Advances in Planar Filters

Abstract

Many microstrip filter configurations exist that exhibit advanced filtering characteristics, rely on new design techniques, or use original methods for filter miniaturization. For each filter type (lowpass, highpass, bandpass, and bandstop), we start with an overview of conventional planar filters, which are often used as a basis for the development of novel configurations, and then proceed to more advanced solutions. We classify the various advanced solutions found in the literature according to the underlying principle of design/operation: i) conventional filters using advanced geometries; ii) filters based on advanced theoretical concepts, such as the slow-wave effect, defected ground structures (DGSs), electromagnetic-bandgap (EBG) structures, or metamaterials (MTMs); and iii) filters based on advanced materials and technologies, such as superconducting, ferroelectric materials, and ferromagnetic materials.

Finally, we present some of the advanced solutions not covered by the classification given above. We provide an overview of surface-integrated waveguide (SIW) filters, followed by the discussion of various tunable and reconfigurable filter topologies. In the end, we present state-of-the art multiband filters.