An electrosurgical device for directing energy to a target volume of tissue includes a coaxial feedline having an inner conductor, an outer conductor coaxially disposed around the inner conductor, and a dielectric material disposed therebetween. An elongated electrically-conductive member is longitudinally disposed at a distal end of the inner conductor； a balun structure is disposed on the outer conductor. An electrically-conductive cylinder is coaxially disposed around a distal portion of the balun structure and a dielectric structure is disposed substantially adjacent to a distal end of the electrically-conductive cylinder and configured to extend to a distal end of the electrically-conductive member. An elongated handle assembly is coaxially disposed around a portion of the outer conductor proximal to the dielectric structure and a shell assembly is disposed at a distal end of the elongated handle assembly. A portion of the shell assembly is configured to extend distally beyond the distal end of the electrically-conductive member.
