Symmetrical Quasi-Reflectionless BSFs

A type of symmetrical bandstop filters (BSFs) with quasi-reflectionless behavior is reported. The engineered BSF configuration is made up of a bandstop section with resistively terminated bandpass sections that are connected at its input/output accesses. These bandpass sections, which exhibit a nearly complementary transfer function with regard to the one of the bandstop section, dissipate the nontransmitted input-signal energy in their loads. The theoretical foundations of the first-order quasi-reflectionless BSF and synthesis examples are detailed. Its extrapolation to higher order and multiband BSFs is also shown. Furthermore, as experimental validation, a 2.35-GHz second-order microstrip prototype is developed and measured.