Communications: radio wave antennas – Antennas – High frequency type loops
Reexamination Certificate
2002-02-25
2003-06-24
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
High frequency type loops
C343S867000
Reexamination Certificate
active
06583764
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a loop antenna device.
BACKGROUND OF THE INVENTION
A conventional loop antenna device is disclosed in German Patent Publication DE 4105826 or Japanese Patent Laid-Open Publication No. 2000-261245. The former conventional loop antenna device is shown in FIG.
8
(
a
) and FIG.
8
(
b
). As shown in FIG.
8
(
a
) and FIG.
8
(
b
), this loop antenna device
51
includes a first antenna
55
and a second antenna
58
. The first antenna
55
has a coil
53
wound around a ferrite rod
52
and a resonant capacitor
54
connected to the coil
53
and constitutes a parallel resonant circuit. The second coil
58
has a circular coil
56
magnetically connected to the coil
53
and a resonant capacitor
57
connected to the circular coil
56
and constitutes a parallel resonant circuit.
When a high frequency is fed to a coil
59
wound around the ferrite rod
52
from a power source
60
, a magnetic field component is generated by the first antenna
55
in the y-axis direction and a magnetic field component is generated by the second antenna
58
in the z-axis direction. Thereby, a composite magnetic field is generated in the y-z-axis direction and a predetermined electric wave corresponding this composite magnetic field is radiated from the loop antenna device
51
when each resonant circuits of the first and second antennas
55
and
58
resonated.
Furthermore, the latter conventional loop antenna device is shown in FIG.
9
. As shown in
FIG. 9
, in this loop antenna, a request signal output circuit
62
which constitutes a transmitter of an antenna
61
includes a crystal oscillator
63
, an oscillating circuit
64
, a D-type flip-flop
65
, two amplification circuits
66
,
67
and a modulation circuit
68
. The output terminals of the amplification circuits
66
,
67
are connected to magnetic field generating parts (coils)
69
,
70
which are disposed while declining with 90 degree each other, respectively. Resonant capacitors
71
,
72
are connected to the coils
69
,
70
, respectively and a resonant circuit is constituted by the coils
69
,
70
and the resonant capacitors
71
,
72
, respectively.
A predetermined pulse signal which is outputted from an output terminal Q
1
of the oscillating circuit
64
is fed to the coil
69
. A pulse signal whose phase is shifted with 90 degree with respect to the pulse signal from the output terminal Q
1
is fed to the coil
70
by the flip-flop
65
. Thereby, a composite magnetic field (a rotational magnetic field) which has directional characteristics of 360 degree is generated by the coils
69
,
70
and a predetermined electric wave corresponding this composite magnetic field is radiated from the antenna
61
in response to a timing of a control signal outputted from a microcomputer
73
.
In the former loop antenna device
51
shown in
FIG. 8
, however, although the first antenna
55
is disposed inside of the circular coil
56
, since empty space is large, the size of the antenna device increases. On the other hand, in the latter conventional antenna
61
, the electric wave continues radiated due to a discharge phenomenon of the resonant capacitors
71
,
72
after the output of the pulse signal is ended. Namely, as shown a wave form of an antenna output in
FIG. 10
, the energy stored in the resonant capacitors
71
,
72
is discharged for a T interval after the output of the pulse signal is ended and the electric wave from the antenna
61
continues radiated. Accordingly, in case that a next data is sent after a certain data is placed on the electric wave and is sent, it is necessary to set a time margin until the end of the discharge of the resonant capacitors
71
,
72
. As a result, it is impossible to increase a data sending speed.
In order to overcome the drawback regarding the data sending speed, for example, it is found to be useful that a damping resistance is connected to the resonant circuit. When a damping is performed by the damping resistance, however, the damping is always performed to the resonant circuit independently of with or without the radiation of the electric wave and the extra energy is consumed. Namely, the energy on the resonant circuit is always consumed by the damping resistance. Thereby, an antenna gain or a radiant efficiency which affect a transceiving (receiving and sending) sensitivity of the electric wave decrease and high input has to be given to the resonant circuit for preventing the decrease of the antenna gain or the radiant efficiency.
A first object of the present invention is to provide a loop antenna device which inhibits the unnecessary radiation of the electric wave and which can increase the sending speed of data placed on the electric wave. A second object of the present invention is to provide a loop antenna device which can achieve the first object and which can perform the damping to the resonant circuit without influencing the antenna gain or the radiant efficiency greatly.
SUMMARY OF THE INVENTION
The invention according to one aspect provides a loop antenna device comprising;
a first loop antenna constituting a resonant circuit by a coil and a resonant capacitor and resonating on the basis of a high frequency signal of a resonant frequency intermittently outputted from an oscillation means; a second loop antenna constituting a resonant circuit by a coil and a resonant capacitor and resonating by an inductive electromotive force led by a mutual induction via a link coil when the first antenna resonates; and a damping means for compulsory eliminating a discharge phenomenon of the resonant capacitor when the radiation of an electric wave is completed and connected to at least one of the first loop antenna and the second loop antenna.
When the first loop antenna resonates by the high frequency signal of the resonant frequency, the second loop antenna resonates by the mutual induction via the link coil and an electric wave is radiated from the loop antenna device. When the radiation of the electric wave is completed, the electric charge stored in the resonant capacitor of the resonant circuit is discharged and a discharge phenomenon generates. However, since this stored energy is consumed as a heat energy by the damping means and the discharge phenomenon is compulsory eliminated, the unnecessary radiation of the electric wave is inhibited. Thereby, it is unnecessary to set a time margin until the unnecessary radiation of the electric wave is completed and the sending speed of data placed on the electric wave can be increased.
The damping means is a switching means whose ON-OFF condition is changed by a digital control signal outputted from a control means, and the resonant circuit constitutes a closed circuit when the switching means is in the ON condition on the basis of the control signal, and the discharge phenomenon of the resonant capacitor is compulsory eliminated by the switching means when the switching means is in the OFF condition in response to the change of the level of the control signal.
When the switching means becomes the ON condition on the basis of the control signal outputted from the control means, the resonant circuit constitutes a closed circuit and resonates. When the level of the control signal is changed and the radiation of the electric wave is completed, the switching means becomes the OFF condition and an internal resistance is generated in the switching means. The electric charge stored in the resonant capacitor is consumed at once as a heat energy by the internal resistance. Thereby, the unnecessary radiation of the electric wave is inhibited.
The switching means are provided on both of the first and second loop antennas and are changed between the ON-OFF condition by the same control signal.
The discharge phenomenon generated in both of the resonant capacitors of the first and second loop antennas is compulsorily eliminated and the reliability of the loop antenna device is improved.
The invention according to another aspect provides a loop antenna device comprising; a first loop antenna constituting a
Hatano Rikuo
Ieda Kiyokazu
Murakami Yuichi
Mushiaki Eiji
Aisin Seiki Kabushiki Kaisha
Burns Doane , Swecker, Mathis LLP
Ho Tan
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