Communications: radio wave antennas – Antennas – Wave guide type
Reexamination Certificate
1999-12-29
2001-11-20
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Wave guide type
C343S772000
Reexamination Certificate
active
06320554
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a feed horn for satellite broadcasting reception. Particularly, the invention is concerned with a feed horn suitable for a parabola antenna having an elliptic reflector with the major axis of the ellipse extending in the horizontal direction.
2. Description of the Prior Art
A conventional feed horn will now be described with reference to
FIGS. 6
to
8
. The feed horn is used in a parabola antenna
41
for the reception of satellite broadcasting signals. The receiving antenna
41
is provided with a circular reflector
42
, the feed horn indicated at
43
, and a reception circuit (not shown). The reflector
42
and the feed horn
43
are opposed to each other. The reflector
42
reflects a signal transmitted from a broadcasting satellite and the reflected wave from the reflector
42
is inputted to the reception circuit through the feed horn
43
.
The feed horn
43
has a horn portion
44
and a cylindrical waveguide
45
connected to the horn portion
44
. The horn portion
44
is provided for making it easier to pick up the reflected wave from the reflector
42
in the reception antenna
41
. The horn portion
44
has an opening
46
of a circular section which is formed in a divergent horn shape from one axial end
44
a
of the horn portion toward a front end
44
b.
The waveguide
45
is a transmission path for conducting a transmitted signal to the reception circuit, with an opening portion
45
a
of a circular section being formed in the interior of the waveguide. One end
45
b
of the opening
45
a
in the axial direction of the waveguide
45
and the axial end
44
a
of the opening portion
46
are connected together and an opposite end
45
c
in the axial direction of the waveguide
45
is connected to the reception circuit.
In the feed horn
43
constructed as above, a signal transmitted from a broadcasting satellite is reflected by the reflector
42
of the receiving antenna
41
and the reflected wave is inputted to the reception circuit via the feed horn
43
.
With the recent tendency to a multi-channel satellite broadcasting, a large number of broadcasting satellites lie on the geostationary orbit and there is now a demand for improvement in directivity in the longitude direction of the receiving antenna so that a reception side of a satellite broadcasting can receive a signal transmitted from only a broadcasting satellite that transmits a desired broadcasting program from among such many broadcasting satellites.
However, in the use of the receiving antenna
41
constituted of both the circular reflector
42
and the feed horn
43
possessing a circular directivity, there is no other method than increasing the area of the circular reflector
42
for improving the directivity, thus giving rise to the problem that the cost of the antenna becomes high.
Moreover, since the feed horn
43
has the opening portion
46
of a circular section constituted of one side face portion which expands in the shape of a horn from one axial end
44
a
toward the front end
44
b
of the horn portion
44
, the transmitted signal is apt to be reflected at the side face of the opening portion
46
. Although this reflection can be diminished by making the inclination of the inner side face of the opening portion
46
steep, it is necessary that the distance D
5
between the one axial end
44
a
and the front end
44
b
of the horn portion
44
be set long. As a result, not only the feed horn
43
becomes longer and larger in size, but also the amount of the material required for fabricating the feed horn
43
increases, thus giving rise to the problem that the cost of the feed horn
43
becomes high. Further, crosstalk is apt to occur because the electromagnetic field distribution in the opening portion
46
of the feed horn
43
is an H
11
mode distribution.
The use of an elliptic reflector may be effective as a method for reducing the area of the circular reflector
42
and improving the directivity in the longitude direction. However, if the feed horn
43
of a circular directivity shown in
FIGS. 7 and 8
is combined with an elliptic reflector, the directivity of the feed horn
43
no longer matches the shape of the reflector, so that not only the reception efficiency is deteriorated but also it becomes easier to pick up noise signals from the surroundings, thus leading to deteriorated directivity of the antenna.
SUMMARY OF THE INVENTION
The present invention has been accomplished for solving the above-mentioned problems and it is an object of the invention to provide a feed horn small in size and having a high elliptic directivity and remedy crosstalk.
According to the first means adopted by the present invention for solving the above-mentioned problems there is provided a feed horn comprising a waveguide of a circular section and a horn portion, the horn portion having a base end connected to the waveguide and being expanded in a horn shape from the base end toward a front end to define an elliptic open end, wherein a plurality of elliptic ridges extending in parallel toward the open end are formed in the shape of concentric ellipses on an inner slant peripheral surface of the horn portion in such a manner that the spacing between two adjacent ridges is equal throughout the whole circumferneces of the ridges and that a virtual plane formed by connecting tip ends of the ridges is in a horn shape along the inner slant peripheral surface of the horn portion.
According to the second means adopted by the invention for solving the foregoing problems, the ridges are formed at the same height from the inner slant peripheral surface of the horn portion.
According to the third means adopted by the invention for solving the foregoing problems, the ridges are formed so that the difference in height between the tip ends of two adjacent ridges is equal with respect to all of adjacent ridges.
According to the fourth means adopted by the invention for solving the foregoing problems, the depth from an intersecting point of a straight line and an oblique line to the bottom of a groove formed by two adjacent ridges is set approximately at a quarter of the wavelength of a transmitted signal, the straight line passing through a center of the groove and parallel to an axis of the horn portion and the oblique line being obtained by connecting the tip ends of the two adjacent ridges.
According to the fifth means adopted by the invention for solving the above-mentioned problems, the horn portion is provided in a base portion thereof with a cylindrical elliptic tapered portion having one end which is circular and an opposite end which is elliptic, the cylindrical elliptic tapered portion having a length approximately half of the wavelength of a transmitted signal.
REFERENCES:
patent: 4658258 (1987-04-01), Wilson
patent: 5486839 (1996-01-01), Rodeffer et al.
patent: 5552797 (1996-09-01), Cook
patent: 5793335 (1998-08-01), Anderson
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Chen Shih-Chao
Wong Don
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