New simple proofs of the two-port stability criterium in terms of the single stability parameter mu(1) (mu(2))

The classical scattering-parameter stability criterium for a linear two-por t makes use of two conditions involving the Rollet parameter K plus one add itional parameter. A new stability criterium was developed by Edwards and S inksky on the basis of a condition on a single parameter, i.e., mu (1) or m u (2). This paper presents a new simpler, and more straightforward set of p roofs of the single-parameter stability criterium for a linear two-port, Th e first proof is algebraic and shows the equivalence of the conditions K > 1, b(i) > 1 with the condition mu (1) > 1 (i = 1, 2), The second proof, whi ch is geometrical, relies only on the classical stability circle concepts i n an improved way with respect to the treatment by Edwards and Sinksky.