A microwave antenna comprises a feedline (20) including a coaxial cable and a radiating section (18) coupled to the feedline. The radiating section includes a choke (19) .An inflow tube (55) is disposed around an outer conductor of the coaxial cable. The inflow tube defines an inlet flow path configured to supply a coolant fluid to the radiating section. A transition collar (53) forms a portion of the choke. The collar is of a dielectric material and has a proximal end and a distal end. The proximal end is coupled to a distal end of the inflow tube. The transition collar further includes at least one outflow aperture (53a) at the proximal end thereof configured to receive the fluid from the distal end of the inflow tube and transition the fluid from the at least one outflow slot to a distal end of the radiating section.
