Communications: radio wave antennas – Antennas – With housing or protective covering
Reexamination Certificate
2001-03-01
2001-10-30
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
With housing or protective covering
C343S7000MS, C343S713000, C343S906000
Reexamination Certificate
active
06310586
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to antennas, and more particularly relates to an on-board antenna used for receiving terrestrial television broadcast signals, etc.
2. Description of the Related Art
A conventional on-board antenna
50
for receiving terrestrial television broadcast signals is shown in FIG.
7
. This conventional antenna
50
includes a rod-shaped radiation conductor
51
which is adjusted so as to resonate at a desired frequency. The angle between the radiation conductor
51
and a pedestal
52
is freely adjusted by using a supporting portion
53
, which functions as a fulcrum. As shown in
FIGS. 8A and 8B
, this antenna
50
is attached on a rear window
61
or on a roof
62
of a vehicle
60
.
Generally, to solve the problem of fading, which particularly occurs when signals are received by a moving antenna, a diversity receiving system is adopted in vehicles. In this system, a plurality of the antennas shown in
FIG. 7
are used, and one of the antennas which exhibits the highest receiving level is selected.
With respect to the conventional antennas as described above, the operational bandwidth of a single antenna is not sufficiently wide. Thus, when a wide bandwidth must be covered, as in a case of receiving television broadcast signals, multiple antennas having different operational bandwidths are prepared. In addition, external circuits such as tuning circuits and amplifying circuits are attached. Accordingly, there has been a problem in that a considerably high total cost is incurred to obtain a wide operational bandwidth. In addition, since a plurality of antennas, each of which is relatively large, is used, the antennas are necessarily attached to the exterior of the vehicle. Thus, there are risks in that the antennas will be damaged or stolen. In addition, there is a problem in that the appearance of the vehicle is degraded.
SUMMARY OF THE INVENTION
In consideration of the above-described situation of the conventional technique, an object of the present invention is to provide an inexpensive and compact wideband antenna which is mountable in a vehicle cabin. In addition, it is also an object of the present invention to increase the working efficiency in an operation of connecting a coaxial cable.
To this end, an antenna of the present invention comprises a radiation conductor unit including an electricity-supplying conductor and a plurality of radiation conductors having different lengths which extend in parallel to each other from the electricity-supplying conductor; a grounded conductor unit which opposes the radiation conductors in an approximately parallel manner with a predetermined distance therebetween; and an insulating casing which contains the radiation conductor unit and the grounded conductor unit, and which is constructed of a main case and a cover which are able to sandwich a coaxial cable for supplying electricity. The radiation conductor unit and the grounded conductor unit are fixed to the main case, and a connecting part of an inner conductor of the coaxial cable and the electricity-supplying conductor and a connecting part of an outer conductor of the coaxial cable and the grounded conductor unit are covered with the cover.
According to the antenna which is constructed as described above, multiple resonances occur between the radiation conductors having different lengths and the grounded conductor unit. Accordingly, the overall frequency characteristics are improved in a frequency band including multiple resonance frequencies, and the operational bandwidth is increased. In addition, since the radiation conductors arranged in parallel to each other individually serve as radiators, the size of the antenna is reduced compared to conventional dipole antennas, so that the installation in a vehicle cabin can be realized. In addition, the coaxial cable for supplying electricity is sandwiched by the main case and the cover which construct the casing, and the connecting part of the coaxial cable and the electricity-supplying conductor and the connecting part of the coaxial cable and the grounded conductor unit are covered with the cover. Accordingly, the operation of connecting the coaxial cable is easily performed while the cover is removed, so that the working efficiency is increased. Preferably, in the above-described construction, the electricity-supplying conductor is provided with a first receiving portion to which the inner conductor of the coaxial cable is connected, and the grounded conductor unit is provided with a second receiving portion to which the outer conductor of the coaxial cable is connected. In addition, the first and the second receiving portions are preferably positioned at the same side of the antenna. In such a case, the position for setting the coaxial cable is clearly defined, so that the inner conductor and the outer conductor of the coaxial cable are more easily connected to the receiving portions.
Although the fist and the second receiving portions may be disposed in the same plane, the vertical distance between the first receiving portion and the grounded conductor unit is preferably larger than a vertical distance between the second receiving portion and the grounded conductor unit. In such a case, a step between the inner conductor and the outer conductor of the coaxial cable is compensated for, so that the coaxial cable may be installed in a horizontal manner, reducing the stress applied at the connecting parts.
Preferably, the coaxial cable is provided with a thickened portion, and the main case and the cover are provided with concavities for receiving the thickened portion. In such a case, even when exterior stress, such as tensile stress, bending stress, etc., is applied, the engaging part of the thickened portion and the concavities receives the stress. Such a stress-receiving construction prevents disconnection of the coaxial cable and maintains a condition in which the connection is stable.
Preferably, at least one of the radiation conductor unit and the grounded conductor unit is provided with a holding portion for holding the coaxial cable, and an end portion of the grounded conductor unit abuts against an inwardly facing side surface of the main case. In such a case, the abutting part of the grounded conductor unit and the inwardly facing side surface receive the tensional stress applied to the coaxial cable. This construction also serves to prevent disconnection of the coaxial cable, so that disconnection of the coaxial cable is more reliably prevented. In addition, the radiation conductors in the radiation conductor unit, the first receiving portion provided to the electricity-supplying conductor, and the second receiving portion provided to the grounded conductor unit are stably positioned. Thus, impedance variation of the antenna containing these components is reduced. Accordingly, impedance matching between the antenna and the coaxial cable is ensured.
REFERENCES:
patent: 5355142 (1994-10-01), Marshall et al.
patent: 5757327 (1998-05-01), Yajima et al.
patent: 5900840 (1999-05-01), Yajima
patent: 6246368 (2001-06-01), Deming et al.
patent: 5-029821 (1993-02-01), None
patent: 12-040908 (2000-02-01), None
Ikeda Tomoki
Takahashi Toshiyuki
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Ho Tan
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