Air-Filled SIW Remote Antenna Unit With True Time Delay Optical Beamforming for mmWave-Over-Fiber Systems

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-integratedwaveguide technology. They adopt a novel improved aperturecoupled 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 RAU's 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 ULA's 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 RAU's beam towards angles up to 51.8 • , with a maximum gain degradation below 0.6 dB. Finally, the optically enabled 1×4 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%.

Broadband Beam-Scanning Phased Array Based on Microwave Photonics

“…On the other hand, the design of antenna elements in microwave optical phased arrays is also a research direction that has gained much attention. An air-filled SIW remote antenna element was proposed in [49]. The designed antenna covered the 25.1-30.75 GHz band and had an isolation higher than 15 dB in that band.…”

Flexible mm-Wave Sigma-Delta-Over-Fiber MIMO Link

“…The work in [23] is a centrally controlled multiple-input-single-output (MISO) system, but the beam direction is fixed. A simple mm-Wave ARoF is studied in [24], in which the signal is directly generated in the optical domain. However, [24] only supports analog beamforming function.…”

“…A simple mm-Wave ARoF is studied in [24], in which the signal is directly generated in the optical domain. However, [24] only supports analog beamforming function. A D-band (110 GHz -170 GHz) ARoF system reached the highest data rate of 352 Gb/s with a 2 × 2 antenna configuration [25].…”

Wideband mm-wave Spectrum-Efficient Transmitter Using Low-Pass Sigma–Delta-Over-Fiber Architecture

“…Filippo Ponzini is with the GFTL ER HDE Optical Systems, Ericsson Research, IT-561 24 Pisa, Italy (e-mail: filippo.ponzini@ericsson.com). The systems in [17] [18] used 64QAM signals with a Mach-Zehnder modulator (MZM) and an external laser source to modulate the radio frequency (RF) signal to the optical domain, which results in high system complexity. The MIMO demonstration of [19] is based on an intermediate-frequencyover-fiber (IFoF) architecture with off-the-shelf hardware.…”