Thomas Starke

We report a $D$ -band waveguide diplexer, with two passbands of 130–134 and 151.5–155.5 GHz, fabricated using micro laser sintering (MLS) additive manufacturing with stainless steel. This is the first demonstration of metal 3-D printing technology for multiport filtering devices at a sub-terahertz (THz) frequency. For comparison, the same diplexer design has also been implemented using computer numerical controlled (CNC) milling. The diplexer, designed using coupling matrix theory, employs an all-resonator and $E$ -plane split-block structure. The two channels are folded for compactness. A staircase coupled structure is used in one channel to increase the isolation performance. The printed waveguide flanges are modified to adapt to the limited printing volume from the MLS. Effects of fabrication tolerance on the diplexer are investigated. An effective and unconventional electroless plating process is developed. The measured average insertion losses of the gold-coated diplexer are 1.31 and 1.37 dB, respectively. The respective frequency shifts from design values are 0.92% and 1.1%, and bandwidth variations are 4% and 15%. From a comprehensive treatment of the end-to-end manufacturing process, the work demonstrates MLS to be a promising fabrication technique for complex waveguide devices at a sub-THz frequency range.

This article explored the use of high-precision metal three-dimensional printing in subterahertz 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 TE ₁₀₁ 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 μm on average has been achieved by the MLS printer. The investigative study tested the boundary of the technology in subterahertz device applications.