This study proposes a compact dual-polarised directive radiator whose complex prototyping is enabled by additive manufacturing. In addition to monolithic implementation, stereolitography followed by metal coating, it also provides high radio-frequency performance, low cost and low weight. Dual-channel simultaneous operation is supported thanks to the integration of an orthomode transducer within the structure. Entirely waveguide based, this compound radiating structure is specially well suited to be 3D-printed, and in principle, it allows scaling to match a specific frequency of operation. Both the antenna concept and the employed advanced manufacturing technique are validated experimentally through the realisation and measurement of two prototypes operating, respectively, at 30 and 60 GHz. The proposed architecture is easily amenable to be grouped in a compact higher-gain array, thus holding strong potential for platform-constrained applications, such as inter-satellite links between CubeSats.