A radio frequency energy transmission device comprises a hollow coaxial electrically conductive cable adapted for conduction of radio frequency (RF) energy, particularly microwave energy, for the ablation of biological tissue. The hollow cable has a proximal end and a distal end and comprises coaxial inner and outer conductors extending substantially the entire length of the cable from the proximal end to a distal end portion of the cable. The inner conductor comprises an elongated electrically conductive tubular member having a hollow, axially extending lumen, and the outer conductor comprises an elongated electrically conductive tubular member disposed in a substantially coaxial relationship over at least a portion of the inner conductor. Dielectricity to impede conduction between the inner and outer conductors is introduced with a vacuum or dielectric medium disposed between the inner and outer conductors. An ablating member, which delivers radio frequency energy, particularly microwave energy, to body tissue is disposed at a distal end portion of the cable. The ablating member can be a helical coil, a monopole of a microstrip circuit.