Abstract:With the use of the even-odd mode analysis theory，a third-order 3 dB directional coupler is analyzed and designed by HFSS. On this basis，a ceramics chip is used as coupling medium，and a high-power third-order 3 dB directional coupler is analyzed and designed with the maximum input power above 17 kW. The adding of the ceramic chip can improve the coupler’s capability of voltage resistance and cut the size of the directional coupler, therefore high-power small-size coupling is achieved. This coupler can be applied to the high-power broadcasting transmitter system.