In this paper, a wideband transition between substrate integrated waveguide (SIW) and rectangular waveguide (RWG) based on bend waveguide is proposed. Inspired by E-plane bend waveguide structures, a stepped and ridged structure is introduced to improve performance. The proposed transition consists of a RWG flange with ridged step and a SIW cavity with a septum inserted. The measured results of the back-to-back transitions agree well with simulations. The results show a return better than 15.6 dB and an insertion loss between 0.55 dB and 1.4 dB from 23.6 GHz to 40 GHz (54.67%).