  Context: Faraday rotation measurements of extragalactic radio sources during
coronal occultation allow assessment of both the electron density distribution
and the three-dimensional magnetic field topology in the outer solar corona.
Aims: We simulate the three-dimensional structure of both the coronal magnetic
field and the electron density distribution in order to reproduce the excess
Faraday rotation measures (RMs) of the occulted radio sources observed during
solar activity minimum. In particular, we infer the tilt of the solar magnetic
axis with respect to the rotation axis. Methods: We compare the output of the
model with Very Large Array (VLA) radio polarimetric measurements of a sample
of extragalactic sources observed in May 1997. Information on the magnetic
field geometry can be retrieved by fine-tuning the set of model free parameters
that best describe the observations. Results: We find that predicted and
observed Faraday rotation measures are in excellent agreement, thus supporting
the model. Our best-fitting model yields a tilt angle $\theta_{RB}=3.3^{\circ}$
of the solar magnetic axis with respect to the solar rotation axis around
Carrington Rotation 1923. This result is consistent with analogous but
independent estimates computed from the expansion coefficients of the
photospheric field observed at the Wilcox Solar Observatory (WSO).
