A calibration method and apparatus for surgical antennas which are arranged to deliver microwave radiation (e.g. having a treatment frequency of 500 MHz to 100 GHz) into biological tissue is disclosed. An emitting region of the antenna is exposed to a plurality of calibration standards each having a different complex impedance at the treatment frequency. In one embodiment the calibration standards are created in a short-circuit-terminated waveguide cavity of variable length. In another embodiment, each calibration standard is a different mixture of two or more liquids. Measurement of the magnitude and phase of signals reflected from the emitting region when exposed to the calibration standard can permit calibration of the antenna, e.g. by generating a mapping function based on the measured values and known or reference values for the calibration standards. Also disclosed is tissue treatment apparatus having an ablation channel for conveying microwave radiation to a surgical antenna at a high power level and a separate measurement channel for conveying microwave radiation to a surgical antenna at a low power level, wherein the measurement channel bypasses noisy components on the ablation channel. A surgical antenna having an impedance transformer for matching an e.g. coaxial feed structure which terminates in one or more radiating elements with tissue to be treated is also disclosed.Linvention concerne un procédé et un appareil détalonnage dantennes chirurgicales qui sont conçues pour délivrer un rayonnement micro-onde (par ex., présentant une fréquence de traitement comprise entre 500 MHz et 100 GHz) dans un tissu biologique. Une zone démission de lantenne est exposée à une pluralité de normes détalonnage présentant chacune une impédance complexe différente à la fréquence de traitement. Dans un mode de réalisation, les normes détalonnage sont créées dans une cavité de guide dondes terminée par un court-circuit, de longueur variable. Dans un autre mode de réalisation
