60 percent efficient K-band TWT using a new diamond rod technology

A 75-W CW (continuous-wave) helix TWT (traveling-wave tube) operating at 20 GHz with an efficiency goal of 60% is being developed for satellite communication systems. The TWT utilizes a unique tube design philosophy where high overall efficiency is obtained with a low-perveance beam. In the past, low-perveance designs resulted in low beam efficiencies. However, due to recent breakthroughs in diamond rod technology and in collector electrode materials, high efficiencies can now be achieved with low-perveance beams. A nonbonded nonbrazed diamond rod fabrication technique has been developed without sacrificing thermal handling requirements. The diamond-supported helix circuit features low RF losses, high interaction impedance, and good thermal handling capability. A breadboard TWT recently demonstrated greater than 100-W CW output power and 54.6% overall efficiency. Computer models indicate that a modification to the present helix taper design will achieve the goal of 60% overall efficiency.>