An electrosurgical generator 100 has: a microwave source 102 for generating a stable microwave signal； a microwave channel 107 for conveying the microwave signal from the microwave source to be output from the generator； a radiofrequency (RF) channel 111 for conveying an RF signal to be output from the generator； and a microwave-to-RF converter 106 able to generate the RF signal from the microwave signal, and deliver the RF signal to the RF channel. The microwave-to-RF converter may include a switching unit with a modulator, and at least one rectifying unit which operates as a full-wave rectifier outputting a square wave. The converter may output a filtered, composite and rectified signal. A switch 104 is used to select microwave or RF mode. The output signal is passed to a surgical probe through a signal combiner 108, such as a switch or diplexer, to protect the generator from reflected energy. The switching unit in the converter may be formed using PIN diodes.
