thermal dissipation. • At 40 GHz (transmission distance = 70 m). TWTs with 20 to 50 Watts of output power, efficiency 15-20% are in pre-production phase. Low efficiency and high voltage (13 BV) would make the associated radiator and power supply prohibitive in weight • At 30 GHz (transmission distance = 50 m). TWTs with 50 Watts of output power, 30 to 40 % inefficiency, could be used. More powerful TWTs or Klystrons exist but would require a more complex thermal system. • At 14-18 GHz (transmission distance = 25-30 m). There exists a large choice of TWTs or Klystrons, with up to several hundred Watts of power capability. Their efficiency, being not the primary characteristic for ground application, is fairly low (35%). They also would require a complex thermal system for cooling and heavy power supplies. • At 12 GHz (transmission distance = 20 m). In this range, there are space qualified TWTs which feature very interesting characteristics: power output 130 Watts efficiency 60% narrow band weight 1,3 kg heat dissipation radiation Associated with a 3 kg, 30% efficient power supply, this TWT would fulfil all constraints of this option. The transmission distance might be much increased, if one can afford larger antennae. For instance, 2 meter antenna/rectenna would increase the transmission distance to 80 meters.
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