D-band Waveguide Diplexer Fabricated Using Micro Laser Sintering

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.