Experimental characterization and control of stability margins in microwave amplifiers.

Abstract

Robust design of microwave amplifiers implies the lack of undesired autonomous frequency components for operating conditions that can be very far from nominal. However, microwave amplifiers are prone to exhibit spurious oscillations of different nature and at different frequencies due to the large band gain of microwave transistors and their intrinsic non-linear behavior. To analyze the robustness of a design with respect to spurious oscillations, local stability analyses at simulation level could be performed. However, reliable models and fine circuit descriptions are not always availabe which often makes simulation impractical to analyze the robustness of an aplifier in terms of stability margin.In this context, the goal of this thesis is to develop an experimental technique to characterize critical resonances departing from accurate measurement data that are coherent with the amplifier normal functioning. The method is based on applying pole-zero identification technique to analyze the stability of microwave circuits in samll.signal and large-signal periodic regimes. A systematic methodology ofr microwave circuit stabilization has also been presented, since this can be very useful for the experimental contro of the stability margins.The proposed experimental technique for microwave circuit stability analysis has been applied to several prototypes in hybrid microstrip technology to demostrate its reliability: an L-band FET amplifier in DC regime, a dual mode WiFi-WIMAX amplifier in large-signal regime, and a GaN power amplifier in both regimes.