Technology
Spacecraft
Multiple Hopping Beam Antennas
Until ACTS, existing communications satellites broadcast a
single beam or "footprint" over a large part of
the earth. This is highly efficient for large-scale, one-way
communication such as television broadcasts, but not for on-demand
two-way communications.
To accommodate real-time, two-way communications for multiple
users, ACTS incorporated 51 tightly focused signal beams (0.3
degree beam width) each with a diameter covering 150 to 200
miles and which have the capability of "hopping"
from one location to another in milliseconds. Smaller spot
beams allow the same frequency to be used over and over because
the spatial isolation between sites prevents interference
from one beam to the next. The tighter beams also permit use
of significantly smaller and less expensive earth station
antennas. Concentrating satellite power into a smaller area
that penetrates through rain also mitigates rain fade. ACTS’
multiple hopping beams and other technologies use less power,
provide three times the communications capacity and offer
data rate communication twenty times faster than similar weight
conventional satellites.
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