A W Band staggered double vane (SDV) loaded traveling wave tube amplifier (TWTA) with two sections separated by a lossy dielectric loaded rectangular wave guide is studied in this paper. The dispersion characteristics and transient analysis of the slow wave structure are analyzed in Computer Simulation Technology Microwave studio (CST MWS) and High Frequency Software Simulator (HFSS). In this amplifier, we propose to use Bragg reflectors on both sides of the slow wave structure (SWS), at the windows for the sheet beam at the electron gun and collector ends; this increases the impedance bandwidth of the RF structure. The attenuator section is comprised of a rectangular waveguide loaded on either side with single lossy dielectric material spanning over 5.5 pitches. The loss profile of the attenuator and loss magnitude is optimized to provide a 20dB loss in separating the input and output sections. A bandwidth of 15GHz ranging from 90-105GHz is obtained through the analysis. In the PIC simulations, a sheet beam of 50mA current is fed with an operating voltage of 18.3kV. The TWTA yields 20dB gain in the 90-105GHz range. © 2019 IEEE.