Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2001-12-14
2004-03-16
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S893000
Reexamination Certificate
active
06707426
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a circularly polarized wave antenna used for performing communication between a geostationary satellite and a mobile station.
2. Description of the Related Art
In mobile units, such as automobiles, in a system for communicating with a geostationary satellite or receiving broadcasts, circularly polarized waves are generally utilized. Accordingly, there is a demand for a small circularly polarized wave antenna for obtaining stable circularly polarized waves over a wide range of wave angles.
FIGS. 18A and 18B
illustrate a typical example of a conventional circularly polarized wave antenna
101
. More specifically,
FIG. 18A
is a perspective view of this antenna, and
FIG. 18B
is a side view of this antenna. The circularly polarized wave antenna
101
is formed of a ground plate
102
and four conductors
103
. Each conductor
103
is formed by extending the central conductor of a coaxial cable
104
. The external conductor of the coaxial cable
104
is soldered to the ground plate
102
, as indicated by a soldering portion
105
. Accordingly, each conductor
103
is fixed on the ground plate
102
in a cantilever form. The conductors
103
are disposed on the ground plate
102
with equal distances d, and tilt in the predetermined directions at a predetermined angle &agr;.
In the circularly polarized wave antenna
101
constructed as described above, mutually in-phase power is supplied to the four conductors
103
so as to generate a spatial phase difference of 90°. Accordingly, a main beam is directed at a certain wave angle, and a circularly polarized wave is radiated in the direction of the wave angle. Also, a conical-surface pattern at the wave angle becomes non-directional. That is, the directivity of the circularly polarized wave antenna
101
becomes as shown in
FIG. 19
as viewed from any azimuth angle. When a geostationary satellite
107
is positioned at a line extending from an inclined line
106
, the circularly polarized wave antenna
101
can always be directed at the geostationary satellite
107
regardless of the direction in which a mobile unit on which the circularly polarized wave antenna
101
is mounted is moved. It is now assumed that the target wave angle ranges from 30° to 60°. In this case, if the tilting angle &agr; of the conductor
103
is set to be about 45°, the length L of the conductor
103
is set to be about 0.65&lgr;
0
, and the distance d between the two opposing conductors
103
is set to be about 0.33&lgr;
0
(where &lgr;
0
indicates the free space wavelength), the optimal directivity for the above-described range of the wave angles can be obtained.
In the above-described conventional circularly polarized wave antenna
101
, the four conductors
103
are disposed on the ground plate
102
with the equal distances d while being tilted at about 45°, and mutually in-phase power is supplied to the conductors
103
. With this configuration, a phase shifter is not required for supplying power, and thus, the configuration of the circularly polarized wave antenna
101
can be simplified. However, as discussed above, since the four conductors
103
(having a length of approximately 0.65&lgr;
0
) are disposed with the equal distances d (approximately 0.33&lgr;
0
) at about 45°, the overall dimensions of the antenna
101
result in 0.33&lgr;
0
×0.33&lgr;
0
×0.46&lgr;
0
. If the frequency of 2.3 GHz (&lgr;
0
=130 mm) is used, the overall dimensions of the antenna
101
increase to 43 mm×43 mm×60 mm. Thus, the antenna
101
is not small enough to be used as a vehicle-mounted antenna. Additionally, since the conductors
103
are fixed to the ground plate
102
only in a cantilever form, they are not mechanically strong. Accordingly, due to vibrations generated in an automobile, the distances d between the conductors
103
may be changed, resulting in increased variations in the characteristics of the antenna
101
, or a large stress may be applied to the soldering portions
105
of the external conductors of the coaxial cables
104
so as to cause a poor connection between the coaxial cables
104
and the ground plate
102
.
SUMMARY OF THE INVENTION
Accordingly, in view of the above-described background, it is an object of the present invention to provide a compact, vibration-resistant circularly polarized wave antenna.
In order to achieve the above object, according to the present invention, there is provided a circularly polarized wave antenna including a quadrilateral columnar member mounted on a printed circuit board. Four radiation conductors are provided on corresponding side surfaces of the dielectric member while tilting in predetermined directions. The bottom ends of the radiation conductors are electrically connected to the printed circuit board, and mutually in-phase power is supplied to the four radiation conductors.
With this configuration, since the four radiation conductors are provided on the corresponding side surfaces of the quadrilateral columnar dielectric member, the length of the radiation conductors can be decreased due to the wavelength reduction factor as a result of the dielectric constant of the dielectric member. Thus, the size of the circularly polarized wave antenna can be significantly reduced. Additionally, the radiation conductors are mechanically orthogonal to each other by the dielectric member, thereby reducing variations in the characteristics or a poor connection caused by external vibrations.
In the aforementioned circularly polarized wave antenna, a through-hole extending in the axial direction may preferably be provided at the center of the dielectric member. Accordingly, the dielectric member can be lighter, and the axial ratio of circularly polarized waves at a desired frequency can be reduced. In this case, the through-hole may be formed in any shape, such as in a quadrilateral shape or in a circular shape when viewed from above, as long as it is symmetrical with respect to the axial line of the dielectric member. If the through-hole is formed in a quadrilateral shape when viewed from above, dimensional variations in molding the dielectric member can be reduced since the through-hole is similar to the outer configuration of the dielectric member.
In the aforementioned configuration, an adjusting portion may be disposed in the through-hole, and a predetermined resonant frequency may be set by adjusting the size or the mounting position of the adjusting portion. With this arrangement, variations in the antenna characteristics caused by dimensional errors of the dielectric member can be easily corrected. Thus, the resonant frequency can be easily set to a desired frequency, and the manufacturing yield can be substantially improved.
For example, the adjusting portion may be a dielectric block which is inserted into the through-hole and is mounted on the printed circuit board. Then, the resonant frequency of the circularly polarized wave antenna can be increased by decreasing the thickness of the dielectric block. Thus, if the resonant frequency is set to a value slightly lower than the desired frequency in advance, the desired resonant frequency can be easily and reliably obtained simply by decreasing the thickness of the dielectric block to a suitable value. Alternatively, the through-hole may be circular when viewed from above, and a screw thread may be formed on the inner wall surface of the through-hole, and the adjusting portion may be a dielectric male screw to be screwed into the screw thread. In this case, the resonant frequency decreases as the dielectric male screw is inserted into a lower portion of the through-hole. In contrast, the resonant frequency decreases as the dielectric male screw is inserted into a higher portion of the through-hole. Thus, the resonant frequency can be easily and reliably set to the desired frequency only by adjusting the screwing position of the dielectric male screw to a suitable position.
In the aforementioned configuration, the dielectric member may inc
Higasa Masahiko
Shigihara Makoto
Alps Electric Co. ,Ltd.
Chen Shih-Chao
Wong Don
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