Design and Extensive NPR Characterization of a Highly Linear SatCom GaN MMIC Doherty PA

Abstract

This article presents the design strategy and extensive noise-to-power ratio (NPR)-focused characterization of a state-of-the-art Doherty power amplifier (DPA) for satellite applications in the Ka-band downlink (17.3–20.3 GHz), fabricated using a commercial 100-nm GaN-Si high electron mobility transistor technology. The design aims for high gain and good intrinsic linearity over a 3-GHz bandwidth by adopting an amplifying chain with limited phase distortion and a Doherty combiner designed to compensate for this residual phase distortion and by optimizing the baseband impedance. Single-tone experimental characterization of the fabricated chip shows that it maintains an output power of 36 dBm with a power-added efficiency (PAE) of 30% across the entire band. The linearity characterization explores the effects of signal statistics and nonlinear dynamics on NPR and discusses critical aspects concerning the comparability of different measurements. Modulations with instantaneous bandwidths up to a record of 2.9 GHz are explored, under which the Doherty PA is able to maintain PAE of at least 25% at 15-dB NPR. This demonstrates the amplifier’s excellent linearity, achieving state-of-the-art performance among integrated power amplifiers (PAs) for satellite communications.