Surface ablation antenna with dielectric loading

1. An electrosurgical device for directing energy to a target volume of tissue, 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 including:

a dielectric layer coaxially disposed around a distal portion of the outer conductor; and

an electrically-conductive layer coaxially disposed around a proximal portion of the dielectric layer;

an electrically-conductive cylinder coaxially disposed around a distal portion of the electrically-conductive layer of the balun;

a dielectric structure disposed substantially adjacent to a distal end of the electrically-conductive cylinder, wherein the dielectric structure longitudinally extends from the distal end of the electrically-conductive cylinder to a distal end of the electrically-conductive member;

an elongated handle assembly coaxially disposed around a portion of the outer conductor at a distal end of the coaxial feedline, wherein the handle assembly is disposed proximal to the dielectric structure; and

a shell assembly disposed at a distal end of the elongated handle assembly, wherein the shell assembly is coupled to a distal portion of the balun.

2. The electrosurgical device of claim 1 , wherein a portion of the inner conductor and the dielectric material of the coaxial feedline extends beyond the outer conductor at a distal end of the coaxial feedline.

3. The electrosurgical device of claim 1 , wherein the electrically-conductive member is electrically coupled to the inner conductor.

4. The electrosurgical device of claim 1 , wherein the balun is a quarter wavelength sleeve.

5. The electrosurgical device of claim 1 , wherein the electrically-conductive layer includes a first portion coaxially disposed around the proximal portion of the dielectric layer, and a second portion disposed proximally to the first portion, the second portion electrically coupled to the outer conductor.

6. The electrosurgical device of claim 1 , wherein the dielectric structure is configured to cover a distal end of the electrically-conductive member.

7. The electrosurgical device of claim 1 , further comprising:

a cooling chamber disposed at least partially about the electrically-conductive member.

8. The electrosurgical device of claim 7 , further comprising:

an inflow tube configured to supply a coolant fluid into the cooling chamber; and

an outflow tube configured to dispense the coolant fluid from the cooling chamber.

9. The electrosurgical device of claim 8 , further comprising:

a coolant source to supply the coolant fluid.

10. The electrosurgical device of claim 1 , wherein the shell assembly is coupled to a distal end of the electrically-conductive layer of the balun.

11. The electrosurgical device of claim 1 , wherein the dielectric layer of the balun extends distally beyond a distal end of the electrically-conductive layer of the balun.

12. A method of manufacturing an electrosurgical device, comprising the steps of:

providing a coaxial feedline having an inner conductor, an outer conductor, and a dielectric material disposed therebetween;

joining an electrically-conductive member to a distal end of the inner conductor at a distal end of the coaxial feedline;

joining a balun to a distal portion of the outer conductor, the balun including a dielectric layer coaxially disposed around the distal portion of the outer conductor and an electrically-conductive layer coaxially disposed around a proximal portion of the dielectric layer;

joining an electrically-conductive cylinder to a distal portion of the electrically-conductive layer of the balun;

forming a dielectric structure having a proximal end disposed substantially adjacent to a distal end of the electrically-conductive cylinder, wherein the dielectric structure longitudinally extends from the distal end of the electrically-conductive cylinder to a distal end of the electrically-conductive member;

joining an elongated handle assembly to the outer conductor at a distal end of the coaxial feedline, wherein the handle assembly is disposed proximal to the dielectric structure; and

joining a shell assembly to a distal end of the elongated handle assembly, wherein the shell assembly is coupled to a distal portion of the balun.

13. The method of manufacturing an electrosurgical device in accordance with claim 12 , wherein the dielectric structure includes a cap of dielectric material configured to cover a distal end of the electrically-conductive member.

14. The method of manufacturing an electrosurgical device in accordance with claim 12 , wherein the shell assembly includes an inner portion and an outer portion disposed about the inner portion.

15. The method of manufacturing an electrosurgical device in accordance with claim 14 , wherein the outer portion of the shell assembly includes an electrically conductive material and the inner portion of the shell assembly includes a dielectric material.

16. The method of manufacturing an electrosurgical device in accordance with claim 14 , wherein the inner portion of the shell assembly includes a flat planar surface having a recess defined therein.

17. The method of manufacturing an electrosurgical device in accordance with claim 16 , wherein the recess is configured to receive at least a portion of the dielectric structure.

18. The method of manufacturing an electrosurgical device of claim 12 , wherein the shell assembly is coupled to a distal end of the electrically-conductive layer of the balun.

19. The method of manufacturing an electrosurgical device of claim 12 , wherein the dielectric layer of the balun extends distally beyond a distal end of the electrically-conductive layer of the balun.