Communications: directive radio wave systems and devices (e.g. – Directive – Including antenna orientation
Reexamination Certificate
1999-04-29
2001-05-22
Phan, Dao (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including antenna orientation
C342S352000, C342S427000
Reexamination Certificate
active
06236361
ABSTRACT:
TECHNICAL FIELD
The present invention relates to antenna control systems and, more particularly, the present invention relates to precise pointing and control of the directional antennas of communications satellites.
BACKGROUND ART
To obtain optimum communication coverage over an area being served by a communications satellite, precise directional satellite antenna control is necessary. Antenna control systems are described in U.S. Pat. Nos. 3,757,336 and 4,418,350.
U.S. Pat. No. 3,757,336 describes a satellite antenna control system that uses a pilot signal, or beacon, transmitted from an earth station to the satellite where it is received, processed, decoded and utilized to control the satellite for tracking and offset.
As a consequence of the higher frequencies employed, narrower antenna beams are being used in communication satellite service. Therefore, much more precise antenna beam pointing accuracies are required. U.S. Pat. No. 4,418,350 describes an antenna control system in which a communications satellite directional antenna can be aimed and controlled. The system makes use of a ground based beacon station that transmits an uplink signal to the satellite, including frequency differentiated communication signals and the beacon signal.
The communications signals and the beacon signal are received by a common directional antenna on the satellite. A microwave network, coupled to a multiple feed horn assembly of the antenna and responsive to the beacon, produces signal components including a sum signal and east-west and north-south error signals. The error signals are indicative of the corresponding angular errors between the desired antenna pointing direction and the direction from the satellite to the beacon station. Subsequent processing of the signal components in a command and control receiver yields steering signals for controlling the antenna pointing direction with respect to the beacon station.
In the communication systems described above, the beacon is transmitted to a reflector on the satellite. The reflector is illuminated by a set of receiving horns arranged in a predetermined manner in the focal plane of the reflector. The positioning and relative phasing of the wave energy applied to the set of feed horns provides the antenna beam coverage desired.
Each of the receive horns is separately amplified and down converted to an intermediate frequency. Because each horn has a separate amplifier, the expected difference in gain on the three channels is a source for pointing errors. Pointing errors introduce interference from nearby beams that could potentially disrupt the communications satellite service.
SUMMARY OF THE INVENTION
In the present invention, a reference signal generated on the satellite is used to equalize the gain of the separate channel amplifiers used in processing the beacon signal to generate an error signal. The reference signal is radiated from a small antenna located in the center of the reflector. The reference signal, by virtue of its wide beam width, strikes each one of a plurality of horns that surround the beacon source with the same power.
It is an object of the present invention to eliminate the error caused by gain variations in separate amplifiers in an antenna pointing control system. It is another object of the present invention to accomplish this by equalizing the gain of the amplifiers used in amplifying the beacon.
It is a further object of the present invention to locally generate a reference signal and to radiate the reference signal from an antenna strategically placed at the center of the reflector, or focusing lens, located on the satellite.
Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.
REFERENCES:
patent: 3718927 (1973-02-01), Howard et al.
patent: 3836972 (1974-09-01), Conway et al.
patent: 3893116 (1975-07-01), Hudspeth et al.
patent: 3931623 (1976-01-01), Sones et al.
patent: 4418350 (1983-11-01), Rosen
patent: 4806932 (1989-02-01), Bechtel
patent: 5128682 (1992-07-01), Kruger et al.
Hughes Electronics Corporation
Phan Dao
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