CNC-Machined and 3-D-Printed Metal G-Band Diplexers for Earth Observation Applications

This work presents two manufacturing approaches for waveguide diplexers applicable to separating two of the G-band, 140–220 GHz, channels used in space borne radiometry of the Earth’s atmosphere. Waveguide diplexing is a lower volume alternative to a quasi-optical, i.e., frequency selective surface-based, system. The two channels considered are 164–167 and 175–191 GHz. The diplexer comprises a Y-junction with two waveguide-cavity filters. Two high-precision fabrication technologies have been utilized: computer numerical control (CNC) machining and 3-D printing. Two units were CNC machined as brass split blocks and a third was 3-D printed monolithically in stainless steel by a microlaser sintering (MLS) process. The latter is an innovative structure that incorporates the diplexer with the waveguide flanges. All devices were gold coated to reduce loss. Measured insertion losses (ILs) in the two channels were 0.6 and 0.34 dB for the CNC-machined diplexers and 1.8 and 0.8 dB for the 3-D printed diplexer. The maximum frequency shifts from design were 0.695 GHz in the CNC diplexers and 1.55 GHz in the 3-D printed diplexer.