A Broad Bandwidth Metamaterial Pillbox Window for W-Band Traveling-Wave Tubes

A low voltage standing wave ratio (VSWR) broad bandwidth pillbox window with metamaterial is proposed for W-band traveling-wave tubes (TWTs) in this paper. The metamaterial structure is designed on a dielectric surface, which decreases the VSWR and broadens the bandwidth of the pillbox window. The cold-test results of the window with metamaterial are presented, which showed that the metamaterial pillbox window (MPW) achieves a bandwidth of 31.5 GHz with VSWR below 1.2, and a bandwidth of 18 GHz with VSWR below 1.1. The ghost mode and the power capacity of the window were also investigated. The results showed that the proposed metamaterial pillbox window is suitable for medium power TWTs. A Ka-band MPW was fabricated and the test results agreed well with the simulation results.