A defrosting system includes an RF signal source, an electrode proximate to a cavity within which a load to be defrosted is positioned, a transmission path between the RF signal source and the electrode, and an impedance matching network electrically coupled along the transmission path between the output of the RF signal source and the electrode. The system also includes power detection circuitry coupled to the transmission path and configured to detect reflected signal power along the transmission path. A system controller is configured to modify, based on the reflected signal power, an inductance value of the impedance matching network to reduce a ratio of the reflected signal power to the forward signal power. The impedance matching network includes a plurality of fixed-value, lumped inductors positioned within a fixed inductor area.