Abstract: A slotted line tuner, also capable of operation as a fully automated tuner, to provide arbitrary termination in high frequency waveguide media for use with frequencies of interest between 1 and 1000 GHz is disclosed. The electrical tuner is adapted to match the impedance of two waveguide media, or enhance or modify the characteristic impedance of a media relative to that of another one. The tuner utilizes a non-conductive rectangular bar vane made out of low loss, low dielectric constant material as the probe, with special gold plated areas, that is inserted through the slot of the line into a reduced height waveguide. The position and depth of this gradual probe penetration creates a continuously variable tuning of the complex impedance, ranging from a very low reflection state up to high reflection states together with an unlimited capability of phase change in its reflection.