In this paper the authors present a simple right-angle transition between a rectangular waveguide (RWG) and Substrate Integrated Waveguide (SIW). The coupling between both waveguide types is realised by using two slots etched in the broad wall of the SIW. Different lengths of the slots create a double resonance behaviour that results in a broad bandwidth of the element. The standard flange of the rectangular waveguide can be easily flush-mounted to the substrate of the SIW, and therefore, the proposed component has a simple mechanical configuration. A sample transition is designed to work in the lower part of the Ka-band. The simulation results show that the proposed component has the return loss better than 15~dB in the bandwidth of 1.9~GHz. The insertion loss is better than 1~dB including the losses of a short section of SIW.