An impedance tuner may include a shunt stub located at a fixed location along the transmission media, and a phase shifter to control the reflection phase. Another embodiment includes an adjustable length shunt stub connected on the transmission media, a variable phase shifter connected between the DUT port and the adjustable length shunt stub, a probe arranged for movement in a direction transverse to the direction of signal propagation. Another embodiment includes a reflection magnitude control system mounted in a fixed position relative to a direction of signal propagation along the transmission media, and a phase shifter to control a reflection phase.