Design of a compact and high performance 263 GHz SB-TWT circuit

A compact, high performance staggered double grating (SDG) slow wave structure (SWS) circuit has been designed for a 263 GHz sheet beam traveling wave tube amplifier (SB-TWTA) for use in an electron paramagnetic resonance (EPR) spectrometer system being developed at UC Davis under National Science Foundation (NSF) Multidisciplinary Research Initiative (MRI) funding. By adopting a phase matching choke, the input/output structure exhibits superior low frequency band edge transmission characteristics. A compact sever is employed to broaden the bandwidth and reduce the overall circuit length thereby benefiting the S-parameters and the electron optical system design. The circuit was fabricated using Nano-CNC milling technology and the transmission and reflection parameters of the circuit were measured prior to diffusion bonding. In order to extend the operating bandwidth of the device, a hybrid mode transmission pill-box CVD window is employed. The Computer Simulation Technology (CST) Microwave Studio (MWS) results indicate the maximum reflection losses (S11) for the circuit over 245–285 GHz are −15 dB, while the transmission coefficient (S21) exceeds −0.5 dB. The maximum VSWR for the pill-box window within a 36 GHz bandwidth is less than 1.25.