Additive manufacturing of a compact Ku-band orthomode transducer

Abstract

This work presents a compact ortho-mode transducer (OMT) built by additive manufacturing in a single-block, reducing the number of parts and flanges and improving the losses and power handling capability. The single-block approach also reduces potential passive intermodulation issues since the number of interfaces between parts is minimized. The presented OMT is based on the T-junction topology, with a short-circuited common circular waveguide where the two rectangular waveguides ports are attached. Both ports are arranged in opposite direction to maintain a symmetry plane for the whole structure in order to obtain a high isolation. Specific matching elements are introduced for each polarization to route the orthogonal modes to the common waveguide. The device is built by Selective Laser Melting (SLM), which imposes a set of specific mechanical restrictions to the 3D model of the OMT. The proposed design incorporates those restrictions, simplifying the geometry of the OMT as much as possible (especially the routing elements) to simplify the manufacturing. After this process, the experimental results show an OMT working in the band from 13.4 to 15.6 GHz (15.2%) with a return loss level higher than 20 dB for both polarizations, insertion loss lower than 0.18 dB and isolation between polarizations better than 45 dB. The OMT has also been tested in radiation connected to a reference horn, measuring a cross-polarization lower than -45 dB. This experimental performance shows that the proposed combination of compact design with single-block SLM manufacturing provides tested results similar to those obtained by high-accuracy milling or spark erosion suitable for satellite applications.