Communications: radio wave antennas – Antennas – With support for antenna – reflector or director
Reexamination Certificate
1999-06-17
2001-02-13
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
With support for antenna, reflector or director
C343S880000
Reexamination Certificate
active
06188372
ABSTRACT:
FIELD OF THE INVENTION
This invention is related to an antenna dish having integrally molded elements which aid in mounting and proper antenna alignment.
BACKGROUND OF THE INVENTION
To use a parabolic satellite antenna, the antenna and its feed must be properly aligned with the satellite. Many satellite transmissions are polarized, and thus the antenna assembly must also be rotated to the proper polarity orientation. A simple parabolic antenna is configured such that the central axis of the parabola passes through the center of the dish. Once the antenna is aimed at the satellite, it may be rotated around this axis to adjust the polarity without losing the satellite alignment. As can be appreciated, however, because the parabolic axis is centrally located, the feed must be centrally positioned in front of the antenna. This configuration blocks a portion of the signal and results in a performance degradation.
To address this problem, many parabolic antennas are designed so that the parabolic vertex is near or at the antenna's lower edge. Antennas of this type are commonly referred to as offset parabolic antennas, since the feed is offset from the antenna edge, thus reducing the signal blockage. Such an antenna arrangement
10
is illustrated in FIG.
1
. As shown, a parabolic antenna
12
has a vertex
14
which is adjacent its lower edge
16
. A line
18
running between the vertex
14
and the focal point
20
defines a boresight to the satellite. A feed horn
22
is mounted at the focal point
20
and directed toward the dish
12
to receive reflected energy. The antenna dish
12
is mounted on an antenna mount
24
. For reasons of balance, antenna mount
24
is generally attached to antenna
12
at or near the middle of the antenna.
The mount
24
is configured to allow the azimuth elevation of the antenna to be adjusted. In addition, the mount
24
is configured to allow the antenna to be rotated about a polarity axis
26
which is parallel to the boresight axis
18
. The polarity axis is shifted from the perpendicular relative to the antenna attachment points. Thus, the mount
24
must be configured with this angular deviation in mind.
FIGS. 2
a
and
2
b
are side and back views, respectively, of a conventional mounting assembly
24
. To compensate for the fact that the vertex of the antenna
12
is not centrally located, a separately mounted polarity plate
30
is provided. Polarity plate
30
, generally formed using stamped steel, affixed to a predetermined location in the back of the antenna
12
after the antenna is manufactured, e.g., by means of bolts
31
. As can be appreciated, both the boresight axis
18
and the polarity axis
26
are perpendicular to a polarity plane
28
. The polarity plate
30
has a flat back plane
32
and is dimensioned such that when the plate
30
is bolted to the back of antenna
12
at the appropriate locations, the back plane
32
is perpendicular to the polarity axis
26
. Rotating the antenna
12
about an axis perpendicular to the back plane
32
permits the polarity of the antenna to be adjusted without altering the directional satellite alignment.
The satellite alignment mechanisms includes a pair of elevation brackets
34
with locking bolts
36
that engage elevation slots
37
and are configured to allow adjustment of the elevation of the antenna. As shown in
FIG. 2
b
, the polarity plate
30
include slots
38
formed in the back plane
32
. The brackets
34
are attached to the polarity plate
30
via bolts
39
which engage slots
38
in the polarity plate
30
so as to allow the antenna to rotate about the polarity axis.
Although accepted in the industry, the use of the separately attached stamped polarity plate, such as shown in
FIGS. 2
a
and
2
b
, has several drawbacks. First, the use of the additional components increases the cost of the antenna and assembly complexity. Separately formed components also decrease accuracy since fabrication tolerance errors for each component are added together, both in the angle of the back plane and the position at which the polarity plate is attached to the antenna. The separately attached plate also increases the number of mechanical stress points on the back of the antenna, and thus may reduce the performance and lifetime of the antenna under wind loads, particularly when the antenna is large. Additionally, care must be taken to ensure that when the antenna mount is assembled, the proper polarity plate
30
is attached. This is a particular concern when several antenna variations, perhaps having different dimensions and vertex locations are assembled in the same place or by the same personnel. If an improper back plane is attached, the error may not be noticed until after the antenna is fully assembled and installed, resulting in potentially costly repair.
Accordingly, it would be beneficial to provide an antenna arrangement which does not require the use of a separately mounted polarity plate.
It would also be advantageous to provide a molded antenna, such as a parabolic antenna, which includes integrally molded mounting components that are configured to provide the proper polarity plate without requiring the attachment of additional reference hardware.
SUMMARY OF THE INVENTION
According to the invention, a molded parabolic antenna is formed having a raised area on the back of the antenna which forms a plane at the proper angle for aligning the antenna system polarity to the satellites. This integrated polarity plate provides a surface to which antenna mounting brackets are attached and obviates the need for a separate polarity plate to be mounted on the antenna. According to a further aspect of the combined antenna polarity and elevation brackets are provided which include slots and scale indicators to permit accurate elevation and polarity adjustments to be made. Because the polarity and alignment slots and scales are formed on the same bracket, preferably with a center pivot, cumulative tolerance errors are reduced. When the antenna rotation setting is complete, the mounting brackets can be locked down to the integrally molded polarity plate with a clamping device or other securing mechanisms.
REFERENCES:
patent: 4404565 (1983-09-01), Gurney et al.
patent: 4692771 (1987-09-01), Rothbarth et al.
patent: 4860021 (1989-08-01), Kurosawa et al.
patent: 5604508 (1997-02-01), Atkinson
patent: 5734356 (1998-03-01), Chang
patent: 5870059 (1999-02-01), Reynolds
patent: 5929817 (1999-07-01), Clark
Abernethy Wallace
Jackson Gordon
Channel Master LLC
Darby & Darby
Tran Chuc D
Wong Don
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