Antenna device

Abstract

An antenna device according to the present invention comprises a dielectric lens, a patch antenna disposed at the focal position of the dielectric lens, a first radio wave absorbing material disposed between the dielectric lens and the patch antenna, and a metal plate disposed between the dielectric lens and the first radio wave absorbing material, wherein the first radio wave absorbing material and the metal plate each have a window for radio waves to pass through that has an opening smaller than the dielectric lens and that is centered at the intersection of a straight line connecting the center of the dielectric lens and the center of the patch antenna.

Description

Antenna device

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

[0002] In the railway business, safe operation and accurate schedule operation are important. Monitoring vehicle speed is crucial for safe operation, especially when stopping at platforms or around curves. In urban areas, timetables are becoming increasingly strict, making vehicle speed monitoring crucial for accurate schedule operation. Furthermore, in situations where there are obstructions in the sky, such as inside tunnels or subways, positioning information from Global Navigation Satellite System (GNSS) satellites cannot be obtained, so accurate vehicle speed information is required to detect the vehicle's position.

[0003] A widely known conventional method for detecting the speed of railway vehicles is to use a tachograph attached to the wheels to measure the number of revolutions of the wheels and calculate the vehicle speed from the number of revolutions of the wheels. However, this type of speed detection method using a tachograph may not accurately detect the speed due to wheel spin.

[0004] In recent years, developments have been underway to detect railway vehicle speed using radio waves, such as millimeter waves, to avoid the effects of wheel slip and accurately detect vehicle speed. For example, a known method involves irradiating a millimeter wave sine wave toward the rail from a speed detection device installed on the railway vehicle, detecting the sine wave reflected from the rail, and calculating the Doppler shift to determine the vehicle speed. In this method, the Doppler shift varies depending on the angle at which the millimeter wave is irradiated from the speed detection device toward the rail. Therefore, accurate speed detection requires accurate irradiation of the millimeter wave within a narrow angular range centered on the designed irradiation angle. Furthermore, because the power of obliquely irradiated millimeter waves returning as backscatter from the smooth rail is small, reliable detection requires sufficient suppression of noise power from unwanted angles, i.e., side lobes, by the antenna.

[0005] For example, Patent Documents 1 and 2 disclose techniques that address the problems associated with the radio wave-based speed detection method. Patent Document 1 proposes a low-sidelobe antenna that generates a narrow-angle beam to irradiate a narrow angular range. Specifically, Patent Document 2 discloses an antenna structure that achieves a narrow-angle beam and low sidelobes by forming a patch antenna on a substrate and directly covering it with a primary lens antenna. Patent Document 2 proposes a technique for achieving a transmitter / receiver with accurate directionality by accurately adjusting the position of a pre-focusing body relative to a dielectric lens.

[0006] Japanese Patent Publication No. 2015-226297 Japanese Patent Publication No. 2000-196346

[0007] The primary lens antenna in the antenna structure of Patent Document 1 can generate a narrow beam when the dielectric constant is low compared to the patch antenna on the substrate. Therefore, the technology of Patent Document 1 limits the materials that can be used for the substrate and lens. Similarly, in the case of Patent Document 2, when the dielectric constant of the substrate is low, the effect of the pre-focusing body may be reduced, and the materials that can be used for the cover that secures the pre-focusing body are limited. Thus, the technologies of Patent Documents 1 and 2 may pose cost issues.

[0008] In view of the above-mentioned problems of the conventional technology, an object of the present invention is to realize an antenna device having narrow beam angle characteristics and low side lobe characteristics at low cost.

[0009] The antenna device according to the present invention comprises a dielectric lens, a patch antenna arranged at the focal position of the dielectric lens, a first radio wave absorbing material arranged between the dielectric lens and the patch antenna, and a metal plate arranged between the dielectric lens and the first radio wave absorbing material, and the first radio wave absorbing material and the metal plate each have a radio wave passage window with an opening smaller than that of the dielectric lens, centered at the intersection with a straight line connecting the center of the dielectric lens and the center of the patch antenna.

[0010] According to the present invention, an antenna device having narrow beam angle characteristics and low side lobe characteristics can be realized at low cost.

[0011] Problems, configurations, and effects other than those described above will become clear from the following description of the embodiments.

[0012] FIG. 1 is a diagram showing an overview of a millimeter-wave speed detection device for railway vehicles. FIG. 2 is a diagram showing an example of the relationship between the irradiation angle of millimeter waves from the antenna device to a smooth metal surface and the power of backscattered waves. FIG. 3 is a diagram showing the configuration of an antenna device according to a first embodiment of the present invention. FIG. 4 is a diagram explaining a preferred form of a radio wave passing window. FIG. 5 is a diagram showing the configuration of an antenna device according to a second embodiment of the present invention. FIG. 6 is a diagram showing the configuration of an antenna device according to a third embodiment of the present invention. FIG. 7 is a diagram comparing beam characteristics between a conventional antenna structure and the antenna structure of the present invention.

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The following description and drawings are examples for explaining the present invention, and some omissions and simplifications have been made as appropriate for clarity of explanation. The present invention can be implemented in various other forms. Unless otherwise specified, each component may be singular or plural.

[0014] In order to facilitate understanding of the invention, the position, size, shape, range, etc. of each component shown in the drawings may not represent the actual position, size, shape, range, etc. Therefore, the present invention is not necessarily limited to the position, size, shape, range, etc. disclosed in the drawings.

[0015] (Outline of Millimeter-Wave Velocity Detector) The following describes an outline of a representative embodiment of the invention disclosed in the present application. The present application discloses an invention of an antenna device suitable for use in a millimeter-wave velocity detector for railway vehicles.

[0016] A millimeter-wave speed detector for railway vehicles requires antenna characteristics with a narrow beam angle and low side lobes. First, the reason for this will be explained.

[0017] Fig. 1 is a diagram showing an overview of a millimeter-wave speed detection device for railway vehicles. As shown in Fig. 1(a), the millimeter-wave speed detection device for railway vehicles irradiates a rail with millimeter waves from an antenna device 100 installed at the bottom of the railway vehicle and receives backscattered waves from the rail. The device then calculates a Doppler velocity Vdpr from the amount of Doppler shift in the frequency of the received backscattered waves, and detects the vehicle speed (speed of the railway vehicle) based on this Doppler velocity Vdpr.

[0018] Specifically, if the vehicle speed is Vcar and the angle of the direction of irradiation of millimeter waves relative to the rail is θ, the Doppler speed Vdpr detected by the millimeter wave speed detection device is expressed by the following relational expression (1). In this relational expression (1), the irradiation angle θ is a fixed value determined by the mounting angle of the antenna device 100. Therefore, the vehicle speed Vcar can be calculated from the Doppler speed Vdpr using relational expression (1). Vdpr = Vcar · cos θ (1)

[0019] Here, if the beam width of the antenna device 100 is 2δ, then as shown in FIG. 1B, the irradiation range 105 of the millimeter waves on the rail has a spread from θ-δ to θ+δ. Therefore, the Doppler velocity Vdpr detected by the millimeter-wave velocity detection device also contains a width error corresponding to the spread of the irradiation range 105. As a result, an error occurs in the calculation result of the vehicle speed Vcar. In order to suppress this error, it is necessary to set the antenna characteristics of the antenna device 100 so that the beam width of the antenna device 100 is as narrow as possible.

[0020] Furthermore, if the antenna device 100 can be installed at a low angle relative to the rail, it is still possible to suppress errors in the calculation results of the vehicle speed Vcar. For example, if the value of δ, which represents the beam width, is assumed to be 5°, then when θ = 45°, the value of θ will have a range of 40° to 50°. As a result, the value of cos θ in the above-mentioned relational expression (1) fluctuates within a range of −9% to +8%, and the detection results of the Doppler speed Vdpr will contain an error of −9% to +8% relative to the actual speed of the railway vehicle. Therefore, the value of the vehicle speed Vcar calculated from the detection results of the Doppler speed Vdpr will also contain a similar error.

[0021] On the other hand, when θ = 30°, even if the value of δ representing the beam width is the same 5°, the fluctuation range of the value of cos θ in relational expression (1) is limited to -5% to +5%. Therefore, it is possible to reduce the error in the value of vehicle speed Vcar calculated from the detection result of Doppler velocity Vdpr compared to when θ = 45°.

[0022] In this way, installing the antenna device 100 at a low angle with respect to the rails has the same effect on errors in the calculation results of the vehicle speed Vcar as narrowing the beam width of the antenna device 100. On the other hand, the lower the installation angle of the antenna device 100, the smaller the power of the backscattered waves traveling from the rails to the antenna device 100, and the lower the received power of the antenna device 100.

[0023] Fig. 2 is a diagram showing an example of the relationship between the irradiation angle of millimeter waves from the antenna device 100 to a smooth metal surface and the power of backscattered waves. In Fig. 2, the horizontal axis represents the irradiation angle of millimeter waves to the metal surface, which corresponds to the angle θ in Fig. 1. The vertical axis represents the power of backscattered waves, shown as a relative value (dB) with the value at θ = 90° as the reference.

[0024] 2 , for example, when θ = 45°, the received power is 45 dB lower than when millimeter waves are radiated from the antenna device 100 directly below the vehicle (θ = 90°), as shown by reference numeral 203. Also, for example, when θ = 30°, the received power is 55 dB lower than when millimeter waves are radiated from the antenna device 100 directly below the vehicle (θ = 90°), as shown by reference numeral 204. Therefore, the side lobes of the antenna device 100 need to be suppressed by 45 dB or more when θ = 45°, and by 55 dB or more when θ = 30°.

[0025] As explained above, in order to enable the antenna device 100 to be installed at a low angle relative to the rail, it is necessary to reduce the side lobes of the antenna. This is the same as narrowing the beam width angle, but this is difficult to achieve with conventional antenna structures.

[0026] The present invention provides an antenna device 100 for use in a millimeter wave speed detection device for railway vehicles, which achieves narrow beam angle characteristics and low side lobe characteristics at low cost. Various embodiments of the present invention will be described below.

[0027] (First embodiment) Fig. 3 is a diagram showing the configuration of an antenna device 100 according to a first embodiment of the present invention. The antenna device 100 shown in Fig. 3 is configured to include a circuit board 301, a patch antenna 302 mounted on the circuit board 301, a dielectric lens 303, a radio wave absorbing material 304, and a metal plate 305.

[0028] Various circuit patterns including the patch antenna 302 are formed on the circuit board 301. In addition to the antenna device 100, various components constituting the millimeter wave velocity detection device may be mounted on the circuit board 301. The circuit board 301 is formed using, for example, a resin material. By using a resin material, it becomes possible to mount various general-purpose semiconductor chips in addition to the patch antenna 302 on the same circuit board 301. This makes it possible to reduce costs, which is advantageous in terms of cost.

[0029] The patch antenna 302 is an antenna element formed using the circuit pattern of the circuit board 301. The patch antenna 302 alone has a relatively wide beam characteristic.

[0030] The dielectric lens 303 is a convex-lens type radio wave lens having a focal position on the patch antenna 302 side, and is arranged in the beam direction of the millimeter waves radiated from the patch antenna 302. In the antenna device 100, the positional relationship between the patch antenna 302 and the dielectric lens 303 is set so that the patch antenna 302 is arranged at the focal position of the dielectric lens 303. As described above, the patch antenna 302 has wide-angle beam characteristics, so by arranging the patch antenna 302 at the focal position of the dielectric lens 303, the beam radiated from the patch antenna 302 is narrowed by the dielectric lens 303. The dielectric lens 303 is formed using, for example, a resin-based material. The size of the dielectric lens 303 is set so that the narrow-angle beam characteristics required for the antenna device 100 are obtained.

[0031] The millimeter waves radiated from the patch antenna 302 contain unwanted beam components radiated in directions offset from the center of the radiation direction, which cause side lobes. A conventional method for suppressing side lobes is to place a primary lens directly above the patch antenna 302 and use this primary lens to narrow the beam incident on the dielectric lens 303. This method of suppressing side lobes using a primary lens is effective when the dielectric constant of the circuit board 301 on which the patch antenna 302 is mounted is sufficiently high relative to the dielectric constant of the primary lens. However, since the dielectric constant of resin materials is generally around 3, in order to fully achieve the side lobe suppression effect of the primary lens, a resin material cannot be used for the circuit board 301, and a ceramic material with a dielectric constant of around 8 must be used. This increases the cost of the antenna device 100.

[0032] Therefore, in the antenna device 100 of this embodiment, a radio wave absorbing material 304 is used instead of the primary lens to suppress side lobes. As shown in Fig. 3, the radio wave absorbing material 304 is disposed between the dielectric lens 303 and the patch antenna 302. A commercially available radio wave absorbing sheet, carbon material, or the like may be used as the radio wave absorbing material 304. Furthermore, a metal plate 305 is disposed between the dielectric lens 303 and the radio wave absorbing material 304. This metal plate 305 is intended to block the power transmitted through the radio wave absorbing material 304 and prevent it from leaking out toward the dielectric lens 303.

[0033] In the antenna device 100, the radio wave absorbing material 304 may be bonded to the metal plate 305, so that they are arranged as an integrated component, or the radio wave absorbing material 304 and the metal plate 305 may be arranged as separate components.

[0034] The radio wave absorbing material 304 and the metal plate 305 each have a radio wave passing window 306 centered on the intersection with a line 307 connecting the center of the dielectric lens 303 and the center of the patch antenna 302. The radio wave passing window 306 is formed by partially cutting out the radio wave absorbing material 304 and the metal plate 305, each centered on the intersection with the line 307. The millimeter waves radiated from the patch antenna 302 pass through this radio wave passing window 306 and are incident on the dielectric lens 303.

[0035] In the radio wave absorbing material 304 and the metal plate 305, the radio wave passing window 306 is formed as an opening smaller than the dielectric lens 303. Preferably, the radio wave passing window 306 is formed as described below.

[0036] 4 is a diagram illustrating a preferred form of the radio wave passing window 306. When the dielectric lens 303 is circular, a conical side surface 308 is formed by connecting the outer diameter of the dielectric lens 303 and the center of the patch antenna 302. In the radio wave absorbing material 304 and the metal plate 305, the radio wave passing window 306 is preferably formed along the intersection line between the conical side surface 308 and the radio wave absorbing material 304 or the metal plate 305, respectively. In this way, the millimeter waves radiated from the patch antenna 302 can be incident on the dielectric lens 303 just enough. In this case, the shape of the radio wave passing window 306 is similar to that of the dielectric lens 303.

[0037] It should be noted that the dielectric lens 303 may be elliptical rather than circular. When the dielectric lens 303 is elliptical, connecting the outer diameter of the dielectric lens 303 and the center of the patch antenna 302 forms a side surface of an elliptical cone. Similarly in this case, it is preferable that the radio wave passing window 306 is formed in the radio wave absorber 304 and the metal plate 305 along the intersection line between the side surface of the elliptical cone and the radio wave absorber 304 or the metal plate 305, respectively. In this case as well, the shape of the radio wave passing window 306 is similar to that of the dielectric lens 303.

[0038] The antenna device 100 of this embodiment has the configuration described above, which makes it possible to block unnecessary beam components from the patch antenna 302 to the dielectric lens 303, and even when a resin material is used for the circuit board 301, it is possible to suppress side lobes as a characteristic of the entire antenna device 100.

[0039] Second Embodiment In the first embodiment, the configuration of the antenna device 100 was described, in which side lobes are suppressed by disposing the radio wave absorber 304 and the metal plate 305 between the dielectric lens 303 and the patch antenna 302. However, there are cases in which side lobes are formed by radio waves leaking out of the dielectric lens 303 due to diffraction of millimeter waves that are radiated from the patch antenna 302 and pass through the radio wave passing window 306. In this embodiment, an example configuration of the antenna device 100 that suppresses side lobes caused by such diffraction will be described.

[0040] Fig. 5 is a diagram showing the configuration of an antenna device 100 according to a second embodiment of the present invention. The antenna device 100 shown in Fig. 5 further includes a radio wave absorbing material 401 disposed between the dielectric lens 303 and the metal plate 305, in addition to the circuit board 301, patch antenna 302, dielectric lens 303, radio wave absorbing material 304, and metal plate 305 described in the first embodiment.

[0041] 5, the radio wave absorbing material 401 is disposed between the dielectric lens 303 and the metal plate 305 so as to surround the periphery of the radio wave passing window 306 formed in the radio wave absorbing material 304 and the metal plate 305. Specifically, the radio wave absorbing material 401 is disposed in a cylindrical shape along the outer periphery of the dielectric lens 303, extending between the dielectric lens 303 and the metal plate 305. As with the radio wave absorbing material 304, the radio wave absorbing material 401 may be, for example, a radio wave absorbing sheet or a carbon material.

[0042] The antenna device 100 of this embodiment has the configuration described above, which makes it possible to suppress side lobes due to diffraction, thereby achieving narrower beam angle characteristics and lower side lobe characteristics than the first embodiment.

[0043] Third Embodiment In the first embodiment, the configuration of the antenna device 100 was described, in which side lobes are suppressed by disposing the radio wave absorbing material 304 and the metal plate 305 between the dielectric lens 303 and the patch antenna 302. However, when the antenna device 100 is mounted on a vehicle, there are restrictions on the sizes of the radio wave absorbing material 304 and the metal plate 305. On the other hand, because the millimeter waves radiated from the patch antenna 302 have a wide angle, it may be difficult to sufficiently block unwanted radio wave components that do not enter the radio wave passing window 306, depending on the sizes of the radio wave absorbing material 304 and the metal plate 305. In this embodiment, an example configuration of the antenna device 100 will be described, in which the side lobes are suppressed by blocking unwanted radio wave components that cannot be blocked by the radio wave absorbing material 304 and the metal plate 305.

[0044] Fig. 6 is a diagram showing the configuration of an antenna device 100 according to a third embodiment of the present invention. The antenna device 100 shown in Fig. 6 includes the circuit board 301, patch antenna 302, dielectric lens 303, radio wave absorber 304, and metal plate 305 described in the first embodiment, as well as the radio wave absorber 401 described in the second embodiment, and further includes a metal wall 501 arranged to surround the periphery of the circuit board 301.

[0045] 6, metal wall 501 is formed continuously around circuit board 301 from radio wave absorber 304 to a position lower than the mounting surface of patch antenna 302 on circuit board 301. Furthermore, metal wall 501 is disposed outside dielectric lens 303 when viewed from a direction perpendicular to the mounting surface of patch antenna 302 on circuit board 301, that is, at a position farther away from the outer periphery of dielectric lens 303 with radio wave passing window 306 as the reference.

[0046] The antenna device 100 of this embodiment has the configuration described above, which makes it possible to block unwanted radio wave components that cannot be blocked by the radio wave absorber 304 or the metal plate 305 with the metal wall 501 and prevent them from leaking out to the dielectric lens 303 side, thereby achieving narrower beam angle characteristics and lower side lobe characteristics than those of the first embodiment.

[0047] Fig. 7 is a comparison diagram of beam characteristics between a conventional antenna structure and the antenna structure of the present invention. Graph 601 in Fig. 7(a) shows an example of antenna characteristics for a conventional antenna structure that has a patch antenna 302 and a dielectric lens 303, but does not have a radio wave absorber 304 or a metal plate 305. Graph 602 in Fig. 7(b) shows an example of antenna characteristics for the antenna device 100 according to the third embodiment of the present invention shown in Fig. 6. In these diagrams showing antenna characteristics, the horizontal axis represents the angle from the center of the main beam, and the vertical axis represents the antenna gain for each angle relative to the center of the main beam, i.e., the amount of side lobe suppression.

[0048] 7A and 7B, graphs 601 and 602 show that the effect of the dielectric lens 303 enables a narrower main beam angle than that of the patch antenna 302 alone. However, in the case of graph 601, the side lobes are relatively large, and it can be seen that neither the side lobe reference value (45 dB) at an angle of 45° indicated by reference numeral 603 nor the side lobe reference value (55 dB) at an angle of 60° indicated by reference numeral 604 is achieved. Note that the side lobe reference values ​​603 and 604 correspond to the side lobe suppression amounts at the aforementioned angles θ = 45° and θ = 30°, respectively. On the other hand, in the case of graph 602, it can be seen that both the side lobe reference values ​​603 and 604 are achieved.

[0049] According to the embodiment of the present invention described above, the following advantageous effects are achieved.

[0050] (1) The antenna device 100 includes a dielectric lens 303, a patch antenna 302 disposed at the focal position of the dielectric lens 303, a radio wave absorbing material 304 disposed between the dielectric lens 303 and the patch antenna 302, and a metal plate 305 disposed between the dielectric lens 303 and the radio wave absorbing material 304. The radio wave absorbing material 304 and the metal plate 305 each have a radio wave passage window 306 with an opening smaller than that of the dielectric lens 303, centered at the intersection with a line 307 connecting the center of the dielectric lens 303 and the center of the patch antenna 302. This configuration allows the antenna device 100 to be realized with sufficiently suppressed side lobes, even if a resin material is used for the circuit board 301 on which the patch antenna 302 is mounted. Therefore, the antenna device 100 with narrow beam angle characteristics and low side lobe characteristics can be realized at low cost.

[0051] (2) The radio wave absorbing material 304 may be bonded to the metal plate 305. This facilitates positioning of the radio wave absorbing material 304 and the metal plate 305 when assembling the antenna device 100, thereby improving the ease of assembly.

[0052] (3) It is preferable that the radio wave passing window 306 has a shape similar to that of the dielectric lens 303. Specifically, in the radio wave absorber 304 and the metal plate 305, it is preferable that the radio wave passing window 306 is formed along the intersection line between the radio wave absorber 304 or the metal plate 305 and the conical side surface 308 or the elliptical conical side surface formed by connecting the outer diameter of the dielectric lens 303 and the center of the patch antenna 302. In this way, the millimeter waves radiated from the patch antenna 302 can be incident on the dielectric lens 303 just enough, thereby making it possible to effectively suppress side lobes.

[0053] (4) As shown in Figures 5 and 6, the antenna device 100 may include a radio wave absorbing material 401 disposed between the dielectric lens 303 and the metal plate 305 so as to surround the periphery of the radio wave passage window 306. In this case, it is preferable that the radio wave absorbing material 401 is disposed along the outer periphery of the dielectric lens 303. In this way, it is possible to suppress side lobes due to diffraction, and to achieve even narrower beam angle characteristics and lower side lobe characteristics.

[0054] (5) As shown in Fig. 6, the antenna device 100 may include a circuit board 301 on which the patch antenna 302 is mounted, and a metal wall 501 arranged to surround the periphery of the circuit board 301. In this case, it is preferable that the metal wall 501 be formed continuously from the radio wave absorbing material 304 to a position lower than the mounting surface of the circuit board 301 on which the patch antenna 302 is mounted. It is also preferable that the metal wall 501 be arranged outside the dielectric lens 303 when viewed from a direction perpendicular to the mounting surface. In this way, the metal wall 501 can block unnecessary radio wave components that cannot be blocked by the radio wave absorbing material 304 or the metal plate 305, thereby achieving even narrower beam angle characteristics and lower side lobe characteristics.

[0055] In the third embodiment, an example of the antenna device 100 including the radio wave absorbing material 401 and the metal wall 501 in addition to the circuit board 301, the patch antenna 302, the dielectric lens 303, the radio wave absorbing material 304, and the metal plate 305 has been described, but the antenna device 100 may include the circuit board 301, the patch antenna 302, the dielectric lens 303, the radio wave absorbing material 304, the metal plate 305, and the metal wall 501 without including the radio wave absorbing material 401. Even in this case, the antenna device 100 can be realized with narrow beam angle characteristics and low side lobe characteristics due to the effect of the metal wall 501.

[0056] The present invention is not limited to the above-described embodiments, but includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

[0057] Furthermore, the present invention is not limited to the above-described embodiment, and various modifications are possible within the scope of the invention.

[0058] REFERENCE SIGNS LIST 100 Antenna device 301 Circuit board 302 Patch antenna 303 Dielectric lens 304 Radio wave absorbing material 305 Metal plate 306 Radio wave passing window 401 Radio wave absorbing material 501 Metal wall

Claims

1. An antenna device comprising: a dielectric lens; a patch antenna arranged at the focal position of the dielectric lens; a first radio wave absorbing material arranged between the dielectric lens and the patch antenna; and a metal plate arranged between the dielectric lens and the first radio wave absorbing material, wherein the first radio wave absorbing material and the metal plate each have a window for passing radio waves, the opening of which is smaller than that of the dielectric lens, centered at the intersection with a line connecting the center of the dielectric lens and the center of the patch antenna.

2. An antenna device according to claim 1, wherein the first radio wave absorbing material is bonded to the metal plate.

3. An antenna device according to claim 1, wherein the radio wave passing window has a shape similar to that of the dielectric lens.

4. An antenna device according to claim 3, wherein in the first radio wave absorbing material and the metal plate, the radio wave passage window is formed along the intersection line between the first radio wave absorbing material or the metal plate and a conical side surface or an elliptical conical side surface formed by connecting the outer diameter of the dielectric lens and the center of the patch antenna.

5. An antenna device according to claim 1, further comprising a second radio wave absorbing material disposed between said dielectric lens and said metal plate so as to surround the periphery of said radio wave passing window.

6. An antenna device according to claim 5, wherein the second radio wave absorbing material is arranged along the outer periphery of the dielectric lens.

7. An antenna device as claimed in claim 1, comprising: a circuit board on which the patch antenna is mounted; and a metal wall arranged to surround the periphery of the circuit board, wherein the metal wall is formed continuously from the first radio wave absorbing material to a position lower than the mounting surface of the patch antenna on the circuit board.

8. The antenna device according to claim 7, wherein the metal wall is disposed outside the dielectric lens when viewed from a direction perpendicular to the mounting surface.

Images