**Abstract**

This chapter intends to show the strong potential brought by metal 3D-printing to the field of waveguide components and antennas. General co-design guidelines are firstly provided. These guidelines enable to benefit from the advantages associated to metal 3D-printing. The implementation of filters and ortho-mode transducers is considered, together with horns and slotted antennas. Finally, multifunctional periodic structures benefiting from metal 3D-printing are discussed.

**Keywords:** 3D-printing, additive manufacturing, selective laser melting, ortho-mode transducers, filters, polarizers, leaky-wave antennas
