Communications: radio wave antennas – Antennas – Spiral or helical type
Reexamination Certificate
1999-09-17
2001-06-26
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
Spiral or helical type
C343S853000, C342S375000
Reexamination Certificate
active
06252562
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to antennas for orbiting satellites.
2. Description of the Related Art
Hitherto, the antennas used by orbiting satellites are either antennas of the omnidirectional type (SPOT, ERS, etc.) or of the steerable directional type (LANDSAT, etc.).
In the latter case, the beam is Gaussian and scanning is carried out with the aid of a pointing mechanism, the antenna itself behaving as a centered parabolic reflector of conventional design.
SUMMARY OF THE INVENTION
One purpose of the invention is to propose an antenna for orbiting satellite which requires no pointing mechanism, which exhibits a greater gain than omnidirectional antennas and which is compact and inexpensive.
To this end, the invention proposes an antenna for retransmitting to the ground images collected by image-capture instruments of an orbiting satellite, characterized in that it comprises a plurality of elementary radiating antennas of the type having a plurality of cords regularly distributed in a helix about one and the same generatrix of revolution as well as means for the equi-amplitude power supply of the various cords, in that these various elementary antennas are aligned and in that the plane in which these various elementary antennas are distributed is intended, when the satellite is in orbit, to be perpendicular to the direction of the speed vector of the satellite and in that it also comprises means for phase-shifting the power supply to these various elementary antennas which are able to carry out electronic steering of the elongate beam generated by the said elementary antennas.
It will be noted that with such a distribution of elementary antennas with a shaped pattern, the transmit beam produced is a beam of elliptic type (known as “fan beans” [sic]) which extends in a direction parallel to that of the speed vector of the satellite.
The steering of this beam to a given longitude makes it possible to reach, throughout the time of transit of a satellite, a station located at this longitude, and to do so without needing to modify this steering as the satellite advances.
It is understood that such an antenna structure does not require complicated electronics and allows high transmission bit rates.
This antenna is advantageously supplemented with the following various characteristics taken alone or according to all their possible combinations:
the number of elementary radiating elements is equal to or greater than five;
the elementary radiating elements are staggered one with respect to another with a spacing which is chosen so as to avoid the grating lobes;
for a transmission frequency of 8000 MHz, the spacing between two elementary antennas is of the order of 19 mm;
the phase-shifting means are coded over three to eight bits;
the phase-shifting means are of the ferrite type.
Other characteristics and advantages of the invention will emerge further from the following description. This description is purely illustrative and nonlimiting. It should be read in conjunction with the appended drawings in which:
REFERENCES:
patent: 4989011 (1991-01-01), Rosen et al.
patent: 5041842 (1991-08-01), Blaese
patent: 5258771 (1993-11-01), Praba
patent: 5345248 (1994-09-01), Hwang et al.
patent: 5986619 (1999-11-01), Grybos et al.
Imbriale Et al.: “An S-Band Phased Array For Multiple Access Communications” NTC77 Conference Record, vol. 2, 1977 vol. 2, 1977.
Glockler: “Phased Array For Millimeter Wave Frequencies” International Journal of Infrared and millimeter Waves., vol. 11, No. 2 Feb. 1990 pp. 101-110.
Blakely & Sokoloff, Taylor & Zafman
Centre National d'Etudes Spatiales
Ho Tan
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