A 3D printed 300 GHz waveguide cavity filter by micro laser sintering

This work explored the use of high-precision metal 3D printing in sub-terahertz waveguide devices and demonstrated a 300 GHz waveguide bandpass filter made by micro laser sintering (MLS) process. The filter structure is composed of five rectangular waveguide cavities (fundamental TE101 mode), two back-to-back right-angle bends and WR-03 waveguide sections. It is made of two identical blocks of stainless steel and two brass plates were used to clamp them together and achieve secure contact in the E-plane cut. The measured response of the as fabricated stainless-steel filter showed minimum passband insertion loss of 4.7 dB due to the degraded effective conductivity of the stainless steel and surface roughness. To reduce the insertion loss, the filter was gold plated using an electro-less process with nickel undercoat layer. Plating the filter significantly improved the passband insertion loss, measured to be between 1.1 and 2.7 dB. Inspection of the filter using an Alicona optical system showed that dimensional accuracy within 15 m on average has been achieved by the MLS printer. The investigative study tested the boundary of the technology in sub-terahertz device applications.