Communications: radio wave antennas – Antennas – With radio cabinet
Reexamination Certificate
2001-11-13
2003-05-06
Clinger, James (Department: 2821)
Communications: radio wave antennas
Antennas
With radio cabinet
Reexamination Certificate
active
06559803
ABSTRACT:
This application claims priority to an application entitled “Portable Communication Terminal with Reduced Specific Absorption Rate”, filed in the Japanese Patent Office on Nov. 13, 2000 and assigned Serial No. 2,000-345,450, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a portable communication terminal, and in particular, to a portable communication terminal with a reduced specific absorption rate (an indicator of the influence of electric waves on the human body).
2. Description of the Related Art
As the use of electronic and electric appliances has rapidly increased, much attention has been paid to the effects on the human body, in particular, the head, when it is exposed to electromagnetic waves radiated from these electronic and electromagnetic appliances. In particular, a specific absorption rate (SAR) is used to quantify the amount of electromagnetic energy absorbed by the human body exposed to electromagnetic waves radiated from a portable communication terminal such as a portable telephone, personal handyphone system (PHS) or personal digital assistant (PDA). In such a portable communication terminal, current concentrates on the antenna of the terminal. As a result, electromagnetic fields are concentrated about the head of the user to which a radiation source, i.e., the feeding point of the antenna, is closely positioned. This results in an increase in SAR. Currently, a number of research efforts are being made to achieve a reduction in SAR. Also, guidelines for the protection of the human body from electromagnetic waves are being established.
FIGS. 8
a
and
8
b
illustrate the structure of a monopole antenna commonly used in conventional portable telephones, and current and voltage distributions exhibited during the operation of the antenna. Referring to
FIG. 8
a,
a printed circuit board (PCB)
1
mounted to a phone body is illustrated. As shown in
FIG. 8
a,
a ¼·&lgr; monopole antenna
2
is connected to the PCB
1
via a feeding point
3
. The monopole antenna
2
includes a pole and an antenna earth plate. Antenna current Ia flowing through the antenna
2
causes earth current Ie to flow through the PCB
1
serving as the earth plate.
FIGS. 9
a
and
9
b
illustrate distributions of near electric field and near magnetic field formed by the antenna current Ia and earth current Ie flowing through the antenna
2
as illustrated in
FIG. 8
b.
In
FIGS. 9
a
and
9
b,
the reference numeral
4
denotes a phone body, and the reference numeral
5
denotes the head of the user. As shown in
FIGS. 9
a
and
9
b,
electromagnetic fields caused by the earth current Ie concentrate on a position near the head
5
. As a result, an increase in SAR occurs.
It may be possible to achieve a reduction in SAR in the above-mentioned configuration by reducing the intensity of near electromagnetic fields acting around the head of the user. In this configuration, however, the antenna structure of
FIGS. 8
a
and
8
b
has the following problems:
(1) In the above mentioned ¼·&lgr; monopole antenna structure, earth current Ie flows through the PCB
1
of the phone body
4
because the PCB
1
serves as an earth plate. However, it is difficult to control the earth current Ie flowing through the PCB
1
. For this reason, it is difficult to control near electromagnetic fields in order to reduce the intensity thereof;
(2) Antenna current Ia concentrates on a position near the feeding point
3
of the antenna. However, the head
5
is typically positioned close to the feeding point
3
; and
(3) Taking into consideration this fact, use of a separate shield plate has been proposed in order to reduce radiation of electromagnetic intensity toward the head. In the above mentioned monopole antenna structure, however, poor shielding effects are obtained because the earth current Ie flowing through the PCB also flows through the shield plate.
SUMMARY OF THE INVENTION
Therefore, the present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a portable communication terminal having an antenna structure capable of reducing the intensity of electromagnetic fields acting around the head of the user without preventing earth current from flowing through a PCB of the terminal.
In accordance with the present invention, this object is accomplished by providing a portable communication terminal comprising: an antenna board mounted to a surface of a printed circuit board mounted with at least one speaker, the surface of the printed circuit board being opposite to a speaker-mounted surface of the printed circuit board; a first antenna element formed, in the form of an antenna pattern, on the antenna board; a coaxial cable for feeding power to the first antenna element; and a first dielectric sleeve mounted to a tip of the coaxial cable.
The portable communication terminal may further comprise a second antenna element formed in the form of an antenna pattern on the antenna board, and a second coaxial cable coaxially fitted around the first dielectric sleeve. The antenna board and the dielectric sleeves may be electrically suspended from the printed circuit board.
REFERENCES:
patent: 6005524 (1999-12-01), Hayes et al.
patent: 6031503 (2000-02-01), Preiss, II et al.
patent: 6259417 (2001-07-01), Kim et al.
Clinger James
Dilworth & Barrese LLP
Samsung Yokohama Research Institute
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