Communications: radio wave antennas – Antennas – Wave guide type
Reexamination Certificate
2000-09-08
2002-11-19
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Wave guide type
C343S7810CA
Reexamination Certificate
active
06483475
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a parabolic antenna for use in satellite broadcasting or satellite communication and more particularly, to a primary radiator and a block-down-converter which constitute the parabolic antenna.
2. Background Art
Conventionally, parabolic antennas which receive radio waves from a plurality of stationary satellites by a single reflector are referred to as “dual-beam antennas” or “multi-beam antennas” and are mainly adapted to receive radio waves from two satellites located on a stationary orbit with a difference of longitude of 8 degrees.
One example of the parabolic antennas is proposed in Japanese Utility Model Laid-Open Publication No. 3-107810 (1991) and
FIG. 27
is a perspective view showing its arrangement. In
FIG. 27
, a dual-beam antenna
100
includes primary radiators
102
and
103
constituting a double primary radiator and a reflector
101
. The primary radiators
102
and
103
and the reflector
101
are coupled with each other by a support arm
104
so as to have a predetermined positional relationship. Radio waves from first and second satellites are reflected by the reflector
101
so as to be, respectively, received by the primary radiators
102
and
103
. In this dual-beam antenna, axes of the primary radiators are disposed so as to extend horizontally at the time of reception.
Meanwhile, circular polarization is employed as polarization in satellite broadcasting, while linear polarization of two kinds, i.e., in vertical and horizontal directions is employed as polarization in satellite communication. Therefore, radio waves from a communication satellite contain a polarization angle dependent on a receiving point and thus, this polarization angle should be adjusted.
A method of adjusting the polarization angle is proposed in Japanese Utility Model Laid-Open Publication No. 6-52217 (1994).
FIG. 28
is a perspective view indicative of one example of adjustment of the polarization angle. As shown in
FIG. 28
, the adjustment is performed by rotating an arm
113
through an angle &thgr;b about an axis of a fixed primary radiator
111
and further, rotating a primary radiator
112
through an angle &thgr;a about its own axis.
FIG. 29
a relationship between antenna diameter D and primary radiator spacing L in the case where difference of longitude between two satellites on a station orbit is 8 degrees and 4 degrees. As shown in
FIG. 29
, the reflector diameter D and the primary radiator spacing L are substantially proportional to each other and an optimum value of the primary radiator spacing at the time the difference of longitude is 4 degrees is smaller than that at the time the difference of longitude is 8 degrees.
FIG. 30
shows a relationship between aperture diameter d of a primary radiator and antenna efficiency &eegr; in a single-beam antenna. As shown in
FIG. 30
, when the aperture diameter d assumes d
opt
, the antenna efficiency &eegr; reaches a maximum &eegr;
max
as follows. If the aperture diameter is small, radiation range over the reflector increases and thus, energy of the reflector spills from the reflector, namely, spill-over happens. On the other hand, if the aperture diameter is large excessively, radiation range decreases and thus, an edge portion of the reflector does not work.
Therefore, in case a dual-beam antenna for receiving radio waves from two satellites with a difference of longitude of 4 degrees is formed by using an antenna having a diameter Do and primary radiators having an optimum aperture diameter d
opt
, the spacing Lo should be larger than d
opt
. As shown in
FIG. 29
, in case a dual-beam antenna is formed by using a reflector having a smaller effective diameter Ds, the spacing L decreases to Ls. If the spacing Ls is smaller than d
opt
, the aperture diameter d necessarily becomes smaller than d
opt
yielding the maximum efficiency &eegr;
max
, so that the antenna efficiency &eegr; drops markedly to &eegr;
o
as shown in FIG.
30
and thus, it becomes difficult to obtain desired reception performance.
SUMMARY OF THE INVENTION
In order to obviate the above mentioned drawbacks, a double primary radiator of the present invention has a construction in which by using a small-diameter parabolic reflector having an effective diameter of, for example, 45 cm, two primary radiators are integrally joined with each other so as to receive radio waves from two satellites having a difference of longitude of, for example, 4 degrees.
In the double primary radiator of the present invention, since apertures of the primary radiators are arranged to face each other inwardly, it is possible to compensate for reduction of radiation area due to defocus caused in the case where a dual-beam antenna is arranged such that a central point of a joint part of the double primary radiators is located in the vicinity of a focal point of the reflector.
Since a block-down-converter of the present invention can be rotated as a whole about a perpendicular radiation axis, tilt angle of the two radiators can be adjusted relative to polarization angle at a time.
In the block-down-converter of the present invention, if an initial shift angle for adjusting polarization angle is set to that of a point located substantially at a center of a longitudinal range of a receiving area, adjustment of the initial shift angle can be substantially optimized throughout the receiving area. Therefore, since it is not necessary to adjust the initial shift angle for each receiving point, the block-down-converters can be mass produced.
Meanwhile, since the block-down-converter of the present invention has a construction in which a double primary radiator and a housing containing a conversion circuit for performing amplification and frequency conversion of received radio waves are integrally molded, the block-down-converter can be produced by a simple process such as injection molding employing a die, thereby resulting in a reduced production cost.
REFERENCES:
patent: 4757324 (1988-07-01), Dhanjal
patent: 5113197 (1992-05-01), Luh
patent: 5426442 (1995-06-01), Haas
patent: 5486839 (1996-01-01), Rodeffer et al.
patent: 5812096 (1998-09-01), Tilford
patent: 6166704 (2000-12-01), Jan et al.
patent: 56-141603 (1981-11-01), None
patent: 58-185409 (1984-10-01), None
patent: 63-184406 (1988-07-01), None
patent: 3-155203 (1991-07-01), None
patent: 3-107810 (1991-11-01), None
patent: 4-150602 (1992-05-01), None
patent: 6-69722 (1994-03-01), None
patent: 6-52217 (1994-07-01), None
patent: 9-36655 (1997-02-01), None
patent: 10-145138 (1998-05-01), None
patent: 11-17440 (1999-01-01), None
Dinh Trinh Vo
Wong Don
LandOfFree
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