  The CFIE used for solving scattering and radiation problems, although a
resonance-free formulation, suffers from an ill-conditioning that strongly
depends on the frequency and discretization density, both in the low- and
high-frequency regime, resulting in slow convergence rates for iterative
solvers. This work presents a new preconditioning scheme for the CFIE that
cures the low- and the high-frequency as well as the dense discretization
breakdown. The new preconditioner for the CFIE is based on a spherical
harmonics analysis and the proper regularization with Helmholtz-type operators.
Numerical results have been obtained to prove the effectiveness of this new
formulation in real scenarios.
