A mmWave-over-fiber distributed antenna system (DAS), in combination with highly efficient air-filled substrate-integrated-waveguide (AFSIW) remote antenna units (RAUs), proves to be a prime candidate to counter the harsh propagation conditions that arise at mmWave frequencies. This paper proposes a system-level model to accurately analyze the link quality of a downlink mmWave-over-fiber wireless link in a time-efficient way. The model includes a realistic antenna description, fiber losses, and non-linear effects of the opto-electrical/electro-optical transducers and the electrical amplifiers. This provides in-depth insight into the signal quality at each stage of the link and enables offline link optimization. In addition, the modular nature allows incorporating more advanced wireless channel models/measurements, which can be used to optimize RAU placement in the future. Finally, the model is validated by means of a measurement campaign, demonstrating good agreement.

System-Level Model for mmWave-over-Fiber Distributed Antenna Systems

In this work, an extremely low-loss passive beamforming circuit based on a Butler matrix (BM) has been reported for implementing a multibeam antenna for 5G cellular applications. Each component of the proposed 4X4 beamforming circuit has been optimized for operation at 28 GHz millimeter wave frequency and the resultant beamformer has a small form factor of 37.7 mm X 23.31 mm, operating bandwidth of 26.5 GHz to 30.5 GHz, minimum return loss of - 37.5 dB, minimum isolation loss of -42 dB, and maximum insertion loss of just 2 dB. This beamforming circuit is ideal for feeding a four-element antenna array in portable applications like 5G mobile handsets operating at 28 GHz frequency.

Design of a Passive Beamforming Circuit with -37.5 dB Return Loss and -42 dB Isolation Loss for a Multibeam Antenna in 5G Applications

This article presents a novel <inline-formula> <tex-math notation="LaTeX">$4\times 4$ </tex-math></inline-formula> Butler matrix implemented in the grounded co-planar waveguide (GCPW) technology, compactly integrated with a highly efficient and broadband <inline-formula> <tex-math notation="LaTeX">$1\times 4$ </tex-math></inline-formula> air-filled substrate integrated waveguide (AFSIW) cavity-backed patch antenna array (AA), giving rise to a broad operational frequency range [23.75, 31 GHz] (26.5%) covering the n257, n258, and n261 fifth-generation (5G) bands. Three novel quadrature hybrid couplers and two crossovers are designed and compared to obtain the optimal building blocks for the Butler matrix. Within each of the supported 5G bands, the measured excess insertion loss of the optimized Butler matrix remains smaller than 3.5dB with a maximal amplitude imbalance of ±0.9dB. Isolation between input ports is higher than 16.4dB. A maximal measured realized gain of 12.3dBi is obtained for the Butler matrix with integrated <inline-formula> <tex-math notation="LaTeX">$1\times 4$ </tex-math></inline-formula> AA while ensuring a −3-dB beamwidth coverage of 110°. The main beamsteering directions of [−40°, −14°, 14°, 40°] exhibit measured deviations that stay within ±3°. The fabricated Butler matrix with AA features a very compact footprint of 21.4 mm <inline-formula> <tex-math notation="LaTeX">$\times$ </tex-math></inline-formula> 46.0 mm <inline-formula> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 2 mm [<inline-formula> <tex-math notation="LaTeX">$2\lambda _{0} \times 4.3\lambda _{0} \times 0.2\lambda _{0}$ </tex-math></inline-formula>].

Bram Hoflack

Papers

A 4 × 4 Millimeterwave-Frequency Butler Matrix in Grounded Co-Planar Waveguide Technology for Compact Integration With 5G Antenna Arrays