JPH11274832A - On-vehicle antenna - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an on-vehicle antenna with which antenna characteristics are not degraded by fixing the antenna to the car body. SOLUTION: A male screw part 10a projected on the lower surface of a metal base 10 for antenna is inserted into a hole 26a opened in a car body 26, the metal base 10 for antenna is fixed on the car body 26 by screwing a nut member 30 from the rear side of the car body 26, and a ground connection is performed in electric conducting state. Besides, a waterproofing member 32 composed of a conductive rubber having elasticity and conductivity is interposed between the metal base 10 for antenna and the car body 26.

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 which is fixed to a vehicle body so that antenna characteristics do not deteriorate.

[0002]

2. Description of the Related Art An example of the structure of a vehicle-mounted antenna will be described with reference to FIG. A case member 12 made of insulating resin or the like is fixed to the upper surface of the substantially flat antenna metal base 10, and a circuit board 14 for mounting an amplifier or the like in a space formed by the case member 12 and the antenna metal base 10.
Is arranged. A power supply fitting 16 is disposed on the upper end of the case member 12 by insert molding or the like, and a conductive fitting 20 provided at the base end of the antenna element 18 is appropriately fixed to the power supply fitting 16 by screwing or the like. And electrical connection is made. Then, the other end of the connection fitting 22 having one end fixed to the power supply fitting 16 is fixed to the circuit board 14, and the base end of the antenna element 18 is electrically connected to the circuit board 14. Further, a coaxial cable 24 or the like is appropriately connected to the circuit board 14 to derive an antenna output. A male screw portion 10a is protrudingly provided substantially at the center of the lower surface of the antenna metal base 10, and is inserted into a hole 26a formed in the vehicle body 26. Then, a washer 28 is fitted into the male screw portion 10a from the back side of the vehicle body 26, and the nut member 30 is further screwed. An elastic waterproof member 32 is interposed between the lower surface of the antenna metal base 10 and the vehicle body 26. Note that the coaxial cable 24 is provided through a hole provided through the male screw portion 10a in the axial direction.

When the nut member 30 is tightened, the antenna metal base 10 is fixed with the lower surface of the antenna metal base 10 along the surface of the vehicle body 26 and the male screw portion 10 is fixed.
a and the ground connection is made. Further, with the tightening of the nut member 30, the waterproof member 32 is elastically deformed, and adheres to both the lower surface of the antenna metal base 10 and the vehicle body 26 to form a watertight structure.
Rainwater or the like is reliably prevented from entering the vehicle through the hole 26a of the vehicle body 26. Conventionally, the waterproof member 3
No. 2 was made of an elastic rubber having an insulating property.

[0004]

In the prior art, FIG.
No inconvenience occurred even with the in-vehicle antenna having the structure shown in FIG. That is, when the applied frequency of the antenna is 88
It is a relatively low frequency signal such as FM broadcast band of up to 108 MHz, and the antenna metal base 1
The dimension of 0 was sufficiently small, and no problem was found due to the fact that it worked as an antenna. However,
1.5 GHz band GPS signal and 1.8 GHz band D
In the case of the in-vehicle antenna using the CS signal as the applicable frequency of the antenna, an abnormality was found in which the antenna characteristics were deteriorated by being fixed to the vehicle body 26 as compared with the case of the in-vehicle antenna alone. This is considered as the following phenomenon. That is, the size of the antenna metal base 10 approaches a size at which the applied frequency can resonate, and can function as an antenna. The metal base for antenna 10 is electrically connected to the vehicle body 26 at the male screw portion 10a, but has elasticity between the metal base for antenna 10 and the vehicle body 26 at portions other than the male screw portion 10a. Since the waterproof member 32 made of rubber is interposed,
As schematically shown in FIG. 3, a metal base 10 for an antenna is provided.
And a vehicle body 26, a capacitance component Ci is generated. Therefore, any one of the antenna functions according to the total length L1 of the antenna metal base 10 or the length L2, L3 from the male screw portion 10a to the tip of the antenna metal base 10,
This is because a relatively wide resonance frequency band is generated due to the capacitance component Ci as a distributed constant, and at least a part of the resonance frequency band coincides with the applied frequency of the antenna.

The present invention has been made in view of the above circumstances, and the resonance frequency generated in a metal base for an antenna is set to be outside the applicable frequency band of the antenna, so that the antenna characteristics do not deteriorate even when the antenna is mounted on a vehicle body. It is intended to provide an antenna for use.

[0006]

In order to achieve the above object, a vehicle-mounted antenna according to the present invention comprises a metal base for an antenna fixed to a vehicle body and grounded in an electrically conductive state. A waterproof member having elasticity and conductivity is interposed between the metal base and the vehicle body.

Further, a male screw portion projecting from the lower surface of the antenna metal base is inserted into a hole formed in the vehicle body, and a nut member is screwed from the back side of the vehicle body to fix the antenna metal base. The antenna may be fixed to the vehicle body and grounded in a gas-conductive state, and a waterproof member having elasticity and conductivity may be interposed between the metal base for the antenna and the vehicle body.

Further, the waterproof member may be a conductive rubber.

[0009]

FIG. 1 shows a first embodiment of the present invention.
This will be described with reference to FIG. FIG. 1 is a longitudinal sectional view showing an example of the structure of the vehicle-mounted antenna. FIG. 2 is a schematic diagram for explaining a resonance frequency of a metal base for an antenna according to an embodiment of the on-vehicle antenna of the present invention.

[0010] Even in the vehicle-mounted antenna of the present invention, FIG.
As shown in FIG. 1, the structure and shape of the conventional vehicle-mounted antenna are almost the same. A feature of the present invention is that a material having not only elasticity but also conductivity, for example, conductive rubber is used as the waterproof member 32.

In this configuration, the waterproof member 32 is made of conductive rubber, so that a watertight structure is formed in the same manner as in the prior art, thereby preventing rainwater or the like from entering the vehicle. Then, as shown in FIG. 2, a resistance component Ro and a capacitance component Co are generated as distributed constants between the antenna metal base 10 and the vehicle body 26. Therefore, the antenna function of the metal base for antenna 10 and the resonance frequency due to the resistance component Ro and the capacitance component Co greatly change from the conventional one, and fall outside the band of the antenna application frequency. Even if the surface of the vehicle body 26 is insulated by the coating film of the vehicle body 26, the value of the capacitance component Co is largely different from the conventional one, and the resonance frequency is also greatly changed. Therefore, even if the vehicle-mounted antenna is attached to the vehicle body 26 and fixed, the good antenna characteristics obtained by the vehicle-mounted antenna alone can be maintained.

[0012] In the vehicle-mounted antenna of the present invention,
The resistance value of the electrically conductive waterproof member 32 is
It is needless to say that the antenna characteristics are not deteriorated even if they are attached to the antenna 6 so that desired characteristics can be maintained. The waterproof member 32 may be any material as long as it has both elasticity and conductivity, and is not limited to rubber, and may be synthetic resin or the like. Further, a composite material in which an elastic material and a conductive material are appropriately combined may be used. Further, the structure for fixing and electrically connecting the antenna metal base 10 to the vehicle body 26 is not limited to the structure using one male screw portion 10a as in the above-described embodiment. It may be formed by two protruding male screw portions or two bolts penetrating the lower surface of the antenna metal base 10.

[0013]

As described above, since the vehicle-mounted antenna according to the present invention is constituted, the following special effects can be obtained.

In any of the vehicle-mounted antennas according to the first and second aspects, the antenna characteristics are not degraded by being fixed to the vehicle body. Therefore, desired antenna characteristics can be maintained in a state where the antenna is mounted on a vehicle.

In the vehicle-mounted antenna according to the third aspect, since conductive rubber is used as the waterproof member, materials having various resistance values are commercially available, and a desired material can be easily obtained. It can be manufactured at low cost.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an example of the structure of a vehicle-mounted antenna.

FIG. 2 is a schematic diagram for explaining a resonance frequency of a metal base for an antenna according to an embodiment of the on-vehicle antenna of the present invention.

FIG. 3 is a schematic diagram for explaining a resonance frequency of a metal base for an antenna in one embodiment of a conventional vehicle-mounted antenna.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Metal base for antennas 10a Male screw part 26 Body body 26a Hole 30 Nut member 32 Waterproof member

Claims (3)

[Claims] 1. A metal base for an antenna is fixed alongside a vehicle body and is connected to the ground in an electrically conductive state. A waterproof member having elasticity and conductivity is provided between the metal base for the antenna and the vehicle body. An in-vehicle antenna characterized by being mounted and configured. 2. A male screw portion projecting from a lower surface of the antenna metal base is inserted into a hole formed in the vehicle body, and a nut member is screwed from the back side of the vehicle body to fix the antenna metal base. A vehicle-mounted antenna fixed to a vehicle body and grounded in an electrically conductive state, wherein a waterproof member having elasticity and conductivity is interposed between the metal base for the antenna and the vehicle body. . 3. The on-vehicle antenna according to claim 1, wherein the waterproof member is made of conductive rubber.