A unilateral device is one whose scattering parameter . This implies that the transistor network has no internal feedback. This requirement is very difficult to achieve at microwave frequency. Theoretically, an external circuit can be used to add feedback such that the effect of internal feedback can be eliminated. This method is called neutralization. However, the result of this technique is satisfactory only when the amplifier is operating at VHF frequency with a narrow bandwidth.
The unilateral transducer power gain is
is a parameter of transistors usually given in the manufacturer's data sheet. , are related to the degree of matching between the transistor and the terminations. Maximum unilateral transducer power gain can be achieved if input and output matching networks can provide maximum power transfer between the transistor and terminations, i.e. they are conjugately matched, and .
Example In a 50 system, a transistor has the following S-parameter at 1.3 GHz.