Overmoded W-band traveling wave tube (TWT) design and test

We report the design and experimental test of a W-band overmoded traveling wave tube amplifier. The TWT circuit is designed to operate in the TM31 mode at 94 GHz and utilizes dielectric loading to suppress unwanted lower order modes. 3-D CST PIC simulations at 31 kV, 310 mA predicted 32 dB of gain and 300 W peak output power. Testing of the overmoded TWT found zero-drive stable operation with full suppression of unwanted modes. Operating at 94.26 GHz, 27 dB of circuit gain (21 dB of device gain) and 55 W peak circuit output power (25 W peak device output power) were measured at 31 kV with 250 mA current on the collector. Simulations predicted 28 dB of circuit gain, in good agreement with experiments.