A plasma tuning rod system is provided with one or more microwave cavities configured to couple electromagnetic (EM) energy in a desired EM wave mode to a plasma by generating resonant microwave energy in one or more plasma tuning rods within and/or adjacent to the plasma. One or more microwave cavity assemblies can be coupled to a process chamber, and can comprise one or more tuning spaces/cavities. Each tuning space/cavity can have one or more plasma tuning rods coupled thereto. The plasma tuning rods can be configured to couple the EM energy from the resonant cavities to the process space within the process chamber and thereby create uniform plasma within the process space.