Abstract: Photonic Band Gap (PBG) structures are utilized in microwave components as filters to suppress unwanted signals because they have the ability to produce a bandstop effect at certain frequency range depending on the structural dimensions. The unique property of PBG structures is due to the periodic change of the dielectric permittivity so interferences are created with the traveling electromagnetic waves. Such periodic arrangement could exist either inside of the dielectric substrate or in the ground plane of a microstrip transmission line structure. This invention provides tunable or switchable planar PBG structures, which contains lattice pattern of periodic perforations inside of the ground plane. The tuning or switching of the bandstop characteristics is achieved by depositing a conducting island surrounded by a layer of controllable thin film with variable conductivities.