A microwave ablation needle (500, 600, 625, 635, 645, 700) comprising: a feedline (510, 732) electrically connected to a microwave antenna (520, 607, 630, 639, 652, 752), and a shaft (350, 514, 606, 632, 641, 655, 701) surrounding the microwave antenna (520, 607, 630, 639, 652, 752) and the feedline (510, 732), the shaft comprising (514, 606, 632, 641, 655, 701) a non-metallic portion and a metallic portion, the non-metallic portion extending axially to be co-extensive with at least a portion of the antenna (520, 607, 630, 639, 652, 752) that radiates microwaves, wherein the microwave antenna (520, 607, 630, 639, 652, 752) comprises: a helical arm (518, 611, 712), being electrically connected to an outer conductor (506, 730) of the feedline (510, 732) at a junction point (517, 736), the helical arm (518, 611, 712) extending in a distal direction from the junction point (517, 736); and a linear arm (519, 720), the linear arm being electrically connected to an inner conductor (502, 727) of the feedline (510, 732), the linear arm (519, 720) extending distally from a distal end of the feedline (510, 732), the linear arm (519, 720) including a first portion (531, 721) surrounded by a dielectric (535, 725); and a second portion (533, 723) free of dielectric, the second portion (533, 723) being distal to the first portion (531, 721). a feedline (510, 732) electrically connected to a microwave antenna (520, 607, 630, 639, 652, 752), and a shaft (350, 514, 606, 632, 641, 655, 701) surrounding the microwave antenna (520, 607, 630, 639, 652, 752) and the feedline (510, 732), the shaft comprising (514, 606, 632, 641, 655, 701) a non-metallic portion and a metallic portion, the non-metallic portion extending axially to be co-extensive with at least a portion of the antenna (520, 607, 630, 639, 652, 752) that radiates microwaves, wherein the microwave antenna (520, 607, 630, 639, 652, 752) comprises: a helical arm (518, 611, 712), being electrically connected to an outer conductor (506, 730) of the feedline (510, 732) at a junction point (517, 736), the helical arm (518, 611, 712) extending in a distal direction from the junction point (517, 736); and a linear arm (519, 720), the linear arm being electrically connected to an inner conductor (502, 727) of the feedline (510, 732), the linear arm (519, 720) extending distally from a distal end of the feedline (510, 732), the linear arm (519, 720) including a first portion (531, 721) surrounded by a dielectric (535, 725); and a helical arm (518, 611, 712), being electrically connected to an outer conductor (506, 730) of the feedline (510, 732) at a junction point (517, 736), the helical arm (518, 611, 712) extending in a distal direction from the junction point (517, 736); and a linear arm (519, 720), the linear arm being electrically connected to an inner conductor (502, 727) of the feedline (510, 732), the linear arm (519, 720) extending distally from a distal end of the feedline (510, 732), the linear arm (519, 720) including a first portion (531, 721) surrounded by a dielectric (535, 725); and a second portion (533, 723) free of dielectric, the second portion (533, 723) being distal to the first portion (531, 721).