A microwave ablation device, comprising: a handle assembly; an outer tubular member extending distally from the handle assembly; an inner tubular member extending through the outer tubular member (Figure 1); a feedline disposed within the inner tubular member, the feedline including an inner conductor, an outer conductor, and a dielectric disposed between the inner conductor and the outer conductor; a first fluid lumen defined between an inner surface of the outer tubular member and an outer surface of the inner tubular member; a second fluid lumen defined between an inner surface of the inner tubular member and an outer surface of the feedline; a tip disposed at a distal end of the outer tubular member and including a tip body having a distal end portion configured for insertion into tissue and a proximal end portion defining an interior chamber in fluid communication with the lumen defined by the outer tubular member; and an antenna assembly operably coupled to the feedline and configured to radiate microwave energy, the antenna assembly having a proximal radiating section and a distal radiating section including an electrically-conductive element, wherein a distal portion of the second fluid lumen is defined between an inner surface of the inner tubular member and an outer surface of the electrically-conductive element, the electrically-conductive element extending beyond the inner tubular member and having a stepped configuration such that the outer diameter of a distal portion is less than the outer diameter of a proximal portion, wherein a distal end of the electrically-conductive element is disposed within the interior chamber defined by the tip body. a handle assembly; an outer tubular member extending distally from the handle assembly; an inner tubular member extending through the outer tubular member (Figure 1); a feedline disposed within the inner tubular member, the feedline including an inner conductor, an outer conductor, and a dielectric disposed between the inner conductor and the outer conductor; a first fluid lumen defined between an inner surface of the outer tubular member and an outer surface of the inner tubular member; a second fluid lumen defined between an inner surface of the inner tubular member and an outer surface of the feedline; a tip disposed at a distal end of the outer tubular member and including a tip body having a distal end portion configured for insertion into tissue and a proximal end portion defining an interior chamber in fluid communication with the lumen defined by the outer tubular member; and an antenna assembly operably coupled to the feedline and configured to radiate microwave energy, the antenna assembly having a proximal radiating section and a distal radiating section including an electrically-conductive element, wherein a distal portion of the second fluid lumen is defined between an inner surface of the inner tubular member and an outer surface of the electrically-conductive element, the electrically-conductive element extending beyond the inner tubular member and having a stepped configuration such that the outer diameter of a distal portion is less than the outer diameter of a proximal portion, wherein a distal end of the electrically-conductive element is disposed within the interior chamber defined by the tip body.