Communications: radio wave antennas – Antennas – Spiral or helical type
Reexamination Certificate
2002-07-05
2004-05-11
Nguyen, Hoang V (Department: 2821)
Communications: radio wave antennas
Antennas
Spiral or helical type
Reexamination Certificate
active
06734831
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a dual-resonance antenna that can be used in two mutually separated frequency bands employed in cellular phones or handyphones (PHS: personal handyphone system).
BACKGROUND ART
The number of cellular phone or PHS subscribers increases from year to year, and because of such an increase in the number of subscribers, the employed frequency is insufficient. When the employed frequency is insufficient because of such an increase in the number of subscribers, two frequency bands are allocated: a frequency band that can be used almost everywhere as the frequency band of cellular phones and a frequency band that can be used in cities. For example, in Europe, cellular phones of a GSM system with a 900 MHz band can be used everywhere, and also cellular phones of DCS system with a 1.8 GHz can be used in cities in order to compensate for the utilized frequency insufficiency. For a cellular phone to be thus used in two frequency bands, it has to be made suitable for operation in two frequency bands. Thus, it has to contain wireless circuitry for each frequency band of the two frequency bands and to be provided with a dual-resonance antenna operating in two frequency bands.
A dual-resonance antenna shown in
FIG. 9
has been suggested as the dual-resonance antenna of such type. This dual-resonance antenna comprises a helically wound coil
121
and a connection member
122
obtained by bending the upper end portion of the coil
121
downward and passing it inside the coil
121
almost along the central axis of coil
121
. Power is fed from a feeder
124
to the end portion of the connection member
122
.
An equivalent circuit of dual-resonance antenna
114
shown in
FIG. 9
is shown in FIG.
10
. As shown in
FIG. 10
, the coil
121
and connection member
122
passing inside the coil
121
are high-frequency coupled, a floating capacitance is generated, and a parallel resonant circuit comprising an inductor L
101
and a capacitor C
101
is equivalently formed. An equivalent element
125
is equivalently formed above this parallel resonant circuit, and an equivalent element
126
is equivalently formed between the parallel resonant circuit and feeder
124
. The equivalent element
125
is formed by the coil
121
, and the equivalent element
126
is formed by the connection member
122
.
In such a dual-resonance antenna
114
, the coil
121
together with the connection member
122
operate as an antenna in a low-frequency band (first frequency band), the parallel resonant circuit is caused to operate as a trap in a high-frequency band (second frequency band), and the connection member
122
operates as an antenna at a high frequency. Thus, the dual-resonance antenna
114
operates at two frequency bands, namely first and second frequency bands.
In such a dual-resonance antenna, the antenna operating in a high-frequency band is formed by a linear connection member
122
. Therefore, the length of connection member
122
has to correspond to the frequency of the second frequency band. The problem, however, is that if the length of connection member
122
is selected so as to correspond to the frequency of the second frequency band, the length of dual-resonance antenna
114
is increased and the size of antenna is difficult to reduce. For this reason, the size reduction of dual-resonance antenna
114
operating in two frequency bands, first frequency band and second frequency band, was attained by decreasing the length of connection member
122
to a level less than that essentially required and connecting a matching circuit with a dual-resonance characteristic.
FIG. 11
shows a VSWR characteristic of dual-resonance antenna
114
with a total length reduced to about 20 mm, which has such a matching circuit connected thereto. In the VSWR characteristic shown in
FIG. 11
, frequency is plotted against the abscissa, a 900 MHz band (890-960 MHz) in the GSM (global system for mobile communication) is a first frequency band, and a 1.7 GHz band (1710-1880 MHz) in a DCS (Digital Cellular System) is a second frequency band. As shown in
FIG. 11
, the worst value of VSWR in the first frequency band is 3.1, the worst value of VSWR in the second frequency band is 2.7, and good VSWR is not obtained.
Furthermore, in the VSWR characteristic shown in
FIG. 11
, the matching circuit shown in
FIG. 12
is connected between the dual-resonance antenna
114
and feeder
124
. In order to obtain a dual-resonance characteristic, this matching circuit is composed by connecting a second inductor L
112
and a third inductor L
113
in series, connecting a capacitor C
111
between the ground and the connection point of the second inductor L
112
and the third inductor L
113
, and connecting the first inductor L
111
between the ground and the initial end of the second inductor L
112
. In this case, the first inductor L
111
is about 15 nH, the second inductor L
112
and third inductor L
113
are about 4.7 nH, and the capacitor C
111
is about 2 pF. Thus, the problem was that the dual-resonance antenna
114
required a complex matching circuit using four or more elements.
Accordingly, it is an object of the present invention to provide a dual-resonance antenna that can be miniaturized without degrading the electric characteristics and that employs a simple matching circuit.
DISCLOSURE OF THE INVENTION
In order to attain this object, the dual-resonance antenna in accordance with the present invention comprises a first coil, a connection member obtained by bending an end portion of the first coil and passing it along almost the central axis inside the first coil, and a second coil connected to the end portion of the connection member.
Furthermore, in the dual-resonance antenna in accordance with the present invention, a first reactance element for matching may be connected in series between the end portion of said second coil and a feeder, and a second reactance element for matching may be connected between the end portion of said second coil and the ground.
Moreover, in the dual-resonance antenna according to the present invention described in the above, a &pgr;-type matching circuit or a T-type matching circuit composed of a third reactance element may be connected between the end portion of the second coil and a feeder.
In accordance with the present invention, since the second coil is connected to the end portion of the connector member passed along almost the central axis inside the first coil, the total length of the dual-resonance antenna can be reduced and the antenna can be miniaturized. Furthermore, despite the size reduction, the second coil with an inherently required length can be used. As a result, a dual-resonance antenna with good electric characteristics can be obtained. Furthermore, since a matching circuit providing a dual-resonance characteristic is not required, a simple circuit with a small number of components can be used as the matching circuit for feeding the dual-resonance antenna.
REFERENCES:
patent: 6016130 (2000-01-01), Annamaa
patent: 6054966 (2000-04-01), Haapala
patent: 6112102 (2000-08-01), Zhinong
patent: 6201500 (2001-04-01), Zurfluh
patent: 63-286008 (1988-11-01), None
patent: 09-139618 (1997-05-01), None
patent: 2000-013278 (2000-01-01), None
patent: 2000-059130 (2000-02-01), None
International Search Report, PCT/JP01/09155 Jan. 8, 2002, pp. 1.
Connolly Bove & Lodge & Hutz LLP
Hume Larry J.
Nguyen Hoang V
Nippon Antena Kabushiki Kaisha
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