Extending the Upper-Passband Range in Planar Bandstop-Type Transversal Filtering Sections

A class of generalized two-path stepped-impedance-line signal-interference transversal filtering section (TFS) for bandstop applications is reported. By avoiding the frequency-periodic behavior intrinsic to its classic uniform-impedance-line bandstop TFS counterpart through the use of stepped-impedance lines in its electrical paths, a broadened upper-passband range is attained in this novel approach of bandstop TFS. This is achieved while maintaining the same filtering performance for the main stopband as in its associated conventional bandstop TFS, which suffers from the generation of odd-numbered-harmonic spurious rejected bands as design drawback. An optimization-based design example of an extended-upper-passband stepped-impedance-line bandstop TFS is shown for validation purposes, from which a 1-GHz microstrip prototype is experimentally developed and tested.