RF Transversal Planar Filters With Dual-Lowpass/Bandpass Response

The optimization-based design of RF / microwave transversal signal-interference planar filters with composite-lowpass /bandpass transfer function is reported. As their basic constituent circuit stage, these filters exploit a transversal filtering section (TFS) composed of two stepped-impedance-transmission-line electrical paths. Thus, by means of constructive / destructive RF-signal-combination mechanisms taking place inside this class of bi-path TFS, sharp-rejection dual-lowpass/bandpass filtering responses with extended upper stopband can be realized. Higher-order designs with increased selectivity / out-of-band-attenuation levels can also be implemented by means of in-series-cascaded multi-TFS circuit arrangements. For experimental-demonstration purposes, two microstrip prototypes consisting of single- and two-TFS-based circuits are designed, fabricated, and characterized.