Reference Phase Adjustment Technique with Cross-Polarization Cancellation for Enhanced Digital Predistortion in Mobile Dual-Polarized Arrays

In this paper, we present a novel methodology to improve the performance of digital predistortion (DPD) in mobile dual-polarized (DP) arrays by employing a reference phase (RP) adjustment technique. The load impedance (LIP) in such arrays depends on the RP of the vertical and horizontal polarizations (VP and HP) through active S-parameters (ASPs). Variations in LIP across RF channels can cause considerable deviations in the performance of power amplifiers (PAs). To address this challenge, we propose an RP adjustment strategy to control the LIP of V, HPs while preserving the intended beam steering angle. This method effectively minimizes LIP variation across RF chains, quantitatively analyzed through metrics like the radius and the distance from the origin of the LIP circle. Furthermore, by optimizing the LIP distribution with the cross-polarization (XP) cancellation, the proposed approach enhances the bandwidth of key performance metrics, including the error vector magnitude (EVM). Validation was conducted using an on-device measurement-based multi-path DPD simulator that incorporates beam pattern effects, PA load modulation, and the influence of ASPs on AM-AM and AM-PM characteristics. The experimental results confirm that the proposed technique is significantly effective in additional linearization performance improvement and XP interference (XPI) elimination in mobile DP arrays.