Communications: radio wave antennas – Antennas – With coupling network or impedance in the leadin
Utility Patent
1999-09-03
2001-01-02
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
With coupling network or impedance in the leadin
C343S757000, C342S357490
Utility Patent
active
06169522
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to antennas and, more particularly, to antennas which generate and steer communication beams toward moving communications nodes.
BACKGROUND OF THE INVENTION
In a high bandwidth communications system, where communications nodes are in motion relative to earth-based subscriber units, a subscriber unit must maintain a link with the moving communications node using a narrow communications beam. A narrow communications beam allows the earth-based subscriber unit to transmit information to, and receive information from, the moving communications node using high data rates. Typically, as a receive or transmit communications beam becomes progressively more narrow, an increasingly higher data rate can be used to communicate information between the communications node and the earth-based subscriber unit due to the increased concentration of energy in the communications beam.
Previous earth-based systems used for acquiring and tracking moving communications nodes, such as satellites placed in a low earth orbit, involve the use of mechanically steered reflector antennas. However, when the moving communications node is a low earth orbiting satellite, the satellite may travel from one horizon to another in only a few minutes. Consequently, the low earth orbiting satellite may be in view of the subscriber unit for only a short period of time while moving rapidly overhead. Therefore, the pointing direction of the mechanically steered reflector antenna requires virtually constant correction in order to maintain the communications link between the satellite and the earth-based subscriber unit, thus causing the mechanical components of the reflector antenna to wear out and require periodic replacement. This periodic replacement increases the cost which an earth-based subscriber must pay in order to receive and transmit high bandwidth information to and from a moving satellite communications node.
Other disadvantages of mechanically steered reflector antennas include a large physical size and an inability to steer the antenna quickly, as is required when communications with one satellite must be suspended at the horizon and another satellite must be acquired at an opposite horizon.
Other techniques for maintaining a link with a moving communications node involve the use of two-dimensional electronically scanned arrays which make use of a digital beamforming network. In a two-dimensional antenna array which uses a digital beamforming network, each transmit antenna element incorporates an individual power amplifier. Additionally, each receive element incorporates an individual low noise amplifier. The need for individual amplification in both the receive and transmit antenna elements, as well as the need to perform a large number of digital operations in the beamforming network, and the need for a large number of interconnections between the beamforming network and the array of antenna elements necessitates substantial complexity in the required electronics. This additional complexity increases the cost of the satellite communications system.
Therefore, what is highly desirable, is a subscriber antenna system with a reduced number of constituent moving parts which provides beam steering towards a moving communications node. What is also highly desirable, is a subscriber antenna system with a reduced number of transmitting and receiving antenna elements in order to reduce the complexity of the beamforming network. These features can lower the cost of the earth-based subscriber equipment and allow the benefits of the satellite communications system to be accessible to a greater number of earth-based subscribers.
REFERENCES:
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patent: 3916415 (1975-10-01), Howery
patent: 4034374 (1977-07-01), Kruger
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patent: 5023634 (1991-06-01), Nishioka et al.
patent: 5686923 (1997-11-01), Schaller
patent: 5936592 (1999-08-01), Ramanujam et al.
Corman David Warren
Dendy Deborah
Ma Stephen Chihhung
Munger A. David
Torkington Richard Scott
Bogacz Frank J.
Ho Tan
Limon Jeff D.
Motorola Inc.
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