Reflectionless Filter Topologies

Abstract

Reflectionless filters are a class of lumped‐element circuits and transmission‐line topologies which, insofar as the elements are ideal, have identically zero reflection coefficients at all ports and at all frequencies from DC to infinity. Developed in the mid 2010's, they differ from previous first‐ and second‐order constant‐resistance implementations in that complex filter responses of arbitrarily high order may be realized without any excess flat loss in the pass‐band. Such filters find considerable use in systems applications where adjoining components may be sensitive to reactive terminations out‐of‐band. While most components are characterized in the lab with broadband, matched terminations (e.g., ) on all of their ports, this is not always representative of the embedding impedances they will see in real systems. Reflectionless filters provide a means of reproducing the laboratory impedance environment for sensitive components while filtering the frequency spectrum and limiting out‐of‐band interactions between functional blocks. Whereas conventional filters can only block unwanted signals from passing, reflectionless filters remove them from the system by dissipation.