and the diameter is constant between openings 112A and 112A.

[0021] The opening 111 is an opening located at the end of the waveguide 110 on the -Y direction side. The opening 111 is circular in an opening plan view. The opening 111A is located closer to the opening 112 than the opening 111, and is circular in an opening plan view. The opening 111A is smaller than the openings 111, 112, and 112A, and is an opening that surrounds the transmitting antenna 120Tx and the receiving antenna 120Rx in an opening plan view.

[0022] Opening 112 is an opening located at the end of waveguide 110 on the +Y direction side. The section that functions as waveguide 110 through which radio waves propagate is the section between openings 111 and 112.

[0023] Opening 112 has a circular shape when viewed from the top. Opening 112A is located closer to opening 111 than opening 112 and has a circular shape when viewed from the top. The diameter of opening 112 is, for example, equal to the diameter of opening 112A and larger than the diameters of openings 111 and 111A. Radio wave lens 130 is attached to opening 112 by attachment portion 117.

[0024] The mounting portion 115 is a portion that extends outward in a plan view at the end of the waveguide 110 on the -Y direction side, and has, for example, a square outer edge in a plan view. The mounting portion 115 is provided to mount the substrate 101 to the waveguide 110. The outer edge of the mounting portion 115 in a plan view is held by a frame portion 105B of the cover 105 that covers the back side (-Y direction side) of the substrate 101. The mounting portion 115 is made of resin, for example.

[0025] The mounting portion 117 is a frame-shaped member that mounts the radio wave lens 130 to the waveguide 110 at the end of the waveguide 110 on the +Y direction side. The mounting portion 117 has an annular shape in a plan view, is fitted into the outer peripheral surface of the waveguide 110 on the +Y direction side, and holds the radio wave lens 130 at a position on the +Y direction side of the opening 112. When the radio wave lens 130 is held by the mounting portion 117, the optical axis of the radio wave lens 130 coincides with the central axis C of the waveguide 110. The mounting portion 117 is made of resin, for example.

[0026] With radio wave lens 130 attached to waveguide 110 as described above by attachment portion 117, the focal point of radio wave lens 130 is located at the center of opening 111 as viewed from the plane of the opening. In other words, the length of waveguide 110 in the extension direction of central axis C is set so that the focal point of radio wave lens 130 is located on the plane of opening 111.

[0027] <Configuration of Transmitter / Receiver 120> The transmitter / receiver 120 is mounted on the surface on the +Y direction side of the substrate 101. The transmitter / receiver 120 is an example of an integrated circuit chip. The transmitter / receiver 120 includes a substrate 121, a transmitting antenna 120Tx, and a receiving antenna 120Rx. The substrate 121 is smaller than the substrate 101 in a plan view and has a square shape, for example. The substrate 121 is provided so as to be located at the center of the opening 111 in a plan view, and more specifically, the substrate 121 is disposed so that the center of the substrate 121 in a plan view is located on the central axis C. Furthermore, the position in the Y direction of the surface on the +Y direction side of the substrate 121 coincides with the position in the Y direction of the opening 111.

[0028] The transmitting antenna 120Tx and the receiving antenna 120Rx are provided on the surface of the substrate 121 on the +Y direction side, with a gap in the Z direction. The transmitting antenna 120Tx and the receiving antenna 120Rx are, for example, antennas of the same shape and size. The transmitting antenna 120Tx transmits radio waves via the waveguide 110, and the receiving antenna 120Rx receives radio waves via the waveguide 110.

[0029] The transmitting antenna 120Tx and the receiving antenna 120Rx are arranged so as to be point-symmetrical with respect to the central axis C in a plan view. Viewing the transmitting antenna 120Tx and the receiving antenna 120Rx in a plan view is synonymous with viewing the transmitting antenna 120Tx and the receiving antenna 120Rx from the opening surface of the opening 111 (plan view).

[0030] The transmitting antenna 120Tx and the receiving antenna 120Rx being point-symmetric with respect to the central axis C in a planar view means that the center of the transmitting antenna 120Tx in a planar view and the center of the receiving antenna 120Rx in a planar view are arranged point-symmetric with respect to the central axis C in a planar view. The center of the transmitting antenna 120Tx in a planar view and the center of the receiving antenna 120Rx in a planar view are both located on the Z axis. Because the central axis C coincides with the optical axis of the radio wave lens 130, the transmitting antenna 120Tx and the receiving antenna 120Rx are arranged offset from the optical axis of the radio wave lens 130.

[0031] Furthermore, the center of the transmitting antenna 120Tx in a planar view and the center of the receiving antenna 120Rx in a planar view are both located on the Z axis, and are arranged so as to be point-symmetrical with respect to the central axis C in a planar view. Therefore, on a cross section obtained by cutting the waveguide 110 in the YZ plane including the optical axis of the radio wave lens 130, the transmitting antenna 120Tx and the receiving antenna 120Rx are arranged so as to be point-symmetrical with respect to the central axis C.

[0032] Since it is not possible to place both the transmitting antenna 120Tx and the receiving antenna 120Rx on the central axis C (the optical axis of the radio wave lens 130), they are placed in this manner to align the transmission and reception characteristics of the transmitting antenna 120Tx and the receiving antenna 120Rx. The transmitting antenna 120Tx and the receiving antenna 120Rx can be realized by, for example, a loop antenna, a patch antenna, a monopole antenna, a dipole antenna, or the like.

[0033] The length of the waveguide 110 in the extension direction of the central axis C is set so that the focal point of the radio wave lens 130 is located on the opening surface of the opening 111, and therefore the position in the extension direction of the optical axis (central axis C of the waveguide 110) of the radio wave lens 130 of the transmitting antenna 120Tx and the receiving antenna 120Rx is equal to the focal position of the radio wave lens 130. Furthermore, the Y-direction position of the surface on the +Y-direction side of the substrate 121 coincides with the Y-direction position of the opening 111, and therefore the focal point of the radio wave lens 130 coincides with the center (a point on the central axis C) of the centers of the transmitting antenna 120Tx and the receiving antenna 120Rx on the surface on the +Y-direction side of the substrate 121.

[0034] The intensity of the radio waves (transmitted waves) radiated from the transmitting antenna 120Tx is strongest in the direction connecting the center of the transmitting antenna 120Tx and the center of the radio wave lens 130. The intensity of the radio waves (received waves) received by the receiving antenna 120Rx is strongest in the direction connecting the center of the receiving antenna 120Rx and the center of the radio wave lens 130. The center of the radio wave lens 130 is located on the optical axis of the radio wave lens 130 (the central axis C of the waveguide 110) and at the center of the thickness of the radio wave lens 130 in the Y direction.

[0035] <Configuration of radio wave lens 130> The radio wave lens 130 may be any lens that can focus radio waves transmitted and received by the transmitting antenna 120Tx and the receiving antenna 120Rx in both directions, and is, for example, a biconvex lens that is circular in a plan view. However, the radio wave lens 130 may also be a single-convex lens. A biconvex lens and a single-convex lens are examples of a convex lens.

[0036] The radio wave lens 130 has surfaces 130A and 130B. The surface 130A is an example of a first surface, and is the surface on the -Y direction side of the radio wave lens 130. The surface 130B is an example of a second surface, and is the surface on the +Y direction side of the radio wave lens 130. The surface 130A is located inside the radar device 100. The surface 130A being located inside the radar device 100 means that the surface 130A is located within the space surrounded by the substrate 101, the waveguide 110, and the radio wave lens 130. The surface 130A does not come into direct contact with the outside air. The surface 130B is part of the outer surface of the radar device 100.

[0037] 1B and 1D, the radio wave lens 130 has recesses 131A and protrusions 132A provided on the surface 130A to reduce multiple reflected waves. The recesses 131A and protrusions 132A are part of the surface 130A. The recesses 131A and protrusions 132A function as an AR (Anti-Reflection) layer. The recesses 131A and protrusions 132A are formed concentrically in a plan view around the optical axis of the radio wave lens 130, and are provided at an equal pitch, for example. Note that the surface 130B is a continuous curved surface that does not have the recesses 131A and protrusions 132A like the surface 130A.

[0038] As an example, on the central side of radio wave lens 130, where the optical axis is located, multiple recessed portions 131A are arranged concentrically around the optical axis in a plan view, and on the outer side of the central side, multiple protruding portions 132A are arranged concentrically around the optical axis in a plan view. In the radial direction of radio wave lens 130, the boundary between the central side where multiple recessed portions 131A are arranged and the outer side where multiple protruding portions 132A are arranged is shown as boundary portion 133A. Neither recessed portions 131A nor protruding portions 132A are present in boundary portion 133A.

[0039] The depth of the recess 131A and the height of the protrusion 132A are set to a depth and height, respectively, on the surface 130A of the radio wave lens 130 that cancel out a first reflected wave that is reflected by the surface 130A of the radio wave that arrives at the radio wave lens 130 from the surface 130A side, and a second reflected wave that is transmitted through the surface 130A, reflected on the back side of the surface 130B, and reaches the surface 130A. Note that the depth of the recess 131A is the depth to which the recess 131A is recessed in the +Y direction relative to a portion of the surface 130A where the recess 131 and the protrusion 132A are not provided. Also, the height of the protrusion 132A is the height to which the protrusion 132A protrudes in the -Y direction relative to a portion of the surface 130A where the recess 131 and the protrusion 132A are not provided.

[0040] The depth of the recessed portion 131A is set to be deeper as it is closer to the optical axis, and the height of the protruding portion 132A is set to be higher as it is farther from the optical axis. This will be described in detail later with reference to FIG.

[0041] Note that the recesses 131A and the protrusions 132A do not have to be arranged at equal pitches as long as they are concentric. Furthermore, the positional relationship between the multiple recesses 131A and the multiple protrusions 132A may be reversed in the radial direction. That is, on the central side of the radio wave lens 130, where the optical axis is located, the multiple protrusions 132A may be arranged concentrically about the optical axis in a plan view, while on the outer side of the central side, the multiple recesses 131A may be arranged concentrically about the optical axis in a plan view.

[0042] 1D , the recessed portions 131A and the protruding portions 132A may be provided symmetrically in a plan view with respect to the optical axis of the radio wave lens 130. Here, as an example, the recessed portions 131A and the protruding portions 132A have a circumferential shape in a plan view, and are formed concentrically in a plan view around the optical axis of the radio wave lens 130. However, for example, the recessed portions 131A and the protruding portions 132A may be recessed portions (grooves) or protruding portions formed in a lattice shape in a plan view with the optical axis of the radio wave lens 130 as the center, or may be recessed portions (grooves) or protruding portions that construct a shape in which regular polygons are arranged without gaps.

[0043] 2A to 2D are diagrams illustrating an example of why multiple reflections occur in the comparative radio wave lens 13. FIG. 2A shows the comparative radio wave lens 13. The comparative radio wave lens 13 has surfaces 13A and 13B. Unlike the radio wave lens 130 of the embodiment, the comparative radio wave lens 13 does not have the recessed portion 131A and the protruding portion 132A, and therefore the surfaces 13A and 13B are continuous curved surfaces. The XYZ coordinates shown in FIG. 2A are the same as those shown in FIGS. 1A to 1D, and the optical axis of the comparative radio wave lens 13 coincides with the Y axis.

[0044] 2A, the solid line indicates a first reflected wave that is reflected by surface 13A of radio waves that arrive at radio wave lens 13 from the surface 13A side. The dashed line indicates a second reflected wave that is reflected by surface 13A and arrives at surface 13A of radio waves that arrive at radio wave lens 13 from the surface 13A side. The first reflected wave and the second reflected wave overlap at surface 13A.

[0045] 2B to 2D show the first reflected wave (solid line) and the second reflected wave (dashed line) as vectors. More specifically, the phase of the vector of the second reflected wave is shown when the phase of the vector of the first reflected wave is set to 0 degrees. Also, in FIGS. 2C and 2D, the phase of the vector of the composite wave of the first reflected wave (solid line) and the second reflected wave (dashed line) is shown by a dashed line.

[0046] 2B , the phases of the first reflected wave and the second reflected wave are different by 180 degrees. In such a case, the magnitude of the vector of the composite wave of the first reflected wave and the second reflected wave becomes zero, and the first reflected wave and the second reflected wave cancel each other out at the surface 13A. In this way, when the first reflected wave and the second reflected wave cancel each other out at the surface 13A, no composite wave is generated at the surface 13A, and therefore multiple reflections can be suppressed.

[0047] 2B, the state in which the first reflected wave and the second reflected wave are 180 degrees out of phase is obtained when a distance twice the thickness of the comparative radio wave lens 13 in the Y direction (the round-trip distance of the second reflected wave from surface 13A to surface 13B) is half (λe / 2) of the electrical length λe of the radio waves within the radio wave lens 13. Only a small portion of the entire comparative radio wave lens 13 obtains this relationship, and there may be cases in which no portion satisfies this relationship is obtained.

[0048] In Fig. 2C, the phase of the second reflected wave is approximately 150 degrees, resulting in a composite vector (dashed line) of the first reflected wave and the second reflected wave. Also, in Fig. 2D, the phase of the second reflected wave is approximately 300 degrees, resulting in a composite vector (dashed line) of the first reflected wave and the second reflected wave. In this way, when a composite wave of the first reflected wave and the second reflected wave is generated, multiple reflections due to the composite wave may occur, making it impossible to reduce multiple reflections.

[0049] 3A to 3C are diagrams illustrating an example of the principle of reducing multiple reflections by the radio wave lens 130 of the embodiment. The XYZ coordinates shown in Fig. 3A are the same as the XYZ coordinates shown in Fig. 1A to 1D, with the origin coinciding with the center of the opening 111 and the optical axis of the radio wave lens 130 coinciding with the Y axis.

[0050] 3A , the solid line indicates a first reflected wave that is reflected by portions of the surface 130A of the radio wave lens 130 other than the recessed portions 131A and the protruding portions 132A of the surface 130A of the radio wave lens 130, among the radio waves that arrive from the surface 130A side of the radio wave lens 130. The first reflected wave indicated by the solid line is equal to the first reflected wave that is reflected by the surface 130A of the comparative radio wave lens 13. The dashed line indicates a second reflected wave that is reflected by portions of the surface 130A of the radio wave that arrives from the surface 130A side of the radio wave lens 130, passes through portions of the surface 130A other than the recessed portions 131A and the protruding portions 132A of the surface 130A, is reflected by the back side of the surface 130B, and reaches the surface 130A. Such a first reflected wave and a second reflected wave overlap at the surface 130A.

[0051] 3B and 3C show the vector phase of the second reflected wave when the vector phase of the first reflected wave is set to 0. Also, in Fig. 3B and 3C, the vector phase of the composite wave of the first reflected wave (solid line) and the second reflected wave (dashed line) is shown by a dashed dotted line.

[0052] 2C , the phase of the second reflected wave that has passed through portions of surface 130A other than recessed portions 131A and protruding portions 132A is approximately 150 degrees, and therefore a composite vector (dashed dotted line) of the first reflected wave and the second reflected wave is generated. In such a case, if recessed portions 131A and protruding portions 132A are configured to obtain first reflected waves having vectors (thick solid lines) that are 180 degrees out of phase with the composite vector, it is possible to prevent the generation of a composite wave on surface 130A and reduce multiple reflections.

[0053] 3C , the phase of the second reflected wave that has passed through portions of surface 130A other than recessed portions 131A and protruding portions 132A is approximately 300 degrees, resulting in a composite vector (dashed line) of the first reflected wave and the second reflected wave. In such a case, if recessed portions 131A and protruding portions 132A are configured to obtain first reflected waves having vectors (thick solid lines) that are 180 degrees out of phase with the composite vector, it is possible to prevent the composite wave from being generated on surface 130A, thereby reducing multiple reflections.

[0054] <Depth of Recess 131A and Height of Protrusion 132A> Here, a method for determining the depth of recess 131A and the height of protrusion 132A will be described.

[0055] If the propagation impedance of radio waves inside the radio wave lens 130 is Zr and the propagation impedance of radio waves in the air is Z0, the reflection coefficient of the surface 130A of the radio wave lens 130 can be expressed by the following equation (1).

[0056]

[0057] Here, Z0 is expressed by the following equation (2).

[0058]

[0059] Furthermore, Zr can be expressed by the following formula (3) using Z0.

[0060] Here, μo is the magnetic permeability of air, εo is the permittivity of air, and εr is the relative permittivity of the material of the radio wave lens 130.

[0061] Using equations (1) to (3), the reflection coefficient Γ1 when radio waves emitted in the +Y direction from the transmitting antenna 120Tx are reflected by the surface 130A of the radio wave lens 130 can be expressed by the following equation (4).

[0062]

[0063] Furthermore, when radio waves are emitted in the +Y direction from the transmitting antenna 120Tx and transmitted through the surface 130A of the radio wave lens 130, the reflection coefficient γ2 is expressed by the following equation (5) when the radio waves are reflected on the back side (-Y direction side) of the surface 130B.

[0064]

[0065] When an approximate calculation is performed while ignoring the propagation loss inside the radio wave lens 130 and the reflection loss at the back side of the surface 130A and the surface 130B, the overall reflection coefficient Γ3 of the lens at the portions of the surface 130A other than the concave portions 131A and the convex portions 132A can be expressed by the following equation (6). Equation (6) shows the reflection coefficient Γ3 as a function of the thickness t of the radio wave lens 130. In other words, the reflection coefficient Γ3(t) expressed in equation (6) is the overall reflection coefficient that takes into account the reflection coefficients Γ1 and Γ2 at the portion of the radio wave lens 130 with thickness t. Note that λ is the wavelength of the radio wave in free space. Also, exp[(jπ / λ)·2t] represents the phase that occurs when the radio wave travels back and forth through the portion with thickness t.

[0066]

[0067] Here, the thickness t of the radio wave lens 130 will be described with reference to Fig. 4. Fig. 4 is a diagram for explaining the thickness t of the radio wave lens 130. The XYZ coordinates shown in Fig. 4 are the same as the XYZ coordinates shown in Figs. 1A to 1D and 3A, with the origin coinciding with the center of the opening 111 and the optical axis of the radio wave lens 130 coinciding with the Y axis.

[0068] As shown in Fig. 4, the thickness t of the radio wave lens 130 is the thickness in the Y direction of the radio wave lens 130 at a position Rt from the central axis in the portion of the surface 130A other than the recessed portions 131A and the protruding portions 132A. In other words, the thickness t of the radio wave lens 130 is the thickness in the Y direction of the portion not including the depth of the recessed portions 131A or the height of the protruding portions 132A at a position Rt from the central axis. Rt represents the radial position of the portion of thickness t. In the case of a symmetrical biconvex spherical lens, Rt can be calculated using the diameter and radius of curvature of the radio wave lens 130.

[0069] 4, the portion of the convex portion 132A indicated by the dashed circle is shown enlarged on the right side. The height of the convex portion 132A relative to the surface 130A is denoted by s. The height s of the convex portion 132A takes a positive value. If, on the surface 130A of the radio wave lens 130, the radio waves reflected by the surface of the convex portion 132A and the radio waves reflected in the −Y direction from the portions of the surface 130A other than the concave portion 131A and the convex portion 132A (including the reflected waves reflected on the back side of the reflecting surface 130B) cancel each other out, it is possible to prevent a composite wave from being generated on the surface 130A, as shown in FIGS. 3B and 3C. To achieve this, the height s of the convex portion 132A needs to satisfy the condition expressed by the following equation (7).

[0070]

[0071] In equation (7), Γar is the reflection coefficient of the radio wave on the surface of the convex portion 132A. Γ3'(t) is obtained by multiplying Γ3(t) in equation (6) by the attenuation coefficient for the height s of the convex portion 132A. Furthermore, because there is an error due to the dielectric constant and dielectric loss of the lens material of the radio wave lens 130, it is necessary to consider the error in equation (7) depending on the characteristics of the material used. For example, equation (7) may contain an error of approximately ±5% for materials with low relative dielectric constants and low dielectric loss, and may contain an error of approximately 20% to 30% for materials with high relative dielectric constants and dielectric loss. Furthermore, in equation (7), exp[(jπ / λ)·s] represents the phase generated by the radio wave propagating through the portion at height s.

[0072] As described above, if the height s of the convex portion 132A satisfies the formula (7), it is possible to prevent a composite wave from being generated on the surface 130A, as shown in Figures 3B and 3C, and it is possible to reduce multiple reflections.

[0073] Regarding equation (7), the height of the convex portion 132A is described as s taking a positive value, but for the depth of the concave portion 131A, by setting s to a negative value, it is possible to calculate the depth s of the concave portion 131A to reduce multiple reflections in the same way as the height s of the convex portion 132A.

[0074] <Experimental Results> The experimental results in Figures 5A and 5C are graphs showing an example of the output strength of the radar detection signal from the receiving antenna 120Rx versus the distance between the radar device 100 and the measurement target. Figures 5B and 5D show an example of experimental results for a comparative radar device. The comparative radar device has a configuration in which the radio wave lens 130 of the radar device 100 is replaced with the comparative radio wave lens 13 shown in Figure 2A.

[0075] 5A to 5D, the horizontal axis represents the distance (mm) between the radar device 100 and the comparative radar device and the measurement object, and the vertical axis represents the output strength (unitless) of the radar detection signal of the radar device 100 and the comparative radar device. The output strength of the radar detection signal is not limited to the strength of the received wave alone, but may also include the strength of multiple reflected waves.

[0076] 5A to 5D show, as an example, the output strength of the radar detection signal received by the receiving antenna 120Rx of the radar device 100 and a comparative radar device when the measurement target is located at a distance of 1970 mm, to show the output strength of the radar detection signal when the measurement target is present. Figures 5A and 5B show the output strength of the radar detection signal on the short-distance side, from 0 mm to 550 mm, and Figures 5C and 5D show the output strength of the radar detection signal on the long-distance side, from 1500 mm to 2000 mm.

[0077] Comparing Figures 5A and 5B, it can be seen that the output strength of the radar detection signal of the radar device 100 of the embodiment shown in Figure 5A is lower at short distances than the output strength of the radar detection signal of the comparative radar device shown in Figure 5B. As an example, assuming that a measurement target can be detected if the output strength of the radar detection signal is 1500 or less, the comparative radar device can only measure up to approximately 170 mm as shown in Figure 5B, while the radar device 100 of the embodiment can measure up to a short distance of approximately 110 mm as shown in Figure 5A. Comparing the output strength of the radar detection signal within the range from approximately 110 mm to approximately 170 mm, it can be seen that the output strength of the radar detection signal of the radar device 100 of the embodiment is significantly reduced compared to the output strength of the radar detection signal of the comparative radar device. This indicates that multiple reflections are significantly reduced by the AR layer formed by the recessed portions 131A and the protruding portions 132A.

[0078] 5C and 5D , the output strength of the radar detection signal from the radar device 100 of the embodiment shown in Fig. 5C has a higher peak value at 1970 mm, where the measurement object is located, compared to the output strength of the radar detection signal from the comparative radar device shown in Fig. 5D , and the output strength of the radar detection signal on the side farther than 1970 mm is lower, confirming that multiple reflections from the measurement object are also reduced. This indicates that the AR layer formed by the recessed portions 131A and the protruding portions 132A significantly reduces multiple reflections, and that the amount of radio waves that reach the receiving antenna 120Rx directly without being reflected from the measurement object is increased.

[0079] As described above, the experimental results shown in Figures 5A to 5D indicate that the radar device 100, which includes a radio wave lens 130 that adds the recessed portions 131A and protruding portions 132A that form an AR layer to the radio wave lens 13 of the comparative radar device, can significantly reduce the effects of multiple reflected waves, significantly shortening the shortest detection distance from 170 mm to 110 mm. Furthermore, the output strength of the radar detection signal when detecting a target object also increased. In other words, it was confirmed that suppressing multiple reflected waves using the radio wave lens 130 that adds the recessed portions 131A and protruding portions 132A that form the AR layer can significantly improve detection performance. It was also confirmed that the output strength of the radar detection signal when detecting a target object also increased.

[0080] <Simulation Results of Gain of Receiving Antenna 120Rx> Figures 6A and 6B are diagrams showing examples of simulation results of the gain of the receiving antenna 120Rx. Figure 6A shows an example of simulation results of the gain of the receiving antenna 120Rx of the radar device 100 of the embodiment, and Figure 6B shows an example of simulation results of the gain of the receiving antenna 120Rx of a comparative radar device. The comparative radar device has a configuration in which the radio wave lens 130 of the radar device 100 is replaced with the comparative radio wave lens 13 shown in Figure 2A.

[0081] 6A and 6B, the 90-degree direction corresponds to the +Y direction. The gain (maximum value) of the receiving antenna 120Rx of the radar device 100 of the embodiment was 19.0 dBi, as shown in FIG. 6A, while the gain (maximum value) of the receiving antenna 120Rx of the comparative radar device was 18.1 dBi. From these results, it was confirmed that the gain of the receiving antenna 120Rx was increased by suppressing multiple reflected waves using the radio wave lens 130, which includes the recessed portions 131A and the protruding portions 132A that form the AR layer. This is thought to be due to the reduction in multiple reflections, which increases the amount of radio waves that reach the receiving antenna 120Rx directly without being reflected from the object being measured.

[0082] <Modifications of Radio Wave Lens 130> Figures 7A and 7B are diagrams showing examples of the configuration of modified radio wave lenses 130M1 and M2. In the radio wave lens 130M1 shown in Figure 7A, convex portions 132A are provided on the surface 130A in a concentric pattern centered on the optical axis, with the height of the convex portions 132A increasing as they approach the optical axis. If the height s of these multiple concentric convex portions 132 is configured to satisfy the above-mentioned formula (7), multiple reflections can be reduced, similar to the radio wave lens 130 shown in Figures 1A to 1D, 3A, and 4A.

[0083] The radio wave lens 130M1 may have recesses 131A instead of the convex portions 132A. In this case, the recesses 131A are provided concentrically around the optical axis on the surface 130A of the radio wave lens 130M1, and the depth of the recesses 131A increases as the recesses 131A approach the optical axis. The depth s of the multiple concentric recesses 131A should be configured to satisfy the above-mentioned formula (7).

[0084] 7B, convex portions 132A are provided on the surface 130A in a concentric pattern centered on the optical axis, with the height of the convex portions 132A decreasing as the convex portions 132A approach the optical axis. If the height s of these multiple concentric convex portions 132 is configured to satisfy the above-mentioned formula (7), multiple reflections can be reduced, similar to the radio wave lens 130 shown in FIGS. 1A to 1D, 3A, and 4A.

[0085] Note that radio wave lens 130M2 may have recesses 131A instead of convex portions 132A. In this case, it is sufficient that recesses 131A are provided concentrically around the optical axis on surface 130A of radio wave lens 130M1, and that the depth of recesses 131A becomes shallower as they approach the optical axis. It is sufficient that the depth s of the multiple concentric recesses 131A satisfies the above-mentioned formula (7).

[0086] 1A to 1D, 3A, and 4A can be made smaller in volume and lighter in weight than the radio wave lenses 130M1 and 130M2 shown in FIGS. 7A and 7B by including both the recessed portion 131A and the protruding portion 132A.

[0087] <Effects> The radio wave lens 130 has a surface 130A (first surface), a surface 130B (second surface), and an optical axis that penetrates the surfaces 130A and 130B. The surface 130A has recesses 131A or protrusions 132A that are provided concentrically or that are provided symmetrically around the optical axis in a plan view, and the depth of the recesses 131A or the height of the protrusions 132A is set according to the distance from the optical axis. Therefore, the recesses 131A, whose depth corresponds to the distance from the optical axis, or the protrusions 132A, whose height corresponds to the distance from the optical axis, can weaken the first reflected wave reflected by the surface 130A and the second reflected wave reflected on the back side of the surface 130B, thereby reducing reflected waves that lead to multiple reflections. Furthermore, since surface 130A is located within a space surrounded by substrate 101, waveguide 110, and electromagnetic lens 130, dust is less likely to adhere to surface 130A.

[0088] Therefore, it is possible to provide a radio wave lens 130 that is resistant to dust adhesion on one surface and can sufficiently reduce reflection.

[0089] Furthermore, the depth of the recess 131A or the height of the protrusion 132A may be set to a depth or height on the surface 130A of the radio wave lens 130 that cancels out a first reflected wave that is reflected by the surface 130A of the radio wave that arrives from the surface 130A side of the radio wave lens 130, and a second reflected wave that is transmitted through the surface 130A, reflected by the back side of the surface 130B, and reaches the surface 130A of the radio wave. Therefore, by using the recess 131A or the protrusion 132A, the first reflected wave that is reflected by the surface 130A and the second reflected wave that is reflected by the back side of the surface 130B can cancel each other out, and reflected waves that lead to multiple reflections can be reduced.

[0090] Therefore, it is possible to provide a radio wave lens 130 that is less likely to have dust adhere to one of its surfaces and that can sufficiently and effectively reduce reflection.

[0091] Furthermore, on surface 130A, in a plan view of surface 130A, recesses 131A and protrusions 132A are arranged concentrically around the optical axis, with protrusions 132A arranged closer to the center than the optical axis and recesses 131A arranged further outward than the center, such that the height of protrusions 132A increases toward the center, the closer they are to the optical axis, and the deeper they are outside than the center, the farther they are from the optical axis; alternatively, recesses 131A may be arranged closer to the center than the optical axis and protrusions 132A may be arranged further outward than the center, the deeper they are nearer to the optical axis, and the deeper they are outside than the center, the farther they are from the optical axis, the higher the height of protrusions 132A. In this way, by including recesses 131A having a regular depth according to the distance from the central axis and protrusions 132A having a regular height, it is possible to use recesses 131A and protrusions 132A to cancel out the first reflected wave reflected by surface 130A and the second reflected wave reflected by the back side of surface 130B, thereby reducing reflected waves that lead to multiple reflections. Furthermore, by including both recesses 131A and protrusions 132A, it is possible to reduce the volume and weight.

[0092] Furthermore, on surface 130A, recesses 131A or protrusions 132A are provided concentrically around the optical axis, and the depth of recesses 131A or the height of protrusions 132A may be deeper or higher as they are closer to the optical axis. In this way, by including recesses 131A with regular depths or protrusions 132A with regular heights according to the distance from the central axis, recesses 131A or protrusions 132A can be used to cancel out a first reflected wave reflected by surface 130A and a second reflected wave reflected on the back side of surface 130B, thereby reducing reflected waves that lead to multiple reflections.

[0093] Furthermore, on surface 130A, recesses 131A or protrusions 132A are provided concentrically around the optical axis, and the depth of recesses 131A may be shallower or the height of protrusions 132A may be lower as they are closer to the optical axis. In this way, by including recesses 131A with regular depths or protrusions 132A with regular heights according to the distance from the central axis, recesses 131A or protrusions 132A can be used to cancel out a first reflected wave reflected by surface 130A and a second reflected wave reflected on the back side of surface 130B, thereby reducing reflected waves that lead to multiple reflections.

[0094] Furthermore, the recesses 131A or the protrusions 132A may be provided at equal pitches in the radial direction relative to the optical axis. By including the recesses 131A with regular depths or the protrusions 132A with regular heights according to the equal pitch distances from the central axis, the recesses 131A or the protrusions 132A can be used to cancel out the first reflected wave reflected by the surface 130A and the second reflected wave reflected by the back side of the surface 130B, thereby reducing reflected waves that lead to multiple reflections.

[0095] Furthermore, the depth s (s<0) of the recess or the height s (s>0) of the convex portion may be expressed by the following equation (8), where F3(t) is the reflection coefficient for the first reflected wave and the second reflected wave at the portion of the first surface other than the recess and the convex portion, t is the thickness of the portion of the first surface other than the recess and the convex portion, λ is the wavelength of the radio wave in free space, and Γar is the reflection coefficient of the radio wave at the surface of the recess or the convex portion.

[0096]

[0097] By using the recess 131A with a depth s or the protrusion 132A with a height s set according to Equation (8), the first reflected wave reflected from the surface 130A and the second reflected wave reflected from the back side of the surface 130B can be weakened, thereby accurately reducing reflected waves that lead to multiple reflections. Furthermore, because there is an error due to the dielectric constant and dielectric loss of the lens material of the radio wave lens 130, it is necessary to consider the error in Equation (8) depending on the characteristics of the material used. For example, Equation (8) may include an error of approximately ±5% for materials with low relative dielectric constants and low dielectric loss, but may include an error of approximately 20% to 30% for materials with high relative dielectric constants and dielectric loss. Furthermore, in Equation (8), exp[(jπ / λ)·s] represents the phase generated by radio waves propagating through a section with height s.

[0098] Therefore, it is possible to provide a radio wave lens 130 that is resistant to dust adhesion on one surface and can reduce reflection with high precision.

[0099] The radio wave lens device 100A includes a waveguide 110 having an opening 111 (first opening) and an opening 112 (second opening), and the radio wave lens 130 fixed to the opening 112 with its surface 130A facing the opening 111. Therefore, the recess 131A, whose depth corresponds to the distance from the optical axis, or the protrusion 132A, whose height corresponds to the distance from the optical axis, can weaken the first reflected wave reflected by the surface 130A and the second reflected wave reflected by the back side of the surface 130B, thereby reducing reflected waves that could lead to multiple reflections. Furthermore, because the surface 130A is located within a space surrounded by the substrate 101, the waveguide 110, and the radio wave lens 130, dust is less likely to adhere to the surface 130A.

[0100] Therefore, it is possible to provide a radio wave lens device 100A in which dust is less likely to adhere to one of the surfaces and reflection can be sufficiently reduced.

[0101] The radar device 100 includes a substrate 101, a transceiver unit 120 (integrated circuit chip) having a transmitting antenna 120Tx and a receiving antenna 120Rx mounted on the substrate 101, and the radio wave lens device 100A. The opening 111 is provided on the substrate 101 side and surrounds the transmitting antenna 120Tx and the receiving antenna 120Rx when viewed from the opening side. The opening 112 is provided further back than the opening 111 in the radiation direction of the transmitting antenna 120Tx. Therefore, the recess 131A, whose depth corresponds to the distance from the optical axis, or the protrusion 132A, whose height corresponds to the distance from the optical axis, can weaken the first reflected wave reflected by the surface 130A and the second reflected wave reflected by the back side of the surface 130B, thereby reducing reflected waves that could lead to multiple reflections. Furthermore, since the surface 130A is located within a space surrounded by the substrate 101, the waveguide 110, and the radio wave lens 130, dust is less likely to adhere to the surface 130A.

[0102] Therefore, it is possible to provide a radar device 100 that is less likely to have dust adhere to one surface and can sufficiently reduce reflection.

[0103] The radio wave lens, radio wave lens device, and radar device according to exemplary embodiments of the present disclosure have been described above. However, the present disclosure is not limited to the specifically disclosed embodiments, and various modifications and changes are possible without departing from the scope of the claims.

[0104] This international application claims priority based on Japanese Patent Application No. 2023-008359, filed on January 23, 2023, the entire contents of which are incorporated herein by reference.

[0105] REFERENCE SIGNS LIST 100 Radar device 100A Radio wave lens device 101 Substrate 110 Waveguide 110A Inner wall surface 111 Opening (an example of a first opening) 112 Opening (an example of a second opening) 120 Transmitter / receiver (an example of an integrated circuit chip) 120Tx Transmitting antenna 120Rx Receiving antenna 121 Substrate 130 Radio wave lens 130A, 130B Surface 131A Concave portion 132A Convex portion 133A Boundary portion

Claims

1. A radio wave lens having a first surface, a second surface, and an optical axis passing through the first surface and the second surface, wherein the first surface has recesses or protrusions provided concentrically or symmetrically about the optical axis in a plan view, and a depth of the recess or a height of the protrusion is set according to a distance from the optical axis. The radio wave lens.

2. The depth of the recess or the height of the protrusion is such that, on the first surface of the radio wave lens, among radio waves arriving from the first surface side with respect to the radio wave lens, a first reflected wave reflected at the first surface and a second reflected wave that passes through the first surface, is reflected on the back side of the second surface, and reaches the first surface cancel each other out. The radio wave lens according to claim 1.

3. On the first surface, in a plan view of the first surface, the recesses and the protrusions are provided concentrically about the optical axis, the protrusions are provided on the center side about the optical axis, the recesses are provided outside the center side, and the height of the protrusions is higher closer to the optical axis on the center side, and the depth of the recesses is deeper farther from the optical axis outside the center side, or the recesses are provided on the center side about the optical axis, the protrusions are provided outside the center side, and the depth of the recesses is deeper closer to the optical axis on the center side, and the height of the protrusions is higher farther from the optical axis outside the center side. The radio wave lens according to claim 2.

4. On the first surface, the recesses or the protrusions are provided concentrically about the optical axis, and the depth of the recesses is deeper or the height of the protrusions is higher closer to the optical axis. The radio wave lens according to claim 2.

5. On the first surface, the recesses or the protrusions are provided concentrically about the optical axis, and the depth of the recesses is shallower or the height of the protrusions is lower closer to the optical axis. The radio wave lens according to claim 2.

6. The recesses or the protrusions are provided at equal pitches in a radial direction with respect to the optical axis. The radio wave lens according to any one of claims 3 to 5.

7. When the depth s (s < 0) of the concave portion or the height s (s > 0) of the convex portion satisfies the following formula (1), where F3(t) is the reflection coefficient of the first reflected wave and the second reflected wave at a portion of the first surface other than the concave and convex portions, t is the thickness of the portion of the first surface other than the concave and convex portions, λ is the wavelength of the radio wave in free space, and Γar is the reflection coefficient of the radio wave at the surface of the concave or convex portion, the radio wave lens according to claim 2. 【Number 1】

8. A waveguide having a first opening and a second opening, The radio wave lens according to claim 1, fixed to the second opening with the first surface facing the first opening side, A radio wave lens device including the same.

9. A substrate, An integrated circuit chip having a transmitting antenna and a receiving antenna and mounted on the substrate, The radio wave lens device according to claim 8, Including, The first opening is provided on the substrate side and surrounds the transmitting antenna and the receiving antenna in a plan view of the opening surface, The second opening is provided on the back side of the first opening in the radiation direction of the transmitting antenna. A radar device.

Images