A microwave system calibration apparatus including an antenna portion configured to deliver microwave energy to tissue, a transmission line portion configured to receive a microwave energy signal from a microwave source and to selectively deliver the microwave energy signal to the antenna portion and a switching mechanism connected between the antenna portion and the transmission line portion. The transmission line includes an inner conductor having a length, an outer conductor concentrically surrounding the inner conductor along the length and a dielectric material separating the inner and outer conductors. The inner conductor or the outer conductor of the transmission line portion is electrically connected to the antenna. The switching mechanism is configured to electrically disconnect the transmission line portion from the antenna portion in a first condition and further configured to connect the inner conductor to the outer conductor in a second condition.
