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 o n two {111}-oriented surfaces of a face-centered-cubic photonic-crysta l substrate. The photonic crystal consists of nonspherical air atoms i n a dielectric matrix having a permittivity of 12. The measurements ar e made at a frequency of 14.5 GHz in the middle of the photonic band g ap. We find that the antenna pattern depends strongly on the fraction of the crystal surface occupied by dielectric material. A surface havi ng a low dielectric fraction yields much narrower patterns in polar an gle than one having a high fraction. We attribute this difference to t he strong excitation of a TE mode by the dipole on the surface having a high dielectric fraction.