An analysis of the suitability of using CW-theory when designing Doherty PAs for wideband or concurrent multi-band operation

In this paper it is analyzed whether the commonly used continuous-wave (CW) based theory can properly describe and predict the behavior of the Doherty power amplifier (DPA) under wideband or concurrent multi-band operation. The analysis shows that the CW-theory in fact fails to do so and that the functionality of the DPA is strongly dependent on how intermodulation frequencies are terminated. In particular, it is shown that the network connecting the main and auxiliary amplifiers needs to function as an impedance inverter at specific odd order intermodulation frequencies, such as the cross-carrier intermodulation in the multi-band case. The theoretical analysis is verified by simulations, demonstrating how the functionality of a concurrent dual-band DPA is distorted despite CW-theory predicting ideal performance in each band. The findings in this paper are an important contribution to the understanding of how to further improve the performance of wideband or concurrent multi-band DPAs.