Experimental demonstration of the origin of photonic bandgap creation and associated defect modes in microwave planar circuits

This paper presents an experimental demonstration of the origin of the Photonic bandgap, using a planar dielectric substrate with a ID finite array of rectangular holes. A microstrip of uniform width placed above the array show's a periodic variation of impedance and refractive index. The measured transmission factor of the line exhibits a strong bandgap. When the width of the microstrip periodically changes in order to keep a constant impedance along the array, the bandgap in the measured transmission totally disappears. This proves that the creation of bandgap is due to the periodic variation of impedances instead of refractive indexes. The effect of the presence of defects is also illustrated. (C) 2004 Wiley Periodicals. Inc