This results into a direct relationship between the achievable transmission distance and frequency: As a maximum transmission distance of one hundred meters is foreseen in all options, this limits the search for microwave sources below 60 GHz. This is reasonable because microwave sources above 60 Ghz are either low power devices (a few watts), or medium power ones (a few 100’s watt) but efficiency is low, or very high power ones (tens to hundreds kW), or not compatible with the power capability of the Powersat demonstrator. 6. DISCUSSIONS OF THE OPTIONS 6.1 Ariane 4 Options For either the tethered or launched free-flyer, using deployable antenna and rectenna, the constraints are the following: • antenna, rectenna diameter ~/m • passive thermal dissipation • power capability -/kilowatt This limits the RF source power to a few ten to hundred watts. Reviewing the available microwave tubes, for ground or space applications, one can find the following possibilities: • At 60 GHz (transmission distance = 100 m). There exist TWTs with a few Watts of output power, with modest efficiencies (15%) - high-power coupled cavity TWTs also exist but would not be compatible with passive
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