EFFECT OF SURFACE-COMPOSITION ON THE RADIATION-PATTERN FROM A PHOTONIC-CRYSTAL PLANAR-DIPOLE ANTENNA

Radiation patterns are measured from a planar-dipole antenna mounted on two {111}-oriented surfaces of a face-centered-cubic photonic-crystal substrate. The photonic crystal consists of nonspherical air atoms in a dielectric matrix having a permittivity of 12. The measurements are made at a frequency of 14.5 GHz in the middle of the photonic band gap. We find that the antenna pattern depends strongly on the fraction of the crystal surface occupied by dielectric material. A surface having a low dielectric fraction yields much narrower patterns in polar angle than one having a high fraction. We attribute this difference to the strong excitation of a TE mode by the dipole on the surface having a high dielectric fraction.