Communications: radio wave antennas – Antennas – Balanced doublet - centerfed
Reexamination Certificate
2001-08-27
2003-03-04
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Balanced doublet - centerfed
C343S7000MS
Reexamination Certificate
active
06529170
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a two-frequency printed antenna that is used as a base station antenna in a mobile communication system, and is used in common for two frequency bands which are separated apart from each other, and to a multi-frequency printed antenna used in common for a plurality of frequency bands which are separated apart from each other, and to a two-frequency or multi-frequency array antenna composed of the two- or multi-frequency printed antennas.
BACKGROUND ART
Antennas such as base station antennas for implementing a mobile communication system are usually designed for respective frequencies to meet their specifications, and are installed individually on their sites. The base station antennas are mounted on rooftops, steel towers and the like to enable communications with mobile stations. Recently, it has been becoming increasingly difficult to secure the sites of base stations because of too many base stations, congestion of a plurality of communication systems, increasing scale of base stations, etc. Furthermore, since the steel towers for installing base station antennas are expensive, the number of base stations has to be reduced from the viewpoint of cost saving along with preventing spoiling the beauty.
The base station antennas for mobile communications employ diversity reception to improve communication quality. Although the space diversity is used most frequently as a diversity branch configuration, it requires at least two antennas separated apart by a predetermined distance, thereby increasing the antenna installation space. As for the diversity branch to reduce the installation space, the polarization diversity is effective that utilizes multiple propagation characteristics between different polarizations. This method becomes feasible by using an antenna for transmitting and receiving the vertically polarized waves in conjunction with an antenna for transmitting and receiving the horizontally polarized waves. In addition, utilizing both the vertically and horizontally polarized waves by a radar antenna can realize the polarimetry for identifying an object from a difference between radar cross-sectional areas caused by the polarization.
Thus, to make effective use of space, it is necessary for a single antenna to utilize a plurality of different frequencies, and in addition, the combined use of the polarized waves will further improve its function.
FIG. 1
is a plan view showing a conventional two-frequency printed antenna disclosed in Japanese patent application laid-open No. 8-37419/1996.
FIG. 2
is a schematic view showing a configuration of a conventional antenna formed as a corner reflector antenna comprising the two-frequency array antenna. In this figures, the reference numeral
101
designates a dielectric board;
102
a
designates a dipole element printed on the first surface of the dielectric board
101
;
102
b
designates a dipole element printed on the second surface of the dielectric board
101
;
103
a
designates a feeder printed on the first surface of the dielectric board
101
;
103
b
designates a feeder printed on the second surface of the dielectric board
101
;
104
designates a passive parasitic element;
105
designates reflectors joined to each other;
106
designates a corner reflector composed of two reflectors
105
joined; and
107
designates subreflectors joined to both ends of the corner reflector
106
. The right and left dipole elements
102
a
and
102
b
constitute a dipole antenna
102
operating at a particular frequency f
1
; and the two feeders
103
a
and
103
b
constitute a twin-lead type feeder
103
. The parasitic element
104
has a length resonating at a frequency f
2
higher than the frequency f
1
. The antenna as shown in
FIG. 2
is a side view of a device configured by adding the corner reflector to the dipole antenna as shown in FIG.
1
. In
FIG. 2
, the dipole antenna
102
and the twin-lead type feeder
103
are shown schematically.
Next, the operation of the conventional antenna will be described.
The dipole antenna has a rather wideband characteristic with a bandwidth of 10% or more. To achieve such a wide bandwidth, however, it is necessary for the height from the reflectors to the dipole antenna to be set at about a quarter of the wavelength of the radio wave or more. Besides, since the dipole antenna forms its beam by utilizing the reflection from the reflectors, when the height to the dipole antenna is greater than a quarter of the wavelength, it has a radiation pattern whose gain is dropped at the front side. Therefore, it is preferable that the height from the reflectors to the dipole antenna be set at about a quarter of the wavelength of the target radio wave.
In the conventional antenna, the dipole antenna
102
fed by the feeder
103
resonates at the frequency f
1
. When the dipole antenna
102
operates at the frequency f
2
higher than the frequency f
1
, the parasitic element
104
disposed over the dipole antenna
102
resonates at the frequency f
2
because of the induction current caused therein by inter-element coupling. Therefore, the dipole antenna
102
and the parasitic element
104
thus arranged can implement two-frequency characteristics. In addition, the beam width can be controlled by utilizing reflected waves from the corner reflector
106
and subreflector
107
.
With the foregoing configuration, the conventional antenna can operate at both frequencies f
1
and f
2
. However, the parasitic element
104
, which is active at the relatively high frequency f
2
and is disposed over the dipole antenna
102
operating at the relatively low frequency f
1
, presents the following problems: First, it is impossible for the dipole antenna
102
and the parasitic element
104
to be placed at the height of a quarter wavelength of the radio waves of the operating frequency at the same time. Second, because of the effect of the current flowing in the dipole antenna
102
even when the parasitic element
104
is active at the frequency f
2
, it is difficult to obtain similar beam shapes by controlling the beam width at the frequency f
1
and f
2
. In addition, the corner reflector and subreflectors needed to achieve the beam control present another problem of complicating the structure of the antenna.
The present invention is implemented to solve the foregoing problems. Therefore, an object of the present invention is to provide a two-frequency antenna, a multi-frequency antenna, and a two-frequency or multi-frequency array antenna composed of the foregoing antennas, which can obtain similar beam shapes at individual operating frequencies when the single antenna is used in common for a plurality of operating frequencies.
Another object of the present invention is to provide a two-frequency antenna, a multi-frequency antenna, and a two-frequency or multi-frequency array antenna composed of the foregoing antennas, each of which has a simple structure and can be used in common for a plurality of operating frequencies.
DISCLOSURE OF THE INVENTION
According to a first aspect of the present invention, there is provided a two-frequency antenna comprising: a feeder, an inner radiation element connected to the feeder and an outer radiation element, all of which are printed on a first surface of a dielectric board; an inductor formed in a gap between the inner radiation element and the outer radiation element printed on the first surface of the dielectric board to connect the two radiation elements; a feeder, an inner radiation element connected to the feeder and an outer radiation element, all of which are printed on a second surface of a dielectric board; and an inductor formed in a gap between the inner radiation element and the outer radiation element printed on the second surface of the dielectric board to connect the two radiation elements.
Thus, the two-frequency antenna can operate at the frequency f
1
at which the sum length of the inner radiation element, the inductor and the outer radiation element becomes about a quarter of the wavelength. As for th
Katagi Takashi
Nishimura Toshio
Nishizawa Kazushi
Ohmine Hiroyuki
Clinger James
Mitsubishi Denki & Kabushiki Kaisha
Wong Don
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