Communications: radio wave antennas – Antennas – Active sleeve surrounds feed line
Reexamination Certificate
1997-02-18
2001-01-23
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Active sleeve surrounds feed line
C343S790000, C343S791000, C343S817000
Reexamination Certificate
active
06177911
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an antenna for a base station used in mobile radio.
BACKGROUND OF THE INVENTION
A dipole antenna called a “sleeve antenna” has been used as an antenna for a base station in mobile radio. In
FIG. 15
, an example of a sleeve antenna in the prior art is illustrated (see, for example, Laid-open Japanese Patent Application No. (Tokkai hei) 8-139521). As shown in
FIG. 15
, outside an outer conductor
50
a
of a coaxial feed line
50
, a ¼-wavelength sleeve-like metal pipe
51
is located with one end connected to the upper end of outer conductor
50
a
. Also, an inner conductor
50
b
of coaxial feed line
50
protrudes from the upper end of outer conductor
50
a
, and a ¼-wavelength antenna element
52
is connected to the protruding inner conductor
50
b
. Thus, a ½-wavelength dipole antenna
53
is formed. Also, another example of a sleeve antenna is disclosed in Laid-open Japanese Patent Application No. (Tokkai hei) 4-329097, and it has a structure as shown in FIG.
16
. In
FIG. 16
, a dipole antenna
57
comprises an antenna element
55
formed by extending an inner conductor
55
of a coaxial feed line
54
upward by a length corresponding to about a ¼ wavelength from the upper end of an outer conductor, and a ¼-wavelength sleeve-like metal pipe
56
located outside coaxial feed line
54
with one end connected to the upper end of the outer conductor. A passive element
59
is supported by a supporting means mounted to metal pipe
56
.
Also, a “colinear array antenna”, a vertically polarized plane wave omnidirectional antenna having a large gain, has been used as an antenna for a base station in mobile radio. A colinear array antenna in the prior art is disclosed in Laid-open Japanese Utility Model Application No. (Tokkai hei) 2-147916, and has a structure as shown in FIG.
17
. In
FIG. 17
, in an outer conductor
60
a
of a coaxial feed line
60
, an annular slit
61
is provided at predetermined spacing. Outside outer conductor
60
a
of coaxial feed line
60
, a pair of ¼-wavelength sleeve-like metal pipes
62
is located on both sides of each annular slit
61
. Thus, a plurality of dipole antenna elements
63
are formed. Between the lowest dipole antenna element
63
and an input terminal
64
, a plural-stage ¼-wavelength impedance conversion circuit
65
is provided for impedance matching. Also, in
FIG. 17
,
60
b
denotes an inner conductor of coaxial feed line
60
.
In the sleeve antenna as shown in
FIG. 15
, the coaxial feed line does not affect the antenna characteristics when the antenna is used as a vertically polarized plane wave antenna. However, the sleeve-like metal pipe forms a balun, and therefore the antenna is a narrow band antenna. Thus, the antenna must be adjusted to have a band that is sufficiently broader than a desired band in view of a difference in the resonance frequency of the antenna that may result due to a variation in the size of a component and a variation in finished size in the manufacturing process. In this case, making the diameter of a sleeve-like metal pipe large is one way to implement a broad band. However, if the diameter of the sleeve-like metal pipe is large, the antenna becomes heavier, and therefore supporting metal fittings provided in a base station become large.
In the sleeve antenna as shown in
FIG. 16
, a directional pattern can be set in any direction by the passive element. Therefore, the antenna is an antenna for a base station that is effective in covering only the range of a specific direction in indoor location, for example. However, in the above structure, the dipole antenna and the passive element are exposed, and therefore the structure is not sufficient for weather resistance and mechanical strength in outdoor location. Furthermore, this structure requires a supporting means for the passive element, and therefore the manufacturing is troublesome.
Generally, in a colinear array antenna having a large gain that is used in a base station, a standing wave ratio (SWR) in a used frequency band is required to be 1.5 or less. In order to implement this, a plural-stage ¼-wavelength impedance conversion circuit is provided to perform impedance matching in the conventional structure as mentioned above (FIG.
17
). Therefore, the structure is complicated, and the entire length of the antenna is long. These problems are factors that prevent the small size and low cost for a base station, while base stations are increasingly installed for securing the number of channels for mobile radio.
SUMMARY OF THE INVENTION
The present invention seeks to provide a narrow and light mobile radio antenna that uses convenient supporting metal fittings provided in a base station.
Also, the present invention seeks to provide a mobile radio antenna that is suitable for outdoor location, has a simple structure, and is easily manufactured.
Furthermore, the present invention seeks to provide a colinear array antenna for mobile radio in which broad band matching characteristics can be obtained without using an impedance conversion circuit, and which has a small and simple structure.
A first structure of a mobile radio antenna according to the present invention comprises a dipole antenna having a coaxial feed line formed of an outer conductor and an inner conductor that are concentrically located with a dielectric therebetween, an antenna element formed by extending the inner conductor upward by a length corresponding to approximately a ¼ wavelength from the upper end of the outer conductor, and a ¼-wavelength sleeve-like conductor having a closed end and an open end located outside the coaxial feed line with the closed end connected to the outer conductor; and an insulating spacer interposed between an inner wall of the sleeve-like conductor and the coaxial feed line at the open end of the sleeve-like conductor; wherein the insulating spacer is configured to control a resonance frequency of the dipole antenna by adjusting an insertion depth of the insulating spacer. According to this first structure of the mobile radio antenna, a broad band can be implemented by changing the insertion depth of the insulating spacer, and therefore the diameters of the antenna element and the sleeve-like conductor can be optimized to minimize the size and weight of the antenna. As a result, a narrow and light mobile radio antenna that uses a convenient supporting metal provided in a base station can be implemented.
In the first structure of the mobile radio antenna of the present invention, an internal thread may be formed on a part of the inner wall of the sleeve-like conductor at the open end by tapping or drawing, and an external thread may be formed around a periphery of the insulating spacer. According to this example, the insertion depth of the insulating spacer can be readily controlled by a thread means comprising an internal thread and an external thread. In particular, according to the structure in which an internal thread is formed by drawing, a sleeve-like conductor having a thin thickness can be used. Therefore, a lighter mobile radio antenna can be implemented.
In the first structure of the mobile radio antenna of the present invention, a plurality of steps may be provided on a part of the inner wall of the sleeve-like conductor at the open end, and a tip end of the insulating spacer may be configured to form a snap fit with the open end of the sleeve-like conductor. According to this example, the mobile radio antenna in which the insertion depth of the insulating spacer does not change even if an external impact such as vibration is given can be implemented in a simple structure.
A second structure of a mobile radio antenna according to the present invention comprises a dipole antenna having a coaxial feed line formed of an outer conductor and an inner conductor that are concentrically located with a dielectric therebetween, an annular slit provided in a predetermined position of the outer conductor as a feed point, and a p
Nakamura Hiroyuki
Ogawa Koichi
Otomo Yasuhiro
Yamabayashi Masaaki
Yuda Naoki
Matsushita Electric - Industrial Co., Ltd.
Morrison & Foerster / LLP
Phan Tho
Wong Don
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