Input-Reflectionless Negative-Group-Delay Bandstop-Filter Networks Based on Lossy Complementary Duplexers

A class of negative-group-delay (NGD) bandstop-filter (BSF) circuits with input-reflectionless behavior are presented. By absorbing the non-transmitted RF-input-signal energy in their circuit volume, they cancel the undesired RF-power reflections that can adversely affect preceding active stages. They are based on a lossy complementary-duplexer approach, in which the lossy BSF channel is used as NGD circuit and its lossy resistively-terminated bandpass-filter-(BPF)-channel counterpart dissipates the non-transmitted RF signal power. The theoretical analysis of the basic input-reflectionless first-order NGD stage and illustrative design examples are presented. In-series-cascaded multi-stage NGD realizations to increase the NGD flatness are also explored. Furthermore, for experimental-validation purposes, a two-stage microstrip prototype with center-frequency reconfiguration and controllable NGD pattern within the spectral range 1.55-2.1 GHz is manufactured and characterized.