This paper presents a method of characterizing

-port networks. It is shown that a large class of lossless

-ports can be characterized by sequences of step-up vectors, i.e., vectors that form successive incident voltages to the networks and are orthonormal at the same time. As a result, lossless networks can be classified into several classes. The most interesting one is, perhaps, the stepup class, which is shown to behave jointly like a unitary operator and a complete step-up operator on separate subspaces of the space of

vectors.