An isolation circuit for an electrosurgical resection system, the isolation circuit comprising: a combination circuit (206) having a first input (203) connectable to receive radiofrequency (RF) electromagnetic radiation (EM) having a first frequency from an RF channel, a second connectable input to receive microwave EM radiation having a second frequency, which is greater than the first frequency, from a microwave channel, and an output (207) in communication with the first and second inputs to transmit RF EM radiation and microwave EM radiation to a common signal path, and a waveguide isolator (200) connected to isolate the microwave channel from RF EM radiation, where the isolator The waveguide comprises a conductive input section, a conductive output section that coincides with the input section, in order to define a guide cavity d and waves within a volume enclosed by the input and output sections, and a DC isolation barrier disposed between the input and output sections, where the output of the combination circuit includes a signal conductor and a conductor to ground, and wherein the isolation circuit comprises a capacitive structure between the grounding conductor of the output, from the combination circuit, and the conductive input section of the waveguide insulator, the capacitive structure being arranged to inhibit coupling of RF EM energy and microwave EM energy leaks.Un circuito de aislamiento para un sistema de resección electroquirúrgica, comprendiendo el circuito de aislamiento: un circuito de combinación (206) que presenta una primera entrada (203) conectable para recibir radiación electromagnética (EM) de radiofrecuencia (RF) que tiene una primera frecuencia desde un canal de RF, una segunda entrada conectable para recibir radiación EM de microondas que tiene una segunda frecuencia, que es mayor que la primera frecuencia, desde un canal de microondas, y una salida (207) en comunicación con la primera y la segunda entradas para así transmitir la radia
