Over-the-Air Linearization of Phased Array Transmitters Under Load Modulation: One-Stage LUT-Aided Approach

This work presents a one-step or one-stage over-the-air (OTA) digital predistortion (DPD) method for millimeter-wave phased-array transmitters that inherently accounts for mutual coupling and power amplifier (PA) load modulation. The proposed approach employs a lookup-table (LUT)-based user-signal reconstruction scheme that directly estimates the far-field main-beam signal from OTA observations, enabling DPD learning under true load-modulated conditions without S-parameter knowledge or PA forward modeling. The LUT is fully identified from OTA and far-field measurements and captures the nonlinear, coupling-dependent, and beam-dependent behavior of the PA array. RF measurement-based experiments demonstrate effective user-end linearization across a wide range of steering angles, with beyond -45 dB adjacent channel power ratios despite severe load-modulation levels. Overall, the method removes the need for directional couplers, lowers hardware complexity, and offers a scalable linearization solution for large phased arrays in future networks.