Transmission-Line Absorptive Bandstop Filters with Wide Passband: Synthesis and Design

This article discusses a rigorous and straightforward method to synthesize and design a transmission-line-based reflectionless bandstop filter with high performance in terms of reflectionless range. Our design strategy targets to allow a reflectionless bandstop filter to feature three distinguished advantages that are incomparable to others. First, the presented filter structure is capable of producing an exceptional broadband impedance matching performance. Second, it can be designed to have an extended upper passband. Third, an N th-order filter has N coupling structures and each of them is used twice in design. Hence, it is required to design and tune only N coupling structures, whereas other design approaches use more than N distinct coupling structures. Although reflectionless filters having one of the aforementioned features have been reported, one exhibiting all the characteristics has never been reported to date. Fabricated filter examples fully validate the design theory.