An electrosurgical apparatus for resection of biological tissue comprises a radiofrequency (RF) generator 300 for generating RF electromagnetic radiation at a first frequency and a microwave signal generator 302 for generating microwave electromagnetic radiation at a second frequency. A feed structure comprises an RF channel 306 that conveys RF radiation from the RF signal generator 300 to a probe and a microwave charnel 304 that conveys the microwave radiation from the microwave signal generator 302 to the probe. The RF channel 306 and microwave channel 304 comprise physically separate signal pathways from the generators 300, 302. The feed structure has a combining circuit 308 with 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 radiation and microwave radiation separately or simultaneously to the probe. The microwave channel 304 includes a waveguide isolator 312 connected to isolate the signal pathway on the microwave channel 304 from the RF radiation. An isolating circuit for an electrosurgical apparatus is also disclosed.
