A microstrip to waveguide transition comprising a waveguide module and a section of printed circuit board (PCB). The waveguide module comprises a waveguide aperture and a repetitive structure, the waveguide aperture being arranged extending through the module for attaching a waveguide to an external side of the module, the repetitive structure comprising a plurality of protruding elements arranged to surround the waveguide aperture on an internal side of the module and to define a passage into the waveguide aperture on the internal side, wherein the repetitive structure is configured to attenuate electromagnetic signal propagation in a frequency band past the repetitive structure while allowing propagation via the passage, the transition further comprising a PCB with a patch antenna connected to a transmission line and arranged to face the passage into the waveguide aperture.