Communications: radio wave antennas – Antennas – With radio cabinet
Reexamination Certificate
2001-07-03
2002-10-22
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
With radio cabinet
C343S841000, C343S851000
Reexamination Certificate
active
06469670
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an antenna device and a portable radio communication device, and particularly to an antenna device and a portable radio communication device capable of reducing electromagnetic waves which are generated therefrom and are to be absorbed into a human body.
2. Description of Related Art
Recently, portable data transmitting/receiving devices capable of transmitting/receiving information by radio communication are significantly developed. Of the portable data transmitting/receiving devices, portable radio communication devices for use in the PHS (Personal Handyphone System) system are spreading rapidly.
The portable radio communication device usually has an antenna for transmitting/receiving signals. Actually, the portable radio communication device itself works as an antenna, and the main body of the portable radio communication device other than the antenna portion also generates electromagnetic waves. So, it is required that, of the electromagnetic waves generated from the portable radio communication device, those to be absorbed into a human body should be suppressed. Specifically, of the electromagnetic waves generated from the portable radio communication device in use, amount of electromagnetic waves to be absorbed into a specific portion of a human body, particularly a head portion, per unit-time per unit-weight is defined as local average SAR (Specific Absorption Rate), and the maximum value of the local average SAR is required to be not more than a prescribed value.
To reduce the maximum value of the local average SAR to be absorbed into a human body, a conductive plate of a predetermined shape may be used. In this case, the conductive plate has its one end connected to a ground conductor which works as an antenna to form a short circuit, and has its other end electrically released from the ground conductor. As a result, input impedance of the electrically released end becomes approximately infinite. At this time, high-frequency current flowing to the ground conductor is suppressed, and thus amount of radiation of the electromagnetic waves is reduced.
FIG. 1
shows a schematic view of a portable radio communication device
20
, which can reduce the maximum value of the local average SAR. The portable radio communication device
20
includes a circuit board (not shown) necessary for performing radio communication, shield case
21
as a ground conductor which shields the circuit board, a conductive plate
22
, an antenna feeding portion
23
, and an antenna
24
. The circuit board, shield case
21
, and conductive plate
22
are enclosed by a housing (not shown) made of nonconductive material. The conductive plate
22
and shield case
21
are connected by a conductor
25
to form a short circuit.
Since the circuit board is shielded by the shield case
21
, various circuits including a transmitting/receiving circuit for communicating with a base station which are mounted on the circuit board do not have bad effects upon each other, and also do not have bad effects upon the antenna
24
and other devices.
The transmitting/receiving circuit on the circuit board in the shield case
21
generates transmission signals of a predetermined signal form, and sends the transmission signals to the antenna
24
via the antenna feeding portion
23
. Then, the antenna
24
transmits the transmission signals to the base station. The antenna
24
receives reception signals from the base station, and sends the reception signals to the transmitting/receiving circuit via the antenna feeding portion
23
. Then, the transmitting/receiving circuit performs processing for the reception signals such as demodulating.
The antenna
24
is a rod antenna made of conductive wire materials, or a helical antenna made of conductive wire materials wound spirally. Otherwise, the antenna
24
may be an antenna of various types such as a stretch type antenna combining the rod antenna and helical antenna. When the portable radio communication device
20
performs radio communication, since the high-frequency current flows to the shield case
21
via the antenna feeding portion
23
, not only the antenna
24
but also the shield case
21
as a ground conductor for the circuit board works as an antenna. That is, whole the portable radio communication device
20
works as an antenna.
When the portable radio communication device
20
is used, the user comes into contact with a speaker of the portable radio communication device
20
. Since the shield case
21
as a ground conductor for the circuit board located behind the speaker also works as an antenna and radiates electromagnetic waves, there will be formed a portion where the value of the local average SAR becomes maximum around an ear of the user which comes into contact with the speaker, and this portion will be referred to as a hot spot.
The portable radio communication device
20
has the conductive plate
22
arranged such that the speaker (not shown) faces the conductive plate
22
, and the conductive plate
22
and a front surface
21
a
of the shield case
21
are approximately parallel with each other with a slight interval therebetween. The interval between the conductive plate
22
and the front surface
21
a
of the shield case
21
depends on a radio communication frequency, and the portable radio communication device
20
can adjust the frequency bandwidth in accordance with the interval.
The conductive plate
22
has its one end along the longitudinal direction connected to the shield case
21
to form a short circuit via the conductor
25
, and has its other end electrically released from the shield case
21
. The length L
3
between the short circuit forming end and the electrically released end is set to be a quarter of the radio communication frequency.
Accordingly, the impedance between the conductive plate
22
and the shield case
21
becomes close to zero at the short circuit forming end, while becoming approximately infinite at the electrically released end. Thus, the high-frequency current has difficulty in flowing from the antenna feeding portion
23
to the conductive plate
22
and the shield case
21
.
As has been described, as an example to reduce the maximum value of the local average SAR to be absorbed into a human body, the portable radio communication device
20
mounts a conductive plate
22
thereto, and reduces the amount of radiation of the electromagnetic waves from the conductive plate
22
and shield case
21
. Thus, the local average SAR of the hot spot can be reduced.
So as to form a short circuit surely between the conductive plate
22
and the shield case
21
of the portable radio communication device
20
, the configuration of the short circuit forming end becomes complicated since, for example, the conductor
25
has to have elasticity. Thus, such configuration leads to high production cost and growth of weight caused by increase of the number of parts etc.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to overcome the above-mentioned drawbacks by providing an antenna device and a portable radio communication device which can reduce the maximum value of the local average SAR to be absorbed into a human body without forming a short circuit between the conductive plate and the ground conductor.
According to the present invention, there is provided an antenna device having an antenna element and a ground conductor which work as an antenna, in which the antenna element is fed via an antenna feeding portion and high-frequency current flows to the ground conductor via the antenna feeding portion, the antenna device including:
high-frequency current suppressing means being a conductive plate of a predetermined shape which has its both ends along one direction electrically opened from the ground conductor.
Furthermore, according to the present invention, there is provided a portable radio communication device which has an antenna device having an antenna element and a ground conductor which work as an antenna
Chen Shih-Chao
Ho Tan
Maioli Jay H.
Sony Corporation
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