A low-power, high-efficiency Ka-band TWTA

The authors describe a NASA-sponsored program whose objective is to develop a high-efficiency, low-power TWTA (traveling wave tube amplifier) operating at 32 GHz and meeting the requirements for the Cassini Mission to study Saturn, planned for launch in 1995. The required RF output power of the helix TWT is 10 W, while the DC power from the spacecraft is limited to about 30 W. This performance level will permit the transmission to Earth of all the data produced in the mission. In order to achieve this efficiency, several novel technologies are incorporated into the TWT, including an advanced dynamic velocity taper characterized by a nonlinear reduction in pitch in the output helix section of the TWT and a Lewis-designed multistage depressed collector using copper electrodes treated for secondary electron emission suppression. Preliminary program results are encouraging: RF output power of 10.6 W has been obtained at 14-mA beam current and 5.2-kV helix voltage with overall TWT efficiency exceeding 40%.<>