Communications: directive radio wave systems and devices (e.g. – Directive – Including a steerable array
Reexamination Certificate
1999-11-19
2001-09-25
Phan, Dao (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a steerable array
C342S372000, C342S374000
Reexamination Certificate
active
06295026
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to antenna systems. More specifically, the present invention relates to an improved method and apparatus for providing a shapeable and directable communication beam.
In satellite communication systems, it is desirable to shape and direct communication beams. The ability to shape and direct communication beams results in efficient use of the finite energy resources of communication satellites, increases communication bandwidth, and reduces interference between beams.
In addition, there is a corresponding increase in communication security. Communicating only with an intended geographical area substantially complicates message interception from geographical areas outside the intended area of communication.
In the past, satellite-based phased array antenna systems were developed that provided bandwidth to communication areas using spot beams (communication beams designed to cover specific areas or “spots” on the Earth's surface). Typically the spot beams were organized into a matrix of evenly shaped and spaced beams (also referred to as pixel beams) designed to provide a total coverage to a large geographical area, such as a state, a nation, or the Earth.
The spot beams were generated using conventional phased array antenna systems. In conventional phased array antenna systems, each radiating antenna element in the array has a corresponding independent radio-frequency (RF) phase shifting circuit for each spot beam produced. Thus, for example, in a communication system incorporating a phased array antenna system with 547 elements, 547 corresponding RF phase shifters determine the shape and direction of a single spot beam.
Because of the complexity associated with determining and implementing the large number of RF phase shifts associated with a single spot beam, communication systems typically fixed the shape and direction of the spot beams to predetermined values. The satellite communication system communicates with users in a spot beam area with a corresponding spot beam signal and communicates with users in another spot beam area with another corresponding spot beam signal.
Fixed spot beam communication systems suffer from beam shaping inflexibility. For a fixed spot beam communication system to provide communication bandwidth to an area, the system must provide communication bandwidth to each spot beam area containing a portion of the area. For example, if a desired area includes subsections of three spot beam areas, the system must provide communication bandwidth to the three entire spot beam areas, including the subsections of the three spot beam areas not included in the desired communication area.
Fixed spot beam communication systems also suffer from beam directing inflexibility. A fixed spot beam communication system provides maximum beam gain at the center of each spot beam. Thus, users near the perimeter of spot beam areas receive lower quality communication service than users near the center of spot beam areas. For example, if a desired communication area is centered between three spot beam areas, the system provides maximum quality coverage to the communication area by using all three corresponding spot beams. Unfortunately, in the attempt to provide high quality coverage to the communication area, the system also provides relatively large amounts of communication energy to the centers of the three spot beam areas where the communication energy is not needed or wanted.
A need has long existed for a method and apparatus for forming a shapeable and directable communication beam.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a method and apparatus for forming a shapeable and directable communication beam.
It is also an object of the present invention to provide a method and apparatus for combining pixel beams to form a shapeable and directable composite beam.
It is a further object of the present invention to provide a method and apparatus for forming a composite beam from pixel beams at intermediate frequencies.
It is a yet further object of the present invention to provide an enhanced direct radiating array antenna system which forms shapeable and directable composite beams.
One or more of the foregoing objects is met in whole or in part by a preferred embodiment of the present invention that provides an improved method and apparatus for forming a shapeable and directable composite beam. The apparatus comprises an enhanced direct radiating array antenna system including a front-end unit, which communicates element signals through corresponding elements of a phased array antenna. The front-end unit includes IF/RF converters to convert between IF element signals and RF element signals.
The apparatus also includes a back-end unit that forms a composite beam from a set of pixel beams by converting between a composite signal and a set of corresponding pixel signals. The back-end unit includes a combiner/splitter which combines the set of pixel signals to form the composite signal or splits the composite signal into the set of pixel signals depending on whether the composite signal is received or transmitted respectively. The back-end unit further includes an amplitude and phase adjusting network which adjusts the phase and amplitude of at least one pixel signal of the set of pixel signals.
The apparatus further includes an interconnecting beamforming network which couples the front-end unit and the back-end unit. The interconnecting beamforming network converts between the pixel signals of the back-end unit and the element signals of the front-end unit.
The method includes determining a desired shape and direction for the composite beam. The method then selects a set of pixel beams with which to form the composite beam. The method further includes converting between a composite signal for communication over the composite beam and a set of pixel signals corresponding to the set of pixel beams. The method determines a set of phase and amplitude adjustments to make to the set of pixel signals. The method then forms the composite beam by performing the set of phase and amplitude adjustments on the set of pixel signals.
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Allen Barry R.
Chen Chun-Hong H.
Kintis Mark
Kuo Steven S.
Yano Kenneth T.
Phan Dao
TRW Inc.
Yatsko Michael S.
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