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 GHz 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 3D printing. Two units were CNC machined as brass split-blocks and a third was 3D printed monolithically in stainless steel by a micro laser sintering 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 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 3D printed diplexer. The maximum frequency shifts from design were 0.695 GHz in the CNC-diplexers and 1.55 GHz in the 3D printed diplexer.