The design and implementation of a novel inkjet-printed flexible broadband multilayer coupler on a polyimide film (Kapton) in substrate integrated waveguide (SIW) technology are demonstrated for the first time. A conformal broadband microstrip-to-SIW interconnect is inkjet-printed and its flexibility is experimentally verified. An inkjet-printed multilayer coupler is designed and fabricated based on the flexible SIW interconnect and its frequency response is discussed. The main challenges concerning the additive fabrication process are also thoroughly covered.