Tapered photonic bandgap microstrip lowpass filters: design and realisation

The application of tapering techniques to two-dimensional photonic bandgap (2D-PBG) microstrip structures allows great improvement in the sidelobe level of the S/sub 11/ scattering parameter and, consequently, a very flat passband. Many tapering windows are proposed for 2D-PBG canonical (straight microstrip line) stopband filters. By suitably designing three rows of tapered periodic structures, which are characterised by different centre frequencies of the stopband, a novel photonic bandgap lowpass filter has been realised and characterised. Numerical simulations show satisfactory agreement with experiments.