The unilateral figure of merit is used to check how the gain of a microwave amplifier will be affected if the unilateral assumption is used. This means that the effect of s12 will be considered zero or negligible. In order to calculate U, the s parameters of the amplifier are required.. The expression for U is given by:

U = {Abs(s11).Abs(s21).Abs(s11).Abs(s22)/[(1 - Abs(s11).Abs(s11))(1-Abs(s22).Abs(s22)).

Once U is determined then the following identity is used to determine the loss or error in gain: 1/(1+U)^2<GT/GTU<1/(1-U)^2. These factors are converted to dB to determine the dB error in gain. Here GT is the transducer power gain of the amplifier. GTU is the unilateral transducer gain. GT is defined as the ratio of the power delivered to the load to the power available from the genrator or source when both ports are conjugate matched.