Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2002-04-15
2003-09-02
Wimer, Michael C. (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S702000
Reexamination Certificate
active
06614398
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to communication apparatuses, such as mobile communication apparatuses, and to antenna structures included in such apparatuses.
2. Description of the Related Art
One type of small antenna provided in mobile communication apparatuses, such as mobile telephones and GPS (Global Positioning System) apparatuses, is a surface-mounted antenna that is produced by forming a radiating electrode on a dielectric or magnetic base member. The radio-wave transmission/reception frequency of the surface-mounted antenna, that is, the resonant frequency of the radiating electrode, is determined by the complex relationship among various factors including the size of the base member, the dielectric constant of the base member when the base member is made of dielectric material, and the size and the shape of the radiating electrode.
When changing the radio-wave transmission/reception frequency of the surface-mounted antenna, that is, when changing the resonant frequency of the radiating electrode, a great amount of time and labor is required to design the surface-mounted antenna. As a result, the cost of the surface-mounted antenna increases.
An antenna structure
1
such as that shown in
FIG. 10A
is proposed. The antenna structure
1
contains a surface-mounted antenna
2
, a board-side control electrode
4
disposed on a mounting board
3
(a circuit board of a communication apparatus), a switch circuit
5
, and a ground conductor
6
. The surface-mounted antenna
2
is a &lgr;/4 transmission line type and is formed by a dielectric or magnetic base member
7
, a radiating electrode
8
, a ground electrode
9
, a feeding electrode
10
, and an antenna-side control electrode
11
.
In the surface-mounted antenna
2
, the ground electrode
9
is disposed on a bottom surface
7
b
of the base member
7
, and the radiating electrode
8
is arranged to extend from a side surface
7
f
to a top surface
7
a
. A first end of the radiating electrode
8
communicates and connects with the ground electrode
9
, thus defining a ground end. A second end of the radiating electrode
8
defines an open end
8
a
. A portion of the open end
8
a
extends from the top surface
7
a
to the side surface
7
d
of the base member
7
.
A first end of the antenna-side control electrode
11
opposes the extended portion of the open end
8
a
with a gap therebetween. A capacitance is generated between the open end
8
a
of the radiating electrode
8
and the antenna-side control electrode
11
. A second end of the antenna-side control electrode
11
is arranged such that it wraps around the side surface
7
d
to the bottom surface
7
b
of the base member
7
. The second end of the antenna-side control electrode
11
opposes the ground electrode
9
with a gap therebetween. The antenna-side control electrode
11
electrically floats.
The feeding electrode
10
is arranged to extend from the bottom surface
7
b
through the side surface
7
d
to the top surface
7
a
of the base member
7
. A top end of the feeding electrode
10
opposes the open end
8
a
of the radiating electrode
8
with a gap therebetween. A second end of the feeding electrode
10
opposes the ground electrode
9
with a gap therebetween.
On the mounting board
3
, a region in which the surface-mounted antenna
2
is mounted is a groundless portion in which the ground conductor
6
is not provided. The board-side control electrode
4
, which electrically floats, and the switch circuit
5
are disposed on the groundless portion. A signal supply source
12
is disposed on the mounting board
3
. A feeding wiring pattern
13
which is electrically connected with the signal supply source
12
is provided on the groundless portion.
In order to mount the surface-mounted antenna
2
on the mounting board
3
, the surface-mounted antenna
2
is mounted on the groundless portion of the mounting board
3
so that the antenna-side control electrode
11
of the surface-mounted antenna
2
is electrically connected with the board-side control electrode
4
of the mounting board
3
, so that the board-side control electrode
4
and the antenna-side control electrode
11
electrically float, and such that the feeding electrode
10
of the surface-mounted antenna
2
is electrically connected with the feeding wiring pattern
13
of the mounting board
3
.
In this state, when the signal supply source
12
supplies a signal through the feeding wiring pattern
13
to the feeding electrode
10
of the surface-mounted antenna
2
, the signal is transferred from the feeding electrode
10
to the radiating electrode
8
by capacitive coupling, and the radiating electrode
8
is excited. Thus, radio waves can be transmitted or received.
FIG. 10B
shows an equivalent circuit diagram of the antenna structure
1
. Referring to
FIG. 10B
, L denotes the inductance of the radiating electrode
8
, R
1
denotes the radiation resistance of the radiating electrode
8
, R
2
denotes the internal resistance of the radiating electrode
8
, C
1
denotes the capacitance between the open end
8
a
of the radiating electrode
8
and the antenna-side control electrode
11
, C
2
denotes the capacitance between the open end
8
a
of the radiating electrode
8
and the feeding electrode
10
, and C
3
denotes the capacitance between the radiating electrode
8
and the ground.
In the antenna structure
1
, when the switch circuit
1
is switched on and when the board-side control electrode
4
is grounded through the switch circuit
5
, the capacitance C
1
between the open end
8
a
of the radiating electrode
8
and the board-side control electrode
4
influences the resonant frequency of the radiating electrode
8
. In contrast, when the switch circuit
5
is switched off, the capacitance C
1
does not influence the resonant frequency of the radiating electrode
8
. Accordingly, the influence of the capacitance C
1
on the radiating electrode
8
varies according to whether or not the switch circuit
5
is switched on or off, and hence the resonant frequency of the radiating electrode
8
varies.
In the antenna structure
1
arranged as described above, the resonant frequency of the radiating electrode
8
can be easily changed by switching the switch circuit
5
on or off without changing the size and the shape of the radiating electrode
8
of the surface-mounted antenna
2
or the size of the base member
7
.
In the antenna structure
1
, the structure of the switch circuit
5
is complex, and the switch circuit
5
is expensive. Thus, the antenna structure
1
is not commercially feasible.
SUMMARY OF THE INVENTION
In order to solve the foregoing problems, preferred embodiments of the present invention provide an antenna structure which has a simple configuration and which is capable of easily changing the resonant frequency of a radiating electrode without changing a surface-mounted antenna. In addition, preferred embodiments of the present invention provide a communication apparatus including such a novel antenna structure.
In order to achieve the foregoing advantages, preferred embodiments of the present invention, an antenna structure includes a surface-mounted antenna including a radiating electrode disposed on a base member, the surface-mounted antenna being a &lgr;/4 transmission line type, a first end of the radiating electrode being a ground end and a second end of the radiating electrode being an open end, a mounting board on which the surface-mounted antenna is mounted, an antenna-side control electrode disposed on the base member of the surface-mounted antenna, the antenna-side control electrode having a capacitance generated between itself and the open end of the radiating electrode, a ground conductor disposed on the mounting board and which functions as ground, a board-side control electrode disposed on the mounting board, which is electrically connected with the antenna-side control electrode, and which electrically floats, and a resonant frequency adjuster having at least one of an induct
Kurita Junichi
Kushihi Yuichi
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
Wimer Michael C.
LandOfFree
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