Communications: radio wave antennas – Antennas – With vehicle
Reexamination Certificate
1999-11-15
2001-05-08
Phan, Tho (Department: 2821)
Communications: radio wave antennas
Antennas
With vehicle
C343S704000
Reexamination Certificate
active
06229493
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a glass antenna device for vehicles of the type wherein two antennas are provided on the same surface of a fixed window glass, such as a rear window glass or a side window glass, for the reception of FM and TV broadcasts and AM broadcasts, respectively, and a transformer is connected to transmission lines extending from the two antennas for performing the impedance conversion of the transmission lines. More particularly, it relates to a vehicle window glass antenna device designed to prevent reductions in the AM broadcasts reception sensitivity.
2. Description of the Related Art
Conventional vehicle window glass antenna devices are equipped with a choke coil to prevent a reduction in the reception sensitivity. The present assignee has proposed in Japanese Patent Laid-open Publication No. HEI 9-018222 a glass antenna device equipped with a transformer devoid of choke coil, such as shown here in
FIG. 4
of the accompanying drawings.
As shown in
FIG. 4
, the proposed glass antenna device
51
includes an exclusive antenna
53
, a compatible antenna
52
formed by defogging heater conductors
55
connected to bus bars
54
(
54
a
,
54
b
), and an impedance conversion transformer
57
. A primary winding of the transformer
57
is connected at its one end
57
a
to the exclusive antenna
53
and at its middle point
57
b
to the compatible antenna
52
via a lead. A secondary winding of the transformer
57
has terminals
57
c
,
57
d
connected to a center conductor
56
a
and an outer conductor
56
b
of a coaxial feeder cable
56
. By virtue of the impedance conversion achieved by the impedance conversion transformer
57
, a practically sufficient degree of reception sensitivity can be obtained even though a conventional choke coil is eliminated.
Because of the impedance conversion transformer associated with the exclusive antenna to eliminate a choke coil, the glass antenna device disclosed in Japanese Patent Laid-open Publication No. HEI 9-018222 achieves practically sufficient reception sensitivity.
However, there is room for improvement in that signal attenuation may occur when a cable interconnecting a receiver-side impedance conversion transformer and an AM receiver is long and hence has a large distribution capacitance.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide a glass antenna device for a vehicle, which is capable of preventing a reduction in the AM reception sensitivity.
To attain the object, the present invention provides a glass antenna device for a vehicle, comprising: an FM antenna and an AM antenna both provided on the same surface of a rear window glass or a fixed window glass at a different position of the vehicle for the reception of FM broadcasts and AM broadcasts, respectively; and an antenna-side impedance conversion transformer connected to the FM antenna and the AM antenna through respective transmission lines for performing the impedance conversion of the transmission lines, and a receiver-side impedance conversion transformer electrically connected to the antenna-side impedance conversion transformer. A cable interconnecting the receiver-side impedance conversion transformer and the input terminal of a receiver for the reception of AM broadcast has a distributed capacitance not in excess of 10 pF.
Because of the distributing capacitance of the cable is not in excess of 10 pF, losses in the transmission lines can be reduced. Thus, the glass antenna device can achieve reception of AM broadcasts at high sensitivity with little attenuation of AM reception signals.
The above and other features and advantages of the present invention will become manifest to those versed in the art upon making reference to the following description and accompanying sheet of drawings in which preferred structural embodiments incorporating the principle of the invention are shown by way of illustrative examples.
REFERENCES:
patent: 5083134 (1992-01-01), Saitou et al.
patent: 5258728 (1993-11-01), Taniyoshi et al.
patent: 5781160 (1998-07-01), Walton
patent: 5945957 (1999-08-01), Kakizawa
patent: 0854534 (1998-07-01), None
patent: 0942486 (1999-09-01), None
patent: 9182222 (1997-01-01), None
Adams & Wilks
Nippon Sheet Glass Co. Ltd.
Phan Tho
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