A Classification of Lossless Three-Ports

Lossless three-port networks can be classified at a single frequency according to their off-diagonal scattering matrix entries. We define four classes: one of these is trivial, consisting of networks that are in effect artificial combinations of a two-port and a one-port, or of three one-ports; the other three network classifications are based on whether is equal to (class E), greater than (class F), or less than (class B) . A particular scatteringvariable normalization can be chosen for networks of classes F and B to make the scattering matrix that of a circulator. This is not possible for a network of class E even if it is a nonreciprocal network. This classification is applied to the design of narrow-band circulators and to some theoretical properties of negative-resistance amplifiers.