Third Order Intermjdulation Distorsion in Microwave Variable Gain Amplifier

This paper presents a study of the third-order intermodulation (IMD) products of dual-gate MESFET amplifier as a function of structure parameters and bias voltage conditions. We give, Part I, some experimental results at 12GHz, in comparison with those obtained by using a single-gate FET. We show the great influence of the second gate load termination on the microwave performances. On the other hand, we propose, Part II, a new and simple equivalent electric circuit which is able to describe the nonlinear behaviour of the dual-gate in microwave frequency range. The validity of this approach is proved by comparison with experimental results. Theoretical predictions show-the relative importance of each nonlinear element on the behaviour.