An electrosurgical device, comprising: 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 longitudinally disposed at a distal end of the inner conductor; a balun structure disposed on the outer conductor; an electrically-conductive cylinder coaxially disposed around a distal portion of the balun structure; characterized by: a dielectric structure (1864, 1862) disposed adjacent to a distal end of the electrically-conductive cylinder, wherein the dielectric structure (840; 1864, 1862) longitudinally extends from the distal end of the electrically-conductive cylinder to a distal end of the electrically-conductive member; a sleeve member including a first sleeve portion and a second sleeve portion, wherein the first sleeve portion is disposed proximal to the dielectric structure (840; 1864, 1862) and the second sleeve portion is disposed distally to the first sleeve portion and configured to partially surround the dielectric structure (840; 1864, 1862); and an electromagnetic window ("W") partially defined by longitudinal edges of the second sleeve portion to allow energy to be radiated from the elongated electrically-conductive member to transfer into tissue in a directional radiation pattern. 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 longitudinally disposed at a distal end of the inner conductor; a balun structure disposed on the outer conductor; an electrically-conductive cylinder coaxially disposed around a distal portion of the balun structure; characterized by: a dielectric structure (1864, 1862) disposed adjacent to a distal end of the electrically-conductive cylinder, wherein the dielectric structure (840; 1864, 1862) longitudinally extends from the distal end of the electrically-conductive cylinder to a distal end of the electrically-conductive member; a sleeve member including a first sleeve portion and a second sleeve portion, wherein the first sleeve portion is disposed proximal to the dielectric structure (840; 1864, 1862) and the second sleeve portion is disposed distally to the first sleeve portion and configured to partially surround the dielectric structure (840; 1864, 1862); and an electromagnetic window ("W") partially defined by longitudinal edges of the second sleeve portion to allow energy to be radiated from the elongated electrically-conductive member to transfer into tissue in a directional radiation pattern. a dielectric structure (1864, 1862) disposed adjacent to a distal end of the electrically-conductive cylinder, wherein the dielectric structure (840; 1864, 1862) longitudinally extends from the distal end of the electrically-conductive cylinder to a distal end of the electrically-conductive member; a sleeve member including a first sleeve portion and a second sleeve portion, wherein the first sleeve portion is disposed proximal to the dielectric structure (840; 1864, 1862) and the second sleeve portion is disposed distally to the first sleeve portion and configured to partially surround the dielectric structure (840; 1864, 1862); and an electromagnetic window ("W") partially defined by longitudinal edges of the second sleeve portion to allow energy to be radiated from the elongated electrically-conductive member to transfer into tissue in a directional radiation pattern.