Design of High Power, Wideband Microwave Frequency Class F Power Amplifiers Using AlGaN/GaN HEMTs

摘要

This thesis presents the theory, design, and implementation of two high power (>10 W) RF power amplifiers operating in the S-band (2 to 4 GHz) and employing the Class F mode of efficiency enhancement. The amplifiers are based around gallium nitride (GaN) high electron mobility transistors (HEMTs) which provide the high power capability. A complex wideband design using synthesized low-pass transforming filters as large-bandwidth matching networks is presented, followed by a more elegant narrowband design employing simple stub matching networks for impedance matching and harmonic control.;Also presented in this thesis is a detailed study into the computer modeling of the GaN HEMT devices in order to accurately predict their behavior when integrated into a system. A complete small-signal circuit model is developed which is capable of predicting the scattering parameters of the devices with a high degree of accuracy to the measured behavior. Large-signal device models of increasing complexity are studied to investigate fundamental behaviors of field-effect transistors for which HEMTs are a subset. Finally, the manufacturer design kit's computer model is investigated and verified for accuracy with the measured results.;An overview of power amplifier design and classes of operation is given, and specifically Class F theory and implementation are analyzed. The efficiency enhancement by waveform shaping is studied, as well as the mechanism of waveform shaping via harmonic manipulation.;Once fabricated and tested, the wideband design is shown to achieve at least 38.8 dBm output power between 2.2 to 3.3 GHz centered around 2.75 GHz, giving a fractional bandwidth of 40%. Over that range, the PA is able to sustain PAE > 40%, with a peak efficiency of 61%. The narrowband design achieves an output power at its center frequency of 3 GHz of 41.48 dBm, or ∼14 W, with the PAE achieving a maximum of approximately 66%.