A New Fabrication Method for Serpentine-Folded Waveguide Slow Wave Structure at $W$ -Band

A serpentine-folded waveguide traveling-wave tube (FWTWT) in W-band was fabricated using chemical machining to pattern 200-μm-thick copper sheets. These were stacked together inside a jig to form the final device. The challenge in realizing a beam hole for electron beam/wave interaction at millimeter wavelengths was addressed by incorporating a circular beam hole realized using stepped chemical machining. The surface characteristics were improved using chemical polishing. This surface was characterized using a scanning electron microscope images and surface roughness measurements. To improve the conductivity further, gold plating with a thickness of 1-2 μm was applied. The fabricated circuit was tested and the cold-test parameters were found to be satisfactory.