  This paper expands on the previously described reflectionless filters - that
is, filters having, in principle, identically-zero reflection coefficient at
all frequencies - by introducing a wide variety of new reflectionless
structures that were not part of the original publication. In addition to
extending the lumped-element derivation to include transmission line filters,
this is achieved by the introduction of a novel method wherein the left- and
right-hand side stop-band terminations are coupled to each other using a
two-port sub-network. Specific examples of the sub-network are given which
increase the stop-band attenuation per filter cell and steepen the cutoff
response without disrupting the reflectionless property or increasing the
insertion-loss in the pass-band. It is noteworthy that a common feature of all
the structures derived by these methods is that most, if not all, of the
reactive elements are of equal normalized value. This greatly simplifies the
tuning requirements, and has facilitated their implementation as monolithic
microwave integrated circuits (MMICs). A number of examples of MMIC
reflectionless filters constructed in this way are presented and their results
compared to the theory.
