During the past two and half decades, light propagation in complex structures has aroused considerable interest of many investigators. Early work of E. Yablonovitch and his co-workers and also by S. John stimulated tremendously the interest of many researchers, who suggested that diffraction by periodic structures might lead to a ‘photonic insulator’ in which propagation of light is forbidden in a certain range of frequencies. These photonic insulators are known as Photonic Band Gap (PBG) structures have a large number of applications in the field of photonics and integrated optics. Many applications in optics and microwaves are emerging by using the concept of PBG materials and structures. This new exciting structures and materials are currently under investigation in many laboratories worldwide.