Directive window 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 of the feedline; and

an electrically-conductive layer coaxially disposed around a proximal portion of the dielectric layer, wherein the dielectric layer extends distally beyond a distal end of the electrically-conductive layer;

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

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.

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-wave 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 , further comprising:

a sleeve member including a first sleeve portion and a second sleeve portion, the second sleeve portion disposed distally to the first sleeve portion,

wherein the first sleeve portion is disposed proximal to the dielectric structure and the second sleeve portion is configured to partially surround the dielectric structure.

11. The electrosurgical device of claim 10 , further comprising an electromagnetic window configured to emit a directional radiation pattern in operation.

12. The electrosurgical device of claim 11 , wherein the electromagnetic window is partially defined by longitudinal edges of the second sleeve portion.

13. The electrosurgical device of claim 11 , wherein the electromagnetic window includes a radio frequency (RF) transparent material.

14. The electrosurgical device of claim 10 , wherein the second sleeve portion includes an engagement portion extending beyond a distal end of the dielectric structure.

15. The electrosurgical device of claim 1 , further comprising a tapered portion having a tip configured to penetrate tissue.