When designing microwave amplifiers, stability is an important factor to consider. Stability is usually measured with the K factor. In a unilateral network, S_12 = 0, and this makes the K factor infinite.
However, we also know that being unilateral means Gamma_in = S_11, and Gamma_out = S_22. What if the network is unilateral, but either S_11 or S_22 are larger than 1? Will the amplifier be unstable despite being unilateral? Is this situation possible at all?