Communications: radio wave antennas – Antennas – With vehicle
Reexamination Certificate
2000-08-10
2001-09-18
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
With vehicle
C343S846000
Reexamination Certificate
active
06292150
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a glass antenna device for vehicles, particularly to a feeding structure in the glass antenna device.
BACKGROUND OF THE INVENTION
Glass antenna devices mounted on a vehicle window have been used widely to receive amplitude modulation waves or frequency modulation waves. Furthermore, glass antennas are beginning to be used as well as rod antennas for mobile communications (automobile telephones).
FIG. 8
shows a conventional antenna device
101
for automobile telephones (e.g. for an 800 MHz band). The antenna device
101
comprises antenna patterns
111
and
112
formed on a rear window glass
105
, a coaxial cable
102
, and a receiver transmitter (not shown).
The substantially linear radiation pattern
111
is connected to a core
121
that is the inner conductor of the coaxial cable
102
. Furthermore, the ground pattern
112
is arranged so that its one edge becomes parallel to and in close proximity to the vehicle body
104
, so that it can be coupled capacitively with the vehicle body
104
. Furthermore, a braided wire that is the outer conductor of the coaxial cable is connected and fixed to the ground pattern with a presser metallic terminal
103
. Thus, the antenna device is grounded to the vehicle body
104
via the ground pattern.
In such an antenna device, however, grounding by the ground pattern is not perfect. Thus, a potential difference may be generated between the ground pattern and the coaxial cable. With this potential difference, a current may flow from the ground pattern to the coaxial cable. This current causes radiation of waves from the coaxial cable. That is, the coaxial cable acts like an antenna.
Thus, in this antenna device, the antenna performance changes when the coaxial cable is turned around, that is the position of the coaxial cable is changed, as if the antenna itself is moved.
Accordingly, in this antenna device, it has been necessary to adjust the antenna taking the instability in the antenna performance due to the position of the coaxial cable into consideration. Thus, considerable time has been required to adjust such an antenna device entirely.
On the other hand, JP-A-6-53721 discloses a connecting structure of a glass antenna, particularly a structure in which the outer conductor of a coaxial cable is connected to a ring by soldering. JP-A-8-130404 also discloses another connecting structure of a glass antenna.
Because the outer conductor of the coaxial cable is connected to the ring by soldering, the glass antennas disclosed in the above-mentioned publications have good electrical connections.
However, even with this structure, the problem of generation of a potential difference between the ground pattern and the coaxial cable remains.
Moreover, positioning the coaxial cable in a vehicle may be restricted depending on the vehicle shape or the location at which the antenna device is mounted. The antenna performance may become poor with the turning that is allowed.
SUMMARY OF THE INVENTION
Thus, it is an object of the present invention to provide a glass antenna device having a ground pattern, which has a stable antenna performance regardless of the position of a coaxial cable.
Furthermore, it is another object of the present invention to provide a glass antenna device whose mounting is unlikely to be restricted by turning of a coaxial cable.
In order to solve the above-mentioned problems, the present invention provides a glass antenna device mounted on a fixed window of a vehicle, comprising a radiation pattern and a ground pattern, the radiation pattern being connected to an inner conductor of a coaxial cable, the ground pattern being coupled capacitively with a body of the vehicle and further being connected to an outer conductor of the coaxial cable in at least two connecting portions.
In the antenna device of the present invention, it is preferable that a distance between two adjacent portions selected from the connecting portions is at least &lgr;/4, where &lgr; is a wavelength that is received or transmitted by the antenna device. Thus an antenna device can be provided in which the potential coupling between the ground pattern and the coaxial cable is further ensured, and in which the antenna performance is stabilized.
In the antenna device of the present invention, it is preferable that a number of the connecting portions is two. Thus, an increase in the number of the assembly steps resulting from the increased connecting portions can be minimized, while the stability in the antenna performance is ensured.
In the antenna device of the present invention, it is preferable that a number of the connecting portions is three. Thus an antenna device can be provided in which the potential coupling between the ground pattern and the coaxial cable is further ensured, and in which the antenna performance is further stabilized.
In the antenna device of the present invention, it is preferable that the ground pattern has a length of at least &lgr;/2, where &lgr; is a wavelength that is received or transmitted by the antenna device.
The present invention is characterized in that the ground pattern is connected to the outer conductor of the coaxial cable in at least two connecting portions. This structure can ensure potential coupling between the ground pattern and the coaxial cable, so that the influence of the imperfect grounding by the ground pattern can be reduced. Moreover, by making the distance between the adjacent connecting portions at least &lgr;/4, the influence of the imperfect grounding can be further reduced.
Thus, the present invention has an effect that the antenna performance is not affected by the position at which the coaxial cable is laid in a vehicle.
That is, the region of the coaxial cable from the last of the connecting portions can be positioned without particular restrictions. Thus, the glass antenna device can be mounted to a vehicle regardless of the vehicle design or the location at which it is mounted. Moreover, the last connecting portion herein refers to the connecting portion that is the farthest from the radiation pattern.
Moreover, when the distance between the adjacent connecting portions is less than &lgr;/4, the potential of the ground pattern might be increased, which may lead to difficulty in feeding. Thus, it is preferable that the distance between the adjacent connecting portions is at least &lgr;/4.
REFERENCES:
patent: 5255002 (1993-10-01), Day
patent: 5268700 (1993-12-01), Hirotsu et al.
patent: 5293174 (1994-03-01), Kropielnicki et al.
patent: 5353039 (1994-10-01), Tsukada et al.
patent: 5406295 (1995-04-01), Baranski et al.
patent: 5479179 (1995-12-01), Hirotsu et al.
patent: 5499034 (1996-03-01), Fujii et al.
patent: 5657029 (1997-08-01), Iijima et al.
patent: 6-53721 (1994-02-01), None
patent: 8-130404 (1996-05-01), None
Doi Ryokichi
Kakizawa Hitoshi
Ho Tan
Merchant & Gould P.C.
Nippon Sheet Glass Co. Ltd.
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