HF Class F design guidelines

Harmonic tuning strategies are required to improve the efficiency and power output capabilities of power amplifiers. Such strategies consist in the use of suitable harmonic terminations both at the input and output active device ports. Class F strategy is a relatively simple approach, being based on output harmonic impedance selection only, while the input network is synthesised to fulfil conjugate matching conditions. Moreover, in high frequency applications, Class F amplifiers are designed controlling a limited number of harmonic impedances, usually up to the third one. In this contribution, the optimum high frequency Class F loading conditions are inferred, accounting for the effects of actual output device behaviour, and deriving useful charts for an effective design.