  A design methodology and synthesis equations are described for lumped-element
filter prototypes having low-pass, high-pass, band-pass, or band-stop
characteristics with theoretically perfect input- and output-match at all
frequencies. Such filters are a useful building block in a wide variety of
systems in which the highly reactive out-of-band termination presented by a
conventional filter is undesirable. The filter topology is first derived from
basic principles. Then the relative merits of several implementations and
tunings are compared via simulation. Finally, measured data on low-pass and
band-pass filter examples are presented which illustrate the practical
advantages as well as showing excellent agreement between measurement and
theory.
