Methods and apparatus for controlling characteristics of a plasma

Methods and apparatus for controlling characteristics of a plasma, such as the spatial distribution of RF power and plasma uniformity, are provided herein. In some embodiments, an apparatus for controlling characteristics of a plasma includes a resonator for use in conjunction with a plasma reactor, the resonator including a source resonator for receiving an RF signal having a first frequency; a return path resonator disposed substantially coaxially with, and at least partially within, the source resonator; and an outer conductor having the source resonator and the return path resonator disposed substantially coaxially with, and at least partially within, the outer conductor, the outer conductor for providing an RF ground connection.