An electrosurgical apparatus is provided in the present invention, having a feed structure comprising a radiofrequency (RF) channel (306) for conveying RF electromagnetic (EM) radiation from an RF signal generator (300) to a probe and a microwave channel (304) for conveying microwave EM radiation from a microwave signal generator (302) to the probe, wherein the RF channel (306) and microwave channel (304) comprise physically separate signal pathways, wherein the feed structure includes a combining circuit (308) having an input connected to the signal pathway on the RF channel (306), another input connected to the signal pathway on the microwave channel (304), and an output connected to a common signal pathway for conveying the RF EM radiation and EM radiation separately or simultaneously to the probe, and wherein the microwave channel (304) includes a waveguide isolator (312) connected to isolate the signal pathway on the microwave channel (304) from the RF EM radiation.