Sub-THz Power Amplifiers: Measurements, Behavioral Modeling, and Predistortion Algorithms

With global international mobile telecommunications (IMTs) traffic expected to grow 10–100 times from ITU-R 2015(as reported by ITU-R in 2015), the terahertz (THz) spectrum offers a promising solution to satisfy such forecasts. However, occupying the THz spectrum comes with its own challenges, an important one being impairments caused by broadband radio frequency components in THz transceivers. Nonlinearities in power amplifiers (PAs) complicate meeting link budget requirements, with amplitude and phase distortions degrading the system's performance, especially when adopting waveforms with high peak-to-average power ratios, such as orthogonal frequency division multiplexing. In this article, we present characterization results of a 300 GHz PA using small-signal and large-signal continuous-wave measurements. Models capturing amplitude-to-amplitude modulation and amplitude-to-phase modulation behavior across 270–330 GHz are developed and verified with wideband measurements, confirming the compression behavior, while nonetheless showing inaccuracies for low input powers due to unaccounted frequency dependencies. Based on the derived models, a predistortion algorithm is designed and analyzed, revealing significant error performance degradation when switching between single- and multicarrier waveforms. We finally show that an appropriate selection of predistorter parameters can significantly improve the performance.