Cascaded triplet and quadruplet filter design using cascade synthesis approach

A unified review of the design of cascaded triplet (CT) and cascaded quadruplet (CQ) filters is presented. A cascade synthesis approach with pole placement is used to synthesize the filter and then Norton transformations are used to put the circuit into a standard form for conversion into CT or CQ form. Sections of the filter containing one finite transmission zero (FTZ) can be converted into bridge tee elements forming the CT sections and sections of filters containing two FTZs are converted into CQ sections. An example is given showing development of equivalent alternative CT and CQ filter structures having all-inductive, all-capacitive or mixed cross-couplings, depending on the location of FTZs with respect to the passband.