Electrosurgical devices with balun structure for air exposure of antenna radiating section and method of directing energy to tissue using same

1. 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 having a radiating section operably coupled to the feedline;

a first balun structure configured to substantially 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 and a second balun disposed so as to at least partially overlap the first balun;

the first balun including:

a first balun insulator disposed around a distal portion of the outer conductor;

a first balun conductor disposed around at least a portion of the first balun insulator;

the second balun including:

a second balun insulator disposed so as to at least partially overlap a proximal portion of the first balun conductor;

a second balun conductor electrically coupled to the outer conductor; and

a second balun structure configured to substantially 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.

2. The energy applicator of claim 1 , wherein the second balun conductor is disposed around at least a portion of an outer peripheral surface of the second balun insulator.

3. The energy applicator of claim 1 , wherein the second balun insulator is a substantially cylindrically-shaped dielectric sleeve.

4. The energy applicator of claim 1 , wherein the second balun conductor is a substantially cylindrically-shaped electrically-conductive sleeve.

5. The energy applicator of claim 1 , wherein the second balun structure includes a first balun and a second balun disposed so as to at least partially overlap the first balun of the second balun structure.

6. The energy applicator of claim 1 , wherein the radiating section includes a first conductive disk and a second conductive disk disposed proximal to the first conductive disk.

7. The energy applicator of claim 6 , further comprising a third balun structure positioned about one wavelength in air from the second conductive disk.

8. 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 having a radiating section operably coupled to the feedline;

a first balun structure configured to substantially confine energy to the radiating section when the energy applicator is energized and disposed in tissue, the first balun structure including:

a first balun insulator disposed around a distal portion of the outer conductor;

a first balun conductor disposed around at least a portion of the first balun insulator; and

a second balun structure configured to substantially 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, wherein the second balun structure includes a second balun insulator disposed so as to at least partially overlap the first balun conductor and a second balun conductor electrically coupled to the outer conductor.

9. The energy applicator of claim 8 , wherein the second balun insulator includes a first portion coaxially disposed around a portion of the outer conductor and a second portion disposed so as to at least partially overlap a proximal portion of the first balun conductor.

10. The energy applicator of claim 8 , wherein the radiating section includes a first conductive disk and a second conductive disk disposed proximal to the first conductive disk.

11. The energy applicator of claim 10 , wherein the second balun structure is positioned about one-half of a wavelength in air from the second conductive disk.

12. The energy applicator of claim 8 , wherein the first balun structure includes a first balun, a second balun, a third balun and a fourth balun disposed so as to at least partially overlap the third balun.

13. 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 having a radiating section operably coupled to the feedline;

a first balun structure configured to substantially 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 first portion of the outer conductor;

a first balun conductor disposed around at least a portion of the first balun insulator;

the second balun portion including:

a second balun insulator including a first portion and a second portion, the first portion coaxially disposed around a second portion of the outer conductor proximal to the first portion of the outer conductor, the second portion of the second balun insulator disposed so as to at least partially overlap a proximal portion of the first balun conductor;

a second balun conductor electrically coupled to the outer conductor; and

a second balun structure configured to substantially 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.