Design and Microfabrication of Transition Waveguides for Traveling Wave Tubes (TWTs)

This study aims to design and fabricate transition waveguides operating at a frequency range of 80–110 GHz using aluminum die electroforming. The CST software is used to calculate the relationship between the transition waveguide length and the transmission properties of the transition waveguide. The return loss (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S_{11}$ </tex-math></inline-formula>) of the transition waveguides is less than −20 dB over the passing band. Aluminum die electroforming is chosen to microfabricate them, and the effects of processing parameters on the quality of the electroformed copper lay have been investigated, such as the electrolyte solution and electroforming current. Dimensional accuracy of the completed transition waveguide is about <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm 5~\mu $ </tex-math></inline-formula> m. The measurement of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S_{11}$ </tex-math></inline-formula> parameter has been carried out, and test finding shows that the measured <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S_{11}$ </tex-math></inline-formula> is between −25 and −20 dB.