Antenna Device

Abstract

Provided is an antenna device which is compact and has a narrow beam width.　This antenna device comprises: a wave guide; a transmission antenna that is provided on a first opening part side of the wave guide and that transmits a radio wave through the wave guide; a reception antenna that is provided on the first opening part side of the wave guide and that receives a radio wave through the wave guide; and a lens that is provided on a second opening part side of the wave guide and through which a radio wave transmitted from the transmission antenna or a radio wave received by the reception antenna passes. The opening area of the first opening part is larger than the opening area of the second opening part. The transmission antenna and the reception antenna are disposed by being shifted from the optical axis of the lens.

Description

[Technical field]

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

[0002] Conventionally, there has been a sensor having an antenna, the antenna having a substrate, a radiating portion formed on the substrate, and a waveguide that internally propagates electromagnetic waves radiated from the radiating portion and radiates them as a beam, the waveguide having a radiation side opening that is longer in a second direction than in a first direction perpendicular to each other, the radiation side opening being larger than an opening on the opposite side to the radiation side opening, the edge of the opening on the opposite side to the radiation side opening being positioned so as to enclose the radiating portion on the substrate surface side on which the radiating portion is formed, the radiation side opening having a dielectric lens (lens), and the electric field surface direction of the radiating portion being the second direction (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-054546 A Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional sensor antennas (antenna devices), the waveguide has a larger radiating side opening than the opening on the opposite side, and the shape of the radiating side opening is longer in the second direction than in the first direction, which are perpendicular to each other, resulting in a flat beam that is narrow in the first direction and wide in the second direction.

[0005] However, in order to narrow the beam width overall in both the first and second directions, it is necessary to increase the diameter of the waveguide, which requires the waveguide to be long. In addition, increasing the diameter of the waveguide also increases the size of the lens. As a result, the antenna device becomes larger.

[0006] Therefore, an object of the present invention is to provide an antenna device that is small and has a narrow beam width. [Means for solving the problem]

[0007] An antenna device according to an embodiment of the present disclosure includes a waveguide, a transmitting antenna provided on a first opening side of the waveguide and transmitting radio waves through the waveguide, a receiving antenna provided on the first opening side of the waveguide and receiving radio waves through the waveguide, and a lens provided on a second opening side of the waveguide and transmitting radio waves transmitted from the transmitting antenna or radio waves received by the receiving antenna, wherein an opening area of ​​the first opening is larger than an opening area of ​​the second opening, and the transmitting antenna and the receiving antenna are positioned offset from the optical axis of the lens. Effect of the Invention

[0008] It is possible to provide a small antenna device with a narrow beam width. [Brief description of the drawings]

[0009] [Figure 1A] 1 is a diagram illustrating an antenna device 100 according to an embodiment. [Figure 1B] 1 is a diagram illustrating an antenna device 100 according to an embodiment. [Figure 2A] FIG. 2 is a cross-sectional view taken along the line AA in FIG. 1A. [Figure 2B] FIG. 2B is a diagram showing a modification of the cross-sectional structure shown in FIG. 2A. [Diagram 3] 2 is a diagram illustrating details of an inner wall surface 110A of a waveguide 110. FIG. [Figure 4A] 10 is a diagram for explaining the condition under which the radiation electric field V1 and the radiation electric field V2 are in opposite phase. FIG. [Figure 4B] 10 is a diagram illustrating a transmission path in a comparative waveguide 50. FIG. [Figure 4C] 10 is a diagram for explaining the direction in which the radio wave intensity is strongest in a comparative antenna device 10 including a comparative waveguide 50. FIG. [Figure 5A] 13 is a diagram showing a simulation result of the beam width of a round-trip beam in an antenna device 10 including a comparative waveguide 50. FIG. [Figure 5B] 11A and 11B are diagrams illustrating simulation results of the beam width of a round-trip beam in the antenna device 100 according to the embodiment. [Figure 6A] 11 is a diagram showing a simulation result of a radiation pattern in the antenna device 10 for comparison. [Figure 6B] 11 is a diagram showing a simulation result of a radiation pattern in the antenna device 10 for comparison. [Figure 7A] 11 is a diagram showing a simulation result of a radiation pattern in the antenna device 10 for comparison. [Figure 7B] 5A to 5C are diagrams illustrating simulation results of a radiation pattern in the antenna device 100 according to the embodiment. [Figure 8A] FIG. 13 is a diagram showing an antenna device 100M according to a modified example of the embodiment. [Figure 8B] FIG. 13 is a diagram showing an antenna device 100M according to a modified example of the embodiment. [Figure 9] A diagram showing a dielectric waveguide 210. [Figure 10] FIG. 2 shows a flat lens 230A having a Fresnel zone 235A. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment to which the antenna device of the present disclosure is applied will be described.

[0011] <Embodiment> <Configuration of Antenna Device 100> 1A and 1B are diagrams showing an antenna device 100 according to an embodiment. FIG. 1A is a perspective view, and FIG. 1B is a diagram showing a part in half section. FIG. 2A is a diagram showing a section taken along line AA in FIG. 1A, and is a diagram showing a cut surface obtained by cutting the waveguide 110 on a YZ plane including the optical axis of the lens 130. FIG. 2B is a diagram showing a modified example of the cross-sectional structure shown in FIG. 2A. Here, unless otherwise specified, the configuration of the antenna device 100 will be described using FIG. 1A, FIG. 1B, and FIG. 2A.

[0012] In the following, the XYZ coordinate system is defined and explained. For convenience of explanation, the -Z direction side is called the lower side or bottom, and the +Z direction side is called the upper side or top, but this does not represent a universal relationship between up and down. Also, viewing from the XZ plane is called a planar view.

[0013] The antenna device 100 includes a substrate 101, a waveguide 110, a transmitting / receiving unit 120, and a lens 130. The antenna device 100 is a device that transmits and receives radio waves, and focuses the transmitted waves into a beam by the lens 130, and also focuses the received beam by the lens.

[0014] 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 almost the same as light. Note that the radio waves transmitted and received by the antenna device 100 may be radio waves in a frequency band other than the millimeter wave band.

[0015] The substrate 101 is a substrate on which the transmitting / receiving 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.

[0016] As an example, the waveguide 110 is a cylindrical, hollow circular waveguide. The waveguide 110 has an inner wall surface 110A, an opening 111, an opening 112, and an attachment portion 115. The inside of the waveguide 110 is a waveguide through which radio waves propagate. 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 the first opening side, and the +Y direction side is an example of the second opening side.

[0017] 1A, 1B, and 2A, the origin of the XYZ coordinates coincides with the center of the aperture 111, and the central axis C of the waveguide 110 coincides with the Y axis. In addition, the central axis C coincides with the optical axis of the lens 130.

[0018] Inner wall surface 110A is the inner wall of cylindrical hollow waveguide 110. Since the opening diameter of opening 111 is larger than the opening diameter of opening 112, waveguide 110 is a truncated cone-shaped cylinder whose opening diameter decreases from opening 111 toward opening 112. Therefore, inner wall surface 110A has a truncated cone shape. The fact that the opening diameter of opening 111 is larger than the opening diameter of opening 112 means that the opening area of ​​opening 111 is larger than the opening area of ​​opening 112. Details of inner wall surface 110A, such as the angle, will be described later with reference to FIG. 3.

[0019] 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 a plan view. As described above, the opening diameter of the opening 111 is larger than the opening diameter of the opening 112, and is, for example, 15 mm (φ15 mm).

[0020] Aperture 112 is an opening located at the end of waveguide 110 on the +Y direction side. Strictly speaking, aperture 112 is offset in the -Y direction from the end of waveguide 110 on the +Y direction side by the amount of step portion 112A (see FIG. 2A); however, since the section that functions as waveguide 110 through which radio waves propagate is the section between apertures 111 and 112, aperture 112 will be described here as being located at the end of waveguide 110 on the +Y direction side. In this sense, step portion 112A may be treated as protruding further in the +Y direction from the end of waveguide 110 on the +Y direction side.

[0021] The opening 112 is circular in a plan view. The opening diameter of the opening 112 is smaller than the opening diameter of the opening 111, and is, for example, 14.3 mm (φ14.3 mm). As shown in FIG. 2A, the opening 112 is provided with a step 112A. The step 112A is a step for attaching the lens 130 to the opening 112. The lens 130 is attached to the waveguide 110 from the +Y direction side.

[0022] 2B, the step 112A may be provided on the -Y direction side of the opening 112. In the case of such a structure, the lens 130 is attached from the opening 111 side of the waveguide 110 through the inside.

[0023] 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.

[0024] With lens 130 attached to waveguide 110 as described above, the focal point of lens 130 is located at the center of opening 111 in a plan view. That is, the length of central axis C of waveguide 110 in the extension direction is set so that the focal point of lens 130 is located on the opening plane of opening 111.

[0025] The transmitting / receiving unit 120 is mounted on the surface of the substrate 101 on the +Y direction side. The transmitting / receiving unit 120 has a substrate 121, a transmitting antenna 120Tx, and a receiving antenna 120Rx. The substrate 121 is smaller than the substrate 101 in a planar view, and is, for example, square. The substrate 121 is provided so as to be located at the center of the opening 111 in a planar view, and more specifically, is disposed so that the center of the substrate 121 in a planar view is located on the central axis C.

[0026] The transmitting antenna 120Tx and the receiving antenna 120Rx are provided on the surface on the +Y direction side of the substrate 121 with a gap therebetween 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.

[0027] 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 aperture surface of the opening 111.

[0028] The transmitting antenna 120Tx and the receiving antenna 120Rx being point symmetrical 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 symmetrical 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. Since the central axis C coincides with the optical axis of the lens 130, the transmitting antenna 120Tx and the receiving antenna 120Rx are arranged offset from the optical axis of the lens 130.

[0029] 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 about 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 lens 130, the transmitting antenna 120Tx and the receiving antenna 120Rx are arranged so as to be point-symmetrical about the central axis C.

[0030] 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 lens 130), they are placed in this manner in order to align the transmission and reception characteristics of the transmitting antenna 120Tx and the receiving antenna 120Rx. Note that 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.

[0031] The length in the extension direction of the central axis C of the waveguide 110 is set so that the focal point of the lens 130 is located on the opening plane of the opening 111, so that the position in the extension direction of the optical axis (central axis C of the waveguide 110) of the lens 130 of the transmitting antenna 120Tx and the receiving antenna 120Rx is equal to the focal position of the lens 130.

[0032] Here, in a cross section parallel to the YZ plane including the optical axis of the lens 130 (cross section shown in FIG. 2A), a straight line connecting the center of the transmitting antenna 120Tx and the center 130C of the lens 130 is indicated by a dashed line, and a straight line connecting the center of the receiving antenna 120Rx and the center 130C of the lens 130 is indicated by a dashed line. Since the transmitting antenna 120Tx and the receiving antenna 120Rx are arranged offset from the optical axis of the lens 130, the straight lines connecting their centers do not coincide. The strength of the radio wave radiated from the transmitting antenna 120Tx is strongest in the direction connecting the center of the transmitting antenna 120Tx and the center 130C of the lens 130, and the strength of the radio wave received by the receiving antenna 120Rx is strongest in the direction connecting the center of the receiving antenna 120Rx and the center 130C of the lens 130.

[0033] The 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 lens 130 may be a single-convex lens. A biconvex lens and a single-convex lens are examples of a convex lens. The lens 130 may be a flat lens such as a flat lens having a Fresnel zone or a flat lens having a metamaterial, but here, a form in which the lens is a biconvex lens will be described.

[0034] <Details of inner wall surface 110A of waveguide 110> Fig. 3 is a diagram illustrating details of inner wall surface 110A of waveguide 110. Like Figs. 2A and 2B, Fig. 3 is a diagram illustrating a cross section obtained by cutting waveguide 110 in the YZ plane including the optical axis of lens 130.

[0035] Here, an explanation will be given of the angle α between the optical axis of lens 130 (central axis C of waveguide 110) and inner wall surface 110A of waveguide 110 in a cross section obtained by cutting waveguide 110 in the YZ plane including the optical axis of lens 130 shown in Fig. 3. Angle α is the angle that inner wall surface 110A makes with the optical axis of lens 130 (central axis C of waveguide 110) in the cross section shown in Fig. 3, and as an example, when the cross section parallel to the YZ plane is viewed from the +X direction side to the -X direction side, a clockwise angle is shown as a positive value. In Fig. 3, an axis Ca parallel to the optical axis of lens 130 (central axis C of waveguide 110) is shown to indicate angle α.

[0036] Angle α is the inclination angle of inner wall surface 110A with respect to central axis C of waveguide 110. Since the opening area of ​​opening 111 is larger than the opening area of ​​opening 112 and the inclination angle of inner wall surface 110A is constant between openings 111 and 112, inner wall surface 110A is inclined so as to face the opening 111 side with respect to central axis C. For this reason, the radio wave radiated from transmitting antenna 120Tx and reflected by inner wall surface 110A is reflected toward the direction of the central axis C.

[0037] That is, the radio waves radiated from the transmitting antenna 120Tx propagate through two propagation paths: Path 1 (dashed line) for the radio waves that directly enter the lens 130, and Path 2 (dotted line) for the radio waves that are reflected by the inner wall surface 110A toward the direction of the central axis C and enter the lens 130.

[0038] Similarly, radio waves propagating from the lens 130 toward the receiving antenna 120Rx propagate through two propagation paths: one in which the radio waves enter the receiving antenna 120Rx directly from the lens 130, and the other in which the radio waves are reflected by the inner wall surface 110A toward the direction of the central axis C and enter the receiving antenna 120Rx.

[0039] The angle α is set to a predetermined angle that creates a relationship in which the beam angle β of the radio wave directly incident on the lens 130 from the transmitting antenna 120Tx is relatively large as shown in FIG. 3, and the radiation electric field V1 on the propagation path Path1 (dashed line) that is incident on a portion outside the center of the lens 130 is in opposite phase to the radiation electric field V2 on the propagation path Path2 (dash-dotted line) of the radio wave that is reflected from the transmitting antenna 120Tx by the inner wall surface 110A and incident on the lens 130. The radiation electric field V1 and the radiation electric field V2 are in opposite phase on a plane P0 perpendicular to the propagation paths Path1 and Path2 within a range where the angle α is the predetermined angle. The beam angle β of the radio wave emitted from the transmitting antenna 120Tx is an angle with respect to an axis CTx that passes through the center of the transmitting antenna 120Tx and is parallel to the central axis C.

[0040] If the angle (radiation angle) of propagation path Path1 with respect to the optical axis of lens 130 (central axis C of waveguide 110) is large, the beam width of the beam radiated in the +Y direction through lens 130 becomes wide, so by making radiated electric fields V1 and V2 out of phase, the direct wave of path Path1, which has a large radiation angle, and the reflected wave of propagation path Path2 are offset (weakened together), thereby narrowing the beam width. Next, the conditions under which radiated electric fields V1 and V2 are out of phase will be described in detail.

[0041] <Conditions for the radiated electric field V1 and the radiated electric field V2 to be in opposite phase> Fig. 4A is a diagram for explaining the condition under which the radiation electric field V1 and the radiation electric field V2 are in opposite phase. Fig. 4A, like Figs. 2A, 2B, and 3, shows a schematic configuration of a cross section obtained by cutting the waveguide 110 in the YZ plane including the optical axis of the lens 130.

[0042] Further, the transmitting antenna 120Tx and the receiving antenna 120Rx are arranged so as to be point-symmetric with respect to the central axis C on a cross section obtained by cutting the waveguide 110 on the YZ plane including the optical axis of the lens 130, and therefore, although the transmitting antenna 120Tx will be described here, the same is true for the receiving antenna 120Rx. In addition to the axis Ca serving as the reference for the angle α, Fig. 4A also shows an axis CTx that passes through the center of the transmitting antenna 120Tx and is parallel to the central axis C.

[0043] If the angle between the axis CTx and a propagation path Path1 (dashed line) of the radio wave directly incident on the lens 130 from the transmitting antenna 120Tx is β1, and the angle between the axis CTx and a propagation path Path2 of the radio wave reflected from the transmitting antenna 120Tx by the inner wall surface 110A and incident on the lens 130 is β2, the following equation (1) is established. Note that the angle β1 is positive when it is counterclockwise with respect to the axis CTx, and the angle β2 is positive when it is clockwise with respect to the axis CTx. β1=β2+2α (1)

[0044] When the angle β1 of the propagation path Path1 is small, it contributes to narrowing the beam width of the beam radiated in the +Y direction through the lens 130, but when the angle β1 is large, it causes the beam width to become wider. Therefore, for radio waves with a relatively large angle β1, if the condition that the radiated electric field V1 and the radiated electric field V2 are in opposite phase on the plane P0 is satisfied, the radio waves with a relatively large angle β1 can be offset (weakened) by the reflected wave. As a result, the strength of the radio waves with a relatively narrow angle β1 can be relatively increased, and a beam can be formed with the radio waves with a relatively narrow angle β1.

[0045] Here, L11 is the length of the section of propagation path Path1 from transmitting antenna 120Tx to the surface of lens 130, L12 is the length of the section of propagation path Path1 within lens 130, and L13 is the length of the section of propagation path Path1 from the surface of lens 130 to plane P0.

[0046] Moreover, L21 is the length of the section of the propagation path Path2 from the transmitting antenna 120Tx to the inner wall surface 110A, and L22 is the length of the section of the propagation path Path2 from the inner wall surface 110A to the surface of the lens 130. Moreover, L23 is the length of the section of the propagation path Path2 inside the lens 130, and L24 is the length of the section of the propagation path Path2 from the surface of the lens 130 to the plane P0. The following equation (2) holds for the lengths L11, L12, L13, L21, L22, L23, and L24. Here, λ is the wavelength of the radio wave transmitted by the transmitting antenna 120Tx, and εr is the dielectric constant of the material of the lens 130. L11+L12×√εr+λ / 2+L13=L21+L22+L23×√εr+L24 (2)

[0047] Therefore, the angle α between the optical axis of lens 130 (the central axis C of waveguide 110) and inner wall surface 110A of waveguide 110 may be set so as to satisfy formula (2). As an example, such angle α is greater than 0 degrees and less than or equal to 45 degrees (0°<α≦45°).

[0048] <Transmission path in a waveguide for comparison> Fig. 4B is a diagram illustrating a transmission path in a comparative waveguide 50. In the comparative waveguide 50 shown in Fig. 4B, the opening area of ​​the opening 52 on the lens 130 side is larger than the opening area of ​​the opening 51 on the side where the transmitting antenna 120Tx is provided. For this reason, the propagation path of the reflected wave (dashed line) that is radiated from the transmitting antenna 120Tx, reflected by the inner wall 50A, and incident on the lens 130 does not intersect with the propagation path of the direct wave (dashed line) that is radiated from the transmitting antenna Tx and directly incident on the lens 130.

[0049] That is, when the opening area of ​​the opening 52 on the lens 130 side is larger than the opening area of ​​the opening 51 on the side where the transmitting antenna 120Tx is provided, as in the comparative waveguide 50, the direct wave and the reflected wave do not cancel each other out, and the beam angle of the beam radiated from the lens 130 becomes large.

[0050] 4C is a diagram for explaining the direction in which the radio wave intensity is strongest in the comparative antenna device 10 including the comparative waveguide 50. As in the description of the antenna device 100 of the embodiment using FIG. 2A, in the comparative antenna device 10, the intensity of the radio wave radiated from the transmitting antenna 120Tx is strongest in the direction connecting the center of the transmitting antenna 120Tx and the center 130C of the lens 130 (the direction of the dashed line), and the intensity of the radio wave received by the receiving antenna 120Rx is strongest in the direction connecting the center of the receiving antenna 120Rx and the center 130C of the lens 130 (the direction of the dashed line). The transmitting antenna 120Tx and the receiving antenna 120Rx are arranged offset from the optical axis of the lens 130, so the straight lines connecting their centers do not coincide.

[0051] <Beam width simulation results> Fig. 5A is a diagram showing the results of a simulation of the beam width of a round-trip beam in an antenna device 10 (see Fig. 4C) including a comparative waveguide 50. In Fig. 5A, the horizontal axis represents the beam angle (degrees) in a YZ plane including the optical axis of the lens 130, and the direction of a beam angle of 90 degrees is the +Y direction relative to the origin of the XYZ coordinate system, 0 degrees is the +Z direction, and 180 degrees is the -Z direction. The vertical axis represents the antenna gain (dBi). Here, the beam width (3 dB beam width) obtained in the beam angle range from the maximum value of the antenna gain to -3 dB is examined.

[0052] Figure 5A shows the total round-trip antenna gain of the antenna gain of the transmitting beam Tx transmitted from the transmitting antenna 120Tx of the comparative antenna device 10 and the antenna gain of the receiving beam Rx received by the receiving antenna 120Rx of the comparative antenna device 10.

[0053] The 3 dB beam width of the round trip antenna gain was in the range of about 65 degrees to about 115 degrees, and in the range of about ±25 degrees with respect to the 90 degree front direction. Thus, it was found that the antenna device 10 including the comparative waveguide 50 (see FIG. 4C) had a larger beam angle and a wider beam width.

[0054] Fig. 5B is a diagram showing simulation results of the round-trip beam width of the antenna device 100 of the embodiment. The horizontal and vertical axes in Fig. 5B are the same as those in Fig. 5A. Here, as in Fig. 5A, the beam width is considered to be 3 dB beam width.

[0055] FIG. 5B shows the total round-trip antenna gain of the antenna gain of the transmission beam Tx transmitted from the transmitting antenna 120Tx of the antenna device 100 of the embodiment and the antenna gain of the receiving beam Rx received by the receiving antenna 120Rx of the antenna device 100 of the embodiment.

[0056] The 3 dB beam width of the round trip antenna gain was in the range of about 76.5 degrees to about 103.5 degrees, which was in the range of about ±13.5 degrees with respect to the 90 degree front direction. Thus, it was found that in the antenna device 100 of the embodiment, the beam angles at both ends of the 3 dB beam width were about half as large as the antenna device 10 including the comparative waveguide 50 (see FIG. 4C), and the beam width was narrowed to about half. This is thought to be the effect of canceling out the large beam angle components.

[0057] <Simulation results of radiation pattern (YZ plane)> Fig. 6A is a diagram showing a simulation result of the radiation pattern (radiation characteristics) of the antenna device 10 for comparison (see Fig. 4C). Fig. 6B is a diagram showing a simulation result of the radiation pattern of the antenna device 100 of the embodiment. Figs. 6A and 6B show directivity as a radiation pattern in a YZ plane including the optical axis of the lens 130 (the central axis C of the waveguide 110). The +90 degree direction is the +Y direction, which is the front direction. The 0 degree direction is the +Z direction.

[0058] In the radiation pattern of the antenna device 10 for comparison shown in Fig. 6A, the gain in the front direction was 10.5 dBi, and the direction in which the maximum gain was obtained was 103 degrees. The direction of 103 degrees corresponds to the direction shown by the dashed line in Fig. 4C. In contrast, in the radiation pattern of the antenna device 100 of the embodiment shown in Fig. 6B, the gain in the front direction was 15.3 dBi, and the direction in which the maximum gain was obtained was 92 degrees.

[0059] Thus, the radiation pattern of the antenna device 100 of the embodiment is improved from 103 degrees to 92 degrees in the maximum gain direction compared to the radiation pattern of the comparative antenna device 10, and the maximum gain is obtained in the substantially front direction. Also, the gain in the front direction is improved by 4.8 dBi from 10.5 dBi to 15.3 dBi. The reason why the maximum gain direction is closer to the +Y direction (front direction) is considered to be the effect of canceling out the components with large beam angles.

[0060] <Simulation results of radiation pattern (XY plane)> Fig. 7A is a diagram showing a simulation result of the radiation pattern of the antenna device 10 for comparison (see Fig. 4C). Fig. 7B is a diagram showing a simulation result of the radiation pattern of the antenna device 100 of the embodiment. Figs. 7A and 7B show the radiation pattern (directivity) on the XY plane including the optical axis of the lens 130 (the central axis C of the waveguide 110). The direction of ±90 degrees is the +Y direction, which is the front direction. The direction of -180 degrees is the +X direction.

[0061] In the radiation pattern of the comparative antenna device 10 shown in Fig. 7A, the gain in the front direction was 10.5 dBi (point m1) and the 3 dB beam width was 24 degrees (range between m2 and m3). In contrast, in the radiation pattern of the antenna device 100 of the embodiment shown in Fig. 7B, the gain in the front direction was 15.3 dBi and the 3 dB beam width was 17.5 degrees (range between m2 and m3).

[0062] Thus, it was confirmed that the radiation pattern of the antenna device 100 of the embodiment has a gain in the forward direction that is improved by 4.8 dBi, from 10.5 dBi to 15.3 dBi, compared to the radiation pattern of the comparative antenna device 10, and the beam width (3 dB beam width) can be narrowed from 24 degrees to 17.5 degrees.

[0063] As described above, since the opening area of ​​the opening 111 is larger than the opening area of ​​the opening 112, the radio waves reflected by the inner wall surface 110A are reflected toward the direction of the central axis C and cancel out with the direct wave having a large beam angle β (see FIG. 3). Therefore, in a configuration in which the transmitting antenna 120Tx and the receiving antenna 120Rx are arranged offset from the optical axis of the lens 130, the radio waves passing through the center of the lens 130 are propagated without being cancelled out, thereby obtaining a beam with a narrow beam width. Moreover, such a beam with a narrow beam width can be realized by a waveguide 110 in which the opening area of ​​the opening 111 is set larger than the opening area of ​​the opening 112. Conventionally, in order to narrow the beam width, it was necessary to increase the diameter of the waveguide, make the waveguide longer, and make the lens larger, but in the antenna device 100 of the embodiment, the beam width can be narrowed by the waveguide 110 in which the opening area of ​​the opening 111 is set larger than the opening area of ​​the opening 112, and such a waveguide 110 can be made compact. In addition, since the waveguide 110 can be made compact, the lens 130 can be made compact. Therefore, the antenna device 100 of the embodiment can be made significantly smaller than conventional antenna devices.

[0064] It is therefore possible to provide a small-sized antenna device 100 with a narrow beam width. Even in a configuration in which the transmitting antenna 120Tx and the receiving antenna 120Rx are arranged offset from the optical axis of the lens 130, the beam width can be narrowed.

[0065] In addition, in a cut surface obtained by cutting the waveguide 110 in the YZ plane including the optical axis of the lens 130 (the central axis C of the waveguide 110), the angle α between the optical axis of the lens 130 (the central axis C of the waveguide 110) and the inner wall surface 110A of the waveguide 110 is set to a predetermined angle that brings about a relationship in which the radiated electric field V1 in the propagation path Path1 of the radio wave directly incident on the lens 130 from the transmitting antenna 120Tx and the radiated electric field V2 in the propagation path Path2 of the radio wave reflected by the inner wall surface 110A from the transmitting antenna 120Tx and incident on the lens 130 are in opposite phase. Therefore, the beam width of the beam radiated from the lens 130 can be effectively narrowed by canceling out the component with a relatively large beam angle β (see FIG. 3) of the radio wave directly incident on the lens 130 from the transmitting antenna 120Tx with the reflected wave. This is also true in the case of reception by the receiving antenna 120Rx.

[0066] The transmitting antenna 120Tx and the receiving antenna 120Rx are positioned at the same position in the extension direction of the optical axis of the lens 130 (the central axis C of the waveguide 110), and the receiving antenna 120Rx is disposed at a position point-symmetrical to the transmitting antenna 120Tx with respect to the optical axis when viewed from the opening surface of the opening 111. Therefore, in a configuration in which the transmitting antenna 120Tx and the receiving antenna 120Rx are disposed offset from the optical axis of the lens 130, the radiation characteristics of the transmitting antenna 120Tx and the receiving antenna 120Rx can be made uniform, and the distribution of the round-trip antenna gain can be made uniform with respect to the beam angle.

[0067] The positions of the transmitting antenna 120Tx and the receiving antenna 120Rx in the extension direction of the optical axis of the lens 130 (the central axis C of the waveguide 110) are equal to the focal position of the lens 130. Therefore, in a configuration in which the transmitting antenna 120Tx and the receiving antenna 120Rx are arranged offset from the optical axis of the lens 130, the transmission and reception characteristics of the transmitting antenna 120Tx and the receiving antenna 120Rx can be optimized.

[0068] In addition, in a cross section obtained by cutting the waveguide 110 in the YZ plane including the optical axis of the lens 130, the angle α between the optical axis of the lens 130 (the central axis C of the waveguide 110) and the inner wall surface 110A of the waveguide 110 is 15 degrees to 45 degrees. Therefore, the components of the direct wave that pass outside the center of the lens 130 can be canceled out, and the radio waves that pass through the center of the lens 130 are propagated without being canceled out, thereby obtaining a beam with a narrow beam width.

[0069] Furthermore, since the waveguide of waveguide 110 is hollow, it is possible to provide antenna device 100 that is small in size and has a narrow beam width with a simple configuration using hollow waveguide 110.

[0070] Furthermore, since the waveguide 110 has a truncated cone shape, it is possible to provide the antenna device 100 that is small in size and has a narrow beam width with a simple configuration using the waveguide 110 having a truncated cone shape.

[0071] Since lens 130 is a convex lens, it is possible to provide antenna device 100 that is small in size and has a narrow beam width with a simple configuration using lens 130 that is made up of a convex lens.

[0072] <Antenna device 100M according to a modified example of the embodiment> Figures 8A and 8B are diagrams showing an antenna device 100M according to a modified example of the embodiment. Figure 8B shows a state in which a lens 130M is removed from the antenna device 100M shown in Figure 8A. The same components as those of the antenna device 100 shown in Figures 1A and 1B are denoted by the same reference numerals, and the description thereof will be omitted.

[0073] Antenna device 100M includes substrate 101, waveguide 110M, transceiver 120, and lens 130M. Waveguide 110M is a rectangular waveguide and has opening 111M in the -Y direction, opening 112M on the +Y direction side, and inner wall surface 110AM. Opening 111M is an example of a first opening, and opening 112M is an example of a second opening.

[0074] The openings 111M and 112M are square in plan view. The opening area of ​​the opening 111M is larger than the opening area of ​​the opening 112M. The waveguide 110M is a rectangular waveguide having a truncated pyramid shape. The inner wall surface 110AM has the same shape as the outer surface of the truncated pyramid shape.

[0075] Lens 130M is a biconvex lens that has four corners in plan view of lens 130 shown in FIGS. 1A and 1B extended to form a square in plan view, and focuses radio waves in the same manner as lens 130.

[0076] In antenna device 100M including waveguide 110M formed of such a rectangular waveguide, radio waves reflected by inner wall surface 110AM are reflected toward the direction of central axis C and cancel out with the direct wave having a large beam angle, as in antenna device 100. Therefore, radio waves passing through the center of lens 130M are propagated without being cancelled out, resulting in a beam with a narrow beam width. In addition, such a beam with a narrow beam width can be realized by waveguide 110M in which the aperture area of ​​opening 111M is set larger than the aperture area of ​​opening 112M, and no large-scale device is required.

[0077] Therefore, it is possible to provide a small antenna device 100M having a narrow beam width. Since the waveguide 110M has a truncated pyramid shape, it is possible to provide a small antenna device 100M having a narrow beam width with a simple configuration using the waveguide 110M having a truncated pyramid shape.

[0078] <Dielectric Waveguide> 9 is a diagram showing a dielectric waveguide 210. The dielectric waveguide 210 is made of a dielectric material having a truncated cone shape with end faces 211 and 212. The dielectric material is, for example, a resin. The end faces 211 and 212 are circular in plan view. The dielectric waveguide 210 can be used in place of the waveguide 110 of the antenna device 100.

[0079] End face 211 is a flat surface, and end face 212 is a concave surface that matches the curved surface on the -Y direction side of lens 130. The area of ​​end face 211 is larger than the area of ​​end face 212 in a plan view. If lens 130 is provided on end face 212 of such dielectric waveguide 210, radio waves can be propagated in the same manner as when waveguide 110 is used. Note that dielectric waveguide 210 may be in a truncated pyramid shape.

[0080] <Modification of lens> FIG. 10 is a diagram showing a flat lens 230A having a Fresnel zone 235A. The flat lens 230A is a disk-shaped lens, and has flat end faces 231A and 232A on both sides of a plate-shaped dielectric substrate. The Fresnel zone 235A is formed on the end face 232A on the +Y direction side of the flat lens 230A made of a dielectric substrate. The Fresnel zone 235A has a plurality of ring parts (parts of the rings shown in black) formed by a pattern of copper foil or the like that shield radio waves, and a plurality of ring parts (parts between the rings shown in black) that are not provided with a pattern of copper foil or the like and transmit radio waves, and functions as a Fresnel lens that focuses radio waves. By using such a flat lens 230A instead of the lens 130, it is possible to focus radio waves in the same way as when the lens 130 is used. The Fresnel zone 235A may be provided on the end face 231A on the -Y direction side.

[0081] Therefore, it is possible to provide a small antenna device with a narrow beam width with a simple configuration using the flat lens 230A having the Fresnel zone 235A. Instead of providing the flat lens 230A having the Fresnel zone 235A, the Fresnel zone 235A may be provided on the end face 211 or 212 of the dielectric waveguide 210 shown in FIG.

[0082] The above describes an antenna device according to an exemplary embodiment of the present disclosure. However, 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.

[0083] This international application claims priority to Japanese patent application No. 2022-035533, filed on March 8, 2022, the entire contents of which are incorporated herein by reference. [Explanation of symbols]

[0084] 100, 100M Antenna Equipment 110, 110M waveguide 110A, 110AM Inner wall surface 111, 111M Opening (example of the first opening) 112, 112M opening (example of second opening) 120 Transmitter / receiver 120Tx transmit antennas 120Rx receiving antenna 130, 130M Lens 210 Dielectric Waveguide 230A Flat Lens 235A Fresnel Zone

Claims

1. A waveguide; a transmitting antenna provided on a first opening side of the waveguide and transmitting radio waves through the waveguide; a receiving antenna provided on a first opening side of the waveguide and receiving radio waves via the waveguide; a lens provided on a second opening side of the waveguide and transmitting radio waves transmitted from the transmitting antenna or radio waves received by the receiving antenna; Including, The opening area of ​​the first opening is larger than the opening area of ​​the second opening, An antenna device, wherein the transmitting antenna and the receiving antenna are positioned offset from the optical axis of the lens.

2. 2. The antenna device according to claim 1, wherein, in a cross section obtained by cutting the waveguide along a plane including the optical axis, an angle between the optical axis and an inner wall surface of the waveguide is set to a predetermined angle that brings about a relationship in which a radiated electric field in a propagation path of radio waves directly incident on the lens from the transmitting antenna and a radiated electric field in a propagation path of radio waves reflected from the transmitting antenna by the inner wall surface and incident on the lens are in opposite phase to each other.

3. The positions of the transmitting antenna and the receiving antenna in the extending direction of the optical axis are equal, The antenna device according to claim 2 , wherein the receiving antenna is arranged at a position point-symmetrical to the transmitting antenna with respect to the optical axis when viewed from the aperture plane of the first opening.

4. The antenna device according to claim 3 , wherein the positions of the transmitting antenna and the receiving antenna in the extending direction of the optical axis are equal to a focal position of the lens.

5. The antenna device according to claim 2 , wherein the predetermined angle is greater than 0 degrees and is equal to or smaller than 45 degrees.

6. 6. The antenna device according to claim 1, wherein the waveguide of the waveguide is hollow.

7. The antenna device according to claim 1 , wherein the waveguide is a dielectric waveguide.

8. The antenna device according to claim 1 , wherein the waveguide has a truncated cone shape or a truncated pyramid shape.

9. The antenna device according to claim 1 , wherein the lens is a convex lens.

10. The antenna device according to claim 1 , wherein the lens is a flat lens having a Fresnel zone or a flat lens having a metamaterial.

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