  We present the results of a multi-frequency analysis of the structural
variability in the parsec-scale jet of the blazar S5 1803+784. More than 90
epochs of observations at 6 frequencies from 1.6 GHz up to 22 GHz have been
combined and analyzed. We discuss an alternative jet model for the source. In
contrast to previously discussed motion scenarios for S5 1803+784, we find that
the jet structure within 12 mas of the core can most easily be described by
seven "oscillating" jet features. We find that the parameters of jet features,
such as core separation, position angle and flux density, change in a periodic
way with a timescale of about 4 years. We also find evidence for a correlation
between these parameters and the total flux density variability. We suggest a
scenario incorporating a periodic form of motion (e.g. rotation, precession),
with a non-negligible geometrical contribution to explain the observational
results.
