JP7563191B2 - Vehicle antenna device - Google Patents

Description

The present invention relates to a vehicle antenna device.

In recent years, automobiles and other vehicles have become capable of transmitting and receiving radio waves in the frequency bands of 4G LTE (Long Term Evolution) (700 MHz band), 5G (sub6 (up to 6 GHz)), quasi-millimeter wave (20 GHz to 30 GHz), and millimeter wave (30 GHz to 300 GHz). In this way, by allowing vehicles to communicate using radio waves in multiple frequency bands, the vehicles themselves are being used as part of a high-speed, large-capacity communications infrastructure.

On the other hand, vehicles are also equipped with antennas that use radio waves in frequency bands below 800 MHz, such as conventional AM, FM, DAB (Digital Audio Broadcast) Band III, and terrestrial digital television (DTV) broadcast waves. Therefore, as the number of types of frequency bands of radio waves transmitted and received in vehicles increases, the range of frequency bands transmitted and received by antennas, including broadcast wave receiving antennas, is expanding. For example, when the above-mentioned broadcast wave receiving antenna and an electronic device that stores sensors that acquire information outside the vehicle are arranged close to each other on the windshield of a vehicle, interference occurs between the broadcast wave receiving antenna and the electronic device, which tends to reduce the antenna gain and to make the electrical isolation between the two devices insufficient. Therefore, for example, Patent Document 1 discloses that a noise removal pattern is provided between the electronic device that stores the sensors and the broadcast wave antenna (terrestrial digital television broadcast wave antenna) arranged on the glass surface to absorb noise arriving at the antenna.

International Publication No. 2019/181623

Vehicle window glass is required not to obstruct the visibility of vehicle occupants. For example, a defogger including an electric heater wire must be installed on the rear glass. Therefore, vehicle window glass is required to reduce the space required for arranging antennas and other electronic devices. However, when a noise removal pattern is arranged on the vehicle window glass as in Patent Document 1, extra space is required for arranging the noise removal pattern. Furthermore, the freedom of layout of the vehicle window glass on which the noise removal pattern is arranged is also limited.

In consideration of the above-mentioned problems, the present invention aims to provide a vehicle antenna device that can reduce interference between antennas placed in close proximity and save space.

The vehicle antenna device according to one aspect of the present invention includes a dielectric constituting a part of a vehicle, a first antenna attached to the dielectric, a second antenna attached near the first antenna and transmitting and receiving radio waves in a higher frequency band than the frequency band of radio waves transmitted and received by the first antenna, and a transmission line connected to the second antenna, the second antenna having a power supply conductor connected to a signal line of the transmission line and a ground conductor connected to a ground line of the transmission line, the ground line having a first ground point connected to the ground conductor and a second ground point connected to an earth potential part of the vehicle.

In the vehicle antenna device described above, the dielectric may include a glass plate, and the second antenna may be fixed directly or indirectly to the glass plate.

In the vehicle antenna device described above, the second antenna may be a planar antenna disposed on the surface of the glass plate.

In the vehicle antenna device described above, the first antenna may be disposed on the surface of the glass plate.

In the vehicle antenna device described above, the dielectric may include a resin, and the second antenna may be fixed directly or indirectly to the resin.

In the vehicle antenna device described above, the first antenna may be fixed directly or indirectly to the resin.

In the above-mentioned vehicle antenna device, the dielectric may include a glass plate, and the first antenna may be disposed on the surface of the glass plate.

In the above-mentioned vehicle antenna device, the resin may be an aerodynamic part of the vehicle.

In the above-mentioned vehicle antenna device, when the length of the ground wire from the first ground point to the second ground point is denoted by _DG , the distance from the ground point of the power feeder of the second antenna to the farthest point of the ground conductor is denoted by L, the wavelength in air in the frequency band received by the first antenna is denoted by λ, the wavelength shortening rate of the dielectric is denoted by k, and M is a positive integer,
(λ/4-λ/16)×(2M-1)≦D _G +L/k≦(λ/4+λ/16)×(2M-1)
The following relation may be satisfied.

In the above-mentioned vehicle antenna device, the wavelength λ may be a central wavelength λ ₀ in air in a frequency band received by the first antenna.

In the above-mentioned vehicle antenna device, the length _DG may be 400 mm or less.

In the vehicle antenna device described above, the first antenna and the second antenna may be positioned at a distance of 30 mm or more.

In the vehicle antenna device described above, the transmission line may include a portion that starts at the connection portion of the second antenna and extends away from the first antenna.

In the vehicle antenna device described above, the first antenna may receive radio waves in a frequency band of 800 MHz or less.

In the vehicle antenna device described above, the first antenna may be configured to receive at least one of radio waves in the DAB (Digital Audio Broadcast) Band III frequency band and radio waves in the frequency band of terrestrial digital television broadcast waves.

In the vehicle antenna device described above, the second antenna may be configured to transmit and receive radio waves in a frequency band of 600 MHz or higher.

In the vehicle antenna device described above, the second antenna may be configured to transmit and receive radio waves in a frequency band of 800 MHz or higher.

In the vehicle antenna device described above, the dielectric may include a windshield.

In the above-mentioned vehicle antenna device, the dielectric may include a rear window.

According to one aspect of the present invention, it is possible to provide a vehicle antenna device that can reduce interference between antennas placed in close proximity and save space.

1 is a diagram illustrating a configuration example of a vehicle antenna device according to an embodiment; 2 is a diagram for explaining details of an antenna according to an embodiment. FIG. FIG. 13 is a diagram for explaining distance _DG and distance L. FIG. 4 is a diagram showing isolation values of the vehicle antenna device. FIG. 4 is a diagram showing isolation values of the vehicle antenna device.

Specific embodiments to which the present invention is applied will be described in detail below with reference to the drawings. However, the present invention is not limited to the following embodiments. Furthermore, in order to clarify the description, the following description and drawings have been omitted and simplified as appropriate. In each drawing, the same elements are given the same reference numerals, and duplicated descriptions are omitted as necessary. In each embodiment, deviations in directions such as parallel, horizontal, and vertical are permitted to the extent that they do not impair the effects of the present invention. Furthermore, in drawings to explain the embodiments, unless a direction is specifically stated, it refers to the direction on the drawing.

(Embodiment)
An example of the configuration of a vehicle antenna device 100 according to an embodiment will be described with reference to Fig. 1. Fig. 1 shows an example of the configuration of a vehicle antenna device according to an embodiment. Fig. 1 is a view seen from inside the vehicle with a glass plate 20 attached to the vehicle. In Fig. 1, the X-axis direction corresponds to the horizontal direction and the vehicle width direction, and the Y-axis direction corresponds to the vertical direction perpendicular to the horizontal direction. Although Fig. 1 will be described as a view seen from inside the vehicle, it may also be referred to as a view seen from outside the vehicle.

The vehicle antenna device 100 is a device that is placed in a vehicle. The vehicle antenna device 100 includes a glass plate 20, an antenna 30, an antenna 40, and a transmission line 70. In this specification, the antenna 30 is also referred to as the first antenna, and the antenna 40 is also referred to as the second antenna. Note that in FIG. 1, the vehicle antenna device 100 includes a glass plate 20, an antenna 30, an antenna 40, and one transmission line 70 for the antenna 40, but may include two or more glass plates 20, antennas 30, antennas 40, and transmission lines 70. A transmission line (not shown) is also connected to the antenna 30.

The glass plate 20 is a dielectric that constitutes part of the vehicle in which the vehicle antenna device 100 is disposed. The glass plate 20 is attached to the metal body 10 of the vehicle and fixed to a body flange formed on the vehicle housing. The upper part of the glass plate 20 is fixed near the end 10a of the metal body 10 with urethane resin or the like. The end 10a is the edge of the end of the metal body 10 that is in physical contact with the upper part of the glass plate 20. The glass plate 20 may be a windshield, a rear window, or a side window.

The antenna 30 is, for example, a broadcast wave antenna, and is configured to be capable of transmitting and receiving at least one type of radio wave in a frequency band of 800 MHz or less. Here, "capable of transmitting and receiving" is used to mean that either or both of transmission and reception are possible. Therefore, the antenna 30 is not limited to an antenna that is dedicated to receiving radio waves in a specific frequency band, but may be an antenna that is capable of both transmission and reception. The antenna 30 is, for example, an antenna that can receive at least one of the radio waves of Band III of the European standard DAB (Digital Audio Broadband) and the radio waves of terrestrial digital television broadcast waves. DAB Band III uses a frequency band of 174 MHz to 240 MHz. Also, terrestrial digital television broadcast waves use a frequency band of 470 MHz to 710 MHz. The antenna 30 may be an antenna capable of receiving FM broadcast wave frequency bands (76 MHz to 108 MHz) and AM broadcast wave frequency bands, or an antenna capable of receiving narrowband ITS (Intelligent Transport Systems) signals including 760 MHz.

The antenna 30 is attached to a dielectric and is disposed on the plate surface of the glass plate 20, which is a dielectric. The antenna 30 is disposed in a position where the vehicle antenna device 100 is disposed so as not to impair the visibility of the vehicle occupants and in a position different from the area where the defogger is disposed. In this embodiment, from the viewpoint of ease of illustration, the antenna 30 is described as being disposed on the upper part of the glass plate 20 and to the right of the center in the width direction, but this is not limited to this. The antenna 30 may be disposed on an aerodynamic part made of resin, such as a rear spoiler, so long as it is disposed on a dielectric, or the dielectric may be air and the antenna 30 may be an aerial wiring.

In FIG. 1, the antenna 30 is a so-called dipole antenna that includes a power supply unit 31, an earth unit 32, and linear elements 33 and 34. Note that the antenna 30 is not limited to a dipole antenna as shown in FIG. 1, but may be a monopole antenna that includes only the power supply unit 31 and the linear element 33 connected to the power supply unit 31. The power supply unit 31 and the earth unit 32 are disposed in close proximity to the metal body 10. The power supply unit 31 and the earth unit 32 are connected to a communication device (not shown) via a transmission line such as a coaxial cable (not shown).

Linear element 33 and line element 34 are antenna elements made of a conductor. Linear element 33 has one end connected to power supply 31 and the other end open. Linear element 33 is, for example, L-shaped. Linear element 33 is connected to power supply 31 at point 33a, with point 33a as the connection point, extends from point 33a in the negative direction of the Y axis to point 33b, and extends from point 33b in the positive direction of the X axis to point 33c.

One end of the line element 34 is connected to the earth part 32, and the other end is an open end. The line element 34 is, for example, U-shaped. The line element 34 is connected to the earth part 32 at point 34a, with point 34a as the connection point, and extends from point 34a in the positive direction of the X-axis to point 34b, extends from point 34b in the negative direction of the Y-axis to point 34c, and extends from point 34c in the negative direction of the X-axis to point 34d.

In FIG. 1, the antenna 30 is configured to include an earth part 32 and a line element 34, but as described above, it may be configured to not include the earth part 32 and the line element 34 (monopole type). In FIG. 1, the line element 33 and the line element 34 are L-shaped and U-shaped, respectively, but may be arbitrarily set according to the vehicle in which the vehicle antenna device 100 is installed. Furthermore, in FIG. 1, the power supply part 31 is arranged on the left side of the glass plate 20, and the ground part 32 is arranged on the right side, but the positions of the power supply part 31 and the ground part 32 may be interchanged.

The antenna 40 is, for example, a communication antenna that transmits and receives radio waves for communication provided by a telecommunications carrier. The antenna 40 transmits and receives radio waves in a higher frequency band than the frequency band received by the antenna 30. The frequency band of radio waves that the antenna 40 can transmit and receive may be 600 MHz or higher, or 800 MHz or higher.

The antenna 40 is attached to a dielectric and is disposed on the plate surface of the glass plate 20, which is a dielectric. The antenna 40 is disposed in a position where the vehicle antenna device 100 is disposed so as not to impair the visibility of the vehicle occupants and in a position different from the area where the defogger is disposed. In this embodiment, from the viewpoint of ease of illustration, the antenna 40 is described as being disposed on the upper part of the glass plate 20 and near the center in the width direction, but this is not limited to this. The antenna 40 may be disposed on an aerodynamic part made of resin, such as a rear spoiler, so long as it is disposed on a dielectric, or the dielectric may be air and the antenna 40 may be an aerial wiring.

The antenna 40 is attached, for example, to the left of the antenna 30 in the vicinity of the antenna 30. The antennas 40 and 30 are arranged, for example, 30 mm or more apart. The rightmost end of the antenna 40 is arranged 30 mm or more away from the leftmost end of the power supply unit 31 of the antenna 30. The distance D _A between the antennas 30 and 40 corresponds to the shortest distance between the conductors of the antennas 30 and 40. If the distance D _A between the antennas 30 and 40 is 30 mm or more, the isolation between the antennas due to the midpoint earth for the antenna 40 is improved as described below. In order to improve the isolation, the distance D _A is preferably 50 mm or more, and more preferably 100 mm or more. If the distance D _A between the antennas is long, the isolation is improved, but if the distance D _A is too long, it becomes difficult to save space in the area where the antennas 30 and 40 are arranged. Therefore, the distance D _A may be 200 mm or less, and preferably 150 mm or less.

The antenna 40 may be a planar antenna, an antenna module, or an encapsulated antenna. A planar antenna is an antenna in which a planar conductor pattern is provided on the main surface of the glass plate 20. A planar antenna may be called a glass print antenna. An antenna module is an antenna in which the antenna conductor has a three-dimensional shape. An encapsulated antenna is an antenna that is encapsulated and disposed between the first and second glass plates in a laminated glass in which the glass plate 20 is a first glass plate and a second glass plate sandwiching a resin interlayer.

The antenna 40 is, for example, directly or indirectly fixed to the glass plate 20. When the antenna 40 is a planar antenna, it is directly fixed to the surface of the glass plate 20. That is, the antenna 40 is fixed so as to be physically connected to the glass plate 20. When the antenna 40 is an antenna module having a three-dimensional shape, it is indirectly fixed to the glass plate 20 via a housing such as a bracket. That is, at least a part or all of the antenna 40 is not physically connected to the glass plate 20, but is indirectly connected to the glass plate 20 via a housing. When the antenna 40 is an encapsulated antenna, it is directly fixed between the first glass and the second glass that constitute the glass plate 20. In the following description, the antenna 40 will be described as a planar antenna.

The antenna 40 is composed of two conductors, a ground conductor 41 and a power supply conductor 42. The ground conductor 41 and the power supply conductor 42 are connected to a transmission line 70 described later. The transmission line 70 is, for example, a coaxial cable, and the ground conductor 41 is connected to the outer conductor of the coaxial cable (transmission line 70). The outer conductor of the coaxial cable is the ground line of the transmission line 70, so the ground conductor 41 is connected to the ground line of the transmission line 70. The power supply conductor 42 is connected to the inner conductor of the coaxial cable (transmission line 70). The inner conductor of the coaxial cable is the signal line of the transmission line 70, so the power supply conductor 42 is connected to the signal line of the transmission line 70.

Here, the antenna 40 will be described in detail with reference to FIG. 2. FIG. 2 is an enlarged view of the antenna 40 according to the embodiment. The antenna 40 is capable of transmitting and receiving radio waves in the frequency bands of 4G LTE to 5G-sub6. The antenna 40 functions as a slot antenna by forming a cutout portion 50 in the metal film (conductor film) 43. Specifically, a first slot 51, a second slot 52, a first connection slot 53, a first wide slot 54, and a second wide slot 55 are formed as the cutout portion 50 in the metal film 43. A pair of power supply portions (power supply points) 60 are arranged so as to straddle the first slot 51. The pair of power supply portions 60 corresponds to a combination of the power supply portion 31 and the earth portion 32.

The first slot 51, which is arranged so that the pair of power supply units 60 straddle it, extends in the positive direction of the Y axis from the lower end (one end) 51a to the upper end (the other end) 51b. The extension direction of the first slot 51 is the positive direction of the Y axis on the surface of the glass plate 20.

The first connection slot 53 is connected to the other end 51b of the first slot 51 and extends to the width change portion 53c in a direction different from the extension direction of the first slot 51. The extension direction of the first connection slot 53 is the positive direction of the X-axis.

The first wide slot 54 is connected to the end (width changing portion) 53c of the first connection slot 53, and has a slot width wider than the first slot 51 and the first connection slot 53. The second slot 52 is connected to one end 51a of the first slot 51, and extends in the positive direction of the X-axis, which is a different direction from the extension direction of the first slot 51.

The second wide slot 55 is directly connected to the end 52e (the end of the extension) of the second slot 52, and has a wider slot width than the second slot 52. The slot width of the second wide slot 55 gradually increases as it extends. The corners of each slot may be bent with a curvature. The end may be the end of the extension of each slot, or may be near the end of the slot just before the end.

The mounting angle of the glass plate 20 relative to the vehicle is preferably, for example, 15° to 90° relative to the ground surface. In other words, the angle of the antenna 40 relative to the ground surface may be the same as the angle of the glass plate 20 relative to the ground surface.

In FIG. 2, the first wide slot 54 has an opening 54d that opens to the upper edge of the metal body 10, adjacent to which the antenna 40 is disposed. The second wide slot 55 has an opening 55f that opens to the upper edge of the metal body 10, adjacent to which the antenna 40 is disposed.

In the metal film 43, the side closer to the corner between the upper edge and the side edge near which the antenna 40 is disposed than the second slot 52 and the first slot 51 functions as the ground conductor 41. On the other hand, the side farther from the corner than the second slot 52 and the first slot 51 functions as the power supply conductor 42. The power supply conductor 42 is also called the core side conductor because it is connected to the signal line 71, which is the core of the coaxial cable that functions as the transmission line 70.

The power supply unit 60 is a pair of power supply units having a power supply conductor side power supply unit (core wire side power supply unit) and a ground conductor side power supply unit, and is arranged so that the pair of power supply units straddles the first slot 51 to supply power to the ground conductor 41 and the power supply conductor 42. The power supply conductor side power supply unit of the power supply unit 60 is connected to the signal line 71, which is the core wire of the transmission line 70, at a connection point 71a. The ground conductor side power supply unit of the power supply unit 60 is connected to the ground line 72, which is the external conductor of the transmission line 70, at a ground point 72a. In this embodiment, an example is shown in which an opening 54d is provided on the upper side of the first wide slot 54 and an opening 55f is provided on the upper side of the second wide slot 55, but the positions of the openings 54d and 55f are not limited to the upper side.

When the opening 54d is formed, the shape and arrangement of the first connection slot 53 cause the upper part of the ground conductor 41 of the metal film 43 to have a linear shape. Therefore, this linear ground conductor 41L has the function of emitting radio waves at a specific frequency, like a linear element.

The second wide slot 55 includes, in addition to the opening 55f, a triangular portion 15α where the triangular portion and the widest portion of the triangle extend, a rectangular portion 15γ, and a wide connection portion 15β between the triangular portion 15α and the rectangular portion 15γ. Because the rectangular portion 15γ is wide, the corresponding portion of the ground conductor 41 becomes thin like a line, forming a line corner conductor 41Lc composed of the line ground conductor 41La and the line ground conductor 41Lb.

The ground conductor 41 and the power supply conductor 42 are metal films formed by printing and baking a paste containing a conductive metal, such as silver paste, on the inside surface (or the outside surface) of the glass sheet 20. Note that the formation method is not limited to this, and a linear or foil-shaped body made of a conductive material, such as copper, may be attached to the window glass with an adhesive or the like on either the inside or outside surface of the window glass, or may be provided inside the window glass if the window glass is laminated glass.

Next, the transmission line 70 will be described with reference to FIG. 1. The transmission line 70 is, for example, a coaxial cable, one end of which is connected to the antenna 40 and the other end of which is connected to a communication device (not shown). A signal line 71, which is an internal conductor of the transmission line 70, is connected to the power supply conductor 42 of the antenna 40 at a connection point 71a. Specifically, the signal line 71 is connected to the power supply conductor side power supply section of the power supply section 60 of the antenna 40 at the connection point 71a. The signal line 71 is connected to the power supply conductor 42 at the connection point 71a, for example, by soldering.

In Fig. 1, the antenna 40 is disposed to the left of the antenna 30, but the positions of the antennas 30 and 40 may be interchanged. In this case, the antennas 30, 40, and the transmission line 70 may be disposed in a manner in which the antennas 30, 40, and the transmission line 70 shown in Fig. 1 are inverted in the left-right direction, and the distance D _A between the antennas 30 and 40 may satisfy the numerical range described above.

The ground wire 72, which is the external conductor of the transmission line 70, is connected to the ground conductor 41 of the antenna 40 at the ground point 72a. The ground wire 72 is connected to the ground conductor 41 at the ground point 72a, for example, by soldering. Specifically, the ground wire 72 is connected to the ground conductor side power supply unit of the power supply unit 60 of the antenna 40 at the ground point 72a. The ground wire 72 is connected to the metal body 10 at the ground point 72b between the antenna 40 and a communication device (not shown). The metal body 10 functions as the earth potential part of the vehicle in which the vehicle antenna device 100 is disposed. Therefore, the ground wire 72 is connected to the ground conductor 41 at the ground point 72a, which is the first ground point, and is connected to the metal body 10, which functions as the earth potential part of the vehicle, at the ground point 72b, which is the second ground point. In other words, the ground wire 72 is connected to the metal body 10, which functions as the earth potential part of the vehicle, via the ground point 72b, which serves as the midpoint earth.

The transmission line 70 includes a portion that starts at the ground point 72a, which is the connection portion of the antenna 40, and extends away from the antenna 30. The transmission line 70 may also start at the ground point 72a, which is the connection portion of the antenna 40, and extend away from the antenna 30 to the ground point 72b, which is the connection point to the metal body 10, which is the earth potential portion. In other words, the transmission line 70 may connect the ground point 72a and the ground point 72b so that the distance from the ground point 72a to the ground point 72b is longer than the shortest distance from the ground point 72a to the ground point 72b.

The ground point 72b, which functions as a midpoint earth, is provided at a position where the distance _DG from the ground point 72a to the ground point 72b along the transmission line 70 is, for example, 400 mm or less. The position of the ground point 72b is determined by the relationship between the distance _DG , the distance L from the position of the power supply unit 60 of the antenna 40 to the farthest position of the ground conductor 41, the wavelength λ in air of the frequency band received by the antenna 30, and the wavelength shortening rate k of the glass plate 20, which is a dielectric.

Before describing the position of the ground point 72b, the distances _DG and L will be described with reference to Fig. 3. Fig. 3 is an enlarged view of the transmission line 70 and the antenna 40 to explain the distances _DG and L.

The distance _DG is the distance along the transmission line 70 between the ground point 72a and the ground point 72b, and is equal to the length of the dotted arrow. The distance L is the distance from the ground point 72a, which is a position on the ground conductor 41 side of the power supply unit 60 of the antenna 40, to a point 415, which is a position on the ground conductor 41 and is the farthest position from the ground point 72a. The distance L is the shortest distance from the ground point 72a to the point 415, and is equal to the length of the dashed arrow. Specifically, the distance L is equal to the length of the line connecting the point 412 located in the negative Y-axis direction of the ground point 72a, the point 413 and the point 414, which are the points at both ends of the linear corner conductor 41Lc, and the point 415.

ここで、Ｍは任意の正の整数（Ｍ≧１）である。なお、アンテナ３０が受信する周波数帯は、広帯域を対象とする場合があるため、接地点７２ｂの位置は、上記式（１）の波長λの代わりに、アンテナ３０が受信する周波数帯の空気中の中心波長λ_０を用いて、“Ｄ_Ｇ＋Ｌ／ｋ”が取り得る範囲を決定してもよい。すなわち、以下に示す式（２）の関係を満たすように設けられてもよい。

The position of the ground point 72b functioning as the midpoint earth is set so that the distance _DG , the distance L, the wavelength λ of the radio wave in the air, and the wavelength shortening rate k of the dielectric material to which the antenna 40 is attached satisfy the relationship of the following formula (1). Note that when the antenna 40 is attached to the glass plate 20, the wavelength shortening rate of the glass plate 20 can be applied as k.

Here, M is any positive integer (M≧1). Since the frequency band received by the antenna 30 may be a wide band, the position of the ground point 72b may be determined to have a range that "D G +L/k" can take by using the central wavelength λ ₀ in the air of the frequency band received by the antenna 30 instead of the wavelength _λ in the above formula (1). In other words, the ground point 72b may be provided so as to satisfy the relationship of the following formula (2).

Next, the isolation between antenna 30 and antenna 40 in vehicle antenna device 100 will be described. The isolation between antenna 30 and antenna 40 is an index value that represents the degree of coupling between antenna 30 and antenna 40, and can also be considered an index value that indicates the degree of interference that antenna 40 receives from antenna 30. In the following description, for the sake of simplicity, the isolation between antenna 30 and antenna 40 will be simply referred to as "isolation."

To evaluate the isolation in the vehicle antenna device 100, the isolation is compared between a vehicle antenna device 100 with a midpoint earth and a configuration in which the vehicle antenna device 100 does not have a midpoint earth. In the following explanation, the configuration in which the vehicle antenna device 100 does not have a ground point 72b that functions as a midpoint earth is referred to as the "default configuration."

To compare the isolation between the vehicle antenna device 100 and the default configuration, the frequencies of the radio waves received by the antenna 30 were set to DAB Band III and each frequency band of terrestrial digital television broadcast waves, and the isolation values were calculated by simulation and evaluated. Note that DAB Band III is a frequency band from 174 MHz to 240 MHz, and terrestrial digital television broadcast waves are a frequency band from 470 MHz to 710 MHz.

In order to calculate the isolation value, in the vehicle antenna device 100, the distance between the antenna 30 and the end 10a of the metal body 10 was set to 10 mm, and the distance D _A between the antenna 30 and the antenna 40 was set to 50 mm. In addition, the distance L was set to 60 mm, and the wavelength shortening rate k of the glass plate 20 was set to 0.66.

First, Fig. 4 will be described. Fig. 4 is a diagram showing the isolation value (embodiment) of the vehicle antenna device 100 in the frequency band of DAB Band III, and the isolation value (comparison example) of the default configuration. Fig. 4 shows, as the embodiment, an embodiment in which the distance _DG is set to 300 mm, and an embodiment in which the distance _DG is set to 350 mm.

Under the above conditions, the central wavelength _λ0 in the air in the DAB Band III frequency band is _λ0 ≈ 1448 mm. Therefore, under the condition of _DG = 300 mm, " _DG + L/k" (≈ 391 mm) satisfies the range of ( _λ0 /4- _λ0 /16) to ( _λ0 /4+ _λ0 /16) with M = 1 in formula (2). Also, under the condition of _DG = 350 mm, " _DG + L/k" (≈ 441 mm) satisfies the range of ( _λ0 /4- _λ0 /16) to ( _λ0 /4+ _λ0 /16) with M = 1 in formula (2).

In Figure 4, the horizontal axis represents frequency and the vertical axis represents isolation value. The lower the isolation value, the smaller the mutual interference between antennas 30 and 40. In other words, the lower the isolation value, the smaller the interference from antenna 30 that antenna 40 experiences, and the greater the receiving sensitivity of antenna 30 can be.

In Fig. 4, the dotted line, the solid line, and the dashed line respectively indicate the isolation value of the default configuration, the isolation value of the configuration in which the distance D _G is set to 300 mm, and the isolation value of the configuration in which the distance D _G is set to 350 mm. As shown in Fig. 4, in the frequency band of 174 MHz to 240 MHz of DAB Band III, the isolation values of the solid line and the dashed line at each frequency are lower than the isolation value of the dotted line. That is, in any frequency of the frequency band of DAB Band III, the vehicle antenna device 100 can reduce the interference that the antenna 30 receives from the antenna 40 by providing the midpoint earth at a position that satisfies the relationship of formulas (1) and (2). Therefore, the vehicle antenna device 100 can reduce the interference between the antenna 30 and the antenna 40 by providing the midpoint earth at a position that satisfies the relationship of formulas (1) and (2), so that the antenna 30 can be arranged near the antenna 40.

Next, Fig. 5 will be described. Fig. 5 is a diagram for comparing the isolation value of the vehicle antenna device 100 and the isolation value of the default configuration in the frequency band of terrestrial digital television broadcast waves. Fig. 5 illustrates an example in which the distance _DG is set to 200 mm. Note that the antenna 40 at this time has the same shape as when the simulation of Fig. 4 was performed, and only the distance _DG was changed.

Under the above conditions, the wavelength λ in the air in the frequency band of terrestrial digital television broadcast waves is in the range of approximately 422 mm to approximately 638 mm. Therefore, under the condition of D _G = 200 mm, "D _G + L/k" (≈ 291 mm) satisfies the range of (λ/4 - λ/16) x 3 to (λ/4 + λ/16) x 3 in formula (1) with M = 2 and λ ≈ 470 mm.

In FIG. 5 as well, the horizontal axis indicates frequency and the vertical axis indicates isolation value. The dotted line and the solid line indicate the isolation value of the default configuration and the isolation value of the configuration in which the distance D _G is set to 200 mm, respectively. As shown in FIG. 5, in the frequency band of 470 MHz to 710 MHz that is the frequency band of terrestrial digital television broadcast waves, the isolation value of the solid line is smaller than the isolation value of the dotted line at 470 MHz to 530 MHz and 615 MHz to 660 MHz. That is, in the frequency band of 470 MHz to 530 MHz and 615 MHz to 660 MHz, the vehicle antenna device 100 can reduce the interference that the antenna 30 receives from the antenna 40 by providing a midpoint earth at a position that satisfies the relationship of formula (1). Therefore, the vehicle antenna device 100 can reduce the interference between the antenna 30 and the antenna 40 at 470 MHz to 530 MHz and 615 MHz to 660 MHz, so that the antenna 30 can be arranged near the antenna 40.

As described above, the vehicle antenna device 100 can reduce the mutual interference between the antennas 30 and 40 even when they are placed close to each other by providing a midpoint earth at a position that satisfies the relationship of formula (1), compared to a configuration without a midpoint earth. In addition, the vehicle antenna device 100 can reduce the mutual interference between the antennas 30 and 40 by providing a midpoint earth, so there is no need to provide a configuration for removing noise between the antennas 30 and 40, making it possible to save space. Therefore, according to the vehicle antenna device 100 of the embodiment, when a broadcast wave antenna and a device that handles signals in a higher frequency band than the broadcast wave are placed close to each other, mutual interference can be reduced, making it possible to save space. In other words, according to the vehicle antenna device 100 of the embodiment, interference between the antennas can be reduced and space can be saved.

(Modification)
In the above-described embodiment, the glass plate 20 has been used as an example of a dielectric constituting a part of the vehicle on which the vehicle antenna device 100 is disposed. However, as described above, the dielectric may be configured to include a resin. The resin may include, for example, an aerodynamic part such as a spoiler of the vehicle on which the vehicle antenna device 100 is disposed. When the dielectric is a resin, at least one of the antennas 30 and 40 may be directly fixed to the resin. In other words, at least one of the antennas 30 and 40 may be physically fixed to the resin. Alternatively, when the dielectric is a resin, at least one of the antennas 30 and 40 may be indirectly fixed to the resin, for example, via a housing. In other words, at least one of the antennas 30 and 40 may not be physically connected to the resin, but may be indirectly fixed, for example, via a housing or the like. In the above-described embodiment, even if the dielectric is configured to include a resin, the same effect as the above-described embodiment can be obtained. That is, even if the glass plate 20, which is a dielectric, is replaced with a resin in the vehicle antenna device 100 according to the embodiment, interference between the antennas can be reduced and space can be saved.

The present invention has been described above in accordance with the above embodiment, but the present invention is not limited to the configuration of the above embodiment, and of course includes various modifications, alterations, and combinations that a person skilled in the art could make within the scope of the invention of the claims of this patent application.

REFERENCE SIGNS LIST 100 Vehicle antenna device 10 Metal body 10a End 20 Glass plate 30, 40 Antenna 31, 60 Power supply section 32 Earth section 33, 34 Line element 41 Ground conductor 41L, 41La, 41Lb Line ground conductor 41Lc Line corner conductor 42 Power supply conductor 43 Metal film 50 Cutout section 51 First slot 51a One end of first slot 51b Other end of first slot 52 Second slot 53 First connection slot 53c Width change section 54 First wide slot 54d Opening of first wide slot 55 Second wide slot 55f Opening of second wide slot 70 Transmission line 71 Signal line 71a Connection point 72 Ground wire 72a, 72b Ground point

Claims (18)

A dielectric body that constitutes a part of the vehicle;
a first antenna attached to the dielectric;
a second antenna attached near the first antenna and configured to transmit and receive radio waves in a frequency band higher than the frequency band of radio waves transmitted and received by the first antenna;
a transmission line connected to the second antenna,
the second antenna has a feed conductor connected to a signal line of the transmission line and a ground conductor connected to a ground line of the transmission line;
the ground wire has a first ground point connected to the ground conductor and a second ground point connected to an earth potential portion of the vehicle;
the dielectric includes a glass plate;
The second antenna is directly or indirectly fixed to the glass plate,
The second antenna is a planar antenna disposed on a surface of the glass plate.
An antenna device for a vehicle. A dielectric body that constitutes a part of the vehicle;
a first antenna attached to the dielectric;
a second antenna attached near the first antenna and configured to transmit and receive radio waves in a frequency band higher than the frequency band of radio waves transmitted and received by the first antenna;
a transmission line connected to the second antenna,
the second antenna has a feed conductor connected to a signal line of the transmission line and a ground conductor connected to a ground line of the transmission line;
the ground wire has a first ground point connected to the ground conductor and a second ground point connected to an earth potential portion of the vehicle;
The length of the ground line from the first ground point to the second ground point is D _G Let L be the distance from the ground point of the feeder of the second antenna to the farthest point of the ground conductor, λ be the wavelength in air in the frequency band received by the first antenna, k be the wavelength shortening rate of the dielectric, and M be a positive integer.
(λ/4-λ/16)×(2M-1)≦D _G +L/k≦(λ/4+λ/16)×(2M-1)
The following relation is satisfied:
An antenna device for a vehicle. The vehicle antenna device according to claim 1 , wherein the first antenna is disposed on a surface of the glass plate. The dielectric material includes a resin.
The vehicle antenna device according to claim 2 , wherein the second antenna is fixed directly or indirectly to the resin. The vehicle antenna device according to claim 4 , wherein the first antenna is fixed directly or indirectly to the resin. the dielectric includes a glass plate;
The vehicle antenna device according to claim 4 , wherein the first antenna is disposed on a surface of the glass plate. The vehicle antenna device according to any one of claims 4 to 6 , wherein the resin is an aerodynamic part of the vehicle. The vehicle antenna device according to claim 2 , wherein the wavelength λ is a central wavelength λ ₀ in air in a frequency band received by the first antenna. 9. The vehicle antenna device according to claim 2 , wherein the length _DG is 400 mm or less. The vehicle antenna device according to any one of claims 1 to 9 , wherein the first antenna and the second antenna are disposed at a distance of 30 mm or more. The vehicle antenna device according to claim 1 , wherein the transmission line includes a portion that starts at a connection portion of the second antenna and extends away from the first antenna. The vehicle antenna device according to any one of claims 1 to 11 , wherein the first antenna receives radio waves in a frequency band of 800 MHz or less. 13. The vehicle antenna device according to claim 12 , wherein the first antenna is configured to be capable of receiving at least one of radio waves in a frequency band of DAB (Digital Audio Broadcast) Band III and radio waves in a frequency band of terrestrial digital television broadcast waves. The vehicle antenna device according to any one of claims 1 to 13 , wherein the second antenna is configured to be capable of transmitting and receiving radio waves in a frequency band of 600 MHz or higher. The vehicle antenna device according to claim 14 , wherein the second antenna is configured to be capable of transmitting and receiving radio waves in a frequency band of 800 MHz or higher. The vehicle antenna device according to any one of claims 1 to 15 , wherein the dielectric material includes a windshield. The vehicle antenna device according to any one of claims 1 to 15 , wherein the dielectric material includes a rear window. The vehicle antenna device according to any one of claims 1 to 17, wherein a distance between the first antenna and the second antenna is 200 mm or less.

Images