University of Oulu

N. Tervo et al., "Digital Predistortion of Phased-Array Transmitter With Shared Feedback and Far-Field Calibration," in IEEE Transactions on Microwave Theory and Techniques, vol. 69, no. 1, pp. 1000-1015, Jan. 2021, doi: 10.1109/TMTT.2020.3038193

Digital predistortion of phased-array transmitter with shared feedback and far-field calibration

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Author: Tervo, Nuutti1; Khan, Bilal1; Kursu, Olli1;
Organizations: 1Department of Information Technology and Electrical Engineering (ITEE), University of Oulu, 90570 Oulu, Finland
Format: article
Version: accepted version
Access: open
Online Access: PDF Full Text (PDF, 10.3 MB)
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Language: English
Published: Institute of Electrical and Electronics Engineers, 2021
Publish Date: 2021-01-05


Digital predistortion (DPD) of a phased array requires that multiple transmit paths must be measured by a feedback (FB) receiver (Rx). In this article, we propose an FB concept for DPD in a time-division-duplex (TDD) phased arrays. We use a single FB line to collect the waveform samples from the parallel transmit paths to the FB Rx. The TDD switches are used to enable and disable individual transmit paths. The FB is calibrated by comparing the FB outputs from individual power amplifiers (PAs) to over-the-air (OTA) measurement reference performed with a frequency-modulated continuous-wave (FMCW) signal. The individual PA measurements are postequalized before the DPD training to model the far-field signal. Three alternative strategies are considered for training the DPD through the calibrated FB line and compared with the OTA DPD. The performance is verified by OTA measurements of a 28-GHz phased-array transmitter and with fifth-generation new radio waveform in terms of total radiated adjacent channel power ratio (TRACPR), cumulative absolute ACP (CACP), and main lobe error vector magnitude (EVM). The best EVM and ACPR performance is achieved by the strategy where the individual PA responses are treated independently. The methods were comparable to the OTA DPD performance, achieving all <-37-dB TRACPR, -29-dBm/MHz CACP, and ≤7 % EVM.

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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: 1
Pages: 1000 - 1015
DOI: 10.1109/TMTT.2020.3038193
Type of Publication: A1 Journal article – refereed
Field of Science: 213 Electronic, automation and communications engineering, electronics
Funding: The research leading to this paper have received funding from Business Finland 5G-VIIMA project, Academy of Finland 6Genesis Flagship (grant no. 318927) and Infotech Oulu Doctoral Programme.
Academy of Finland Grant Number: 318927
Detailed Information: 318927 (Academy of Finland Funding decision)
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