This paper describes a transition from conductor-backed-coplanar waveguide (CB-CPW) with substrate-integrated coaxial line (SICL) to substrate integrated waveguide (SIW). The transition is designed for the C-band frequency range. The CBCPW slot lines play the main role in widening the bandwidth. These CPW slot lines are providing excitation of both even and odd mode waves in SIW, which improves the impedance bandwidth. Using the proposed concept, the measured single-mode impedance bandwidth of 63.34%, the minimum insertion loss of 0.16 dB, and the overall loss below 25% are achieved. The simulated results are found to be in good agreement with the experimental prototype developed in the laboratory