Surgical apparatus for introducing material through a needle into biological tissue, the apparatus comprising: a power source for delivering microwave energy, a needle that is insertable into biological tissue, the needle having: an elongate body terminating with an insertion tip; a longitudinal channel formed within the body for transporting material to or from the tissue, wherein the longitudinal channel extends through the insertion tip and terminates at an opening in the insertion tip; and a coaxial antenna comprising an inner conductor along the inside wall of the channel and an outer conductor coaxial with the inner conductor and separated from it by a first dielectric material, and a first signal path and a second signal path, each of the first signal path and the second signal path connecting the needle to the power source, wherein the insertion tip is made from a second dielectric material and is arranged to create a matched condition between the first dielectric material and a representative tissue impedance for the microwave energy, wherein the power source is arranged to deliver energy having a plurality of frequencies, wherein the needle is connected to receive energy from the power source via the first signal path for conveying energy having a first frequency for performing tissue ablation and the second signal path for conveying energy having a second frequency for performing tissue measurements, and the coaxial antenna is connected to couple the received energy into biological tissue at the insertion tip, and wherein the second frequency is greater than the first frequency. a power source for delivering microwave energy, a needle that is insertable into biological tissue, the needle having: an elongate body terminating with an insertion tip; a longitudinal channel formed within the body for transporting material to or from the tissue, wherein the longitudinal channel extends through the insertion tip and terminates at an opening in the insertion tip; and a coaxial antenna comprising an inner conductor along the inside wall of the channel and an outer conductor coaxial with the inner conductor and separated from it by a first dielectric material, and an elongate body terminating with an insertion tip; a longitudinal channel formed within the body for transporting material to or from the tissue, wherein the longitudinal channel extends through the insertion tip and terminates at an opening in the insertion tip; and a coaxial antenna comprising an inner conductor along the inside wall of the channel and an outer conductor coaxial with the inner conductor and separated from it by a first dielectric material, and a first signal path and a second signal path, each of the first signal path and the second signal path connecting the needle to the power source, wherein the insertion tip is made from a second dielectric material and is arranged to create a matched condition between the first dielectric material and a representative tissue impedance for the microwave energy, wherein the power source is arranged to deliver energy having a plurality of frequencies, wherein the needle is connected to receive energy from the power source via the first signal path for conveying energy having a first frequency for performing tissue ablation and the second signal path for conveying energy having a second frequency for performing tissue measurements, and the coaxial antenna is connected to couple the received energy into biological tissue at the insertion tip, and wherein the second frequency is greater than the first frequency.