Communications: radio wave antennas – Antennas – With spaced or external radio wave refractor
Reexamination Certificate
2000-08-17
2002-06-11
Wimer, Michael C. (Department: 2821)
Communications: radio wave antennas
Antennas
With spaced or external radio wave refractor
C343S7810CA, C342S368000
Reexamination Certificate
active
06404398
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 conventional phased arrays (CPAs) 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.
CPAs have fine steering capability, but are difficult to implement when many simultaneous beams are required. Further, CPAs suffer from sun in view of grating lobes, frequency-dependent pointing, and (in the receive case) amplifier compression from high-power jammers in the array element's global field of view.
The spot beams were generated using CPAs in which 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 CPA 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.
U.S. Pat. No. 6,005,515 (Allen. et al., issued Dec. 21, 1999) describes a direct radiating array (DRA) that uses a “global pixel beams” concept to provide multiple communication beams to conveniently and reliably point a beam from one prescribed location to another without the complexity of large numbers of phase shifting circuits required by a conventional phased array (CPA) antenna system.
DRAs, which produce many simultaneous beams, can be easily implemented, but lack the fine-steering capability of the CPA. Further, DRAs suffer from the same problems as CPAs, namely, sun in view of grating lobes, frequency-dependent pointing, and amplifier compression from high-power jammers in the array element's global field of view.
U.S. application Ser. No. 09/443,526, entitled “Enhanced Direct Radiating Array,” filed Nov. 19, 1999 in the names of Chun-Hong H. Chen, et al., now U.S. Pat. No. 6,295,026, describes an enhanced DRA (EDRA) by adding to U.S. Pat. No. 6,005,515 a fine pointing and beam shaping capability that is needed in many military and commercial satellite communication applications to maximize the coverage gain and thus increase the data rate and communication capacity. U.S. application Ser. No. 09/505,816, entitled “Nulling Direct Radiating Array,” filed Feb. 17, 2000 in the name of Chun-Hong H. Chen, now U.S. Pat. No. 6,275,188, further extended the DRA concept to a nulling DRA (NDRA) useful in applications that require active anti-jamming capabilities. DRAs, EDRAs and NDRAs provide improvements over their predecessors, but still have limitations which may limit their usefulness in certain applications. For example, EDRAs suffer from the same problems as CPAs and DRAs, namely, sun in view of grating lobes, frequency-dependent pointing, and amplifier compression from high-power jammers in the array element's global field of view. This invention addresses such potential problems and provides a solution.
SUMMARY OF THE INVENTION
The preferred embodiment is useful in an antenna system for transmitting or receiving a plurality of pixel beams of satellite communication signals, including a first pixel beam and a second pixel beam. In such an environment, a preferred apparatus embodiment comprises a plurality of antenna array elements conducting element signals corresponding to the plurality of pixel beams. The antenna array elements include a first element and a second element. A focusing device is arranged to couple individual pixel beams of the plurality of pixel beams to individual elements of the plurality of antenna array elements. The first pixel beam is coupled to the first element and the second pixel beam is coupled to the second array element. A processing module is coupled to the element signals.
A preferred method embodiment of the invention is useful in an antenna system for transmitting or receiving a plurality of pixel beams of satellite communication signals, including a first pixel beam and a second pixel beam. The transmitting and receiving involves using a plurality of antenna array elements, including a first element and a second element. In such an environment, the method comprises focusing individual pixel beams of the plurality of pixel beams relative to individual elements of the plurality of antenna array elements, including focusing the first pixel beam relative to the first element and focusing the second pixel beam relative to the second element.
By using the foregoing techniques, satellite communication uplink applications can be implemented in a way which overcomes the potential problems discussed previously. That is, many simultaneous beams can be easily implemented, while maintaining the fine steering capability of the CPA. Moreover, the foregoing techniques do not suffer from the problems discussed above in connection with CPAs, DRAs and EDRAs.
REFERENCES:
patent: 4236161 (1980-11-01), Ohm
patent: 5576721 (1996-11-01), Hwang et al.
patent: 6005515 (1999-12-01), Allen et al.
Brundrett David L.
Chen Chun-Hong H.
Koretzky Edward V.
Kuo Steven S.
McAndrews Held & Malloy Ltd.
TRW Inc.
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