Abstract: The present disclosure relates to a multilayer electromagnetic waveguide that includes a plurality of layers forming guide channels for an electromagnetic wave, and at least one transition device including at least one dielectric layer between two guide channels, referred to as coupled guide channels, extending as an extension. Each transition device includes at least one adaptation channel extending in a longitudinal direction, and each adaptation channel is defined by two electrically conductive walls. At least one wall extends along the dielectric spacer layer from one end of the coupled guide channel, over a length suitable for optimizing the transmission of an electromagnetic wave between the two coupled guide channels.