  We present a flexible method that can calculate Bloch modes, complex band
structures, and impedances of two-dimensional photonic crystals from scattering
data produced by widely available numerical tools. The method generalizes
previous work which relied on specialized multipole and FEM techniques
underpinning transfer matrix methods. We describe the numerical technique for
mode extraction, and apply it to calculate a complex band structure and to
design two photonic crystal antireflection coatings. We do this for frequencies
at which other methods fail, but which nevertheless are of significant
practical interest.
