An electrosurgical ablation system includes an energy source adapted to supply energy to an energy delivery device. The energy delivery device includes a handle assembly configured to couple a pair of antennas extending from a distal end thereof to the energy source for application of energy to tissue. A power splitting device is operatively associated with the handle assembly and has an input adapted to connect to the energy source and a pair of output channels operably coupled to the respective pair of antennas. A phase shifter is operatively associated with the handle assembly and is operably coupled to the pair of output channels. The phase shifter is configured to selectively shift a phase relationship between the pair of output channels.
