Evaluation of Integrated GaN Diodes as Varactors for Tunable MMIC PAs from C- to K-Band

Variable capacitors (varactors) can act as powerful enablers for reconfigurable RF power amplifiers (PAs) in microwave monolithic integrated circuit (MMIC) technology. While their use for custom impedance tuning has been widely explored for sub-6 GHz frequencies, an experimental work is here performed to address the prospective use of RF power Schottky diodes as varactors for MMIC PAs operating from C to K band. Small- and large-signal measurements of diodes with different layouts are reported for two modern Gallium Nitride (GaN) High-Electron-Mobility Transistor (HEMT) process technologies. Capacitance and quality factor (Q-factor) of the varactors have been extracted, obtaining a measured tuning range in the frequency bands of interest of about 20% to 40% for the two technologies. The measured Q-factors, while decreasing with frequency, result to be up to 100 in the lower frequency bands, while being comparable to an equivalent integrated capacitor in the higher frequency bands.