An electrosurgical ablation system, comprising: an energy source adapted to supply energy to an energy delivery device, device; an energy delivery device including a handle assembly coupled to a pair of antenna probes (15a, 15b) extending from a distal end thereof to the energy source which probes being configured for insertion into tissue for application of energy to the tissue; a power splitting device operatively associated with the handle assembly and having an input adapted to connect to the energy source and a pair of output channels (151a, 151b) operably coupled to the respective pair of antenna probes (15a, 15b); and a phase shifter operatively associated with the handle assembly and operably coupled to the pair of output channels (151a, 151b), the phase shifter configured to selectively shift a phase relationship between the pair of output channels (151a, 151b); further comprising: a switch assembly disposed on the handle assembly, operably coupled to the phase shifter, and configured to be operated by a user to selectively shift a phase of one of the channels (151a, 151b) relative to the other of the channels (151a, 151b) in order to modify the ablation pattern or geometry in the tissue, and further comprising at least one rectifier disposed in operative communication with the energy source to monitor reflected power detected on the pair of output channels (151a, 151b), wherein the energy source controls the energy supplied to the energy delivery device based on the detected reflected power. an energy source adapted to supply energy to an energy delivery device, device; an energy delivery device including a handle assembly coupled to a pair of antenna probes (15a, 15b) extending from a distal end thereof to the energy source which probes being configured for insertion into tissue for application of energy to the tissue; a power splitting device operatively associated with the handle assembly and having an input adapted to connect to the energy source and a pair of output channels (151a, 151b) operably coupled to the respective pair of antenna probes (15a, 15b); and a phase shifter operatively associated with the handle assembly and operably coupled to the pair of output channels (151a, 151b), the phase shifter configured to selectively shift a phase relationship between the pair of output channels (151a, 151b); further comprising: a switch assembly disposed on the handle assembly, operably coupled to the phase shifter, and configured to be operated by a user to selectively shift a phase of one of the channels (151a, 151b) relative to the other of the channels (151a, 151b) in order to modify the ablation pattern or geometry in the tissue, and further comprising at least one rectifier disposed in operative communication with the energy source to monitor reflected power detected on the pair of output channels (151a, 151b), wherein the energy source controls the energy supplied to the energy delivery device based on the detected reflected power. a switch assembly disposed on the handle assembly, operably coupled to the phase shifter, and configured to be operated by a user to selectively shift a phase of one of the channels (151a, 151b) relative to the other of the channels (151a, 151b) in order to modify the ablation pattern or geometry in the tissue, and further comprising at least one rectifier disposed in operative communication with the energy source to monitor reflected power detected on the pair of output channels (151a, 151b), wherein the energy source controls the energy supplied to the energy delivery device based on the detected reflected power.