This paper presents an innovative impedance tuner architecture aiming at on-wafer characterization. The proposed impedance tuner is composed of an integrated attenuator, which can be tuned in an analog manner, and a transmission line. Thanks to the use of an external short-circuited probe, the effective length of the transmission line can be modified, leading to a phase shift of the reflection coefficient while the attenuator controls its magnitude. Measurement-based results are presented to prove the precision obtained using the external short-circuited probe, while simulation-based results show the performance of the overall system. The system allows complete coverage of the 140-220 GHz band with 2. 5-4.2dB maximum reflection coefficients and minimum reflection coefficients greater than 20 dB, which can be continuously tuned. On the other hand, thanks to the short-circuited probe, virtually, continuous tuning of the phase is also achievable.