  This paper introduces a time-domain combined field integral equation for
electromagnetic scattering by a perfect electric conductor. The new equation is
obtained by leveraging the quasi-Helmholtz projectors, which separate both the
unknown and the source fields into solenoidal and irrotational components.
These two components are then appropriately rescaled to cure the solution from
a loss of accuracy occurring when the time step is large. Yukawa-type integral
operators of a purely imaginary wave number are also used as a Calderon
preconditioner to eliminate the ill-conditioning of matrix systems. The
stabilized time-domain electric and magnetic field integral equations are
linearly combined in a Calderon-like fashion, then temporally discretized using
an appropriate pair of trial functions, resulting in a marching-on-in-time
linear system. The novel formulation is immune to spurious resonances, dense
discretization breakdown, large-time step breakdown and dc instabilities
stemming from non-trivial kernels. Numerical results for both simply-connected
and multiply-connected scatterers corroborate the theoretical analysis.
