Multi-band reflectionless filtering impedance transformers

A type of double-functionality filtering impedance transformer with multi-band and input-reflectionless capabilities is presented. It exploits a multi-passband filtering/impedance-transformation channel loaded with a complementary resistively-terminated multi-bandstop branch at its input node that dissipates the input-signal energy in the stopband regions of the former. This multi-band/multi-operational circuit approach could result in insertion-loss and circuit-size advantages when employed in complete RF front-end chains by relaxing the need for isolators or attenuators for inter-block matching. A coupling-matrix-based formulation for its design and theoretical examples of first-order dual-band and second-order triple-band realizations are provided. Furthermore, for experimental-demonstration purposes, a 1.9/2.1-GHz dual-band microstrip prototype is built and tested.