MEMS COMPATIBLE SEVER FOR 220 GHZ ULTRA WIDE BAND TWTA: DESIGN AND PARTICLE-IN-CELL ANALYSIS

We report a MEMS (micro-electro-mechanical systems) compatible distributed loss type sever design for the 220 GHz double vane half period staggered traveling-wave tube amplifier (TWTA) [1]. The cold test simulations for a full TWT model including input/output couplers and broadband tapered vane transitions incorporating the sever, predicted a return loss ([S.sub.11]) of < -10 dB in the pass band (205 GHz-275 GHz) while an insertion loss/isolation ([S.sub.21]) of ~ -27dB. The return loss of the TWT circuit did not degrade by the inclusion of the sever (< -10 dB) while still maintaining a good isolation ([S.sub.21]) for the RF signal. Particle-In-Cell (PIC) simulation analysis for the full 220 GHz TWT circuit (a) without sever and (b) with sever was conducted. With the inclusion of the sever, the TWTA showed generally a stabilized output response for all cases. The maximum power from the long sever case was ~ 25 W for [P.sub.in] ~ 50 mW and the gain was ~ 27dB. The reverse power was decreased to ~ 30 mW. For the short sever, the PIC results were even better with a maximum output power of ~ 62 W and a gain of ~ 30.92 dB with a reduced reverse power of ~ 5mW for an input power of 50 mW at 220 GHz. The FFT spectrum of the RF signal at the output port also showed a spectrally pure waveform at 220 GHz.