An antenna includes excitation terminals responsive to an RF source to supply an RF electromagnetic field to a plasma that processes a workpiece in a vacuum chamber. A matching network includes first and second portions respectively between the source and terminals and between the terminals and the antenna plasma excitation coil. In response to indications of impedance matching between the source and its load, currents flowing between (1) the first portion and the terminals and (2) the terminals and the coil are controlled so the latter exceeds the former. The indications control impedances of the first and second portions or the first portion impedance and the source frequency. The coil can include a transformer having a primary winding coupled to the excitation terminals and a multi-turn plasma excitation secondary winding.