System and method for treating tissue using an expandable antenna

An electrosurgical system for treating tissue, the system comprising:

• an electrosurgical generator;
• and
• a microwave ablation device configured to operably couple to the electrosurgical generator, the microwave ablation device including:
• a radiating portion defining a longitudinal axis and configured to deliver energy from the electrosurgical generator to tissue, the radiating portion having an outer conductor and an inner conductor disposed within the outer conductor and separated by a dielectric material disposed on the inner conductor;
• wherein one of the inner conductor or the outer conductor is movable relative to the other to cause at least a portion of the outer conductor to expand radially relative to the longitudinal axis.