Communications: directive radio wave systems and devices (e.g. – Directive – Including antenna orientation
Reexamination Certificate
1998-10-30
2001-07-31
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including antenna orientation
C342S357490, C701S224000
Reexamination Certificate
active
06268826
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of satellite communications. More particularly, the present invention relates to an improved method of determining the initial parameters necessary to correctly aim a satellite dish or antenna at a particular target geosynchronous satellite from which a communications signal is to be received.
BACKGROUND OF THE INVENTION
Geosynchronous satellites are used, for example, to relay data, voice, telephony and analog/digital television signals from an uplink location to one or many users at various downlink locations. Geosynchronous satellites are placed in orbit in the Earth's equatorial plane at an altitude of 35,784 kilometers. At this altitude, the orbital period of the satellite equals one sidereal day (86,156 seconds). In other words, the satellite orbits the Earth at approximately the same speed as the Earth rotates about it's axis. The result is that the satellite appears stationary to observers on the Earth's surface and can relay communications signals along a direct line-of-sight to all earth-based receivers which are not beyond the horizon of the satellite.
Typically, satellite receiving antennas include a parabolic reflecting dish that focuses the transmitted satellite signal onto an antenna feed. The feed converts the electromagnetic wave energy to electrical signals that can be decoded and/or displayed by the equipment of the end user, for example, a television set.
Because the transmission of communications signals from the satellite is along a direct line-of-sight path, an antenna used to receive such signals from geosynchronous satellites must be pointed accurately toward the satellite in its orbital position. Antennas with large dish apertures have a higher gain than smaller dishes and, therefore, require more accurate aiming at the broadcasting satellite. The dish aperture is the shape of the antenna as viewed down its boresight axis.
The parameters used to describe the direction in which a satellite antenna is pointed are typically azimuth (measured in degrees from the direction of true North at the antenna site) and elevation (measured in degrees from the local horizontal plane). The necessary azimuth (“AZ”) and elevation (“EL”) to aim an antenna at a particular satellite are easily determined from simple geometric considerations once the latitude and longitude of the antenna, and the longitude of the satellite being targeted are known.
FIG. 1
illustrates a typical satellite dish
101
which is aimed to communicate with a satellite
102
in geosynchronous orbit. As illustrated, the elevation (EL) of the dish is the angle between the radio axis of the dish and the horizontal plane. The azimuth (AZ) of the dish is the angle between the vertical plane containing the radio axis of the dish and true North (N).
Satellite antenna systems typically include the necessary electronic components for monitoring the antenna's azimuth and elevation. Motorized systems capable of moving the antenna can then be placed in a feedback loop with the azimuth and elevation monitoring systems. With such a loop, the antenna can be automatically moved from a known orientation to one in which is it accurately aimed at a target satellite corresponding to a specified azimuth and elevation.
An antenna's azimuth can be roughly measured using a magnetic compass to determine true North. However, because the Earth's magnetic field varies locally at each point on the Earth's surface, the compass reading alone cannot result in a perfectly accurate determination of the antenna's actual azimuth. Therefore, the aim of the satellite will also contain an error factor.
Consequently, there is a need in the art for a method and apparatus of aiming a satellite antenna which more accurately determines the azimuth of the satellite antenna so that the antenna can be more precisely aimed at a target satellite.
SUMMARY OF THE INVENTION
Consequently, it is an object of the present invention to meet the above-described needs and others. Specifically, it is an object of the present invention to provide a method and apparatus for more precisely determining the required azimuth of a satellite antenna so that the antenna can be more accurately aimed. It is an additional object of the present invention that the method and apparatus of the present invention be implemented so that it can be easily operated by the average person without training or technical ability in satellite communications.
Additional objects, advantages and novel features of the invention will be set forth in the description which follows or may be learned by those skilled in the art through reading these materials or practicing the invention. The objects and advantages of the invention may be achieved through the means recited in the attached claims.
To achieve these stated and other objects, the present invention may be embodied and described as a method for aiming a satellite antenna at a target satellite by determining a local magnetic variation in Earth's magnetic field; and calculating an azimuth at which the antenna is to be aimed which is corrected for the local magnetic variation. The determination of the local magnetic variation is accomplished by receiving location designation data from a user which designates a location of the antenna; and determining the local magnetic field variation corresponding to that location.
Determination of the local magnetic field variation is performed using a model which represents variations in Earth's magnetic field. Preferably, the model used is the International Geomagnetic Reference Field (IGRF) model.
When receiving location designation data, the system of the present invention may be receiving the longitude and latitude of the antenna if known and input by the user. Alternatively, the system may be receiving location designation data comprising a well-known location designator, such as the ZIP Code of the antenna, input by the user. Where the ZIP Code is input, the method of the present invention includes matching the ZIP Code to a longitude and latitude of the ZIP Code.
The method also includes receiving target satellite designation data from the user. Receiving target satellite designation data may include receiving the longitude of the target satellite if it is known to and input by the user. Alternatively, the method may include receiving a name of the target satellite from the user and determining a longitude of the satellite by referencing a look-up table correlating satellite names and longitudes.
The present invention also encompasses a method of aiming a satellite antenna which does not include correcting for local variation in the Earth's magnetic field. Such a method includes the steps of receiving a ZIP Code input by a user; from the ZIP Code, determining a latitude and longitude of the antenna; and calculating an azimuth at which the antenna is to be pointed to receive signals from the target satellite based on the latitude and longitude.
This method also includes receiving a designation of the target satellite input by a user; from the designation, determining a longitude of the satellite; and calculating an azimuth and elevation at which the antenna is to be pointed to receive signals from the target satellite based on the latitude and longitude of the antenna and the longitude of the satellite.
The present invention also encompasses an apparatus for aiming a satellite antenna at a target satellite which includes a processor; a user input device through which a user can input a designation of a location of the antenna to the processor; and a memory unit connected to the processor. The processor, using the designation of the location of the antenna, accesses a model of local variation of Earth's magnetic field stored in the memory unit, and corrects parameters for aiming the antenna based on variation of Earth's magnetic field at the location of the antenna.
A look-up table is stored in the memory unit which correlates ZIP Codes with latitude and longitude.
Hardy Fred
Holborow Clive
King Jim
Schmidt Mark
Kananen Ronald P.
Motorola Inc.
Mull Fred H
Rader Fishman & Grauer
Tarcza Thomas H.
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