Physics
Scientific paper
Jan 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002iaf..confe.769s&link_type=abstract
IAF abstracts, 34th COSPAR Scientific Assembly, The Second World Space Congress, held 10-19 October, 2002 in Houston, TX, USA.,
Physics
Scientific paper
A microwave wireless power transmission has a large phased array antenna which focuses its beam onto a ground rectenna. The microwave beam is steered using retrodirective phase control which has the necessary safety feature of always focusing the beam onto the rectenna. It is not possible for the beam to "wander" around the countryside. In order for the retrodirective phase control technique to work, it is necessary to distribute a very stable phase reference throughout the antenna to each subarray. A photonics system which modulates an RF signal onto a laser which is then transmitted via fiber optic cables over the 500 meter transmit antenna. Since there will be regions of various temperature ranges over the antenna due to the heat generated in the microwave tubes, the DC/DC converters at each subarray, and the DC power line I2R losses. The photonics system must be able to maintain a stable phase reference despite varying temperature increases in the fiber optic cables. In a study to determine the induced phase changes over various temperatures for a number of commercially available fiber optic cables, a test program has been initiated at the NASA Johnson Space Center. In addition to the regular fiber cables being tested, special cables with a low coefficient of thermal expansion have been investigated. In each test the phase of a microwave signal transmitted over the fiber cables is measured while the operating temperature is varied inside a thermal test chamber. This paper describes a possible configuration for the photonics system within the transmit array, the test system, and the test results. Recommendations for future studies are also included.
Arndt Dickey G.
Schaeper Herbert R.
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