Electrosurgical apparatus

1. Electrosurgical apparatus for resection of biological tissue, the apparatus comprising:

a radiofrequency (RF) signal generator for generating RF electromagnetic (EM) radiation having a first frequency;

a microwave signal generator for generating microwave EM radiation having a second frequency that is higher than the first frequency;

a probe arranged to deliver the RF EM radiation and the microwave EM radiation separately or simultaneously from a distal end thereof;

a feed structure for conveying the RF EM radiation and the microwave EM radiation to the probe, the feed structure comprising an RF channel for connecting the probe to the RF signal generator, and a microwave channel for connecting the probe to the microwave signal generator,

wherein the RF channel and microwave channel comprise physically separate signal pathways from the RF signal generator and microwave signal generator respectively,

wherein the feed structure includes a combining circuit having a first input connected to the separate signal pathway on the RF channel, a second input connected to the separate signal pathway on the microwave channel, and an output connected to a common signal pathway for conveying the RF EM radiation and the microwave EM radiation separately or simultaneously along a single channel to the probe,

wherein the microwave channel includes a waveguide isolator connected to isolate the separate signal pathway on the microwave channel from the RF EM radiation,

wherein the waveguide isolator comprises:

a conductive input section,

a conductive output section which mates with the input section to define a cylindrical body having a waveguide cavity within a volume enclosed by the input and output sections, and

a DC isolation barrier arranged between the input and output sections,

wherein the output on the common signal pathway includes a signal conductor and a ground conductor,

wherein the feed structure includes a capacitive structure between the ground conductor of the output on the common signal pathway and the conductive input section of the waveguide isolator, the capacitive structure being arranged to inhibit coupling of the RF EM energy and leakage of the microwave EM energy,

wherein the capacitive structure is provided by the DC isolation barrier and a microwave choke formed on the input section of the waveguide isolator, and

wherein the microwave choke comprises an annular channel extending axially from the distal end of the input section of the waveguide isolator.

2. Electrosurgical apparatus according to claim 1 , wherein the DC isolation barrier includes a rigid insulating spacer element mounted between the input and output sections of the waveguide isolator.

3. Electrosurgical apparatus according to claim 2 , wherein the DC isolation barrier includes an insulating film mounted on a portion of an inner surface of the input section at a junction with the rigid insulating spacer element.

4. Electrosurgical apparatus according to claim 1 , wherein the first and second inputs to and the output from the combining circuit are electrically floating with respect to the RF signal generator and microwave signal generator.

5. Electrosurgical apparatus according to claim 1 , wherein the combining circuit is located in a housing, and the probe is connectable to an output port formed in the housing.

6. Electrosurgical apparatus according to claim 5 having an insulating sleeve at the output port of the housing to isolate the housing from the combining circuit.

7. An isolating circuit for electrosurgical apparatus for resection of biological tissue, the isolating circuit comprising:

a combining circuit having a first input connectable to receive radiofrequency (RF) electromagnetic (EM) radiation having a first frequency from an RF channel, a second input connectable to receive microwave EM radiation having a second frequency that is higher than the first frequency from a microwave channel, and an output in communication with the first and second inputs for conveying the RF EM radiation and the microwave EM radiation to a common signal pathway, and

a waveguide isolator connected to isolate the microwave channel from the RF EM radiation,

wherein the waveguide isolator comprises a conductive input section, a conductive output section which mates with the input section to define a waveguide cavity within a volume enclosed by the input and output sections, and a DC isolation barrier arranged between the input and output sections,

wherein the output from the combining circuit includes a signal conductor and a ground conductor,

wherein the isolating circuit comprises a capacitive structure between the ground conductor of the output from the combining circuit and the conductive input section of the waveguide isolator, the capacitive structure being arranged to inhibit coupling of the RF EM energy and leakage of the microwave EM energy,

wherein the capacitive structure is provided by the DC isolation barrier and a microwave choke formed on the input section of the waveguide isolator, and

wherein the microwave choke comprises an annular channel extending axially from a distal end of the input section of the waveguide isolator.

8. The isolating circuit according to claim 7 , wherein the DC isolation barrier includes a rigid insulating spacer element mounted between the input and output sections of the waveguide isolator.