Linearity and Efficiency Optimisation in Microwave Power Amplifier Design

In this contribution the minimisation of asymmetry between lower and upper side band intermodulation products will be discussed, starting from a Volterra analysis approach. Base-band and harmonic device terminations effects will be analysed, identifying novel conditions minimising IMD asymmetry and IM₃ power levels. Such conditions, not relying on base-band terminations, are the basis for IM₃ products minimisation via second harmonic load selection. The proposed criterion is then verified by harmonic load-pull measurements on a GaN HEMT under two-tone excitation. Measurements agree with the analysis, demonstrating a null IMD asymmetry and 6 dBc increase in C/I₃, without affecting output power (34 dBm @ 1dB compression) and power added efficiency performance (65% @ 1 dB compression).