Authors:	I. Lima de Paula, L. Bogaert, O. Caytan, J. Van Kerrebrouck, A. Moerman, M. Muneeb, Q. Van den Brande, G. Torfs, J. Bauwelinck, H. Rogier, P. Demeester, G. Roelkens, S. Lemey
Title:	Air-Filled SIW Remote Antenna Unit with True Time Delay Optical Beamforming for mmWave-over-Fiber Systems
Format:	International Journal
Publication date:	10/2022
Journal/Conference/Book:	Journal of Lightwave Technologies (invited)
Volume(Issue):	40(20) p.6961-6975
DOI:	10.1109/JLT.2022.3187555
Citations:	8 (Dimensions.ai - last update: 24/11/2024) 4 (OpenCitations - last update: 11/11/2024) Look up on Google Scholar
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Abstract

A low-complexity and efficient mmWave-over-fiber remote antenna unit (RAU) is proposed that enables broadband transmission and wide-angle squint-free beam steering in the full [26.5-29.5] GHz n257 5G band. It leverages an in-house developed optical beamforming network (OBFN), implemented on a silicon photonics integrated circuit, and a broadband optically enabled 1x4 uniform linear array (ULA), enabling grating-lobe-free beam steering between [-50◦, 50◦]. The antenna elements (AEs) of the ULA are implemented in air-filled substrate-integrated-waveguide technology. They adopt a novel improved aperture-coupled feeding scheme to achieve high efficiency, high isolation and minimal back radiation over a broad frequency band. Each AE is compactly integrated and co-optimized with a dedicated opto-electrical transmit chain, maximizing the RAUs performance, including beamforming flexibility and energy efficiency, while minimizing its size. The separately packaged OBFN implements true-time-delay beamforming by means of four switchable optical delay lines that are capable of discretely tuning the delay difference between AEs with a resolution of 1.6 ps, up to a maximum delay of 49.6 ps to fully exploit the ULAs full grating-lobe-free scan range. Measurements show that the AEs are excellently matched in the [25.1-30.75] GHz band, exhibit high isolation (>15 dB) in the operating band, and feature a stable peak gain of 6.8+-0.72 dBi with a beamwidth of at least 95◦. Additionally, optical beamforming was successfully demonstrated by steering the RAUs beam towards angles up to 51.8◦, with a maximum gain degradation below 0.6 dB. Finally, the optically enabled 1x4 ULA successfully establishes a 64-QAM wireless communication link at 2.2 Gbaud (13.2 Gbps) while beam steering up to 50◦ with an error vector magnitude below 7.6%.