Microwave ignition plug for coupling microwave energy

Microwave spark plug (1) for coupling microwave energy into a combustion chamber (18) of an engine, wherein an elongated housing (2) with an elongated hollow space (10) forming a waveguide on the interior and a microwave window (8) arranged at one end of the hollow space (10), which closes off the waveguide (10) with respect to the combustion chamber (18), wherein the waveguide (10) has, at the other end opposite the microwave window (8), a connection element (4) for a high-frequency supply line, the connection element (4) has a high-frequency inlet cross-sectional geometry (7) that differs from an effective high-frequency outlet cross-sectional geometry at the microwave-side window, and the transition from the high-frequency inlet cross-sectional geometry at one end of the waveguide (10) to the high-frequency outlet cross-sectional geometry at the other end of the waveguide proceeds continuously. The microwave spark plug can be screwed into conventional bores for spark plugs and permits the safe coupling of microwave energy into a combustion chamber of an internal combustion engine.