The sliding load (or sliding termination) was developed because it is not possible to make a broad band termination with calibration standard return loss requirements across a wide frequency range. In essence it is used to generate a series of equal mismatches whose mechanical position and resultant phase shifts are used to subtend a circle near the center of the Smith chart. From that circle the exact center of the Smith chart can be determined from the perpendicular bi - sector of the chords (six mechanical locations). This calculation is transparent to the user.
