An electrosurgical instrument comprising: a coaxial cable configured to convey microwave energy and an electroporation signal; a rod-shaped radiating tip portion extending in a longitudinal direction away from a distal end of the coaxial cable; wherein the radiating tip portion comprises: a proximal coaxial transmission line for receiving and conveying the microwave energy, the proximal coaxial transmission line including an inner conductor, an outer conductor and a dielectric material separating the inner conductor from the outer conductor; and a distal needle tip mounted at a distal end of the proximal coaxial transmission line, the distal needle tip comprising a rigid dielectric sleeve that extends the longitudinal direction from a distal end of the proximal coaxial transmission line, wherein the rod-shaped radiating tip portion has an outer diameter less than an outer diameter of the coaxial cable, wherein the rigid dielectric sleeve surrounds an elongate conductive element that is electrically connected to the inner conductor of the proximal coaxial transmission line and extends beyond a distal end of the outer conductor of the proximal coaxial transmission line, wherein the elongate conductive element is configured to operate as a half wavelength transformer for the microwave energy to thereby radiate the microwave energy from the distal needle tip into biological tissue, wherein the elongate conductive element terminates at an active electrode exposed on a distal end of distal needle tip, the elongate conductive element being electrically connected to the active electrode, and wherein the active electrode is axially spaced from a return electrode that is electrically connected to the distal end of the outer conductor of the proximal coaxial transmission line, the active electrode and return electrode being configured to, when the electroporation signal is received by the rod-shaped radiating tip portion, establish an electric field for electroporation of biological tissue at the distal needle tip. a coaxial cable configured to convey microwave energy and an electroporation signal; a rod-shaped radiating tip portion extending in a longitudinal direction away from a distal end of the coaxial cable; wherein the radiating tip portion comprises: a proximal coaxial transmission line for receiving and conveying the microwave energy, the proximal coaxial transmission line including an inner conductor, an outer conductor and a dielectric material separating the inner conductor from the outer conductor; and a distal needle tip mounted at a distal end of the proximal coaxial transmission line, the distal needle tip comprising a rigid dielectric sleeve that extends the longitudinal direction from a distal end of the proximal coaxial transmission line, a proximal coaxial transmission line for receiving and conveying the microwave energy, the proximal coaxial transmission line including an inner conductor, an outer conductor and a dielectric material separating the inner conductor from the outer conductor; and a distal needle tip mounted at a distal end of the proximal coaxial transmission line, the distal needle tip comprising a rigid dielectric sleeve that extends the longitudinal direction from a distal end of the proximal coaxial transmission line, wherein the rod-shaped radiating tip portion has an outer diameter less than an outer diameter of the coaxial cable, wherein the rigid dielectric sleeve surrounds an elongate conductive element that is electrically connected to the inner conductor of the proximal coaxial transmission line and extends beyond a distal end of the outer conductor of the proximal coaxial transmission line, wherein the elongate conductive element is configured to operate as a half wavelength transformer for the microwave energy to thereby radiate the microwave energy from the distal needle tip into biological tissue, wherein the elongate conductive element terminates at an active electrode exposed on a distal end of distal needle tip, the elongate conductive element being electrically connected to the active electrode, and wherein the active electrode is axially spaced from a return electrode that is electrically connected to the distal end of the outer conductor of the proximal coaxial transmission line, the active electrode and return electrode being configured to, when the electroporation signal is received by the rod-shaped radiating tip portion, establish an electric field for electroporation of biological tissue at the distal needle tip.