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. The device also includes an electrically-conductive cylinder coaxially disposed around a distal portion of the balun structure, and a dielectric structure disposed substantially adjacent to a distal end of the electrically-conductive cylinder, wherein the dielectric structure longitudinally extends from the distal end of the electrically-conductive cylinder to a distal end of the electrically-conductive member.
