WO2020138181A1 - Composite antenna device for vehicle - Google Patents

Abstract

Provided is a composite antenna device for a vehicle, by which common mode noise can be reduced and a deterioration in reception performance can be avoided. The composite antenna device for a vehicle comprises: an antenna base 10; a roof conductor 20; a circuit board 30; an antenna element 40; a coaxial cable 50; an intermediate grounding section 60; and a circuit board grounding section 70. The roof conductor 20 is electrically connected to the antenna base 10 and to a vehicle roof R. The intermediate grounding section 60 electrically connects a grounding wire 52 to the antenna base 10 at a position close to the loop conductor 20 such that the antenna base is at the same potential as the roof conductor 20. The circuit board grounding section 70 electrically connects a ground pattern 31 to the antenna base 10 and is disposed such that the distance from the roof conductor 20 to the circuit board grounding section 70 is the same as or greater than the distance from the roof conductor 20 to the intermediate grounding section 60.

Description

Composite antenna device for vehicle

The present invention relates to a vehicular composite antenna device, and more particularly to a vehicular composite antenna device capable of reducing common mode noise in a composite antenna compatible with a plurality of frequency bands.

As a vehicle composite antenna device, one that can receive AM broadcasts and FM broadcasts is generally used. Recently, there is a small and low-profile antenna device such as a so-called shark fin antenna (for example, Patent Document 1). In the case of the composite antenna device for a vehicle, there are various restrictions such as a height restriction and a small space inside the case. In recent years, various information devices have been installed in vehicles for safety and comfort. Accordingly, it is necessary to support a plurality of frequency bands, and it is necessary to fit an antenna element suitable for each frequency band in a small space.

In the low-profile antenna device as described above, the ground washer breaks the paint film on the vehicle roof by fastening the nut to the boss provided on the antenna base for fixing the antenna base to the vehicle roof, and the antenna base causes the vehicle to break. Electrically connects to the roof. As a result, the metal vehicle body is configured as a so-called body ground. The signal output of the antenna device is input to the receiver inside the vehicle using the coaxial cable.

JP 2012-204996A

In the conventional vehicle composite antenna device as described above, the ground wire of the coaxial cable is connected to the ground pattern of the circuit board. The ground pattern of the circuit board is electrically connected to the antenna base with a screw or the like for fixing the circuit board to the antenna base. That is, the ground wire of the coaxial cable is connected to the antenna base via the ground pattern of the circuit board, and the antenna base is body-grounded to the vehicle body via the ground washer. Therefore, there is a potential stray capacitance between the ground line of the coaxial cable and the antenna base. This stray capacitance causes the common mode noise riding on the ground line of the coaxial cable from the receiver side in the vehicle to propagate to the circuit board. The common mode noise propagated to the circuit board causes fluctuations in the potential of the ground pattern on the circuit board. That is, the common mode noise causes the ground level of the circuit board to be unstable. Further, a part of the common mode noise is converted into normal mode noise and becomes noise for the antenna element.

Specifically, in the case of a vehicle composite antenna device, a receiver for a frequency band other than the AM/FM wave band, for example, a receiver for GNSS, DAB, V2X, TEL, etc. There was a case where the band noise was generated. The noise in the AM/FM wave band is the common mode noise propagating from the ground line of the coaxial cable. In particular, in the case of a composite antenna device for a vehicle, a plurality of coaxial cables for handling signals in a plurality of frequency bands are drawn into the antenna device in a state where they are in close proximity and run side by side. Common mode noise propagating through the ground line of the above was also superimposed on the ground line of the coaxial cable for the AM/FM wave band. Therefore, the common mode noise makes the ground level of the circuit board unstable, and the partially converted normal mode noise becomes noise of the AM/FM antenna element, which deteriorates the antenna performance. Therefore, it has been desired to develop a vehicle composite antenna device capable of reducing common mode noise particularly in the AM/FM wave band.

In view of such circumstances, the present invention aims to provide a vehicle composite antenna device capable of reducing common mode noise and avoiding deterioration of reception performance.

In order to achieve the above-mentioned object of the present invention, a vehicle composite antenna device according to the present invention is electrically connected to an antenna base installed on a vehicle roof and the antenna base, and also electrically connected to the vehicle roof. A roof conducting portion that conducts, a circuit board that is mounted on the antenna base and has a ground pattern, and that is provided on or connected to the circuit board, and is configured to be compatible with a plurality of frequency bands. A plurality of antenna elements, a plurality of coaxial cables each including a signal core wire and a ground ground wire, which are connected to signal outputs from the plurality of antenna elements, and the roof to the same potential as the roof conducting portion. An intermediate ground part that electrically connects the ground line of the coaxial cable to the antenna base at a position close to the conducting part, and a circuit board ground part that electrically connects the ground pattern of the circuit board to the antenna base. And a circuit board ground section, which is arranged such that the distance from the section to the circuit board ground section is the same as or farther than the distance from the roof conducting section to the intermediate ground section.

-Here, the ground line of the coaxial cable may be connected to the ground pattern of the circuit board.

Also, the roof conduction part is provided on the ground washer for fixing the antenna base to the vehicle roof, and the intermediate ground part may be arranged near the boss where the ground washer is arranged.

Also, the intermediate ground portion may be provided in the antenna base and arranged in the insertion hole for inserting the coaxial cable.

Also, the intermediate ground section may be any terminal that can hold the ground wire of the coaxial cable.

Also, the intermediate ground portion may be a relay connector configured to electrically connect the ground line of the coaxial cable to the antenna base.

Also, the coaxial cable may be placed on the antenna base away from the antenna element to the extent that it does not affect the reception performance of the antenna element.

Also, the plurality of antenna elements may include at least a composite antenna element for AM/FM.

Also, the circuit board may be one that is erected on the antenna base or placed in parallel.

Also, the antenna base may be composed of an insulating base made of resin and a conductive base fixed to the insulating base and smaller than the insulating base.

The vehicle composite antenna device of the present invention has an advantage that common mode noise can be reduced and reception performance deterioration can be avoided.

FIG. 1 is a schematic diagram for explaining the configuration of a vehicle composite antenna device of the present invention. FIG. 2 is a schematic diagram for explaining another configuration of the vehicle composite antenna device of the present invention. FIG. 3 is a schematic perspective view for explaining a specific example of the intermediate ground portion of the vehicle composite antenna device of the present invention. FIG. 4 is a schematic perspective view for explaining another specific example of the intermediate ground portion of the vehicle composite antenna device of the present invention. FIG. 5 is a schematic perspective view for explaining still another specific example of the intermediate ground portion of the vehicle composite antenna device of the present invention. FIG. 6 is a schematic enlarged side view for explaining still another specific example of the intermediate ground portion of the vehicle composite antenna device of the present invention. FIG. 7 is a schematic enlarged side view for explaining still another specific example of the intermediate ground portion of the vehicle composite antenna device of the present invention. FIG. 8 is a schematic plan view for explaining yet another specific example of the intermediate ground portion of the vehicle composite antenna device of the present invention. FIG. 9 is a diagram for explaining the position of the intermediate ground portion on which the evaluation experiment of the common mode noise reduction effect of the vehicle composite antenna device of the present invention was performed.

Hereinafter, modes for carrying out the present invention will be described together with illustrated examples. The vehicular composite antenna device of the present invention is a vehicular composite antenna device capable of supporting a plurality of frequency bands. FIG. 1 is a schematic diagram for explaining the configuration of a vehicle composite antenna device of the present invention, FIG. 1(a) is a side view, and FIG. 1(b) is a plan view. As shown in the drawings, the vehicle composite antenna device of the present invention includes an antenna base 10, a roof conducting portion 20, a circuit board 30, an antenna element 40, a coaxial cable 50, an intermediate ground portion 60, and a circuit board ground. It is mainly composed of a section 70. Further, when it is installed in a vehicle, it is covered with an antenna cover 1 having an internal space for housing an antenna element, a circuit board, and the like. In the following description, it is assumed that the vehicle composite antenna device is a low-profile antenna device, but the present invention is not limited to this.

The antenna base 10 is installed on the vehicle roof R. The antenna base 10 is arranged outside the vehicle compartment and has the circuit board 30 and the like mounted thereon. The antenna base 10 may be anything that functions as a ground for the circuit board 30 and the antenna element 40 to be attached, and may be made of a conductor. It may also be a so-called resin base. That is, the antenna base 10 may be composed of an insulating base made of resin and a conductive base fixed to the insulating base and smaller than the insulating base.

The roof conducting portion 20 electrically conducts to the antenna base 10 and also to the vehicle roof R. Specifically, the roof conducting portion 20 may be a ground washer. The ground washer includes, for example, a toothed washer and a legged washer. In the illustrated example, a washer with a leg is used as the roof conducting portion 20. The roof conducting portion 20 which is a washer with legs is coaxially sandwiched when the boss 11 provided on the antenna base 10 is fastened with the bolt 12. Then, when the bolt 12 is fastened to the boss 11 in order to fix the antenna base 10 to the vehicle roof R, the claw portion at the tip of the ground washer breaks the coating film of the vehicle roof R. As a result, the antenna base 10 is electrically connected to the vehicle roof R, which is a metal plate, via the ground washer. Therefore, the metallic vehicle roof R becomes a so-called body ground.

The circuit board 30 is mounted on the antenna base 10 and has a ground pattern 31. The ground pattern 31 serves as a ground for the amplifier circuit and the like mounted on the circuit board 30. The ground pattern 31 may be provided, for example, by solid earth around the screw hole for fixing the circuit board 30 to the antenna base 10. The circuit board 30 in the illustrated example is an example in which it is erected on the antenna base 10. However, the present invention is not limited to this, and the circuit board 30 may be placed in parallel with the antenna base 10. An amplifier circuit 32 and the like are mounted on the circuit board 30. The amplifier circuit 32 is used to amplify the received signal. For example, when the vehicle composite antenna device of the present invention is configured as a composite antenna capable of receiving signals in both the FM frequency band and the AM frequency band, the amplifier circuit 32 also includes a plurality of frequency bands, that is, the FM frequency band. And a plurality of frequency band-specific amplifier circuits provided according to the AM frequency band. A power supply circuit and the like may be mounted on the circuit board 30.

The vehicle composite antenna device of the present invention is provided with a plurality of antenna elements 40. In the illustrated example, the plurality of antenna elements 40 are provided on the circuit board 30. That is, the antenna element 40 is provided on the circuit board 30 by patterning formation. The antenna element 40 in the illustrated example is merely a schematic one, and the present invention is not limited to these shapes and arrangements. Further, a patch antenna or the like may be provided on the antenna base 10. Specific examples of the plurality of antenna elements 40 include antenna elements for FM, AM, DAB, V2X, TEL, and GNSS. However, the present invention is not limited to this, and may be any element as long as it is an antenna element used for a vehicle. Further, it may include an AM/FM composite antenna element in which a capacitive antenna and a resonant antenna are combined. That is, a conductive member having a predetermined antenna capacity is configured to function as a capacitive antenna and used as an AM antenna element, and a conductive antenna and a coil are combined to function as a resonance antenna. It may be used as.

The coaxial cable 50 includes a signal core wire 51 and a ground wire 52. The core wire 51 of the coaxial cable 50 is connected to the signal output from the antenna element 40. Specifically, the core wire 51 may be connected to the power feeding portion of the antenna element 40 or the output of the amplifier circuit 32 on the circuit board 30. A plurality of such coaxial cables 50 are provided for the plurality of antenna elements 40, respectively. The coaxial cable 50 is pulled out of the vehicle composite antenna device through the insertion hole 13 provided in the antenna base 10. The insertion hole 13 serves as a cable inlet. Then, the coaxial cable 50 is drawn into the vehicle through the cable drawing port provided in the vehicle roof R as well. The connector 53 is connected to the inside of the coaxial cable 50. Then, it may be connected to a receiver inside the vehicle through the connector 53.

The intermediate ground portion 60 electrically connects the ground wire 52 of the coaxial cable 50 to the antenna base 10 at a position close to the roof conducting portion 20 to the same potential as the roof conducting portion 20. That is, the intermediate ground portion 60 is provided near the roof conducting portion 20. In the illustrated example, the claw portion at the tip of the ground washer that is the roof conducting portion 20 is a portion having the same electric potential as the vehicle roof R. The potential is almost the same as that of the antenna base 10 via the boss 11 and the bolt 12. Therefore, the intermediate ground portion 60 may be arranged near the boss 11, for example. By providing the intermediate ground portion 60, the ground wire 52 of the coaxial cable 50 has substantially the same potential as the vehicle roof R, which is so-called body ground, before the ground pattern 31 of the circuit board 30 when viewed from the roof conducting portion 20. Become. Therefore, the common mode noise propagating through the ground wire 52 of the coaxial cable 50 propagates directly to the vehicle roof R without passing through the circuit board 30.

The intermediate ground portion 60 may electrically connect the ground wires 52 of some of the coaxial cables 50 to the antenna base 10, but the ground wires 52 of all the coaxial cables 50 are electrically connected to the antenna base 10. It is preferable to conduct to. This is because the common mode noise can propagate not only to the coaxial cable for the AM/FM wave band but also to the coaxial cable for other frequency bands. Therefore, even if it is intended to reduce the common mode noise in the AM/FM wave band, the ground lines 52 of all the coaxial cables 50 are electrically connected to the antenna base 10 by the intermediate ground section 60, so that it is most effective. A high noise reduction effect can be obtained.

In the illustrated example, the intermediate ground portion 60 has a concave shape integrally formed with the antenna base 10. At the position where the intermediate ground portion 60 is arranged, the outer protective coating of the coaxial cable 50 is peeled off to expose the ground wire 52, and the ground wire 52 is sandwiched between the concave intermediate ground portions 60 and electrically conducted by, for example, soldering. good. As a result, the ground wire 52 of the coaxial cable 50 drawn into the vehicle composite antenna device has substantially the same potential as the vehicle roof R.

The circuit board ground portion 70 electrically connects the ground pattern 31 of the circuit board 30 to the antenna base 10. The composite antenna device for a vehicle of the present invention is configured such that the intermediate ground portion 60 has substantially the same potential as the vehicle roof R before the ground pattern 31 of the circuit board 30 when viewed from the roof conducting portion 20. Therefore, in order to electrically connect the ground pattern 31 of the circuit board 30 to the antenna base 10 farther than the intermediate ground portion 60, the circuit board ground portion 70 has a distance from the roof conducting portion 20 to the circuit board ground portion 70. It may be arranged at a position farther than the distance from the roof conducting portion 20 to the intermediate ground portion 60. That is, the circuit board ground portion 70 including a screw boss for fixing the circuit board 30 to the antenna base 10 may be provided at a position farther from the intermediate ground portion 60 when viewed from the roof conducting portion 20. The circuit board ground portion 70, which is a screw boss, may be integrally molded with the antenna base 10. In the illustrated example, the circuit board ground portions 70 respectively provided at two corners of the circuit board 30 are arranged farther from the intermediate ground portion 60 when viewed from the roof conducting portion 20. When the circuit board 30 is fixed to the circuit board ground portion 70 provided on the antenna base 10 with a screw, the ground pattern 31 on the circuit board 30 is electrically connected to the antenna base 10 via the screw. The electrically conducting position may be located farther from the roof conducting part 20 than the intermediate ground part 60. The distance from the roof conducting portion 20 may be an electrical distance rather than a physical distance.

In the above-described illustrated example, an example in which the distance from the roof conducting portion 20 to the circuit board ground portion 70 is longer than the distance from the roof conducting portion 20 to the intermediate ground portion 60 is shown. However, the present invention is not limited to this. For example, the circuit board ground portion 70 may be arranged such that the distance from the roof conducting portion 20 to the circuit board ground portion 70 is the same as the distance from the roof conducting portion 20 to the intermediate ground portion 60. That is, the distance from the circuit board ground portion 70 to the intermediate ground portion 60 may be the same or longer as viewed from the roof conducting portion 20. As a result, the intermediate ground portion 60 and the circuit board ground portion 70 have substantially the same potential when viewed from the roof conducting portion 20.

With the vehicle composite antenna device of the present invention configured in this way, the stray capacitance between the ground line 52 of the coaxial cable 50 and the antenna base 10 is reduced. Then, the common mode noise propagates to the vehicle roof R from the roof conducting portion 20 which is so-called body ground. As a result, the common-mode noise riding on the ground line of the coaxial cable from the receiver side in the vehicle hardly propagates to the circuit board. Therefore, even in a vehicle composite antenna device capable of supporting a plurality of frequency bands, it is possible to reduce common mode noise in the AM/FM wave band and avoid deterioration of reception performance.

Further, as shown in FIG. 1B, the coaxial cable 50 may be arranged on the antenna base 10 apart from the antenna element 40 to the extent that the reception performance of the antenna element 40 is not affected. Specifically, in the drawing of FIG. 1B, the upper coaxial cable 50 is arranged on the antenna base 10 at a distance from the antenna element 40 to the extent that the reception performance of the antenna element 40 is not affected. In the vehicle composite antenna device of the present invention, the plurality of antenna elements 40 are arranged in a small space within the antenna cover 1, so that the coaxial cable 50 arranged in the vehicle composite antenna device affects the antenna element 40. obtain. Therefore, for example, with respect to the antenna element 40 arranged so as to pass near the center of the antenna base 10 in the short side direction, the antenna element 40 is coaxial so as to pass through the peripheral portion of the antenna base 10 to the extent that reception performance is not affected as much as possible. The cable 50 may be arranged.

Next, another example of the vehicle composite antenna device of the present invention will be described with reference to FIG. 2A and 2B are schematic diagrams for explaining another configuration of the composite antenna device for a vehicle of the present invention. FIG. 2A is a side view and FIG. 2B is a plan view. In the figure, the parts denoted by the same reference numerals as in FIG. 1 represent the same things. In the example shown in FIG. 1, the circuit board 30 is erected on the antenna base 10, but in the example shown in FIG. 2, the circuit board 30 is placed parallel to the antenna base 10. Further, among the antenna elements 40, the AM/FM composite antenna element is shown as a so-called umbrella type element. The umbrella-shaped element includes a top portion and a roof-shaped inclined portion that is inclined from the top portion to both sides. The umbrella-shaped element may be formed by bending one conductive plate into an umbrella shape or may be formed by combining two conductive plates. The shape of the umbrella-shaped element is not limited to the illustrated example. Moreover, the example in which the intermediate ground portion 60 is arranged in the insertion hole 13 is shown. Also in this example, at the position where the intermediate ground portion 60 is arranged, the outer protective coating of the coaxial cable 50 may be peeled off to expose the ground wire 52, so that the intermediate ground portion 60 is electrically connected.

As illustrated, in this example, the intermediate ground portion 60 is arranged in the insertion hole 13. By arranging the intermediate ground portion 60 in the insertion hole 13, for example, the degree of freedom in arranging other components on the antenna base 10 and wiring layout of the coaxial cable 50 is increased. Also in this example, the intermediate ground portion 60 may be integrally molded with the antenna base 10. Further, a separate intermediate ground portion 60 capable of sandwiching the ground wire 52 of the coaxial cable 50 may be fixed to the antenna base 10 with a screw or the like.

In the illustrated example, a toothed washer is used as the roof conducting portion 20. The intermediate ground portion 60 is provided in the vicinity of the roof conducting portion 20, similarly to the example shown in FIG. The intermediate ground portion 60 electrically connects the ground wire 52 of the coaxial cable 50 to the antenna base 10 at a position close to the roof conductive portion 20 to the same level as the roof conductive portion 20. With such a configuration, the common mode noise propagating through the ground wire 52 of the coaxial cable 50 is directly propagated to the vehicle roof R without passing through the circuit board 30, so that the common mode noise can be reduced. Become.

Also in the illustrated example, in order to conduct the ground pattern 31 of the circuit board 30 to the antenna base 10 at a position that is the same as or more distant from the roof conductive portion 20 to the intermediate ground portion 60, the circuit board ground portion 70 includes: The distance from the roof conducting portion 20 to the circuit board ground portion 70 is the same as or longer than the distance from the roof conducting portion 20 to the intermediate ground portion 60. Specifically, in the drawing of FIG. 2B, the circuit board ground portion 70 may be arranged at two corners on the left side of the circuit board 30. Then, for example, the two corners on the right side of the circuit board 30, which are close to the roof conducting portion 20, may simply be the fixing bosses 71 of the circuit board 30. The fixing boss 71 is used to screw the circuit board 30 at a position where the ground pattern 31 does not exist. As a result, the circuit board 30 is stably placed on the antenna base 10, and the circuit board ground portion 70 is provided at a position that is the same as or farther from the intermediate ground portion 60 when viewed from the roof conducting portion 20. The ground pattern 31 can be electrically connected to the antenna base 10.

Further, in the vehicle composite antenna device of the present invention, the ground wire 52 of the coaxial cable 50 may be connected to the ground pattern 31 of the circuit board 30 as shown in FIG. 2, for example. In the composite antenna device for a vehicle of the present invention, since the ground line 52 of the coaxial cable 50 has substantially the same potential as the vehicle roof R due to the intermediate ground part 60, the ground line 52 of the coaxial cable 50 ahead of the intermediate ground part 60. Common-mode noise does not propagate through. Then, with respect to the signal propagating through the core wire 51, signal leakage to the outside and intrusion of radio waves from the outside are blocked by the shield effect of the ground wire 52. Further, since the ground line 52 is also connected to the ground pattern 31 of the circuit board 30, the ground pattern 31 of the circuit board 30 and the ground line 52 have the same potential, so that the ground of the circuit board 30 is further stabilized.

A specific example of the intermediate ground portion of the vehicle composite antenna device of the present invention will be described below. However, the present invention is not limited to these specific examples, and the intermediate ground portion electrically connects the ground line of the coaxial cable to the antenna base at a position close to the roof conducting portion to the same potential as the roof conducting portion. Anything is possible.

FIG. 3 is a schematic perspective view for explaining a specific example of the intermediate ground portion of the vehicle composite antenna device of the present invention. In the figure, the parts denoted by the same reference numerals as in FIG. 1 represent the same things. As shown in the figure, the intermediate ground portion 60 may be formed of a sandwiching terminal capable of sandwiching the ground wire 52 of the coaxial cable 50. The sandwiching terminal in the illustrated example is a so-called crimp terminal. The intermediate ground portion 60, which is a crimp terminal, has a holding portion 61 for holding the ground wire 52 of the coaxial cable 50, and a screw hole 62 for electrically connecting and fixing the antenna base 10. The sandwiching portion 61 peels off the outer protective coating of the coaxial cable 50 and caulks the portion where the ground wire 52 is exposed to electrically connect the portions.

FIG. 4 is a schematic perspective view for explaining another specific example of the intermediate ground portion of the vehicle composite antenna device of the present invention. In the figure, the parts denoted by the same reference numerals as those in FIG. 3 represent the same things. In the example of FIG. 3, a crimp terminal is shown as a sandwiching terminal of the intermediate ground portion 60, but in this example, the sandwiching terminal of the intermediate ground portion 60 is a so-called screw stop terminal. The intermediate ground portion 60, which is a screw terminal, has a holding portion 61 for holding the ground wire 52 of the coaxial cable 50, and a screw hole 62 for electrically connecting and fixing the antenna base 10. The outer sheath protective coating of the coaxial cable 50 is peeled off from the holding portion 61, and the screw hole 62 is fixed to the antenna base 10 with a screw while sandwiching the exposed portion of the ground wire 52, so that electrical conduction is achieved.

FIG. 5 is a schematic perspective view for explaining still another specific example of the intermediate ground portion of the vehicle composite antenna device of the present invention. In the figure, the parts denoted by the same reference numerals as those in FIG. 4 represent the same things. The intermediate ground portion 60, which is a screw terminal in the illustrated example, has a soldering opening 65 in a sandwiching portion 61 that sandwiches the ground wire 52 of the coaxial cable 50. In a state in which the outer protective coating of the coaxial cable 50 is peeled off from the sandwiching portion 61 and the portion where the ground wire 52 is exposed is sandwiched, solder is poured from the solder opening 65 to be electrically conducted. That is, it may be conducted by crimping or may be conducted by solder.

The intermediate ground portion 60 configured in this way may be screwed into a screw hole provided in the antenna base 10 to be fixed, but a bolt 12 is used for the boss 11 provided in the antenna base 10. The intermediate ground portion 60 may be coaxially fastened together with the ground washer. That is, the bolt 12 may be passed through the screw hole 62 of the intermediate ground portion 60 and fastened together with the ground washer. As a result, it becomes possible to electrically connect the vehicle roof R at a position closest to the ground washer, which is a roof conducting portion having the same electric potential. Further, the ground washer itself may be configured to function as an intermediate ground portion. That is, the ground washer may be provided with the sandwiching portion 61, and the ground wire 52 may be swaged so as to be electrically connected directly.

FIG. 6 is a schematic enlarged side view for explaining still another specific example of the intermediate ground portion of the vehicle composite antenna device of the present invention. In the figure, the parts denoted by the same reference numerals as in FIG. 1 represent the same things. Further, only the periphery of the intermediate ground portion 60 is shown in an enlarged manner, and other portions are omitted. As illustrated, the intermediate ground portion 60 may be composed of a relay connector. The intermediate ground portion 60, which is a relay connector, is configured to electrically connect the ground wire 52 of the coaxial cable 50 to the antenna base 10. For example, as shown in the drawing, by fixing the ground terminal 63 of the relay connector to the antenna base 10 directly with a screw or the like, the ground wire 52 of the coaxial cable 50 is electrically connected to the antenna base 10. As a result, the ground line 52 has substantially the same potential as the roof conducting portion 20. The relay connector may be configured such that the signal core wire 51 of the coaxial cable 50 and the signal wire 64 are wired inside the vehicle composite antenna device as in the illustrated example. The relay connector may be, for example, a so-called multipolar coaxial connector so as to correspond to a plurality of coaxial cables for signals in a plurality of frequency bands. In the illustrated example, the coaxial cables from the receiver inside the vehicle are individually connected to the relay connector, but the present invention is not limited to this, and a plurality of cables are connected at once using a wire harness. It may be configured to be capable.

The intermediate ground portion of the vehicle composite antenna device of the present invention may be provided on a boss for fixing the antenna base 10 to the roof. FIG. 7 is a schematic enlarged side view for explaining still another specific example of the intermediate ground portion of the vehicle composite antenna device of the present invention. In the figure, the parts denoted by the same reference numerals as in FIG. 1 represent the same things. Further, only the periphery of the intermediate ground portion 60 is shown in an enlarged manner, and other portions are omitted. As illustrated, in this example, the intermediate ground portion 60 is provided on the boss 11 provided on the antenna base 10. That is, the intermediate ground portion 60 is integrally molded with the boss 11. With this structure, the conductive portion of the antenna base 10 can be downsized. Therefore, for example, when the present invention is applied to a so-called composite base including an insulating base made of resin and a conductive base fixed to the insulating base and smaller than the insulating base, the conductive base can be downsized, which is convenient.

FIG. 8 is a schematic plan view for explaining still another specific example of the intermediate ground portion of the vehicle composite antenna device of the present invention. In the figure, the parts denoted by the same reference numerals as in FIG. 1 represent the same things. Further, only the antenna base 10 and the intermediate ground portion 60 are shown, and the other portions are not shown. As shown, in this example, the antenna base 10 is shown to be a composite base. The antenna base 10 which is a composite base is a combination of an insulating base 15 and a conductive base 16. The conductive base 16 is smaller than the insulating base 15 and is fixed to the insulating base 15. The insulating base 15 is made of a hard member to form the bottom of the antenna device and to fix the antenna cover. Even with such a composite base, it is possible to use the intermediate ground portion 60 similar to the above-described illustrated example. In the illustrated example, the example using the intermediate ground conductive plate 66 is shown. The conductive base 16 is generally made of a material to which solder is hard to attach. Therefore, the intermediate ground conductive plate 66 is used so that the soldering can be easily performed. The intermediate ground conductive plate 66 may be made of a material such as a copper plate on which solder can be easily placed. The sizes and shapes of the conductive base 16 and the conductive plate 66 for the intermediate ground are not limited to those in the illustrated example, and can be variously changed according to the arrangement of each component of the vehicle composite antenna device. In this example, the intermediate ground portion 60 may be integrally provided with the intermediate ground conductive plate 66. The intermediate ground conductive plate 66 may be fixed to the conductive base 16 with screws or the like so as to be electrically conductive.

Next, the effect of reducing the common mode noise of the vehicle composite antenna device of the present invention will be described using experimental data. FIG. 9 is a diagram for explaining the position of the intermediate ground portion on which the evaluation experiment of the common mode noise reduction effect of the vehicle composite antenna device of the present invention was performed. In the figure, the parts denoted by the same reference numerals as in FIG. 1 represent the same things. In the above-described illustrated example, when the distance from the roof conducting portion 20 to the circuit board ground portion 70 is set to be longer than the distance from the roof conducting portion 20 to the intermediate ground portion 60, common mode noise is generated. It was explained that there is a reduction effect. It was also explained that the distance from the roof conducting portion 20 to the circuit board ground portion 70 may be the same as the distance from the roof conducting portion 20 to the intermediate ground portion 60, but this is also evaluated. The results of the experiment are shown and described. That is, in the evaluation experiment, the common mode noise reduction effect was measured when the distance from the roof conducting portion 20 to the intermediate ground portion 60 was changed with respect to the distance from the roof conducting portion 20 to the circuit board ground portion 70. .. In the figure, the inner circle of the double circle is the position of the roof conducting portion 20, and the outer circle is the distance to the circuit board ground portion 70. As illustrated, specifically, the intermediate ground portion has the same distance (60a) as the roof conducting portion 20, the same distance as the circuit board ground portion 70 (60b), and the distance (more than the circuit board ground portion 70). The effect of reducing common mode noise when arranged at the position of 60c) was measured. It should be noted that the illustrated example is merely a schematic diagram described for easy understanding, and the actual distance is not limited to this example.

More specifically, the vehicle composite antenna device used in the evaluation experiment is a composite antenna device having an FM antenna element, a GNSS antenna element, and a TEL antenna element. Then, the difference in FM output and the difference in GNSS output when the pseudo noise signal was superimposed on the signal generator to the coaxial cable 50 connected to the TEL antenna element were measured. In the measurement, the TEL coaxial cable, the FM coaxial cable, and the GNSS coaxial cable were each provided with and without the intermediate ground portion. Further, when the intermediate ground portion was provided, the distance from the roof conductive portion to the intermediate ground portion was changed with respect to the distance from the roof conductive portion to the circuit board ground portion. The results are shown in the table below.

As shown in Table 1, when the intermediate ground portion is provided and the position thereof is arranged at the same distance (60a) as the roof conducting portion 20 or the same distance (60b) as the circuit board ground portion 70, the FM output is obtained. It can be seen that both the GNSS output and the GNSS output have lower values than the case where the intermediate ground portion is not provided. That is, it can be seen that the pseudo-random signal (common mode noise) propagating to the ground line of the TEL coaxial cable propagates to the vehicle roof, not to the circuit board due to the intermediate ground portion. Therefore, it can be seen that the effect of reducing the common mode noise is high when the “distance to the circuit board ground portion 70 ”≧“the distance to the intermediate ground portion 60 ”with respect to the roof conduction 20. It should be noted that even if the intermediate ground portion is provided, the effect of reducing the common mode noise is low when the intermediate ground portion is arranged at a position farther (60c) than the circuit board ground portion 70.

It should be noted that the vehicle composite antenna device of the present invention is not limited to the above-described illustrated examples, and it is needless to say that various modifications can be made without departing from the gist of the present invention.

1 Antenna Cover 10 Antenna Base 11 Boss 12 Bolt 13 Insertion Hole 15 Insulating Base 16 Conductive Base 20 Roof Conducting Part 30 Circuit Board 31 Ground Pattern 32 Amplifier Circuit 40 Antenna Element 50 Coaxial Cable 51 Core Wire 52 Ground Wire 53 Connector 60 Middle Ground Part 61 Clamping Part 62 Screw Hole 63 Ground Terminal 64 Signal Line 65 Solder Opening 66 Intermediate Ground Conductive Plate 70 Circuit Board Ground Part 71 Fixing Boss R Vehicle Roof

Claims (10)

A composite antenna device for a vehicle capable of supporting a plurality of frequency bands, the composite antenna device for a vehicle comprising:
An antenna base installed on the vehicle roof,
A roof conducting portion that electrically conducts to the antenna base and also electrically conducts to the vehicle roof,
A circuit board mounted on the antenna base and having a ground pattern,
A plurality of antenna elements provided on the circuit board or connected to the circuit board and configured to be compatible with a plurality of frequency bands,
A plurality of coaxial cables consisting of a core wire for signal and a ground wire for ground, which are respectively connected to signal outputs from the plurality of antenna elements,
An intermediate ground portion that electrically connects the ground wire of the coaxial cable to the antenna base at a position close to the roof conductive portion to the same potential as the roof conductive portion,
A circuit board ground part for electrically connecting the ground pattern of the circuit board to the antenna base, wherein the distance from the roof conductive part to the circuit board ground part is the same as the distance from the roof conductive part to the intermediate ground part. Or, the circuit board ground portion, which is arranged at a farther position,
A composite antenna device for a vehicle, comprising: The composite antenna device for a vehicle according to claim 1, wherein the ground wire of the coaxial cable is also connected to a ground pattern of a circuit board. The vehicle composite antenna device according to claim 1 or 2, wherein the roof conducting portion is provided in a ground washer for fixing the antenna base to the vehicle roof, and the intermediate ground portion is provided with a ground washer. A composite antenna device for a vehicle, which is arranged near a boss. The composite antenna device for a vehicle according to claim 1 or 2, wherein the intermediate ground portion is provided in an insertion hole provided in the antenna base for inserting a coaxial cable. Antenna device. The composite antenna device for a vehicle according to any one of claims 1 to 4, wherein the intermediate ground portion includes a sandwiching terminal capable of sandwiching a ground wire of a coaxial cable. The vehicle composite antenna device according to any one of claims 1 to 4, wherein the intermediate ground portion includes a relay connector configured to electrically connect a ground wire of a coaxial cable to an antenna base. A composite antenna device for a vehicle, comprising: The composite antenna device for a vehicle according to any one of claims 1 to 6, wherein the coaxial cable is arranged on the antenna base away from the antenna element to an extent that does not affect the reception performance of the antenna element. A composite antenna device for a vehicle, comprising: The vehicle composite antenna device according to any one of claims 1 to 7, wherein the plurality of antenna elements include at least an AM/FM composite antenna element. The composite antenna device for a vehicle according to any one of claims 1 to 8, wherein the circuit board is erected on an antenna base or placed in parallel. The composite antenna device for a vehicle according to any one of claims 1 to 9, wherein the antenna base includes an insulating base made of resin and a conductive base fixed to the insulating base and smaller than the insulating base. Characteristic vehicle composite antenna device.

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