| 摘要 |
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. The controllable thin film layer could be photoconductive or temperature sensitive that allows change in its conductivity to occur by means of light illumination or temperature variation. Instead of depositing the controllable thin film with variable conductivity, freestanding thin film such as MEMS structures can also be utilized as the medium between the conducting islands and the ground plane. According to this invention, bandstop characteristics of the planar PBG structure are switched off when the controllable thin film is conductive or the freestanding thin film is in contact with the conducting islands and the ground plane. Meanwhile the bandstop characteristics are switched on when the controllable thin film is resistive or the freestanding thin film is not in contact with the conducting islands. At the end, switching uniplanar-compact PBG (UC-PBG) structures with photoconductive or temperature sensitive material, which is deposited inside of the gaps located in the ground plane, is also described.
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