Lossy Signal-Interference Filters and Applications

Lossy signal-interference transversal filtering sections (TFSs) composed of two in-parallel transmission-line segments with input-output matching lines-reflective-type part-and open-ended stubs with input resistors-lossy part-are presented. First, in their bandstop and dual-band bandpass versions, this class of lossy TFS is applied to the design of filtering networks with input-/two-port-quasi-reflectionless (QR) stopbands, such as wide-band bandstop filters (BSFs) and dual-band bandpass filters (BPFs). Furthermore, multistage circuit architectures made up of equal and dissimilar lossy TFSs for higher rejection and broader stopband realization, respectively, and higher selectivity dual-band BPF synthesis are described. Subsequently, in its bandpass counterpart, the conceived approach of lossy TFS is exploited to develop single-/multistage sharp-rejection bandpass filters (BPFs) with a flattened transmission band. The operational foundations of the engineered types of lossy TFSs for the suggested applications and theoretical design examples are provided. In addition, for experimental-validation purposes, four microstrip filter prototypes are manufactured and characterized, as follows: 2-GHz two-stage symmetrical QR BSFs with similar and frequency-contiguous bandstop TFSs for higher rejection and broader stopband shaping, respectively, a 1.4/2.6-GHz input-QR dual-band bandpass TFS, and a 2-GHz five-stage lossy BPF with enhanced passband amplitude flatness and spectrally enlarged attenuated bands.