A microwave ablation probe (112; 411; 2211; 2411) comprising: a probe body (412; 2412) comprising a shielded portion (115; 417; 2212; 2414) and a radiation window (119; 419; 2419) that is at least partially transparent to microwave energy, wherein the shielded portion of the probe body comprises a metal cannula; a coaxial cable (151; 2451) within the probe body (412; 2412) comprising: a center conductor (121; 2432), a dielectric material (141; 2431) surrounding the center conductor of the cable, and an outer conductor (131; 2432) having an outer conductor distal boundary, wherein the center conductor (121; 2432) comprises a radiating portion that extends beyond a distal boundary (133; 505; 1105; 1405; 1505; 1605; 1705; 1905; 2005; 2405) of the outer conductor (131; 2432), wherein the radiating portion is configured for emission of microwave energy, wherein the radiating portion is aligned with the radiation window (119; 419; 2419); a cap (161; 511; 1411; 1611; 1915; 2214) located at a probe distal end, the cap comprising a cap proximal boundary (164; 516; 1116; 1216; 1316; 1416; 1516; 1616; 1716; 2116; 2416); wherein the outer conductor distal boundary (133; 505; 1105; 1405; 1505; 1605; 1705; 1905; 2005; 2405) or the cap proximal boundary (164; 516; 1116; 1216; 1316; 1416; 1516; 1616; 1716; 2116; 2416) varies in its distance from the probe distal end; and a choke comprising: a choke contact between the metal cannula and the outer conductor, and a choke length extending between the choke contact and a distal end of the metal cannula, wherein the choke contact varies in its distance from the probe distal end. a probe body (412; 2412) comprising a shielded portion (115; 417; 2212; 2414) and a radiation window (119; 419; 2419) that is at least partially transparent to microwave energy, wherein the shielded portion of the probe body comprises a metal cannula; a coaxial cable (151; 2451) within the probe body (412; 2412) comprising: a center conductor (121; 2432), a dielectric material (141; 2431) surrounding the center conductor of the cable, and an outer conductor (131; 2432) having an outer conductor distal boundary, wherein the center conductor (121; 2432) comprises a radiating portion that extends beyond a distal boundary (133; 505; 1105; 1405; 1505; 1605; 1705; 1905; 2005; 2405) of the outer conductor (131; 2432), wherein the radiating portion is configured for emission of microwave energy, wherein the radiating portion is aligned with the radiation window (119; 419; 2419); a cap (161; 511; 1411; 1611; 1915; 2214) located at a probe distal end, the cap comprising a cap proximal boundary (164; 516; 1116; 1216; 1316; 1416; 1516; 1616; 1716; 2116; 2416); a center conductor (121; 2432), a dielectric material (141; 2431) surrounding the center conductor of the cable, and an outer conductor (131; 2432) having an outer conductor distal boundary, wherein the center conductor (121; 2432) comprises a radiating portion that extends beyond a distal boundary (133; 505; 1105; 1405; 1505; 1605; 1705; 1905; 2005; 2405) of the outer conductor (131; 2432), wherein the radiating portion is configured for emission of microwave energy, wherein the radiating portion is aligned with the radiation window (119; 419; 2419); a cap (161; 511; 1411; 1611; 1915; 2214) located at a probe distal end, the cap comprising a cap proximal boundary (164; 516; 1116; 1216; 1316; 1416; 1516; 1616; 1716; 2116; 2416); a choke contact between the metal cannula and the outer conductor, and a choke length extending between the choke contact and a distal end of the metal cannula, wherein the choke contact varies in its distance from the probe distal end.