An 
surgical instrument configured to concurrently dissect and coagulate tissue. In an embodiment, the 
surgical instrument comprises a 
handle and a shaft extending distally from the 
handle. The shaft includes an outer hypotube, a lumen coaxially-disposed within the hypotube and extending beyond a distal end thereof, a coaxial feedline coaxially-disposed within the lumen, and having an inner conductor and an outer conductor disposed coaxially about the inner conductor, and a 
coolant tube coaxially-disposed between the lumen and the coaxial feedline to form an inflow conduit and an outflow conduit. The instrument further includes a dissecting head 
assembly coupled to a distal end of the shaft. The dissecting head 
assembly includes a 
dielectric core having a substantially planar radiating surface and at least one non-radiating surface, a reflective 
coating disposed on the at least one non-radiating surface of the 
dielectric core, and a blade extending from the radiating surface.