An on-shell method that combines plane-wave and finite-difference techniques for the calculation of dispersion curves and transmission spectra for electromagnetic fields in photonic band-gap crystals is presented. The overall problem is decomposed into a field problem of determining the plane-wave scattering from an individual crystalline layer and a conventional one-dimensional network problem of combining this scattering to obtain the band structure of the entire crystal or the scattering properties of a crystal with a finite thickness. Results of the calculation are compared with experimental data measured using ultrawideband microwave pulses for a two-dimensional photonic band-gap crystal. © 1995 American Institute of Physics.