JP3218186B2 - In-vehicle antenna device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle-mounted antenna device for receiving FM / AM broadcasts, and more particularly, to a vehicle-mounted antenna device for extracting a signal with little signal attenuation.

[0002]

2. Description of the Related Art Generally, a principle structure as shown in FIG. 4 is employed as a basic structure of a vehicle-mounted antenna. As shown in the drawing, a metal cylinder d for antenna ground accommodating an antenna element c is assembled into an antenna hole b formed in a vehicle body a from the back side of the vehicle body a. The signal received by the antenna element c is output from a signal extraction hole e formed in the antenna earth metal cylinder d.

By the way, the performance of antenna reception is as follows.
Ideally, the relationship between the received signal voltage (VO) of the antenna element c and the final extraction voltage (VE) is equal. However, stray capacitance is generated by the above-described antenna structure, and the signal is expressed by the following relational expression. Attenuation occurs. VO = VE × CE / (CS + CE) Here, CE is an element equivalent capacitance, and CS is a capacitance (floating capacitance) generated between the antenna element c and the antenna earth metal cylinder d.

[0004]

According to the above-mentioned relationship, in order to pursue the ideal performance of the antenna, it is required that CS be extremely small. In view of such a problem, an antenna structure as shown in FIG. 5 has conventionally been adopted. This is achieved by assembling an insulating member cylinder d ′ for housing an antenna element c from the back side of the vehicle body a into an antenna hole b formed in the vehicle body a, and further disposing an electrode cylinder f on the inner surface of the insulating member cylinder d ′. ing. Then, a contact electrode spring g is assembled to the antenna element c, and a signal is output from the electrode cylinder f when the contact electrode spring g contacts the electrode cylinder f.

In the above configuration, since the contact electrode spring g is in contact with the electrode cylinder f, CS occurs between the electrode cylinder f and the earth metal e. Therefore, CS is reduced by reducing the outer diameter of the electrode cylinder f without changing the inner diameter of the earth metal e. Here, since CS is generally inversely proportional to the distance, the distance (between electrodes)
Is larger, CS is smaller.

In the configuration of FIG. 5 described above, there is a limit to the reduction of CS. To further reduce CS, the inner diameter of the electrode cylinder f must be further reduced, and the contact electrode spring g must be further reduced in size. Must. However, since the contact electrode spring g always moves up and down, it must be increased to have a certain strength.
In addition, the distance between the antenna element c and the electrode cylinder f must be maintained to some extent. For this reason, it has been considered difficult to further reduce the size and to further reduce CS.

On the other hand, as one of the feeding structures to the antenna element in the antenna device, there is a structure shown in FIG. FIG.
6A and 6B are an external view (A) and a cross-sectional view (B) of a power supply unit. As shown in FIG. 6B, the antenna element 1 is inserted into a hot tube 2 located around the outside thereof, And slides in and out of the vehicle body (not shown) while contacting the inner peripheral surface of the vehicle body. The hot tube 2 is connected to a power supply coaxial cable (not shown) or the like, and forms a power supply point for extracting a reception voltage. A ground metal 4 is arranged outside the hot tube 2 via an insulator 3 made of an insulating member. The ground metal 4 is connected to a ground wire of a coaxial cable (not shown) for feeding, so that a feeding circuit in the antenna device can be configured. The power supply unit shown in FIG. 6 is arranged and attached to the lower surface of the vehicle body by a top nut 5 fastened from the upper surface of the vehicle body (not shown) to the female screw portion formed on the earth metal 4. The length of the hot tube 2 in the longitudinal direction is set to a length that can substantially cover the moving stroke of the antenna element in order to restrict the swing of the antenna element 1. However, since both the hot tube 2 and the earth metal 4 are in a state where the entire area of the peripheral surface faces each other, the area of the counter electrode which affects the stray capacitance described above is large. For this reason, it is difficult to set the antenna characteristics to an ideal state.

The present invention has been devised to solve the above-mentioned technical problems, and has as its object to provide a vehicle-mounted antenna device that reduces stray capacitance and improves antenna performance.

[0009]

In order to achieve this object, the invention according to claim 1 is directed to an in-vehicle vehicle in which an antenna capable of receiving FM / AM broadcast is extended and retracted from an antenna hole formed in a vehicle body. The antenna device has a coil-shaped or rod-shaped antenna element and an inner diameter substantially equal to or slightly larger than the outer diameter of the antenna element, and is slidably held in contact with the antenna element. A hot tube, a substantially cylindrical ground metal having a relatively large diameter that is provided so as to be in contact with the lower surface of the vehicle body, and through which the hot tube is inserted, and an insulating member located outside the hot tube. the constituting at least have been feeding section, at least a hot tube of the hot tube or the ground metal
On the side, will be cut-off parts are formed on the circumferential surface thereof, the
The notch should be in the above hot tube or earth metal.
Excluding a pair of supporting portions provided between the annular portion and the annular portion.
It is characterized in that it is formed in a range .

According to a second aspect of the present invention, in the vehicle-mounted antenna device according to the first aspect, the longitudinal direction of the hot tube is provided.
The length in the direction is approximately the same as that of the above earth metal
It is characterized by being formed .

[0011]

[0012]

According to the first and second aspects of the present invention, the antenna element
Hot tube and earth metal
Since the notch was formed at least on the hot tube side,
The facing area between the hot tube and the earth metal
Can be reduced independently of the longitudinal length,
Ensure that there is sufficient contact between the
In addition, reduce stray capacitance to improve antenna performance
be able to. And the annular part in the hot tube
The shape is stable as it leaves the support
To stabilize contact with the antenna element
Can be. Also, adjust the longitudinal length of the hot tube.
By forming the length approximately equal to that of the base metal.
Therefore, the antenna element to be inserted is
Sufficient flexural rigidity in the event of swinging can be sufficiently ensured.

[0013]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
FIG. 1 is a cross-sectional view showing the structure of a power supply unit, which is a main part of an in-vehicle antenna device 10 according to the present invention. In FIG.
The feed unit 10 includes an antenna element 11, a hot tube 12, an insulator 13, and a ground metal 14, similarly to the structure shown in FIG .

As shown in FIG. 2, the hot tube 12 has an inner diameter substantially equal to or slightly larger than the outer diameter of the antenna element 11, and comes into contact with the antenna element 11 when the antenna element 11 is inserted. And can be slidably held. The length of the hot tube 12 in the longitudinal direction is substantially equal to the length of the earth metal 14, which will be described later, and the bending rigidity when the inserted antenna element 11 swings is secured. A plurality of cutouts 15 and 16 are formed on the peripheral surface of the hot tube 12. Of the notch portions 15 and 16, the notch portion indicated by reference numeral 15 is provided in the middle of the longitudinal direction and at one end, and
And a range excluding a pair of support portions 19 provided between the annular support portions 17 and 18 for maintaining the shape as a hot tube. The removed portion corresponds to a range from one end of the annular support portion 17 to the other end of the hot tube 12 in the longitudinal direction. Each of the notches 15 and 16 is formed by a slot or a notch whose peripheral wall is cut off. The notch 16 formed in the range extending to the other end in the longitudinal direction of the hot tube 12 has a pair of struts 20 extending to the other end in the longitudinal direction at the same phase position as the strut 19. I have. The support portions 19 and 20 are left positioned symmetrically with respect to the center of the circle of the hot tube 12. This is for supporting the antenna element 11 inserted therein with a good balance. The annular support portion 18 located at one longitudinal end of the annular support portion of the hot tube 12 is provided with a terminal portion 18a to which a core wire of a power supply coaxial cable (not shown) is connected.

On the other hand, the earth metal 14, as shown in FIG. 3, is constituted by a cylindrical member having a relatively large diameter through which the hot tube 12 can be inserted.
A plurality of notches 21 and 22 are formed. Missing part 2
Of the parts 1 and 22, the notched part indicated by the reference numeral 21 is a long hole-shaped part formed in the circumferential direction at a position continuous with the female screw part 23 formed at one end in the longitudinal direction of the earth metal 14. It is constituted by an opening. The female screw portion 23 corresponds to a portion where a top nut (a member indicated by reference numeral 5 in FIG. 6) is fastened when the female screw portion is mounted on the vehicle body. Of the missing parts,
The notched portion indicated by reference numeral 22 is a portion where only the support portion 26 is left symmetrically with respect to the annular support portion 25 located at the other end in the longitudinal direction from the vicinity of the flange portion 24 with the cross-sectional center therebetween. Applicable. The flange portion 24 is provided for positioning an insulating member (not shown) between the antenna device 10 and the vehicle body used when the antenna device 10 is mounted on the vehicle body. The annular support portion 25 is provided to maintain the shape of the earth metal 14, similarly to the above-described hot tube 12. In addition, mounting brackets 27 for mounting to the vehicle body are respectively provided on the support portions 26 by integral molding.

Since the present embodiment has the above configuration,
The insulator 13 and the hot tube 12 are sequentially inserted into the ground metal 14, and the hot tube 12
The antenna element 11 is inserted into the inside of the device to obtain an assembled state as shown in FIG. For the hot tube 12, for the terminal portion 18 a of the annular support portion 18,
The core wire of the power supply coaxial cable (not shown) is connected, and the ground metal wire of the power supply coaxial cable is connected to the ground metal 14 to form a power supply circuit.

In the antenna device assembled in the state shown in FIG. 1, the opposed metal portions of the hot tube 12 and the earth metal 14, which are conductors opposed to each other with the insulator 13 interposed therebetween, are omitted. The area of the facing surface is reduced. For this reason, the stray capacitance generated at the opposing metal portion is reduced, and it is possible to extract the reception voltage without causing a loss.

When the antenna element 11 slides in the hot tube 12, the length of the hot tube 12 in the longitudinal direction is equal to the length of the earth metal 14 in the longitudinal direction. 14, the rigidity of the antenna element 11 against shaking can be increased.
Thereby, the behavior when the antenna element 11 slides can be prevented from becoming unstable, and the antenna element 11 can be smoothly protruded and retracted into and out of the vehicle body.

In the above embodiment, the structure of the antenna element is not specified, but, for example, a coil antenna or a rod antenna can be applied. Either the used method or the manual method can be used. Further, the total length of the antenna element is effective for reducing the capacity, which is a condition required when a short antenna element of about 15 cm is used, but is not limited to such a length, and may be longer, for example. , 0.8 to 1 m long.

[0020]

As is apparent from the above description, the claims
According to the inventions described in (1) and (2), a power supply path to the antenna element
Make up the hot tube and earth metal at least
Since a notch is formed on the hot tube side,
The facing area between the probe and the earth metal
Hot chew can be reduced independent of length
While maintaining sufficient contact between the antenna and the antenna element
Can reduce capacity and improve antenna performance
You. And, in the hot tube, the annular part and the support part
Since the shape is to be left, the shape is stably maintained.
To stabilize the contact with the antenna element.
You. Also, adjust the length of the hot tube in the
By forming the length approximately equal to that of the barrel,
When the inserted antenna element swings
In this case, sufficient bending rigidity can be ensured. Moreover,
Since it is only necessary to obtain the missing portion by processing without requiring a special circuit configuration, it is possible to secure a stable antenna characteristic without increasing the cost.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a power supply unit corresponding to a main part of an in-vehicle antenna device according to the present invention.

FIG. 2 is a perspective view for explaining a structure of a hot tube used in the power supply unit shown in FIG.

FIG. 3 is a perspective view for explaining a structure of a ground metal used in the power supply unit shown in FIG. 1;

FIG. 4 is a diagram illustrating the principle of an antenna.

FIG. 5 is an explanatory diagram of a conventional example of an antenna device.

FIGS. 6A and 6B are diagrams for explaining a structure of a feeding unit in a conventional antenna device, where FIG. 6A is an external view and FIG. 6B is a cross-sectional view.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Feed part 11 Antenna element 12 Hot tube 14 Earth metal 15, 16, 21, 22 Missing part

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-244620 (JP, A) JP-A-63-121324 (JP, A) JP-A-57-190401 (JP, A) 134714 (JP, U) Shokai Sho 57-23607 (JP, U) Shokai Sho 61-78412 (JP, U) Shoko 43-821 (JP, Y1) (58) Field surveyed (Int. ⁷ , DB name) H01Q 1/10 H01Q 1/27 H01Q 1/50

Claims (2)

(57) [Claims] 1. An FM antenna through an antenna hole formed in a vehicle body.
In an in-vehicle antenna device in which an antenna capable of receiving / AM broadcast is mounted so as to expand and contract, the antenna device has a coil-shaped or rod-shaped antenna element and an inner diameter substantially equal to or slightly larger than the outer diameter of the antenna element. A hot tube that is slidably held in contact with the antenna element, and is disposed substantially in contact with the lower surface of the vehicle body, and has a substantially cylindrical shape having a relatively large diameter through which the hot tube is inserted. A ground metal and a power supply unit having at least an insulating member located outside the hot tube, and at least a hot tube side of the hot tube or the ground metal ,
Become the lacking part on the peripheral surface is formed, the cut-off parts are the upper
An annular portion of the hot tube or earth metal
Formed in a range excluding a pair of support parts installed between annular parts
An in- vehicle antenna device characterized in that: 2. The on-vehicle antenna device according to claim 1, wherein the length of the hot tube in the longitudinal direction is equal to the length of the arc tube.
An in-vehicle antenna device having a length substantially equal to that of a metal .