Lossy multiband filters and ghost passbands

This paper is applicable to the implementation of lossy multiband prototype models and filters based on planar and other lower-Q resonators. This work is particularly relevant for multilayer microstrip and planar waveguide filters. We investigate the effect of losses on multiband filters and find that these pose additional challenges compared to single band filters. The multiband synthesis method used here is based on a reactance transform technique. It produces filter prototypes with an appended resonator structure. Ghost passbands with narrow bandwidths may be used under specific conditions to enhance the suppression between two passbands.