High reliability impedance tuners used in high power measurements suffer fast heating and consequently thermal expansion of the central conductor, which has a very small mass and is thermally isolated from the tuner housing. This leads to false measurements or catastrophic tuner failure (short) of either the DUT or the tuner. A method is introduced for allowing the center conductor to expand linearly without deforming and risking loss of accuracy first and catastrophic failure later. Practical tests have shown significant thermal behavior improvement.

High reliability impedance tuners used in high power measurements suffer fast heating and consequently thermal expansion of the central conductor, which has a very small mass and is thermally isolated from the tuner housing. This leads to false measurements or catastrophic tuner failure (short) of either the DUT or the tuner. A method is introduced for allowing the center conductor to expand linearly without deforming and risking loss of accuracy first and catastrophic failure later. Practical tests have shown significant thermal behavior improvement.