|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: ||6/2022|
|Journal/Conference/Book: ||Journal of Lightwave Technologies
|Citations: ||Look up on Google Scholar
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%.