Fourth‐order nonlinear distortion to the power spectrum of RF amplifiers

Abstract

Abstract Even‐order intermodulation distortions are often considered easy to filter in narrowband radio frequency (RF) wireless systems because they are usually located far away from the desired passband and adjacent bands. However, even‐order intermodulation distortions have recently attracted more interest with the increasing popularity of wideband RF applications. The authors' previous work was devoted to establishing the power spectrum model of second‐order intermodulation distortion. Motivated by the latest efforts on RF power amplifier linearization with second‐order and fourth‐order intermodulation, our focus now is to establish a power spectrum model of fourth‐order intermodulation distortion which can be used to discuss the fourth‐order impacts on the passband and adjacent bands. Here, together with the authors' previous work on the odd‐order intermodulation, a relatively comprehensive power spectrum model is presented here, including second‐, third‐, fourth‐, and fifth‐order intermodulation, which offers a broader view for spectrum planners and RF designers. With qualitative and quantitative reasoning, we further explain that higher‐order (i.e., n>5) IM distortions of a weakly nonlinear amplifier are indeed negligible. The experiment measurement at the end of this paper validates the spectrum model.