Communications: radio wave antennas – Antennas – With radio cabinet
Reexamination Certificate
2002-05-30
2004-08-24
Clinger, James (Department: 2821)
Communications: radio wave antennas
Antennas
With radio cabinet
C343S900000
Reexamination Certificate
active
06781550
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an antenna device and a portable equipment, and more particularly, relates to an antenna device capable of preventing degradation in antenna gain during a call, and a portable equipment using the same.
BACKGROUND ART
Recently, mobile phones are increasingly becoming widespread.
FIG. 17
is a schematic diagram of a conventional mobile phone, and
FIG. 18
shows a schematic cross-sectional view taken along line XVIII—XVIII of
FIG. 17 and a
schematic graph of a current distribution in an antenna. The conventional mobile phone will now be described with reference to
FIGS. 17 and 18
.
Referring to
FIGS. 17 and 18
, a conventional mobile phone
101
includes in its main body a liquid crystal display portion
105
, operation keys
106
for inputting a telephone number and the like, a speaker
104
and a microphone
103
for listening and speaking over the phone, respectively, and an antenna for communication with a base station. The antenna, which is formed from a non-retracted antenna
151
and a linear extension antenna
102
, is retractable in the main body of mobile phone
101
.
FIGS. 17 and 18
show the state where the antenna is retracted in the main body of mobile phone
101
. As shown in
FIGS. 17 and 18
, when the antenna is retracted in main body
108
of mobile phone
101
, non-retracted antenna
151
sticks out of main body
108
, and extension antenna
102
is accommodated within main body
108
. On the other hand, when mobile phone
101
is used for a phone call or the like, the antenna is stretched out of main body
108
of mobile phone
101
as shown in
FIG. 19
so that extension antenna
102
is exposed outside main body
108
.
FIG. 19
shows a schematic cross sectional view of the state where the antenna is stretched out of the main body of the mobile phone of
FIG. 17 and a
schematic graph of a current distribution in the antenna.
FIG. 19
corresponds to FIG.
18
.
Referring to
FIGS. 18 and 19
, the mobile phone includes a metal boss
150
in order to fix the antenna formed from non-retracted antenna
151
and linear extension antenna
102
to main body
108
in a stretchable manner. Metal boss
150
is a cylindrical boss having a hole, and the antenna is slidably inserted into the hole. When the antenna is retracted as shown in
FIG. 18
, the antenna is fixed by contact between the sidewall of the hole in metal boss
150
and the surface of the region of the antenna that is located under non-retracted antenna
151
. When the antenna is stretched as shown in
FIG. 19
, the antenna is fixed by contact between the sidewall of the hole in metal boss
150
and the surface of an antenna end
111
located at the end of the antenna.
Metal boss
150
is fixed to a housing of main body
108
of mobile phone
101
, and the like. Main body
105
of mobile phone
101
accommodates therein a circuit substrate
109
having transmitting/receiving circuit elements arranged thereon. A power feed pin
110
is mounted on the surface of circuit substrate
109
. Power feed pin
110
contacts the outer peripheral surface of metal boss
150
.
When the antenna is retracted as shown in
FIGS. 17 and 18
, the circuit elements formed on circuit substrate
109
are electrically connected to non-retracted antenna
151
through power feed pin
110
, metal boss
150
and the region of the antenna that is located under non-retracted antenna
151
. Moreover, when the antenna is stretched as shown in
FIG. 19
, the circuit elements formed on circuit substrate
109
are electrically connected to extension antenna
102
through power feed pin
110
, metal boss
150
and antenna end
111
.
However, the conventional mobile phone of
FIGS. 17
to
19
has the following problems.
Since metal boss
150
contacting the antenna is also a conductor, it acts as if it were a part of antenna when the antenna transmits and receives radio waves. For example, when a current flows through non-retracted antenna
151
of
FIG. 18
(e.g., when non-retracted antenna
151
receives radio waves), it flows not only through non-retracted antenna
151
but also through metal boss
150
. Moreover, when extension antenna
102
of
FIG. 19
transmits and receives radio waves, a current flows not only through extension antenna
102
but also through metal boss
150
. In other words, due to the presence of metal boss
150
, non-retracted antenna
151
and extension antenna
102
act as if they were an antenna having an electrically discontinuous diameter. Accordingly, the current distribution in the antenna does not have a sinusoidal profile, as shown in
FIGS. 18 and 19
. With such a non-sinusoidal current distribution in the antenna, target impedance characteristics cannot be obtained even if the respective lengths of non-retracted antenna
151
and extension antenna
102
are designed so that they resonate in response to the radio waves of a target frequency.
Moreover, as shown in
FIGS. 18 and 19
, the presence of metal boss
150
increases a current value in the region near main body
108
of mobile phone
101
. This results in increased electric-field and magnetic-field strengths (electromagnetic-field strength) in the region near main body
108
. The user holds main body
108
of mobile phone
101
by hand and also holds main body
108
near the head for a phone call. In this case, since metal boss
150
of main body
108
located in a region relatively close to the human body produces a relatively strong electromagnetic field, the presence of the human body affects the antenna gain more strongly. The antenna gain is thus reduced by the influence of the human body, resulting in degraded communication quality.
Moreover, metal boss
150
is formed from a metal having relatively larger specific gravity than a material of the housing of mobile phone
101
and the like such as plastic. Reduction in size and weight has been strongly demanded for mobile phone
101
, and the use of a metal boss is one of the factors that hinder reduction in weight of the mobile phone.
The present invention is made to solve the above problems, and it is an object of the present invention to provide an antenna device and a portable equipment that are capable of preventing degradation in communication quality.
It is another object of the present invention to provide an antenna device and a portable equipment that enable reduction in weight.
DISCLOSURE OF THE INVENTION
An antenna device according to one aspect of the present invention includes a linear antenna, a fixing member and a power feed member. The fixing member is formed from a dielectric, and holds a portion of the antenna. The power feed member contacts the antenna. The fixing member holds the antenna in a movable manner.
In this structure, the fixing member such as a boss for holding a portion of the antenna is formed from a dielectric, whereby the antenna and the fixing member can be prevented from acting as if they were an antenna having an electrically discontinuous diameter. As a result, a current flowing through the antenna can be prevented from unnecessarily flowing through the fixing member. This enables the current distribution in the antenna to have an approximately sinusoidal profile, whereby the impedance characteristics of the antenna can be prevented from being varied from the designed characteristics.
When the antenna device of the present invention is applied to a portable equipment such as a mobile phone, the fixing member is mounted to the main body of the portable equipment. In using such a portable equipment, the main body thereof is often held by hand and retained near the head of the human body. In other words, the fixing member is located in a region relatively close to the human body. In the antenna device of the present invention, the fixing member is formed from a dielectric, so that no current will unnecessarily flow through the fixing member. Accordingly, an electromagnetic field that is conventionally formed by the current flowing through the fixing member will not be formed. Since a current flowing th
Fukasawa Toru
Imanishi Yasuhito
Ohmine Hiroyuki
Shoji Hideaki
Clinger James
Mitsubishi Denki & Kabushiki Kaisha
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