Electrosurgical instrument for performing ablation or electroporation of biological tissue

An electrosurgical instrument for delivering electromagnetic energy to biological tissue at a treatment site, the electrosurgical instrument comprising:

• a coaxial transmission line comprising an inner conductor, an outer conductor, and a dielectric material separating the inner conductor from the outer conductor, the coaxial transmission line being arranged to convey microwave electromagnetic (EM) energy;
• a radiating tip mounted at a distal end of the coaxial transmission line to receive the microwave EM energy from the coaxial transmission line and emit the microwave EM energy as a field around the radiating tip;
• an auxiliary transmission line extending along the coaxial transmission line towards the radiating tip, the auxiliary transmission line being arranged to convey electromagnetic energy having an electroporation waveform;
• and
• a microelectrode array mounted on the radiating tip and electrically connected to the auxiliary transmission line,
• wherein the microelectrode array is configured to receive the electromagnetic energy having an electroporation waveform from the auxiliary transmission line to thereby generate an electric field at the radiating tip for electroporation of biological tissue.