An orthomode transducer allows the combination or separation of orthogonal waveguide modes. This paper presents a stepped orthomode transducer (OMT) for Ka-band, developed for polarimetric radar applications to reduce the number of antenna elements. The OMT is produced by stereolithography 3D printing and then manually metallized with conductive paint. A CST simulation model is presented, which considers mechanical and manufacturing related constraints such as electrical conductivity and surface roughness. For applying the conductive paint, a split block design with two halves and a constructive gap, which was also accounted in the simulation, is developed. The impact on the performance compared to a lossless and monolithic structure is analyzed. A sample of the 3-port OMT is fabricated and measurements are performed. The comparison of the simulated and measured S-parameters shows that the designed structure works as intended and the correspondence of the model with reality is sufficient.

Since 3D printing technology can already be observed as state of the art for rapid prototyping manufacturing processes for high frequency components, the metallization of plastic printed objects becomes a crucial part that is not straight forward. Conductivity and surface roughness influence the performance of an additive manufactured microwave component. Using an orthomode transducer (OMT) optimized for the automotive radar band, various metallization techniques are applied to stereolithography printed prototypes. Applied metallizations are conductive silver paint, galvanic and vacuum coated gold. An stepped OMT design is used and simulations considering reduced conductivity as well as surface roughness are compared to measurements. All coating techniques show a sufficient agreement and demonstrate applicability.