Phase Characterization of Intermodulation Products Including Electrothermal Memory Effects

This communication presents a model for an equivalent hypothetical load impedance which improves the correspondence between simulations and experimental measurements in microwave HEMT amplifiers with memory effects that are not explained using purely electrical models and may thus be attributed to thermal effects. The proposed load impedance has been obtained from measurements of magnitude and phase for third-order intermodulation (IM) products accomplished by a simple but effective experimental method based on a two-tone test. Closed-form theoretical expressions for the IM products are derived employing a Simplified Newton (SN) approach, concluding that IM products's variation with frequency separations is related to the load impedance seen by the drain node of the amplifier. An equivalent load impedance and its circuit model are presented, and a good agreement between measurements and simulations is achieved when they are inserted