  The conditioning and accuracy of various inverse surface-source formulations
are investigated. First, the normal systems of equations are discussed. Second,
different implementations of the zero-field condition are analyzed regarding
their effect on solution accuracy, conditioning, and source ambiguity. The
weighting of the Love-current side constraint is investigated in order to
provide an accurate problem-independent methodology.
  The transformation results for simulated and measured near-field data show a
comparable behavior regarding accuracy and conditioning for most of the
formulations. Advantages of the Love-current solutions are found only in
diagnostic capabilities. Regardless of this, the Love side constraint is a
computationally costly way to influence the iterative solver threshold, which
is more conveniently controlled with the appropriate type of normal equation.
  The solution behavior of the inverse surface-source formulations is mostly
influenced by the choice of the reconstruction surface. A spherical Huygens
surface leads to the best conditioning, whereas the most accurate solutions are
found with a tight, possibly convex hull around the antenna under test.
