A microwave energy delivery device, comprising: a coaxial feedline having an inner conductor, an inner dielectric insulator coaxially disposed about the inner conductor, and an outer conductor coaxially disposed about the inner dielectric; a radiating portion operably coupled to a distal end of the coaxial feedline, the radiating portion including: a radiating portion inner conductor operably coupled to and extending from a distal end of the coaxial feedline inner conductor; a shielding outer conductor helically wrapped about the radiating portion inner conductor and operably coupled to the coaxial feedline outer conductor; and a shielding dielectric positioned between the radiating portion inner conductor and the shielding outer conductor; and a cap operably coupled to a distal end of the radiating portion inner conductor and the shielding outer conductor and providing an electrical connection therebetween; wherein: 1. the width of the shielding outer conductor varies according to the longitudinal position thereof along the coaxial feedline inner conductor; or 2. the helix angle of the shielding outer conductor varies according to the longitudinal position thereof along the coaxial feedline inner conductor; or 3. the pitch of the helix angle of the shielding outer conductor varies according to the longitudinal position thereof along the coaxial feedline inner conductor; and the microwave energy delivery device further comprising a temperature sensor (134, 1534) disposed at a distal end thereof. a coaxial feedline having an inner conductor, an inner dielectric insulator coaxially disposed about the inner conductor, and an outer conductor coaxially disposed about the inner dielectric; a radiating portion operably coupled to a distal end of the coaxial feedline, the radiating portion including: a radiating portion inner conductor operably coupled to and extending from a distal end of the coaxial feedline inner conductor; a shielding outer conductor helically wrapped about the radiating portion inner conductor and operably coupled to the coaxial feedline outer conductor; and a shielding dielectric positioned between the radiating portion inner conductor and the shielding outer conductor; and a cap operably coupled to a distal end of the radiating portion inner conductor and the shielding outer conductor and providing an electrical connection therebetween; wherein: 1. the width of the shielding outer conductor varies according to the longitudinal position thereof along the coaxial feedline inner conductor; or 2. the helix angle of the shielding outer conductor varies according to the longitudinal position thereof along the coaxial feedline inner conductor; or 3. the pitch of the helix angle of the shielding outer conductor varies according to the longitudinal position thereof along the coaxial feedline inner conductor; and a radiating portion inner conductor operably coupled to and extending from a distal end of the coaxial feedline inner conductor; a shielding outer conductor helically wrapped about the radiating portion inner conductor and operably coupled to the coaxial feedline outer conductor; and a shielding dielectric positioned between the radiating portion inner conductor and the shielding outer conductor; and a cap operably coupled to a distal end of the radiating portion inner conductor and the shielding outer conductor and providing an electrical connection therebetween; wherein: 1. the width of the shielding outer conductor varies according to the longitudinal position thereof along the coaxial feedline inner conductor; or 2. the helix angle of the shielding outer conductor varies according to the longitudinal position thereof along the coaxial feedline inner conductor; or 3. the pitch of the helix angle of the shielding outer conductor varies according to the longitudinal position thereof along the coaxial feedline inner conductor; and 1. the width of the shielding outer conductor varies according to the longitudinal position thereof along the coaxial feedline inner conductor; or 2. the helix angle of the shielding outer conductor varies according to the longitudinal position thereof along the coaxial feedline inner conductor; or 3. the pitch of the helix angle of the shielding outer conductor varies according to the longitudinal position thereof along the coaxial feedline inner conductor; and the microwave energy delivery device further comprising a temperature sensor (134, 1534) disposed at a distal end thereof.