W-Band and D-Band Traveling-Wave Tube Circuits Fabricated by 3D Printing

We present the fabrication and electromagnetic testing of serpentine waveguide traveling-wave tube amplifier circuits operating in the W-band (75-110 GHz) and D-band (110-170 GHz) frequency ranges. The circuit structures were fabricated in a split-block configuration in a photopolymer material using a commercial digital light processing (DLP) 3D printer and, subsequently, covered with a conducting layer by Au sputtering and Cu electroplating. Two-port S-parameter measurements of the W-band circuit demonstrate a transmission band from ~87-104 GHz, with a 26.7-dB return loss and a 0.55-dB insertion loss measured at 95 GHz. The D-band circuit demonstrates a transmission band from ~139 to 145 GHz, with a 21.5-dB return loss and a 2.4-dB insertion loss measured at 140 GHz.