Communications: directive radio wave systems and devices (e.g. – Directive – Including a satellite
Utility Patent
1999-11-08
2001-01-02
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a satellite
C342S372000
Utility Patent
active
06169513
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to satellite communications systems including antennas and devices for receiving and transmitting microwave signals, specifically, to systems including multiple beam phased array antennas, antenna feeds, and beam forming networks.
BACKGROUND OF THE INVENTION
In satellite communication systems, microwave signals are beamed between one or more ground stations and a satellite, or from one satellite to another satellite. In the ground station to satellite communication systems, each beam of signals is controlled to ensure a specific area of coverage, for example, a wide beam may cover a large area such as a country or continent, while a narrow beam may cover a small area such as a specific ground station. Additionally, a plurality of beams may be simultaneously radiated to cover a plurality of independent coverage areas. This technique is commonly referred to as multiple beam coverage. The present invention addresses the generation and positioning of independent multiple beams.
Networks which include multiple beam phased array antennas and devices for transmitting and receiving microwave signals are known for satellite communication systems, as evidenced by, for example, U.S. Pat. No. 3,953,857, issued Apr. 27, 1976, entitled “Airborne Multi-mode Radiating and Receiving System”, by F. Jenks. Other examples include U.S. Pat. No. 4,521,781, issued Jun. 4, 1985, entitled “Phase Scanned Microstrip Array Antenna”, by Campi et. al.; U.S. Pat. No. 4,652,880, issued Mar. 24, 1987, entitled “Antenna Feed Network”, by Moeller et. al.; U.S. Pat. No. 4,734,700, issued Mar. 29, 1988, entitled “Group Antenna with Electronically Phased-Controlled Beam”, by Brunner; U.S. Pat. No. 4,766,438, issued Aug. 23, 1988, entitled “Three Dimensional Feed Through Lens with Hemispherical Coverage”, by Tang; and U.S. Pat. No. 4,799,065, issued Jan. 17, 1989, entitled “Reconfigurable Beam Antenna”, by Thompson.
The conventional multiple beam phased array antennas and beam forming networks employ machined or electro-formed horns, separate filters, and delay line or ferrite phase shifters. These devices are coupled to wave guides and coaxial transmission lines, as well as other microwave components. These conventional configurations are relatively large and heavy. Large and heavy antennas are a disadvantage because the antennas are typically deployed in spacecraft where increased size and weight lead to increased launch costs. The conventional phased array antennas are also difficult and expensive to implement on a recurring basis because their components, the horns, filters and phase shifters, are individual electrical devices whose characteristics may vary from device to device. Additionally, it is difficult and expensive to assemble these devices into antennas in a manner which ensures that uniform antenna characteristics are maintained throughout the array.
Recently, the number of satellites deployed in geosynchronous orbit about the earth has increased significantly. The increase in the number of deployed satellites has lead to an increase in the number of microwave signals being transmitted from both the deployed satellites and communication networks based on the surface of the earth. As a result, higher interference levels are being experienced as the deployed satellites and the earth based networks attempt to communicate.
Thus, there remains a need for an efficient, light weight, easy to implement satellite communication system that minimizes interference from other systems.
OBJECTS AND ADVANTAGES OF THE INVENTION
It is a first object and advantage of this invention to provide a reliable satellite communication system that transmits and receives microwave signals utilizing different spectral regions, or frequency bands, at high radio frequencies.
Another object and advantage of this invention is to provide an antenna designed to include flexible beam placement, narrow beam width, and reduced weight components.
Another object and advantage of this invention is to provide an antenna, antenna feeds, and a beam forming network that places two or more independent, narrow beams anywhere in the coverage area of the antenna.
Another object and advantage of this invention is to provide an antenna element design having a plurality of radiators, wherein a stochastic process is used to select radiator positions and beams within an array.
Further objects and advantages of this invention will become more apparent from a consideration of the drawings and ensuing description.
SUMMARY OF THE INVENTION
The foregoing and other problems are overcome and the objects of the invention are realized by apparatus in accordance with embodiments of this invention. More particularly, this invention is directed to providing a reliable satellite communication system that includes a multiple beam phased array antenna, antenna feeds, and beam forming networks.
To ensure reliable satellite communications, and lessen the effect of interference from other communication systems, this invention transmits microwave signals at different spectral regions at high radio frequencies. Additionally, this invention employs an improved antenna design. The improved antenna design integrates, into a single system, an antenna element, a beam forming network, and integrated circuits which feed a beam from the beam forming network to an associated antenna element. The integrated circuits are hereinafter simply referred to as a feeding circuit in a sending configuration, and a receiving circuit in a receiving configuration. The single system provides flexibility of beam placement, narrow beam width, and reduced system weight. Flexible beam placement enables large area coverage and allows the system to serve many sites in near real time with a high gain beam. Narrowing the beam width of the high gain beam allows the system to partially offset the added propagation losses experienced by transmissions at high radio frequencies. The remainder of the propagation losses are compensated for by adding transmitter power. Generally, added transmitter power results in an increase in the overall weight of the system. However, this invention negates the increased weight due to the added transmitter power by reducing the weight of the antenna element and beam forming network. In fact, this invention reduces the weight of the antenna element, beam forming network, the feeding circuits and the receiving circuits so that the entire antenna system is lighter than conventional antenna systems used in satellite communications systems.
In the preferred embodiment of the sending array configuration, the antenna elements include a plurality of radiators and a plurality of band pass filters. The beam forming network preferably includes a plurality of stripline power dividers and a plurality of power distributors. The feeding circuits preferably include a plurality of impedance-matching isolators, a plurality of solid state power amplifiers, a plurality of n:1 signal combiners, a plurality of monolithic microwave integrated circuits (MMICs), and a plurality of phase shifters. In the preferred embodiment, beam positioning and beam width control information is derived by a phase control algorithm. The phase control algorithm operating, for example from a ground station, sends commands to a phase control algorithm storage unit in the satellite. The phase control algorithm storage unit, in cooperation with a phase and gain controller, uses the ground commands to derive control information which is passed to the feeding circuits supporting selected radiators. As the feeding circuits receive a signal from the beam forming network the control information is interpreted to modify the phase and gain of the signal. The feeding circuits then pass the modified signal to the selected antenna elements where it is outputted as a radiated beam.
In the preferred embodiment of the receiving array configuration, the antenna elements include a plurality of radiators, a plurality of low noise amplifiers, and a plurality of drivers. The receiving circuit pr
Perman & Green LLP
Phan Dao L.
Space Systems Loral, Inc.
Tarcza Thomas H.
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