Abstract: A new method to design wideband transition from double-ridge waveguide to coaxial line is introduced in this investigation. The proposed design of the transition is based on the theory of mode conversion and impedance matching. The Chebyshev type of impedance matching network is employed, a new mode converter structure between the coaxial line and the ridge waveguide has been used for design. The characteristics of the transition in microwave frequencies are analyzed and simulated by full-wave analysis software. According to this ideal, a couple of transitions have been finished. The predicted superduper performance has been confirmed experimentally in the range of 6.5～18 GHz.