Skip to Main Content
A linear three-terminal device is imbedded in a lossless passive network N and the properties of the complete system, as measured at two specified terminal pairs, are described by the open-circuit impedances and . A search for properties of which are invariant under the transformation N leads to the quantity where is the real part of . Quantity is independent of the choice of and is (consequently) invariant under permutations of the three terminals and also under replacement of the open-circuit impedances by short-circuit admittances. If exceeds unity at a specified frequency, then can always be chosen to make and positive and zero at that frequency. Quantity is identifiable as the available power gain of the resulting unilateral structure. An arbitrary coupling network may be decomposed into a portion which accomplishes unilateralization and a remaining complementary portion which provides feedback around the unilateralized structure. Such decomposition brings some of the notions of elementary feedback theory to bear upon nonunilateral circuit analysis and offers a viewpoint from which signal flow and power flow are simply related.