Targeting the transition from a coaxial wave guide to a coplanar wave guide (CPW), a microwave and millimeter-wave wide-band coaxial-to-coplanar transition is proposed. This design connects the coaxial inner conductor to the CPW center conductor in a perpendicular manner to directly couple, on the same plane, the radial high-frequency electric field in the coax to the gap between the CPW's center conductor and ground plane. The performance of the proposed transition was compared with those of the conventional transition by experiments and electromagnetic field simulations, and it was found that the proposed method is independent of CPW shape and that it exhibits good matching performance in comparison to the conventional method especially in high-frequency bands above 15 GHz.