Sub-optimal matching method for dual-band class-J power amplifier using real frequency technique

A passive network possessing an input impedance which is positive real in nature poses difficulties with regard to obtaining an optimal impedance for power amplifiers (PAs) with two uncorrelated frequencies. In this context, this study presents a sub-optimal dual-band matching method via real frequency technique. Theoretical analysis is presented for voltage waveform with four independent variables and boundary conditions are given for not lower than zero region. To increase the possibility of acquiring a matching network, a sub-optimal but broad design space is defined according to acceptable performance. It is more practical to match dual-band or broadband PAs because a single fundamental harmonic impedance point could be corresponding to a set of the second harmonics in the new design space, vice versa. Thus, the sub-optimal solution space is bounded from region-to-region between the required fundamental and second harmonic impedances. An enhanced cost function based on driving point function that could better describe harmonic impedance mismatching degree is also proposed for harmonics control. Finally, a dual-band PA is designed to demonstrate the general matching method. The peak efficiency is about 70% and saturated output power is 41 dBm in both bands.