University of Oulu

N. Tervo et al., "Combined Sidelobe Reduction and Omnidirectional Linearization of Phased Array by Using Tapered Power Amplifier Biasing and Digital Predistortion," in IEEE Transactions on Microwave Theory and Techniques, vol. 69, no. 9, pp. 4284-4299, Sept. 2021, doi: 10.1109/TMTT.2021.3092357

Combined sidelobe reduction and omnidirectional linearization of phased array by using tapered power amplifier biasing and digital predistortion

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Author: Tervo, Nuutti1; Khan, Bilal1; Aikio, Janne P.1;
Organizations: 1Faculty of Information Technology and Electrical Engineering (ITEE), University of Oulu, 90570 Oulu
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 4.4 MB)
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Language: English
Published: Institute of Electrical and Electronics Engineers, 2021
Publish Date: 2021-08-11


Power amplifier (PA) efficiency and linearity are among the key drivers to reduce energy consumption while enabling high data rates in the fifth-generation (5G) millimeter-wave phased array transmitters. Analog per-branch phase and amplitude control is used to steer the beam, suppress the sidelobes, and form zeros to the desired spatial directions. The amplitude control of individual PA inputs makes nonlinearity vary from antenna to antenna, which challenges the common digital predistortion (DPD) used to linearize the array. In this article, we implement an amplitude control for beamforming by tuning the PA gate bias. Varying the output powers via PA biasing makes the nonlinear characteristics observed at the individual PA outputs similar that helps the array DPD to linearize also individual PAs. The technique is validated by both simulations and measurements. As a measurement platform, we use a 28-GHz phased array transceiver equipped with 64 antenna elements and 16 radio frequency chains. The desired beam shape is synthesized by controlling the per-antenna over-the-air-power with PA gate bias. Then, the system is linearized by training DPD with a reference antenna. The DPD is demonstrated with 100-MHz-wide 5G new radio modulated waveform. The best example case showed -23.5-dB maximum sidelobe level (SLL) with 4.9% error vector magnitude and -40.8-dB total radiated adjacent channel power ratio with DPD. The proposed approach enables simultaneous reduction of beam pattern SLL, achieves good linearity in all directions, and maintains the PA efficiency.

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Series: IEEE transactions on microwave theory and techniques
ISSN: 0018-9480
ISSN-E: 1557-9670
ISSN-L: 0018-9480
Volume: 69
Issue: 9
Pages: 4284 - 4299
DOI: 10.1109/TMTT.2021.3092357
Type of Publication: A1 Journal article – refereed
Field of Science: 213 Electronic, automation and communications engineering, electronics
Funding: Keysight Technologies is acknowledged for laboratory equipment and 5GNR waveform support.
Copyright information: © The Authors 2021. This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see