Photonic band effects in a two-dimensional array of dielectric spheres in the millimeter-wave region

The transmission and phase-shift spectra for millimeter electromagnetic wav es are obtained for a two-dimensional (2D) square lattice array made of Si3 N4 spheres of, diameter similar or equal to 3.2 mm. The results are compare d with the theoretical 2D photonic-band structures that take account Of the lifetime effect due to the radiative energy decay. It is found that the in cidence-angle dependence of he observed transmission spectra is in excellen t agreement with the calculated in-plane dispersion curves of the photonic bands and that the frequency dependence of the phase shift agrees well with the calculated lifetime-broadened density of states. The radiative lifetim es of the photonic bands are estimated to be about ten times longer than th ose of whispering gallery modes of an isolated sphere, though the magnitude s depend rather strongly on the wave vector and band index.