an apparatus for dynamically matching a radio - frequency source for semiconductor processing to a load , and particularly adapted for plasma sputtering and etching processes , comprises an admittance matching network utilizing magnetically saturable inductors . a dc bias signal is provided to optimize the operating point of the saturable reactor with respect to the hysteresis characteristic of the core material . a control signal characterized by a phase error and a magnitude derived from the signal reflected from the load is applied to control the magnetizing current flowing through the inductors . the invention discloses a structure for the inductors which provides efficient coupling of the control current , while inherently rejecting rf currents reflected back from the load to the inductor current source .