Communications: radio wave antennas – Antennas – Within conductive apertured wall
Reexamination Certificate
2000-03-02
2002-11-26
Phan, Tho (Department: 2821)
Communications: radio wave antennas
Antennas
Within conductive apertured wall
C343S846000
Reexamination Certificate
active
06486847
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a monopole antenna mainly used for mobile communication, and more specifically, to a monopole antenna suitable for base stations.
2. Description of the Related Art
Prior art antennas are shown in
FIGS. 36 and 37
.
A first prior art antenna shown in
FIG. 36
will be described as follows.
FIG. 36
shows one technique to change the directivity of the vertical plane of the antenna, and FIGS.
37
(A)-
37
(D) show examples of radiation directivity of monopole antennas.
FIG. 36
shows a ground conductor
111
, a coaxial power supply part
112
, and an antenna element
113
connected to the coaxial power supply part
112
on the ground conductor
111
. In this case, a monopole antenna has an axis symmetric structure where the ground conductor
111
is shaped like a disk, the coaxial power supply part
12
is located at the center of the surface of the ground conductor
111
, and the antenna element
113
is connected to the coaxial power supply part
12
in a manner to be perpendicular to the ground conductor
111
. The radio waves of the antenna are nondirectional with respect to the horizontal plane of the antenna.
A method of changing the directivity of the radio waves on the vertical surface in a monopole antenna is to change the size of the ground conductor
111
. When the ground conductor
111
have a finite size, radio waves diffract at the edge of the ground conductor
111
. The size of the diffraction depends on the size of the ground conductor
111
; the larger the ground conductor
111
is, the smaller the diffraction becomes, and vice versa. The entire radio waves of the antenna are the sum of the radio waves from the antenna element
113
and the diffraction waves from the edge of the ground conductor
111
. If the antenna is divided into two sides: the top side having the antenna element
113
and the bottom side below the ground conductor
111
, fewer radio waves flow to the bottom side and more radio waves are applied to the top side with increasing the ground conductor
111
in size. Also, the maximum radiation direction approaches the horizontal plane of the antenna. On the other hand, as the ground conductor
111
becomes smaller, more radio waves flow to the bottom side, making the maximum radiation direction approach the upright direction of the antenna. However, when the diameter of the ground conductor
111
is equal to or below ½ wavelength, the radio waves flow equally to the top and bottom sides, exhibiting directivity in the form of the number
8
on the vertical plane of the antenna. At this moment, the maximum radiation direction is the horizontal plane of the antenna.
FIGS. 37
show the radiation directivity when the ground conductor
111
has a diameter of about ½ wavelength (
37
A), about 0.8 wavelength (
37
B), and about
3
wavelength (
37
C). In
FIGS. 36 and 37
, X and Y indicate the direction parallel to the surface of the ground conductor
111
and Z indicates the direction perpendicular to the ground conductor
111
. The radio directivity is calibrated in 10 dB, and the unit used is dBd, referred to the gain of a dipole antenna.
Thus a monopole antenna can change the directivity of the radio waves on the vertical plane of the antenna by changing the ground conductor
111
in size.
The second prior art antenna will be described with reference to
FIG. 38
showing a technique to change the directivity of an antenna.
FIG. 38
illustrates a monopole antenna array provided with two antenna elements, and
FIG. 39
shows an example of radiation directivity.
The antenna array comprises a ground conductor
121
, coaxial power supply parts
122
and
123
, antenna elements
124
and
125
, power supply paths
126
and
127
, and a power distribution/composition circuit
128
. The antenna elements
124
and
125
are connected to the coaxial power supply parts
122
and
123
, respectively, on the ground conductor
121
. The coaxial power supply parts
122
and
123
are connected to the power distribution/composition circuit
128
via the power supply paths
126
and
127
, respectively. The ground conductor
121
is provided on the XY plane.
The following will describe the case where there are two antenna elements
124
and
125
, and radio waves are strong in the X axis direction.
The antenna elements
124
and
125
are arranged ½ wavelength apart from each other on the X axis to be symmetric with respect to the origin point, and currents to be supplied have a phase difference of 180 degrees. At this moment, the array factors become co-phase in the +X and −X directions to reinforce each other. When the antenna is symmetric with respect to the ZX plane and the ZY plane, the radio waves become symmetric with respect to the ZX plane and the ZY plane. The waves to be radiated become strong in the +X direction and the −X direction where the radiation waves from the antenna elements
124
and
125
have the same phase. Furthermore, changing the size of the ground conductor
121
or the distance between the antenna elements allows the directivity of the radio waves on the vertical plane of the antenna to change.
FIG. 39
shows as an example the radiation directivity when the antenna elements are made of a ¼ wavelength metallic wire, the antenna elements are supplied with power at a one to one ratio, and the ground conductor is a rectangle having one side of 2.75 wavelength parallel to the X axis and the other side of 2.25 wavelength parallel to the Y axis. In
FIG. 39
, X and Y. indicate the direction parallel to the plane of the ground conductor
121
, and Z indicates the direction perpendicular to the ground conductor
121
. The radio directivity is calibrated in 10 dB, and the unit is dBd, referred to the gain of a dipole antenna.
Thus, an antenna capable of changing the directivity of radio waves is achieved by arranging the antenna elements so as to form an array at an appropriate interval and by providing the antenna elements with an appropriate phase difference and an appropriate power distribution ratio.
However, the first prior art antenna has the following drawback; intensifying the radiation in the horizontal direction of the antenna requires a two-dimensionally large ground conductor
111
, which is against miniaturization of the monopole antenna. A monopole antenna is not allowed to occupy so large an area on the ceiling, which is one of the best sites indoors for a monopole antenna. Hence the first prior art antenna, which must be large in size because of its being difficult to be small two dimensionally, is unsuitable.
On the other hand, the second prior art antenna can intensify radio waves by providing directivity in the horizontal direction of the antenna. However, it requires to have the power supply paths
126
and
127
and the power distribution/composition circuit
128
, which causes a intrinsic loss in these components
126
,
127
, and
128
due to the structure of the circuit. Another loss is caused when the waves radiated from one antenna element
124
(
125
) are undesirably received by the other antenna element
125
(
124
) due to poor isolation between the antenna elements. These losses deteriorate the radiation efficiency. The latter-mentioned loss in particular leads to a reflection loss as the entire antenna array, and the reflected signal may reversely flow to each device connected to the antenna, thereby badly affecting the characteristics of each device. In order to secure excellent antenna characteristics, the former-mentioned loss should be reduced in the power supply paths and the power distribution/composition circuit
128
, and the latter case requires to establish good isolation between the antenna elements. In the former case, components having a fewer loss can be employed as the power supply paths
126
and
127
and the power distribution/composition circuit
128
. The latter case needs to extend the distance between the antenna elements. Hence, the antenna array in the secon
Matsuyoshi Toshimitsu
Ogawa Koichi
Yamamoto Atsushi
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