Multi-Level Outphasing with OTA Combining: 2D Beamforming and Measurements with Large Arrays

In this paper, we develop and demonstrate the feasibility of a multi-level outphasing array transmitter with over-the-air (OTA) combining at 28 GHz for future 6G mmWave systems. Furthermore, first steps towards multi-user outphasing operation are taken through optimizing the beamforming weights, by minimizing interference towards a secondary user angle, while keeping the main-lobe towards the primary user. The measurement setup includes adaptive beamforming using off-the-shelf beamformers, a custom designed 4×8 antenna array, mounted on a rotator, and a fixed OTA observation antenna. The results show that the relevant OTA signal quality measures, error vector magnitude (EVM) and total radiated power adjacent channel leakage ratio (TRP-ACLR), satisfy the 3GPP requirements for mmWave systems, and that outphasing with over-the-air combining is a valid option for phased-arrays systems. Furthermore, the results show that the system may support multi-user operation through proper beamformer design, minimizing interference towards the directions of the other served users.