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 220GHz 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 (S11) of < −10 dB in the pass band (205GHz–275GHz) while an insertion loss/isolation (S21) of ∼−27 dB. The return loss of the TWT circuit did not degrade by the inclusion of the sever (< −10 dB) while still maintaining a good isolation (S21) for the RF signal. Particle-In-Cell (PIC) simulation analysis for the full 220GHz 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 ∼ 25W for Pin ∼ 50mW and the gain was ∼ 27 dB. The reverse power was decreased to ∼ 30mW. For the short sever, the PIC results were even better with a maximum output power of ∼62W 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 220GHz. Received 20 March 2013, Accepted 10 May 2013, Scheduled 19 July 2013 * Corresponding author: Anisullah Baig (abaig@ucdavis.edu).