PROBLEM TO BE SOLVED: To provide an electrosurgical device with a balun structure for air exposure of an antenna radiating section, and to provide a method of using the same.SOLUTION: An energy applicator 100 for directing energy to tissue includes: a feedline 110 having an inner conductor, an outer conductor and a dielectric material disposed therebetween; and an antenna assembly 12 having radiating sections 105, 140 operably coupled to the feedline. The energy applicator also includes: a first balun structure 108 configured to substantially confine energy to the radiating section when the energy applicator is energized and disposed in tissue; and a second balun structure configured to substantially prevent energy emitted from the radiating section from propagating proximal to the second balun structure 129 along the feedline when the energy applicator is energized but not disposed in tissue.