Characterization of Amplitude Modulation Bias Coupling for Solid-State High-Power Amplifiers

A method is developed and validated to empirically characterize unwanted spectral coupling from a non-ideal power supply bias to the radio frequency (RF) output for solid-state high-power amplifiers (HPAs) operating in saturation. Specifically, the method currently addresses how power supply ripple amplitude modulates the RF carrier output by characterizing an amplitude modulation bias coupling (AMBC) factor as a function of carrier frequency and power supply ripple frequency. With this coupling factor, one is able to use an analytical predictive model to understand the impact of various levels of bias ripple voltages on the HPA output spectrum. The approach examines the relative AM sideband levels in the frequency domain to empirically quantify the level of mixing that occurs since it is difficult to measure such small variations of interest in the time domain. A commercially available gallium nitride HPA and standard test equipment are used to demonstrate the characterization process.