The invention provides a plurality of plasma tuning rod subsystems. The plasma tuning rod subsystems can comprise 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. Some of the plasma tuning rods can be configured to couple the EM energy from one or more of the resonant cavities to the process space within the process chamber and thereby create uniform plasma within the process space.