Loop antenna device

Details Loop antenna device Loop antenna device

2001-02-20

2003-12-16

Wong, Don (Department: 2821)

Communications: radio wave antennas

Antennas

Loop type

C343S713000, C343S867000

Reexamination Certificate

active

06664936

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a loop antenna device for generating a magnetic field. The loop antenna device is adapted to be disposed as an antenna in the vicinity of a conductor made of metal.
2. Related Art
One of the conventional loop antenna devices is disclosed in German Patent Publication DE 41 05 826 A1. The conventional loop antenna device includes a first antenna A
1
and a second antenna A
2
. The first antenna A
1
has a coil L
2
wound around a ferrite rod and a resonant capacitor C
2
connected thereto in parallel which constitutes a parallel resonant circuit. The second antenna A
2
has a circular coil L
1
accommodating therein the ferrite bar B and a resonant capacitor C
1
connected in parallel with the circular coil L
1
which constitutes a parallel resonant circuit. The ferrite rod
52
is also wound with coil L
3
to which an amount of current is fed from a power source S.
In the foregoing structure, the ferrite rod
52
is rotated through an angle so as to establish a magnetic coupling between the first antenna A
1
and the second antenna A
2
.
FIG.
6
(
b
) of the present application shows an equivalent circuit of a conventional structure as shown in FIG.
6
(
a
). In this case, when the loop antenna device is oscillated by a power supply S, a magnetic field component Hz is generated by the coil L
1
and makes an angle of 90 degrees relative to a magnetic field component Hy generated by the coil L
2
. It is to be noted that the magnetic field component Hz and the magnetic field component Hy extend in the z-direction and y-direction, respectively.
For example, when the loop antenna device
51
is part of a key-less entry system, the loop antenna device
51
is disposed in a door handle of a vehicle. In this case, since a magnetic field component has a plurality of axial components, the axial components cross in an orthogonal manner relative to the conductor such as the door parts. As shown in
FIG. 7
, the loop antenna device
51
is fixed such that the magnetic field component Hz crosses in an orthogonal manner relative to the conductor plate such as a door part in the vicinity of the conductor plate
57
.
When the loop antenna device
51
is used for one part of a key-less entry system, the loop antenna device is disposed in spaced apart relation to the conductor plate
57
at a predetermined distance in order to secure an antenna characteristic. Otherwise, when the loop antenna device
51
is disposed in the vicinity of the conductor plate
57
, the loop antenna device
51
is assembled by adjusting an antenna constant. In the condition shown in
FIG. 7
, when the power supply is oscillated, a radiation magnetic field Hz in a z-direction is generated on an inner portion of the coil. Then, as the magnetic field component −Hz is reflected by the conductor plate
57
, the reflected magnetic field component (e.g., Hz) is denied by the magnetic field component −Hz generated by the coil. The loop antenna may be disposed apart from the conductor
57
in order to avoid the above-mentioned problem, however, if the loop antenna
51
is disposed apart from the conductor
57
, it is necessary that the thickness of the door handle on a direction perpendicular to the vehicle door comes wider whereby the size of the vehicle door having the door handle becomes too large.
SUMMARY OF THE INVENTION
It is, therefore, one of the objects of the present invention to provide a loop antenna device without the forgoing drawbacks.
It is another object of the present invention to provide a loop antenna device having a radiated magnetic field generated by the coil of the loop antenna device when the loop antenna device is disposed in the vicinity of a conductor.
In order to attain the foregoing objects, a loop antenna device located close to a conductor includes an antenna for generating a magnetic field component perpendicular to the conductor, and an electromagnetic absorbing member disposed between the antenna and the conductor.
Further, a loop antenna device includes a first antenna having a first resonant circuit comprised by a first coil and a first condenser connected to the first coil, a second antenna including a second resonant circuit comprised by a second coil wound in a direction perpendicular to the wound direction of the first coil outside of the first antenna, a link coil wound in the same wound direction of the first coil and connected to the second coil, and a second condenser connected to the link coil, a case made of a conductor material accommodating the first antenna and the second antenna, and an electromagnetic wave absorbing member disposed between the case and at least one of the first coil and the second coil.


REFERENCES:
patent: 3659094 (1972-04-01), Nakahara et al.
patent: 4679052 (1987-07-01), Ohe et al.
patent: 5495213 (1996-02-01), Ikeda
patent: 6154179 (2000-11-01), Kohno
patent: 6163305 (2000-12-01), Murakami et al.
patent: 6181130 (2001-01-01), Hoshi et al.
patent: 6229492 (2001-05-01), Lee et al.
patent: 6259412 (2001-07-01), Duroux
patent: 41 05 826 A 1 (1991-02-01), None
patent: 2 243 955 (1991-11-01), None

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