Scalable Coupling Emulation for Active Antenna Arrays Under Load Modulation

Abstract

This letter addresses measurement-based coupling emulation of power amplifier (PA) arrays with more than four elements, enabling scalable characterization of multiantenna transmitters (TXs). A refined estimation procedure for driver gain is proposed, improving the convergence stability and accuracy over prior methods, while also addressing the estimation of the involved load reflection coefficients. Measurements with up to 16-PA arrays demonstrate reliable error convergence and accurate S-parameter recovery, while we also confirm the anti-symmetric variation of the load reflection coefficient with beamforming angle. The results show a reduced branch-to-branch injection-error variance compared to prior art methods, further supporting the scalability of the proposed estimator. Furthermore, combined far-field adjacent-channel power ratio (ACPR) and error vector magnitude (EVM) metrics for a phased-array TX exhibit the expected symmetry versus beam angle and reveal direction-dependent nonlinearity, validating realistic array-level radiated performance after spatial combining. Notably, this work also integrates a 5G-NR compliant waveform for the first time in a coupling-emulation framework, paving the way for efficient modeling and linearization of next-generation wireless TXs under load modulation.