0.22 THz sheet beam TWT amplifier: System design and analysis

The device components of 0.22 THz sheet beam TWT amplifier, comprised of a staggered double grating array waveguide, have been designed for broadband THz operation (~ 30 %) of the fundamental passband (TE-mode). The optimally designed input coupler has ≤1 dB insertion loss at 0.22 THz with ~ 75 GHz (34 %) 1-dB matching bandwidths. The designed RF window utilizing thin mica provides a coupling bandwidth spanning multiple octaves. The collector is designed to have a jog for collecting the spent beam along the RF path coupled to the output RF-window. Computer simulations show the collector hybridized with a WR-4 window has ~ 60 GHz matching bandwidth with ~ -0.5 dB insertion loss at 0.22 THz. The beam focusing structure design, for pulse operation, allows the elliptical sheet beam to have 73 % beam transmission. Most of the TWT circuit components have been designed and currently a full modeling effort is being conducted.