A microwave antenna including a feedline, a radiating section, an inflow hypotube, a puck, a transition collar and a sleeve. The feedline includes a coaxial cable including an inner and outer conductor, and a dielectric disposed therebetween. The radiating section includes a dipole antenna coupled to the feedline and a trocar coupled to the distal end of the dipole antenna. The inflow hypotube is disposed around the outer conductor and configured to supply fluid to the radiating portion. The puck includes at least two ribs with inflow slots defined between two adjacent ribs. The transition collar is coupled to the distal end of the inflow hypotube and the first end of the puck. The transition collar includes at least two outflow slots configured to receive fluid from a distal end of the inflow hypotube and to transition the fluid from the outflow slots to a distal end of the radiating section. The sleeve overlays the two outflow slots of the transition collar, the puck and at least the distal portion of the radiating section. The sleeve forms a fluid-tight seal with the transition collar proximal the outflow slots and defines a first gap for transitioning the fluid to exit the outflow slots of the transition collar to the distal end of the radiating section.