This article presents the design and analysis of a staggered double-vane (SDV) slow-wave structure (SWS) for W-band amplifier, with 20-dB gain and a very high bandwidth (25%). The use of dual Bragg reflector at either end of the interaction structure increases the impedance matching and the radio frequency (RF) coupling efficiency at the input and output ports, thereby reducing the RF leakage at the electron gun and collector ends, from 15% to 25% to less than 0.6%. The attenuator section is simple to fabricate and optimally designed in order to provide an effective isolation (>20 dB) between the input RF signal in the input section and the RF signal reflected from the output section. The dispersion analysis, the transmission analysis of each section, and the beam-wave interactions were simulated using the Dassault system's computer simulation technology (CST) eigenmode solver, time-domain solver, and the particle-in-cell (PIC) solver, respectively. The proposed design of the SDV SWS conclusively provides an enormous bandwidth of 25 GHz with 20-dB gain for W-band amplifier, when compared to its solid-state counterparts and earlier reported work as per the author's knowledge. © 1973-2012 IEEE.