Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2002-09-19
2004-07-27
Clinger, James (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S846000
Reexamination Certificate
active
06768462
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a diversity antenna, and to a wireless communication apparatus employing it.
2. Description of the Prior Art
In recent years, with the advancement of communication technology, wireless communication apparatuses have come to be made compact. One type of small-size antenna used in such wireless communication apparatuses is the inverted-F antenna. The inverted-F antenna uses an element of which the length equals ¼ of the wavelength, and permits the feed point to be located at the center of the element. Thus, the inverted-F antenna is suitable for miniaturization. By using two such inverted-F antennas, it is possible to build a diversity antenna.
FIG. 7
is an external perspective view of a conventional diversity antenna. The conventional diversity antenna
50
is composed of a plate-shaped inverted-F antenna
60
and a plate-shaped inverted-F antenna
70
. The plate-shaped inverted-F antennas
60
and
70
are arranged on the top surface of a chassis
51
of a wireless communication apparatus.
The inverted-F antenna
60
is composed of a plate
61
, a grounding plate
62
, a feed wire
63
, and a feed point
64
. The inverted-F antenna
70
is composed of a plate
71
, a grounding plate
72
, a feed wire
73
, and a feed point
74
.
The plates
61
and
71
are each formed as a rectangular metal conductor, the lengths of the sides of which are determined according to the frequency used. The grounding plates
62
and
72
are also metal conductors, which serve to ground the plates
61
and
71
, respectively, to the chassis
51
of the wireless communication apparatus. The feed wires
63
and
73
feed ultra-high-frequency current to the feed points
64
and
74
to excite the plates
61
and
71
, respectively. The feed points
64
and
74
are where the largest amount of current can be fed to the plates
61
and
71
, respectively. The chassis
51
of the wireless communication apparatus is box-shaped.
In
FIG. 7
, the plane that is parallel to the top surface of the chassis
51
of the wireless communication apparatus and on which the inverted-F antennas
60
and
70
are arranged is called the horizontal plate H, and the direction perpendicular to the top surface of the chassis
51
of the wireless communication apparatus is called the vertical axis V.
FIGS. 8A and 8B
are diagrams showing the directivity patterns of the conventional diversity antenna
50
shown in FIG.
7
and described above.
FIG. 8A
is a diagram showing the directivity patterns of the inverted-F antenna
60
with respect to the vertical axis V, where the directivity pattern for vertically polarized radio waves is indicated with a solid line
80
and the directivity pattern for horizontally polarized radio waves is indicated with a broken line
81
.
FIG. 8B
is a diagram showing the directivity patterns of the inverted-F antenna
70
with respect to the vertical axis V, where the directivity pattern for vertically polarized radio waves is indicated with a solid line
82
and the directivity pattern for horizontally polarized radio waves is indicated with a broken line
83
.
The conventional structure described above, however, has the following disadvantages. The directivity patterns of the inverted-F antennas
60
and
70
with respect to the vertical axis V shown in
FIGS. 8A and 8B
clearly show the following. First, for vertically polarized radio waves, the inverted-F antennas
60
and
70
exhibit lower gains below the top surface of the chassis
51
of the wireless communication apparatus on which they are arranged than above that surface, and have null points in the direction of the vertical axis V. Second, the inverted-F antennas
60
and
70
exhibit lower gains for horizontally polarized radio waves as indicated with broken lines than for vertically polarized radio waves as indicated with solid lines. Thus, combining antennas of this type to build a diversity antenna does not help to overcome low gains in particular directions or on particular polarization planes. Such a diversity antenna may operate satisfactorily in applications where the system employing it is used in a fixed state or position and requires transmission and reception of radio waves polarized in a particular way, but not where the system is used in an unpredictable state or position and requires transmission and reception of radio waves polarized in any way and traveling in and from any direction.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a diversity antenna free from the disadvantages mentioned above, and -to provide a wireless communication apparatus employing such a diversity antenna.
To achieve the above object, according to the present invention, the following improvements are made. The first and second antennas no longer have, in their directivity patterns with respect to the vertical axis V, null points in the direction of the vertical axis V as are observed conventionally. Thus, the first and second antennas exhibit gains in all directions, and are thus largely non-directional. Moreover, lower gains for horizontally polarized radio waves than for vertically polarized radio waves as are observed conventionally are improved. In diversity operation, the improved gains of the first and second antennas for horizontally polarized radio waves make it possible to cope satisfactorily with radio waves polarized on different polarization planes.
Specifically, according to the present invention, a diversity antenna is provided with: a first inverted-F antenna composed of a first elongate conductor portion, a first grounding conductor portion formed at one side of the first elongate conductor portion so as to be substantially perpendicular to the first elongate conductor portion, and a first feeding conductor portion formed at another side of the first elongate conductor portion so as to be substantially perpendicular to the first elongate conductor portion; and a second inverted-F antenna composed of a second elongate conductor portion, a second grounding conductor portion formed at one side of the second elongate conductor portion so as to be substantially perpendicular to the second elongate conductor portion, and a second feeding conductor portion formed at another side of the second elongate conductor portion so as to be substantially perpendicular to the second elongate conductor portion. The first and second inverted-F antennas are arranged so that the center axes of the first and second elongate conductor portions are substantially perpendicular to each other and that the center axes of the first and second feeding conductor portions are substantially parallel to each other.
Thus, according to the present invention, it is possible to reduce the differences between the gains for vertically polarized radio waves and the gain for horizontally polarized radio waves. This makes it possible to realize a diversity antenna that copes with both vertically and horizontally polarized radio waves.
According to the present invention, the first inverted-F antenna has a first printed circuit board, the first grounding conductor portion is electrically connected to the ground pattern of the first printed circuit board, and the first feeding conductor portion is electrically connected to the feed point of the first printed circuit board. On the other hand, the second inverted-F antenna has a second printed circuit board, the second grounding conductor portion is electrically connected to the ground pattern of the second printed circuit board, and the first and second printed circuit boards are arranged substantially parallel so as to face each other.
Thus, according to the present invention, the first and second antennas have no null points in the direction of the vertical axis V for either vertically or horizontally polarized radio waves, and therefore exhibit gains in all directions, i.e., are largely non-directional. In addition, the first and second antennas are arranged so that their center axes are perpendicular
Itagaki Kenji
Umehara Naoko
Clinger James
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
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