Antenna Device

Abstract

To provide a technology for an antenna device that configures and includes a patch antenna that can improve gain in a direction at a low elevation angle when viewed from the center of a radiating element. SOLUTION: The patch antenna (20) includes a plate-shaped radiating element (31) and a pair of parasitic elements (40-1, 40-2) disposed on either side of the radiating element (31) at a distance from the radiating element (31) in a plan view of the radiating element (31) viewed from a direction perpendicular to the plate surface of the radiating element (31). Preferably, the pair of parasitic elements (40-1, 40-2) are disposed such that, in the plan view, the longitudinal direction of each of the pair of parasitic elements (40-1, 40-2) is aligned with the direction of a line segment connecting the center of the radiating element (31) and a feed point, and the pair of parasitic elements (40-1, 40-2) are disposed at positions sandwiching the line segment.

Description

[Technical field]

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

[0002] Patch antennas are known as planar antennas with small-area radiating elements that are rectangular or circular. Patch antennas have a wide range of applications, and Patent Document 1 discloses a patch antenna that can receive circularly polarized satellite signals and linearly polarized terrestrial signals and can be installed at a low height. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2003-347838 A Summary of the Invention [Problem to be solved by the invention]

[0004] Conventional patch antennas generally have a configuration in which a plate-shaped radiating element and a plate-shaped ground plane are arranged parallel to each other, and the directivity is strong in the normal direction to the plate surface of the radiating element (the direction of an elevation angle of 90 degrees as seen from the center of the radiating element). Therefore, while the gain is relatively high in the direction of a high elevation angle as seen from the center of the radiating element, the gain can sometimes be low in the direction of a low elevation angle.

[0005] The problem to be solved by the present invention is to provide a technology for an antenna device that constitutes and includes a patch antenna that can improve gain in a direction at a low elevation angle as viewed from the center of the radiating element. [Means for solving the problem]

[0006] A first aspect of the present invention is a patch antenna comprising a plate-shaped radiating element and a parasitic element arranged at a distance from the radiating element when viewed in a planar view of the radiating element from a direction perpendicular to the plate surface of the radiating element.

[0007] According to the first aspect, a parasitic element is provided at a distance from the radiating element in a plan view of the radiating element viewed from a direction perpendicular to the plate surface of the radiating element. This parasitic element can change the radiation characteristics of radio waves, making it possible to realize a technology that can improve the gain in a direction at a low elevation angle as viewed from the center of the radiating element.

[0008] A second aspect of the present invention is a patch antenna related to the first aspect, wherein the parasitic element is arranged such that, when viewed in the planar view, its longitudinal direction is aligned along the direction of a line segment connecting the center of the radiating element and the feed point.

[0009] Further, a third aspect of the present invention is a patch antenna according to the first or second aspect, wherein the length of the parasitic element in a longitudinal direction is 0.52 or more times the maximum length of the radiating element in the planar view.

[0010] A fourth aspect of the present invention is a patch antenna according to any one of the first to third aspects, wherein the length of the parasitic element in the longitudinal direction is 0.89 times or less the maximum length of the radiating element in the planar view.

[0011] The second to fourth embodiments can be suitable for improving the gain in a direction at a low elevation angle as viewed from the center of the radiating element.

[0012] A fifth aspect of the present invention is the patch antenna according to any one of the first to fourth aspects, wherein the parasitic element is provided on the same surface of the dielectric body as the surface on which the radiating element is provided.

[0013] According to the fifth aspect, by providing a parasitic element on the same surface of the dielectric on which the radiating element is provided, it becomes possible to easily manufacture a patch antenna that exhibits the effects according to any one of the first to fourth aspects.

[0014] A sixth aspect of the present invention is the patch antenna according to any one of the first to fifth aspects, wherein the interval is equal to or less than 0.51 times the maximum length of the radiating element in the plan view.

[0015] Further, a seventh aspect of the present invention is a patch antenna according to any one of the first to sixth aspects, wherein a difference between a height Hp of the upper surface of the parasitic element and a height Hr of the upper surface of the radiating element is 0≦Hp-Hr<α×0.05, where α is the maximum length of the radiating element in the planar view.

[0016] According to the sixth or seventh aspect, a configuration suitable for improving the gain in a direction at a low elevation angle as viewed from the center of the radiating element can be obtained.

[0017] An eighth aspect of the present invention is the patch antenna according to any one of the first to seventh aspects, wherein the parasitic elements are provided in pair on both sides of the radiating element.

[0018] A ninth aspect of the present invention is a patch antenna according to the eighth aspect, wherein the pair of parasitic elements includes a first parasitic element and a second parasitic element whose longitudinal length is longer than that of the first parasitic element.

[0019] According to an eighth aspect, a pair of parasitic elements are provided on both sides of the radiating element. By providing the pair of parasitic elements, the maximum radiation direction of the radiating element is a direction perpendicular to the plate surface of the radiating element. According to a ninth aspect, the pair of parasitic elements includes a first parasitic element and a second parasitic element whose longitudinal length is longer than that of the first parasitic element. The pair of parasitic elements changes the radiation characteristics of the radio wave, making it possible to change the maximum radiation direction of the radiating element to a desired direction.

[0020] In addition, a tenth aspect of the present invention is an in-vehicle antenna device having a patch antenna according to any one of the first to ninth aspects, comprising a housing installed in a predetermined position and orientation on a vehicle, and a support portion that supports the patch antenna so that the patch antenna is for vertical polarization when the housing is installed in the predetermined position and orientation.

[0021] According to the tenth aspect, it is possible to realize an in-vehicle antenna device for vertical polarization with improved gain in the direction of a low elevation angle as viewed from the center of the radiating element. [Brief description of the drawings]

[0022] [Figure 1] 1A and 1B are perspective external views showing a configuration example of an in-vehicle antenna device and a conceptual diagram showing a usage example. [Diagram 2] 2 is a diagram for explaining an example of the internal configuration of the vehicle-mounted antenna device; [Diagram 3] 3 is a longitudinal sectional view of the vehicle-mounted antenna device taken along the line III-III in FIG. 2. [Figure 4] 4 is a gain characteristic graph on the H plane (YZ plane) of an in-vehicle antenna device. [Diagram 5] A graph of gain characteristics in the H plane when the conductor length of a pair of parasitic elements is changed. [Figure 6] This is a table showing the relative half-power angle in the H plane when the conductor length of a pair of parasitic elements is changed. [Figure 7A] This is a table showing the maximum radiation direction on the H plane when the conductor length of the second parasitic element is made longer than the conductor length of the first parasitic element. [Figure 7B] FIG. 4 is an internal configuration diagram of the vehicle-mounted antenna device showing the conductor length. [Figure 8] 13A and 13B are diagrams illustrating the wiring direction of a coaxial cable in a modified example. [Figure 9] 13 is a diagram showing a modified example in which the height of the upper surfaces of a pair of parasitic elements and the height of the upper surface of a radiating element are changed. [Figure 10] A graph of gain characteristics on the H plane when the top surface height difference h is changed. [Figure 11] FIG. 13 is a diagram showing a modified example in which a pair of parasitic elements is provided outside the periphery of the radiating element. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] An example of an embodiment to which the present invention is applied will be described below, but the form to which the present invention can be applied is not limited to the following embodiment.

[0024] In addition, in this embodiment, the directions are defined as follows. First, in the patch antenna 20 having a structure in which the radiating element 31 and the ground plate 33 (also called the ground conductor plate) are laminated with the dielectric substrate 32 in between (see FIG. 3), the direction from the dielectric substrate 32 toward the radiating element 31 is called the "radiating direction". The radiation direction is not a bidirectional direction from the dielectric substrate 32 toward the radiating element 31 and from the radiating element 31 toward the dielectric substrate 32, but a fixed direction. In addition, three orthogonal axes in a left-handed system are defined. The coordinate origin of the three orthogonal axes is the center of the plate surface of the radiating element 31. To make the directions of the three orthogonal axes easy to understand, reference directions indicating directions parallel to the axial directions of the three orthogonal axes are added to each figure. The reason for using the reference directions is that the origin of the three orthogonal axes is, to be precise, the center of the plate surface of the radiating element 31. These directions are shown only for reference of the directions.

[0025] As for the three orthogonal axes of the left-handed system, the direction perpendicular to the plate surface of radiating element 31 (the normal direction to the plate surface of radiating element 31) is defined as the Z-axis direction, and the direction of radiation is defined as the Z-axis positive direction. Also, the direction along the direction of the line segment connecting the center of radiating element 31 and feed point (also referred to as core wire attachment hole) 31h is defined as the X-axis direction (see FIG. 2), and the direction from the center of radiating element 31 toward feed point 31h is defined as the X-axis positive direction. It is self-evident that the Y-axis and Y-axis positive directions are the three orthogonal axes of the left-handed system, and that the X-axis positive direction and Z-axis positive direction are defined.

[0026] To define the directions in another way, when viewed from the center of radiating element 31 (origin of the three orthogonal axes), the direction along the plate surface of radiating element 31 (plate surface direction) is taken as the azimuth direction, the direction at an elevation angle of 90 degrees is the positive direction on the Z axis, the direction from the center of radiating element 31 toward feed point 31h is the positive direction on the X axis, and when this positive direction on the X axis is taken as the 12 o'clock direction, the 3 o'clock direction is the positive direction on the Y axis. The plate surface direction of radiating element 31 may also be called the azimuth direction, azimuth angle direction, etc.

[0027] In this specification, the X-axis direction means a direction parallel to the X-axis, and includes both the positive and negative directions of the X-axis. The same applies to the Y-axis and Z-axis directions. Therefore, each axis direction is the reference direction shown in each figure.

[0028] In patch antenna 20, the E-plane is the electric field plane and the H-plane is the magnetic field plane of radiating element 31, and when viewed from the center (origin of the three orthogonal axes) of radiating element 31, the XZ-direction plane including the X-axis and Z-axis directions is the E-plane, and the YZ-direction plane including the Y-axis and Z-axis directions is the H-plane. In other words, the E-plane is a plane including a direction perpendicular to the plate surface of radiating element 31 and the direction of a line connecting the center of radiating element 31 and feed point 31h, and the H-plane is a plane perpendicular to the E-plane and including a direction perpendicular to the plate surface of radiating element 31.

[0029] FIG. 1 is a perspective external view showing a configuration example of an in-vehicle antenna device 10 according to the present embodiment, and a conceptual diagram showing a usage example.

[0030] The vehicle-mounted antenna device 10 is an on-vehicle antenna for 5.9 GHz V2X (Vehicle-to-everything; vehicle-to-vehicle, road-to-vehicle, etc.) communication equipped with a patch antenna, and is installed at a predetermined position and in a predetermined orientation on the vehicle 3 and connected to a V2X controller 5 via a coaxial cable 4.

[0031] The vehicle-mounted antenna device 10 is installed above the windshield inside the vehicle (e.g., near the rearview mirror) so that the radiation direction (positive Z-axis direction) faces forward, which is the forward movement direction of the vehicle 3, the positive Y-axis direction faces to the right in the forward movement direction of the vehicle 3, and the negative Y-axis direction faces to the left in the forward movement direction of the vehicle 3.

[0032] The installation position and the number of the vehicle-mounted antenna devices 10 can be appropriately changed according to the environmental conditions such as the assumed communication target. For example, the vehicle-mounted antenna devices 10 may be installed in multiple locations. The installation location may be, for example, the top of the dashboard, the mounting portion of the bumper or license plate, or a pillar portion such as an A-pillar. The radiation direction may be set to face the rear of the vehicle 3 on the rear window inside the vehicle. Here, rear means the backward moving direction of the vehicle 3. The radiation direction may be set to face the right or left of the vehicle 3. Here, right means the right side in the forward moving direction of the vehicle 3, and left means the left side in the forward moving direction of the vehicle 3. In addition, if the vehicle 3 has a structure that ensures the performance conditions of waterproofing and dustproofing, the vehicle 3 may be installed on the roof of the vehicle 3.

[0033] The vehicle-mounted antenna device 10 of this embodiment has a rectangular parallelepiped appearance, and the patch antenna 20 is built into a case having a divided structure of a first housing 11 and a second housing 12 that are divided in the radiation direction. Then, the support part 13 for vehicle body mounting provided on the side of the housing is mounted on the vehicle 3, so that the patch antenna 20 functions suitably as an antenna for vertical polarization. In this embodiment, the support part 13 is a boss for inserting a bolt or a screw used for installing the vehicle-mounted antenna device 10, and is configured to be provided on both the left and right side surfaces of the housing (both sides in the Y-axis direction) as viewed from the vehicle 3, but the setting position and the number of the support parts 13 can be appropriately selected. In addition, the method of installing and fixing the vehicle-mounted antenna device 10 is not limited to the method using bolts or screws, and other methods may be used, and accordingly, the support part 13 can also adopt a structure suitable for the method, such as a clip structure, as appropriate.

[0034] Support unit 13 supports first housing 11 and second housing 12 so that first housing 11 and second housing 12 are installed in a predetermined position and a predetermined orientation on vehicle 3. By installing first housing 11 and second housing 12 in a predetermined position and a predetermined orientation on vehicle 3, support unit 13 is in a position to support patch antenna 20 so that patch antenna 20 functions as an antenna for vertical polarization.

[0035] Fig. 2 is a diagram for explaining an example of the internal configuration of the vehicle-mounted antenna device 10, and is a diagram showing the inside of the second housing 12 as viewed from the positive direction of the Z axis with the first housing 11 removed. Fig. 3 is also a diagram for explaining an example of the internal configuration of the vehicle-mounted antenna device 10, and is a vertical cross-sectional view of the vehicle-mounted antenna device 10 including the first housing 11, taken along cross section III-III in Fig. 2.

[0036] The first housing 11 defines an upper housing space 11a which is a recess, and the second housing 12 defines a lower housing space 12a which is a recess. The upper housing space 11a and the lower housing space 12a become one continuous housing space when the first housing 11 and the second housing 12 are assembled. The patch antenna 20 is installed in the housing space so as to fit mainly in the lower housing space 12a.

[0037] The patch antenna 20 includes an antenna body 30 and a pair of parasitic elements 40 (40-1, 40-2).

[0038] The antenna body 30 has, for example, a rectangular shape when viewed from the positive direction of the Z axis, and includes, from the top in Fig. 3, a radiating element 31, a dielectric substrate 32, and a ground plate 33. The antenna body 30 can be produced by applying the manufacturing method for printed circuit boards, similar to conventional patch antennas.

[0039] The radiating element 31 has a rectangular plate shape when viewed from the positive direction of the Z axis, and is provided with a core wire attachment hole 31h, which is a through hole in the Z axis direction for inserting and fixing the core wire 41 of the coaxial cable 4, at a position offset (displaced position) from the center of the plate surface in the positive direction of the X axis (direction along the polarization plane of the linearly polarized wave of the patch antenna 20). This core wire attachment hole 31h is a power feed point. Therefore, the same reference symbol is used and it is appropriately referred to as the power feed point 31h. In this embodiment, the radiating element 31 is designed to be square when viewed from the positive direction of the Z axis, with the length of one side being 13.5 mm. Note that in FIG. 3, the thickness of the radiating element 31 and the ground plate 33 in the Z axis direction is intentionally drawn large to make the structure easy to understand, but in reality, they can be formed as thin plate-like thin films.

[0040] When viewed from the positive direction of the Z axis, the dielectric substrate 32 has an area larger than that of the radiating element 31. The dielectric substrate 32 has a core wire insertion hole (not shown) that penetrates in the Z axis direction at a position that communicates with the core wire attachment hole 31h of the radiating element 31 during assembly.

[0041] The ground plate 33 has the same shape as or a slightly smaller shape than the bottom surface of the dielectric substrate 32, and has a core wire insertion hole (not shown) that communicates with the core wire attachment hole 31h of the radiating element 31 and the core wire insertion hole of the dielectric substrate 32 during assembly. The board coaxial connector 22 is attached to the bottom surface of the ground plate 33 through an insertion hole (not shown) provided in the bottom of the second housing 12 so as to be coaxial with the core wire insertion hole of the ground plate 33.

[0042] The pair of parasitic elements 40 (40-1, 40-2) are composed of rod-shaped plate conductors (metal plates) when viewed from the positive direction of the Z axis, and are provided on both sides of the radiating element 31 in a plan view of the radiating element 31 seen from a direction perpendicular to the plate surface of the radiating element 31, which is the Z axis direction (plan view of the radiating element 31 seen from the positive direction of the Z axis), at positions spaced a predetermined distance b from the end side of the radiating element 31. In a configuration where there is no distance between the parasitic element 40 and the radiating element 31, the parasitic element 40 acts as if it were part of the radiating element 31, and there is a risk that the frequency obtained by the patch antenna 20 will change.

[0043] More specifically, the pair of parasitic elements 40-1, 40-2 are arranged, for example, on the periphery of the upper surface of the dielectric substrate 32, with their respective longitudinal directions oriented along the direction of a line segment (X-axis direction) connecting the center of the radiating element 31 and the feed point 31h when viewed from the Z-axis positive direction, at positions sandwiching the line segment between the parasitic elements 40-1, 40-2. Hereinafter, one of the pair of parasitic elements 40-1, 40-2 (e.g., the lower side in FIG. 2, the negative Y-axis side) is also referred to as the first parasitic element 40-1 as appropriate, and the other parasitic element 40-2 (upper side in FIG. 2, the positive Y-axis side) is also referred to as the second parasitic element 40-2 as appropriate.

[0044] During assembly, the antenna main body 30 is fixed to the bottom of the second housing 12. More specifically, a protrusion 12t protruding in the positive direction of the Z axis is provided on the bottom of the second housing 12. The lower surface (the end surface on the negative side of the Z axis) of the ground plate 33 is abutted against the tip of the protrusion 12t, and the antenna main body 30 and the protrusion 12t are fixed. The fixing method can be appropriately selected, and for example, the ground plate 33 and the protrusion 12t may be bonded. In addition, the space between the second housing 12 and the antenna main body 30 (ground plate 33) may be an air layer (space), or a resin layer that is an electrically insulating material. If a resin layer is used, resin may be used to serve as both a space filler and a bonding agent.

[0045] Next, the effect of the patch antenna 20 of this embodiment will be described. In describing the effect, the maximum length of the diagonal of the radiating element 31 as viewed from the positive direction of the Z axis is referred to as the "maximum length of the radiating element", and as shown in FIG. 2, the maximum length of the radiating element is expressed as "α". In this embodiment, the radiating element 31 is a square shape with one side of 13.5 mm, so the maximum length of the radiating element α is 19.1 mm. The conductor length of each of the parasitic elements 40-1 and 40-2 (the length in the longitudinal direction of the parasitic elements 40-1 and 40-2) and the interval b between the radiating element 31 and the parasitic elements 40-1 and 40-2 are expressed as a magnification with respect to the maximum length of the radiating element α, and the actual length is also added in parentheses immediately after. For example, when the conductor length is expressed as 0.86α (about 16.5 mm), it indicates that the length is 0.86 times the maximum length of the radiating element α of 19.1 mm, and the approximately 16.5 mm in the parentheses is the actual length.

[0046] First, Fig. 4 is a gain characteristic graph on the H plane (YZ plane), and shows the antenna gain with the Y-axis positive direction on the H plane set to 0 degrees and the Y-axis negative direction set to 180 degrees. 90 degrees is the Z-axis positive direction, which corresponds to an elevation angle of 90 degrees as seen from the center of the radiating element 31. The solid line shows the antenna gain characteristic of the patch antenna 20 of this embodiment, in which the conductor length of each of the parasitic elements 40-1 and 40-2 is 0.86α (about 16.5 mm) and the interval b is 0.25α (about 4.75 mm). Meanwhile, the dashed line shows the antenna gain characteristic of a comparative configuration corresponding to the prior art, in which the pair of parasitic elements 40-1 and 40-2 is omitted.

[0047] As shown in FIG. 4, when focusing on the ranges of 0 degrees to 45 degrees and 135 degrees to 180 degrees, which are low elevation angle directions as viewed from the center of radiating element 31, the gain is improved compared to a configuration in which the pair of parasitic elements 40-1, 40-2 is omitted, demonstrating the beneficial effect of providing the pair of parasitic elements 40-1, 40-2.

[0048] Next, Fig. 5 is a gain characteristic graph plotting the minimum value of the gain at low elevation angles (0 degrees to 45 degrees and 135 degrees to 180 degrees in the case where the Y-axis positive direction in the H-plane is 0 degrees and the Y-axis negative direction is 180 degrees) in the case where the conductor length of the pair of parasitic elements 40-1 and 40-2 is changed, and the gain characteristic graph in the case where the conductor length is changed with different intervals b is shown by changing the line type. Specifically, the solid line is a gain characteristic graph in the case where the interval b is 0.51α (about 9.75 mm), the dashed line is a gain characteristic graph in the case where the interval b is 0.38α (about 7.25 mm), and the dashed double-dashed line is a gain characteristic graph in the case where the interval b is 0.25α (about 4.75 mm). Fig. 6 is a table showing the relative values ​​of the half-power angles in the H-plane in the case where the interval b of the pair of parasitic elements 40-1 and 40-2 is 4.75 mm and the conductor length is changed. In Figure 6, the conductor length in the top row shown as "none" corresponds to a comparative configuration in which the pair of parasitic elements 40-1, 40-2 are omitted, and the relative value (half-value angle relative value) is shown when the half-value angle of this comparative configuration is set to "1.000".

[0049] As shown in Fig. 5, as the conductor length of each of the parasitic elements 40-1 and 40-2 is increased, the minimum value of the gain in the direction of a low elevation angle also increases. The gain peaks when the conductor length is approximately 0.89α ​​(approximately 17.0 mm), and when the conductor length exceeds this, the minimum value of the gain shows a tendency to decrease. However, as the conductor length increases, the size of the patch antenna 20 also increases accordingly. Therefore, taking into consideration the impact on the miniaturization of the patch antenna 20 (which also reduces the size of the vehicle-mounted antenna device 10), it is desirable for the conductor length to be 0.89α ​​(approximately 17.0 mm), which is 0.89 times the maximum radiating element length α or less.

[0050] On the other hand, as for the lower limit of the conductor length, as shown in FIG. 6, when the conductor length is 10 mm, the half-value angle can be increased by 1.2% compared to the comparative configuration, and if the length is longer than this, the half-value angle can be further improved. When the conductor length is 8 mm, the half-value angle increases by 0.7% compared to the comparative configuration. Therefore, the conductor length that increases the half-value angle by 1% compared to the comparative configuration is (10+8)×(1 / (1.2+0.7))=approximately 9.47 mm according to simple proportional calculation. Therefore, it is desirable that the conductor length that can increase the half-value angle by 1% or more compared to the comparative configuration is 0.52α (approximately 9.99 mm) or more, which is 0.52 times or more the maximum length α of the radiating element, with a margin.

[0051] Also, when the interval b in FIG. 5 is focused on, when the interval b is increased in the order of 0.25α (about 4.75 mm), 0.38α (about 7.25 mm), and 0.51α (about 9.75 mm), the minimum value of the gain in the direction of low elevation angles also increases overall. However, when the conductor length is about 0.89α, the increase in the gain when the interval b is 0.38α (about 7.25 mm) is smaller than the increase in the gain when the interval b is 0.51α (about 9.75 mm) compared to the gain when the interval b is 0.25α (about 4.75 mm). Therefore, it is expected that the gain will not increase significantly if the interval b is increased to a certain extent. And, if the interval b is increased, the size of the patch antenna 20 will increase accordingly. Therefore, in order to strike a balance with miniaturization of the patch antenna 20 (miniaturization of the vehicle-mounted antenna device 10), it is desirable for the interval b to be 0.51α (approximately 9.75 mm) or less, which is 0.51 times the maximum length α of the radiating element.

[0052] As described above, according to this embodiment, in the patch antenna 20, it is possible to improve the gain in the direction of a low elevation angle as viewed from the center of the radiating element 31.

[0053] An example of an embodiment to which the present invention is applied has been described above, but the forms to which the present invention can be applied are not limited to the above-described forms, and components can be added, omitted, or modified as appropriate.

[0054] [Variation 1] For example, in the above embodiment, the conductor length of each of the parasitic elements 40-1 and 40-2 is the same. In contrast, the conductor length of the first parasitic element 40-1 and the conductor length of the second parasitic element 40-2 may be different. FIG. 7A is a table showing the maximum radiation direction on the H plane when the conductor length d of the second parasitic element 40-2 is fixed and the conductor length c of the first parasitic element 40-1 is changed. FIG. 7B is a diagram showing an example of the internal configuration of the vehicle-mounted antenna device 10 corresponding to FIG. 2 in order to show the conductor length c of the first parasitic element 40-1 and the conductor length d of the second parasitic element 40-2. In FIG. 7A, the configuration in the top row where the conductor length c is "none" corresponds to a configuration in which only the second parasitic element 40-2 is arranged and the first parasitic element 40-1 is not arranged. The maximum radiation direction indicates the azimuth angle in the H plane, which is a YZ plane with the positive direction of the Z axis, which corresponds to an elevation angle of 90 degrees as seen from the center of the radiating element 31, set to 0 degrees, and the positive direction of the Y axis set to 90 degrees.

[0055] As shown in FIG. 7A, for example, when the conductor length of the second parasitic element 40-2 is fixed and the conductor length of the first parasitic element 40-1 is changed, the maximum radiation direction changes. Specifically, when the conductor length d is fixed and the conductor length c is gradually increased from 6 mm, the azimuth angle of the maximum radiation direction gradually approaches 0 degrees. Then, although not shown, when the conductor length c is increased to the same length as the conductor length d, the azimuth angle of the maximum radiation direction becomes 0 degrees. Therefore, by configuring the patch antenna 20 by changing each of the conductor lengths c and d, the maximum radiation direction can be changed. One of the reasons why the change is necessary is the installation environment of the vehicle-mounted antenna device 10. Specifically, for example, when the vehicle-mounted antenna device 10 is installed in the vehicle 3, the wiring direction of the coaxial cable may be restricted due to the layout inside the vehicle. For example, the configuration is not limited to the configuration in which the coaxial cable 4 is inserted perpendicularly to the plate surface of the radiating element 31 as shown in FIG. 3, but may be configured to wire the coaxial cable 4a parallel to the plate surface by adopting a connector structured to make the wiring direction parallel to the plate surface of the radiating element 31 as shown in FIG. 8. This wiring direction may affect the radiation characteristics of radio waves, and the maximum radiation direction may deviate from the expected direction (for example, the front of the vehicle 3) when installed. In view of the effect of the wiring configuration of the patch antenna 20 on the radiation characteristics of radio waves, the conductor length of each of the parasitic elements 40-1 and 40-2 may be appropriately set, so that the maximum radiation direction may be changed to a desired radiation direction when the vehicle-mounted antenna device 10 is installed on the vehicle 3. In addition, even when the desired radiation direction is deviated from the front of the vehicle, such as an antenna for an ETC (Electronic Toll Collection System), the same application is possible by changing the conductor length of each of the parasitic elements 40-1 and 40-2 according to the radiation direction. It is sufficient that the conductor length of at least one of the parasitic elements 40-1, 40-2 is 0.89α ​​(approximately 17.0 mm) or less, which is 0.89 times the maximum radiating element length α. It is more preferable that both satisfy this condition. Furthermore, it is sufficient that the spacing b of at least one of the parasitic elements 40-1, 40-2 is 0.51α (approximately 9.75 mm) or less, which is 0.51 times the maximum radiating element length α. It is more preferable that both satisfy this condition.

[0056] [Modification Example 2] In the above embodiment, an example is shown in which each of the pair of non-powered elements 40-1 and 40-2 is provided at the peripheral edge of the upper surface of the dielectric substrate 32 so that the upper surfaces of the pair of non-powered elements 40-1 and 40-2 are at the same height as the upper surface of the radiating element 31. In contrast, for example, as shown in FIG. 9, the pair of non-powered elements 40-1 and 40-2 may be provided such that the height of their upper surfaces is different from the height of the upper surface of the radiating element 31. More specifically, in FIG. 9, an example is shown in which the height of the upper surfaces of each of the non-powered elements 40a-1 and 40a-2 is higher than the height of the upper surface of the radiating element 31. Here, with reference to FIG. 10, the gain characteristics in the H-plane (YZ-direction plane) when the difference in height (upper surface height difference) h between the two shown in FIG. 9 is changed will be described. The upper surface height difference h is represented by Hp - Hr, where Hp is the height of the upper surface of each of the non-powered elements 40a-1 and 40a-2 and Hr is the height of the upper surface of the radiating element 31. Hp and Hr are heights with reference to the upper surface of the dielectric substrate 32.

[0057] FIG. 10 is a gain characteristic graph in the azimuth angle in the H-plane (YZ-direction plane) with the positive direction of the Y-axis being 0 degrees and the negative direction of the Y-axis being 180 degrees, showing the gain characteristic graphs when the upper surface height difference h is changed by changing the line type. Specifically, the solid line is the configuration with the upper surface height difference h = 0 (when Hp = Hr), the dashed line is the configuration with the upper surface height difference h = 0.05α (when Hp > Hr and the difference between the two is 0.05α (about 1 mm)), the one-dot chain line is the configuration with the upper surface height difference h = 0.1α (when Hp > Hr and the difference between the two is 0.1α (about 2 mm)), and the two-dot chain line is the configuration with the upper surface height difference h = -0.05α (when Hp < Hr and the difference between the two is 0.05α (about 1 mm)). For each configuration, the conductor lengths c and d of each of the non-powered elements 40a-1 and 40a-2 are 0.86α (about 16.5 mm), and the interval b is 0.25α (about 4.75 mm).

[0058] First, the average value of gain (average gain) in the azimuth angle range of 0 degrees to 180 degrees for the configuration of h=-0.05α shown by the two-dot chain line in Fig. 10 was calculated, and the average gain in the azimuth angle range of 0 degrees to 180 degrees for the configuration of h=0 shown by the solid line was compared. The average gain for h=-0.05α was 1.655831 dBi, and the average gain for h=0 was 3.784148 dBi, so the average gain obtained for the configuration of h=-0.05α is significantly lower than the average gain obtained for the configuration of h=0. Therefore, the difference between the height Hp of the top surface of each parasitic element 40a-1, 40a-2 and the height Hr of the top surface of the radiating element 31 is preferably 0 mm≦Hp-Hr. Next, when focusing on the ranges of 0 degrees to 45 degrees and 135 degrees to 180 degrees, which are low elevation angles as viewed from the center of the radiating element 31, the configuration of h=0.05α shown by the dashed line in FIG. 10 and the configuration of h=0.1α shown by the dashed line have lower gains at low elevation angles than the configuration of h=0. The configurations of h=0.05α and h=0.1α have almost the same gains at low elevation angles. Therefore, the difference between the height Hp of the upper surface of each of the parasitic elements 40a-1 and 40a-2 and the height Hr of the upper surface of the radiating element 31 is preferably Hp-Hr<0.05α. From the above, it is preferable that 0mm≦Hp-Hr<0.05α. It is sufficient that the height Hp of the upper surface of at least one of the pair of parasitic elements 40-1 and 40-2 is 0mm≦Hp-Hr<0.05α. It is more preferable that both satisfy this condition.

[0059] In addition, the outer shape of the antenna main body 30 as viewed from the positive direction of the Z axis is not limited to the rectangular shape illustrated in FIG. 2, but may be a circle or the like. In addition, the outer shape of the radiating element 31 as viewed from the positive direction of the Z axis is not limited to the rectangular shape illustrated in FIG. 2, but may be a circle or the like. Since the maximum length α of the radiating element is the maximum length of the diagonal of the radiating element 31 as viewed from the positive direction of the Z axis, when the outer diameter of the radiating element 31 as viewed from the positive direction of the Z axis is a circle, the maximum length α of the radiating element is the maximum length of the diameter of the radiating element 31. In addition, the longitudinal direction of either one of the pair of parasitic elements 40-1, 40-2 may be arranged so as to follow the direction of the line segment connecting the center of the radiating element 31 and the feeding point 31h as viewed from the positive direction of the Z axis (the X-axis direction). It is more preferable that both satisfy this condition.

[0060] [Variation 3] In the above embodiment, the pair of parasitic elements 40-1, 40-2 are formed in a long and thin plate shape and provided on the upper surface periphery of the dielectric substrate 32. In contrast to this, as shown in FIG. 11, the pair of parasitic elements 40b-1, 40b-2 may be provided as flat plate parts or thin film parts parallel or approximately parallel to each other outside the periphery of the radiating element 31. For example, they may be arranged by being attached to the inner surface of the second housing 12. The pair of parasitic elements 40b-1, 40b-2 in this modification have a rectangular plate or thin film shape, and are arranged on both sides of the antenna body 30, sandwiching a line segment connecting the center of the radiating element 31 and the power feed point 31h, with their longitudinal directions aligned along the X-axis direction (the direction of the line segment connecting the center of the radiating element 31 and the power feed point 31h).

[0061] [Other variations] In the above embodiment, the patch antenna 20 including a pair of parasitic elements 40 (40-1, 40-2) is illustrated, but a configuration including one parasitic element may be used. For example, a configuration including only one of the parasitic elements 40-1, 40-2 may be used. The shape of the parasitic element as viewed from the positive direction of the Z axis is not limited to the rod shape (strictly speaking, rectangular shape) as illustrated in the above embodiment, but may be a quadrilateral shape such as a rectangle whose short side length as viewed from the positive direction of the Z axis is longer, a polygonal shape, a circular shape, an elliptical shape, or the like.

[0062] As described above in detail, according to this embodiment and each modification, it is possible to improve the gain in the direction of a low elevation angle as viewed from the center of the radiating element. The material of the dielectric substrate 32 can be an inexpensive material such as glass, in addition to the commonly used ceramic.

[0063] The dielectric substrate 32 may be a glass epoxy resin substrate designated by the National Electrical Manufacturers Association (NEMA) as FR-4, a paper phenol substrate designated by the XPC symbol, a paper epoxy substrate designated by the FR-3 symbol, a glass composite substrate designated by the CEM-3 symbol, a glass polyimide substrate, a fluorine (ceramic) substrate, a glass PPO substrate, etc. By appropriately selecting these materials according to the required cost and performance, a suitable patch antenna can be obtained.

[0064] In addition, in a planar view of the radiating element from a direction perpendicular to the plate surface of the radiating element, the shape of the radiating element can be a polygon such as a rectangle, or a polygon with the corners notched, or a circle, ellipse, or the like. [Explanation of symbols]

[0065] 10... Vehicle-mounted antenna device 11…1st cabinet 12…Second housing 13...Support part 20…Patch antenna 22...Coaxial connector for circuit board 30…Antenna body 31...Radiating element 31h…Power supply point (core wire mounting hole) 32...Dielectric substrate 33...Main plate 40 (40-1, 40-2), 40a (40a-1, 40a-2), 40b (40b-1, 40b-2) ... Parasitic elements 4, 4a…coaxial cable

Claims

1. A planar radiating element; a parasitic element provided at a position spaced apart from the radiating element in a plan view of the radiating element seen from a direction perpendicular to a surface of the radiating element; The base plate and Equipped with The parasitic element does not overlap with the ground plane when viewed from the perspective of the radiating element side with respect to the ground plane, The parasitic elements are provided in pairs on both sides of the radiating element. Antenna device.

2. The parasitic element is provided such that, in the plan view, the longitudinal direction is along the direction of a line segment connecting the center of the radiating element and the power supply point.

2. The antenna device according to claim 1.

3. The pair of parasitic elements includes a first parasitic element and a second parasitic element having a longitudinal length longer than that of the first parasitic element.

2. The antenna device according to claim 1.

4. The ground plane is provided at a position spaced apart from the parasitic element. An antenna device according to any one of claims 1 to 3.

5. The ground plane is provided at a position facing at least one of the radiating element and the parasitic element. An antenna device according to any one of claims 1 to 3.

6. The base plate has a planar shape, An infinite plane including a surface of the parasitic element on the ground plane side intersects with an infinite plane including a surface of the ground plane on the radiating element side. An antenna device according to any one of claims 1 to 3.

7. The base plate has a planar shape, an infinite plane including a surface of the parasitic element on the side of the radiating element intersects with an infinite plane including a surface of the ground plane on the side of the radiating element; An antenna device according to any one of claims 1 to 3.

8. The dielectric constant between the radiating element and the ground plane is different from the dielectric constant between the parasitic element and the ground plane. An antenna device according to any one of claims 1 to 3.

9. In the plan view, the ground plane and at least a part of the radiating element overlap each other. An antenna device according to any one of claims 1 to 3.

10. The parasitic element is provided at a position away from the center of gravity of the radiating element in the plan view. An antenna device according to any one of claims 1 to 9.

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