A simple right-angle transition between a rectangular waveguide (RWG) and a substrate integrated waveguide (SIW) is proposed. Two slots etched on the broad wall of the SIW are used to couple the waveguides. To obtain a wide bandwidth of operation the slots have different lengths to create a double resonance behaviour. The proposed component has a simple mechanical configuration with the flange of the standard RWG flush-mounted to the substrate of the SIW. A sample transition is designed to work in the lower part of the Ka-band. The experimental results agree well with numerical predictions. The proposed component has 6.6% bandwidth and insertion loss below 0.5 dB.