Communications: radio wave antennas – Antennas – Slot type
Reexamination Certificate
2001-02-26
2002-10-08
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Slot type
C343S7000MS
Reexamination Certificate
active
06462714
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a wireless handset using a slot antenna. More specifically, it relates to a wireless handset for use in a communication system switching a plurality of call frequencies and employing different transmit/receive frequencies, in particular, a wireless handset mounting a slot antenna.
DESCRIPTION OF THE RELATED ART
Wireless handsets have been made smaller and thinner in order to improve portability, and at the same time, various small antennas mounted on such wireless handsets have been developed. Among them, a slot antenna utilizing a coaxial resonator can be incorporated without any protrusion, and in particular, Japanese Non-examined Patent Publication No. 9-74312 proposes a coaxial resonant slot antenna which is made smaller in which its central conductor (power supply conductor) is not in contact with a resonator case (conductive cubic). This coaxial resonant slot antenna is a magnetic current type antenna, and there is an influence between the magnetic current generated in the slot and a magnetic current in the same phase generated on a surface opposite a main surface provided with the slot in the conductive cubic, so as to realize single-side directional. Since an electromagnetic wave having frequencies above about 2 GHz can easily be absorbed into the head of the user in a call state of the handset, a single-side directional antenna which allows no electric power to be radiated to the user side is used to reduce power consumption. Similarly, in respect of received power, the single-side directional also increases antenna gain on the opposite side of the head to enhance handset sensitivity.
Since the antenna includes a resonator construction, the volume is directly proportional to the bandwidth. Thus, when the antenna is applied to a handset of broad bandwidth wireless communication system having a large capacitance using a plurality of carrier frequencies, the bandwidth to be provided for the antenna is expanded, and the antenna volume is increased.
Generally, a bandwidth for use in the call between a specific base station and a wireless handset is much narrower than that of the whole system. For each call, the resonant frequency of the antenna is suitably changed to the frequency for use in the call. The bandwidth to be provided for the antenna is reduced, so as to reduce the antenna volume. For this reason, in the slot antenna utilizing a coaxial resonator, Japanese Non-examined Patent Publication No. 11-46115 proposes a tunable slot antenna comprising at least one island conductor provided in a slot, wherein a variable capacitance circuit changes a capacitance value between the island conductor and the wall surface of a conductive cubic, so as to extensively vary the resonant frequency of the antenna. The construction example thereof is shown in FIG.
14
.
The antenna comprises a narrow strip conductor
40
disposed in the resonant axial direction of the inner space of a conductive cubic
1
of generally rectangular parallelepiped and so as to be insulated from the conductive cubic
1
, and an electric wave transmit/receive slot
2
formed in the top surface of the conductive cubic
1
so as to intersect the strip conductor
40
, in which a radio frequency power supply circuit
7
supplies radio frequency power through a power supply conductor
5
and an island conductor
6
between a connection portion
41
set in the strip conductor
40
and the wall surface of the conductive cubic
1
.
An island conductor
42
is provided in the slot
2
so as to be insulated from the conductive cubic
1
, and a variable capacitance circuit
10
connected between the island conductor
42
and the wall surface of the conductive cubic
1
is connected through a control line
50
to a control circuit
30
. The control signal from the control circuit
30
varies the capacity value of the variable capacitance circuit
10
, so as to change the capacitance value between the strip conductor
40
and the wall surface of the conductive cubic
1
through the island conductor
42
, or between the island conductor
42
and the wall surface of the conductive cubic
1
. When the capacitance value between the strip conductor
40
and the wall surface of the conductive cubic
1
is varied through the island conductor
42
, the electric current phase on the strip conductor
40
just below the slot
2
is changed. The length of the strip conductor
40
associated with the resonant frequency of the coaxial resonant slot antenna is varied equivalently.
When varying the capacitance value between the island conductor
42
and the wall surface of the conductive cubic
1
as ground potential, for example, if the capacitance value is enough large, the potential of the island conductor
42
is almost equal to the potential of the wall surface of the conductive cubic
1
as ground potential, so as to equivalently reduce the width of the slot
2
by the size of the island conductor
42
. Partial reduction of the width of the slot
2
corresponds to an increase in the length of the slot
2
. Consequently, the capacitance value of the variable capacitance circuit
10
is varied, so as to equivalently change the length of the slot
2
associated with the resonant frequency of the coaxial resonant slot antenna.
The matching conditions of the tunable slot antenna can be determined by both the electric current phase on the strip conductor
40
just below the slot
2
and the length of the slot
2
. Increasing the capacitance value can equivalently increase both the strip conductor length and the slot length, thereby maintaining the matching conditions of the antenna. According to the foregoing principle, the antenna simultaneously and equivalently varies the length of the strip conductor just below the slot and the slot length, so as to extensively change the resonant frequency of the antenna while maintaining the impedance matching state of the antenna.
SUMMARY OF THE INVENTION
In the conventional tunable slot antenna proposed in Japanese Non-examined Patent Publication No. 11-46115 described above, since the strip conductor
40
is provided in the conductive cubic
1
, the manufacturing process is complex, and the manufacture cost is high.
Further, since the island conductor
42
is provided so as to intersect the strip conductor
42
in the conductive cubic
1
, the island conductor
42
must be disposed near the central portion of the slot
2
. The variable capacitance circuit
10
connected to the island conductor
42
disposed near the central portion of the slot
2
must be also disposed near the central portion of the slot
2
, that is, in the central portion of the antenna. In order to add a control signal to the variable capacitance circuit
10
present in the central portion of the antenna, the control line
50
is provided toward the central portion of the antenna. However, since most electric power is radiated from the slot
2
of the slot antenna, the radiated power is reduced depending on the routing of the control line
50
. In Japanese Non-examined Patent Publication No. 11-46115 described above, there is also described a method of applying a DC voltage from one end near the slot
2
of the strip conductor
40
through the through hole and high resistance element to the island conductor
42
. According to this method, a control signal can be applied to the island conductor
42
without reducing radiated power. There are, however, the following two problems.
One of the problems is that, when the variable capacitance circuit
10
is a circuit continuously varying the capacitance value with a DC voltage value, and a radio frequency power value inputted to the antenna is increased, the radio frequency power coupled to the island conductor
42
is superimposed on a DC voltage applied to the variable capacitance circuit
10
and the capacitance value is inconstant, and the resonant frequency of the tunable antenna is inconstant. For this reason, when the circuit continuously varying the capacitance value by the DC voltage value is used as the var
Okabe Hiroshi
Takei Ken
Antonelli Terry Stout & Kraus LLP
Dinh Trinh Vo
Hitachi , Ltd.
Wong Don
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