SRC-336

Rectenna Technology Program: Ultra Light 2.45 GHz Rectenna and 20 GHz Rectenna

Commissioned by NASA Lewis Research Center. Who paid for a study is recorded because it bears on how its conclusions should be read, not because it makes them wrong.

Published claims resting on this source

• CLM-0938 A 1988 NASA paper says a rectenna built on mylar reached 85 per cent efficiency. The 1987 final report of the contract it cites says mylar managed 70 per cent, and that 85 per cent needed a different plastic.
• CLM-0939 The 85 per cent figure that later papers quote flat was one component on a bench, in moving air, with an error bar, at one power level. The array number beside it was an estimate, not a measurement.
• CLM-0940 Two NASA efforts to build rectennas at much higher frequencies than the standard 2.45 GHz ended without a working device. One concluded the approach it had chosen would not work; the other simply ran out without completing anything.
• CLM-0941 In space there is no air to carry away the waste heat, so a rectenna's output is limited by how much waste heat it can radiate. The report puts that ceiling at about 2.33 kW of DC per square metre.
• CLM-0969 If the tubes are only 70 per cent efficient, the transmitter's own face is not big enough to get rid of the heat they make, even spread perfectly evenly. At 85 per cent it is comfortable. The tipping point is almost exactly the efficiency the 1975 study said its tubes achieved.

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