Two-dimensional metallic photonic crystals with different lattice period an
d/or filling factor are combined to provide an ultrawide photonic bandgap s
tarting from zero frequency. It is shown that either sharp resonances or re
latively broad transmission windows with high transmission level can be cre
ated in this gap by inserting a small number of point defects in the crysta
ls. Results from experiments carried out between 27 and 50GHz are presented
.