Antenna device

An antenna device includes: an antenna element for vertically polarized waves, having a first straight line portion of which one end serves as a power feeding point, and an annular portion of which one end is connected to another end of the first straight line portion; and a first dielectric cover covering the antenna element from outside. An antenna device includes: an antenna element for vertically polarized waves, having a first straight line portion of which one end serves as a power feeding point, and an annular portion of which one end is connected to another end of the first straight line portion; and a second dielectric cover covering the first straight line portion and the annular portion from outside.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is based on PCT filing PCT/JP2018/036776, filed Oct. 2, 2018, which claims priority to JP 2017-197978, filed Oct. 11, 2017, the entire contents of each are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an antenna device suitable for use in a vehicle or the like.

BACKGROUND ART

Conventionally, as an omnidirectional antenna, there has been known a collinear array antenna in which a length of a straight line portion is λ/2 and a length of a delay portion is λ/2, for example (see Non Patent Literature 1). However, when such a collinear array antenna is used as an antenna for a vehicle which is required to reduce its height, it is difficult to ensure a sufficient antenna element length, and a gain obtained in a horizontal plane is low.

CITATION LIST

Non Patent Literature

SUMMARY OF INVENTION

Technical Problem

The present invention has been made in view of these circumstances, and an object of the present invention is to improve a horizontal plane gain while maintaining a-non directivity characteristic by bringing a dielectric body close to an antenna element even when it is difficult to ensure a sufficient antenna element length.

Solution to Problem

A first aspect of the present invention is an antenna device. The antenna device includes an antenna element for vertically polarized waves, including a first straight line portion of which one end serves as a power feeding point, and an annular portion of which one end is connected to another end of the first straight line portion, and a first dielectric cover covering the antenna element from outside.

A second aspect of the present invention is an antenna device. The antenna device includes an antenna element for vertically polarized waves, including a first straight line portion of which one end serves as a power feeding point, and an annular portion of which one end is connected to another end of the first straight line portion, and a second dielectric cover covering the first straight line portion and the annular portion from outside.

According to the first aspect, it is preferable that a second dielectric cover covering the first straight line portion and the annular portion from the outside is further included.

According to second aspect, it is preferable that a distance between the antenna element and the second dielectric cover is equal to or less than 0.01 times a wavelength of an operating frequency of the antenna element.

According to the first aspect, it is preferable that the first dielectric cover has a portion facing the first straight line portion substantially in parallel.

According to the first aspect, it is preferable that a distance between the antenna element and the first dielectric cover is equal to or less than 0.04 times a wavelength of an operating frequency of the antenna element.

A third aspect of the present invention is an antenna device. The antenna device includes an antenna element for vertically polarized waves, including a first straight line portion of which one end serves as a power feeding point, and an annular portion of which one end is connected to another end of the first straight line portion, anda dielectric core positioned along the first straight line portion and positioned inside or outside the annular portion.

According to the first or second aspect, it is preferable that a dielectric core positioned along the first straight line portion and positioned inside or outside the annular portion is further included.

According to any one of the first to third aspects, it is preferable that the antenna element is a collinear array antenna in which a second straight line portion is connected to another end of the annular portion and the annular portion serves as a delay portion.

According to any one of the first to third aspects, it is preferable that second straight line portion may include a bent portion at an end portion opposite to one end connected to the annular portion.

A fourth aspect of the present invention is an antenna device. The antenna device includes an antenna element for vertically polarized waves, including a first straight line portion of which one end serves as a power feeding point, and an annular portion of which one end is connected to another end of the first straight line portion, and a third dielectric cover covering at least a part of the antenna element from outside and having an opening at a side of an end portion of the antenna element opposite to the power feeding point, wherein the antenna element extends outside the opening.

According to the fourth aspect, it is preferable that a distance between the antenna element and the third dielectric cover is equal to or less than 0.01 times a wavelength of a working frequency of the antenna element.

Any combinations of the above constituent elements, and expressions of the present invention that are converted in methods and systems are also effective as aspects of the present invention.

Advantageous Effects of Invention

According to the antenna device of the present invention, even in a situation in which it is difficult to ensure a sufficient antenna element length, for example, in an application for a vehicle, it is possible to improve the horizontal plane gain while maintaining the non-directivity characteristic by bringing the dielectric close to the antenna element.

DESCRIPTION OF EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. The same or equivalent components, members, processes, or the like illustrated in the drawings are denoted by the same reference numerals, and a repetitive description thereof will be appropriately omitted. In addition, the embodiments are not intended to limit the invention, and all the features and combinations thereof described in the embodiments are not necessarily essential to the invention.

First Embodiment

FIG. 1is a perspective view of an antenna device1according to a first embodiment of the present invention,FIG. 2is a front sectional view thereof, andFIG. 3is an enlarged plan sectional view thereof.FIG. 4is a perspective view of the first embodiment in which an outer cover20as a first dielectric cover is removed from the antenna device1, andFIG. 5is a perspective view of a collinear array antenna10as an antenna element included in the antenna device1. The collinear array antenna10is used for, for example, V2X (Vehicle to Everything: Vehicle to Vehicle, Road to Vehicle) communication, and a wavelength for use is λ (about 51 mm). In addition, orthogonal X, Y, and Z-axis directions are defined inFIGS. 2 and 3. A ground conductor plate50inFIG. 2is on an XY plane, and a Z axis is perpendicular to the XY plane.

As shown inFIGS. 1 to 5, the antenna device1includes the collinear array antenna10as an antenna element, an outer cover20as a first dielectric cover that entirely covers the collinear array antenna10from outside, an inner cover30as a second dielectric cover that is arranged inside the outer cover20, and a dielectric core40.

As shown inFIG. 5, the collinear array antenna10has a first (lower) straight line portion11of which one end serves as a power feeding point15insulated from the ground conductor plate50, an annular delay portion13of which one end is connected to another end of the first straight line portion11, and a second (upper) straight line portion12connected to another end of the annular delay portion13. An upper end portion of the second straight line portion12is a bent portion12abent into an inverted L-shape. The annular delay portion13has a structure spirally wound for one turn, and is used for phase adjustment between the first straight line portion11and the second straight line portion12. As shown inFIG. 2, the first straight line portion11and the second straight line portion12are arranged on the ground conductor plate50and are on a straight line perpendicular to the ground conductor plate50(parallel to the Z axis) except for the bent portion12aof the second straight line portion12. In a case in which the antenna device1is attached to a vehicle body roof, the vehicle body roof functions as the ground conductor plate50, and the antenna device1is arranged substantially perpendicular to (that is, substantially the vertical direction) a horizontal plane (a plane perpendicular to the direction of gravity) so as to be used for vertically polarized waves suitable for the V2X communication. The bent portion12aat the upper end of the second straight line portion12is formed to shorten a height of the collinear array antenna10in the Z-axis direction. That is, when there is no restriction on the height, the entire second straight line portion12may have a straight line shape. However, since the height is required when the entire second straight line portion12has the straight line shape, the bent portion12ais provided to reduce the height in the present embodiment. Therefore, when the bent portion12ais extended in the Z-axis direction, the length is the same as when the entire second straight line portion12has the straight line shape.

The outer cover20is an exterior case that entirely covers the collinear array antenna10from the outside. As shown inFIG. 3, a side surface portion of the outer cover20surrounds the entire circumference of the collinear array antenna10in a cylindrical shape so as to have a portion which face the first straight line portion11and the second straight line portion12of the collinear array antenna10substantially in parallel to the first straight line portion11and the second straight line portion12, and is arranged so as to be concentric with the annular delay portion13. As shown inFIG. 4, the inner cover30has a cylindrical shape which has a length reaching the annular delay portion13from a lower end of the collinear array antenna10, and is arranged so as to be concentric with and in non-contact with the annular delay portion13and the outer cover20. A thickness of the outer cover20and a thickness of the inner cover30are 0.5 mm (about 0.01λ) The dielectric core40has a cylindrical shape which has a length reaching the inside of the annular delay portion13from the lower end of the collinear array antenna10, and is arranged so as to be concentric with and in non-contact with the annular delay portion13. The outer cover20may be provided with a hole21for feeding power to the power feeding point15.

FIG. 6is an explanatory diagram by simulation showing a relationship between a distance between the outer cover20and the collinear array antenna10and a horizontal plane average gain. In this case, the simulation was performed at a wavelength for V2X communication of 51 mm on an assumption that the ground conductor plate50on the XY plane was horizontally arranged and the inner cover30and the dielectric core40were not present. Here, the distance is a clearance between the annular delay portion13of the collinear array antenna10and the outer cover20, a distance of 0.02λ corresponds to about 1 mm, and a distance of 0.04λ corresponds to about 2 mm. As shown inFIG. 6, when the outer cover20entirely covers the collinear array antenna10(“OUTER COVER IS IN CLOSE CONTACT”, “DISTANCE 0.02λ”, and “DISTANCE 0.04λ”), the horizontal plane average gain is improved as compared with a case in which the outer cover20does not cover the entire collinear array antenna10(“WITHOUT OUTER COVER”). The reason for this is that there is a premise that the collinear array antenna10is limited in the length in the Z-axis direction for the application for the vehicle and a sufficient length cannot be secured, but shortage of the length of the collinear array antenna10can be compensated by a wavelength shortening effect due to a dielectric constant of the outer cover20.

FromFIG. 6, it can be easily estimated that the horizontal plane gain decreases as the distance between the outer cover20and the collinear array antenna10becomes larger than 0.04λ. Therefore, it is desirable to set the distance between the outer cover20and the collinear array antenna10to be equal to or less than 0.04λ (more preferably 0.02λ or less), so that the horizontal plane gain can be sufficiently improved and a size (height) of the antenna device1can be reduced.

FIG. 7is a directional characteristic diagram by simulation showing a relationship between a directional angle and the horizontal plane gain. A precondition of the simulation is the same as those inFIG. 6. In addition, the directional angle of 180° inFIG. 7coincides with an X direction inFIG. 3. As shown inFIG. 7, fluctuation of the horizontal plane gain accompanying the change in the directional angle when the entire collinear array antenna10is covered with the outer cover20(“OUTER COVER IS IN CLOSE CONTACT”, “DISTANCE 0.02λ”, and “DISTANCE 0.04λ”) is not significantly different from the fluctuation of the horizontal plane gain when the collinear array antenna10is not entirely covered with the outer cover20(“WITHOUT OUTER COVER”), and an omnidirectional property can be substantially maintained even when the entire collinear array antenna10is covered with the outer cover20.

FIG. 8is an explanatory diagram by simulation showing a relationship between a distance between the inner cover30and the collinear array antenna10and the horizontal plane average gain. In this case, the simulation was performed assuming that the ground conductor plate50on the XY plane was horizontally arranged and the outer cover20and the dielectric core40were not present. Here, the distance is a clearance between the annular delay portion13of the collinear array antenna10and the inner cover30, a distance of 0.005λ corresponds to about 0.25 mm, and a distance of 0.01λ corresponds to about 0.5 mm. As shown inFIG. 8, when the inner cover30is provided (“DISTANCE 0.005λ” and “DISTANCE 0.01λ”), the horizontal plane average gain is improved as compared to when the inner cover30is not provided (“WITHOUT INNER COVER”). The reason for this is that there is a premise that the collinear array antenna10is limited in the length in the Z-axis direction for the application for the vehicle and the sufficient length cannot be secured, but the shortage of the length of the collinear array antenna10can be compensated by the wavelength shortening effect due to a dielectric constant of the inner cover30.

FromFIG. 8, it can be easily estimated that the horizontal plane gain decreases as the distance between the inner cover30and the collinear array antenna10becomes larger than 0.01λ. Therefore, it is desirable to set the distance between the inner cover30and the collinear array antenna10to be equal to or less than 0.01λ (more preferably 0.005λ or less), so that the horizontal plane gain can be sufficiently improved. As seen from the result when the outer cover20is in close contact with the annular delay portion13inFIG. 6, it can be easily estimated that when the inner cover30is in close contact with the annular delay section13of the collinear array antenna10, the horizontal plane average gain is lower than the horizontal plane average gain when the distance between the inner cover30and the collinear array antenna10is 0.005λ, but is improved as compared to the horizontal plane average gain when the collinear array antenna10is not covered with the inner cover30.

FIG. 9is a directional characteristic diagram by the simulation showing the relationship between the directional angle and the horizontal plane gain. The precondition of the simulation is the same as that inFIG. 8. In addition, the directional angle of 180° inFIG. 9coincides with the X direction inFIG. 3. As shown inFIG. 9, the fluctuation of the horizontal plane gain accompanying the change in the directional angle when the collinear array antenna10is covered with the inner cover30(“DISTANCE 0.005” and “DISTANCE 0.01λ”) is not significantly different from the fluctuation of the horizontal plane gain when the collinear array antenna10is not covered with the inner cover30(“WITHOUT INNER COVER”), and the non-directivity characteristic can be maintained even when the collinear array antenna10is covered with the inner cover30.

FIG. 10is an explanatory diagram by the simulation showing the horizontal plane average gain when the dielectric core40is not provided and when the dielectric core40is provided at the center of the annular delay portion13. InFIG. 10, the simulation was performed assuming that the outer cover20and the inner cover30were not present. Also, inFIG. 10, a distance between the dielectric core40and the annular delay portion13when the dielectric core40is provided is set to 0.005λ. As shown inFIG. 10, when the dielectric core40is provided (“WITH CORE”), the horizontal plane average gain is improved as compared to the horizontal plane average gain when the dielectric core40is not provided (“WITHOUT CORE”). From the results ofFIGS. 6 and 8described above, it can be easily estimated that when the distance between the annular delay portion13and the dielectric core40is equal to or less than 0.005λ, the horizontal plane gain is higher than the horizontal plane average gain when the distance between the annular delay portion13and the dielectric core40is larger than 0.005λ. Therefore, it is preferable to set the distance between the annular delay portion13and the dielectric core40to be equal to or less than 0.005λ.

FIG. 11is a directional characteristic diagram by the simulation showing the relationship between the directional angle and the horizontal plane gain. The precondition of the simulation is the same as those inFIG. 10. In addition, the directional angle of 180° inFIG. 11coincides with the X direction inFIG. 3. As shown inFIG. 11, the fluctuation of the horizontal plane gain accompanying the change in the directional angle when the dielectric core40is provided (“WITH CORE”) is not significantly different from the fluctuation of the horizontal plane gain when the dielectric core40is not provided (“WITHOUT CORE”), and the non-directivity characteristic can be maintained even when the dielectric core40is provided.

According to the present embodiment, the following effects can be obtained.

(1) By providing the dielectric outer cover20that in proximity covers the entire collinear array antenna10as the antenna element from the outside, the horizontal plane average gain of the antenna device1can be improved. In addition, the fluctuation in the horizontal plane gain accompanying the change in the directional angle is small, and the non-directivity characteristic can be substantially maintained. Further, the outer cover20can be used as the exterior case.

(2) By providing the dielectric inner cover30inside the outer cover20so as to proximity cover the first straight line portion11and the annular delay portion13, the horizontal plane average gain of the antenna device1can be improved. In addition, the fluctuation in the horizontal plane gain accompanying the change in the directional angle is small, and the non-directivity characteristic can be substantially maintained.

(3) The outer cover20has the portion facing the first straight line portion11and the second straight line portion12of the collinear array antenna10substantially in parallel to the first straight line portion11and the second straight line portion12, so that the wavelength shortening effect due to the dielectric constant of the outer cover20can be effectively used.

(4) By providing the dielectric core40positioned along the first straight line portion11and inside the annular delay portion13, the horizontal plane average gain of the antenna device1can be improved. In addition, the fluctuation in the horizontal plane gain accompanying the change in the directional angle is small, and the non-directivity characteristic can be substantially maintained.

Second Embodiment

FIG. 12is a front view showing an antenna device2according to a second embodiment of the present invention while omitting the outer cover20and the inner cover30, andFIG. 13is an enlarged plan view thereof. In this case, a dielectric core45is a cylinder which has a length reaching the annular delay portion13from the lower end of the collinear array antenna10, and is arranged along the first straight line portion11and outside of the annular delay portion13so as to be in non-contact with the annular delay portion13. Other configurations are similar to those of the first embodiment described above.

FIG. 14is a directional characteristic diagram by simulation showing a relationship between the directional angle and the horizontal plane gain when the dielectric core45is not provided and when the dielectric core45is provided. The simulation was performed assuming that the outer cover20and the inner cover30are not present. InFIG. 14, the horizontal plane average gain is 3.42 dBi when the dielectric core45is provided (“WITH CORE”), the horizontal plane average gain is 3.28 dBi when the dielectric core45is not provided (“WITHOUT CORE”), and therefore the horizontal plane average gain when the dielectric core45is provided is higher than the horizontal plane average gain when the dielectric core45is not provided. As shown inFIG. 14, even when the dielectric core45is provided outside the annular delay portion13, there is no significant difference in the fluctuation of the horizontal plane gain accompanying the change in the directional angle as compared to that when the dielectric core45is not provided, and the omnidirectional property can be maintained.

Third Embodiment

FIG. 15is a front view showing an antenna device3according to a third embodiment of the present invention while omitting the outer cover20and the dielectric core40, andFIG. 16is an enlarged plan view thereof. In this case, instead of the cylindrical inner cover30according to the first embodiment, a semi-cylindrical (semicircular arc) inner cover35is arranged so as to surround a half of a circumference of the annular delay portion13of the collinear array antenna10. Other configurations are similar to those of the first embodiment described above.

FIG. 17is a directional characteristic diagram by simulation showing a relationship between the directional angle and the horizontal plane gain when the semi-cylindrical inner cover35is not provided and when the semi-cylindrical inner cover35is provided. The simulation was performed assuming that the outer cover20and the dielectric core40are not present. InFIG. 17, the horizontal plane average gain is 3.42 dBi when the semi-cylindrical inner cover35is provided (“WITH INNER COVER (SEMI-CYLINDER)”), the horizontal plane average gain is 3.28 dBi when the semi-cylindrical inner cover35is not provided (“WITHOUT INNER COVER”), and therefore the horizontal plane average gain when the semi-cylindrical inner cover35is provided is higher than the horizontal plane average gain when the semi-cylindrical inner cover35is not provided. In addition, even when the semi-cylindrical inner cover35is provided, there is no significant difference in the fluctuation of the horizontal plane gain accompanying the change in the directional angle, and the non-directivity characteristic can be maintained.

Fourth to Sixth Embodiments

FIG. 18is a front sectional view of an antenna device4according to a fourth embodiment of the present invention, andFIG. 19is an enlarged plan sectional view thereof.FIG. 20is a front sectional view of an antenna device5according to a fifth embodiment of the present invention, andFIG. 21is an enlarged plan sectional view thereof.FIG. 22is a front sectional view of an antenna device6according to a sixth embodiment of the present invention, andFIG. 23is an enlarged plan sectional view thereof. Each of the fourth to sixth embodiments relates to a holding structure for the collinear array antenna10. In the antenna device4according to the fourth embodiment, one support portion25supporting an upper portion of the collinear array antenna10is provided integrally with the outer cover20inside the outer cover20. In the antenna device5according to the fifth embodiment, two support portions25,26supporting the upper portion and a lower portion of the collinear array antenna10are provided integrally with the outer cover20inside the outer cover20. In the antenna device6according to the sixth embodiment, a support portion27linearly supporting the collinear array antenna10from four directions is provided integrally with the outer cover20inside the outer cover20. The fourth to sixth embodiments are the same as the structure in which the inner cover30and the dielectric core40are omitted in the first embodiment described above, except that each has the holding structure.

FIG. 24is an explanatory diagram showing the horizontal plane average gain in cases of the fourth, fifth and sixth embodiments having the holding structure of the collinear array antenna10and in the case in which there is no holding structure of the collinear array antenna10. In any cases, the distance between the annular delay portion13of the collinear array antenna10and the outer cover20is 0.02λ. In the fourth and fifth embodiments, the same horizontal plane average gain as that in the case in which there is no holding structure of the collinear array antenna can be ensured.

Although the present invention has been described above by taking the embodiments as an example, it will be understood by those skilled in the art that various modifications can be made to each component and each processing process of the embodiments within the scope of the claims. Hereinafter, a modification will be described.

The dielectric inner covers30,35according to the first embodiment and the third embodiment of the present invention are arranged so as to cover the lower half of the collinear array antenna10, but may be arranged so as to cover the upper half of the collinear array antenna10, that is, the second straight line portion12from the annular delay portion13. Similarly, the dielectric cores40,45according to the first embodiment and the second embodiment are arranged with respect to the lower half of the collinear array antenna10, but may be arranged on the upper half of the collinear array antenna10, that is, from the annular delay portion13to the second straight line portion12.

In the sixth embodiment of the present invention, the support portion27that linearly supports the collinear array antenna10from the four directions is provided inside the outer cover20, but the support portion27may be configured to support the collinear array antenna10in three or more directions. The support portion27that linearly supports the collinear array antenna10from five or more directions may be provided inside the outer cover20.

As shown inFIG. 4of the first embodiment, the inner cover30covers to a region reaching the annular delay portion13from the lower end of the collinear array antenna10from the outside, but the embodiment is not limited thereto. For example, as shown inFIG. 25A, the inner cover30may cover to a region that does not reach the annular delay portion13from the lower end of the collinear array antenna10from the outside. Alternatively, as shown inFIG. 25B, the inner cover30may cover to a region beyond the annular delay portion13from the lower end of the collinear array antenna10from the outside. That is, the inner cover30covers at least a part of the collinear array antenna10from the outside, and has an opening at a side of an end portion of the collinear array antenna10opposite to the power feeding point15. Then, the collinear array antenna10extends outside the opening.

In the first embodiment described above, such a case is explained that the inner cover30has a cylindrical shape and the cover30covers at least a part of the collinear array antenna10from the outside. However, the embodiment is not limited thereto. For example, the inner cover30may have a shape that overlaps a part of the collinear array antenna10in the vicinity of the collinear array antenna10. More specifically, as shown inFIG. 26, the inner cover30has a columnar support portion37that overlaps the collinear array antenna10in one direction. In an example shown inFIG. 26, the support portion37overlaps the collinear array antenna10from a front side in a front-rear direction of the vehicle. In addition, the support portion37is provided with a fixing portion38holding the collinear array antenna10. In the example shown inFIG. 26, a case where three fixing portions38are provided is shown. That is, the inner cover30overlaps with a part of the collinear array antenna10in the vicinity of the collinear array antenna10while holding the collinear array antenna10with the fixing portions38. The inner cover30may be provided with the support portion37in a plurality of directions.

The embodiments described above can also be applied to a shark fin type antenna. In this case, an outer cover of the shark fin type antenna corresponds to the outer cover20shown in the embodiment.

REFERENCE SIGNS LIST