Microwave transmission through a periodic three-dimensional metal-wire network containing random scatterers

We have measured the transmission of microwave radiation through a nearly cubic metal-wire network with a lattice constant of 1 cm and a length of 8 cm on each side. We observe a sharp drop in the transmission below a cutoff frequency nc59.33 GHz when the structure is empty. The gap persists when the network is filled with randomly positioned Teflon spheres, but nc is reduced by the ratio of the phase velocities in air and in a random medium of Teflon spheres and air. When aluminum spheres are substituted for some of the Teflon spheres, transmission peaks appear within the gap. The average transmission in an ensemble of random configurations shows a broadening of the band edge associated with precursors to localized states in this small sample. This indicates that the statistics of the localization transition can be studied in larger samples. @S0163-1829~97!50614-X#