Optimizing the Q value in three-dimensional metallic photonic band gap crystals

A metallic photonic band gap crystal with different defect structures is fabricated. The structure is designed and built to operate in the 8–26 GHz frequency range. Defects with sharp peaks in the transmission are created by removing portions of the metallic rods in a single defect layer. A high quality factor (Q) for the defect state is obtained by larger filling ratios and spatial separations between the unit cells. An optimized value of Q⩾300 is found for three unit cell metallic photonic band gap structure. The experimental observations agree very well with theoretical calculations using the transfer matrix method.