A system for monitoring ablation size, comprising: a generator ; and a microwave antenna configured to transmit microwave energy from the generator to tissue to form an ablation zone (A), the microwave antenna including: an elongate shaft ; a plurality of proximal spaced-apart electrodes (52a-52h) disposed on the elongate shaft, each of the plurality of proximal spaced-apart electrodes having an impedance associated therewith and corresponding to a radius of the ablation zone; a distal electrode disposed on the elongate shaft distally of the plurality of proximal spaced-apart electrodes; a distal radiating section disposed within the elongate shaft; a first sensor in operative communication with at least one of the plurality of proximal spaced-apart electrodes and configured to provide real-time information pertaining to the impedance of said at least one of the plurality of proximal electrodes; and a second sensor in operative communication the distal electrode; wherein said system includes a controller, said controller is configured to monitor the impedance of the proximal electrodes, trigger a detection when a predetermined electrode impedance corresponding to a radius of the ablation zone is reached at the one or more electrodes, and adjust the amount of microwave energy from the generator to the microwave antenna. a generator ; and a microwave antenna configured to transmit microwave energy from the generator to tissue to form an ablation zone (A), the microwave antenna including: an elongate shaft ; a plurality of proximal spaced-apart electrodes (52a-52h) disposed on the elongate shaft, each of the plurality of proximal spaced-apart electrodes having an impedance associated therewith and corresponding to a radius of the ablation zone; a distal electrode disposed on the elongate shaft distally of the plurality of proximal spaced-apart electrodes; a distal radiating section disposed within the elongate shaft; a first sensor in operative communication with at least one of the plurality of proximal spaced-apart electrodes and configured to provide real-time information pertaining to the impedance of said at least one of the plurality of proximal electrodes; and a second sensor in operative communication the distal electrode; wherein said system includes a controller, said controller is configured to monitor the impedance of the proximal electrodes, trigger a detection when a predetermined electrode impedance corresponding to a radius of the ablation zone is reached at the one or more electrodes, and adjust the amount of microwave energy from the generator to the microwave antenna. an elongate shaft ; a plurality of proximal spaced-apart electrodes (52a-52h) disposed on the elongate shaft, each of the plurality of proximal spaced-apart electrodes having an impedance associated therewith and corresponding to a radius of the ablation zone; a distal electrode disposed on the elongate shaft distally of the plurality of proximal spaced-apart electrodes; a distal radiating section disposed within the elongate shaft; a first sensor in operative communication with at least one of the plurality of proximal spaced-apart electrodes and configured to provide real-time information pertaining to the impedance of said at least one of the plurality of proximal electrodes; and a second sensor in operative communication the distal electrode; wherein said system includes a controller, said controller is configured to monitor the impedance of the proximal electrodes, trigger a detection when a predetermined electrode impedance corresponding to a radius of the ablation zone is reached at the one or more electrodes, and adjust the amount of microwave energy from the generator to the microwave antenna. <EOS>