Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2001-06-01
2002-08-13
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S702000
Reexamination Certificate
active
06433746
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an antenna system mounted on a radio unit such as a portable telephone, and to a radio unit using this antenna system.
2. Description of the Related Art
FIG. 4
is a schematic perspective view showing an example of a surface-mount type antenna. The surface-mount type antenna
1
shown in
FIG. 1
has a rectangular-parallelepiped shaped substrate
2
which is formed of a dielectric body. A radiation electrode
3
is formed on the top surface
2
a
of this substrate
2
. The left end side (shown in
FIG. 4
) of the radiation electrode
3
is extended to a side surface
2
b
of the substrate
2
, and the left end
3
a
of the radiation electrode
3
forms an open (unconnected) end. On a side surface
2
c
of the substrate
2
, a feeding electrode
4
is extended from the bottom side toward the upper side, and is connected continuously to the right end portion of the radiation electrode
3
, wrapping around the top surface
2
a
of the substrate
2
.
Such a surface-mount type antenna
1
is mounted on a circuit board, using the bottom surface
2
d
of the substrate
2
as a mounting surface, and is conductively connected to a radio unit circuitry
5
formed on the circuit board, via the feeding electrode
4
. With the radiation electrode
3
and the radio unit circuitry
5
thus conductively connected, for example, when a signal is supplied by the radio unit circuitry
5
to the radiation electrode
3
through the feeding electrode
4
, the radiation electrode
3
is excited by the signal, and the signal (radio wave) is transmitted to the outside. On the other hand, when a signal is received, the signal flows in the direction opposite to that during the above-described transmission, and the received signal is supplied to the radio unit
5
. In this manner, the surface-mount type antenna
1
performs an antenna operation of transmitting/receiving the signal (radio wave).
Meanwhile, the frequency band is determined by the effective line length of the signal of the radiation electrode
3
. Conversely, the effective line length of the signal of the radiation electrode
3
is determined in accordance with the frequency band of the radio wave transmission/reception based upon a given specification. With the miniaturization of radio units, there is a need also to miniaturize surface-mount type antennas
1
as described above. As the frequency band of the radio wave transmission/reception required for the surface-mount type antennas
1
becomes low, the effective line length of the signal of the radiation electrode
3
must be set to be long, but it can be difficult to ensure a long effective line length in order to perform radio wave transmission/reception in a desirable low frequency band, due to the miniaturization of the surface-mount type antennas
1
.
Accordingly, an antenna system
7
as shown in
FIG. 5
has been proposed. In
FIG. 5
, the antenna system
7
is shown as being mounted on a circuit board
11
of a radio unit
10
such as a portable telephone. The antenna system
7
shown in
FIG. 5
, comprises a surface-mount type antenna
1
as described above which constitutes a surface-mount type antennas portion, and a metallic plate
8
which is conductively connected to the radiation electrode
3
of the surface-mount type antenna
1
. In this antenna system
7
, by conductively connecting the metallic plate
8
to the radiation electrode
3
, the effective line length of the signal of the radiation electrode
3
is equivalently elongated by the increment of the installed metallic plate
8
. This facilitates the transmission/reception of radio waves at a required low frequency.
The antenna system
7
is mounted on a circuit board
11
of a radio unit, for example, in an installation configuration as shown in FIG.
5
. Specifically, radio unit circuits (
5
) such as a signal processing circuit and a controlling circuit, are formed on the circuit board
11
, and a shield case
13
for shielding these radio unit circuits is provided on this circuit board
11
. The top surface of the shield case
13
is parallel with the surface of the circuit board
11
and the top surface
2
a
and the bottom surface
2
d
of the substrate
2
of the surface-mount type antenna
1
. The surface-mount type antenna
1
of the antenna system
7
is mounted on the circuit board
11
in the vicinity of the shield case
13
, using the bottom surface
2
d
of the substrate
2
of the surface-mount type antenna
1
as a mounting surface. The metallic plate
8
of the antenna system
7
is disposed above the shield case
13
with a space therebetween so that the surface of the metallic plate
8
is parallel with the top surface of the shield case
13
.
The circuit board
11
on which the antenna system
7
and the radio unit circuits are provided, are housed in, for example, a case
12
as shown by a chain line in FIG.
5
. When the radio unit
10
is a portable telephone, a battery for power in the radio unit is disposed on the blank portion on the circuit board
11
as shown in FIG.
5
.
Meanwhile, there is now increased demand for a radio unit
10
such as a portable telephone which has a reduced thickness D. In order to reduce the thickness the radio unit
10
, the spacing between the metallic plate
8
of the antenna system
7
and the top surface of the shield case
13
must be made very narrow. However, the entire surface of the metallic plate
8
is opposed to the top surface of the shield case
13
with a space therewith, and the shield case
13
and the surface of the circuit board
11
are equivalent to the ground, and hence, by reducing the spacing between the metallic plate
8
and the shield case
13
as described above, the electrostatic capacitance between the metallic plate
8
and the shield case
13
, in other words, the electrostatic capacitance between the metallic plate
8
and the ground, significantly increases. This increase in the capacitance causes problems such as a reduction in the antenna gain, and the narrowing of the frequency bandwidth of radio wave transmission/reception.
SUMMARY OF THE INVENTION
It is an object of the present invention to solve the above-described problems. It is, furthermore, an object of the invention to provide an antenna system capable of meeting the demands for the transmission/reception of lower frequency radio waves, and capable of reducing the thickness of a radio unit without deteriorating antenna performance, and also to provide a radio unit using this antenna system.
In order to achieve the above-described objects, the present invention provides, in a first aspect, a surface-mount type antenna which comprises a surface-mount type antenna portion which is configured by forming, on a substrate, a radiation electrode for radio wave transmission/reception, and a metallic plate which is conductively connected to the radiation electrode of the surface-mount type antenna portion, and which performs radio wave transmission/reception together with the radiation electrode. The surface-mount type antenna portion is mounted on a circuit board of a radio unit, using the bottom surface of the substrate as a mounting surface, and the metallic plate is provided so as to be isolated from the circuit board. The metallic plate is preferably disposed adjacent to the long-side surface of the substrate of the surface-mount type antenna portion with a space therebetween so that the surface of the metallic plate is non-parallel with the bottom surface of the surface-mount type antenna portion.
The present invention provides, in a second aspect, a radio unit which includes an antenna system in accordance with the above-described first aspect.
In the radio unit in accordance with the second aspect, it is preferable that the metallic plate of the antenna system be disposed so that the surface thereof is opposed to the corresponding end surface of a circuit board with a spacing therebetween.
In the present invention having the above-described features, the metallic plate of the antenn
Kushihi Yuichi
Yamaki Kazuhisa
Ho Tan
Murata Manufacturing Co. Ltd.
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