This article presents the design of a mode launcher for launching TE011 mode in a cylindrical cavity. In the given design, TE011 mode is excited from the top wall of the cylindrical cavity using a rectangular waveguide. This type of top wall excitation of the cavity has been used keeping in view the application of the proposed launcher in coupling analysis of a coaxial magnetron. The proposed design is verified by launching TE011 mode in a cylindrical cavity, which is designed to operate at 9.3 GHz with the maximum quality factor. The value of quality factor obtained analytically is 31 030 and the same is verified by comparing it with simulation results obtained from CST and HFSS. Return loss and insertion loss of the mode launcher are obtained as 40.24 and 0.12 dB at 9.3 GHz, respectively. The frequency tunability of the cavity is also studied by changing the length of the cavity by making the bottom wall movable and a tuning range of 200 MHz is achieved. Performance of the top wall excitation is also compared with the conventional TE011 mode excitation from the rectangular waveguide through the side wall of the cavity, and both are in good agreement.