Antenna device

Abstract

The present invention provides an antenna device in which an increase in EIRP is suppressed and which has good radio wave reception sensitivity.　The antenna device comprises: a substrate; an integrated circuit chip that has a transmission antenna and a reception antenna and that is mounted on the substrate; a waveguide that has a first opening which is provided to the substrate side and which surrounds the transmission antenna and the reception antenna in a view of the opening face, a second opening which is provided further back than the first opening in the radiation direction of the transmission antenna, and a first inner wall surface which connects the first opening and the second opening; a radio wave lens that is fixed in the second opening; and a first radio wave absorbent body that is disposed to the first opening side in the space surrounded by the first inner wall surface. At least part of the first radio wave absorbent body is positioned inward of a first route of first direct waves that are radiated from the transmission antenna, that reach the radio wave lens directly, and that pass through the radio wave lens. The first radio wave absorbent body is positioned outward of a second route of second direct waves that pass through the radio wave lens and that directly reach the reception antenna.

Description

Antenna device

[0001] The present disclosure relates to an antenna device.

[0002] Conventionally, there has been a lens antenna that includes a first horn (conical horn) made of a metal conductor, a second horn made of a plastic material with radio wave absorbing properties, and a lens that controls the power distribution at the opening of the second horn. Because no radio wave absorber is attached to the inner wall of the first horn, there is nothing to block microwaves, and the power density distribution at the opening of the lens is not affected (see, for example, Patent Document 1).

[0003] Japanese Patent Application Publication No. 10-284931

[0004] However, when transmitting and receiving radio waves, if the gain of the antenna is increased to improve the radio wave receiving sensitivity, there is a risk that the EIRP (EIRP_Equivalent Isotropically Radiated Power) of the radio waves during transmission will exceed the upper limit of EIRP regulated by the Radio Law, etc., and if the gain of the antenna is reduced to suppress the increase in EIRP, there is a risk that sufficient radio wave receiving sensitivity will not be obtained.

[0005] Therefore, an object of the present invention is to provide an antenna device that suppresses an increase in EIRP and has good radio wave receiving sensitivity.

[0006] An antenna device according to an embodiment of the present disclosure comprises a substrate, an integrated circuit chip having a transmitting antenna and a receiving antenna and mounted on the substrate, a waveguide having a first opening provided on the substrate side and surrounding the transmitting antenna and the receiving antenna when viewed from the opening surface, a second opening provided further back than the first opening in the radiation direction of the transmitting antenna, and a first inner wall surface connecting the first opening and the second opening, a radio wave lens fixed to the second opening, and a first radio wave absorber arranged on the side of the first opening in the space surrounded by the first inner wall surface, wherein at least a portion of the first radio wave absorber is located inside a first path of a first direct wave that is radiated from the transmitting antenna, reaches the radio wave lens directly, and passes through the radio wave lens, and the first radio wave absorber is located outside a second path of a second direct wave that passes through the radio wave lens and reaches the receiving antenna directly.

[0007] It is possible to provide an antenna device that suppresses an increase in EIRP and has good radio wave receiving sensitivity.

[0008] 1A . FIG. 1B is a diagram illustrating an antenna device according to an embodiment. FIG. 1C is a diagram illustrating an antenna device according to an embodiment. FIG. 1D is a perspective view showing a radio wave absorber of the antenna device according to an embodiment. FIG. 1E is a diagram illustrating an example of the position of an inner wall surface of a radio wave absorber of the antenna device according to an embodiment. FIG. 1F is a diagram illustrating an example of absorption of reflected waves by a radio wave absorber of the antenna device according to an embodiment. FIG. 1G is a diagram illustrating an example of a first path and a second path in the cross section according to an arrow A-A in FIG. 1A . FIG. 1H is a diagram illustrating an example of radiation characteristics of a comparative antenna device. FIG. 1H is a diagram illustrating an example of radiation characteristics of a comparative antenna device. FIG. 1H is a diagram illustrating an example of radiation characteristics of an antenna device 100 according to an embodiment. FIG. 1H is a diagram illustrating an example of radiation characteristics of an antenna device 100 according to an embodiment. FIG. 1H is a diagram illustrating an example of the configuration of an antenna device according to a first modified example of the embodiment. FIG. 1H is a diagram illustrating an example of the configuration of an antenna device according to a first modified example of the embodiment. FIG. 1H is a diagram illustrating an example of the configuration of an antenna device according to a second modified example of the embodiment. FIG. 1H is a diagram illustrating an example of the configuration of an antenna device according to a second modified example of the embodiment. FIG. 1H is a diagram illustrating an example of the configuration of an antenna device according to a second modified example of the embodiment. FIG. 1H is a diagram illustrating an example of the configuration of an antenna device according to a second modified example of the embodiment. FIG. 10 is a diagram illustrating an example of the configuration of an antenna device according to a third modified example of the embodiment.

[0009] Hereinafter, an embodiment to which the antenna device of the present disclosure is applied will be described.

[0010] <Embodiment> <Configuration of Antenna Device 100> Figures 1A, 1B, and 1C are diagrams illustrating an antenna device 100 according to an embodiment. Figure 1D is a perspective view illustrating a radio wave absorber 140 of the antenna device 100 according to an embodiment. Figure 1A is a perspective view, Figure 1B is a diagram illustrating a partial half cross section, and Figure 1C is a front view. Figure 2A is a diagram illustrating a cross section along the arrows A-A in Figure 1A, and is a diagram illustrating a cut surface obtained by cutting the waveguide 110 in the YZ plane including the optical axis of the radio wave lens 130. Here, unless otherwise specified, the configuration of the antenna device 100 will be described using Figures 1A, 1B, 1C, 1D, and 2A.

[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 antenna device 100 includes a substrate 101, a waveguide 110, a transmitting / receiving unit 120, a radio wave lens 130, a radio wave absorber 140, and a radio wave absorber 150. The radio wave absorber 150 is an example of a first radio wave absorber, and the radio wave absorber 140 is an example of a second radio wave absorber. The antenna device 100 does not necessarily have to include the radio wave absorber 140, but here, a configuration in which the antenna device 100 includes the radio wave absorber 140 will be described.

[0013] Antenna device 100 is a device for transmitting and receiving radio waves, and improves reception sensitivity by narrowing the radiation pattern of the transmitted waves with radio wave lens 130 and focusing the received radio waves with a lens. Furthermore, antenna device 100 suppresses an increase in EIRP by attenuating the transmitted waves with radio wave absorber 150, and absorbs multiple reflected waves generated internally by multiple reflections with radio wave absorber 140.

[0014] For example, the antenna device 100 can be used as a radar device that receives a reflected wave from an object to be measured and measures the distance to the object. The distance to the object can be measured based on the time it takes for a radio wave to travel from the time it is transmitted as a transmitted wave until the time it is received as a reflected wave.

[0015] In Japan, the Radio Law stipulates an upper limit for the EIRP (equivalent isotropically radiated power) of transmitted waves. International guidelines also exist, and similar limits apply in other countries. When a conventional antenna device transmits and receives radio waves, the antenna gains of the transmitted and received waves are equal. Therefore, increasing the antenna gain to improve radio wave reception sensitivity in a conventional antenna device can result in the EIRP of the transmitted waves exceeding the upper limit stipulated by the Radio Law. Reducing the antenna gain to suppress the EIRP can result in insufficient radio wave reception sensitivity. The antenna device 100 of this embodiment solves these problems by attenuating the transmitted waves with a radio wave absorber 150, thereby suppressing the increase in EIRP and improving reception sensitivity.

[0016] Furthermore, in general, in a radar device that measures the distance to a measurement target, the closer the measurement target is, the lower the detection accuracy becomes due to the effects of multiple reflections. This is because the closer the measurement target 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 the detection accuracy decreases, the shortest detectable distance (shortest detection distance) becomes longer. The antenna device 100 of this embodiment solves this problem by using a radio wave absorber 140.

[0017] 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, the radio wave lens 130, and the radio wave absorber 140. 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.

[0018] The radio waves transmitted and received by the antenna 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 in a manner similar to that of light. However, the radio waves transmitted and received by the antenna device 100 may be radio waves with frequencies belonging to a band other than the millimeter wave band.

[0019] <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.

[0020] <Configuration of Waveguide 110> The waveguide 110 is, for example, a cylindrical, hollow circular waveguide. The waveguide 110 has an opening 111, an opening 112, 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 −Y direction side of the waveguide 110 is an example of a first opening side, and the +Y direction side is an example of a second opening side. In addition, the +Y direction is an example of a radiation direction of the transmitting antenna 120Tx of the transmitting / receiving unit 120.

[0021] 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.

[0022] Inner wall surface 110A is the inner wall surface of cylindrical, hollow waveguide 110. Waveguide 110 has, for example, a cylindrical shape in which the opening diameter of opening 111 and the opening diameter of opening 112 are equal. Therefore, inner wall surface 110A has a cylindrical shape with a constant diameter. Note that the opening diameter of opening 111 may be larger than the opening diameter of opening 112, or the opening diameter of opening 112 may be larger than the opening diameter of opening 111.

[0023] The opening 111 is an opening located at the end of the waveguide 110 on the −Y direction side. The opening 111 is circular when viewed from the opening surface.

[0024] 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.

[0025] The opening 112 has a circular shape in a plan view. The diameter of the opening 112 is, for example, equal to the diameter of the opening 111. A radio wave lens 130 is attached to the opening 112 by an attachment portion 117.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] <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.

[0030] 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.

[0031] 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).

[0032] 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.

[0033] 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-symmetric with respect to the central axis C in a planar view. Therefore, in 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 symmetric with respect to the central axis C in the +Z direction and the -Z direction.

[0034] 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.

[0035] 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.

[0036] 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, and 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.

[0037] <Configuration of Radio Wave Lens 130> The radio wave lens 130 may be any lens capable of focusing 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. The radio wave lens 130 may also be a flat lens such as a flat lens with a Fresnel zone or a flat lens with a metamaterial, but here we will describe a configuration in which the radio wave lens is a biconvex lens.

[0038] <Configuration of radio wave absorber 140> Radio wave absorber 140 is disposed in approximately half of the space on the −Y direction side inside waveguide 110. Radio wave absorber 140 is, for example, a member molded from a resin mixed with magnetic material or dielectric powder, and is a member that causes radio wave loss. Radio wave absorber 140 has opening 141, opening 142, and inner wall surface 143. Opening 141 is an example of a third opening, opening 142 is an example of a fourth opening, and inner wall surface 143 is an example of a second inner wall surface.

[0039] Radio wave absorber 140 is disposed such that the central axis, which is parallel to the Y axis of the substantially truncated cone-shaped space surrounded by inner wall surface 143 between openings 141 and 142, coincides with central axis C of waveguide 110. Furthermore, since central axis C of waveguide 110 coincides with the optical axis of radio wave lens 130, the central axis of radio wave absorber 140 coincides with central axis C of waveguide 110 and the optical axis of radio wave lens 130.

[0040] The opening 141 is provided on the opening 111 side, is smaller than the opening 111 and the substrate 101 when viewed from the opening plane of the opening 111, and is an opening that surrounds the transmitting antenna 120Tx and the receiving antenna 120Rx. The opening 141 is also smaller than the opening 142 when viewed from the opening plane, and is arranged concentrically. As an example, the position of the opening 141 in the Y direction is aligned with the opening 111 of the waveguide 110 (see FIG. 2A ), and the centers of the opening 141 and the opening 111 are aligned when viewed from the opening plane.

[0041] Opening 142 is provided further back (closer to opening 112) than opening 141 in the radiation direction, and is larger than opening 141. Opening 142 is larger than opening 141 in the opening plane view, and is arranged concentrically. The position of opening 142 in the Y direction is slightly on the +Y direction side of the center of openings 111 and 112 of waveguide 110, as shown in FIG. 2A . The length between openings 141 and 142 of radio wave absorber 140 may be determined depending on the length of waveguide 110 in the Y direction, the shape of inner wall surface 143, etc.

[0042] Inner wall surface 143 is an inner wall surface that connects opening 141 and opening 142. Inner wall surface 143 has inner wall surfaces 143A, 143B, 143C, 143D, 143E, and 143F from the −Y direction side to the +Y direction side. The end of inner wall surface 143A on the −Y direction side is opening 141, and inner wall surface 143A is a cylindrical wall surface (a wall surface corresponding to the inner circumferential surface of a cylinder) with a constant diameter, and inner wall surface 143B is connected to the end on the +Y direction side.

[0043] Inner wall surface 143B is a wall surface (a wall surface corresponding to the outer peripheral surface of the truncated cone) extending in a truncated cone shape from the end of inner wall surface 143A on the +Y direction side, and inner wall surface 143C is connected to the end on the +Y direction side. Inner wall surface 143C is formed as a plane parallel to the XZ plane and has an annular shape when viewed from the opening surface. The end on the +Y direction side of inner wall surface 143B is connected as an opening to the center of inner wall surface 143C when viewed from the opening surface of radio wave absorber 140. Inner wall surface 143D is connected to the outer edge of inner wall surface 143C.

[0044] Inner wall surface 143D is a side surface that extends in a truncated cone shape from the end of inner wall surface 143C on the +Y direction side, and inner wall surface 143E is connected to the end on the +Y direction side. Inner wall surface 143E is a side surface that extends in a cylindrical shape from the end on the +Y direction side of inner wall surface 143D, and has a constant diameter in the Y direction. Inner wall surface 143F is connected to the end on the +Y direction side of inner wall surface 143E.

[0045] The inner wall surface 143F is a side surface that extends in a truncated cone shape from the end of the inner wall surface 143E on the +Y direction side, and the end of the inner wall surface 143F on the +Y direction side is the opening 142.

[0046] The radio wave absorber 140 has a space surrounded by the inner wall surface 143 as described above, so that the primary radiation wave radiated from the transmitting antenna 120Tx in the +Y direction (radiation direction) does not come into contact with the inner wall surface 143. In other words, the inner wall surface 143 is located outside the radiation path of the primary radiation wave radiated from the transmitting antenna 120Tx. The primary radiation wave is a direct wave radiated from the transmitting antenna 120Tx and directly transmitted through the radio wave lens 130 without being reflected. The radiation path of the primary radiation wave radiated from the transmitting antenna 120Tx is the same as the first path P1 (see FIG. 2D ) taken by the first direct wave described below, and the primary radiation wave radiated from the transmitting antenna 120Tx is the same as the first direct wave described below. Details of this configuration will be described using FIG. 2B .

[0047] <Position of inner wall surface 143> Figure 2B is a diagram illustrating an example of the position of the inner wall surface 143 of the radio wave absorber 140. Figure 2B is a diagram in which, compared to Figure 2A, radio waves (transmitted waves) radiated from the transmitting antenna 120Tx, radio waves (received waves) received by the receiving antenna 120Rx, the aperture angle α of the radio wave lens 130, the diameter D of the radio wave lens 130, and the focal length FP of the radio wave lens 130 are added. The radio waves (transmitted waves) radiated from the transmitting antenna 120Tx are primary radiation waves. Note that in Figure 2B, some reference numerals are omitted for ease of viewing.

[0048] The aperture angle α of the radio wave lens 130 is the aperture angle of the radio wave lens 130 as seen from the focal point of the radio wave lens 130, and is an angle equivalent to the primary radio wave radiation angle of the transmitting and receiving antenna, which serves as the primary radiator, when the transmitting and receiving antenna is placed at the focal point of the radio wave lens 130.

[0049] The aperture angle α of the radio wave lens 130 is expressed by the following equation (1) using the diameter D of the radio wave lens 130 and the focal length FP of the radio wave lens 130. The aperture angle α depends on the type and specific structure of the transmitting and receiving antennas (transmitting antenna 120Tx and receiving antenna 120Rx) of the transmitting and receiving unit 120.

[0050]

[0051] The inner wall surface 143 of the radio wave absorber 140 is located outside the area represented by the aperture angle α. Because the area represented by the aperture angle α is included in the radiation path of the primary radiation wave radiated from the transmitting antenna 120Tx, the inner wall surface 143 is located outside the radiation path of the primary radiation wave radiated from the transmitting antenna 120Tx. The radio wave absorber 140 has the inner wall surface 143 shaped to be located outside the area represented by the aperture angle α, so as not to obstruct the radiation path of the primary radiation wave radiated from the transmitting antenna 120Tx. Furthermore, because the radio wave absorber 140 is located outside the area represented by the aperture angle α, it is configured not to obstruct the path of radio waves (received waves) that pass through the radio wave lens 130 from outside the antenna device 100 and are received by the receiving antenna 120Rx. Therefore, the antenna device 100 is able to detect a measurement target with high accuracy without a decrease in detection sensitivity due to attenuation of the transmitted and received waves within the radiation path.

[0052] 2B , radio waves (transmitted waves) as primary radiation waves radiated from transmitting antenna 120Tx are indicated by thick dashed lines, and radio waves (received waves) received by receiving antenna 120Rx are indicated by thick dashed lines. As indicated by the thick dashed lines, the primary radiation waves are radiated within the range of aperture angle α of radio wave lens 130 and pass through radio wave lens 130 without reaching inner wall surface 143. Furthermore, as indicated by the thick dashed lines, the received waves are focused as they pass through radio wave lens 130 and reach receiving antenna 120Rx without reaching inner wall surface 143.

[0053] 2B , the aperture angle of radio wave lens 130 is smaller than that of opening 112 of waveguide 110 when viewed from the focal point of radio wave lens 130. However, if the aperture angle of opening 112 of waveguide 110 is smaller than the aperture angle of radio wave lens 130 when viewed from the focal point of radio wave lens 130, then inner wall surface 143 should have a shape that is positioned outside the area expressed by aperture angle β of opening 112, which is calculated by the following equation (2).

[0054] 2B , the position of the focal point of radio wave lens 130 is the intersection point between the optical axis of radio wave lens 130 and the surface of substrate 121 of transceiver 120. For this reason, the aperture angle β of opening 112 as viewed from the intersection point between the optical axis of radio wave lens 130 and the surface of substrate 121 of transceiver 120 should satisfy the following formula (2), where Dd is the diameter of opening 112 and L is the distance between the intersection point and the center of opening 112.

[0055]

[0056] <Absorption of Reflected Waves by Radio Wave Absorber 140> Figure 2C is a diagram illustrating an example of absorption of reflected waves by radio wave absorber 140. In Figure 2C, the dimensions of the received waves and corners shown in Figure 2B are omitted, and some reference numerals are also omitted. Figure 2C shows transmitted wave 1 that is radiated from transmitting antenna 120Tx and passes through the center of radio wave lens 130, and transmitted waves 2 and 3 that are radiated from transmitting antenna 120Tx and pass through the radio wave lens 130 outside the center.

[0057] Transmission wave 1 passes through radio wave lens 130 with almost no reflection from the surface on the -Y direction side. When transmission wave 2 passes outside the center of radio wave lens 130, a portion of it is reflected, generating reflected wave 2. Reflected wave 2 is reflected toward inner wall surface 110A of waveguide 110, but reaches inner wall surface 143 of radio wave absorber 140 and is absorbed by radio wave absorber 140. Note that if radio wave absorber 140 were not present, reflected wave 2 would be reflected from the surface on the -Y direction side of radio wave lens 130, and then reflected from inner wall surface 110A of waveguide 110 as shown by the thin dashed line, and may reach transmitter / receiver unit 120 as a multiple-reflected wave.

[0058] Similarly to the transmitted wave 2, when the transmitted wave 3 passes outside the center of the radio wave lens 130, a portion of the transmitted wave 3 is reflected, generating a reflected wave 3. The reflected wave 3 is reflected toward the inner wall surface 110A of the waveguide 110, but reaches the inner wall surface 143 of the radio wave absorber 140 and is absorbed by the radio wave absorber 140. If the radio wave absorber 140 were not present, the reflected wave 3 would be reflected by the surface on the −Y direction side of the radio wave lens 130, and then reflected by the inner wall surface 110A of the waveguide 110 as shown by the thin dashed line, and may reach the transmitting / receiving unit 120 as a multiple-reflected wave.

[0059] In addition to these transmission waves 2 and 3, there are cases where a transmission wave, such as transmission wave 1, that reaches the center of the radio wave lens 130 closer to the center of the radio wave lens 130 than transmission waves 2 and 3 is reflected by the surface on the −Y direction side of the radio wave lens 130, and cases where a transmission wave that reaches the outside of the radio wave lens 130 closer to the outside of the radio wave lens 130 than transmission waves 2 and 3 is reflected by the surface on the −Y direction side of the radio wave lens 130. If the radio wave absorber 140 were not present, these reflected waves would be further reflected, causing multiple reflected waves that could reach the transmitter / receiver 120.

[0060] Furthermore, if the radio wave absorber 140 were not present, multiple reflected waves may occur due to reflection on the surface of the substrate 101 .

[0061] However, in reality, most of the multiple reflected waves can be absorbed because the radio wave absorber 140 is arranged as shown in Fig. 2C. In this way, the multiple reflected waves can be absorbed by the radio wave absorber 140, and therefore the reception of the multiple reflected waves by the receiving antenna 120Rx can be suppressed.

[0062] When the receiving antenna 120Rx receives multiple reflected waves, they become indistinguishable from received waves that have passed through the radio wave lens 130 and arrived directly at the receiving antenna 120Rx, reducing the detection accuracy of received waves that have passed through the radio wave lens 130 and arrived directly at the receiving antenna 120Rx. The closer the object to be measured is, the lower the detection accuracy becomes due to the effect of multiple reflections, and therefore the longer the shortest detection distance becomes.

[0063] The antenna device 100 of the embodiment includes the radio wave absorber 140 as described above, and therefore can suppress reception of multiple reflected waves by the receiving antenna 120Rx. The antenna device 100 of the embodiment can improve detection accuracy of the received waves at the receiving antenna 120Rx, thereby shortening the minimum detection distance and improving detection performance.

[0064] <Configuration of radio wave absorber 150> The radio wave absorber 150 will be described using Fig. 2D in addition to Fig. 1A to Fig. 1D and Fig. 2A to Fig. 2C. Fig. 2D is a diagram showing an example of the first path P1 and the second path P2 in a cross section taken along the line A-A in Fig. 1A.

[0065] The radio wave absorber 150 is provided to attenuate radio waves emitted from the transmitting antenna 120Tx. By attenuating the transmitted waves, the power of the transmitted waves is kept below the upper limit of the Radio Act, while the received waves are not attenuated, thereby realizing high reception sensitivity of the receiving antenna 120Rx. Like the radio wave absorber 140, the radio wave absorber 150 is, for example, a member molded from a resin mixed with magnetic or dielectric powder, and is a member that causes radio wave loss.

[0066] When viewed from the opening surface of the opening 111, the radio wave absorber 150 is located inside the opening 141 of the radio wave absorber 140, and is provided on the upper (+Z) side of the inner wall surfaces 143A and 143B of the inner wall surface 143 of the radio wave absorber 140. Here, the configuration of the radio wave absorber 150 will be described using the radial direction of the opening 141 of the radio wave absorber 140.

[0067] The outer surface in the radial direction of the radio wave absorber 150 is in contact with the inner wall surfaces 143A and 143B. Therefore, the boundary between the radio wave absorber 150 and the radio wave absorber 140 is curved.

[0068] In the Y direction, the radio wave absorber 150 is formed from the surface on the -Y direction side of the radio wave absorber 140 to a position between the end on the -Y direction side and the end on the +Y direction side of the inner wall surface 143B. The position in the Y direction of the surface on the -Y direction side of the radio wave absorber 140 is the same as the position in the Y direction of the opening 141. Therefore, when viewed from the opening surface of the opening 111, the radio wave absorber 150 overlaps with part of the substrate 101 and also overlaps with part of the transceiver unit 120 mounted on the surface on the +Y direction side of the substrate 101.

[0069] 1C and 1D , the radio wave absorber 150 is C-shaped when viewed from the plane of the opening 111, and is provided on the upper side of the inner wall surfaces 143A and 143B of the inner wall surface 143 in a state where the letter C is rotated 90 degrees clockwise. In other words, as shown in Fig. 1C , the radio wave absorber 150 is arranged so as to be located above the transmitting antenna 120Tx, diagonally above the +X direction side of the transmitting antenna 120Tx, and diagonally above the −X direction side of the transmitting antenna 120Tx when viewed from the plane of the opening 111.

[0070] 1C and 1D , the radio wave absorber 150 has a recess 151 recessed in the +Z direction so as to straddle the transmitting antenna 120Tx when viewed from the opening surface of the opening 111. The surface of the recess 151 facing the central axis C is composed of three flat surfaces, for example. A chamfered portion 151A is formed between a portion of the surface of the recess 151 facing the central axis C on the +Y direction side and the surface of the radio wave absorber 150 on the +Y direction side. The chamfered portion 151A is a portion obtained by obliquely chamfering the corner between the surface of the recess 151 facing the central axis C and the surface of the radio wave absorber 150 on the +Y direction side.

[0071] 1C and 1D, the recess 151 is not limited to a configuration formed by three flat surfaces, and may be curved in an arc shape, for example. Also, the radio wave absorber 150 does not have to have the chamfered portion 151A.

[0072] As an example, the radio wave absorber 150 is formed integrally with the radio wave absorber 140, but it may also be produced separately from the radio wave absorber 140 and attached to the radio wave absorber 140. When the radio wave absorber 150 is formed integrally with the radio wave absorber 140, it can be produced by, for example, integral molding or cutting. In the cross-sectional view of Fig. 2D, the radio wave absorber 150 and the radio wave absorber 140 are shown with different types of hatching in order to distinguish the radio wave absorber 150 from the radio wave absorber 140.

[0073] As shown in FIG. 2D , the radio wave absorber 150 is disposed on the opening 111 side in the space surrounded by the inner wall surface 110A of the waveguide 110. This is because the transmitting antenna 120Tx is located on the opening 111 side. At least a portion of the radio wave absorber 150 is located inside the first path P1 of the first direct wave that is radiated from the transmitting antenna 120Tx and reaches the radio wave lens 130 directly. This is to attenuate the first direct wave. In addition, the radio wave absorber 150 is located outside the second path P2 of the second direct wave that passes through the radio wave lens 130 and reaches the receiving antenna 120Rx directly. This is to achieve high and excellent reception sensitivity of the receiving antenna 120Rx without attenuating the second direct wave.

[0074] Here, the first direct wave is a transmission wave that is radiated from the transmitting antenna 120Tx, reaches the radio wave lens 130 directly, and passes through the radio wave lens 130. The first path P1 is a three-dimensional path that the first direct wave can pass through between the transmitting antenna 120Tx and the radio wave lens 130, and is a three-dimensional spatial region through which the first direct wave can pass. "At least a portion of the radio wave absorber 150 is located inside the first path P1" means that at least a portion of the radio wave absorber 150 is located within a three-dimensional spatial region through which the first direct wave can pass. The first path P1 is the same as the radiation path of the primary radiation wave radiated from the transmitting antenna 120Tx. The primary radiation wave radiated from the transmitting antenna 120Tx is the same as the first direct wave.

[0075] The three-dimensional spatial region through which the first direct wave can pass is the spatial region connecting the outer edge of the radio wave lens 130 and the outer edge of the transmitting antenna 120Tx. Note that, when the opening 112 of the waveguide 110 is located more inward than the outer edge of the radio wave lens 130, the three-dimensional spatial region through which the first direct wave can pass is the spatial region connecting the opening 112 of the waveguide 110 and the outer edge of the transmitting antenna 120Tx.

[0076] The second direct wave is a received wave that arrives from outside (the +Y direction side of) the radio wave lens 130, passes through the radio wave lens 130, and reaches the receiving antenna 120Rx directly. The second path P2 is a three-dimensional path that the second direct wave can pass through between the receiving antenna 120Rx and the radio wave lens 130, and is a three-dimensional spatial region through which the second direct wave can pass. The radio wave absorber 150 being located outside the second path P2 of the second direct wave means that the entire radio wave absorber 150 is located outside the three-dimensional spatial region through which the second direct wave can pass, and that the entire radio wave absorber 150 is not located inside the three-dimensional spatial region through which the second direct wave can pass.

[0077] The three-dimensional spatial region through which the second direct wave can pass is the spatial region connecting the outer edge of the radio wave lens 130 and the outer edge of the receiving antenna 120Rx. Note that, when the opening 112 of the waveguide 110 is located more inward than the outer edge of the radio wave lens 130, the three-dimensional spatial region through which the second direct wave can pass is the spatial region connecting the opening 112 of the waveguide 110 and the outer edge of the receiving antenna 120Rx.

[0078] Furthermore, the radio wave absorber 150 is provided on the transmitting antenna 120Tx side of the central axis C of the waveguide 110 when viewed from the opening surface of the opening 111. The radio wave absorber 150 attenuates the radio waves radiated by the transmitting antenna 120Tx, and is not located inside the second path P2 of the radio waves received by the receiving antenna 120Rx, so it is provided on the transmitting antenna 120Tx side of the central axis C of the waveguide 110 when viewed from the opening surface of the opening 111. The central axis C coincides with the optical axis of the radio wave lens 130.

[0079] It has been explained that the radio wave absorber 140 may have a shape in which the inner wall surface 143 is located outside the region represented by the aperture angle α expressed by equation (1) or outside the region represented by the aperture angle β of the opening 112 calculated by equation (2). However, the radio wave absorber 140 may have a configuration in which the inner wall surface 143 is located outside the first path P1 and the second path P2.

[0080] <Simulation Results> In order to verify the effect of the radio wave absorber 150, a simulation was performed on a comparative antenna device that does not include the radio wave absorber 150 and the antenna device 100 of the embodiment that includes the radio wave absorber 150, and the radiation characteristics of the transmitting antenna 120Tx and the receiving antenna 120Rx were calculated. The comparative antenna device has a configuration in which the radio wave absorber 150 is removed from the antenna device 100 of the embodiment.

[0081] 3A and 3B are diagrams showing an example of radiation characteristics of a comparative antenna device. 3C and 3D are diagrams showing an example of radiation characteristics of the antenna device 100 of the embodiment. 3A and 3C show radiation characteristics in an XY cross section passing through the central axis C, and 3B and 3D show radiation characteristics in a YZ cross section passing through the central axis C. In FIGS. 3A to 3D, the central axis C is located on a straight line connecting -90 degrees and 90 degrees.

[0082] The radiation characteristics of the comparative antenna device shown in Figures 3A and 3B were calculated by setting the receiving sensitivity of the receiving antenna 120Rx to a desired high level and setting the configurations of the transmitting antenna 120Tx and the receiving antenna 120Rx to the same level. Note that the radiation characteristics of the transmitted wave are shown by a solid line, and the radiation characteristics of the received wave are shown by a dashed line.

[0083] In Figure 3A, the radiation characteristics of the transmitted wave and the received wave are equal, and the radiation characteristics of the transmitted wave (solid line) and the radiation characteristics of the received wave (dashed line) completely overlap, so only the radiation characteristics of the transmitted wave represented by the solid line are shown. Also, in Figure 3B, it can be seen that the radiation characteristics of the transmitted wave on the +Z direction side are misaligned with the radiation characteristics of the received wave on the -Z direction side. This is because the transmitting antenna 120Tx is located above the central axis C, and the receiving antenna 120Rx is located below the central axis C.

[0084] The gain of the transmitted and received waves (antenna gain) of the comparative antenna device was both 15.4 dB. Because the receiving sensitivity of the receiving antenna 120Rx was set to a desired high level, the power of the transmitted waves (EIRP) exceeded the upper power limit set by the Radio Law.

[0085] In Fig. 3C, it can be seen that the radiation characteristics of the transmitted wave and the received wave are different, and the gain of the transmitted wave is smaller than the gain of the received wave. In Fig. 3D, it can also be seen that the gain of the transmitted wave is smaller than the gain of the received wave.

[0086] The antenna device 100 of the embodiment had a gain of 12.1 dB for the transmitted wave and a gain of 15.3 dB for the received wave. Although the receiving sensitivity of the receiving antenna 120Rx was set to a desired high level, the power of the transmitted wave was able to be kept below the upper power limit set by the Radio Law. Therefore, it was confirmed that by providing the radio wave absorber 150, it is possible to obtain high and good receiving sensitivity while keeping the power of the transmitted wave below the upper power limit set by the Radio Law.

[0087] <Effects> The antenna device 100 includes a substrate 101, a transceiver unit 120 having a transmitting antenna 120Tx and a receiving antenna 120Rx and mounted on the substrate 101, a waveguide 110 having an opening 111 (first opening) provided on the substrate 101 side and surrounding the transmitting antenna 120Tx and the receiving antenna 120Rx in an opening plane view, an opening 112 (second opening) provided on the back side of the opening 111 (first opening) in the radiation direction of the transmitting antenna 120Tx, and an inner wall surface 110A (first inner wall surface) connecting the opening 111 (first opening) and the opening 112 (second opening), and and a radio wave absorber 150 (first radio wave absorber) arranged on the side of the opening 111 (first opening) in the space surrounded by the inner wall surface 110A (first inner wall surface), wherein at least a portion of the radio wave absorber 150 (first radio wave absorber) is located inside a first path of a first direct wave that is radiated from the transmitting antenna 120Tx, reaches the radio wave lens 130 directly, and passes through the radio wave lens 130, while the radio wave absorber 150 (first radio wave absorber) is located outside a second path of a second direct wave that passes through the radio wave lens 130 and reaches the receiving antenna 120Rx directly. Therefore, high reception sensitivity can be obtained while attenuating the transmitted wave without attenuating the received wave.

[0088] Therefore, it is possible to provide an antenna device 100 that suppresses an increase in EIRP and has good radio wave receiving sensitivity.

[0089] Furthermore, the transmitting antenna 120Tx and the receiving antenna 120Rx are arranged on either side of the central axis C (the optical axis of the radio wave lens 130). Therefore, the first path P1 of the first direct wave and the second path P2 of the second direct wave are offset above and below the central axis C, respectively, and the radio wave absorber 150 can be arranged so as to be located inside the first path P1 and outside the second path P2. Therefore, by utilizing the difference in position between the first path P1 and the second path P2, it is possible to provide an antenna device 100 that suppresses an increase in EIRP and has good radio wave receiving sensitivity.

[0090] Furthermore, the radio wave absorber 150 (first radio wave absorber) is provided on the transmitting antenna 120Tx side of the central axis C (the optical axis of the radio wave lens 130) when viewed from the opening surface of the opening 111 (first opening). By providing the radio wave absorber 150 on the first path P1 side, it is possible to provide an antenna device 100 that is easy to attenuate the transmitted waves, suppresses an increase in EIRP, and has good radio wave receiving sensitivity.

[0091] The antenna device 100 further includes a cylindrical radio wave absorber 140 (second radio wave absorber) provided inside the inner wall surface 110A (first inner wall surface), and the radio wave absorber 140 (second radio wave absorber) is provided on the opening 111 (first opening) side and is smaller than the opening 111 (first opening) and the substrate 101 when viewed from the opening surface of the opening 111 (first opening). The radio wave absorber 140 (second radio wave absorber) has an opening 141 (third opening) that surrounds the transmitting antenna 120Tx and the receiving antenna 120Rx, an opening 142 (fourth opening) that is provided deeper than the opening 141 (third opening) in the radiation direction and is larger than the opening 141 (third opening), and an inner wall surface 143 (second inner wall surface) that connects the opening 141 (third opening) and the opening 142 (fourth opening). Therefore, it is possible to provide an antenna device 100 that reduces the effect of multiple reflections, improves detection performance, suppresses an increase in EIRP, and has good radio wave receiving sensitivity.

[0092] Furthermore, since the radio wave absorber 150 (first radio wave absorber) is formed integrally with the radio wave absorber 140 (second radio wave absorber), the radio wave absorbers 140 and 150 can be manufactured simultaneously, thereby reducing the number of parts, and it is also possible to simultaneously position the radio wave absorbers 140 and 150 relative to the transmitting antenna 120Tx and the receiving antenna 120Rx.

[0093] 4A and 4B are diagrams showing an example of the configuration of an antenna device 100M1 according to a first modification of the embodiment. Here, differences between the antenna device 100M1 and the antenna device 100 will be described. Of the components of the antenna device 100M1, the same components as those of the antenna device 100 are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0094] The antenna device 100M1 has a configuration in which the radio wave absorber 140 is removed from the antenna device 100, and a radio wave absorber 150 is attached to the surface on the +Y direction side of the substrate 101. The position and size of the radio wave absorber 150 of the antenna device 100M1 are the same as the position and size of the radio wave absorber 150 of the antenna device 100. For example, if the effect of multiple reflections is small, it is not necessary to include the radio wave absorber 140 as in the antenna device 100M1.

[0095] Furthermore, in the antenna device 100M1, since the radio wave absorber 150 is attached to the substrate 101, it is possible to achieve higher positioning accuracy of the radio wave absorber 150 with respect to the transmitting antenna 120Tx. For example, even if misalignment occurs between the substrate 101 and the cover 105 or the waveguide 110 when the antenna device 100 is mounted on a vehicle or the like, the position of the radio wave absorber 150 with respect to the transmitting antenna 120Tx will not be displaced, and therefore it is possible to attenuate transmitted waves with high accuracy.

[0096] The antenna device 100M1 has good radio wave reception sensitivity because the radio wave absorber 150 attenuates the transmitted waves while not attenuating the received waves. Furthermore, the radio wave absorber 150 is positioned with high precision relative to the transmitting antenna 120Tx, so the transmitted waves can be attenuated with high precision.

[0097] 5A to 5D are diagrams illustrating an example of the configuration of an antenna device 100M2 according to a second modification of the embodiment. Here, differences between the antenna device 100M2 and the antenna devices 100 and 100M1 will be described. Among the components of the antenna device 100M2, components that are the same as those of the antenna devices 100 and 100M1 are assigned the same reference numerals, and descriptions thereof will be omitted.

[0098] First, the description will be made using Figures 5A to 5C. The antenna device 100M2 has a configuration in which the radio wave absorber 140 is removed from the antenna device 100, and a radio wave absorber 150M2 is attached to the surface of the substrate 101 on the +Y direction side. The radio wave absorber 150M2 differs from the radio wave absorber 150 of the antenna devices 100 and 100M1 in that, when viewed from the opening surface of the opening 111, it covers the transmitting antenna 120Tx and is attached to the surface of the transceiver unit 120 by three legs 151M2 that protrude in the -Y direction. For example, if the effect of multiple reflections is small, it may not be necessary to include the radio wave absorber 140, as in the antenna device 100M2.

[0099] For example, when attenuating the transmission wave so that the power falls below the upper power limit set by the Radio Law from a state in which the gains of the transmitting antenna 120Tx and the receiving antenna 120Rx are equal, if it is better to cover the transmitting antenna 120Tx as viewed from the opening surface of the opening 111, then a radio wave absorber 150M2 can be used to cover the transmitting antenna 120Tx as viewed from the opening surface of the opening 111.

[0100] Furthermore, in the antenna device 100M2, the radio wave absorber 150M2 is attached to the substrate 101 in the same manner as in the antenna device 100M1, and therefore higher positioning accuracy of the radio wave absorber 150M2 with respect to the transmitting antenna 120Tx can be achieved. For example, even if misalignment occurs between the substrate 101 and the cover 105 or the waveguide 110 when the antenna device 100 is mounted on a vehicle or the like, the position of the radio wave absorber 150M2 with respect to the transmitting antenna 120Tx will not be displaced, and therefore the transmitted waves can be attenuated with high accuracy.

[0101] Since the radio wave absorber 150M2 can attenuate the transmitted waves while achieving high reception sensitivity without attenuating the received waves, it is possible to provide the antenna device 100M2 with good radio wave reception sensitivity. Furthermore, since the radio wave absorber 150 is positioned with high precision relative to the transmitting antenna 120Tx, the transmitted waves can be attenuated with high precision.

[0102] The radio wave absorber 150M2 may cover a part of the transmitting antenna 120Tx when viewed from the surface of the opening 111. In other words, the radio wave absorber 150M2 may be configured to cover at least a part of the transmitting antenna 120Tx when viewed from the surface of the opening 111. Fig. 5D shows a configuration in which the radio wave absorber 150M2 covers the upper half of the transmitting antenna 120Tx when viewed from the surface of the opening 111.

[0103] The radio wave absorber 150M2 can attenuate the transmission wave by covering at least a part of the transmitting antenna 120Tx when viewed from the opening surface of the opening 111. Furthermore, the attenuation rate of the transmission wave can be set by adjusting the vertical length of the radio wave absorber 150M2 and adjusting the proportion of the radio wave absorber 150 that covers the transmitting antenna 120Tx.

[0104] 6A to 6C are diagrams illustrating an example of the configuration of an antenna device 100M3 according to a third modification of the embodiment. Here, differences between the antenna device 100M3 and the antenna device 100 will be described. Of the components of the antenna device 100M3, the same components as those of the antenna device 100 are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0105] <Configuration of antenna device 100M3> The antenna device 100M3 has a configuration in which the radio wave absorber 140 of the antenna device 100 is omitted, a waveguide 110M3 is included instead of the waveguide 110, and a radio wave absorber 150M3 is included instead of the radio wave absorber 150 and is fixed to the waveguide 110 with a holder 155.

[0106] <Configuration of Waveguide 110M3> Waveguide 110M3 has opening 111, opening 112, recess 113A, inner wall surface 114A, inner wall surface 115A, and inner wall surface 116A. The central axes of opening 111, opening 112, recess 113A, inner wall surface 114A, inner wall surface 115A, and inner wall surface 116A are aligned on central axis C.

[0107] The openings 111 and 112 correspond to the openings 111 and 112 of the waveguide 110 .

[0108] The recess 113A is provided on the -Y direction side of the opening 111, and is a portion into which the holder 155 is fitted. The recess 113A is a cylindrically recessed portion from the surface on the -Y direction side of the waveguide 110M3 toward the +Y direction side. The central axis of the recess 113A coincides with the central axis C. The radial length of the recess 113A is longer than the radius of the opening 111. Therefore, when the waveguide 110M3 is viewed from the opening surface on the -Y direction side, the recess 113A is larger than the opening 111.

[0109] The inner wall surface 114A is a cylindrical wall surface (a wall surface corresponding to the inner circumferential surface of a cylinder) with a constant diameter, and is connected to the +Y direction side of the opening 111. The diameter of the inner wall surface 114A is equal to the diameter of the opening 111.

[0110] The inner wall surface 115A is a wall surface (a wall surface corresponding to the outer peripheral surface of the truncated cone) extending from the end of the inner wall surface 114A on the +Y direction side, and the opening 112 is located at the end on the +Y direction side. The inner wall surface 115A is located outside the region represented by the opening angle α expressed in Equation (1). The inner wall surface 115A is also located outside the first path P1 and the second path P2 shown in FIG. 2D .

[0111] The inner wall surface 116A is a cylindrical wall surface (a wall surface corresponding to the inner peripheral surface of a cylinder) provided on the +Y direction side of the opening 112, and is larger than the opening 112 when viewed from the opening surface of the waveguide 110M3.

[0112] <Configuration of radio wave absorber 150M3 and holder 155> The radio wave absorber 150M3 has a disk shape and has a through-hole 151M3 located on the +Y direction side of the receiving antenna 120Rx. The through-hole 151M3 penetrates approximately half of the radio wave absorber 150M3 on the -Z direction side in the Y direction. The through-hole 151M3 has a cylindrical inner wall surface (a wall surface corresponding to the inner circumferential surface of a cylinder) with a constant diameter.

[0113] Like the radio wave absorber 150, the radio wave absorber 150M3 is, for example, a molded member made of resin mixed with magnetic or dielectric powder, and is a member that causes radio wave loss. The holder 155 is preferably non-metallic and is made of a dielectric material. For example, the holder 155 can be made of resin or ceramic.

[0114] When held by the holder 155, the radio wave absorber 150M3 covers the transmitting antenna 120Tx and exposes the receiving antenna 120Rx from the through-hole 151M3 when viewed from the opening surface of the waveguide 110M3. The inner wall surface of the through-hole 151M3 is located outside the second path P2 shown in Fig. 2D. Therefore, the first direct wave output from the transmitting antenna 120Tx is attenuated by the radio wave absorber 150M3, but the second direct wave reaching the receiving antenna 120Rx is not attenuated by the radio wave absorber 150M3 because it passes through the inside of the through-hole 151M3.

[0115] Holder 155 is a disk-shaped member larger than radio wave absorber 150M3, and has recess 155A formed along central axis C from the -Y direction side, and opening 155B provided on the +Y direction side of recess 155A. Recess 155A and opening 155B are circular and centered on central axis C when holder 155 is viewed from the -Y direction side. Recess 155A has a cylindrical inner wall surface (a wall surface corresponding to the inner circumferential surface of a cylinder) with a constant diameter, and opening 155B, which has a smaller diameter than recess 155A, communicates with the end on the +Y direction side. Recess 155A and opening 155B penetrate holder 155 in the Y direction.

[0116] A radio wave absorber 150M3 is fitted into the cylindrical inner wall surface of the recess 155A. In this state, the edge of the opening 155B is located outside the transmitting antenna 120Tx and the receiving antenna 120Rx when viewed from the opening surface of the opening 111 of the waveguide 110M3. In other words, the edge of the opening 155B is located outside the first path P1 and the second path P2 shown in FIG. 2D .

[0117] By attaching the radio wave absorber 150M3 to such a holder 155 and fitting the holder 155 into the recess 113A of the waveguide 110M3, the radio wave absorber 150M3 can be attached to the waveguide 110M3 as shown in FIGS. 6A to 6C.

[0118] When the radio wave absorber 150M3 is attached to the waveguide 110M3, the radio wave absorber 150M3 is located inside the first path P1 of the first direct wave output from the transmitting antenna 120Tx, but outside the second path P2 of the second direct wave reaching the receiving antenna 120Rx. Therefore, the radio wave absorber 150M3 can attenuate the transmitted wave while obtaining high reception sensitivity without attenuating the received wave, and it is possible to provide the antenna device 100M3 with good radio wave reception sensitivity.

[0119] Furthermore, in the antenna device 100M3, the radio wave absorber 150M3 is attached to the waveguide 110M3, so that the accuracy of positioning between the waveguide 110M3 and the radio wave absorber 150M3 can be improved.

[0120] The holder 155 is only required to be able to hold the radio wave absorber 150M3 as described above, and is not limited to a disk shape and may have various other shapes.

[0121] The above describes an antenna device according to an exemplary embodiment of the present disclosure, but the present disclosure is not limited to the specifically disclosed embodiment, and various modifications and variations are possible without departing from the scope of the claims.

[0122] This international application claims priority based on Japanese Patent Application No. 2022-200579, filed on December 15, 2022, the entire contents of which are incorporated herein by reference.

[0123] 100, 100M1, 100M2, 100M3 Antenna device 101 Substrate 110, 110M3 Waveguide 110A Inner wall surface (an example of a first inner wall surface) 111 Opening (an example of a first opening) 112 Opening (an example of a second opening) 113A Recess 114A Inner wall surface 115A Inner wall surface 116A Inner wall surface 120 Transmitter / receiver (an example of an integrated circuit chip) 120Tx Transmitting antenna 120Rx Receiving antenna 121 Substrate 130 Radio wave lens 140 Radio wave absorber (an example of a second radio wave absorber) 141 Opening (an example of a third opening) 142 Opening (an example of a fourth opening) 143 Inner wall surface (an example of a second inner wall surface) 150, 150M2, 150M3 Radio wave absorber (an example of a first radio wave absorber) 151 Recess 151A Chamfered portion 151M3 Through hole 155 Holder

Claims

1. A substrate; an integrated circuit chip mounted on the substrate, the integrated circuit chip having a transmitting antenna and a receiving antenna; a waveguide having a first opening provided on the substrate side and surrounding the transmitting antenna and the receiving antenna in an opening plane view, a second opening provided on a deeper side than the first opening in a radiation direction of the transmitting antenna, and a first inner wall surface connecting the first opening and the second opening; a radio wave lens fixed to the second opening; a first radio wave absorber disposed on the first opening side in a space surrounded by the first inner wall surface; Equipped with at least a portion of the first radio wave absorber is located inside a first path of a first direct wave that is radiated from the transmitting antenna, directly reaches the radio wave lens, and transmits through the radio wave lens; The antenna device, wherein the first radio wave absorber is located outside a second path of a second direct wave that passes through the radio wave lens and directly reaches the receiving antenna.

2. The antenna device according to claim 1 , wherein the first radio wave absorber covers at least a portion of the transmitting antenna when seen from an opening surface of the first opening.

3. 3. The antenna device according to claim 1, wherein the transmitting antenna and the receiving antenna are disposed on either side of an optical axis of the radio wave lens.

4. The antenna device according to claim 3 , wherein the first radio wave absorber is provided closer to the transmitting antenna than the optical axis is when viewed from the opening surface of the first opening.

5. a cylindrical second radio wave absorber provided inside the first inner wall surface, The second wave absorber is a third opening provided on the first opening side, smaller than the first opening and the substrate when viewed from the opening surface of the first opening, and surrounding the transmitting antenna and the receiving antenna; A fourth opening portion is provided on a rear side of the third opening portion in the radial direction and is larger than the third opening portion; a second inner wall surface connecting the third opening and the fourth opening; The antenna device according to claim 1 , further comprising:

6. The antenna device according to claim 5 , wherein the second inner wall surface of the second radio wave absorber is located outside the first path and the second path.

7. The antenna device according to claim 6 , wherein the first radio wave absorber is integrally formed with the second radio wave absorber.