Microwave resonant cavities running at 2.45 GHz are now being investigated for use in the high power remote plasma processings. The present paper deals with the design of two coupling devices, e.g., one coaxial cavity and one TM012mode cylindrical cavity, using an antenna coupling. Their main attractive feature is the ability to run at powers as high as 3 and 6 kW, respectively. A basic model used to describe the wave–plasma interaction is developed and leads to the main consequences for the cavities conception thanks to the deduced equivalent electrical circuits. Their high efficiency is experimentally demonstrated for nitrogen, oxygen, air, and argon.