Antenna device

Communications: radio wave antennas – Antennas – With radio cabinet

Reexamination Certificate

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Details

C343S7000MS, C343S725000, C343S895000

Reexamination Certificate

active

06232925

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an antenna device provided for a portable radio, such as a portable phone (cellular phone), and in particular to an antenna device capable of transmitting and/or receiving data in two different frequencies.
International Publication WO95/12224 discloses an antenna device provided for a portable radio, such as a portable phone, which can be used during carriage. The antenna device resonates at two different frequencies to make it possible to use the portable radio in a plurality of frequency bands.
The antenna device
100
will be explained with reference to
FIGS. 7
to
9
. As shown in
FIG. 7
, the antenna device
100
comprises a fixed antenna part
103
including a first helical antenna element
101
and a second helical antenna element
102
. Each of the first helical antenna element
101
and the second helical antenna element
102
is made up of a pair of loading coils wound spirally around a cylindrical insulated sleeve
104
. The pairs of the loading coils are further wound spirally together.
The base end of each helical antenna element
101
,
102
is connected with a conductive sleeve
105
mounted on the lower end of the insulated sleeve
104
so as to be connected electrically with a transmitting and receiving circuit of a portable radio (not illustrated) via the conductive sleeve
105
.
FIG. 8
is an equivalent circuit diagram of the fixed antenna part
103
. The first helical antenna element
101
and the second helical antenna element
102
are resonated at different resonant frequencies f
11
, f
12
according to the connection with the conductive sleeve
105
. Accordingly, as shown in
FIG. 9
, the fixed antenna part
103
is capable of transmitting or receiving data in a frequency band wider than that of an antenna to be resonated at a frequency f
10
(shown by the chain line in the figure).
The antenna device
100
is also provided with a sliding antenna part
107
made up of a bar-like rod antenna element covered with an insulated cover
106
in the upper part. The sliding antenna part
107
is insertable into the insulated sleeve
104
and the conductive sleeve
105
, and used as a whip antenna resonated at a frequency f
10
when the sliding antenna part
107
is pulled out from the portable radio so as to connect the lower end thereof electrically with the conductive sleeve
105
.
Therefore, the antenna device
100
is capable of transmitting or receiving data in either of a state where the sliding antenna part
107
is stored and a state where it is pulled out. As shown in
FIG. 9
, a radio signal can be transmitted or received in a wide band including the two frequencies f
11
, f
12
in either state.
On the other hand, frequency bands to be used in recent mobile communication equipment differ. For example, it is a 900 MHz band for portable phones and automobile phones, and it is a 1.9 GHz band for PHS (Personal Handy-phone System). Therefore, a portable radio usable in either communication system is desired so that an antenna device compatible with dual bands, capable of transmitting or receiving data in either band is required.
The antenna device
100
achieves transmission and receipt in a wide band according to the fixed antenna part
103
by adjusting the two helical antenna elements to be resonated at the two comparatively close frequencies f
11
, f
12
. Therefore, the antenna device
100
cannot meet the above-mentioned requirement. In order to meet the requirement with the configuration the same as the antenna device
100
, two helical antenna elements
101
,
102
having different expanded lengths need to be connected parallel and directed outward with respect to the conductive sleeve
105
, corresponding with two completely different frequency bands f
1
, f
2
so that the appearance of the portable radio is spoiled as well as the number of parts is increased to complicate the assembly.
In order to solve the problem, the applicant has proposed an antenna device
110
to be resonated at completely different frequency bands f
1
, f
2
by providing two helical antennas
112
,
113
connected in series on a feeding metal fixture
111
to elongate linearly and adjusting the expanded length and the winding pitch of each helical antenna as shown in FIG. 10 (Japanese Patent Application No. 10-164616).
However, the antenna device
110
, which is required to form helical antennas
112
,
113
such that they are resonated in the two respective bands f
1
, f
2
to be used, involves a problem in that a processing step of the loading coils is needed, and thus it is difficult to mass-produce a helical antenna with the designed value but the resonant frequency can be irregular per each antenna device
110
.
SUMMARY OF THE INVENTION
The invention is for solving the problems, and an object thereof is to provide an antenna device capable of transmitting or receiving in a portable radio in the frequency bands used in two different communication systems without the performance irregularity even in the case of the mass production.
In order to solve the problems, a first aspect of the antenna device comprises a feeding metal fixture mounted on a housing of a portable radio, and an antenna element provided elongating linearly on the feeding metal fixture, comprising an upper antenna element and a lower antenna element connected electrically in series, with the base end of the lower antenna element connected electrically with the feeding metal fixture,
wherein the antenna element is resonated at a first frequency f
1
as a quarter wave ground antenna, and the antenna element is resonated at a second frequency f
2
lower than the frequency three times as much as the first frequency f
1
as a three quarter wave ground antenna by having the inductance per unit length along the linearly elongating direction of the upper antenna element larger than the inductance per unit length along the same direction of the lower antenna element.
The quarter wave antenna element to be resonated at the first frequency f
1
can also be resonated at the second frequency f
2
lower than the frequency three times as much as the first frequency f
1
as a three quarter wave ground antenna by having the inductance per unit length along the elongating direction of the upper antenna element larger than the inductance per same unit length of the lower antenna element so that the SWR hardly changes even if it is used as it is. Therefore, by adjusting the inductance per unit length along the elongating direction of the upper antenna element to be larger, the antenna element having one end connected with the feeding metal fixture can be resonated at optional first frequency f
1
and second frequency f
2
so as to provide a portable radio capable of transmitting or receiving in two different frequency bands.
In a second aspect of the antenna device, the upper antenna element and the lower antenna element are formed with an antenna pattern printed on a printed wiring board in a bent shape.
Since the antenna pattern is printed on the printed wiring board in a bent shape, it functions as an antenna, and thus it can provide an antenna element in place of the loading coil.
Since parts of the antenna element can be formed by printing on a printed wiring board, antenna patterns with the same shape can be obtained accurately by an etching step without the performance irregularity even in the case of the mass production.
Moreover, since the shape can hardly be deformed even against external force, the antenna characteristics can be maintained stably.
In a third aspect of the antenna device, the upper antenna element is formed with a loading coil, the lower antenna element is formed with an antenna pattern printed on a printed wiring board in a bent shape, and the base end of the loading coil is connected with the tip of the antenna pattern.
Since the lower antenna element can be formed by printing on a printed wiring board, antenna patterns with the same shape can be obtained accurately after an etching step without the performance irregularity even i

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