Design and Development of an X-band Pulsed Helix TWT for Space Application

Abstract

A compact X-band power booster TWT was designed and developed for space applications that provides minimum of 350W of peak RF output power with 25% duty over a bandwidth of 800MHz with RF efficiency of 22% and minimum gain of 27 dB. This TWT uses an electron gun operating at a cathode voltage of 6 kV and current of 275 mA with beam filling factor of 0.5. The electron beam is focused using PPM structure with peak field of 2600G generated using Sm2Co17 magnets. The SWS comprises tungsten tape helix supported by three azimuthally, symmetrically placed T-shaped APBN support-rods inside a metallic envelope. The dimensions of SWS were derived using the in-house parametric codes and optimized using Eigen-mode solver of CST Studio to achieve the required dispersion characteristics. The beam-wave interaction analysis was carried out using the in-house 1D-codes and was optimized using 3D PIC simulations. The SWS employs positive velocity taper near the output coupler in order to enhance RF interaction efficiency and to reduce the second harmonic content. The length of the SWS is around 93 mm. A 3-stage depressed collector is used to enhance the overall efficiency of the TWT. A prototype TWT is developed and tested for performance and has achieved overall efficiency of 45% with TWT length of 250 mm and weight of 980 grams. This TWT is subjected for operational temperature cycling at +70°C and -20°C and also random vibration to verify the structural integrity and has met the requirements.