مرکز منطقه ای اطلاع رساني علوم و فناوري

Abstract :

A linear three-terminal device $Z$ 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 $Z_{11}, Z_{12}, Z_{21},$ and $Z_22$ . A search for properties of $Z$ which are invariant under the transformation N leads to the quantity $U = frac{|Z_{21}-Z_{12}|^2}{4(R_{11}R_{22}-R_{12}R_{21})}$ where $R_{jk}$ is the real part of $Z_{jk}$ . Quantity $U$ is independent of the choice of $N$ and is (consequently) invariant under permutations of the three terminals and also under replacement of the open-circuit impedances by short-circuit admittances. If $U$ exceeds unity at a specified frequency, then $N$ can always be chosen to make $R_{11}$ and $R_{22}$ positive and $Z_{12}$ zero at that frequency. Quantity $U$ 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.