Communications: radio wave antennas – Antennas – With radio cabinet
Reexamination Certificate
2002-06-24
2004-01-13
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
With radio cabinet
C343S7000MS, C343S895000
Reexamination Certificate
active
06677907
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an antenna device and a mobile terminal and more particularly to an antenna device contained in a mobile phone and a mobile phone using the antenna device.
BACKGROUND ART
Antennas contained in housings of mobile phones are conventionally known as receiving/transmitting antennas for the mobile phones.
These antennas are classified into linear antennas and plate antennas depending on their characteristics.
FIG. 20
is a schematic plan view of a mobile phone containing a dipole antenna that is one of conventional linear antennas. Referring to
FIG. 20
, a conventional mobile phone
1
x
has a housing
10
and an antenna device
3
x
accommodated in housing
10
. Antenna device
3
x
has a substrate
11
and a dipole antenna
121
provided on substrate
11
. Dipole antenna
121
has two meander-like antenna portions
121
a
and
121
b
respectively connected to a feed point
12
. The electrical length of dipole antenna
121
is &lgr;/2.
During a call, the direction in which such a dipole antenna
121
extends (the direction indicated by an arrow
125
) is approximately at a 30° angle with respect to a vertical direction. Therefore, dipole antenna
121
is known as an antenna which allows for reduction of polarization loss for a wave polarized vertically to the ground (a vertically polarized wave) at the time of a call.
FIG. 21
is a diagram showing a radiation pattern of the conventional dipole antenna shown in FIG.
20
. As shown in
FIG. 21
, when mobile phone
1
x
is placed upright, particularly when the electrical length of the antenna is &lgr;/2×A (A is an integer), a null point
134
of the radiation pattern as indicated by solid lines
131
and
132
is in a horizontal plane. This disadvantageously reduces the gain.
FIG. 22
is a graph showing the relation between the electrical length of the antenna and the current distribution on the antenna element in the conventional dipole antenna. As shown in
FIG. 22
, in the dipole antenna having an electrical length of &lgr;/2, the maximum value of the current distribution exists at the portion where the electrical length of the antenna is &lgr;/4, that is, at the central portion of the antenna. As a hand easily touches this portion, an antenna gain degrades particularly when a hand touches it.
FIG. 23
is a plan view of a mobile phone having a conventional plate antenna. Referring to
FIG. 23
, a mobile phone
1
y
has a housing
10
and an antenna device
3
y
accommodated in housing
10
. Antenna device
3
y
has a substrate
11
and a plate antenna
122
provided on substrate
11
. Plate antenna
122
is connected to a feed point
12
.
Such a plate antenna
122
easily receives and transmits both a vertically polarized wave and a horizontally polarized wave with respect to the ground. Advantageously, degradation amount of gains when a finger touches the antenna is small as compared with a linear antenna, since the current in the vicinity of the feed point is dispersed.
Plate antenna
122
, however, for example a patch antenna, requires about &lgr; as the total perimeter of the antenna, the size of the antenna inevitably increases and thus mobile phone
1
y
itself increases in size.
The present invention is therefore made to solve the above problems. An object of the present invention is to provide an antenna device capable of receiving and transmitting both a vertically polarized wave and a horizontally polarized wave, being reduced in size and having small gain degradation during a call.
DISCLOSURE OF THE INVENTION
An antenna device in accordance with the present invention includes a substrate and an antenna provided on the substrate and having an electrical length of approximately (&lgr;/2)×A (A is an integer). The antenna includes a plate antenna portion positioned at a portion where an electrical length from an end portion is approximately &lgr;/4+(&lgr;/2)×B (B is an integer), and a linear antenna portion connected to the plate antenna.
In the antenna device thus configured, the linear antenna portion can mainly receive and transmit either one of a vertically polarized wave or a horizontally polarized wave, and the plate antenna portion can receive and transmit both the vertically polarized wave and the horizontally polarized wave. As a result, both the vertically polarized wave and the horizontally polarized wave can be received and transmitted, resulting in a high gain antenna.
Furthermore, since the electrical length of the antenna is approximately (&lgr;/2)×A (A is an integer), the current is large at the portion where the electrical length from the end portion of the antenna is approximately &lgr;/4+(&lgr;/2)×B (B is an integer). However, this portion is provided with the plate antenna portion and therefore the current can be distributed. Accordingly, even when a finger is placed on this portion, degradation in gain can be reduced.
Furthermore, since the antenna includes the linear antenna portion, the antenna can be reduced in size as compared with an antenna configured only with a plate antenna portion.
More specifically, the present invention can provide an antenna having a high gain even at the time of a call, assuring a gain when the terminal is placed upright, and having a small size.
Preferably, the linear antenna portion includes at least one selected from the group consisting of a monopole antenna, a zigzag antenna, a meander line antenna and a helical antenna.
More preferably, the substrate has a main surface having conductivity. The antenna further includes a connection portion connected to the main surface of the substrate. In this case, since the antenna is connected to the main surface having conductivity, an image is formed on the substrate. As a result, the electrical length of the antenna is approximately double the physical length of the antenna, so that the physical length of the antenna can be shortened. Therefore, the antenna device can be reduced in size.
Preferably, the substrate has a main surface and a side surface continuous with the main surface, and the antenna is provided on the side surface. In this case, since the main surface is not provided with an antenna, other device and the like can be placed on the main surface.
A mobile terminal in accordance with the present invention includes a housing and an antenna device contained in the housing. The antenna device includes a substrate and an antenna provided on the substrate and having an electrical length of approximately (&lgr;/2)×A (A is an integer). The antenna includes a plate antenna portion positioned at a portion where an electrical length from an end portion is approximately &lgr;/4+(&lgr;/2)×B (B is an integer), and a linear antenna portion connected to the plate antenna portion.
In the mobile terminal thus configured, the linear antenna portion can mainly receive and transmit either one of a vertically polarized wave or a horizontally polarized wave and a plate antenna portion can receive and transmit both the horizontally polarized wave and the vertically polarized wave. As a result, both the vertically polarized wave and the horizontally polarized wave can be received and transmitted, resulting in a mobile terminal having a high gain antenna device.
Furthermore, since the electrical length of the antenna is approximately (&lgr;/2)×A (A is an integer), the current is large at the portion where the electrical length from the end portion of the antenna is approximately &lgr;/4+(&lgr;/2)×B (B is an integer). However, since this portion is provided with the plate antenna portion, the current can be dispersed. Therefore, even when a finger or the like is placed on this portion, degradation in gain can be reduced.
Furthermore, the antenna includes the linear antenna portion, and thus the antenna and the mobile terminal can be reduced in size as compared with an antenna configured only with a plate antenna portion.
In addition, since the antenna device is contained in the housing, the antenna device is less affe
Fukasawa Toru
Imanishi Yasuhito
Ohmine Hiroyuki
Shoji Hideaki
Ho Tan
Mitsubishi Denki & Kabushiki Kaisha
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