An energy applicator for directing energy to tissue, comprising: a feedline having an inner conductor, an outer conductor coaxially disposed around the inner conductor, and a dielectric material disposed therebetween; an antenna assembly (12, 280) having a radiating section operably coupled to the feed line; a first balun structure configured to confine energy to the radiating section when the energy applicator is energized and disposed in tissue, wherein the first balun structure includes a first balun portion and a second balun portion disposed so as to at least partially overlap the first balun portion, the first balun portion including a first balun insulator disposed around a distal portion of the outer conductor of the feedline and a first balun conductor disposed around at least a portion of the first balun insulator and having a proximal portion in contact with the outer conductor, the first balun insulator extending distally beyond a distal-most end of the first balun conductor, the second balun portion including a second balun insulator disposed so as to at least partially overlap the proximal portion of the first balun conductor, wherein the second balun insulator includes a proximal portion disposed in contact with the outer conductor of the feedline, a distal portion disposed in contact with the first balun conductor and parallel to the proximal portion of the second balun insulator, an intermediate portion interconnecting and perpendicular to the proximal and distal portions of the second balun insulator, and a second balun conductor disposed around the outer periphery of the second balun insulator and electrically coupled to the outer conductor of the feedline; and a second balun structure configured to prevent energy emitted from the radiating section from propagating proximal to the second balun structure along the feedline when the energy applicator is energized but not disposed in tissue. a feedline having an inner conductor, an outer conductor coaxially disposed around the inner conductor, and a dielectric material disposed therebetween; an antenna assembly (12, 280) having a radiating section operably coupled to the feed line; a first balun structure configured to confine energy to the radiating section when the energy applicator is energized and disposed in tissue, wherein the first balun structure includes a first balun portion and a second balun portion disposed so as to at least partially overlap the first balun portion, the first balun portion including a first balun insulator disposed around a distal portion of the outer conductor of the feedline and a first balun conductor disposed around at least a portion of the first balun insulator and having a proximal portion in contact with the outer conductor, the first balun insulator extending distally beyond a distal-most end of the first balun conductor, the second balun portion including a second balun insulator disposed so as to at least partially overlap the proximal portion of the first balun conductor, wherein the second balun insulator includes a proximal portion disposed in contact with the outer conductor of the feedline, a distal portion disposed in contact with the first balun conductor and parallel to the proximal portion of the second balun insulator, an intermediate portion interconnecting and perpendicular to the proximal and distal portions of the second balun insulator, and a second balun conductor disposed around the outer periphery of the second balun insulator and electrically coupled to the outer conductor of the feedline; and a second balun structure configured to prevent energy emitted from the radiating section from propagating proximal to the second balun structure along the feedline when the energy applicator is energized but not disposed in tissue.