Communications: radio wave antennas – Antennas – With radio cabinet
Reexamination Certificate
2001-04-13
2003-03-11
Le, Hoanganh (Department: 2821)
Communications: radio wave antennas
Antennas
With radio cabinet
C343S900000, C343S901000
Reexamination Certificate
active
06531986
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an antenna for wireless mobile communication systems and more particularly, to a retractable or extendable antenna for portable radio device, such as portable information terminals, portable or cellular phones, and so on, which is capable of improving impedance matching in the extended state and the retracted state.
2. Description of the Related Art
Conventionally, there are-several types of antennas for wireless mobile communication systems. An antenna of this type designed for portable radio device such as cellular phones typically has a linear whip element and a helical element fixed to one end of the whip element. The antenna is attached to the casing of the device in such a way that the whip element can be retracted into the casing and can be pulled out therefrom as necessary.
With the conventional portable radio devices having the antenna of this type, when the user operates the device, the whip antenna element is usually extended from the casing to reduce the antenna performance degradation due to the bad effect caused by the user himself or herself (ie., a human body). On the other hand, when the user does not operate the device, the whip element is retracted into the casing to facilitate carrying of the device.
When the antenna is pulled out from the casing, the whip and helical elements are located outside the casing. In this extended state, only the whip element is active and provides the desired antenna operation. On the other hand, when the antenna is pushed into the casing, the whip element is retracted into the casing while the helical element is located outside. In this retracted state, only the helical element is active and provides the desired antenna operation.
An example of the conventional antenna structures of this type is disclosed in the Japanese Non-Examined Patent Publication No. 9-186519 published in 1997 (which corresponds to the Japanese Patent No. 2,692,670 issued in 1999)
FIGS. 1A and 1B
show schematically the structure of a prior-art antenna
101
of this type.
The antenna
101
, which is mounted slidably on a casing
120
, comprises a conductive, linear whip element
106
and a conductive helical (i.e., coil-shaped) element
117
.
The whip element
106
is covered with a dielectric protection film
107
. A conductive stopper
109
is fixed to the bottom end of the element
106
. The stopper
109
prevents the element
106
from being detached from the casing
120
and serves to feed electric power to the element
106
in the extended state. A feeder or feeding part
104
is fixed to the top end of the element
106
by way of a dielectric separator
105
. The feeder
104
serves to feed electric power to the element
106
when the element
106
is retracted into the casing
120
. The separator
105
serves to separate electrically the helical element
117
from the whip element
106
.
The helical element
117
, which is covered with a dielectric
102
, is fixed to the feeder
104
at its opposite side to the whip element
106
. The helical element
117
is electrically disconnected from the whip element
106
with the separator
105
.
The antenna
101
is attached slidably to the casing
120
with a conductive support
108
. The support
108
is fixed to the casing
120
and is electrically connected to a specific radio circuit (not shown) provided in the casing
120
.
When the whip element
106
is pulled out from the casing
120
(i.e., the antenna
101
is in the extended state), as shown in
FIG. 1A
, both the whip and helical elements
106
and
117
are located outside the casing
120
and at the same time, the stopper
109
is contacted with the support
108
. In this state, the whip element
106
is electrically connected to the radio circuit provided in the casing
120
by way of the stopper
109
and the support
108
, thereby feeding electric power to the element
106
. Thus, the element
106
is activated and performs its operation.
On the other hand, when the whip element
106
is pushed into the casing
120
(i.e., the antenna
101
is in the retracted state), as shown in
FIG. 1B
, only the helical element
117
is located outside the casing
120
and at the same time, the feeder
104
is contacted with the support
108
. In this state, the helical element
117
is electrically connected to the radio circuit provided in the casing
120
by way of the feeder
104
and the support
108
, thereby feeding electric power to the element
117
. Thus, the element
117
is activated and performs its operation.
As explained above, only the whip element
106
is activated when the antenna
101
is in the extended state while only the helical element
117
is activated in the retracted state. Therefore, impedance matching can be improved in each state. Thus, in recent years, the prior-art antenna
101
has been extensively used for portable radio devices such as cellular phones.
FIG. 2
shows a graph showing the relationship between the bandwidth of the prior-art antenna
101
and the length of the casing
120
in the retracted state. The curves of
FIG. 2
indicate the bandwidth values where the return loss is equal to or less than −10 dB. The curves were obtained by numeric calculation under the condition that the resonance frequency of the helical element
117
was set as 800 MHz and 1.5 GHz without changing the shape and size of the element
117
.
As seen from
FIG. 2
, the bandwidth varies as the casing length changes when the operating frequency is 800 MHz. This means that there is a value of the casing length that maximizes the bandwidth. Unlike this, when the operating frequency is 1.5 GHz, the bandwidth is kept approximately constant in spite of change of the casing length. Thus, it is unable to be said that there is a value of the casing length that maximizes the bandwidth. Also, as seen from
FIG. 2
, the bandwidth for 1.5 GHz is as low as approximately equal to half (½) to one-fifth (⅕) the bandwidth for the 800 MHz.
As described above, with the prior-art antenna
101
shown in
FIGS. 1A and 1B
, there is a problem that the obtainable bandwidth for the operating frequency of 1.5 GHz is not as wide as desired in the retracted state. In other words, satisfactory impedance matching is not implemented with respect to the helical element
117
that is activated in the retracted state.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a retractable/extendable antenna for portable radio device that expands the bandwidth for the operating frequency of 1.5 GHz.
Another object of the present invention is to provide a retractable/extendable antenna for portable radio device that makes it possible to realize satisfactory impedance matching in both the extended and retracted states.
The above objects together with others not specifically mentioned will become clear to those skilled in the art from the following description.
According to a first aspect of the present invention, a retractable/extendable antenna for portable radio device is provided, which is operable in an extended state and a retracted state. The antenna comprises:
(a) a casing;
(b) a first antenna element attached retractably or extendably to the casing;
the first element being formed by a linear antenna element;
the first element being located outside the casing and fed with electric power to be active in the extended state;
the first element being located inside the casing and fed with no electric power to be inactive in the retracted state; and
(c) a second antenna element connected mechanically to one end of the first element and disconnected electrically therefrom;
the second element being formed by a linear antenna element and shorter than the first element;
the second element being located outside the casing and fed with no electric power to be inactive in the extended state;
the second element being located outside the casing and fed with electric power to be active in the retracted state.
With the retractable/extendable ante
Le Hoang-anh
NEC Corporation
Scully Scott Murphy & Presser
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