An electrosurgical device for directing energy to a target volume of tissueincludes a coaxial feedline having an inner conductor, an outer conductor andadielectric material disposed therebetween. A proximal cylindrical dielectricsleeve iscoupled to the inner conductor at a distal end of the coaxial feedline. Adistal cylindricaldielectric sleeve is coupled to the inner conductor. First and seconddielectric segmentsare coupled to the inner conductor and disposed between the proximalcylindricaldielectric sleeve and the distal cylindrical dielectric sleeve. The devicealso includes anelongated shaft overlying the proximal cylindrical dielectric sleeve, thefirst dielectricsegment, the second dielectric segment and the distal cylindrical dielectricsleeve. Theelongated shaft includes an opening defined therethrough, wherein the openingis atleast partially aligned with the first dielectric segment. A balun structureis disposed onthe elongated shaft, at least partially overlying the opening in the elongatedshaft.
