Communications: radio wave antennas – Antennas – Slot type
Reexamination Certificate
2000-01-24
2001-02-13
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Slot type
C343S746000, C343S750000
Reexamination Certificate
active
06188369
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to antenna architectures and, more particularly, to slot antenna structures utilizing a coaxial resonator for use with mobile communication units including, but not limited to, cellular radiotelephone handsets in wireless communications systems.
Wireless telecommunication systems are known to employ portable or handheld mobile communication units such as for example cellular radiotelephone handsets operatively associated with a limited number of wireless communication resources and a remote system resource controller. As the cellular handsets require smaller size and less thickness, miniaturization or “down-sizing” of the antenna module adapted for use with such units has become more critical in recent years. Until today, several approaches to the small-size antenna have been proposed and developed. One previously known approach is to use a slot antenna incorporating a coaxial resonator. An exemplary coaxial-resonator slot antenna has been disclosed in U.S. patent application Ser. No. 08/708,563 filed Sep. 5, 1996. The slot antenna disclosed is structurally designed so that its centrally disposed elongate or “strip” conductor is kept in non-contact with a flat rectangular box-like conductive frame body of the resonator to miniaturize the antenna. This antenna also features in absence of any particular outer projections facilitating mounting of the antenna into the enclosure of a cellular radiotelephone handset.
Since the prior art small-size slot antenna has such resonator structure, the volume thereof is proportional to its impedance matching bandwidth—that is, the smaller the volume, the less the bandwidth. Accordingly, in cases where the antenna is practiced at communication units of a broad-band wireless communication system with an increased capacity by use of a plurality of different carrier frequencies allocated thereto, the impedance matching frequency band to be achieved by the antenna might be widened enlarging the antenna in size and in volume.
As readily appreciated to a person skilled in the art, those frequencies used for telephone interconnect calls between one particular base station and its associated wireless communication units, such as cellular handsets, are much less than the frequency band inherently allocated to the entire communication system. Accordingly, adaptively changing the antenna's impedance matching center frequency to a presently selected frequency for a telephone call attempt may render narrower the antenna's inherent frequency band, which in turn downsizes the antenna. One typical antenna module incorporating this approach is a tunable slot antenna as disclosed in copending U.S. patent application (Ser. No. 09/035,848, filed Mar. 6, 1998. This antenna is a coaxial resonator-used slot antenna including a variable capacitive element connected between a selected location at or near one end of a built-in strip conductor, which end is far from a connection point of the strip being supplied with high-frequency electric power, and an opposing plate of a rectangular box. The antenna may vary in impedance matching center frequency by varying the capacitance value of the variable capacitance element. An exemplary structure of the tunable slot antenna is shown in
FIGS. 10
a
and
10
b.
The tunable slot antenna shown in
FIGS. 10
a
-
10
b
includes a conductive flat box
1
. The box
1
has therein an elongate strip-like conductor
3
that is electrically insulated from the box
1
and extends along the axis of resonance. The box
1
has a top plate surface in which a slot
2
is formed overlying and crossing the strip
3
. Strip
3
has one end at which a connection point
10
is disposed and its opposite end has a small opening
11
defined for disposal of an island conductor
4
. The connection point
10
is operatively coupled to a high frequency or radio frequency (RF) power supply circuit
7
, which operates to supply RF power between the connection point
10
and its opposing part of the bottom plate of the box
1
. RF power supply
7
is associated with a certain element for elimination of unwanted high frequency current drain, and a variable direct current (DC) power supply
9
. A variable capacitive element
6
is connected between a selected location at or near the far end of strip
3
with small hole
11
and its opposing part of the top plate of the box
1
. Variable capacitor
6
receives a DC voltage from DC power supply
9
via strip
3
and RF current drain eliminator
8
.
In the antenna structure of
FIGS. 10
a
-
10
b
, the variable capacitor
6
may vary in capacitance value in response to receipt of a DC voltage applied from variable DC power supply
9
thereby causing a current flowing in strip
3
just beneath slot
2
to likewise change in phase. Such strip current phase change may in turn serve to permit strip
3
to change in length equivalently or “virtually,” which length closely relates to the resonant frequency of the tunable slot antenna shown. This makes it possible for the antenna to change or modify the impedance matching center frequency, that is, resonant frequency.
BRIEF SUMMARY OF THE INVENTION
The coaxial resonator-based slot antenna taught by U.S. patent application Ser. No. 08/708,563 and the tunable slot antenna proposed in the prior U.S. patent application based on Japanese Patent Application No. 9-54825 are such that the matching condition is determinable depending on both the strip current phase and the slot length. In this respect, suppose in the
FIG. 10
antenna that the capacitor
6
is varied in capacitance altering the current phase of strip
3
. If this is the case, as the resonant frequency varies, so does the resultant matching condition, thereby rendering it difficult to efficiently supply the antenna with RF power. The prior art approaches are also faced with a problem: the inability to permit the resonance frequency to vary over a wide range while achieving such efficient RF power supply to the antenna. This can be said because the variable capacitor for suppressing the variation range of the matching state to the extent that RF power is efficiently supplied to the antenna remains extremely less in both absolute capacitance value and changeable quantity.
It is therefore an object of the present invention to provide a new and improved slot antenna structure capable of avoiding the problems encountered with the prior art.
It is another object of the invention to provide an improved tunable slot antenna capable of permitting the resonant frequency to vary over an extended range while maintaining the antenna matching condition required.
It is a further object of the invention to provide a tunable slot antenna capable of forcing both the length of a slot and the length of as trip-like conductor immediately underlying the slot to equivalently vary or change at a time, thereby widening the resonant frequency variable range while maintaining the antenna matching condition required.
According to one aspect of the present invention, a tunable slot antenna includes a conductive box with a slot formed in one principal surface thereof, and a conductor insulatively disposed or “embedded” inside the box to spatially intersect the slot. Alternating current (AC) power is fed between a connection point of the conductor and the box. The box also includes an island-like conductor which is formed in the slot to be electrically isolated from the box, and electrical circuitry connected between the island and a wall plate of the box for permitting the capacitance therebetween to vary in value.
In accordance with another aspect of the invention, a tunable slot antenna is provided which includes a flat conductive box of a generally parallelepipedic shape or rectangular prism shape, and an elongate conductor or “strip” member insulatively embedded inside the box. The box has in its upper plate surface a slot overlying the conductive strip to spatially cross the same. The s trip has one end where a connection point is disposed and connected there
Okabe Hiroshi
Takei Ken
Hitachi , Ltd.
Mattingly Stanger & Malur, P.C.
Nguyen Hoang
Wong Don
LandOfFree
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