Communications: radio wave antennas – Antennas – Antenna components
Reexamination Certificate
2000-12-20
2002-08-13
Phan, Tho (Department: 2821)
Communications: radio wave antennas
Antennas
Antenna components
C343S912000
Reexamination Certificate
active
06433757
ABSTRACT:
FIELD OF THE INVENTION
The present invention is related to telecommunications antennas and, in particular, to alignment of microwave reflector antennas.
BACKGROUND
Microwave antennas for line-of-sight terrestrial communications and earth station satellite communications often use large curved reflectors and are sometimes referred to as “dish” antennas. The reflector comprises a metal material to reflect radio waves. For receiving signals, the large reflector is used to collect and focus electromagnetic waves into a receiver to obtain a stronger signal at the receiver. For transmitting, this type of antenna has a highly directional characteristic, resulting in efficient transmission of signals to a distant target.
FIG. 1
shows a typical antenna
100
comprising a main reflector
110
. Antenna
100
depicted in
FIG. 1
uses a particular arrangement of reflectors known as Gregorian optics. A typical commercially available antenna of this type is the 3.7 -meter earth station antenna which is available from Andrew Corporation 10500 W. 153rd St. Orland Park, Ill. 60462. In accordance with this arrangement, a subreflector
120
is suspended in front of the main reflector
110
by several struts
122
running from the main reflector
110
to subreflector
120
. Subreflector
120
is substantially aligned with the axis of symmetry of main reflector
110
. Protruding from main reflector
110
along the axis of symmetry and into the focal point of the reflector assembly is the so-called “feed horn”
130
. Feed horn
130
is a hollow waveguide through which radio signals at the antenna are coupled to electronic instruments such as receivers and transmitters. Feed horn
130
may conduct signals from a microwave transmitter coupled to antenna
100
. The signals from the transmitter (not shown) are emitted from feed horn
130
, strike subreflector
120
, and then are reflected back to main reflector
110
. From there, the signals are sent forth from antenna
100
to reach a distant target. Conversely, for receiving, the signals from a remote target strike main reflector
110
, are collected and focused upon subreflector
120
, the curvature of which causes the signals to become somewhat more focused and to be coupled into antenna feed horn
130
.
Alignment of such an antenna is important to its performance because of the high degree of directionality of the antenna and the distances typically traversed by a radio signal, which may range from 10-30 miles in the case of terrestrial links to around 22,300 miles in the case of a satellite in geosynchronous orbit. At these distances, even a slight angular misalignment can cause loss of signal path. Misalignment or distortion in the shape of the antenna can also cause both received and transmitted signals to be weakened. At microwave frequencies, even slight distortions in the antenna or the waveguides used to coupled signals to and from the antenna can seriously affect signal quality. Sufficient distortions in the shape of the antenna can cause more complex forms of signal impairments, affecting frequency response and phase relationships.
Another aspect of antenna alignment relates to the polarization of the signal, referring to the orientation of the electric and magnetic components of the signal as it propagates. In order to successfully transmit a signal from one antenna to another, the receiver must be receptive to the same polarization emitted by the transmitter. Otherwise, even though the transmitting antenna may be directed to transmit signals at the receiving antenna, the signal may not be received if the transmitted signal is polarized in a substantially vertical direction while the receiver is receptive to signals that are polarized in a relatively horizontal direction. A corresponding receiver and transmitter must be aligned in terms of polarization.
Generally, adjustments are provided in the mounting of the antenna to allow coarse and fine positioning of the entire antenna assembly to point at a desired target. Furthermore, the orientation of the polarization for received or transmitted electromagnetic waves may be altered by rotating the feed horn, along with the associated waveguide couplers and such attached to the back end of the feed horn. Generally a feed horn assembly can be rotated within a reflector assembly. In one common arrangement, the base of the feed horn, the “feed hub” is circular and concentrically nested into the so-called “vertex opening” at the center of the reflector. Once the feed horn assembly has been rotated to an optimum position, clamping fasteners around the perimeter of the feed hub are tightened to secure the feed horn assembly to the reflector.
For example,
FIG. 1
shows a mounting ring
112
attached to reflector
110
such that mounting ring
112
surrounds the vertex opening at the back of reflector
110
. Feed hub
132
is concentric with, and seated within, mounting ring
112
. Feed hub
132
rigidly supports feed horn
130
and rotation of feed hub
132
accomplishes rotation of feed horn
130
. Feed hub
132
comprises a number of fastener positions
136
and
137
where clamping fasteners may be placed to secure feed hub
132
in place within mounting ring
112
.
In attempting to rotate the feed horn during polarization alignment, service personnel have difficulty finding a suitable place to apply torque to rotate the feed hub because feed hub
132
tends to bind with mounting ring
112
. In many cases, tubular extension
134
is provided that protrudes behind the feed hub and is concentric with the feed tube. The manufacture of antenna intended that tubular extension of the antenna, be gripped by operational personal and used to rotate feed horn
130
. However, tubular extension
134
is usually so short that for only one hand to adequately engage the tube. Furthermore, tubular extension
134
is of small diameter, increasing the difficulty with which service personnel can grip and apply torque to precisely rotate the feed horn assembly.
Often, in lieu of using this torque tube extension, service personnel will use other attachments to feed horn
130
to more easily apply torque. Although not shown in
FIG. 1
, waveguide couplers/combiners and electronic units, such as receiver front-ends, may be attached behind extension
134
. When antenna
100
is configured with waveguide couplers/combiners and electronic units, feed hub
132
tends to bind even further with mounting ring
112
, due to the cantilever affect from the weight of to waveguide and electronic units on the interfacing surfaces of feed hub
132
and mounting ring
112
. The waveguide and/or electronics equipment presents a technician with a more prominent handhold for torqueing the feed tube assembly. However, applying torque to these sensitive components is risky and can result in the distorting or inadvertent breaking of waveguide feed components, potentially degrading or interrupting communications. Such damage can be extremely costly to repair. Moreover, some types of damage may be subtle enough to cause latent problems which are difficult and expensive to troubleshoot at a later time.
Thus, there is a need for an improved method by which a technician may easily and precisely align the polarization of the microwave antenna without exerting forces upon sensitive parts of the feed system.
The present invention provides for an improved method by which a feed system may be rotated within an antenna to facilitate the adjustment of polarization. The present invention provides for a novel polarization adjustment tool that engages the feed hub nested within the main reflector mounting ring. A technician using such a device may exert a torque directly to the feed hub without applying forces to other more delicate parts of the feed system.
In accordance with an exemplary embodiment, long lever arm is provided by the tool so that a technician may apply torqueing forces with less effort applied at the handle. The long lever arm improves the accessibility of the adjustment and dramatically improves the precision with which the feed asse
Phan Tho
WorldCom, Inc.
LandOfFree
Antenna polarization adjustment tool does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Antenna polarization adjustment tool, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Antenna polarization adjustment tool will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2941039